DEMAND FLOW DEVICE, DEMAND FLOW CONTROL SYSTEM AND METHOD

专利摘要:
demand flow device, demand flow control system and method. The present invention relates to a demand flow device (2502) that is configured to interface with a chilled water plant controller to optimize the performance of chilled water plant components. the demand flow device (2502) includes a communication device that receives sensor data associated with the chilled water plant components (2700). sensor data measures the operating variables of the chilled water plant. the demand flow device (2502) includes a demand flow controller in communication with the communication device. the demand flow controller uses sensor data to: determine an optimal pressure setpoint as a function of a desired chilled water delta t; controlling a flow of chilled water through chilled water plant components as a function of the ideal pressure setpoint and the desired chilled water delta t; and adjusting, through the controller, the setpoint of the ideal pressure, in response to the detection of activation events, to perform a restoration of the critical zone of the desired chilled water delta t.
公开号:BR112013030776B1
申请号:R112013030776-5
申请日:2012-05-04
公开日:2021-09-14
发明作者:Robert Higgins；Brendan McMasters
申请人:Siemens Industry, Inc；
IPC主号:

专利说明:

CROSS REFERENCE
[001] The present patent document is a continuation in part of and indicates the priority benefit provided under 35 U.S.C. §120 to co-pending U.S. Patent Application no. Serial 12/758,780 filed 04-12-2010, which is a continuation in part of copending U.S. Patent Application no. 12/507,806 filed on 07-23-2009. The entire contents of which are expressly incorporated herein for all purposes to the extent permitted by law. TECHNICAL FIELD
[002] The invention relates generally to cooling systems with chilled water comfort and industrial process refrigeration, and in particular to methods and apparatus to efficiently operate chilled water cooling systems. BACKGROUND
[003] Many commercial buildings and other buildings and campuses are cooled by chilled water plants. In general, these chilled water plants produce chilled water that is pumped into air handlers to cool the building's air. Chillers, air handlers, and other components of a chilled water plant are designed to operate at a specific chilled water inlet and outlet temperature, or Delta T. At the Delta T of the design, these components are at their highest efficiency and can produce cooling output at their rated capacity. The low Delta T, which occurs when the inlet and outlet temperature is closer than the design Delta T, reduces the chilled water plant's efficiency and cooling capacity and causes the chilled water plant to use more energy than that required for a given demand.
[004] Chilled water plants are designed to satisfy a maximum possible cooling demand of a building, campus, or the like, also known as design condition. In the design condition, the chilled water plant components are at the higher end of their capacity, where the system consumes less energy. However, it is rare that such high demand for refrigeration is needed. In fact, almost all chilled water plants operate below project conditions 90% of the year. For example, cool weather conditions can cause refrigeration demand to drop considerably. When cooling demand is reduced, Delta T is also often reduced. This means that for the most part, almost all chilled water plants are operating at a low Delta T and less than ideal efficiency. This chronic low Delta T is known as Low Delta T Syndrome.
[005] Many mitigation strategies have been developed to eliminate the Low Delta T Syndrome, such as the use of sophisticated sequence arrangement programs and ON/OFF selection algorithms for equipment, but none of them have proven to completely solve this phenomenon. In most examples, the chilled water plant operator simply pumps more water to the system's air handlers to increase their output, but this has the combined effect of further reducing the already low Delta T. In addition, increased pumping in the secondary circuit results in more pumping energy being used than necessary.
[006] From the discussion below, it will be apparent that the present invention is focused on the deficiencies associated with the prior art while providing numerous additional advantages and benefits not contemplated or possible with prior art constructs. SUMMARY
[007] Demand flow provides a method and apparatus for the highly efficient operation of chilled water plants. In fact, when compared to traditional operating schemes, demand flow provides substantial energy savings while fulfilling cooling output requirements. In general, the demand flow controls the pumping of chilled water, condenser water, or both, according to a constant Delta T line. This reduces energy usage, reduces or eliminates Low Delta T Syndrome, while allowing a chilled water plant to satisfy cooling demand. In one or more modalities, the constant Delta T line can be restored to another Delta T line to satisfy changing cooling demands while still saving energy.
[008] Low Delta T Syndrome has and continues to plague chilled water plants, causing excessive energy use and artificial reductions in capacity. This prevents chilled water plants from meeting cooling demands, even at partial load. The demand flow and your operational strategy eliminate these problems and provide additional benefits as will be described here.
[009] In one embodiment, the demand flow provides a method for the efficient operation of a chilled water plant. The method may comprise adjusting a chilled water Delta T, and controlling the chilled water flow through one or more components to maintain the chilled water Delta T through one or more chilled water plant components. The chilled water Delta T includes an inlet chilled water temperature and an leaving chilled water temperature in chilled water plant components. In one or more modalities, the chilled water Delta T can be maintained by increasing the chilled water flow rate to reduce the chilled water Delta T and decreasing the chilled water flow rate to increase the chilled water Delta T. Typically, the chilled water flow will be controlled through one or more chilled water pumps.
[0010] A critical zone reset can be performed to adjust the chilled water Delta T when one or more activation events occur. Generally speaking, critical zone restoration provides a new or restored Delta T setpoint to adjust output or cooling capacity as needed. The chilled water Delta T can be restored in a number of ways. For example, the chilled water Delta T can be reset by adjusting the inlet chilled water temperature, adjusting the leaving chilled water temperature, or both. Controlling the flow of chilled water through chilled water plant components to maintain the chilled water Delta T in this way substantially reduces Low Delta T Syndrome in the chilled water plant. In fact, the reduction may be such that Low Delta T Syndrome is eliminated in the chilled water plant.
[0011] A variety of occurrences can include activation events for a critical zone restoration. For example, opening a chilled water valve on an air handler unit beyond a particular threshold can be an activation event. In addition, an increase or decrease in chilled water temperature on a chilled water plant bypass, or a change in flow rate of a tertiary pump beyond a particular threshold can be trigger events. The humidity level in an operating room/operating room, a manufacturing environment, or other space can also be a triggering event.
[0012] The condenser water flow can also be controlled according to the method. For example, the method may comprise establishing a Delta T of condenser water which comprises a low entering condenser water temperature and an leaving condenser water temperature in a condenser. The condenser can use the low inlet condenser water temperature to provide a refrigerant sub-cooling that is highly beneficial to the cooling effect and efficiency of the cooler. Condenser water Delta T can be maintained by adjusting the flow of condenser water through the condenser, such as through one or more condenser water pumps.
[0013] Condenser water Delta T maintenance allows the condenser to provide stack-free refrigerant sub-cooling even at low condenser water inlet temperature. Condenser water Delta T can be maintained by controlling the leaving condenser water temperature, the leaving condenser water temperature is controlled by adjusting the condenser water flow through one or more condenser water pumps.
[0014] In another embodiment, a method is provided for operating one or more pumps in a chilled water plant. This method may comprise pumping water at a first flow through a chiller with a first pump, and adjusting the first flow to maintain a first Delta T through the chiller. The first Delta T can comprise a chiller inlet temperature and chiller outlet temperature that provide beneficial refrigerant superheat in a chiller evaporator regardless of chilled water plant loading conditions.
[0015] The method may also comprise pumping water at a second rate through an air handler unit with a second pump, and adjusting the second flowrate to maintain a second Delta T through the air handler unit. The second Delta T may comprise an air handler unit inlet temperature and an air handler unit outlet temperature that provide the desired cooling output in the air handler unit regardless of chilled water plant load conditions . In one or more modalities, the first Delta T and second Delta T can be similar or identical to balance the first flow and the second flow and reduce bypass mixing in a chilled water plant bypass. Bypass mixing is a common cause of Low Delta T Syndrome and its reduction is thus highly advantageous.
[0016] The method may include a critical zone restoration to increase refrigeration output. For example, the second flow can be increased by restoring the second Delta T when an air handler unit water valve opens beyond a particular limit. This increase in the second flow causes an increase in the cooling output to the air handler.
[0017] The method can be used in a variety of chilled water plant configurations. To illustrate, the method may comprise pumping water through a distribution circuit from the chilled water plant to the second pump at a third flow with a third pump, and adjusting the third flow to maintain a third Delta T. The capacity cooling in the air handler of this mode can be increased by a restoration of the critical zone. For example, the third flow can be increased by restoring the third Delta T when the second flow provided by the second pump is beyond a particular limit. As above, increasing the third flow increases the cooling capacity in the air handler.
[0018] The method can also control the flow of water from the condenser. For example, the method might include pumping condenser water at a fourth flow through a chiller condenser with a fourth pump, and adjusting the fourth flow to maintain a fourth Delta T in the condenser. The fourth Delta T can comprise an inlet condenser water temperature and an outlet condenser water temperature that provides refrigerant sub-cooling and prevents refrigerant from being piled up regardless of chilled water plant load conditions. For example, the entering condenser water temperature can be lower than an isobaric temperature so that the condenser water provides refrigerant sub-cooling.
[0019] In one embodiment, a controller is provided to control one or more pumps of a chilled water plant. The controller may comprise an input configured to receive sensor information from one or more sensors, a processor configured to control a flow provided by one or more pumps to maintain a Delta T across a chilled water plant component, and a configured output to send one or more signals to one or more bombs. The processor can also generate one or more signals that control the flow provided by one or more pumps. Delta T can comprise an inlet temperature and an outlet temperature.
[0020] The processor can be configured to maintain Delta T when increasing or decreasing flow based on sensor information. The processor can also be configured to perform a critical zone restoration by lowering Delta T in response to sensor information indicating that additional cooling capacity is desired in the component. Sensor information can be a variety of information. For example, sensor information can be temperature information. Sensor information can also or alternatively be operating information selected from the group consisting of air handler chilled water valve position, VFD Hz, pump speed, chilled water temperature, air handler water temperature. condenser, and at the chilled water plant bypass temperature.
[0021] The processor can be configured to maintain Delta T by controlling the Delta T outlet temperature. The outlet temperature can be controlled by adjusting the flow rate through the chilled water plant component. For illustration purposes, the flow rate can be adjusted by increasing the flow to lower the outlet temperature and decreasing the flow to raise the outlet temperature. The Delta T maintained by the controller can be similar to a Delta T by design for the component. This allows the component to operate efficiently according to your manufacturer's specifications.
[0022] The demand flow, in other exemplary modalities, can also be implemented according to the logic of the demand flow variable pressure curve (VPCL). Demand Flow VPCL represents an operating strategy that optimizes the total energy consumption of the chiller, chilled water pump, condenser water pump, cooling tower fan, and air handling unit over a calculated efficiency curve. The operating strategy represented by the demand flow VPCL individually and holistically optimizes the active set values of the pressure curve for each of the operable pumps within a chilled water plant. In response to optimizing the active set pressure curve values for each of the pumps, the speed and energy usage associated with the cooling tower fan and air handling unit can also be adjusted and optimized.
[0023] In an exemplary modality, a demand flow device configured to interface with a chilled water plant controller is provided to optimize the performance of one or more chilled water plant components over a range of conditions of demand. The demand flow device includes a communication device configured to receive sensor data associated with one or more chilled water plant components, where the sensor data measures the chilled water plant operating variables, a flow controller of demand in communication with the communication device. The demand flow controller is configured to utilize the received sensor data: determine an ideal pressure setpoint as a function of a desired chilled water Delta T; controlling a chilled water flow through one or more chilled water plant components as a function of the ideal pressure setpoint and the desired chilled water Delta T; and adjust, through the chilled water plant controller, the ideal pressure setpoint, in response to one or more detected trigger events, to perform a critical zone restoration of the desired chilled water Delta T.
[0024] In another modality, a demand flow control system is provided for implementing variable pressure control logic in an existing chilled water plant controller to optimize the performance of one or more water plant components cooled in a range of demand conditions. The demand flow control system includes a demand flow controller in communication with the existing chilled water plant controller. The demand flow controller, in turn, is configured to receive sensor data from one or more chilled water plant components coupled to the existing chilled water plant controller: determine an ideal pressure setpoint as a function of a Delta T of the desired chilled water and sensor data received for each of the chilled water plant components, where the ideal pressure setpoint is iteratively determined for each of the chilled water plant components. chilled water plant; communicate the ideal pressure setpoint to the existing chilled water plant controller; and controlling, through the existing chilled water plant controller, a chilled flow through each of the chilled water plant components as a function of the ideal pressure setpoint and the desired chilled water Delta T.
[0025] In another modality, a demand flow control method is provided that uses variable pressure control logic to optimize the performance of one or more chilled water plant components in a range of operable demand conditions in an existing chilled water plant. The demand flow method includes detecting an inlet chilled water temperature and an leaving chilled water temperature in one or more chilled water plant components; communicating the sensed entering chilled water temperature and the sensed leaving chilled water temperature to a demand flow controller; the calculation of an ideal pressure setpoint in the demand flow controller, where the ideal pressure setpoint is calculated as a function of a Delta T of the desired chilled water and the inlet temperature of the detected chilled water and the leaving chilled water temperature detected for a demand flow controller; communicating the ideal pressure setpoint to an existing chilled water plant controller; and controlling a chilled water flow through one or more chilled water plant components.
[0026] Other systems, methods, features and advantages of the invention will or will become apparent to a person skilled in the art upon examination of the figures and detailed description below. All such additional systems, methods, features and advantages are intended to be included within this description, are within the scope of the invention and are protected by the embodiments. Additional features and advantages of the disclosed embodiments are described in and will be apparent from the following detailed description and figures. BRIEF DESCRIPTION OF THE FIGURES
[0027] The components in the figures are not necessarily to scale and, on the other hand, emphasis is placed on illustrating the principles of the invention. In the figures, reference numerals designate corresponding parts throughout the different views.
[0028] FIG. 1 is a block diagram illustrating an exemplary uncoupled chilled water plant;
[0029] FIG. 2 is a block diagram illustrating the Low Delta T Syndrome in an exemplary chilled water plant;
[0030] FIG. 3 is a block diagram illustrating overflow in an exemplary chilled water plant;
[0031] FIG.4 is a block diagram illustrating an exemplary direct primary chilled water plant;
[0032] FIG. 5 is a block diagram illustrating the components of an exemplary chiller;
[0033] FIG. 6A is an exemplary pressure enthalpy graph illustrating the refrigeration cycle;
[0034] FIG. 6B is an exemplary pressure enthalpy graph illustrating refrigerant superheat in the refrigeration cycle;
[0035] FIG. 6C is an exemplary pressure enthalpy graph illustrating refrigerant superheat in the refrigeration cycle;
[0036] FIG. 7 is a table illustrating the benefits of a low condenser water inlet temperature in an exemplary condenser;
[0037] FIG. 8 is an exemplary pressure enthalpy graph illustrating the benefits of demand flow in an exemplary chiller;
[0038] FIG. 9A is a graph illustrating the relationship between flow and shaft speed;
[0039] FIG. 9B is a graph illustrating the relationship between total design head and shaft speed;
[0040] FIG. 9C is a graph illustrating the relationship between energy use and shaft speed;
[0041] FIG. 9D is a graph illustrating an exemplary Delta T line with a pumping curve and an energy curve;
[0042] FIG. 10 is a block diagram illustrating an exemplary controller;
[0043] FIG. 11A is a flowchart illustrating an exemplary controller in operation;
[0044] FIG. 11B is a flowchart illustrating an exemplary controller in operation;
[0045] FIG. 12 is a table illustrating exemplary critical zone resets activated by air temperature;
[0046] FIG. 13 is a table illustrating exemplary critical zone restorations activated by chilled water valve positions;
[0047] FIG. 14 is a block diagram illustrating an exemplary uncoupled chilled water plant;
[0048] FIG. 15 is a table illustrating exemplary VFD Hertz activated critical zone restorations;
[0049] FIG. 16 is a cross-sectional view of an exemplary condenser;
[0050] FIG. 17 is a table illustrating demand flow benefits in an exemplary chilled water plant;
[0051] FIG. 18 is a table illustrating the linear relationship between entering and leaving condenser water temperatures in an exemplary condenser;
[0052] FIG. 19 is a table illustrating compressor power changes under demand flow in an exemplary chilled water plant;
[0053] FIG. 20 is a pressure enthalpy graph illustrating changes in the refrigeration cycle under demand flow in an exemplary chiller;
[0054] FIG. 21 is a table illustrating the effect on energy and capacity on demand flow in an exemplary chilled water plant;
[0055] FIG. 22 is a graph illustrating the log mean temperature difference with demand flow in an exemplary chilled water plant;
[0056] FIG. 23A is a table illustrating the relationship between chilled water flow and Delta T in an exemplary chilled water plant at a low Delta T;
[0057] FIG. 23B is a table illustrating demand flow flexibility with an exemplary constant cooling capacity;
[0058] FIG. 23C is a table illustrating demand flow flexibility with an exemplary constant flow;
[0059] FIG. 24 is a table illustrating airside energy changes under demand flow in an exemplary chilled water plant;
[0060] FIG. 25 is a block diagram illustrating an exemplary demand flow device that interfaces with a controller of an exemplary chilled water plant;
[0061] FIG. 26 is a block diagram of the exemplary demand flow device that includes a demand flow processor and memory configured to store a demand flow control routine for executing demand flow variable pressure curve logic;
[0062] FIG. 27 is a block diagram illustrating an exemplary chilled water plant operable in accordance with the principles of demand flow variable pressure curve logic presented herein;
[0063] FIG. 28 is a flowchart illustrating an exemplary demand flow condenser routine or algorithm in operation;
[0064] FIG. 29 is a flowchart illustrating an exemplary demand flow evaporator routine or algorithm in operation;
[0065] FIG. 30 is a flowchart illustrating an exemplary routine or algorithm for determining the P exponent variable for a particular pump; and
[0066] FIG. 31 is a block diagram illustrating the exemplary chilled water plant shown in FIG. 27 which operates according to the principles of the demand flow variable pressure curve logic presented here. DETAILED DESCRIPTION
[0067] In the following description, numerous specific details are presented in order to provide a more complete description of the present invention. It will be apparent, however, to the person skilled in the art, that the present invention can be practiced without these specific details. In other examples, well-known features have not been described in detail so as not to obscure the invention.
[0068] Demand flow as described herein refers to methods and apparatus to reduce or eliminate Low Delta T Syndrome and to improve chilled water plant efficiency. Demand flow can be implemented in retrofit projects for existing chilled water plants as well as new chilled water plant installations or designs. As used herein, chilled water plant refers to cooling systems that use chilled water to provide comfortable cooling or chilled water for some process need. Such chilled water plants are typically, but not always, used to cool campuses, industrial complexes, commercial buildings, and more.
[0069] In general and as will be described later, demand flow uses variable flow or the pumping of chilled water within a chilled water plant to combat Low Delta T Syndrome and substantially increase the efficiency of a plant. chilled water plant. Variable flow under demand flow maintains a Delta T for chilled water plant components that is at or near the design Delta T for components. As a result, the demand stream substantially increases the operational efficiency of chilled water plants and their components, resulting in substantial savings in energy costs. The increased efficiency provided by the demand flow also provides the benefit of reduced pollution. In addition, demand flow also increases the life expectancy of chilled water plant components by operating these components close to or at their specific chilled water inlet and outlet temperatures, or design Delta T, as opposed to techniques traditional or other pumping variables.
[0070] Demand flow provides increased efficiency irrespective of demand or cooling load by operating chilled water plant components in a synchronous manner. In one or more embodiments, this occurs by controlling the pumping of chilled water and condenser water in one or more pumps to maintain a Delta T on particular components or points in a chilled water plant. Generally speaking, demand flow operates in individual water condensers or water pumps to maintain a Delta T through a particular component or point of a chilled water plant. For example, primary chilled water pumps can be operated to maintain a Delta T through a chiller, secondary chilled water pumps can be operated to maintain a Delta T through plant air handlers, and condenser water pumps can be operated to maintain a Delta T through a condenser.
[0071] Controlling the individual pumps (and the flow rate) in this way results in the synchronized operation of a chilled water plant, as will be described later. This synchronized operation balances flow rates in the chilled water plant, which significantly reduces or eliminates Low Delta T Syndrome and related inefficiencies.
[0072] In traditional chilled water plants, variable flow is controlled according to a minimum pressure differential, or Delta P, at some location(s) in the plant or chilled water system. Demand flow is distinct from these techniques in its focus on Delta T rather than Delta P. With demand flow, an ideal Delta T can be maintained on all chilled water plant components regardless of load conditions (this is, the demand for refrigeration). Maintaining a constant or stable Delta T allows for wide variations in chilled water flow, resulting in energy savings not only in pumping energy but also in chiller energy consumption. For example, the Delta T of a chiller can be maintained, by controlling flow through chilled water or condenser water pumps, close to or to chiller design parameters regardless of load conditions to maximize efficiency of the evaporator heat exchanger and cooler condenser tube bundles.
[0073] On the other hand, traditional variable flow schemes vary the flow within much narrower bands, and are thus unable to provide the cost and energy savings of demand flow. This is because traditional flow control schemes control the flow to produce a particular pressure difference, or Delta P, rather than the Delta T. Furthermore, traditional variable flow schemes seek to maintain only the Delta P at just some point in the predetermined system, ignoring the low Delta T. This results in flows that are much higher than required to generate and deliver the desired amount of cooling output, in large part to compensate for inefficiencies caused by the low Delta T.
[0074] Due to the fact that flows are controlled by the demand flow to maintain a Delta T and not maintain Delta P or a particular cooling output in plant air handlers, there may be situations where the flow rate is too low for produce the desired amount of cooling output in certain areas based on system diversity. To combat this, the demand stream includes a feature denoted here as a reset critical zone that allows the Delta T held by the demand stream to be reset to another value, typically lower, based on a specific system need that does not is being fully satisfied at the required system flow. This could be due to inadequate piping, improperly sized air handlers for the load being served, or any number of unanticipated system malfunctions. As will be described later, this allows additional cooling to be provided while maintaining a new Delta T or generally restored by increasing the chilled water flow. Demand flow application has a synergistic effect on air handlers as well as chillers, pumps and other components of a chilled water plant. This results in reduced net energy usage while maintaining or even increasing the rated capacity for the chilled water plant. As will be described later, under demand flow little or no excess energy is used to provide a given level of cooling.
[0075] Preferably, the Delta T maintained by the demand stream should be close to or to the design Delta T of a chilled water plant component to maximize component efficiency. The advantages of maintaining Delta T can be seen through a cooling capacity equation, such as Tons = ((GPM * Delta T)/K),
[0076] where Tons is the cooling capacity, GPM is the flow, and K is some constant. As this equation shows, when Delta T is lowered, so is the cooling capacity.
[0077] It should be noted that although it is described here with reference to a particular capacity equation, it will be understood that the operation and demand flow benefits can also be shown with a variety of capacity equations. This is generally because the relationships between cooling capacity, flow, and constant Delta are linear.
[0078] The advantages of keeping Delta T can be seen from the following example. For a constant value of 24 to K, 1000 Tons of capacity can be generated by providing a flow rate of 1500 GPM at a design Delta T of 16 degrees. 500 Tones of capacity can be generated by providing 750 GPM at a 16 degree Delta T. However, at a low Delta T as typically found in traditional systems, a higher flow rate may be required. For example, at an 8 degree Delta T, 500 Tons of capacity would require a flow of 1500 GPM. If the Delta T is lowered further, such as up to 4 degrees, the cooling capacity should be 250 Tons at 1500 GPM. Where the chilled water plant's pumps, or other components, can only be capable of a maximum flow of 1500 GPM, the chilled water plant may not be able to satisfy the desired demand of 500 Tons, albeit at the Delta T of project, the chilled water plant is capable of a capacity of 1,000 Tons at 1,500 GPM. I. LOW DELTA T SYNDROME
[0079] Low Delta T Syndrome will now be described with respect to FIG. 1 illustrating an exemplary uncoupled chilled water plant. As shown, the chilled water plant comprises a main circuit 104 and a secondary circuit 108. Each circuit 104, 108 can have its own inlet and outlet water temperature, or Delta T. It should be noted that the demand flow it also benefits direct/primary chilled water plants (ie non-decoupled chilled water plants) as well, as will be described further below.
[0080] During the operation of an uncoupled chilled water plant, chilled water is produced in a production or primary circuit 104 by one or more chillers 112. This chilled water can be circulated in the primary circuit 104 by one or more primary chilled water pumps 116. The chilled water from the primary circuit 104 can then be distributed in a building (or other structure) by a distribution or secondary circuit 108 in fluid communication with the primary circuit 104. Within the secondary circuit 108, the chilled water can be circulated by one or more secondary chilled water pumps 120 to one or more air handlers 124. The air handlers 124 allow heat from the building air to be transferred to the chilled water, such as through an or more heat exchangers. This supplies the building with cooling air. Typically, building air is forced or blown through a heat exchanger of an air handler 124 to better cool a volume of air. The chilled water leaves the air handlers 124 and returns to the secondary circuit 108 at a higher temperature due to the heat that the chilled water has absorbed through the air handlers.
[0081] The chilled water then leaves the secondary circuit 108 and returns to the primary circuit 104 at a higher temperature. As can be seen, the primary circuit 104 and the secondary circuit 108 (as well as the chilled water plant components attached to these circuits) have an entering water temperature and an leaving water temperature, or Delta T. In an ideal situation, the inlet and outlet temperatures for both circuits should be in their respective design Delta Ts. Unfortunately, in practice, chilled water circuits operate at a chronic low Delta T.
[0082] Low Delta T occurs due to a variety of reasons. In some cases, the low Delta T occurs because of an imperfect chilled water plant design. This is relatively common due to the complexity of chilled water plants and the difficulty in getting a perfect design. For purposes of illustration, the air handlers 124 of the secondary circuit 108 may not have been correctly selected and thus the chilled water does not absorb as much heat as expected. In this case, the chilled water from secondary circuit 108 enters primary circuit 104 at a cooler temperature than expected, resulting in a low Delta T. It should be noted that, due to imperfect design and/or operation, a chilled water plant may operate at a low Delta T under various loads, including design condition loads.
[0083] Low Delta T also occurs as the cooling output is lowered to satisfy a load that is less than the design condition. When the outlet is lowered, chilled water flow, chilled water Delta T, and other factors become unpredictable, often resulting in a low Delta T. In fact, in practice, it has been seen that traditional Delta P flow control schemes invariably result in a low Delta T in some, if not all, chilled water plant components.
[0084] For example, to reduce the cooling output of design conditions, one or more chilled water valves of the chilled water plant's air handlers 124 may be closed (partially or completely). This reduces the flow of chilled water through the air handlers 124 and less cold air is thereby provided. However, now that the chilled water valves are partially closed, the chilled water absorbs less heat from the air as it flows through the air handlers 124 at a higher rate than necessary as evidenced by the lower Delta T than the from the project. In this way, the chilled water coming out of the air handlers 124 is not as "hot" as it once was. As a result, the chilled water leaving the secondary circuit 108 to the primary circuit 104 is cooler than desired, causing a low Delta T in both circuits.
[0085] To illustrate with a specific example, an exemplary chilled water plant is provided in FIG. 2. In the example, the chilled water produced in primary circuit 104 is 40 degrees. As can be seen, the chilled water exiting the air handlers 124 may be at 52 degrees instead of the predicted 56 degrees because the chilled water valves have been closed and the chilled water flow rate is too high for the current load. Due to the fact that there is no overflow flow at bypass 128, the secondary loop leaving chilled water temperature is still 40 degrees. Assuming the system has a 16-degree design Delta T, there is now a 12-degree low Delta T that is 4 degrees lower than the design Delta T. It is observed here that the low Delta T itself reduces capacity and causes excess energy to be used to provide a certain cooling output. As can be seen from the capacity equation, Tons = ((GPM * Delta T)/K),
[0086] Tons capability is significantly reduced by the low Delta T. To compensate, a higher flow rate or GPM must be required, which leads to excessive pumping energy use for such cooling demand.
[0087] With reference back to FIG. 1, another cause of low Delta T is by-pass mixing caused by excessive flow within primary circuit 104, secondary circuit 108, or both. Bypass mixing and overflow are known causes of low Delta T and are traditionally quite difficult to eliminate, especially with Delta P flow control schemes. In fact, a common cause of overflow is over-pumping water cooled by inefficient Delta P control schemes (as shown by the example above). For this reason, flow imbalances and bypass mixing are commonplace in chilled water plants that use Delta P flow control schemes. It should be noted that bypass mixing can occur even in the design condition because, just like with any complex machinery, chilled water plants are rarely perfect. In fact, chilled water plants are often designed with primary chilled water pump flow rates that do not match the flow rates of secondary pumps.
[0088] In uncoupled chilled water plants, a decoupler or bypass 128 connecting the primary circuit 104 and the secondary circuit 108 is provided for handling the flow imbalances between the circuits. This typically occurs as a result of excessive flow or excessive pumping in one of the circuits. Bypass 128 accepts overflow from one circuit in general by allowing it to cycle to the other circuit. It should be noted that overflow is not limited to any particular circuit and that there can be overflow in all circuits as well as an imbalance of flow between them.
[0089] Excessive flow generally indicates that too much energy has been expended in pumping the chilled water, as will be described later through the affinity laws, and also exacerbates the problems of low Delta T. For illustration purposes when using FIG. 3, which illustrates an exemplary chilled water plant that has an excessive flow, the chilled water from the air handlers 124 and the secondary circuit 108 mixes with the feed water from the primary circuit 108 at bypass 128 when there is a primary chilled water flow. or over-distribution. The resulting mixture of these two water streams is hotter than the design chilled water which is then distributed to the air handlers 124.
[0090] For illustration purposes, an excess flow of 300 gallons per minute (GPM) of water at 54 degrees from secondary circuit 108 must mix with water cooled at 40 degrees from primary circuit 104 at bypass 128, which raises the temperature of the secondary circuit chilled water to 42 degrees. The chilled water from the secondary circuit now has a higher temperature than the chilled water from the primary circuit. This causes a low Delta T in primary circuit 104 and secondary circuit 108 and a corresponding reduction in cooling capacity.
[0091] Bypass mixing of the chilled water stream is also undesirable because it exacerbates the low Delta T. For purposes of illustration, when the air handlers 124 sense high water temperature caused by bypass mixing or fail to meet the cooling demand due to high water temperature, their chilled water valves open to allow through a stream. additional water through the air handlers 124 to increase the cooling capacity of the air. In traditional Delta P systems, 120 secondary chilled water pumps must also increase the chilled water flow rate to increase the cooling capacity of the air in the 124 air handlers. This increase in flow causes additional imbalances in flow (ie, more overflow) at bypass 128 between the primary circuit 104 and the secondary loop 108. The increased overflow exacerbates the low Delta T by causing additional bypass mixing which lowers the Delta T even further.
[0092] Overflow and bypass mixing also cause excessive energy usage for a given cooling demand. In some situations, additional pumping energy is used to increase the flow rate in the primary circuit 104 to better balance the flow in the secondary circuit 108 and prevent bypass mixing. Additionally or alternatively, an additional chiller 112 may have to be placed in-line or an additional chiller energy may be used to generate sufficient chilled water in the primary circuit 104 to compensate for the heating effect of the bypass mixture in the chilled water supply. On the air supply side, air handlers 124 may attempt to compensate for reduced capacity caused by high water temperatures by moving larger volumes of air. This is typically accomplished by increasing power so that one or more fans 132 move additional air through the air handlers 124, as will be further described through the affinity laws.
[0093] In many cases, these measures (eg increased chilled water pumping, opening of air handler water valves, increased air movement of the air supply) do not fully compensate for the artificial reduction in cooling capacity caused by low Delta T. As such, the chilled water plant is simply unable to satisfy the demand for cooling even though this level of demand may be below its rated cooling capacity. In addition to starter chillers, the chilled water plant is using substantially more energy than is needed to provide the desired cooling output with much of the excess energy being expended in compensating for the low Delta T effects.
[0094] It should be understood that Low Delta T also occurs in direct-primary chilled water plant configurations (ie, uncoupled chilled water plants), even though such configurations generally do not have the problem of mixing water from return of the building with the water from the production feed. Direct-primary systems invariably have a plant or system bypass, 3-way valves, or both, in order to maintain a minimum flow through the system. For example, FIG. 4 illustrates an exemplary direct-primary chilled water plant that has such a bypass. Similar to an uncoupled chilled water plant, excessive flow can occur in these bypasses or 3-way valves. Thus, low Delta T issues such as excessive chiller energy, excessive pumping energy, and reduced system capacity are also present in direct-primary configurations. In fact, the low Delta T problems are the same regardless of the plant configuration. This has been shown in practice by the fact that Low Delta T Syndrome occurs in both types of chilled water plants.
[0095] The effect of low Delta T with respect to coolers will now be described further. FIG. 5 illustrates an exemplary cooler 112. For illustrative purposes, the dashed line of FIG. 5 outlines which components are part of the sample cooler 112 and which are not, where the components within the dashed line are part of the cooler. Of course, it should be understood that a chiller may include additional components or fewer components than those shown.
[0096] As can be seen, the cooler 112 comprises a condenser 508, a compressor 520 and an evaporator 512 connected by one or more refrigerant lines 536. The evaporator 512 can be connected to a primary circuit or another of a power plant of chilled water through one or more chilled water lines 532.
[0097] In operation, chilled water can enter evaporator 512 where it transfers heat to a refrigerant. This evaporates the refrigerant, which causes the refrigerant to turn into refrigerant vapor. The chilled water heat transfer cools the water, allowing the water to return to the primary circuit through chilled water lines 532. For illustration purposes, water chilled to 54 degrees can be cooled to 42 degrees by transferring heat to the chilled water 40 degrees inside a 512 evaporator. The water cooled to 42 degrees can then be used to cool a building or other structures, as described above.
[0098] For the refrigeration cycle to continue, the refrigerant vapor produced by the evaporator 512 is condensed back into liquid form. This condensation of refrigerant vapor can be carried out by condenser 512. As is known, refrigerant vapor can only condense on a surface of a lower temperature. Due to the fact that refrigerant has a relatively low boiling point, refrigerant vapor has a relatively low temperature. For this reason, a compressor 520 can be used to compress the refrigerant vapor, raising the temperature and pressure of the vapor.
[0099] The increased temperature of the refrigerant vapor allows the vapor to condense at a higher temperature. For example, without compression the refrigerant vapor might be at 60 degrees, while with compression the vapor might be at 97 degrees. In this way, condensation can occur below 97 degrees and not below 60 degrees. This is highly beneficial because it is generally easier to provide a condensing surface that has a lower temperature than the increased temperature of the refrigerant vapor.
[00100] The refrigerant vapor enters the condenser 508 where its heat can be transferred to a condensing medium, causing the refrigerant to return to a liquid state. For example, condenser 508 may comprise a shell and tube design where the condensing medium flows through the tubes of the condenser. In this way, refrigerant vapor can condense in the tubes inside the condenser envelope. As discussed herein, the condensing medium is condenser water, although it should be understood that other fluids or media may be used. After condensation, the refrigerant then returns through a refrigerant line 536 and pressure reducer 528 back to evaporator 508, where the refrigeration cycle continues.
[00101] The condenser 508 can be connected to a cooling tower 524 or other cooling device by one or more condenser water lines 540. Due to the fact that the condenser water absorbs heat from the refrigerant vapor, the Condenser water must be cooled to keep its temperature low enough to condense the refrigerant vapor. Condenser water can be circulated between condenser 508 and cooling tower 524 by one or more condenser water pumps 516. This provides a condenser cooling water supply that allows for continuous condensing of refrigerant vapor. It should be noted that although a cooling tower 524 is used to cool the water in the embodiment of FIG. 4, other condenser water supplies can be used.
[00102] The operation of a chiller can also be shown using a pressure-enthalpy graph as shown in FIG. 6A. In the graph, pressure is plotted on the vertical axis, enthalpy on the horizontal axis. At point 604, the refrigerant can be in a fairly saturated or mostly liquid state in an evaporator. As the refrigerant absorbs heat from the chilled water in the evaporator, its enthalpy increases the transformation of the refrigerant to refrigerant vapor at point 608. The portion of the graph between point 604 and point 608 represents the cooling effect of the chiller . During this time, the absorption of heat from the chilled water by the refrigerant cools the chilled water.
[00103] A compressor can then be used to increase the temperature and pressure of the refrigerant vapor from point 608 to point 612. This is known as "rise". This elevation allows the refrigerant vapor to condense in the condenser as described above. Between point 612 and point 616, the refrigerant vapor transfers heat to the condenser water and condenses in the condenser, turning the vapor into a liquid once more. The refrigerant then passes through a pressure reducer between point 616 and point 604, which reduces the temperature and pressure of the liquid refrigerant so that it can be used in the evaporator and continue the refrigeration cycle.
[00104] As will be described later, problems associated with low Delta T in the condenser often result in cooler failure due to lack of minimum lift under part load conditions. When the pressure differential between the condenser and evaporator drops too low, a condition known in the industry as "stacking" occurs. This is a condition where refrigerant builds up in the condenser, lowering the saturated evaporator pressure and temperature to critical points. The refrigerant also has a great affinity with oil and the stack will therefore trap a good portion of the oil charge in the condenser, which causes the cooler to close at any number of low pressure, low evaporator temperature, or problems. low oil pressure.
[00105] Due to the fact that most traditional condenser water pumping systems operate at a constant volume, the cooling towers are also in full flow conditions. As the load on the cooling tower decreases, the operating range remains relatively constant, reducing tower efficiency. On the other hand, in variable flow condenser water systems, the operating range decreases with flow. This allows for lower condenser inlet water temperatures and the associated reduction in chiller energy and cooling tower fan energy described later in this narrative.
[00106] Low Delta T also results in very ineffective condenser water pump efficiency (KW/Ton) and limits the amount of refrigerant sub-cooling available to the chiller through seasonally low condenser water inlet temperatures. At a given load, for each degree of condenser inlet water temperature that is reduced, compressor power is reduced by about 1.5% and the nominal chiller tonnage is increased by about 1%. Thus, as will be described later, operation of chillers at the lowest possible condenser water inlet temperature is highly desirable.
[00107] In addition, the low Delta T in the evaporator reduces the refrigeration effect of the refrigeration cycle. As will be described later, this reduces the temperature of the refrigerant vapor produced by the evaporator. II. DEMAND FLOW
[00108] Overall, the demand stream comprises systems and methods to combat Low Delta T Syndrome while increasing chilled water system and plant efficiency. As demonstrated above, traditional chilled water control schemes lead directly to energy and capacity inefficiencies evidenced by Low Delta T Syndrome, high KW/Ton, and reduced airside capacity. The above description also demonstrates that there is a direct conflict between most traditional control schemes and optimizing system energy and applicable capacity. This is most clearly evidenced by pressure differential, or Delta P, chilled water pump control schemes, which ignore increased energy use and reduced system capacities. Traditionally designed Delta P-based pumping schemes inevitably lead to a system that behaves with Low Delta T Syndrome as the system load varies.
[00109] In a perfect world, the Delta T of the chilled water must be the same in the primary, secondary, and any tertiary or other circuits of a chilled water plant. Operating the chilled water plant components to your selected or design Delta T always produces the most applicable capacity and highest system efficiencies. So, in a perfect world, the Delta T of the chilled water must match the Delta T of the project. To generate this ideal situation, the control algorithms for the selection, design, installation and pumping of chilled water plant components must be perfect. Unfortunately, this perfection is extraordinarily rare or never achieved in practice, and disparities in the design, loading and installation of chilled water plants are always present.
[00110] Unlike traditional control schemes, a core demand flow principle should operate as close to the project's Delta T as possible where an emphasis is placed on satisfying cooling demand, as will be described below with respect to critical zone restorations. This allows a chilled water plant to operate at high efficiency regardless of the cooling load. This is unlike traditional control schemes, where operating at partial or uniform design loads uses substantially more energy than is needed because of the Low Delta T Syndrome that plagues these traditional systems.
[00111] In addition, because the pumps are controlled to maintain a Delta T as close as the design Delta T, the chilled water plant uses energy efficiently regardless of the load on the plant. When compared to traditional control schemes, energy use is substantially lower under the demand flow as can be seen from the table below. The values indicated in the table are taken from actual measurements of an operational demand flow implementation.
[00112] For purposes of illustration, FIG. 7 is a table of an actual demand flow application that shows the energy reductions that can be achieved by reducing the condenser water inlet temperature. FIG. 8 is a pressure-enthalpy diagram comparing P 804 condenser water pumping and constant volume Delta P chilled water pumping schemes to demand flow pumping 808. As can be seen, lift is reduced while the cooling effect is increased by undercooling 812 and overheating refrigerant 816 compared to traditional constant volume pumping 804.
[00113] Demand flow has a measurable, sustainable and reproducible effect on chilled water plants because it is grounded in solid scientific fundamental principles that, as such, are measurable and can be predicted. The gains in efficiency and applicable capacity that result from applying demand flow will be described as follows.
[00114] A fundamental premise of the energy efficiency of pumping with variable flow chilled water plants known as affinity laws consists of the following laws:
[00115] Law 1: The flux is proportional to the shaft rotation speed, as shown by the equation (Q1/Q2) = (N1/N2)
[00116] where N is the shaft rotation speed and Q is the volumetric flow (eg CFM, GPM or L/s. This is illustrated by flow line 936 shown in the graph in FIG. 9A.
[00117] Law 2: The pressure or column is proportional to the square of the shaft velocity, as shown by the equation (H1/H2) = (N1/N2)A2
[00118] where H is the pressure or column developed by the pump or fan (for example, in feet or meters). This is illustrated by the pumping curve 916 shown in the graph of FIG. 9B.
[00119] Law 3: Power is proportional to the cube of the shaft speed, as shown by the equation (P1/P2) = (N1/N2)A3
[00120] where P is the axis power (eg W). This is illustrated by the power curve 920 shown in the graph of FIG. 9C.
[00121] Affinity laws indicate that the chilled water pressure drop (also denoted as TDH or as H above) is related to the change in flow squared, while energy utilization is related to the change in flow to the cube. Therefore, in the demand flow, as the flow rate is reduced, the cooling capacity or output is proportionally reduced, but the energy usage is reduced exponentially.
[00122] FIG. 9D is a graph illustrating an exemplary constant Delta T line 904. Line 904 is indicated as a constant Delta T line because all points on the line were generated with the same Delta T. In the graph, the horizontal axis represents flow rate , while the vertical axis represents pressure. Thus, as shown, the Delta T 904 line shows, for a constant Delta T, the flow needed to produce a particular cooling output. In one or more embodiments, the Delta T 904 line can be defined by a capacity equation, such as Tons = ((GPM * Delta T)/K),
[00123] which provides that an increase or decrease in flow (GPM) causes a proportional increase or decrease in cooling output (Tone). It should be noted that although a particular Delta T line 904 is shown in FIG. 9D, it should be understood that Delta T 940 line may be different for various chilled water plants or chilled water plant components.
[00124] In general, the demand flow seeks to maintain the flow for a given cooling output in the Delta T 904 line. This results in substantial efficiency gains (ie, energy savings) while the demand for the refrigeration. On the other hand, the flow rate determined by traditional control schemes is often substantially higher than that provided by the Delta T 904 line. This has been shown in practice and is often recorded in the operational records of traditional chilled water plants . FIG. 9D illustrates an exemplary recorded point 908 showing flow as determined by traditional control schemes, and a demand flow point 912. The demand flow point 912 represents the flow rate for a given cooling outlet under demand flow principles.
[00125] Typically, the 908 registered point as determined by traditional control schemes will have a higher flow rate than is required by the chilled water plant to satisfy actual cooling demands. For example, in FIG. 9D, registered point 908 has a higher throughput than demand flow point 912. This is, at least partially, because traditional control schemes must compensate for inefficiencies caused by low Delta T with higher flow rates and increased cooling output.
[00126] With the demand flow, the flow rate is adjusted along the line of Delta T 904, linear to the load, which means that the chilled water plant, and its components, operate at or near the Delta T of the project. In this way, the low Delta T is eliminated or significantly reduced by the demand flow. In this way, the desired demand for cooling can be satisfied at a lower flow rate and cooling output compared to traditional control schemes. This is due in large part because the chilled water plant does not have to compensate for the inefficiencies of the low Delta T.
[00127] FIG. 9D overlays the aforementioned pumping curve 916 and power curve 920 to illustrate the efficiency gains provided by the demand flow. As shown, the pumping curve 916 represents the total design column (TDH) or pressure drop on its vertical axis and the capacity or speed of the axis on its horizontal axis. Affinity laws dictate that shaft speed is linearly proportional to flow. Thereby, the pumping curve 916 can be superimposed as in FIG. 90 to illustrate the efficiency gains provided by the demand flow. Affinity laws also dictate that the pumping curve 916 is a square function. Thus, it is possible to see from the graphs that since the flow is reduced linearly along the Delta T 204 line, the TDH is reduced exponentially.
[00128] The 920 energy curve as shown represents the energy usage on its vertical axis and the axis velocity (which, as indicated, has been shown to be linearly proportional to the flow rate) on its horizontal axis. Under the laws of affinity, the 920 energy curve is a function of the cube. Thus, it can be seen that as the flow is reduced, energy use is reduced exponentially, even more than TDH. Stated another way, energy use increases exponentially as a function of the cube as flow increases. For this reason, it is highly desirable to operate the system pumps in such a way that the minimum flow rate necessary to obtain a particular cooling output is provided.
[00129] It can be seen that a substantial amount of energy savings occurs when operating a chilled water plant with demand flow. FIG. 9D highlights the differences in energy use between the demand flow point 912, and the recorded point 908. As can be seen from the energy curve 920, in the cooling output indicated by these points, the excessive energy use 932 between the registered point 908 and the point 912 of demand flow is substantial. Again, this is because of the exponential increase in energy use as the flow rate increases.
[00130] FIG. 9D also highlights the differences in TDH between the demand flow point 912 and the registered point 908. As can be seen, the registered point 908 once again has a substantially higher TDH than is necessary to satisfy the demand of current refrigeration. On the other hand, at point 912 of demand flow, the TDH is much lower. As can be seen from the pumping curve 916, the excessive TDH 924 between the recorded point 908 and the demand flow point 912 is substantial. In this way, substantially less work is expended by the chilled water plant's pumps under demand flow compared to traditional control schemes. This is beneficial as less stress is placed on the pumps, which extends their service life. III. OPERATIONAL STRATEGY of demand flow
[00131] To aid in the description of demand flow, the term operational strategy will be used here to refer to the principles, operations and algorithms applied to chilled water plants and their components to obtain demand flow benefits for use plant energy and cooling capacity. Operational strategy beneficially influences aspects common to most, if not all, chilled water plants. As will be described below, these aspects include chilled water production (eg chillers), chilled water pumping, pump tower fan operation, condenser water cooling, and condenser fan operation. air side. Applying the operational strategy significantly reduces or eliminates Low Delta T Syndrome when operating chilled water plant components at or near the project's Delta T, regardless of load conditions. This in turn optimizes energy use and applic- able capacity for the chilled water plant components and the plant as a whole.
[00132] In one or more modalities, the operational strategy can be incorporated and/or implemented by one or more control devices or components of a chilled water plant. FIG. 10 illustrates an exemplary controller that can be used to implement operational strategy. In one or more embodiments, the controller can accept input data or information, perform one or more operations on the input in accordance with the operating strategy, and provide a corresponding output.
[00133] Controller 1000 can comprise a processor 1004, one or more inputs 1020, and one or more outputs 1024. Input 1020 can be used to receive data or information from one or more sensors 1028. For example, information about the chilled water, condenser water, refrigerant, or operational characteristics of chilled water plant components detected by one or more sensors 1028 may be received through an input 1020.
[00134] Processor 1004 may then perform one or more operations on the information received through one or more inputs 1020. In one or more embodiments, the processor may execute one or more instructions stored in a memory device 1012 to perform those operations . Instructions may also be routed over the wire to processor 1004 such as in the example of an ASIC or an FPGA. It should be noted that memory device 1012 can be internal or external to processor 1004 and can also be used to store data or information. Instructions can be in the form of machine-readable code in one or more modalities.
[00135] The operational strategy can be incorporated by one or more instructions in such a way that, when executing the instructions, the controller 1000 can operate a chilled water plant or a component thereof according to the demand flow. For example, one or more algorithms can be run to determine when increases or decreases in chilled/condenser water flow should be run to keep chilled/condenser water pumping in or near a Delta T line Since instructions are executed on the information of one or more 1020 inputs, a corresponding output can be provided via one or more 1024 outputs of controller 1000. As shown, an output 1024 of controller 1000 is connected to a VFD 1032. The VFD 1032 can be connected to a cooled condenser, or another cooling tower pump or fan (not shown). In this way, the 1000 controller can control the pumping of the chilled water plant's pumps.
[00136] It should be noted that the operational strategy can be considered the provision of external control operations that control the components of a chilled water plant. For example, in the case of a retrofit, a 1000 controller or the like can apply the demand flow to a chilled water plant without requiring changes to existing plant components. The 1000 controller can control VDFs from existing power plants and pumps, for example. In some embodiments, VFDs can be installed in one or more chilled water pumps, condenser water, or other pumps to allow control of these pumps by operational strategy. One or more sensors can also be installed, or existing sensors can be used by the 1000 controller in one or more modalities.
[00137] FIG. 11A is a flowchart illustrating the exemplary operations that can be performed by a controller 1024 to execute the operational strategy. It should be understood that some steps described here may be performed in a different order than those described here, and that there may be fewer steps or additional steps in various modalities that correspond to various aspects of the operating strategy described here but not shown in the flowchart.
[00138] In the mode shown, sensor information is received in step 1104. For example, sensor information regarding inlet chilled water temperature, outlet water temperature, or both of a water plant component cooled, can be received. The temperature, pressure, or other characteristics of the refrigerant can also be received. In addition, operational characteristics such as the position of chilled water valves on air handlers, the speed or output of VFDs, the speed or flow of pumps, as well as other information can be received.
[00139] In step 1108, based on the information received in step 1104, the controller can determine whether to ramp up or down on one or more pumps to maintain a Delta T that is preferably close to or to the Delta T of the project. For example, with reference to FIG. 1, if the leaving chilled water temperature in an air handler 124 indicates a low Delta T, the flow rate in the secondary circuit 108 can be adjusted by a secondary chilled water pump 120 to maintain the design Delta T through a manipulator of air 124.
[00140] In step 1112, an output can be provided, such as on a VFD or another pump controller, or even on a pump directly to increase or decrease the flow as determined in step 1108. In this example above, with When flow is reduced, the chilled water remains in the air handler 124 for a longer period of time. This causes the enthalpy of the chilled water to increase because it is exposed to the hot building air by the air handler 124 for a longer period of time.
[00141] The increase in the chilled water enthalpy raises the leaving chilled water temperature of the air handler 124. When the water leaves the secondary circuit 108 the leaving water temperature of the secondary circuit is high. In this way, Delta T can be increased to close to or the design Delta T (which reduces or eliminates Low Delta T Syndrome).
[00142] Although the above example describes the maintenance of the Delta T in a 124 air handler, the Delta T can be maintained in this manner in other chilled water plant components, including primary, secondary, or other circuits, as well as within plant components. For example, in one or more embodiments, a chilled water plant controller can change the flow rate of one or more condenser water pumps to maintain a Delta T across a chiller component, such as the chiller condenser. .
[00143] As briefly discussed above, the operational strategy may also include one or more critical zone restorations. In one or more modalities, a restoration of the critical zone changes the Delta T for which the flow is controlled. Essentially, restoration of the critical zone alters the Delta T line for which the flow is controlled by the operational strategy. This allows the operational strategy to satisfy the cooling demand by operating according to multiple Delta T lines. In practice, these Delta T lines will typically be close to the Delta T line generated in the project's Delta T. The operational strategy is thereby flexible and can satisfy various cooling demands while efficiently operating the chilled water plant close to or to the Delta T of the project.
[00144] A critical zone reset can be used to increase or decrease the cooling output, such as when increasing or decreasing the chilled water flow. In one or more modalities, a critical zone restoration can be used to increase cooling output by increasing chilled water flow. This can occur in situations where the cooling demand cannot be satisfied by operating a chilled water plant at a particular Delta T. For example, if cooling demand cannot be satisfied, a critical zone reset can be used to restore the current Delta T held by the operating strategy to a new value. For illustrative purposes, Delta T maintained by an operational strategy can be reset from 16 degrees to 15 degrees. To produce this lower Delta T value in chilled water plant components, the chilled water flow rate can be increased to maintain the new Delta T value across one or more chilled water plant components. The increased flow rate provides additional chilled water to chilled water plant components, which in turn provides increased cooling output to satisfy demand. For example, increased chilled water flow to the air handlers should give the air handlers additional fresh air capacity.
[00145] It should be noted that critical zone restorations can also occur when a chilled water plant, or its components, is producing too much or too much cooling output. For example, if cooling demand is lowered, a critical zone reset can change the Delta T to be held so that it is closer to the project's Delta T. In the case above, for example, the Delta T can be reset from 15 degrees back to 16 degrees when cooling demand is lowered. Therefore, the chilled water flow rate can be reduced, which reduces the cooling output. Typically, a linear setpoint Delta T restoration is calculated based on the system dynamics as verified during the commissioning process.
[00146] FIG. 12 is a table illustrating an example of a restored critical zone for an exemplary air handler unit. As can be seen, the Delta T can be reset to a lower value to provide more chilled water flow, thereby lowering the air temperature of the air handler unit feed. It can also be seen that restoring the Delta T to a higher value raises the supply air temperature by reducing the chilled water flow to the air handler unit.
[00147] In operation, the value to which the Delta T is restored can be determined in several ways. For example, new values for entering and leaving water temperatures (ie, a restored Delta T) can be determined according to a formula or an equation in some modalities. In other embodiments, a set of predetermined set points can be used to provide the restored Delta T value. This can be described with respect to FIG. 12 which illustrates an exemplary group of set points 1204. Generally speaking, each point of set 1204 provides a Delta T value for a given trigger event. In FIG. 12, for example, each point in set 1204 provides a Delta T value for the temperature of the air supply in question to an air handler unit. The 1204 set points can be determined during demand flow setup or commissioning, and can be adjusted later if desired.
[00148] If the new or restored Delta T value is still insufficient to satisfy the cooling demand, another critical zone restoration can be activated to restore the Delta T again that is maintained by the operational strategy. In one or more modalities, critical zone restorations can occur until the chilled water plant can satisfy the cooling demand.
[00149] In one or more modalities, a restoration of the critical zone alters the Delta T to be maintained by an incremental amount, such as a degree. This helps to ensure that the Delta T to be maintained is close to the Delta T of the project. While slightly reduced efficiency may result in chilled water components, the benefits of substantially reducing or eliminating low Delta T outweigh the slight reduction in efficiency. When compared to traditional control schemes, demand flow efficiencies will remain substantial.
[00150] Circumstances that result in a restoration of the critical zone will be indicated here as an activation or activation event. As indicated, critical zone resets can be activated when chilled water plant components are producing too much or too little cooling output. To determine if plant components are producing too much or too little cooling output, the operational strategy can use information from one or more sensors. As will be described later, this information may include the characteristics of the chilled water within a chilled water plant (for example, temperature or flow), the operational characteristics of one or more components of the chilled water plant, or the air or environmental conditions (for example, temperature or humidity) of a space, as well as other information. Referring to FIG. 12, for example, an activator could be the temperature of the supply air to an air handler unit. For illustration purposes, if the supply air temperature does not match a desired supply air temperature, a critical zone reset can be activated.
[00151] As alluded to above, Delta T can also be increased by the operational strategy as a consequence of a restoration of the critical zone. For example, if cooling demand is lowered, Delta T can be reset to a higher value by a critical zone reset. An example of resetting the Delta T to a higher value for a lower cooling output (ie, the rise in the supply air temperature of the air handler unit) is shown in FIG. 12. Similar to the above, an increase in Delta T by a critical zone restoration can be triggered by various events or conditions.
[00152] FIG. 11B is a flowchart illustrating exemplary operations, including the critical zone restoration operation(s), that may be performed by a controller 1024. In step 1116, the information received in step 1104 can be processed to determine if an activation has occurred. If this has occurred, a restoration of the critical zone may occur which restores the Delta T line for which pumping is controlled. For example, operational characteristics provided by one or more sensors, such as the position of the air handler chilled water valves, the speed or VFD output, the chilled water temperature in a plant bypass, or other information, can cause a restoration of the critical zone, as will be described later.
[00153] If a critical zone reset occurs, the controller will use the Delta T reset value or the Delta T line reset in step 1108 to determine if an increase or decrease in flow is required. Then, as discussed above, an outlet can be provided to one or more pumps to effect this change in flow rate. If a critical zone restoration does not occur, the controller can continue to use the Delta T line or the current Delta T and control the flow accordingly. It should be noted that the steps of FIGURES 11A and 11B may occur continuously or may occur over various time periods. In this way, critical zone restorations and flow rates can be adjusted continuously or in desired time periods, respectively.
[00154] The demand flow operational strategy will now be described with respect to the operation of chilled water pumps and condenser water pumps. As will become apparent from the following discussion, control of pumping or flow by operational strategy has a highly beneficial effect on chilled water production (eg chillers), chilled water pumping, pumping water from the condenser, cooling tower fan operation, and airside fan operation. A. COOLED WATER PUMP OPERATION
[00155] As described above, the chilled water pumps provide the flow of chilled water through the chilled water plant. In one or more embodiments, chilled water pumps provide the flow of chilled water through the primary, secondary, tertiary, or other circuits of a chilled water plant.
[00156] In one or more modalities, the operational strategy controls such chilled water pumps in such a way that their flow is at or near the Delta T line described above. As described above with respect to the graph of FIG. 90, operating chilled water pumps according to a Delta T line results in substantial energy savings especially when compared to traditional control schemes.
[00157] Operation of chilled water pumps according to a Delta T line can be accomplished in several ways. Generally speaking, such an operation maintains the flow in one or more pumps at or near the Delta T line. The operating strategy may use different methods depending on the position or type of chilled water pump. For example, different operations can be used to control the flow rate of a chilled water pump depending on whether the pump is in a primary, secondary, tertiary, or another circuit. In one or more modes, the flow rate provided by a chilled water pump can be controlled by a variable frequency drive (VFD) connected to the pump. It should be understood that other devices, including chilled water pump devices themselves, can be used to control flow rate, pumping speed, or the like.
[00158] Typically, but not always, the operational strategy controls flow through one or more chilled water pumps to maintain a temperature at one or more points in the chilled water plant. One or more sensors can be used to detect the temperature at these points. The flow rate can then be adjusted to maintain a temperature in accordance with temperature information from the sensors. In this way a Delta T can be maintained at one or more points in the chilled water plant.
[00159] With reference to FIG. 1, in one embodiment, the operational strategy can control the secondary chilled water pumps 120 to maintain a Delta T, preferably at or near the design Delta T, through the air handlers 124. This operates the secondary chilled water pumps 120 conforms to the Delta T line and ensures that the air handlers 124 can provide their rated cooling capacity while operating efficiently. As indicated above, a particular Delta T can be maintained by increasing or decreasing the flow through the secondary chilled water pumps 120.
[00160] The operational strategy may also control the primary chilled water pumps 116 to maintain a Delta T at one or more points in the chilled water plant. For example, primary chilled water pumps 116 can be operated to maintain a Delta T for primary circuit 104, secondary circuit 108, or both. Again, this can be accomplished by increasing or decreasing the flow rate of one or more primary chilled water pumps 116.
[00161] As can be seen from the capacity equation, the relationship between Delta T and flow is linear. Thus, by maintaining a particular Delta T across the primary and secondary circuits 104, 108, the flows will typically be close to or in equilibrium. This reduces or eliminates the overflow that causes a reduction or elimination of bypass mixing.
[00162] It should be noted that other ways to eliminate offset mixing can be used in one or more modalities. In one embodiment, the primary chilled water pumps 116 can be controlled to maintain a temperature within an offset 128 of the chilled water plant. Due to the fact that the temperature within the offset 128 is the result of the offset mixing, maintaining the temperature within the offset also controls the offset mixing. In this way, the drift mixing, and its combining effect on the low Delta T, can be greatly reduced and, in many cases, effectively eliminated. In one embodiment, the temperature maintained may be such that there is an equilibrium or near equilibrium between the primary and secondary circuits 104, 108, reducing or eliminating the by-pass mixing.
[00163] For illustration purposes, the overflow in secondary circuit 108 can be determined by measuring the chilled water temperature within bypass 128. If the bypass temperature is close to or equal to the return water temperature of the air handlers 124 , there is additional secondary flow and the speed of the primary chilled water pump 116 can be increased until the chilled water temperature in the bypass drops to close to or the chilled water temperature in the primary circuit 104. If the bypass temperature is close to or equal to the chilled water supplying the primary circuit 104, there is an excess primary flow. The speed of the primary chilled water pump 116 can be decreased until the bypass temperature drops to a mid-point between the return chilled water temperature of the air handlers 124 and the primary circuit 104. The bypass temperatures in this "dead range" "has no restorative effect on primary pump speeds. In one or more embodiments, the primary chilled water pump 116 speed may not decrease below the primary chilled water pump Delta T set point.
[00164] In another modality, the operational strategy can control the primary chilled water pumps 116 to reduce or eliminate excess flow by combining the chilled water flow in the primary circuit 104 with the chilled water flow in the secondary circuit 108. A or more sensors can be used to determine the flow of the secondary circuit 108 to allow the primary chilled water pumps 116 to match the flow.
[00165] The critical zone restorations will now be described with respect to the operation of the chilled water pumps in accordance with the operational strategy. As indicated, a restoration of the critical zone can change the Delta T line for which the chilled water pumps are operated. Generally speaking, a restoration of the critical zone can occur when there is too much or too little refrigeration output as can be determined through one or more sensors. A critical zone restoration can occur for different chilled water pumps at different times and/or based on information from different sensors.
[00166] With reference to FIG. 1, for example, a critical zone reset for the secondary chilled water pumps 120 can be activated if it is determined that there is insufficient chilled water flow to the air handlers 124 to satisfy the cooling demand. This determination can be made based on various pieces of information (typically collected by one or more sensors). For example, when the cooling air of an air handler 124 is warmer than desired, a restoration of the critical zone can occur.
[00167] In one embodiment, the position of one or more chilled water valves within an air handler 124 may indicate that there is insufficient chilled water flow and trigger a critical zone reset. For example, opening a chilled water valve beyond 85% or other threshold may indicate that air handler 124 is "lacking" chilled water and trigger a critical zone reset. In one embodiment, critical zone restoration may incrementally lower the Delta T to be held through the air handler 124, causing an increase in chilled water flow through the air handler. The air handler 124 can now satisfy the cooling demand. Otherwise, the air handler chilled water valve must remain open beyond the limit and additional critical zone resets can be activated until the cooling demand can be satisfied. When cooling is satisfied, the chilled water valves close, which prevents additional critical zone restorations.
[00168] FIG. 13 is a table illustrating critical zone resets for an exemplary air handler unit. In this mode, critical zone resets are activated by the position of the chilled water valve of the air handler unit. As can be seen, once the chilled water valve modulates to 100% open, the Delta T is reset to lower values to provide additional chilled water flow to the air handler unit. In operation, a chilled water pump that supplies chilled water to the air handler unit, such as a secondary or tertiary chilled water pump, can be used to provide additional chilled water flow. It should be noted that FIG. 13 also shows that critical zone restorations can be used to increase Delta T when the position of a chilled water valve moves from open to closed.
[00169] Critical zone resets can also be activated for the 116 primary chilled water pumps. In one or more embodiments, a critical zone reset can be activated for the 116 primary chilled water pumps to ensure there is little or no bypass mixing in a chilled water plant. In one or more modalities, excessive flow, if any, can be detected by detecting the water temperature in the bypass. An increase or decrease in water temperature within the bypass can trigger a critical zone restoration. For example, when the water temperature in the bypass increases, pumping in the primary circuit can be increased to maintain balance between the primary and secondary circuits. In one embodiment, the VFD for a 116 primary chilled water pump can be adjusted at + or -1 hertz per minute until equilibrium or near equilibrium is produced. In operation, the operational strategy will typically result in excess flow that oscillates between zero and negligible flow, resulting in a significant reduction or elimination of diversion mixing. It should be noted that critical zone restoration can occur continuously in some modalities because the flow balance in a branch can be highly variable and dynamic.
[00170] For example, in one mode, the temperature in the offset can be measured and controlled, such as by adjusting the frequency of the production pump VFD, up to a set point of 48 degrees. This set point temperature can be variable up to some degree by the system and is determined at commissioning. Since the temperature in the bypass rises above said set point, an indication of excessive distribution water flow compared to chilled production water flow is known. The demand flow production pump algorithms can then be reset, via a critical zone reset, to increase the VFD frequency by 1 Hz per minute until an hour when the decoupler temperature drops below the set point minus one 2 degree dead range. These parameters are also system variable and will be determined at system commissioning. Deviation temperatures below the stipulated point + dead band indicate that excess production water flow has been obtained and the production pumping control algorithm is then inverted by the same frequency per unit of time, but never above the original set point of Delta T. This control strategy allows the production pumping to satisfy dynamic load conditions in the secondary or distribution circuits. This reduces the Low Delta Syndrome to its lowest obtainable level in all uncoupled pump systems as designed. It should be noted that VFD minimum frequencies can be adjusted during commissioning to match the manufacturer's minimum flow requirements.
[00171] The operational strategy, including its critical zone restorations, can be applied to various configurations of decoupled chilled water plants. FIG. 14 illustrates an exemplary chilled water plant that has a primary circuit 104, a secondary circuit 108, and a tertiary circuit 1404. As is known, the secondary circuit 108 may be a distribution line that carries the chilled water to the tertiary circuit 1404. It should be noted that a plurality of 1404 tertiary circuits may be provided in some chilled water plants. Generally speaking, tertiary circuit 1404 has at least one tertiary chilled water pump and one or more air handlers 124 that provide cooling to one or more buildings or other structures.
[00172] In operation, the 1408 tertiary chilled water pumps can be operated to maintain a Delta T through the 124 air handlers. As described above, these Delta Ts are preferably close to or in the design Delta T for the handlers of air 124. Secondary chilled water pumps 120 can be operated to maintain a Delta T through the tertiary pumps 204. Preferably, this Delta T is close to or in the design Delta T for the tertiary circuit 204. The water pumps 116 primary chillers can be operated to maintain a Delta T through the 112 chillers. This Delta T is preferably close to or in the design Delta T for the chillers.
[00173] In chilled water plants that have one or more 1404 tertiary circuits, critical zone restorations can also be activated based on various criteria. For illustration purposes, the critical zone resets for the 1408 tertiary chilled water pumps can be activated based on the position of the chilled water valves on the 124 air handlers. The critical zone resets for the 120 secondary chilled water pumps can be activated based on the flow rate of the 1408 tertiary chilled water pumps, as indicated by the speed of the pumps, the VFD output of the pumps, or the like. A high flow rate in the 1404 tertiary chilled water pumps may indicate that the 1404 tertiary circuit(s) or 1408 tertiary pumps are "lacking" chilled water. In this way, a critical zone restoration can be activated to provide excess chilled water flow to tertiary circuits 1404 from secondary circuit 208 by increasing the flow rate in one or more secondary chilled water pumps 120.
[00174] For illustration purposes, in one mode, when any VFD frequency of tertiary chilled water pump 1404 reaches 55 Hz, the Delta T set points of secondary circuit pump 208 can be adjusted linearly through a reset of critical zone in order to prevent the tertiary pump VFD frequencies from rising above 55 Hz or another frequency threshold. Set points, frequency limits, or both, can be determined during commissioning or demand flow installation in a chilled water plant.
[00175] FIG. 15 is a table illustrating critical zone restorations for a tertiary chilled water pump. In this mode, critical zone restorations are activated by the operating frequency (Hz) of a tertiary water pump VFD. As can be seen, the Delta T can be reset to a lower value when the tertiary pump VFD (or other tertiary pump speed or flow indicator) increases. As indicated, decreasing the Delta T value causes increased chilled water flow to the tertiary pump, allowing the cooling demand to be satisfied. The frequencies at which critical zone restorations occur and their associated Delta T values can be determined during installation or demand flow commissioning in the chilled water plant. It should be noted that Delta T can also be increased when the frequency or speed of the tertiary pump decreases.
[00176] Critical zone restorations for the primary chilled water pumps 116 can take place as described above to maintain an equilibrium or near equilibrium, which greatly reduces or eliminates the offset mixing between the primary and secondary circuits 104, 108.
[00177] It should be noted that in one or more modalities the critical zone restorations can be activated for the most critical zone of a chilled water plant subsystem. A critical zone in this sense can be considered as a parameter that must be maintained to provide the desired conditions in an area or in a process. Such parameters may include the air handler supply air temperature, the space temperature/humidity, the bypass temperature, the chilled water valve position, the pump speed, or the VFD frequency. For illustration purposes, tertiary chilled water pumps, such as building pump systems on campus projects, can be restored from your Delta T line based on the most critical zone in the building. Distribution pumping can be restored from your Delta T line based on the VFD HZ of the most critical tertiary pump in the system. B. CONDENSER WATER PUMP OPERATIONS
[00178] Generally speaking, condenser water pumps provide a flow of condenser water to allow refrigerant to condense inside a chiller. This condensation is an important part of the refrigeration cycle because it allows the refrigerant vapor to return to a liquid form to continue the refrigeration cycle. In one or more embodiments, the application of the operational strategy causes the condenser water pumps to be operated according to a Delta T line, resulting in substantial energy savings.
[00179] FIG. 16 illustrates an exemplary condenser 512 comprising a plurality of condenser tubes 1604 within a shell 1608. Refrigerant vapor may be contained in shell 1608 such that refrigerant vapor contacts condenser tubes 1604. In operation, condenser water flows through condenser tubes 1604, causing condenser tubes 1604 to have a lower temperature than that of refrigerant vapor. As a result, the refrigerant vapor condenses in the condenser tubes 1604 while the heat from the steam is transferred to the condenser water through the condenser tubes.
[00180] In one or more modes, the operational strategy influences the temperature of the refrigerant and condenser water by controlling the flow of condenser water through the 1604 condenser tubes. Reducing the condenser water flow causes the water to remain inside the 1604 condenser tubes for a longer period of time. In this way, an increased amount of heat is absorbed from the refrigerant vapor, which causes the condenser water to exit the condenser at a higher temperature and higher enthalpy. On the other hand, increasing the condenser water flow reduces the time the condenser water stays inside the 1604 condenser tubes. In this way, less heat is absorbed and the condenser water leaves the condenser at a lower temperature and lower enthalpy.
[00181] As indicated, a problem caused by low Delta T in a chiller is stacking. The operational strategy combats the stacking problem caused by low Delta T of condenser water at low inlet condenser water temperatures. In one or more modalities, this is done by controlling the condenser water flow in accordance with a Delta T line. In this way, the minimum lift requirements of a chiller can be maintained and the stacking problem is substantially reduced when not deleted. In one or more embodiments, lift requirements can be maintained by controlling the temperature of the saturated condenser refrigerant by controlling the leaving condenser water temperature in the condenser. The operational strategy can control the leaving condenser water temperature by controlling the flow rate and temperature of the condenser water, as discussed above. Because the saturated condenser refrigerant pressure increases or decreases with the saturated condenser refrigerant temperature, Delta P or rise in the cooler can be maintained by controlling the flow of condenser water.
[00182] In operation, the operational strategy may control one or more condenser water pumps, such as through a VFD, to maintain a Delta T across the condenser. Consequently, a leaving condenser water temperature in the condenser and rise in the cooler are also maintained.
[00183] In addition, to combat stacking, the demand flow operational strategy can also be configured to beneficially influence mass flow, lift, or both, in a chiller 112 by operating the condenser 516 water pumps of according to a Delta T line. Generally speaking, mass flow refers to the amount of refrigerant circulated within a chiller for a given load, while elevation refers to the pressure/temperature differential across which the refrigerant has to be transferred. The amount of mass flow and lift dictates the energy usage of the compressor 520 of a chiller. In this way, operating the condenser water pumps 516 in accordance with the operating strategy provides efficiency gains by reducing compressor energy use.
[00184] The compressor 520 of a chiller can be thought of as a refrigerant vapor pump that transfers the low pressure, low temperature gas from the evaporator 508 to the condenser 512 at a higher pressure and a higher temperature state. The energy used in this process can be expressed by the equation E = MF * (L/K),
[00185] where E is the energy used, MF is the mass flow, L is the elevation, and K is a refrigerant constant. As can be seen from this equation, reducing mass flow or elevation decreases energy use.
[00186] The mass flow (or weight of refrigerant) that must be circulated through a chiller 112 to produce the cooling effect (RE) required for a given amount of work or output (Tons) can be described by the MF formula = Tones * (K/RE),
[00187] where K is any constant. Simply stated, this formula says that increasing the cooling effect reduces the coolant weight, or mass flow, that needs to be circulated through the cooler for a given amount of work. Increasing the cooling effect also increases the applicable capacity of a chiller while reducing compressor power for a given amount of work.
[00188] The cooling effect can be increased in several ways. One way to increase the cooling effect is by sub-cooling the refrigerant in the condenser. Sub-cooling can be performed by lowering the entering condenser water temperature into the condenser. As is well known, the entering condenser water temperature is a function of the cooling tower design and environmental conditions. A lower condenser water inlet temperature allows the condenser to produce a lower refrigerant temperature as the refrigerant exits the condenser. Operation at the coldest seasonally available condenser inlet water temperature that is allowed by the condenser provides the greatest sub-cooling while operating within its manufacturer's specifications.
[00189] The sub-cooling of the refrigerant reduces its temperature below saturation and decreases the amount of "evaporations" that occur during the expansion cycle or throttling process. Evaporation is a term used to describe the amount of refrigerant used to cool the subcooled condenser refrigerant to saturated evaporator temperatures. No useful cooling effect is obtained by this "evaporated" refrigerant and is considered as a deviation from the cooling effect. Therefore, the higher the subcooling, the greater the useful cooling effect per cycle.
[00190] FIG. 17 is a table illustrating the benefits of sub-cooling in a chilled water plant where demand flow is applied. In general, the table quantifies the demand flow compressor energy changes. In the table, the design CoPr is calculated from known chiller performance data. Operating CoPr is a design CoPr adjustment based on the current chiller operating RE and HC.
[00191] As can be seen, the top row of the table shows that the design efficiency is 0.7 KW/Ton and the CoPr as 8.33. The second row is a snapshot of the chiller operating conditions prior to the demand flow implementation. The third row is the same cooler at roughly the same environmental/load condition after the demand flow. The fourth row is the efficiency that the chiller can provide under the best operating conditions. The change in the nominal tonnage and the efficiency obtained in this cooler with the improvement of RE must be observed. Tonnage is increased by 30%, while efficiency is improved by more than 50%.
[00192] As described above with respect to FIG. 6A, the refrigeration cycle can be illustrated by a pressure-enthalpy graph. Referring now to FIG. 6B, the beneficial effects of subcooling can also be shown by a pressure-enthalpy plot. As shown in FIG. 6B, the sub-cooling of the refrigerant in the condenser reduces the refrigerant enthalpy at point 616 to a point 628. The sub-cooled refrigerant can then enter the evaporator at a point 624. As can be seen, this magnifies the effect the refrigeration from point 604 to point 624.
[00193] Another factor that contributes to compressor energy is the pressure differential between the evaporator and the condenser, or Delta P, that a compressor has to transfer the refrigerant transversely. As indicated above, this Delta P is commonly known in the industry as elevation, and is usually expressed in terms of the temperature difference between the saturated refrigerant in the evaporator and the condenser. The effect of the rise in compressor energy can be seen in the energy equation E = MF * (L/K),
[00194] where L is the elevation. For example, according to the equation, an increase in elevation causes an increase in energy use, whereas a decrease in elevation reduces energy use.
[00195] Speaking in practical terms, the saturated pressure of the evaporator can be considered as a relative constant. This pressure can be determined by the evaporator leaving chilled water temperature. For example, one or more set points or a table can be used to determine the pressure of the saturated refrigerant in the evaporator. The difference between the leaving chilled water temperature and the saturated refrigerant temperature is known as the evaporator approach temperature.
[00196] In one or more modalities, the elevation reduction in accordance with the demand flow operating strategy can be effected by reducing the refrigerant pressure in the condenser. This can be achieved by reducing the leaving condenser water temperature in the condenser because the saturated condenser refrigerant pressure is adjusted by the leaving condenser water temperature and the design approximation for the saturated refrigerant temperature. Design approach temperature may vary depending on the quality of a chiller. For example, an inexpensive chiller may be approx. 4 degrees or more, whereas a better quality chiller may be approx. 1 degree or less.
[00197] In constant volume pumping systems, the leaving condenser water temperature is generally linearly related to the entering condenser water temperature into a condenser. Therefore, reducing the entering condenser water temperature reduces the leaving condenser water temperature. FIG. 19 is a table illustrating the linear relationship of entering and leaving condenser water temperatures in an exemplary condenser to constant volume pumping.
[00198] As noted above, a reduced leaving condenser water temperature reduces the refrigerant pressure in the condenser, under-cooling the refrigerant and thereby enhancing the cooling effect. Reducing the refrigerant pressure in the condenser also reduces lift. In this way, reducing the entering condenser water temperature has the dual benefit of increasing the cooling effect and reducing the rise.
[00199] Reducing the condenser water inlet temperature to just above freezing, in theory, should have an ideal practical effect on mass flow and lift. Unfortunately, chillers have minimal lifting requirements (which generally vary by chiller manufacturer, production, and model). Saturated refrigerant condensing pressures must be maintained at or above these minimum points to provide a sufficient pressure differential (ie, the Delta P of the refrigerant) to drive the refrigerant through the throttling or expansion process in the condenser. If these pressure requirements are not met, the refrigerant will cause stacking and cause the chiller to shut off from various chiller safety devices.
[00200] Unlike constant flow systems, the operational strategy can control the rise, regardless of the entering condenser water temperature, by adjusting the condenser water flow rate. This is highly advantageous because it allows the use of a lower condenser water inlet temperature. By allowing for lower inlet condenser water temperatures without stacking, the operating strategy significantly reduces compressor power by increasing sub-cooling (and the cooling effect) and lift. In practice, the operational strategy's subcooling can be increased to maximum allowable limits to maximize energy savings. The demand-flow method of controlling the rise, independent of the entering condenser water temperature and through condenser water pumping algorithms, is unique to the industry.
[00201] Furthermore, due to the fact that traditional condenser water pumping systems operate at a constant volume, the cooling towers are always in full flow conditions, even in part load condition. In a constant flow control scheme, when the load on the cooling tower decreases the operating range or Delta T on the tower decreases, which reduces tower efficiency. On the other hand, the operating strategy Delta T in the cooling tower is maintained at or near the Delta T of the tower design through the condenser water pumping algorithms described above. This is significant as lower tower deposit temperatures can be achieved for the same amount of cooling tower fan energy because efficiencies have been increased. Lower tower deposit temperatures correspond to lower condenser entering condenser water temperatures. It is important to note that condensers and cooling towers are selected at common Delta T design points, typically 10 degrees, as an industry standard.
[00202] In the operational strategy, the minimum cooling tower fan energy is maintained, for a certain set point of the sump temperature by controlling the condenser water pump to a constant Delta T algorithm as described above. This method of controlling cooling tower efficiency, regardless of tower load, by pumping condenser water, is unique to the industry. There is a synergy that develops between the chiller, condenser water pumping, and cooling tower subsystems by operating them under a demand-flow strategy that reduces the net energy of the system.
[00203] It should be noted here that another way in which the operational strategy increases the effect of refrigeration is by increasing the superheat of the refrigerant in the evaporator. A benefit of increased refrigerant superheat is that it reduces the refrigerant mass flow requirements per cycle. This reduces energy usage by the compressor. As can be seen in FIG. 6C, the superheat of the refrigerant generated in the evaporator extends the cooling effect from the 608 point to a 620 point which has a higher enthalpy.
[00204] With the operational strategy, the refrigerant superheat is kept constant across the chiller load range by controlling the chilled water pump(s) for a constant Delta T algorithm based on the design Delta T conditions . This method of controlling chiller superheat for design conditions, regardless of evaporator load, through chilled water pumping algorithms is unique to the industry.
[00205] In traditionally operated chilled water plants, the chilled water in the evaporator that has a low Delta T significantly reduces and sometimes eliminates refrigerant overheating in the chiller evaporator. Reducing or eliminating refrigerant superheat in the evaporator reduces the cooling effect. For example, in FIG. 6C, the reduction of refrigerant superheat may cause the refrigeration effect to retract from point 620 to point 608.
[00206] Refrigerant that is not heavily saturated because of the low Delta T of the chilled water is insufficiently overheated and can cause compressor damage because the refrigerant is insufficiently vaporized. In fact, manufacturers often add eliminator screens on top of the evaporator sections to break up larger drops of refrigerant that have not been superheated and have not vaporized properly before entering the compressor. If these drops reach the compressor, they cause excessive compressor noise and damage the compressor. In this way, demand flow provides the additional benefit of preventing the formation of such droplets by maintaining or increasing the refrigerant's superheat to properly vaporize the refrigerant before it reaches the compressor.
[00207] In one or more modalities, the operational strategy maintains refrigerant superheat by controlling the chilled water pumps according to a Delta T line. In this way, the refrigerant superheat can be maintained at or near design conditions, regardless of evaporator load. When compared to a traditional chiller operating at a low Delta T, the refrigerant superheat is typically much higher under the operational strategy.
[00208] For purposes of illustration, with reference to FIG. 1, the primary chilled water pump 116 of a primary circuit 104 may be controlled according to a Delta T line as described above. In this way, a Delta T can be maintained in cooler 112. As can be seen from FIG. 5, this maintains the Delta T of chilled water in the evaporator 508 of the chiller which is connected to the primary circuit by one or more chilled water conduits 532. As a result of maintaining the Delta T of chilled water in the evaporator 508, overheating of the refrigerant can be kept near or in design condition in the evaporator.
[00209] As can be seen, a synergy develops between the chiller water and the condenser water pumping subsystems as a result of maintaining the Delta T in accordance with the operational strategy. For example, controlling condenser inlet water temperature, condenser leaving water temperature, and condenser pump flow rate provides a synergistic effect on chiller energy, condenser pump energy, and condenser pump efficiency. cooling tower. It should be understood that the ideal condenser pump, chiller and cooling tower fan power combinations can be verified during commissioning or installation operating strategy. IV. USE OF DEMAND FLOW ENERGY
[00210] As shown from the above, chilled water plant control systems/schemes can positively or negatively influence the capacity and energy utilization of a chilled water plant. In general, traditional control schemes focus almost entirely on Delta P, thereby resulting in artificial capacity reductions and excess energy usage for a given load. Demand flow reduces energy use and maximizes chilled water plant capacity, regardless of load.
[00211] The following describes the reductions in energy use provided by the demand flow in chilled water plant subsystems, including chilled water pumps, condenser water pumps, compressors, cooling tower fans, and the airside fans. A. COOLED WATER PUMPS
[00212] The fundamental premise behind variable flow chilled water applications is best understood through the laws of affinity. The affinity laws indicate that system charge (tones) and flow (GPM) are linear, system flow and pressure drop (TDH) are a squared function, and system flow and energy are a function of the cube. Therefore, when system load is reduced the amount of chilled water flow is reduced proportionately, but energy is reduced exponentially.
[00213] As noted earlier in this narrative, traditional Delta P-based chilled water pumping algorithms can reduce flow, but not enough to avoid Low Delta T Syndrome systems. building falls from the project conditions, the relation between the load (Tons) and the flow (GPM) of the system is described by the equation Tons = (GPM * Delta T/K),
[00214] Maintaining a Delta T value at or near design parameters through the Demand Flow Operational Strategy optimizes flow (GPM) around system equipment selection criteria and specifications, thereby optimizing work and pumping energy. Furthermore, the ideal flow rates provided by the demand flow reduce energy use exponentially as seen through the laws of affinity.
[00215] As described above, the use of the chilled water pump to control the Delta T of the system design has the dual effect of optimizing chiller energy through superheat as well as chilled water pump energy. In addition, as will be described below, the airside capacity will also be increased and fan power will be reduced as a direct result of the demand flow operational strategy. B. CONDENSER WATER PUMPS
[00216] Affinity laws also apply to capacitor-side energy. Once the building load drops from the design conditions, the relationship between the system load (Tons) and the condenser water flow (GPM) is also as described by the affinity laws. Maintaining a Delta T at or near design parameters through demand flow control algorithms optimizes the flow (GPM) around the original system equipment selection criteria, thereby optimizing pump work and energy. - ment. Similar to chilled water pumps, energy-using condenser water pumps (as well as other pumps) decrease exponentially as flow is decreased.
[00217] As noted earlier in this narrative, traditional constant volume based condenser water pumping strategies result in a very low operating Delta T across the condenser, minimizing the ability to reduce compressor energy through sub-cooling of the soda. Using the operational strategy on condenser water pumps has the triple effect of optimizing pump power requirements, cooling tower efficiency, and managing minimum lift requirements at the chiller, even at inlet water temperatures very low condenser As will be further proven later in this narrative, cooling tower efficiency will also be increased and fan power will be reduced as a direct result of this demand-flow control strategy.
[00218] Changes in demand flow condenser water pump energy usage can be determined in the same way as chilled water pumping energy. It should be noted that in the unusual case that condenser water pumps are small (eg, low power) relative to the nominal chiller tonnage, the condenser water system will operate at or near the Delta T of the design under conditions of higher loads under demand flow may in some cases cause the chilled water plant to use slightly higher energy than operating at a low Delta T of the condenser water. However, operating in this manner under demand flow maintains the proper rise in the condenser even when operating at a very low inlet condenser water temperature. This maximizes subcooling which typically more than compensates for any increase caused by operating near or in the design Delta T at higher load conditions. The optimal operational Delta T will typically be determined during the commissioning or configuration process through field testing. C. COMPRESSORS
[00219] Compressor energy reductions derived by applying a demand-flow operating strategy are best quantified by calculating the associated change in Refrigerant Coefficient of Performance (COPR). COPR is the measure of efficiency in the refrigeration cycle based on the amount of energy absorbed in the evaporator compared to the amount of energy expended in the compression cycle. The two factors that determine COPR are the effect of refrigeration and the heat of compression. Compression heat is the caloric energy equivalent to the work done during the compression cycle. The heat of compression is quantified as the difference in enthalpy between the refrigerant entering and leaving the compressor. This relationship can be indicated as COPR = (RE/HC),
[00220] where RE is the effect of refrigeration and HC is heat of compression. For optimal COPR, the refrigerant superheat should be as high as possible and the refrigerant subcooling should be as low as possible.
[00221] The use of chilled water pumping, condenser water pumping, and cooling tower fan subsystems to achieve optimal COPR is unique to the industry and critical to demand-flow technology.
[00222] Compressor energy changes under demand flow will also be explained now. The design COPR is calculated from known chiller performance data, while the operation COPR is a design adjustment based on the actual cooling effect and heat of compression. For example, the table in FIG. 19 contains design refrigerant properties and measurements of a Carrier chiller (trademark of Carrier Corporation) before and after an actual demand flow retrofit. The top row of this worksheet shows that the design efficiency is 0.7 KW/Ton and the design COPR is 8.33. The second row is the measured operating parameters of the chilled water system before demand flow implementation. The third row is the measured operating parameters of the chilled water system with the demand flow applied. The fourth row is the efficiency that the chiller is capable of achieving under the best operating conditions. The change in nominal tonnage and efficiency obtained in this cooler with the improvement of the cooling effect should be noted. Tonnage is increased by 30%, while efficiency is improved by more than 50%.
[00223] These data are now applied to the pressure and enthalpy diagram in FIG. 20 in order to graphically illustrate the fundamental changes in the refrigeration cycle before and after the demand flow is applied. As can be seen, when comparing the before 2004 graph and the after 2008 graph of demand flow, there is an increased cooling effect and a reduced lift (no stacking) under the demand flow. As can also be seen, the demand flow application increased the 2012 subcooling as well as the 2016 coolant overheating. D. COOLING TOWER FANS
[00224] On-demand flow cooling tower fan power is approximately linear to the load in a well-maintained system that operates at the lowest sump temperatures achievable under current environmental conditions. Condenser water inlet temperature or cooling tower fan setpoints can be set equal to the design temperature approach + cooling tower sump temperature for wet bulb. Changes in cooling tower fan power can be based on actual condenser water inlet temperature, nominal in-line tonnage, measured tonnage, and in-line cooling tower fan power.
[00225] A table of a working system with the operational demand flow strategy applied is shown in FIG. 21. In this case study, the cooling tower fan set point was lowered from 83 degrees to 61 degrees to demonstrate the change in energy between subsystems when the entering condenser water temperature drops. The table is read from right to left. E. AIRSIDE FANS
[00226] The energy and capacity of the air-side fan is directly affected by Low Delta T Syndrome and by the by-pass mixing in the plant. For example, a 2 degree rise in chilled water temperature can increase the variable air volume air handler unit fan power by 30% under design load conditions. This loss of efficiency can be directly quantified using basic heat exchanger calculations. It should be noted that airside work and energy are affected by Low Delta T Syndrome in the same way as other system heat exchangers with a loss of applicable capacity and increased energy consumption.
[00227] The heat transfer equation Q = U*A*LMTD, where Q is the total heat transferred, U is the total heat transfer coefficient of the heat exchanger material, A is the surface area of the heat exchanger. heat, and LMTD is the log mean temperature difference, is one way of looking at the effects of Low Delta T Syndrome in air handler chilled water coils. On chilled water coils, the LMTD describes the relationship between the inlet/outlet air side and the inlet/outlet water side. In the context of demand-flow systems where the chilled water is moving more slowly (higher Delta T) there is some discussion that the total heat transfer coefficient, U, is reduced, resulting in less efficient coil performance. While it may be true that U is reduced, it is more than offset by the effects of feeding cooler chilled water into a demand flow system, which is reflected in the higher LMTD. In fact, the higher LMTD more than offsets any theoretical U-shaped reductions as seen in the following example.
[00228] More specifically, LMTD analysis shows that reducing CHWS to the coil by lowering the chiller set points or by eliminating mixing in the plant offset can dramatically improve coil performance. The table in FIG. 22 provides an LMTD analysis that details the potential changes in airside coil capacity in the demand stream. With the exemplifying data of FIG. 22, a capacity increase of 25% is achieved.
[00229] FIG. 23A illustrates the relationship between chilled water flow and Delta T in a system with Low Delta T Syndrome. FIG. 23B illustrates a demand flow system coil with decreasing chilled water supply temperatures and GPM associated with a constant chilled water return temperature and load. FIG. 23C illustrates potential increased coil capacity at design chilled water flows with decreased feed chilled water temperatures. This example illustrates the flexibility of a demand-flow operating strategy to overcome particular problems in a given system.
[00230] The total air side cooling load is calculated by the equation Qt = 4.5*CFM*(h1 - h2), where the inlet air enthalpy is h1 and the outlet air enthalpy is h2. For example, based on this formula and the following assumptions, fan energy usage after demand flow is applied can be calculated/quantified.
[00231] The monthly mean air handler unit (AHU) load (Qt) is known from previous analysis.
[00232] The AHU CFM is linear for the load.
[00233] The AHU inlet air enthalpy (h1) is known from design information or direct measurement.
[00234] Based on the above, the monthly average AHU CFM can be determined by the equation CFMavg = CFMdesign * (Qtavg/Qtmax □)
[00235] where Qtavg is the monthly mean AHU Qt and Qtmax is the maximum AHU Qt. The monthly average exhaust air enthalpy can be determined by the equation h2avgh1 + (Qtavg/4.5) * CFMavg
[00236] where Qt.sub.avg is the monthly average AHU Qt and CFM.sub.avg is the monthly average AHU CFM. It should be noted that the value of 4.5 is a constant that can be adjusted for site position based on air density.
[00237] The example data in FIG. 24 illustrate the results of these calculations and assumptions for a system that has a maximum connected load of 1,000 tons at 315,000 CFM. The minimum airside CFM is 35% and the minimum AHU SAT is as indicated. As can be seen, demand flow provides numerous advantages. V. SINGLE SPECIFIC ADVANTAGES FOR DEMAND FLOW
[00238] As can be seen from the above, demand flow provides a unique operating strategy in the HVA/C industry. In addition, the demand flow and its operational strategy are the first that, specifically: 1. Utilize external control operations in chilled water production pumping subsystems to optimize the evaporator refrigerant superheat, or the enthalpy of the refrigerant leaving the evaporator, thereby beneficially influencing the mass flow component of the compressor's energy use. Controlling chilled water pumps, such as via VFDs, to close to or to the manufacturer's designed evaporator Delta T (eg, design Delta T) when using demand flow chilled water pumping operations controls the refrigerant overheats at the chiller manufacturer's design conditions regardless of the percentage charge in a chiller at any one time. This optimizes the enthalpy of the refrigerant leaving the evaporator and reduces chiller compressor energy compared to a chiller operating at a Delta T lower than the design Delta T (ie, a low Delta T).
[00239] Demand flow also uses external control operations in chilled water distribution pumping subsystems to obtain the project's Delta T regardless of chilled water plant load conditions, thereby eliminating Low Delta Syndrome T in the chiller water subsystem. 2. Utilize external control operations in condenser water pumping and cooling tower fan subsystems to optimize condenser refrigerant sub-cooling, or the enthalpy of refrigerant leaving the condenser (and entering the evaporator). In this way, the mass flow component of the compressor energy equation, as described above, is beneficially influenced. The demand flow control operations in the cooling tower fan and condenser water pumping subsystems generally determine the final operating saturated pressure/temperature differential between the evaporator and condenser in the chiller (i.e., the elevation). This beneficially influences the mass flow and lift components of the compressor energy equation discussed above.
[00240] As indicated, the saturated evaporator pressure can be considered as a relative constant because the chilled water inlet and outlet conditions are kept constant. However, condenser inlet water temperatures, and pressures when constant volume condenser water pumps are used, are varied according to environmental and load conditions. Therefore, the saturated condenser pressure condition can be manipulated, through the leaving condenser water temperature, to control the minimum pressure differential required by the chiller manufacturer. The demand flow constant Delta T variable flow operations control the condenser water pumps, such as through VFDs, to maintain the manufacturer's minimum pressure differential (ie, rise) between the evaporator and condenser or all the time.
[00241] Demand flow also combines condenser water flow with chiller load and in this way reduces condenser water flow through the cooling tower under all part-load conditions. As indicated, part load conditions exist approximately 90% of the time in most chilled water plants. When the flow of water from the condenser is reduced, the approximation of the deposit temperature from the cooling tower to the wet bulb is also reduced. This is an almost linear relationship with about half the approach temperature of the original cooling tower design. This results in lower cooling tank temperatures at any part load at the same power as the cooling tower fan. In turn, lower cooling tower sump temperatures result in lower condenser entering condenser water temperatures, providing subcooling to the refrigerant in the condenser.
[00242] In addition, demand flow uses external control operations in the condenser water pumping subsystem to achieve close to or in the Delta T of design for a condenser regardless of chiller load conditions, thereby eliminating Chiller Syndrome. Low Delta T in the condenser water subsystem. 3. Utilize external collaborative control operations between production and distribution circuits in order to balance the flow between the circuits, minimizing or eliminating excessive flow and bypass mixing that contribute to Low Delta T Syndrome, such as in an uncoupled chilled water plant. This produces the most applicable airside capacity at any chilled water flow rate. This also allows the primary or production circuit pumping to satisfy the varying load conditions of the distribution pumping system. Under the flow of demand, Low Delta Syndrome is reduced to its lowest possible level when it is not effectively eliminated. 4. Utilize critical zone restorations to satisfy increases in cooling demand while controlling the chilled water pumping according to a Delta T line. Critical zone restorations can also be used to decrease cooling output by restoring the Delta T line. 5. Operate chilled water plants and their components at minimum part-load pumping pressures to minimize chilled water valve bypass and resulting super-cooling, thereby decreasing the load on the system. 6. Produce a synergistic reduction in chilled water plant energy use, as well as an increase in applicable capacity by synchronizing chilled water pumping, condenser water pumping, compressor operation, cooling tower operation, and airside operation. SAW. DEVICE OR DEMAND FLOW CONTROLLER
[00243] The operational strategy discussed and presented here refers to the principles, operations and algorithms applied to one or more components of the chilled water plant to implement a logical control strategy of the demand flow variable pressure curve to obtain the advantages and the benefits discussed above. The operational strategy can be implemented in alternative modalities to beneficially influence and optimize the performance of an existing chilled water plant and the components included or operable in it. Alternate mode and configuration can be used to control pressure and flow rates through one or more pumps and compressors operable within a chilled water plant. Controlled pressure and flow rates can, in turn, reduce or eliminate Low Delta T Syndrome by operating chilled water plant components in or near the project's Delta T, regardless of demand conditions and/or water requirements. refrigeration.
[00244] FIG. 25 illustrates an exemplary 2500 demand flow control system that can be used to implement the operational strategy on a new chilled water plant system or upgrade an existing chilled water plant. In one or more embodiments, the exemplary demand flow control system 2500 includes a demand flow controller 2502 coupled or in communication with the controller 1000 (see FIG. 10). Here, the phrases "coupled to", "in communication with", and the like are defined to refer to components that are directly connected to each other or indirectly connected through one or more intermediate components. Such intermediate components can include hardware and software-based elements.
[00245] Controller 1000, in this exemplary mode, comprises processor 1004, inputs 1020 configured to receive data or information from sensors 1028, and outputs 1024 configured to provide control signals, setpoint information and other commands to the drive variable frequency (VFD) 1032 or other outputs. Data or information received or collected through sensors 1028 describe and characterize chilled water, condenser water, refrigerant, flow rate or other operating and variable parameters of chilled water plant components detected by one or more sensors 1028 may be received via a 1020 input.
[00246] Processor 1004 may then execute one or more processing routines or algorithms against the data or information received through one or more inputs 1020. The operational strategy includes the control and analysis routines that include the embedded and described algorithms by the methods presented and illustrated by the attached flowcharts. The operational strategy can be executed or implemented by the demand flow controller 2502 and the results communicated to processor 1004 and memory 1012. Alternatively, processor 1004 can continue to execute the original inefficient control and analysis routines executed in connection with a routine control routine of subsystem 2508. The results of the control routine of subsystem 2508 can be overridden or otherwise overridden by the results provided by demand flow controller 2502 as will be discussed in more detail below. As discussed above, in the performance of control routines, algorithms, or other defined series of steps, tasks, or activities, processor 1004 may execute one or more computer executable instructions stored in memory device 1012. Computer executable instructions may include program logic, drivers and communication protocols required for information exchange, sensor data, demand flow information, and pressure setpoints. Computer executable instructions may also be wired or projected onto processor 1004. Memory device 1012 may cooperate with or include an external storage device, an accessible device or component used to store data or information.
[00247] The demand flow device 2502, either alone or in cooperation with the controller 1000 and the processor 1004, stores the operational strategy routines and algorithms comprising a demand flow control routine 2600 stored in a memory 2602 (See FIG. 26). The operational strategy routines and algorithms incorporated in the demand flow control routine 2600 allow the demand flow device 2502 to operate the chilled water plant and/or one or more components thereof according to demand flow principles in the demand flow in general and the variable pressure control demand flow in particular. Examples of operational strategy routines and algorithms incorporated in the demand flow control routine 2600 are shown and discussed in relation to FIGS. 28 and 29 and the methods associated therewith. Hardware comprising the demand flow device 2502 and/or the computer executable instructions, processes, and compiled logic can be encrypted to prevent modification and ensure optimal operation.
[00248] The demand flow controller 2502 can accept input data or information, for example, from the controller 1000, to perform one or more operations, calculations and/or control processes in real-time or near real-time in relation to the input data in accordance with the operating strategy, and provides a corresponding output. The corresponding output can be received, for example, by controller 1000 and stored in memory 1012 as will be discussed in more detail below. Alternatively, the corresponding output can be provided directly to one or more of the chilled water plant components.
[00249] FIG. 26 illustrates the configuration of demand stream device 2502 that may be coupled to controller 1000. Demand stream device 2502 may include a demand stream processor 2604 coupled to memory 2602. Memory 2602 stores the flow control routine demand 2600 which includes algorithms that incorporate the presented methods to determine when the pressure setpoint increases or decreases associated with each of the one or more pumps that control chilled/condenser water flow should be performed to maintain the chilled/condenser water at or near a desired Delta T.
[00250] When the 2600 demand flow control routine has executed the operational strategy to determine an ideal pressure setpoint, the 2604 demand flow processor accesses a 2606 communication module to provide the ideal pressure setpoint determined (as identified by reference numeral 2504) to controller 1000 and/or memory 1012. In particular, demand flow controller 2502 can communicate the calculated ideal pressure setpoint 2504 via a communication bus 2506 to the 1012 memory. The sample 2504 ideal setpoint can be communicated through the 1004 controller or it can bypass the 1004 controller and be provided directly to the 1012 memory.
[00251] Regardless of the way in which the exemplary ideal setpoint 2504 is provided, the information or values can be stored in a stack or memory location 2506 defined within memory 1012. Memory stack 2506 can store and organize a or more design parameters and/or detected or measured cues for use by the demand flow control routine 2600. Memory stack 2506 can also store and organize one or more of the design parameters and/or measured cues that, by in turn, they are accessible by the control routine of subsystem 2508. The control routine of subsystem 2508, in this example, encompasses the original inefficient control and analysis routines. The results and variables used and produced by processor 1004 executing the control routine of subsystem 2508 can be stored in predefined memory locations within memory stack 2506.
[00252] Memory stack 2506, in this exemplary embodiment, is accessible to processor 1004 and demand stream device 2502 (and more particularly demand stream processor 2604 operable within demand stream device 2502). The 2502 demand stream device can communicate with and access a 2510 driver in order to facilitate communications with memory stack 2506. For example, the 2510 driver can translate information and protocols to ensure reliable communications between systems and the programming of the demand flow device 2502 (and the included demand flow control routine 2600) and the existing controller 1000 to be upgraded or augmented.
[00253] The 2510 driver provides a mechanism whereby one or more design parameters and/or measured tokens stored in the 2506 memory stack can be read or otherwise used by the 2604 demand flow processor and the flow control routine demand 2600. Similarly, the 2510 driver provides a mechanism whereby the set pressure values and the calculated values determined by the legacy 1000 controller can be overridden or otherwise overridden, for example, by the ideal pressure setpoint 2504 determined by the demand flow device 2502.
[00254] In another embodiment, the demand flow control routine 2600 can be stored, for example, in an auxiliary memory (not shown) such as: a memory card, a memory stick, a floppy disk, a universal serial bus ("USB") memory device, or any other device operable to store executable computer data or instructions. The auxiliary memory can, in turn, be coupled to and/or communicated with the memory device 1012. In this way, the software or wired instructions to perform the demand flow variable pressure curve logic control can be run and/or integrated into the 1000 controller. Alternatively, updates or upgrades can be loaded or stored in an auxiliary memory and transferred to the demand stream device 2502 via the 2606 communication module.
[00255] The 2606 communication module may include hardware and software elements necessary for exchanging information between the demand stream device 2502 and the demand stream processor 2604 and a processor 1004. For example, the communication module 2606 may include hardware components such as a USB port, an Ethernet port, other networking capabilities to enable communications over a wide area network (WAN), a local area network (LAN) and/or a wireless network configured according to, for example, IEEE 802.11x. The communication module 2606 may also include software elements such as communication drivers, formatting algorithms, and translation tools configured to facilitate the exchange of information or data between the demand stream processor 2604, which may operate accordingly. with a first programming language, and processor 1004 which may be operating in accordance with a second programming language. For example, the software elements of the 2606 communication module can convert or otherwise translate the received sensor information or data, or the operational strategy results communicated, into another readable or exchangeable format, such as an Extensible Markup Language (XML ). Communication module 2506 may also cooperate with driver 2510 to convert or otherwise translate information or results into one or more proprietary communication formats or protocols.
[00256] The demand flow device 2502 may also include a 2608 input/output (I/O) interface configured to provide additional visual information, generate a graphical user interface (GUI) and/or receive user input via a keyboard or other input device. The 2608 I/O interface can also couple with a touch screen display device configured to generate a graphical user interface (GUI) and/or to receive one or more user input through a capacitive or resistive interface. bet on the display screen. Alternatively, the 2608 I/O interface may include or cooperate with one or more buttons or keys arranged and configured to receive user input. The 2608 I/O interface provides a means by which a user and/or a system configurator can directly access the demand flow device 2502 without having to couple the controller 1000. In this way, the demand flow device demand 2502 can be used independently of the 1000 legacy controller.
[00257] The demand flow processor 2604 and the demand flow control routine 2600 stored in memory 2602 can cooperate and exchange the information necessary to implement the operational strategy related to at least the logic of the variable pressure curve of demand flow as indicated here. The 2600 demand flow control routine can include control algorithms and routines programmed and designed to optimize the performance of each of one or more chilled water plant components with respect to one or more remaining components. For example, the demand flow control routine 2600 might include: a demand flow evaporator routine 2610; a demand flow condenser routine 2612 and a demand flow pump routine 2614. Each of these routines 2610 to 2614 can be arranged and programmed to determine the stipulated optimal pressure values to be maintained in one or more components and pumps such as the secondary and tertiary pumps that operate within and in connection with chilled water plant circuits. By operating each of the pumps at their stipulated optimal pressure determined values, the pumps can be synchronized and coordinated to achieve or maintain an optimal pressure and flow between components and circuits, in turn, an optimal Delta T can be maintained in each of the 2700 chilled water plant components (see FIG. 27). The control algorithms and routines contained or incorporated within the demand flow control routine 2600 are discussed and illustrated in relation to the method presented herein and illustrated at least in FIGS. 28 and 29.
[00258] The 2610 Demand Flow Evaporator routine can be configured and programmed to determine an optimum evaporator pressure setpoint based, for example, on one or more design parameters and/or detected measured cues. For example, evaporator 2710 (see FIG. 27) may have been specified or designed according to one or more design parameters which may include: (GPM); an operating pressure differential (PSID); an output capability (Tones); and the design Delta T. One or more of these measured parameters can be detected or sensed by sensors 2710a and 2710b. Sensors 2710a and 2710b can be flow sensors, pressure sensors, temperature sensors, or any combination of these.
[00259] As used herein, the sensors for each of the chilled water plant 2700 components (see FIG. 27) are identified by the reference numeral of the component being monitored (ie, the numeral the reference for the evaporator is "2710") and a letter "a" for the supply side and a letter "b" for the return side of each component. In this way, sensors 2710a and 2710b are known for monitoring and reporting the parameters and operating conditions related to the feed side output and the return side input of evaporator 2710, respectively.
[00260] The demand flow condenser routine 2612 can be configured and programmed, similar to the demand flow condenser routine 2612, to determine an ideal condenser pressure setpoint based on, for example, design parameters and/or the operating conditions detected or measured. For example, condenser 2712 (see FIG. 27) can be characterized by one or more design parameters such as flow rate (GPM); the operating pressure (PSID); the output capacity (Tones); and a design Delta T. One or more measured or operational parameters can be detected or sensed by sensors 2712a and 2712b.
[00261] The demand flow pump routine 2614 can be used to calculate and determine ideal pressure set points for the compressor 2714, and the secondary pump 2720 (as well as any tertiary pumps, etc.) operable within the water plant Exemplary Variable Pressure Curve Logic Control Cooled 2700 shown in FIG. 27. VII. LOGIC OF THE DEMAND FLOW VARIABLE PRESSURE CURVE (VPCL)
[00262] Figures 27, 28, and 29 respectively illustrate the exemplary chilled water plant 2700 configured to operate in conjunction with the demand flow device 2502, and the algorithms and processes for determining optimal pressure setpoints associated with the condenser and evaporator operable in it. FIG. 30 illustrates an algorithm and process for calculating the operating pressure exponent used by the condenser and evaporator routines discussed and presented here.
[00263] FIG. 27 illustrates the exemplary chilled water plant 2700 which includes a primary circuit 104 and secondary circuit 108. The components of the exemplary chilled water plant are shown here coupled or in communication with the controller 1000 and the demand flow device 2502. cooler 112, in fluid communication with primary circuit 104, comprises condenser 2712, compressor 2714 and evaporator 2710 coupled through refrigerant lines 2736 and expansion valve 2738. Evaporator 2710 can be connected to a primary circuit or another from a chilled water plant by one or more chilled water lines 2732. Demand flow device 2502, via controller 1000, performs demand flow control routine 2600 to control operation, for example , compressor 2714, a condenser water pump 2730, and water pumps 2716 and 2720 operable in the primary and secondary circuits, respectively.
[00264] In this exemplary mode, the demand flow control routine 2600 receives, through processor 1004, memory 1012 (specifically memory stack 2506) and input 1020, the sensor data and communicates each of the stipulated values from the subsequently calculated optimal pressure control to the compressor and operable water pumps within the 2700 chilled water plant. FIG. 27 illustrates the demand flow device 2502 that communicates an ideal pressure setpoint A (which may be the ideal pressure setpoint 2504 discussed previously with respect to FIG. 25) to the water pump 2716. Similarly, the pump of water from condenser 2730 which controls or adjusts the pressure within chiller 112 receives an optimized pressure setpoint B. Secondary and tertiary pressure pumps, such as the sample water pump 2720, will similarly receive stipulated points of optimal pressure (represented by the reference identifier "C"). With Delta T control between the 112 chiller and the primary and secondary fluid circuits, the operation of the 2744 cooling tower fan and 2746 air handling unit can be controlled and tuned to similarly optimize your fan performance and usage. energy as indicated by the reference identifiers "D" and "E", respectively.
[00265] Sensor data related to the measured and operating parameters that occur throughout the 2700 chilled water plant can be detected by sensors 2714a, 2714b, 2730a, 2730b, 2716a, 2716b, 2720a and 2720b arranged at the feed and return points adjacent to compressor 2714, condenser water pump 2730, and water pumps 2716 and 2720, respectively. The detected sensor data can, in turn, be communicated to input 1020 for use by processor 1004 (and stored where applicable in memory 1012 and specifically in memory stack 2506).
[00266] In this manner, the demand flow device 2502 evaluates each of the operable components within the chilled water plant 2700 based on design characteristics, measured operating performance, and current load requirements. The demand flow control routine 2600 operable within the demand flow device 2502 then calculates in real or near real time an optimal pressure setpoint for each of the components to control the flow and ultimately regulate the Delta T through each of the components in order to implement the operating strategy of the demand flow variable pressure curve logic.
[00267] The demand flow variable pressure curve (VPCL) logic as implemented by the demand flow control routine 2502 optimizes the total energy of the chilled water plant 2700 system by synchronizing the operation of the individual operating components in the same. In particular, the individual components are synced to an efficiency curve calculated against the current load ambient condition detected by sensors 2714a, 2714b, 2730a, 2730b, 2716a, 2716b, 2720a and 2720b.
[00268] In order to maximize user comfort and optimize system efficiency, the demand flow control routine 2502 uses a detailed optimization algorithm and process to minimize chiller 112 energy usage. The demand flow variable pressure device provides the mechanism by which energy usage can be controlled by optimizing the set pressure values of the 2714 compressor, and the 2716, 2720 and 2730 pumps which in turn allows for control water temperature and flow rate throughout the 2700 chilled water plant. A. CONDENSER
[00269] Figures 28 and 29 illustrate the illustrative algorithms and processes for determining the set ideal pressure values associated with the condenser and evaporator that can be implemented by the demand flow device 2502 and the flow control routine. demand 2600. FIG. 28 is an operational flowchart 2800 of the procedures, steps and tasks that can be implemented by the demand flow control routine 2600, and more particularly the demand flow condenser routine 2612 which is a part of the flow control routine demand 2600 in order to optimize the performance and efficiency of the 2712 condenser (see FIG. 27).
[00270] An initial step or task undertaken to use the principles of demand presented for the variable pressure curve logic is to identify and review the design parameters of one or more components operating interconnected with the 2700 chilled water plant For example, before starting the implementation of the presented algorithm and optimization routine, the user or designer can enter or provide one or more design parameters to memory 2602, memory 1012 or any other database or storage location accessible (block 2802). Design parameters can include: the design condenser flow (GPM); the condenser design pressure differential (PSID); the capacity of the design condenser (Tones). Design parameters can also include baseline or project chilled water Delta T which represents the full load chilled water Delta T at the time of commissioning of the 2700 chilled water plant. demand flow 2604, and more specifically the demand flow condenser routine 2612, with a baseline performance envelope against which the condenser 2712 can be evaluated.
[00271] The demand flow control routine 2600 and the demand flow condenser routine 2612 are also configured, as shown in block 2804, to empirically calculate an operating pressure exponent (P exponent) based on the parameters measured from condenser 2712 operating in cooler 112. In this exemplary mode, the exponent of the operating pressure is calculated according to the formula: Exponent P = A(xA2) + Bx + C
[00272] where x is the Delta P or the pressure change measured through the condenser 2712 (see block 2804) and the constants A, B and C are calculated for each chilled water plant 2700. This relationship is discussed in more depth with respect to FIG. 30. In particular, FIG. 30 illustrates a pressure exponent algorithm and routine 3000 that can be used to empirically derive distinct pressure exponents and a total pressure exponent curve that fits or otherwise connects to each of the distinct pressure exponents. The total exponent pressure curve, and more particularly the equation describing the total exponent pressure curve, is used in turn by the condenser routine to determine the operating pressure exponent shown above.
[00273] When the 3000 pressure exponent routine initializes, the Delta P or pressure differential (PSID) across the 2712 condenser is measured at a variety of pump speeds specified on the 2730 condenser water pump. The pressure exponent routine 3000 records the pump speed in Hertz (Hz) and the pressure differential (PSID) across the 2712 condenser when the 2730 condenser water pump is operating at a part load (PLV) value that corresponds to 25%, 50%, 75% and 100% of pumping capacity (block 3002). The pressure exponent for each distinct partial load (PLV) value is calculated as a function of the maximum operating pressure differential (PSID) of the system, the pump speed in Hertz, and the operating pressure differential measured at a given PLV . The formula to calculate one of the distinct P exponents for a given PLV is: Operating PSD of PLV = Maximum Operating PSID * (Pump Speed/60) APLV of Exponent P
[00274] The maximum operating pressure differential (PSID) is a known design value, and the pump speed (Hz) and operating pressure differential (PSID) are measured and/or empirically derived values. In this way, it is possible to calculate a distinct pressure exponent (PExponentPLV) for each set of variables associated with a given partial load value (PLV). Indicated in another way, by balancing the left and right sides of the above formula, the distinct pressure exponent (P Exponent PLV) can be derived for a given partial load value (eg 25%, 50%, 75% and 100 % of pumping capacity) and the operating pressure differential measured at the PLV in question (block 3004). The resulting distinct pressure exponents (P ExponentPLV-25%, PExponentPLV_50%, PExponentPLV-75% and PExponentPLV-100%) can be plotted according to the measured operating pressure differential in order to define the curve of the exponent of the total pressure. The equation describing the total pressure exponent curve (block 3006) can be derived based on these plotted values.
[00275] Once the equation describing the total pressure exponent curve has been derived, the pressure exponent 3000 routine ends and returns to operating flowchart 2800. At this point, the equation describing the total pressure exponent curve can be used to calculate the operating pressure exponent for any pressure differential (PSID). An exemplary total exponent pressure curve equation can be defined as: P Exponent = -0.00031 * (xA2) + 0.00031x + 1.9358
[00276] where x is the Delta P or the pressure change measured through the condenser 2712 (see block 2804) and the constant A is equal to -0.00031, the constant B equals 0.0031 and the constant C is equal to 1.9358.
[00277] This part of the 2612 demand flow condenser routine can be thought of as the design or configuration part of the routine, whereas the remaining steps and operations can be characterized as the running or operational part of the routine.
[00278] The 2612 demand flow condenser routine uses sensors 2712a and 2712b to detect and measure the pressure differential (PSID) across condenser 2712. In this modality, sensors 2712a and 2712b can be specified water immersion sensors with an appropriate range (eg (20° - 120°F)) to measure the Delta-T elevation of the condenser water. In other modalities and configurations, temperature sensors can be high precision or higher precision (± 0.5°F) sensors arranged to detect minor variations in condenser and/or cooled water flow throughout all parts of the plant of chilled water 2700. In addition, the demand flow control routine sensors 2712a and 2712b and/or their components or subsystems can be configured and arranged to measure a chilled water supply temperature (CWS) (sensor 2712a) and the chilled water return temperature (CHR) (sensor 2712b) associated with condenser 2712 (in block 2806).
[00279] The demand flow condenser routine 2612 can subsequently use the sensed and measured information of pressure and temperature to calculate a flow (GPM) through the condenser 2712 (in block 2808). In particular, the demand flow processor 2604 accesses the values stored, for example, in memory stack 2506 (or memory 2602 if previously accessed and stored locally) as directed by demand flow control routine 2600. condenser is calculated according to the formula:
[00280] Measured Condenser Flow = T&B GPM * (Measured Condenser Delta P (PSID)/Project Condenser P Delta (PSID)) A6
[00281] where the test and balance (T&B) GPM represents the actual flow measured by the hydronic balancer of the condenser water system. This is often different from "design" or full rated condenser flow due to the unique piping system at each customer's plant. As discussed previously, sensors 2712a and 2712b can be high precision pressure sensors arranged to measure supply pressure (via sensor 2712a) and back pressure (via 2712b). The difference between the measured supply and return pressures represents the differential or pressure loss across the 2712 condenser.
[00282] With the determination of the measured condenser flow (GPM), the demand flow condenser routine 2612 and the demand flow control routine 2600 (as shown in block 2810) calculate the current condenser output capacity (Shades). The current condenser capacity can be calculated according to the formula: Condenser Capacity (Tone) = Measured Condenser Flow * ((CWR-CWS)/24)
[00283] In this way, the demand flow condenser routine 2612 that is part of the demand flow control routine 2600 can empirically calculate the output capacity of each condenser 2712 that operates in conjunction with the chilled water plant 2700.
[00284] The demand flow control routine 2600 and the demand flow condenser routine 2612 can, in turn, use the results of the preceding steps and calculations to determine a virtual Delta T (see block 2812). The virtual Delta T represents a hypothetical chilled water Delta T or equivalent that must be present if a constant volume pumping algorithm was used under current operating conditions. The virtual Delta T can be calculated according to the formula Delta T Virtual = Project Delta T * (Condenser Capacity (Tons) / Project Condenser Capacity (Ton))
[00285] The demand flow control routine 2600 and the demand flow condenser routine 2612 may, in block 2814, use the results and information from one or more of the preceding algorithm steps to determine a set point of the pressure curve for the 2712 condenser. The pressure curve setpoint can be determined according to the formula: PC Setpoint = Design Condenser Delta P (PSID) * (Virtual Delta T/Line Delta T Basal) AP Exponent
[00286] where the baseline Delta T represents the full load Delta T chosen or selected at the time of commissioning the 2700 chilled water plant. The baseline Delta T can (and will often) match the project Delta T.
[00287] In another modality, the demand flow control routine 2600 and the demand flow condenser routine 2612, in block 2814, can use the parameters and information from one or more of the preceding steps of the algorithm together with the value of the measured active pressure differential (PSID) to directly determine the pressure curve set point for the 2712 condenser. The pressure curve set point according to this alternative mode can be determined according to the formula: Point setting PC = Delta P of the Condenser Active (PSID) * (Delta T Measured T/Delta T of the project) A(P Exponent)
[00288] The calculated pressure curve set point can, in turn, be communicated from the demand flow control routine 2600 and the demand flow processor 2604 through the 2606 communications module to the 2730 pump (see block 2816 ). During operation, if the condenser water temperature detected by sensor 2712b rises above or exceeds a threshold level that corresponds, for example, to the supply chilled water temperature setpoint plus a small dead range temperature (by 1°F), then demand flow device 2502 and demand flow control routine 2600 initiate an override to linearly increase or raise the 1032 VFD associated with the 2730 condenser water pump to full speed. When the chilled water temperature exceeds the threshold, a loss of communication occurs while the temperature exceeds the sensor's ability to sense temperature. The subsequent increased flow provided by the elevated 1032 VFD limits further heat transfer, thereby causing the temperature to decline and communications to be restored. The VFD 1032 can also be programmed to start a ramp down after, for example, 15 min. at full speed. B. EVAPORATOR
[00289] FIG. 29 is a 2900 operational flowchart for implementing the variable pressure curve logic operational strategy implemented by the demand flow control routine 2600 to optimize the performance and efficiency of the 2710 evaporator (see FIG. 27).
[00290] In the part or stage of the design of the 2610 demand flow evaporator routine, one or more design parameters are received and organized in memory 2602, in memory 1012 or in any database or accessible storage location (as shown in block 2902). Design parameters can, as discussed previously, include: a design condenser flow (GPM); a design condenser pressure differential (PSID); the capacity of the design condenser (Tones); a baseline or project chilled water Delta T representing the full load chilled water Delta T calculated at the time of commissioning of the 2700 chilled water plant. In another embodiment, arranged design parameters can be supplemented or augmented by a current or active pressure differential (PSID) value measured through the 2710 evaporator. Using these design and/or measured parameters, the performance envelope against which the 2710 evaporator is to be evaluated can be established by the demand stream 2604 and by the demand stream condenser evaporator 2610a.
[00291] An exponent of the specific evaporator pressure (Exponent P) can be empirically derived and calculated by the demand flow control routine 2600 and the demand flow evaporator routine 2610. The pressure exponent (Exponent P) can be based on measured parameters of evaporator 2710 operating in cooler 112. The exponent of pressure can be calculated according to the formula: Exponent P = A(xA2) + Bx + C
[00292] where x is the Delta P or the pressure change measured across the evaporator 2710 (see block 2904) and the constants A, B and C are calculated for each chilled water plant 2700. As discussed previously in relation to capacitor 2730, FIG. 30 illustrates a pressure exponent 3000 algorithm and routine that can be used to empirically derive distinct pressure exponents and a total pressure exponent curve that fits or otherwise connects to each of the distinct pressure exponents. The total pressure exponent curve, and more particularly the equation describing the total pressure exponent curve, is used in turn by the evaporator routine to determine the operating pressure exponent shown above.
[00293] The equation that has been derived from the pressure exponent curve, the pressure exponent 3000 routine is completed and returns to operating flowchart 2900. At this point, the equation describing the total pressure exponent curve can be used to calculate the operating pressure exponent for any pressure differential (PSID) as discussed previously.
[00294] The 2610 demand flow evaporator routine begins the operational or running part of the routine by using sensors 2710a and 2710b to detect and measure the pressure differential (PSID) across the evaporator 2710. Sensors 2710a and 2710b and /or components or subsystems thereof may also be configured and arranged to measure a feed chilled water temperature (CWS) (sensor 2710a) and return chilled water temperature (CHR) (sensor 2710b) associated with the evaporator 2710 ( in block 2906.
[00295] The 2610 demand flow evaporator routine, in turn, calculates a flow rate (GPM) through the 2710 evaporator (in block 2908) based on the detected and measured information of pressure and temperature. In particular, the demand flow processor 2604 accesses the sensed values stored in, for example, memory stack 2506 of memory 2602 as directed by demand flow control routine 2600. Condenser flow rate should be calculated in accordance with the formula: Measured Evaporator Flow = T&B GPM * (Delta P of Measured Evaporator (PSID)/Delta P of Design Evaporator (PSID))A(.6)
[00296] where T&B |GPM represents the flow rate of the full flow evaporator. As discussed previously, sensors 2710a and 2710b can be high precision pressure sensors arranged to measure supply pressure (via sensor 2710a) and back pressure (via 2710b). The measured supply and return flow represents the pressure differential or loss across the 2710 evaporator.
[00297] With the determination of the measured evaporator flow (GPM), the demand flow evaporator routine 2610 and the demand flow control routine 2600 can (as shown in block 2910) calculate the evaporator output capacity current (Tone) according to the formula: Evaporator Capacity (Tone) = Evaporator Flow Measured * ((CWR - CWS)/24)
[00298] In this way, the demand flow evaporator routine 2610 empirically calculates the output capacity of each evaporator 2710 in operation together with the chilled water plant 2700.
[00299] The demand flow control routine 2600 and the demand flow evaporator routine 2610, in turn, use the results of one or more of the preceding steps and calculations to determine a virtual Delta T (see block 2912). As discussed previously, the virtual Delta T represents an equivalent chilled water Delta T that would result if a constant volume pumping algorithm were used under current operating conditions. The virtual Delta T can be calculated according to the formula Delta T Virtual = Project Delta T * (Evaporator Capacity (Tone) / Project Evaporator Capacity (Tone))
[00300] The demand flow control routine held 2600 and the demand flow evaporator routine 2610, in block 2914, use the results and information from one or more of the preceding algorithm steps to determine a curve fitted point pressure curve for the 2710 evaporator. The setpoint of the pressure curve can be determined according to the formula PC Setpoint = Evapor Delta P. of the project (PSID) * (Virtual Delta T/Delta T of the Baseline) A (Exponent T)
[00301] where the Baseline Delta T represents the total load Delta T chosen or selected at the time of commissioning of the 2700 chilled water plant. The Baseline Delta T can (and will often) match the project Delta T.
[00302] In another modality, the demand flow control routine 2600 and the demand flow evaporator routine 2610, in block 2914, can use the results and information from one or more of the preceding algorithm steps together with the value of the measured active pressure differential (PSID) to determine the pressure curve set point for the 2710 evaporator. The pressure curve set point according to this alternative modality can be determined according to the Setpoint formula of PC = Delta P of Evap. Active (PSID) * (Delta T Measured/Delta T of the project) A(Exponent P)
[00303] The demand flow evaporator routine 2610 and the demand flow control routine 2600 can cooperate to implement a portion of the critical zone restoration of the operational strategy (see block 2916) in order to adjust the operation of the plant. 2700 chilled water to changed demand requirements. For example, if cooling demand is lowered, then a critical zone reset can change the current or operating Delta T linearly to the project Delta T. In operation, a decrease in demand from the 2700 chilled water plant can trigger a critical zone restoration that causes the current operating Delta T of 15 degrees to change to the project Delta T of 16 degrees. Therefore, the pressure setpoint for one or more pumps operating throughout the 2700 chilled water plant can be lowered in order to decrease the flow of chilled water through it. The setpoint of critical zone restoration can be calculated according to the linear formula: Y = M*X+B,
[00304] where M is the slope of the line as defined by (Y2 - Y1)/(X2 - X1);
[00305] X is the current value of the chosen critical zone parameter; and
[00306] B is the Y-intercept value. The Y-intercept value is selected from the minimum or maximum Y-M* (minimum or maximum critical zone value (CZ)). Minimum or maximum critical zone (CZ) values are site-specific parameters selected or identified at the time of commissioning of the chilled water plant 2700 and demand flow device 2502. For example, in one implementation, the humidity within a building or area may be of importance to a user, in which case critical zone values can be selected based on measured values of humidity and/or temperature in the area of interest. In another embodiment, sensor 2746b can monitor the temperature and flow in air handling unit 2746 in order to determine if and when the supply temperature drops below a threshold or value necessary to provide the desired refrigeration. In this mode, the operation and performance of the 2746 air handling unit can provide feedback of the minimum required critical zone (CZ) value or control the demand flow device 2502. Other values and parameters can be determined on the basis of requirements of a specific implementation.
[00307] The demand flow evaporator routine 2610 and the demand flow control routine 2600 can, as indicated in block 2918, determine the temperature in the decoupler or bypass 128 connecting the primary circuit 104 and the secondary circuit 108 The sensed temperature difference can, in turn, be used to determine the existence of a flow unbalance between circuits 104 and 108. The temperature at decoupler 128 would be between predetermined minimum and maximum temperatures, and the link shift can be calculated using a linear equation that adjusts the pressure setpoint (as indicated by reference "C") associated with the 2720 water pump to balance the flow between these circuits.
[00308] The value of the calculated pressure curve or critical zone restoration can, in turn, be communicated from the demand flow control routine 2600 and the demand flow processor 2604 through the communications module 2606 to the pump 2716 (See block 2920). Changing the operating pressure of the 2716 pump to the calculated or new pressure curve setpoint changes the pressure and flow through the 2710 evaporator.
[00309] Subsequently, the demand flow pump routine 2614 can determine (in block 2922) whether additional components, pumps, etc., require evaluation and restoration. If additional pumps and compressors need evaluation, then demand flow pump routine 2614 calculates a new or optimal pump setpoint for the additional pump (see block 2924). Demand flow pump routine 2614 repeats (in block 2926) the calculations for each identified and/or operational pump at chilled water plant 2700.
[00310] The adjusted point(s) of the calculated pressure curve can, in turn, be communicated from the 2600 demand flow control routine and the 2604 demand flow through the 1606 communications module to the remaining pump(s) (see block 2928).
[00311] To illustrate with a specific example, an exemplary chilled water plant optimized and controlled according to the demand flow variable pressure curve logic is shown in FIG. 31. In the example, the 44-degree chilled water produced in primary circuit 104 is circulating at a flow rate equal to 899 gallons per minute (GPM) to maintain a pressure differential of 2.6 (PSID) across the 2710 evaporator. the secondary circuit 108 circulates the chilled water through the secondary pump 2720 at a flow rate of 899 GPM (with the VFO 1032 driving the secondary pump at 45 Hz) and a PSID of 36. At this flow rate and pressure differential, the unit of 2746 air handling receives sufficient chilled water flow to re-cool the 3100 office space to a desired temperature. The temperature of the chilled water leaving the air handling unit 2746, in this example, increases from 44 degrees to 60 degrees and circulates from the secondary circuit 108 back to the primary circuit 104. In a similar fashion, the heat of the water chilled to 60° degrees is transferred from evaporator 2710 to condenser 2712 through a refrigeration cycle established between the two components. Condenser 2712 and cooling tower 2744 cooperate with condenser pump 2730 to maintain a flow rate of 618 GPM and a PSID of 7 across condenser 2712. With flow balance between these circuits as a function of stipulated pressure values associated with the 2716, 2720 and 2730 pumps, the 2710 evaporator, 2712 condenser and 2746 air handling unit can be operated efficiently at pressure and flow rates outside their original design parameters. This, in turn, provides additional operational flexibility as well as increased efficiency because no component or element is required to compensate for the inefficient operation of the remaining components under varying demand conditions.
[00312] Although various embodiments of the invention have been described, it will be apparent to those skilled in the art that many more embodiments and implementations are possible that are within the scope of the present invention. Furthermore, the various features, elements and embodiments described herein can be claimed or combined in any combination or arrangement.

权利要求:
Claims (25)
[0001]
1. Demand flow device (2502) configured to interface with an existing chilled water plant controller (1000) to control the performance of one of a plurality of chilled water plant subsystems with respect to remaining subsystems of the plurality of chilled water plant subsystems over a range of load conditions, the demand flow device (2502) comprising, a communication device configured to receive sensor data (1028; 2710a, 2710b, 2712a, 2712b, 2714a, 2714b, 2716a, 2716b, 2730a, 2730b) associated with the one of the chilled water plant subsystems, where the sensor data (1028; 2710a, 2710b, 2712a, 2712b, 2714a, 2714b, 2716a, 2716b, 2730a, 2730b) ) measure operating variables of the chilled water plant; a demand flow controller in communication with the communication device, the demand flow controller (2502) configured to use the sensor data (1028; 2710a, 2710b, 2712a, 2712b, 2714a, 2714b, 2716a, 2716b, 2730a , 2730b) received, characterized by determining an ideal pressure setpoint as a function of a Delta T of chilled water, controlling a chilled water flow through one of the chilled water plant subsystems as a function of the setpoint the ideal pressure and Delta T of the chilled water; and adjust, via the 1000 chilled water plant controller, the ideal pressure setpoint, in response to one or more detected activation events, to perform a chilled water Delta T critical zone restoration, where the ideal pressure setpoint is determined as a function of a measured pressure differential, a ratio of a measured Delta T to a design Delta T, and a site-specific exponent.
[0002]
2. Demand flow device (2502) according to claim 1, characterized in that the chilled water Delta T is a function of a measured chilled water inlet temperature and a measured chilled water outlet temperature detected in one or more chilled water plant components.
[0003]
3. Demand flow device (2502) according to claim 1, characterized in that the function, with the measured Delta T expressed as measured ΔT, the design Delta T expressed as design ΔT, the differential of measured pressure expressed as ΔP measured and the Exponent P is an exponent of pressure, it is defined as Stipulated Pressure Point = ΔP Measured *
[0004]
4. Demand flow device (2502), according to claim 1, characterized in that the ideal pressure set point controls a flow provided by a circulatory pump associated with one of the subsystems of the chilled water plant.
[0005]
5. Demand flow device (2502), according to claim 4, characterized in that the flow rate is determined to maintain the Delta T of the chilled water through one of the chilled water plant subsystems.
[0006]
6. Demand flow device (2502) according to claim 1, characterized in that the critical zone restoration adjusts the ideal pressure setpoint to match a different chilled water Delta T.
[0007]
7. Demand flow device (2502), according to claim 1, characterized in that the one of the chilled water plant subsystems is selected from the group consisting of: an evaporator; a condenser (508); a compressor (520) and a chilled water pump (116).
[0008]
8. Demand flow device (2502) according to claim 7, characterized in that the ideal pressure set point represents an ideal component pressure set point for one of the chilled water plant subsystems .
[0009]
9. Demand flow device (2502) according to claim 7, characterized in that the chilled water pump comprises multiple chilled water pumps in operation throughout the chilled water plant.
[0010]
10. Demand flow device (2502) according to claim 1, characterized in that the demand flow controller (2502) is configured to identify a predetermined chilled water Delta T and set a water Delta T chilled water based on the predetermined chilled water Delta T, the chilled water Delta T comprising an inlet chilled water temperature and an exit chilled water temperature in one or more chilled water plant components and the flow controller (2502) is configured to control the chilled water flow to maintain the Delta T of chilled water through one or more chilled water plant components.
[0011]
11. Demand flow control system (2500) for implementing variable pressure control logic in an existing chilled water plant controller (1000) to synchronize the performance of one or more chilled water plant components along of a range of demand conditions, the demand flow control system (2500) comprising a demand flow controller (2502) in communication with the controller (1000) of the existing chilled water plant, the water flow controller. demand (2502) configured to receive sensor data from one or more chilled water plant components coupled to the existing chilled water plant controller; characterized by determining an ideal pressure setpoint as a function of a Delta T of the desired chilled water and sensor data (1028; 2710a, 2710b, 2712a, 2712b, 2714a, 2714b, 2716a, 2716b, 2730a, 2730b) received for each of the one or more chilled water plant components, with the ideal pressure setpoint determined iteratively for each of the one or more chilled water plant components; communicate the ideal pressure setpoint to the existing chilled water plant controller (1000); and control, through the existing chilled water plant controller, a chilled water flow through each of the chilled water plant's one or more components as a function of the ideal pressure setpoint and the desired chilled water Delta T , where the ideal pressure setpoint is determined as a function of a measured pressure differential, a ratio of a measured Delta T to a design Delta T, and a site-specific exponent.
[0012]
12. Demand flow control system (2500) according to claim 11, characterized in that the demand flow controller (2502) is also configured to adjust the ideal pressure setpoint in response to one or more trigger events detected to perform a desired chilled water Delta T critical zone restoration.
[0013]
13. Demand flow control system (2500), according to claim 12, characterized in that the activation event is selected from the group consisting of: opening of a chilled water valve; a change in a detected chilled water temperature; a change in flow from a pump; and a change in a humidity level within a sensed space.
[0014]
14. Demand flow control system (2500) according to claim 12, characterized in that the critical zone restoration adjusts the ideal pressure setpoint to match a different desired chilled water Delta T.
[0015]
15. Demand flow control system (2500) according to claim 11, characterized in that the desired chilled water Delta T is evaluated with respect to a measured chilled water inlet temperature and an outlet temperature of measured chilled water detected in one or more chilled water plant components.
[0016]
16. Demand flow control system (2500), according to claim 11, characterized in that the Delta T of the desired chilled water in one or more components of the chilled water plant is maintained by increasing the point adjusting the ideal pressure and consequently the chilled water flow rate to reduce a detected chilled water Delta T with respect to the desired chilled water Delta T; and decreasing the ideal pressure setpoint and consequently the chilled water flow rate to increase the detected chilled water Delta T with respect to the desired chilled water Delta T.
[0017]
17. Demand flow control system (2500), according to claim 11, characterized in that the one or more components of the chilled water plant are selected from the group consisting of: an evaporator (512); a condenser (508); a compressor (520) and a chilled water pump (116).
[0018]
18. Demand flow control system (2500) according to claim 17, characterized in that the ideal pressure set point represents an ideal component pressure set point for each of the one or more components of the chilled water plant.
[0019]
19. Demand flow control method that uses variable pressure control logic to control the performance of one or more chilled water plant components over a range of demand conditions operable in an existing chilled water plant, the demand flow control method comprising, detecting an inlet chilled water temperature and an outlet chilled water temperature in one or more chilled water plant components; communicating the sensed inlet chilled water temperature and the sensed leaving chilled water temperature to a demand flow controller (2502); characterized by, the calculation of an ideal pressure setpoint in the demand flow controller (2502), with the ideal pressure setpoint being calculated as a function of a Delta T of the desired chilled water and inlet temperature sensed chilled water and sensed leaving chilled water temperature to a demand flow controller (2502); communicating the ideal pressure setpoint to an existing chilled water plant controller; and controlling a chilled water flow through one or more chilled water plant components as a function of the communicated ideal pressure setpoint, with the ideal pressure setpoint being determined as a function of a differential of measured pressure, a ratio of a measured Delta T to a design Delta T, and a site-specific exponent.
[0020]
20. Demand flow control method according to claim 19, characterized in that the calculation of the ideal pressure set point is a function of a design characteristic of the one or more components of the chilled water plant.
[0021]
21. Demand flow control method according to claim 19, characterized in that the detection of the chilled water inlet temperature and the chilled water outlet temperature also comprises the detection of a chilled water flow through one or more chilled water plant components.
[0022]
22. Demand flow control method according to claim 19, characterized in that it also comprises the iterative calculation of the ideal pressure set point for each of the one or more components of the chilled water plant.
[0023]
23. Demand flow control method, according to claim 19, characterized in that the chilled water flow control also comprises, increasing the ideal pressure set point and consequently the chilled water flow rate to reduce a detected chilled water Delta T with respect to the desired chilled water Delta T; and decreasing the ideal pressure setpoint and consequently the chilled water flow rate to increase the detected chilled water Delta T with respect to the desired chilled water Delta T.
[0024]
24. Demand flow control method according to claim 19, characterized in that it also comprises adjusting the ideal pressure setpoint, in response to one or more detected activation events, to perform a restoration of the Delta T critical zone of the desired chilled water.
[0025]
25. Demand flow control method, according to claim 24, characterized in that the activation event is selected from the group consisting of: opening of a chilled water valve; detecting a change in a detected chilled water temperature; detecting a change in pump flow; and detecting a change in a humidity level within a detected space.

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法律状态:
2018-12-11| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|

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2019-08-20| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|

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2021-04-06| B06A| Patent application procedure suspended [chapter 6.1 patent gazette]|

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2021-07-06| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|

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2021-09-14| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 04/05/2012, OBSERVADAS AS CONDICOES LEGAIS. |

优先权:

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申请号 | 申请日 | 专利标题

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US13/149,563|US8774978B2|2009-07-23|2011-05-31|Device and method for optimization of chilled water plant system operation|

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US13/149,563|2011-05-31|

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PCT/US2012/036435|WO2012166288A1|2011-05-31|2012-05-04|Device and method for optimization of chilled water plant system operation|

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