method for efficient operation of a chilled water plant and controller to control one or more pumps

专利摘要:
DEMAND FLOW PUMPING. The present invention relates to Demand Flow, which operates chilled water plants with substantially improved efficiency, regardless of plant load conditions. In general, the Demand Flow uses an operational strategy that controls the pumping of chilled water and condenser water according to a constant Delta T line, which is typically close to or in the project Delta T. This reduces or eliminates Low Delta T Syndrome and reduces energy use by chilled water and condenser pumps for certain load conditions. The operation of chilled water pumps in this way creates a synergy that generally balances flow rates through the plant, reducing the mix of undesirable bypass and energy use in air handler fans and other water plant components. icy. In plant coolers, the application of Demand Flow increases the cooling effect through coolant subcooling and overheating, as it prevents stacking. The Demand Flow includes a critical zone readjustment feature that allows the Delta T line to be constant (...).
公开号:BR112012001358B1
申请号:R112012001358-0
申请日:2010-05-12
公开日:2020-12-08
发明作者:Robert Higgins
申请人:Siemens Industry, Inc；
IPC主号:

专利说明:

BACKGROUND OF THE INVENTION Field of the Invention
[0001] The invention relates in general to comfort cooling systems and industrial process cooling and in particular to methods and apparatus for efficiently operating chilled water cooling systems. Related Technique
[0002] Many commercial and other buildings and campuses are cooled by cold water plants. In general, these chilled water plants produce chilled water that is pumped to air handlers to cool building air. Chillers, air handlers, and other components of a chilled water plant are designed to operate at a specific chilled water temperature going in and out, or Delta T. In the design Delta T, these components are at their highest efficiency and can produce cooling output at its rated capacity. Low Delta T, which occurs when the inlet and outlet temperatures become closer than the design Delta T, reduces the efficiency and cooling capacity of the chilled water plant and causes the chilled water plant to use more energy than that required for a given demand.
[0003] Chilled water plants are designed to meet the maximum possible cooling demand of a building, campus, or the like, also known as the project condition. In the design condition, the components of the chilled water plant are at the upper end of their capacities, where the system is more energy efficient. However, it is rare that this high demand for cooling is necessary. In fact, almost all chilled water plants operate below project conditions for 90% of the year. For example, brake weather conditions can cause the demand for cooling to drop considerably. When the demand for cooling is reduced, Delta T is also often reduced. This means that most of the time, almost all chilled water plants are operating with a low Delta T and less than optimal efficiency. This chronic low Delta T is referred to as Low Delta T Syndrome.
[0004] Many mitigation strategies have been developed to address the Low Delta T Syndrome, such as through the use of sequencing programs and ON / OFF equipment selection algorithms, but none has proven to completely solve this phenomenon. In most cases, the chilled water plant operator simply pumps more water to the system's air handlers to increase its output, but this has the aggravating effect of further reducing the already low Delta T. Also, the pumping increased in the secondary circuit results in more energy use than needed for pumping.
[0005] From the following discussion, it will be clear that the present invention addresses the shortcomings associated with the prior art while providing many additional advantages and benefits not contemplated or possible with the prior art constructs. SUMMARY OF THE INVENTION
[0006] Demand Flow provides a method and apparatus for highly efficient operation of chilled water plants. In fact, when compared to traditional operating schemes, Demand Flow provides substantial energy savings while meeting cooling output requirements. In general, Demand Flow controls pumping of chilled water, condenser water, or both according to a constant Delta T line. This reduces energy use, reduces or eliminates Low Delta T Syndrome, while allowing an ice water plant to meet the demand for cooling. In one or more modalities, the constant Delta T line can be reconfigured to another Delta T line to meet cooling demands that change at the same time while remaining energy efficient.
[0007] Low Delta T Syndrome has and continues to afflict cold water plants causing overuse of energy and artificial reductions in capacity. This prevents chilled water plants from meeting cooling demands, even under partial load. The Demand Flow and its operational strategy address these issues and provide additional benefits as will be described in this document.
[0008] In one embodiment, the Demand Flow provides a method for efficient operation of a chilled water plant. The method can comprise determining a chilled water Delta T, and controlling chilled water flow rate 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 a chilled water inlet temperature and an chilled water outlet temperature in the chilled water plant components. In one or more embodiments, the chilled water Delta T can be maintained by increasing the chilled water flow rate to reduce the chilled water Delta T and decreased the chilled water flow rate to increase the chilled water Delta T. Typically, the chilled water flow rate will be controlled by one or more chilled water pumps.
[0009] A critical zone reset can be performed to adjust the chilled water Delta T when one or more trigger events occur. In general, critical zone reconfiguration provides a new or reconfigured Delta T setpoint to adjust the output or cooling capacity when necessary. The cold water Delta T can be reconfigured in several ways. For example, the chilled water Delta T can be reconfigured by adjusting the chilled water inlet temperature, adjusting the chilled water outlet temperature, or both. Controlling the chilled water flow rate through the chilled water plant components to maintain the chilled water Delta T in this way substantially reduces the Low Delta T Syndrome in the chilled water plant. In fact, the reduction may be such that the Low Delta T Syndrome is eliminated at the ice water plant.
[00010] A variety of occurrences can be triggering events for a critical zone reset. For example, opening a chilled water valve on an air handling unit beyond a particular limit can be a trigger event. In addition, an increase or decrease in the temperature of the chilled water in a diversion of the chilled water plant, or a change in the flow rate of a tertiary pump beyond a particular limit can be trigger events. The humidity level in an operating room / operating room, production environment, or other space can also be a trigger event.
[00011] The flow rate of condenser water can also be controlled according to the method. For example, the method may comprise establishing a condenser water Delta T comprising a low condenser water inlet temperature and a condenser water outlet temperature in a condenser. The condenser can use the low condenser water inlet temperature to provide refrigerant subcooling which is highly beneficial for the cooling effect and efficiency of the cooler. The condenser water Delta T can be maintained by adjusting the flow rate of condenser water through the condenser, such as through one or more condenser water pumps.
[00012] The maintenance of the condenser water Delta T allows the condenser to provide subcooling of refrigerant without build-up even at the low condenser water inlet temperature. The condenser water Delta T can be maintained by controlling the condenser water outlet temperature, the condenser water outlet temperature is controlled by adjusting the condenser water flow rate through one or more water pumps. condenser.
[00013] In another embodiment, a method is provided to operate one or more pumps in an ice water plant. This method can comprise pumping water at a first flow rate through a chiller with a first pump, and adjusting the first flow rate to maintain a first Delta T through the chiller. The first Delta T can comprise a chiller inlet temperature and a chiller outlet temperature that provides beneficial refrigerant overheating in a chiller evaporator regardless of the chilled water plant's load conditions.
[00014] The method can also comprise pumping water at a second flow rate through an air handling unit with a second pump, and adjusting the second flow rate to maintain a second Delta T through the air handling unit. The second Delta T may comprise an air handling unit inlet temperature and an air handling unit outlet temperature that provides the desired cooling outlet in the air handling unit regardless of the load conditions of the chilled water plant. In one or more modalities, the first Delta T and the second Delta T can be similar or equal to balance the first flow rate and the second flow rate and reduce the diversion mix in a chilled water plant bypass. Bypass mixing is a common cause of Low Delta T Syndrome and is therefore highly advantageous.
[00015] The method may include a critical zone reset to increase cooling output. For example, the second flow rate can be increased by reconfiguring the second Delta T when a water valve on the air handling unit opens beyond a particular limit. This increase in the second flow rate causes an increase in the cooling output in the air handler.
[00016] The method can be used in a variety of chilled water plant configurations. To illustrate, the method can comprise pumping water through a distribution circuit from the chilled water plant to the second pump at a third flow rate with a third pump, and adjusting the third flow rate to maintain a third Delta T. The cooling capacity in the air handling of this modality can be increased by reconfiguring the critical zone. For example, the third flow rate can be increased by reconfiguring the third Delta T when the second flow rate provided by the second pump is beyond a particular limit. As above, increasing the third flow rate increases the cooling capacity in the air handler.
[00017] The method can also control condenser water flow rate. For example, the method may include pumping condenser water at a fourth flow rate through a cooler condenser with a fourth pump, and adjusting the fourth flow rate to maintain a fourth Delta T in the condenser. The Delta T room can comprise a condenser water inlet temperature and a condenser water outlet temperature that provides refrigerant subcooling and prevents refrigerant accumulation regardless of the chilled water plant's load conditions. For example, the condenser water inlet temperature may be less than a wet bulb temperature for the condenser water to provide refrigerant subcooling.
[00018] In one embodiment, a controller is provided to control one or more pumps from a chilled water plant. The controller can comprise an input configured to receive sensor information from one or more sensors, a processor configured to control a flow rate provided by one or more pumps to maintain a Delta T through a component of the chilled water plant, and a output configured to send one or more signals to one or more pumps. The processor can also generate the one or more signals that control the flow rate provided by one or more pumps. Delta T can comprise an inlet temperature and an outlet temperature.
[00019] The processor can be configured to maintain the Delta T by increasing or decreasing the flow rate based on information from the sensor. The processor can also be configured to perform a critical zone reconfiguration by decreasing the Delta T in response to sensor information indicating additional cooling capacity is desired in the component. The sensor information can be a variety of information. For example, the sensor information can be temperature information. The sensor information can also or alternatively be selected operating information from the group consisting of air handler chilled water valve position, VFD Hz, pump speed, chilled water temperature, condenser water temperature, and chilled water plant bypass temperature.
[00020] The processor can be configured to maintain the 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. To illustrate, the flow rate can be adjusted by increasing the flow rate to decrease the outlet temperature and decrease the flow rate to raise the outlet temperature. The Delta T maintained by the controller can be similar to a design Delta T for the component. This allows the component to operate efficiently according to its manufacturer's specifications.
[00021] Other systems, methods, characteristics and advantages of the invention will become or become apparent to an individual skilled in the art as a result of examining the figures and detailed description below. It is understood that all systems, methods, characteristics and additional advantages are within the scope of the invention. BRIEF DESCRIPTION OF THE FIGURES
[00022] The components in the figures are not necessarily to scale, instead the emphasis is placed on illustrating the principles of the invention. In the figures, similar reference numerals designate corresponding parts across all different views.
[00023] Figure 1 is a block diagram illustrating an exemplary decoupled chilled water plant; figure 2 is a block diagram illustrating Low Delta T Syndrome in an exemplary chilled water plant; Figure 3 is a block diagram that illustrates excess flow in an exemplary chilled water plant; Figure 4 is a block diagram illustrating an exemplary direct primary chilled water plant; Figure 5 is a block diagram illustrating components of an exemplary cooler; Figure 6A is a pressure graph - exemplary enthalpy that illustrates the refrigeration cycle; Figure 6B is a pressure graph - exemplary enthalpy that illustrates sub-cooling in the refrigeration cycle; Figure 6C is a pressure graph - exemplary enthalpy that illustrates refrigerant overheating in the refrigeration cycle; Figure 7 is a pressure graph - exemplary enthalpy that illustrates the Demand Flow benefits in an exemplary cooler; Figure 8A is a graph that illustrates the relationship between flow rate and axis speed; Figure 8B is a graph that illustrates the relationship between total design lift height and shaft speed; Figure 8C is a graph that illustrates the relationship between energy use and axis speed; Figure 8D is a graph showing an exemplary Delta T line with a pumping curve and an energy curve; Figure 9 is a block diagram illustrating an exemplary controller; Figure 10A is a flow chart illustrating an exemplary controller in operation; Figure 10B is a flow chart illustrating an exemplary controller in operation; Figure 11 is a graph showing an exemplary reconfiguration of critical zones triggered by air temperature; Figure 12 is a graph illustrating an exemplary reconfiguration of critical zones triggered by chilled water valve positions; Figure 13 is a block diagram illustrating an exemplary decoupled chilled water plant; Figure 14 is a graph that illustrates exemplary reconfiguration of critical zones triggered by VFD Hertz; Figure 15 is a cross-sectional view of an exemplary capacitor; Figure 16 is a pressure - enthalpy graph that illustrates changes in the refrigeration cycle under Demand Flow in an exemplary cooler; DETAILED DESCRIPTION OF EXAMPLE MODALITIES
[00024] In the description below, several specific details are enumerated in order to provide a more complete description of the present invention. However, it will be apparent to an individual skilled in the art that the present invention can be practiced without these specific details. In other instances, well-known features have not been described in detail so as not to obscure the invention.
[00025] Demand Flow, as described in this document, refers to methods and devices to reduce or eliminate Low Delta T Syndrome and to improve the efficiency of the chilled water plant. The Demand Flow can be implemented in modernization projects of chilled water plants as well as in new installations or projects of chilled water plants. As used in this document, chilled water plant refers to cooling systems that use chilled water to provide comfort cooling or chilled water for any process need. These chilled water plants are typically, but not always, used to cool campuses, industrial complexes, commercial buildings, and so on.
[00026] In general and as will be further described below, Demand Flow or pumping chilled water into a chilled water plant to address Low Delta T Syndrome and to substantially increase the efficiency of a chilled water plant. Variable flow under Demand Flow maintains a Delta T for chilled water plant components that are at or near the design Delta T for the components. As a result, Demand Flow substantially increases the operating 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, the Demand Flow also increases the life expectancy of the chilled water plant components by operating these components near or at their inlet and outlet temperatures. specified chilled water, or Delta T design, different traditional variable or other pumping techniques.
[00027] Demand Flow provides increased efficiency regardless of demand or cooling load operating chilled water plant components synchronously, in one or more modes, this occurs by controlling pumping of chilled water and condenser water in one or more pumps to maintain a Delta T in particular components or points of a chilled water plant. In general, Demand Flow operates on individual condenser or water pumps to maintain a Delta T through a particular component or point in 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 the plant's air handlers, and condenser water pumps can be operated. operated to maintain a Delta T through a condenser.
[00028] The control of individual pumps (and flow rate) in this way results in synchronized operation of a chilled water plant, as will be further described below. This synchronized operation balances flow rates at the chilled water plant, which significantly reduces or eliminates Low Delta T Syndrome and related inefficiencies.
[00029] In traditional chilled water plants variable flow is controlled according to a minimum pressure differential, or Delta P, at any 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 optimal Delta T can be maintained in all components of the chilled water plant regardless of load conditions (ie , cooling demand). Maintaining a constant or sustained Delta T allows for large variations in the flow of chilled water, which results in energy savings not only in pumping energy but also in cooling energy consumption. For example, the Delta T of a chiller can be maintained, by controlling the flow rate through the chilled water or condenser water pumps, nearby or in the chiller design parameters regardless of load conditions to maximize beam efficiency of heat exchanger tubes from the evaporator and cooler condenser.
[00030] Conversely, traditional variable flow schemes vary the flow within much narrower intervals, and therefore are unable to achieve Demand Flow cost and energy savings. This is because traditional flow control schemes control flow rate to produce a particular pressure difference, or Delta P, instead of a Delta T. Additionally, traditional variable flow schemes only seek to maintain Delta P only in a few predetermined system locations , ignoring low Delta T. This results in flow rates that are much higher than required to generate and distribute the desired amount of cooling output, largely to compensate for the inefficiencies caused by the low Delta T.
[00031] Because flow rates are controlled by Demand Flow to maintain a Delta T and not to maintain Delta P or a particular cooling outlet in the plant's 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 the diversity of the system. To address this, the Demand Flow includes a feature referenced in this document as a critical zone reconfiguration that allows the Delta T maintained by the Demand Flow to be reconfigured to another, typically lower, value based on a specified system need that does not. is being fully met at the required flow rate of the system. This may be due to inadequate piping, incorrectly sized air handlers for the load being served, or any amount of unforeseen anomalies. As will be further described below, this allows additional cooling to be provided by maintaining a new one or by reconfiguring Delta T generally by increasing the flow of chilled water.
[00032] Demand Flow application has a synergistic effect on air handlers as well as on coolers, pumps, and other components of an ice water plant. This results in reduced net energy use while maintaining or even increasing the rated capacity for the chilled water plant. As will be further described below, under Demand Flow, little or no excess energy is used to provide a given level of cooling.
[00033] Preferably, the Delta T maintained by the Demand Flow will be close to or in the design Delta T of a component of a chilled water plant to maximize the efficiency of the component. Advantages of maintaining Delta T can be seen through the equation
of the cooling capacity, such as K, where Tons is the cooling capacity, GPM is the flow rate, and K is some constant. As this equation shows, when Delta T is reduced, so is its cooling capacity.
[00034] It is noted that although described in this document with reference to a particular capacity equation, it will be understood that the operation and benefits of Demand Flow and can also be shown with a variety of capacity equations. This is generally because the relationships between cooling capacity, flow rate, and constant Delta T are linear.
[00035] The advantages of maintaining Delta T can be seen in 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 to a 16 degree design Delta T. 500 Tons of capacity can be generated by supplying 750 GPM to 16 degree Delta T. However, at a low Delta T as commonly seen in traditional systems, a higher flow rate must be required. For example, at an 8 degree Delta T, 500 tons of capacity should require a flow rate of 1500 GPM. If Delta T is reduced further, such as to 4 degrees, the cooling capacity must be 250 Tons at 1500 GPM. Where chilled water plant pumps, or other components, may only be capable of a maximum flow rate of 1500 GPM, the chilled water plant must not be able to meet the desired demand of 500 Tons, even if, in the Delta T design, the chilled water plant is capable of 1000 Tons of capacity at 1500 GPM. I. LOW DELTA T SYNDROME
[00036] Low Delta T Syndrome will now be described with reference to figure 1 which illustrates an exemplary depleted chilled water plant. As shown, the chilled water plant comprises a primary circuit 104 and a secondary circuit 108. Each circuit 104,108 can have its own water inlet and outlet temperature, or Delta T. It is noted that Demand Flow also benefits chilled water plants direct / primary (ie cold water plants not uncoupled) as will be further described below.
[00037] During operation of an uncoupled chilled water plant, chilled water is produced in a production or primary circuit 104 by one or more coolers 112. This chilled water can be circulated in primary circuit 104 by one or more pumps. primary chilled water 116. Chilled water from the primary circuit104 can then be distributed to a building (or other structure) via a distribution or secondary circuit 108 in fluid communication with the primary circuit104. Within secondary circuit 108, chilled water can be circulated by one or more secondary chilled water pumps 120 to one or more air handlers 124. Air handlers 124 allowing the heat from the building air to be transferred to the cold water, such as through one or more heat exchangers. This provides cool air for the building. Typically, building air is forced or blown through an air handler heat exchanger 124 to better cool an air volume. The chilled water exits the air handlers 124 and returns to the secondary circuit 108 at a higher temperature due to the heat that the chilled water absorbs through the air handlers.
[00038] The chilled water then leaves secondary circuit 108 and returns to primary circuit 104 at the highest temperature. As can be seen, both primary circuit 104 and secondary circuit 108 (as well as a chilled water plant component connected to these circuits) have an inlet water temperature and an outlet water temperature, or Delta T. ideal situation, the inlet and outlet temperatures for both circuits should be in their respective Delta T designs. Unfortunately, in practice, the cold water circuits operate at a chronic low Delta T.
[00039] Low Delta T occurs for a variety of reasons. In some cases, low Delta T occurs due to an imperfect design of the chilled water plant. This is relatively common due to the complexity of chilled water plants and the difficulty in obtaining a perfect project. To illustrate, air handlers 124 of secondary circuit 108 may not have been selected properly and therefore cold water does not absorb as much heat as expected. In this case, the chilled water from the secondary circuit 108 enters the primary circuit104 at a colder temperature than expected resulting in a low Delta T. It is observed that, due to imperfect design and / or operation, a chilled water plant may be operating low Delta T under various loads, including design load conditions.
[00040] Delta T lows also occur when cooling output is reduced to meet a load that is less than the design condition. When the outlet is reduced, the flow of chilled water, Delta T of chilled water, and other factors often become unpredictable resulting in low Delta T. In fact, in practice, it has been observed that traditional Delta P flow control schemes have invariably result in low Delta T in some, if not all, chilled water plant components.
[00041] For example, to reduce cooling output from the design conditions, one or more chilled water valves of the air handlers of the chilled water plant 124 can be closed (partially or completely). This reduces the flow of chilled water through the air handlers 124 and therefore less chilled air is supplied. However, now that the chilled water valve is partially closed, the chilled water absorbs less heat from the air when it flows through the air handlers 124 at a higher rate than necessary as evidenced by Delta T less than design . Therefore, the cold water coming out of the air handlers 124 is not as "hot" as it once was. As a result, the chilled water leaving secondary circuit 108 to primary circuit 104 is cooler than desired, causing low Delta T in both circuits.
[00042] To illustrate with a specific example, an exemplary chilled water plant is provided in figure 2. In the example, the chilled water produced in primary circuit 104 is at 40 degrees. As can be seen, chilled water coming out of air handlers 124 may be at 52 degrees instead of expected 56 degrees because the chilled water valve was closed and the chilled water flow rate is too high for the current load. Because there is no excess flow distribution at diversion 128, the temperature of the chilled water leaving the secondary circuit 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 smaller than the design Delta T. It is observed here that the Delta T bass itself reduces capacity and causes excess energy to be used to provide a given cooling output. As can be seen from the capacity equation
Tons capacity is significantly reduced by the low Delta T. To compensate, a higher flow rate or GPM must be required leading to excessive use of pumping energy for the given cooling demand.
[00043] Again with reference to figure 1, another cause of low Delta T is a mixture of deviation caused by excess flow within primary circuit 104, secondary circuit 108, or both. Bypass mixing and overflow are known causes of low Delta T and have traditionally been extremely difficult to address, especially with Delta P flow control schemes. In fact, a common cause of overflow is over-pumping water frozen by inefficient Delta P control schemes (as shown by the example above). For this reason, flow balances and bypass mixing are commonplace in chilled water plants that use Delta P flow control schemes. It is noted that bypass mixing can also occur in the design condition due to, as with any machinery complex, chilled water plants are rarely perfect. In fact, chilled water plants are often designed with primary chilled water pump flow rates that do not correspond to secondary pump flow rates.
[00044] In decoupled chilled water plants, a decoupler or bypass 128 that connects primary circuit 104 and secondary circuit 108 is provided to manipulate flow balances between circuits. This typically occurs as a result of overflow or overpumping in one of the circuits. Deviation 128 accepts excess flow from one circuit generally allowing it to flow to the other circuit. It is observed that excess flow is not limited to any particular circuit and that there may be excess flow in all circuits in addition to an imbalance of flows between them.
[00045] Excessive flow generally indicates a lot of energy is being spent to pump ice water, as will be described later through the Affinity Laws, and also exacerbates the problems of low Delta T. To illustrate using figure 3, which illustrates a water plant exemplary ice cream having excess flow, ice water from air handlers 124 and secondary circuit 108 mixes with water supply from primary circuit 108 at diversion 128 when there is primary excess or chilled water flow distribution. The resulting mixture of these two water streams produces chilled water that is hotter than design, which is then distributed to the 124 air handlers.
[00046] To illustrate, flow in excess of 300 gallons per minute (GPM) of water at 54 degrees from secondary circuit 108 should mix with ice water from primary circuit 104 to 40 degrees at diversion 128 by raising the temperature of the secondary ice water circuit to 42 degrees. The secondary chilled water circuit now has a higher temperature than the primary chilled water circuit. This causes low Delta T in primary circuit 104 and secondary circuit 108 and a corresponding reduction in cooling capacity.
[00047] Cold water flow diversion mix is also undesirable because this exacerbates low Delta T. To illustrate, when air handlers 124 perceive the high water temperature caused by the diversion mix or are unable to meet the demand for cooling due to the high water temperature, its chilled water valves open to allow additional water flow through the air handlers 124 to increase air cooling capacity. In traditional Delta P systems, secondary chilled water pumps 120 must also increase the chilled water flow rate to increase air cooling capacity in air handlers 124. This increase in the flow rate causes additional imbalances in the flow rate. flow (i.e., excess excess flow) at offset 128 between primary circuit 104 and secondary circuit 108. The increased excess flow exacerbates low Delta T caused by additional diversion mixing that further reduces Delta T.
[00048] Excess flow and diversion mix also cause excess energy use for a given cooling demand. In some situations, additional pumping energy is used to increase the flow rate in primary circuit 104 to better balance the flow of secondary circuit 108 and prevent diversion from mixing. In addition or alternatively, an additional chiller 112 may need to be brought in line or additional cooling energy may be used to generate sufficient chilled water in the primary circuit 104 to compensate for the bypass mixture heating effect in the chilled water supply. On the air supply side, air handlers 124 can try to compensate for the reduced capacity caused by the high water temperature by moving larger volumes of air. This is typically achieved by increasing the power to one or more fans 132 to move additional air through the air handlers 124, as will be further described through the Affinity Laws.
[00049] In many cases, these measures (for example, increased pumping of chilled water, opening of water valves for air handlers, increased air movement of the air supply) do not fully compensate for the artificial reduction in cooling capacity caused by low Delta T. Therefore, the chilled water plant is simply unable to meet the demand for cooling even when this level of demand may be below its rated cooling capacity. In situations where these measures are able to compensate for the artificial reduction in capacity, such as starting additional chillers, the chilled water plant is using substantially more energy than necessary to provide the desired cooling output with much of the excess energy being spent to compensate the effects of low Delta T.
[00050] It will be understood that low Deltas T also occur in direct configurations - chilled water plant primaries (ie, uncoupled chilled water plants), even if these configurations do not generally have the problem of mixing return water from the building with supply of production water. Direct - primary systems invariably have a plant or system bypass, 3 outlet valves, or both in order to maintain minimum flow through the system. For example, figure 4 illustrates an exemplary direct primary chilled water plant that has a deviation like this. Similar to the decoupled chilled water plant, excess flow can occur in these bypasses or 3-outlet valves. Therefore, problems of low Delta T, such as excess cooling energy, excess 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's configuration. This has been shown in practice by the fact that the Low Delta T Syndrome occurs in both types of ice water plants.
[00051] The effect of low Delta T with respect to coolers will be described further now. Figure 5 illustrates an exemplary chiller 112. For illustrative purposes, the dashed line in figure 5 outlines the components that are part of the exemplary chiller 112 and those that are not, with the components within the dashed line being part of the chiller. Naturally, it will be understood that a chiller may include additional components or less components than shown.
[00052] As can be seen, the cooler 112 comprises a condenser 508, a compressor 520 and an evaporator 512 connected through one or more refrigerant lines 536. The evaporator 512 can be connected and a primary or other circuit of a water plant ice through one or more lines of ice water 532.
[00053] In operation, cold water can enter the evaporator 512 where it transfers heat to a refrigerant. This evaporates the refrigerant causing the refrigerant to become refrigerant vapor. The heat transfer from the chilled water cools the water allowing the water to return to the primary circuit through the chilled water lines 532. To illustrate, chilled water at 54 degrees can be cooled to 42 degrees by transferring heat to refrigerant at 40 degrees within a 512 evaporator. Chilled water at 42 degrees can then be used to cool a building or other structures, as described above.
[00054] In order to continue the refrigeration cycle, the refrigerant vapor produced by the evaporator 512 is condensed back to liquid form. This condensation of refrigerant vapor can be carried out by condenser 512. As is known, refrigerant vapor can condense only on a lower temperature wall. Because the refrigerant has a relatively low boiling point, the 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.
[00055] The increased temperature of the refrigerant vapor allows the vapor to condense at a higher temperature. For example, without compression the refrigerant vapor can reach 60 degrees, while with compression the vapor can reach 97 degrees. Therefore, condensation can occur below 97 degrees instead of 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.
[00056] The refrigerant vapor enters condenser 508 where its heat can be transferred to a condensation medium, causing the refrigerant to return to a liquid state. For example, condenser 508 may comprise a design of a housing and a tube where the condensation medium flows through the tubes of the condenser. In this way, the refrigerant vapor can condense in the tubes inside the condenser housing. As discussed in this document the condensation medium is condenser water, although it will be understood that other fluids or media can be used. After condensing, the refrigerant then returns through a refrigerant line 536 and pressure reducer 528 back to the evaporator 508 where the refrigeration cycle continues.
[00057] The condenser 508 can be connected to a cooling tower 524 or other cooling device through one or more lines of condenser water 540. Due to the condenser water absorbing heat from the refrigerant vapor, the condenser water tsendo that 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 the cold condenser water supply that allows for continuous condensation of refrigerant vapor. It is noted that although the cooling tower 524 is used to cool the water in the mode of figure 4, other condenser water supplies can be used.
[00058] The operation of a chiller can also be shown through a pressure graph - enthalpy as shown in figure 6A. In the graph, pressure is plotted on the vertical axis while enthalpy is on the horizontal axis. At point 604, the refrigerant can be in a highly saturated state or mainly liquid in the evaporator. As the refrigerant absorbs heat from the chilled water in the evaporator, its enthalpy increases by transforming the refrigerant into refrigerant vapor at point 608. The part of the graph between point 604 and point 608 represents the cooling effect of the cooler. During this time, the heat absorption of the chilled water by the refrigerant cools the chilled water.
[00059] 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 "elevation." This elevation allows 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, transforming the vapor into liquid again. The refrigerant then passes through a pressure reducer between point 616 and point 604, which reduces both the temperature and the pressure of the refrigerant so that it can be used in the evaporator and continue the refrigeration cycle.
[00060] As will be further described below, problems associated with low Delta T in the condenser often result in cooling failure due to a lack of minimum lift under partial load conditions. When the differential pressure between the condenser and evaporator falls too low, a condition known in the industry as "build-up" occurs. This is a condition where the refrigerant accumulates in the condenser, decreasing the saturated pressure and temperature of the evaporator to critical points. The refrigerant also has a great affinity for oil and therefore accumulation will trap a large part of the oil charge in the condenser causing the chiller to shut down in any number of low pressure, low evaporator temperature, or low oil pressure problems.
[00061] Due to traditional condenser water pumping systems operating at constant volume, cooling towers are also in low flow conditions. While the load on the cooling tower decreases, the operational range remains relatively constant, reducing the efficiency of the tower. In contrast to variable flow water condenser systems, the operating range decreases with flow. This allows lower condenser water inlet temperature and the reduction of associated cooling energy and cooling tower fan energy described further below in this narrative.
[00062] Low Delta T also results in very low condenser water pump efficiency (KW / Ton) and limits the amount of refrigerant subcooling available to the chiller through seasonally low condenser water inlet temperatures. At a given load, for all degrees the condenser water inlet temperature is reduced, the compressor energy is reduced by approximately 1.5% and the nominal tonnage of the cooler is increased by approximately 1%. Therefore, as will be further described below, operating the chillers at the lowest possible condenser water inlet temperature is highly desirable.
[00063] Additionally, low Delta T in the evaporator reduces the cooling effect of the refrigeration cycle. As will be further described below, this reduces the refrigerant vapor temperature produced by the evaporator. II. DEMAND FLOW
[00064] In general, Demand Flow comprises systems and methods to address Low Delta T Syndrome while increasing the efficiency of the plant and the chilled water system. As demonstrated above, traditional cold water system control schemes directly lead 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 the most traditional control schemes and optimization of the system's delivery capacity and energy. This is most clearly evidenced by the pressure differential, or Delta P, frozen water pumping control schemes, which ignore increased energy use and reduced system capacities. Delta P-based pumping schemes traditionally inevitably produced a system that runs with Low Delta T Syndrome when the system load varies.
[00065] In a perfect world, the Delta T of chilled water must be the same on the primary, secondary circuit, and any tertiary or other circuits of a chilled water plant. Cold water plant operating components in your design or selected Delta T always produce your highest delivery capacity and highest system efficiency. Therefore, in a perfect world, Delta T of chilled water must match the design Delta T. To generate this ideal situation, the selection, design, installation and pumping control algorithms of the chilled water plant 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.
[00066] Unlike traditional control schemes, a central Demand Flow principle is to operate as close to the project's Delta T as possible with emphasis placed on meeting cooling demand, as will be described below with respect to critical zone reconfigurations. This allows a chilled water plant to operate at high efficiency, regardless of the cooling load. This is the opposite of traditional control schemes, where operation on partial loads or even design uses substantially more energy than necessary due to the Low Delta T Syndrome that afflicts these traditional systems.
[00067] Additionally, because the pumps are controlled to maintain a Delta T as close to or equal to 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 less under Demand Flow as can be seen from the flowchart. Values indicated in the graph were taken from actual measurements of an operational Demand Flow implementation.
[00068] To illustrate, figure 7 is a graph of an actual Demand Flow application that shows the energy reductions obtainable by reducing the condenser water inlet temperature. Figure 7 is a pressure-enthalpy diagram that compares condenser water pumping schemes of constant volume 804 and chilled water pumping by Delta P for pumping by Demand Flow 808. As can be seen, the elevation is reduced although the cooling effect is increased by subcooling 812 and overheating of refrigerant 816 when compared to traditional constant volume pumping 804.
[00069] The Demand Flow has a measurable, sustainable, and reproducible effect in ice water plants due to the fact that it is based on solid scientific fundamental principles that, as such, are both measurable and predictable. The gains in efficiency and delivery capacity that result from the application of Demand Flow will be described below.
[00070] A fundamental premise of pumping energy efficiency with variable flow chilled water plants known as the Affinity Laws consists of the following laws: - Law 1: Flow is proportional to the rotation speed of the ei-xo, as shown by equation
where N is the rotation speed of the axis and Q is the volumetric flow rate (for example, CFM, GPM, or L / s. This is illustrated by the flow line 936 shown in the graph in figure 8A. - Law 2: Pressure or pumping height is proportional to the square of the shaft speed, as shown by the equation
where H is the pressure or pumping height developed by the pump or fan (for example, foot or m). This is illustrated by the pumping curve 916 shown in the graph in figure 8B. - Law 3: Power is proportional to the axis speed cube, as shown by the equation
, where P is power of the axis (for example, W). This is illustrated by the 920 energy curve shown in the graph in figure 8C.
[00071] The Affinity Laws determine that a drop in the pressure of chilled water (also referred to as TDH or as H above) is related to the change in the flow rate squared, while energy use is related to the change in the flow rate to the cube . Therefore, in Demand Flow, as the flow rate is reduced, the cooling or output capacity is reduced proportionately but the energy use is reduced exponentially.
[00072] Figure 8D is a graph showing an exemplary constant Delta T 904 line. Line 904 is referred to as a constant Delta T line because all points on the line have been generated with equal Delta T. In the graph, the horizontal axis represents the flow rate while the vertical axis represents pressure. Therefore, as shown, the Delta T 904 line shows, for a constant Delta T, the flow rate required to produce a particular cooling output. In one or more modalities, the Delta T 904 line can be defined by a capacity equation, such as,
which predicts that an increase or decrease in the flow rate (GPM) causes a proportional increase or decrease in the cooling output (Tones). It is noted that although a particular Delta T 904 line is shown in figure 8D, it will be understood that the Delta T 940 line may be different for various chilled water plants or chilled water plant components.
[00073] In general, Demand Flow seeks to maintain the flow rate for a given cooling output on the Delta T 904 line. This results in substantial efficiency gains (ie energy savings) while meeting cooling demand. In contrast, the flow rate determined by traditional control schemes is higher, often substantially, than that provided by the Delta T 904 line. This has been shown in practice and is often recorded in the operational records of chilled water plants traditional. Figure 8D illustrates an exemplary registered point 908 that shows the flow rate as determined by traditional control schemes, and a Demand Flow point 912. Demand Flow point 912 represents the flow rate for a given cooling output under Demand Flow principles.
[00074] Typically, the registered point 908 as determined by traditional control schemes will have a higher flow rate than is required by the chilled water plant to meet the actual cooling demand. For example, in Figure 8D, the registered point 908 has a higher flow rate than the Demand Flow point 912. This is, at least partially, due to traditional control schemes having to compensate for inefficiencies caused by the low Delta T with higher flow rates and increased cooling output.
[00075] With Demand Flow, the flow rate is adjusted along the Delta T 904 line, linear to the load, which means that the chilled water plant, and its components, operate at or near the Delta T of project. In this way, low Delta T is eliminated or significantly reduced by the Demand Flow. Therefore, the desired cooling demand can be achieved at a lower flow rate and cooling output when compared to traditional control schemes. This is due in large part to the cold water plant not having to compensate for the inefficiencies of low Delta T.
[00076] Figure 8D superimposes the pumping curve 916 and energy curve 920 mentioned above to illustrate the efficiency gains provided by the Demand Flow. As shown, the 916 pumping curve represents the total design lift height (TDH) or pressure drop on its vertical axis and axis capacity or speed on its horizontal axis. The Laws of Affinity determine that the speed of the axis is linearly proportional to the flow rate. Therefore, the pumping curve 916 can be superimposed as in figure 8D to illustrate efficiency gains provided by Demand Flow. The Affinity Laws also state that the 916 pumping curve is a quadratic function. Therefore, it can be seen from the graphs that when the flow rate is reduced linearly along the Delta T 204 line, the HRT is reduced exponentially.
[00077] The 920 energy curve as shown represents the energy use on its vertical axis and the axis velocity (as exposed 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 cubic function. Therefore, it can be seen either when the flow rate is reduced, energy use is reduced exponentially, even more than HRT. Put another way, energy use increases exponentially according to a cubic function when the flow rate increases. For this reason, it is highly desirable to operate pump systems so that the minimum flow rate required to obtain a particular cooling output is provided.
[00078] It can be seen that a substantial amount of energy savings occurs when operating a Demand Flow chilled water plant. Figure 8D highlights the differences in energy use between the Demand Flow point 912, and the recorded point 908. As can be seen from the 920 energy curve, at the cooling output indicated by these points, the excess energy use 932 between registered point 908 and Demand Flow point 912 is substantial. Again, this is due to the exponential increase in energy use when the flow rate increases.
[00079] Figure 8D 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 again has a substantially higher TDH than is necessary to meet the demand for current cooling. In contrast, at the Demand Flow point 912, HRT is much lower. As can be seen from the pumping curve 916, the excess TDH 924 between the registered point 908 and the Demand Flow point 912 is substantial. Therefore, substantially less work is expended by the Demand Flow chilled water plant pumps when compared to traditional control schemes. This is beneficial because much less effort is put on the pumps, extending their service life. III. DEMAND FLOW OPERATIONAL STRATEGY
[00080] To assist in the description of Demand Flow, the term operational strategy will be used in this document to reference the principles, operations, and algorithms applied to chilled water plants and their components to obtain the Demand Flow benefits for use of power and cooling capacity of the plant. The operational strategy beneficially influences aspects common to most, if not all, of the cold water plants. As will be described below, these aspects include chilled water production (for example, coolers), chilled water pumping, condenser water pumping, cooling tower fan operation, and air side fan operation. The application of the operational strategy significantly reduces or eliminates the Low Delta T Syndrome by operating components of a chilled water plant at or near the project Delta T, regardless of load conditions. This in turn optimizes the energy use and supply capacity for components of the chilled water plant and the plant as a whole.
[00081] In one or more modalities, the operational strategy can be incorporated and / or implemented by one or more devices or control components of a chilled water plant. Figure 9 illustrates an example controller that can be used to implement the operational strategy. In one or more modes, the controller can accept input data or information, perform one or more operations on the input according to the operational strategy, and provide a corresponding output.
[00082] Controller 1004 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 chilled water , condenser water, refrigerant, or operating characteristics of chilled water plant components detected by one or more 1028 sensors can be received via a 1020 input.
[00083] Processor 1004 can then perform one or more operations on the information through one or more inputs 1020. In one or more embodiments, the processor can execute one or more instructions stored in a memory device 1012 to perform these operations. Instructions can also be recorded on processor 1004 as in the case of an ASIC or FPGA. It is noted that the memory device 1012 can be internal or external to the processor 1004 and can also be used to store data or information. Instructions can be machine-readable code in one or more modes.
[00084] The operational strategy can be incorporated by one or more instructions so that, by executing the instructions, controller 1004 can operate an ice water plant or the same component according to Demand Flow. For example, one or more algorithms can be run to determine when an increase or decrease in the chilled / condenser water flow rate should be performed to maintain pumping of chilled / condenser water on or near a Delta T line. Once , the instructions being executed in the information of one or more inputs 1020, a corresponding output can be provided through one or more outputs 1024 of controller 1004. As shown, an output 1024 of controller 1004 is connected to a VFD 1032. VFD 1032 can be connected to a chilled water, condenser pump, or other cooling tower pump or fan (not shown). In this way, controller 1004 can control pumping at the chilled water plant pumps.
[00085] It is observed that the operational strategy can be thought of as providing external control operations that control components of a chilled water plant. For example, in the case of a modernization, a 1004 controller or the like can apply Demand Flow to a chilled water plant without requiring changes to the plant's existing components. Controller 1004 can control existing plant VFDs and pumps for example. In some modalities, VFDs can be installed in one or more chilled water pumps, condenser water, or other pumps to allow control of these pumps by the operational strategy. One or more sensors can also be installed or existing sensors can be used by controller 1004 in one or more modes.
[00086] Figure 10A is a flowchart that illustrates exemplary operations that can be performed by a 1024 controller to execute the operational strategy. It will be understood that some steps described in this document may be performed in a different order than described in this document, and that there may be fewer or additional steps in various modalities that correspond to various aspects of the operational strategy described in this document, but not shown in the flow diagram.
[00087] In the mode shown, the sensor information is received in step 1104. For example, sensor information can be received with respect to the chilled water inlet temperature, water outlet temperature, or both from a water plant component. ice water. Temperature, pressure, or other characteristics of the refrigerant can also be received. Also, operating characteristics such as the position of the chilled water valve on the air handlers, the speed or output of VFDs, the speed or flow rate of pumps, as well as other information can be received.
[00088] In step 1108, based on the information received in step 1104, the controller can determine whether to increase or decrease one or more pumps to maintain a Delta T that is preferably close to or equal to the design Delta T. For example, with reference to figure 1, if the chilled water outlet temperature in an air handler 124 indicates low Delta T, the flow rate in the secondary circuit 108 can be adjusted by the secondary chilled water pump 120 to maintain Delta T design through a 124 air handler.
[00089] In step 1112, an output can be provided, such as for a VFD or other pump controller, or even for a pump directly to increase or decrease the flow rate as determined in step 1108. In this example above, reducing the flow rate, 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 building's air heating by the air handler 124 for a longer period of time.
[00090] The increase in chilled water enthalpy raises the chilled water outlet temperature of the air handler 124. When the water leaves the secondary circuit 108, the outlet temperature of the secondary circuit is high. In this way, Delta T can be increased to close to or equal to the design Delta T (reducing or eliminating the Low Delta T Syndrome).
[00091] Although the above example describes the maintenance of Delta T in a 124 air handler, Delta T can be maintained in this way in other components of chilled water plant, including primary, secondary circuit, or other circuits as well as within plant components. For example, in one or more embodiments, a controller at a chilled water plant can change the flow rate of one or more condenser water pumps to maintain a Delta T through a chiller component, such as the chiller condenser. .
[00092] As briefly discussed above, the operational strategy may also include one or more critical zone reconfigurations. In one or more embodiments, a critical zone reconfiguration changes the Delta T for which the flow rate is controlled. In essence, reconfiguring the critical zone changes the Delta T line for which the flow rate is controlled by an operational strategy. This allows the operational strategy to meet the demand for cooling by operating according to several Delta T lines. In practice, these Delta T lines will typically be close to the Delta T line generated in the project Delta T. The operational strategy is therefore flexible and capable of meeting several cooling demands at the same time as it efficiently operates the chilled water plant close to or equal to the design Delta T.
[00093] A critical zone reconfiguration can be used to increase or decrease the cooling output, such as increasing or decreasing the flow of chilled water. In one or more embodiments, a critical zone reconfiguration can be used to increase the cooling output by increasing the flow of chilled water. This can occur in situations where the demand for cooling cannot be met by operating an ice water plant on a particular Delta T. For example, if the cooling demand cannot be met, a critical zone reset can be used to reset the current Delta T maintained by the operational strategy to a new value. To illustrate, the Delta T maintained by an operational strategy can be reconfigured from 16 degrees to 15 degrees. To produce this lower Delta T value in the chilled water plant components, the chilled water flow rate can be increased to maintain the new Delta T value through one or more components in the chilled water plant. The increased flow rate provides additional chilled water for chilled water plant components that in turn provide increased cooling output to meet demand. For example, increased chilled water flow to air handlers should provide air handlers with additional air cooling capacity.
[00094] It is noted that critical zone reconfigurations can also occur when a chilled water plant, or components of the same, station producing too much or too much cooling output. For example, if the cooling demand is reduced, a critical zone reconfiguration can change the Delta T to be maintained so that it is closer to the design Delta T. In the example above, for example, Delta T can be reconfigured from 15 degrees back to 16 degrees when the cooling demand is reduced. Consequently, the chilled water flow rate can be reduced which reduces the cooling output. Typically, a linear reconfiguration of a Delta T setpoint is calculated based on the dynamics of the system as discovered during the activation process.
[00095] Figure 11 is a graph that illustrates an example of a critical zone reconfiguration for an exemplary air handling unit. As can be seen, Delta T can be reconfigured to a lower value to provide more chilled water flow in this way by lowering the supply air temperature of the air handling unit. It can also be seen that resetting Delta T to a higher value raises the supply air temperature by reducing the flow rate of chilled water to an air handling unit.
[00096] In operation, the value for which Delta T is reset can be determined in several ways. For example, new values for water inlet and outlet temperature (that is, a reconfigured Delta T) can be determined according to the formula or equation in some modalities. In other embodiments, a set of predetermined set points can be used to provide the reset value of Delta T. This can be described with reference to figure 11 which illustrates an exemplary set of set points 1204. In general, each set point configuration1204 provides a Delta T value for a given trigger event. In figure 11 for example, each setpoint 1204 provides a Delta T value for a given air temperature of the air handling unit supply. Setup points 1204 can be determined during Demand Flow setup or activation, and can be adjusted later if desired.
[00097] If the new value or reset value of Delta T is still insufficient to meet the demand for cooling, another reset of the critical zone can be triggered to reconfigure the Delta T that is maintained by the operational strategy. In one or more modalities, reconfigurations of the critical zone can occur until the chilled water plant is able to meet the demand for cooling.
[00098] In one or more modalities, a critical zone reconfiguration changes the Delta T to be maintained by an incremental quantity, such as a degree. This helps to ensure that the Delta T to be maintained is close to the design Delta T. While it may result in a slight reduction in the efficiency of the 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 efficiency gains will remain substantial.
[00099] The circumstances that result in a critical zone reset will be referred to in this document as a trigger or trigger event. As explained, reconfigurations of critical zones can be triggered when components of a chilled water plant are producing too much or too little cooling output. To determine whether plant components are producing too much or too little cooling output, the operational strategy may use information from one or more sensors. As will be further described below, this information may include chilled water characteristics within a chilled water plant (for example, temperature or flow rate), operating characteristics of one or more chilled water plant components, air or environmental (for example, temperature or humidity) of a space, as well as other information. With reference to figure 11 for example, a trigger can be the supply air temperature of an air handling unit. To illustrate, if the supply air temperature does not correspond to a desired supply air temperature, a critical zone reconfiguration can be triggered.
[000100] As mentioned above, Delta T can also be increased by the operational strategy as a result of a critical zone reconfiguration. For example, if the cooling demand is reduced, Delta T can be reconfigured to a higher value through a critical zone reconfiguration. An example of redetermining Delta T to a higher value to decrease the cooling output (that is, raising the supply air temperature of the air handling unit) is shown in figure 11. Similar to the above, an increase in Delta T through a critical zone reconfiguration can be triggered by various events or conditions.
[000101] Figure 10B is a flowchart that illustrates exemplary operations, which include reconfiguration of critical operation zone (s), which can be performed by a 1024 controller. In step 1116, information received in step 1104 can be processed to determine if a trigger has occurred. If so, a critical zone reconfiguration can occur that reconfigures the Delta T line by which the pumping is controlled. For example, operating characteristics provided by one or more sensors, such as the position of the air handler's chilled water valves, VFD speed or outlet, chilled water temperature, a plant deviation, or other information can cause a reconfiguration of critical zone, as will be further described below.
[000102] If a critical zone reset occurs, the controller will use the reset Delta T value or the reset Delta T line in step 1108 to determine whether an increase or decrease in flow rate is required. Then, as discussed above, an outlet for one or more pumps can be provided to effect these changes in the flow rate. If a critical zone reconfiguration does not occur, the controller can continue to use the current Delta T or Delta T line and consequently control the flow rate. It is observed that the steps of Figures 11A and 11B can occur continuously or can occur over several periods of time. In this way, critical zone reconfigurations and flow rates can be adjusted continuously or within the desired time periods, respectively.
[000103] The Demand Flow operational strategy will now be described with respect to the operation of chilled water pumps and condenser water pumps. As will be apparent from the following discussion, control of pumping or flow rate by the operational strategy has a highly beneficial effect on the production of chilled water (for example, coolers), pumping of chilled water, pumping of condenser water, operation of cooling tower fan, and air side fan operation. A. Cold Water Pump Operation
[000104] As described above, chilled water pumps provide chilled water flow through the chilled water plant. In one or more embodiments, chilled water pumps provide chilled water flow through primary, secondary, tertiary circuits, or other circuits in an ice water plant.
[000105] In one or more modalities, the operational strategy controls these chilled water pumps so that their flow rate is on or near the Delta T line described above. As described above with respect to the graph in figure 8D, the operation of chilled water pumps according to a Delta T line results in substantial energy savings especially when compared to traditional control schemes.
[000106] Operation of chilled water pumps according to a Delta T line can be achieved in several ways. In general, this operation maintains flow rate at one or more pumps on or near the Delta T line. The operational strategy may use different methods depending on the location 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 on the primary, secondary, tertiary, or other circuit. In one or more embodiments, the flow rate provided by an ice water pump can be controlled by a variable frequency drive (VFD) connected to the pump. It will be understood that other devices, including devices from the chilled water pumps themselves, can be used to control flow rate, pumping speed, or the like.
[000107] Typically, but not always, the operational strategy controls flow rate through one or more chilled water pumps to maintain the 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 the temperature according to temperature information from the sensors. In this way, a Delta T can be maintained at one or more points in the chilled water plant.
[000108] Referring to figure 1, in one embodiment, the operational strategy can control secondary ice water pumps 120 to maintain a Delta T, preferably equal to or close to the design Delta T, through air handlers 124. This operation secondary chilled water pumps 120 according to the Delta T line and ensures that air handlers 124 can provide their rated cooling capacity while operating efficiently. As stated above, a particular Delta T can be maintained by increasing or decreasing the flow rate through the secondary ice water pumps 120.
[000109] The operational strategy may control 116 primary chilled water pumps to maintain a Delta T at one or more points of the chilled water plant equally. 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 achieved by increasing or decreasing the flow rate of one or more primary chilled water pumps 116.
[000110] As can be seen from the capacity equation, the relationship between Delta T and flow rate is linear. Therefore, maintaining a particular Delta T across primary and secondary circuits 104,108, flow rates will typically be close to or equal to equilibrium. This reduces or eliminates excess flow causing a reduction or elimination of bypass mix.
[000111] It is observed that other ways to eliminate diversion mix can be used in one or more modalities. In one embodiment, primary chilled water pumps 116 can be controlled to maintain the temperature within a deviation 128 of the chilled water plant. Because the temperature within the bypass 128 is the result of mixing the bypass, maintaining the temperature within the bypass also controls the mixing of the bypass. In this way, the deviation mix, and its effect that makes up the low Delta T, can be greatly reduced, in many cases, effectively eliminated. In one embodiment, the temperature maintained can be such that there is an equilibrium or close to an equilibrium between the primary and secondary circuits 104,108, reducing or eliminating deviation mix.
[000112] To illustrate, excess flow in secondary circuit 108 can be determined by measuring the chilled water temperature within diversion 128. If the temperature of the diversion is close to or equal to the return water temperature of air handlers 124, there is excess 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 equal to the chilled water temperature in the primary circuit 104. If the bypass temperature is close or equal to the temperature of the chilled water in the primary circuit104, there is an excess of primary flow. The speed of the primary chilled water pump 116 may be decreased until the bypass temperature drops to a central point between the chilled water return temperature of the air handlers 124 and the primary circuit104. Deviation temperatures in this "deadband" have no effect on resetting the primary pump speeds. In one or more embodiments, the speed of the primary chilled water pump 116 may not decrease below the Delta T setpoint of the primary chilled water pump.
[000113] In another embodiment, the operational strategy can control primary chilled water pumps 116 to reduce or eliminate excess flow corresponding to the chilled water flow rate in primary circuit 104 with a chilled water flow rate in secondary circuit 108. One or more sensors can be used to determine flow rate of secondary circuit 108 to allow primary chilled water pumps 116 to match the flow rate.
[000114] Critical zone reconfigurations will now be described with respect to the operation of chilled water pumps according to the operational strategy. As explained, a critical zone reconfiguration can change the Delta T line and the chilled water pumps are operated. In general, a critical zone reconfiguration can occur when there is too much or too little cooling output as determined by one or more sensors. A critical zone reconfiguration can occur for different chilled water pumps at different times and / or based on different sensor information
[000115] Referring to figure 1 for example, a critical zone reconfiguration for secondary chilled water pumps 120 can be triggered if it is determined that there is insufficient chilled water flow for air handlers 124 to meet the demand for cooling. This determination can be made based on various information (typically collected by one or more sensors). For example, when cooled air from an air handler 124 is hotter than desired, a critical zone reconfiguration can occur.
[000116] 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 reconfiguration. For example, opening a chilled water valve in addition to 85% or another limit may indicate that air handler 124 is "starved" by chilled water and trigger a critical zone reconfiguration. In one embodiment, reconfiguration of the critical zone can incrementally decrease the Delta T to be maintained through the air handler 124 causing an increase in the rate of chilled water flow through the air handler. The air handler 124 can now meet the cooling demand. If not, the air handler's chilled water valve must remain open beyond the limit and reconfigurations of additional critical zones can be triggered until the cooling demand can be met. When cooling is achieved, the chilled water valves close which avoids additional critical zone reconfigurations.
[000117] Figure 12 is a graph that illustrates critical zone reconfigurations for an exemplary air handling unit. In this mode, the critical zone reconfigurations are triggered by the position of the chilled water valve of the air handling unit. As can be seen, when the chilled water valve modulates towards 100% open, Delta T is reconfigured to decrease values to provide additional chilled water flow to an air handling unit. In operation, a chilled water pump providing chilled water to an air handling unit, such as the secondary or tertiary chilled water pump, can be used to provide the additional chilled water flow. It is noted that figure 12 also shows that critical zone reconfigurations can be used to increase Delta T when the position of a chilled water valve moves from open to closed.
[000118] Critical zone reconfigurations can also be triggered for primary chilled water pumps 116. In one or more embodiments, a critical zone reconfiguration can be triggered for primary chilled water pumps 116 to ensure that there is little or no mixing diversion in an ice water plant. In one or more modalities, excess flow, if any, can be detected by monitoring the water temperature in the diversion. An increase or decrease in water temperature within the bypass can trigger a critical zone reconfiguration. For example, when the water temperature in the diversion increases, pumping in the primary circuit can be increased to maintain a balance between the primary and secondary circuits. In one embodiment, the VFD for the primary chilled water pump 116 can be adjusted by + or - 1Hz per minute until equilibrium is produced or close to equilibrium. In operation, the operational strategy will typically result in excess flow that fluctuates between zero and negligible flow that results in significant reduction or elimination of deviation mix. It is observed that reconfiguration of the critical zone can occur continuously in some modalities due to the balance of the flow in a deviation that can be highly variable and dynamic.
[000119] For example, in one embodiment, the temperature in the bypass can be measured and controlled, such as through a production pump VFD frequency adjustment, to a setpoint of 48 degrees. This setpoint temperature can be variable to a few degrees by the system and is determined at installation. When the temperature in the bypass rises above said set point, an indication of excess flow of distribution water when compared to the flow of chilled production water is known. The Demand Flow production pump algorithms can then be reconfigured, through a critical zone reconfiguration, to increase the frequency of VFD by 1Hz per minute up to a moment where the temperature in the decoupler drops below the setpoint minus one 2 degree dead band. These parameters are also variable by system and must be determined when installing the system. Deviation temperatures below the setpoint + deadband indicates that excess flow of production water was obtained and the algorithm to control pumping is then reversed at equal frequencies per unit of time, but never above the original Delta T setpoint. This control strategy allows production pumping to meet the dynamic load conditions on the secondary or distribution circuits. This reduces Low Delta Syndrome to its lowest achievable level in all pumping systems decoupled as constructed. It is noted that minimum VFD frequencies can be configured during installation to match the manufacturer's minimum flow requirements.
[000120] The operational strategy, including its critical zone reconfigurations, can be applied to various configurations of decoupled chilled water plants. Figure 13 illustrates an exemplary chilled water plant that has a primary circuit 104, a secondary circuit 108, and a tertiary circuit 1404. As is known, secondary circuit 108 can be a distribution line that carries chilled water to the tertiary circuit 1404. It is noted that a plurality of tertiary circuits 1404 can be provided in some chilled water plants. In general, tertiary circuit 1404 has at least one tertiary chilled water pump and one or more air handlers 124 that provide cooling for one or more buildings or other structures.
[000121] In operation, 1408 tertiary chilled water pumps can be operated to maintain a Delta T via air handlers 124. As described above, this Delta T is preferably close to or equal to the design Delta T for handlers air coolers 124. Secondary chilled water pumps 120 can be operated to maintain a Delta T through tertiary pumps 204. Preferably, this Delta T is close to or equal to the design Delta T for tertiary circuit 204. Chilled water pumps Primary 116 can be operated to maintain a Delta T through coolers 112. This Delta T is preferably close to or equal to the design Delta T for coolers.
[000122] In chilled water plants that have one or more 1404 tertiary circuits, critical zone reconfigurations can also be triggered based on several criteria. To illustrate, critical zone reconfigurations for chilled water tertiary pumps 1408 can be triggered based on the position of chilled water valves on air handlers 124. Critical zone reconfigurations for secondary chilled water pumps 120 can be triggered based on rate flow rate of 1408 chilled water tertiary 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 tertiary circuit (s) 1404 or tertiary pumps 1408 are "hungry" for chilled water. Therefore, a critical zone reconfiguration can be triggered to provide additional 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.
[000123] To illustrate, in one embodiment, when the VFD frequency of any 1404 tertiary chilled water pump reaches 55Hz, the Delta T set points of secondary circuit pump 208 can be reconfigured linearly through a critical zone reconfiguration in order to keep the tertiary pump VFD frequencies from rising higher than 55Hz or the other frequency limit. Set points, frequency limits, or both can be determined during the installation of the Demand Flow in an ice water plant.
[000124] Figure 14 is a graph that illustrates the critical zone reconfigurations for a tertiary chilled water pump. In this mode, critical zone reconfigurations are triggered by the operating frequency (Hz) of a tertiary water pump VFD. As can be seen, Delta T can be reset to a lower value when the tertiary pump VFD (or other tertiary pump speed or flow rate indicator) increases. As explained, reducing the Delta T value causes an increased flow of chilled water to the tertiary pump allowing the cooling demand to be met. The frequencies where critical zone reconfigurations occur and their associated Delta T values can be determined during Demand Flow setup or installation at the chilled water plant. It is observed that Delta T can also be increased when the frequency or speed of the tertiary pump decreases.
[000125] Critical zone reconfigurations for primary chilled water pumps 116 can occur as described above to maintain an equilibrium or close to an equilibrium by greatly reducing or eliminating deviation mix between the primary and secondary circuits 104,108.
[000126] It is observed that in one or more modalities, reconfigurations of the critical zone can be triggered for the most critical zone of a subsystem of an ice water plant. A critical zone in this sense, can be thought of as a parameter that, while having to be maintained to provide the desired conditions in the area or process, these parameters may include, air handling feed air temperature, space temperature / humidity, deviation temperature , chilled water valve position, pump speed, or VFD frequency. To illustrate, tertiary water pumping, such as building pumping systems on campus projects, can be reconfigured outside of your Delta T line based on the most critical zone in the building. Distribution pumping can be reconfigured outside of your Delta T line based on the most critical tertiary pump VFD HZ in the system. B. Condenser Water Pump Operations
[000127] In general, condenser water pumps provide a flow of condenser water to allow condensation of refrigerant inside a chiller. this condensation is an important part of the refrigeration cycle as it allows refrigerant vapor to return to a liquid form to continue the refrigeration cycle. In one or more modalities, the application of the operational strategy causes condenser water pumps to be operated according to a Delta T line, resulting in substantial energy savings.
[000128] Figure 15 illustrates an exemplary condenser 512 comprising a plurality of condenser tubes 1604 within a housing 1608. The refrigerant vapor may be maintained in the housing 1608 so that the refrigerant vapor contacts the condenser pipes 1604. In operation, condenser water flows through condenser tubes 1604, causing condenser tubes 1604 to have a lower temperature than refrigerant vapor. As a result, the refrigerant vapor condenses in the condenser tubes 1604 when heat from the vapor is transferred to the condenser water through the condenser tubes.
[000129] In one or more embodiments, the operational strategy influences the temperature of the refrigerant and condenser water by controlling the flow rate of the condenser water through the condenser tubes 1604. Lowering the flow rate of the condenser causes the water remains inside the condenser tubes 1604 for a longer period of time. Therefore, an increased amount of heat is absorbed by the refrigerant vapor causing the condenser water to escape from the condenser at a higher temperature and enthalpy. On the other hand, increasing the flow rate of the condenser water reduces the time that the condenser water stays inside the condenser tubes 1604. Therefore, less heat is absorbed and the condenser water leaves the condenser at a lower temperature and enthalpy.
[000130] As stated, a problem caused by low Delta T in a chiller is build-up. The operational strategy addresses the build-up problem caused by low Delta T condenser water at low condenser water inlet temperatures. In one or more embodiments, this is achieved by controlling the flow rate of condenser water according to a Delta T line. In this way, a minimum chiller lift requirement can be maintained and the accumulation problem substantially reduced if not eliminated. . In one or more embodiments, elevation requirements can be maintained by controlling saturated condenser refrigerant temperature through the condenser water outlet temperature control in the condenser. The operational strategy can control condenser water outlet temperature by controlling the flow rate of the condenser water temperature, as discussed above. Due to the saturated condenser refrigerant pressure increasing or decreasing with the saturated condenser refrigerant temperature, Delta P or elevation in the chiller can be maintained by controlling the flow of condenser water.
[000131] In operation, the operational strategy can control one or more condenser water pumps, such as through a VFD, to maintain a Delta T through the condenser. Consequently, a condenser water outlet temperature in the condenser and elevation in the chiller are also maintained.
[000132] Additionally, to address accumulation, the Demand Flow operational strategy can also be configured to beneficially influence mass flow, elevation, or both in a cooler 112 operating 516 condenser water pumps according to a line of Delta T. In general, mass flow refers to an amount of refrigerant circulated within a cooler for a given load, whereas elevation refers to the pressure / temperature differential that the refrigerant has to be transferred through. The amount of mass flow and elevation determines the energy use of a 520 chiller compressor. Therefore, the operation of 516 condenser water pumps according to the operational strategy provides efficiency gains by reducing the energy use of the compressor.
[000133] A cooler compressor 520 can be thought of as a refrigerant vapor pump that transfers low-pressure, low-temperature gas from evaporator 508 to condenser 512 in a state of higher pressure and higher temperature. The energy used in this process can be expressed by the equation,
where E is the energy used, MF is the mass flow, L is elevation, and K is a refrigerant constant. As can be seen from this equation, decreasing mass flow or elevation decreases energy use.
[000134] The mass flow (or weight of refrigerant) that being circulated through a cooler 112 to produce the cooling effect (RE) required for a given amount of work or output (Tons) can be described by the formula,
, where K is some constant. Simply stated, this formula says that the increased cooling effect decreases the weight of refrigerant, or mass flow, which needs to be circulated through the cooler for a given amount of work. Increasing the cooling effect also increases the ability to supply a cooler while reducing the compressor's energy for a given amount of work.
[000135] The cooling effect can be increased in several ways. One way to increase the cooling effect is to sub-cool the refrigerant in the condenser. Sub-cooling can be achieved by lowering the condenser water inlet temperature in the condenser. As it is known, condenser water inlet temperature is a function of cooling tower design and environmental conditions. The lower condenser water inlet temperature allows the condenser to produce a lower refrigerant temperature when the refrigerant leaves the condenser. Operating at the coldest condenser water inlet temperature available seasonally permitted for the condenser provides the greatest subcooling while operating within the manufacturer's specifications.
[000136] Subcooling the refrigerant reduces its temperature below saturation and decreases the amount of "flooding" that occurs during the expansion cycle or control process. Flood is a term used to describe the amount of refrigerant used to cool the refrigerant from the temperatures of the subcooled condenser to that of the saturated evaporator. No useful cooling effect is achieved by this "flooded" refrigerant and is considered a displacement of the cooling effect. Therefore, the greater the subcooling, the greater the useful cooling effect per cycle.
[000137] Table 1 is a graph that illustrates the benefits of subcooling in a chilled water plant where Demand Flow has been applied. In general, the graph quantifies the energy displacements of the Demand Flow compressor. In the graph, Project CoPr is calculated from known chiller performance data. Operating CoPr is an adjustment from the Project CoPr based on the current RE and HC chiller operation. Table 1

[000138] As can be seen, the top line of the graph shows the project efficiency as being 0.7 KW / Ton and CoPr as 8.33. The second line is a photograph of the chiller's operating conditions before the Demand Flow implementation. The third line is the same chiller at approximately the same environmental / load condition after the Demand Flow. The fourth line is the efficiency that the chiller is able to obtain in the best operating conditions. The change in tonnage and nominal efficiency obtained in this chiller must be observed, improving the RE. Tonnage is increased by 30% while efficiency is improved by more than 50%
[000139] As described above with respect to figure 6A, the refrigeration cycle can be illustrated by a pressure - enthalpy graph. With reference now to figure 6B, the beneficial effects of subcooling can also be shown through a pressure graph - enthalpy. As shown in figure 6B, subcooling the refrigerant in the condenser reduces the enthalpy of the refrigerant from point 616 to a point 628. The subcooled refrigerant can then enter the evaporator at a point 624. As can be seen, this extends the cooling effect from point 604 to point 624.
[000140] Another contributor to compressor energy is the pressure differential between the evaporator and condenser or, Delta P, that a compressor has to transfer refrigerant through. As stated above, this Delta P is commonly known in the industry as elevation, and is commonly expressed in terms of the temperature difference between the saturated refrigerant in the evaporator and the condenser. The elevation effect on the compressor energy can be seen in the energy equation,
, where L is elevation. For example, according to the equation, an increase in elevation causes an increase in energy use while a decrease in elevation reduces energy use.
[000141] Practically speaking, the saturated evaporator pressure can be considered a relative constant. This pressure can be determined by the chilled water outlet temperature of the evaporator. For example, one or more set points or a graph can be used to determine the saturated refrigerant pressure in the evaporator. The difference between the chilled water outlet temperature and the saturated refrigerant temperature is known as the evaporator approach temperature.
[000142] In one or more modalities, the elevation reduction according to the Demand Flow operational strategy can be obtained by reducing the refrigerant pressure in the condenser. This can be achieved by reducing the condenser water outlet temperature in the condenser because the refrigerant pressure in the saturated condenser is set by the condenser water outlet temperature and the approach designed for saturated refrigerant temperature. The projected approach temperature can vary depending on the quality of a cooler. For example, a cheap cooler may have a 4 degree or more approach, while a better quality cooler may have a 1 degree or less approach.
[000143] In constant volume pumping systems, the condenser water outlet temperature is generally linearly related to the condenser water inlet temperature in a condenser. Therefore, reducing the condenser water inlet temperature reduces the condenser water outlet temperature.
[000144] Table 2 is a graph that illustrates the Demand Flow benefits in an exemplary chilled water plant;

[000145] Table 3 is a graph that illustrates the linear relationship of the condenser inlet and outlet water temperatures in an exemplary condenser at constant volume pumping. Table 3

[000146] As explained above, a reduced condenser water outlet temperature reduces the refrigerant pressure in the condenser, sub-cooling the refrigerant and thereby extending the cooling effect. Reducing the refrigerant pressure in the condenser also reduces the lift. Therefore, reducing the temperature of water entering the condenser has the double benefit of increasing the cooling effect and reducing elevation.
[000147] Reducing the temperature of the water entering the condenser to just above freezing, in theory, should have the optimal practical effect on mass flow and elevation. Unfortunately coolers have minimal elevation requirements (which generally vary by cooler manufacturer, type, and model). Condensation pressures of saturated refrigerant must be maintained at or above these minimum points to provide sufficient differential pressure (ie Delta P of the refrigerant) to drive the refrigerant through the control process or expansion process in the condenser. If these pressure requirements are not met, the refrigerant will cause build-up and shutdown of the chiller from various chiller safety devices.
[000148] Unlike constant flow systems, the operational strategy can control elevation, regardless of the condenser water inlet temperature, by adjusting the condenser water flow rate. It is highly advantageous because it allows the use of lower condenser water inlet temperatures. By allowing lower condenser water inlet temperatures, without accumulation, the operational strategy significantly reduces the compressor energy by increasing sub-cooling (and the cooling effect) and elevation. In practice, the operational cooling strategy can be increased to the maximum allowable limits to maximize energy savings. The Demand Flow method of controlling elevation, regardless of condenser water inlet temperature and through condenser water pumping algorithms, is unique in the industry.
[000149] Additionally, due to the traditional condenser water pumping systems operating at a constant volume, cooling towers are always in full flow conditions, even under partial load conditions. In a constant flow control scheme, as the load on the cooling tower decreases the operational amplitude or Delta T in the tower decreases, which reduces the efficiency of the tower. On the contrary, with the Delta T operating strategy in the cooling tower, it is maintained at or near the Delta T tower design through pumping algorithms described previously. This is significant due to the fact that lower tower collection temperatures are obtainable for the same amount of cooling tower fan energy due to increased efficiencies. The lower tower collection temperatures correspond to lower condenser water inlet temperatures in the condenser. It is important to note that condensers and cooling towers are selected from common Delta T design points, typically 10 degrees, as an industry standard.
[000150] In the operational strategy, minimum cooling tower fan energy is maintained, for a given collection temperature set point by controlling the condenser water pump for a constant Delta T algorithm as described. This method for controlling cooling tower efficiency, regardless of tower load, by pumping condenser water is unique in the industry. There is a synergy that develops between the chiller, pumping condenser water and cooling tower subsystems operating them under the Demand Flow strategy that reduces the net energy of the system.
[000151] It is observed here that another way for the operational strategy to increase the cooling effect is to increase the overheating of the refrigerant in the evaporator. A benefit of increased refrigerant overheating is that it reduces the mass flow requirements of refrigerant per cycle. This reduces the energy use by the compressor. As can be seen in figure 6C, the overheating of the refrigerant generated in the evaporator extends the cooling effect from point 608 to a point 620 having a higher enthalpy.
[000152] With the operational strategy, the superheat of the refrigerant kept constant through the load amplitude of the chiller controlling the chilled water pump (s) for a constant Delta T algorithm based on design Delta T conditions. This method of controlling chiller overheating for design conditions, regardless of the evaporator load, using chilled water pumping algorithms is unique in the industry.
[000153] In traditionally operated chilled water plants, chilled water in the evaporator having a low Delta T significantly reduces and sometimes eliminates the overheating of the refrigerant in the chiller evaporator. Reducing or eliminating refrigerant overheating in the evaporator reduces the cooling effect. For example, in figure 6C, the reduction of refrigerant overheating can cause the cooling effect to retract from point 620 to point 608.
[000154] Refrigerant that is not strongly saturated due to the low Delta T of chilled water is insufficiently overheated and can cause damage to the compressor due to the refrigerant being insufficiently vaporized. In fact, manufacturers often add eliminating screens to the top of the evaporator sections to break larger droplets of refrigerant that have not been overheated and vaporized properly before they enter the compressor. If these droplets reach the compressor, they cause excessive noise and damage to the compressor. Therefore, the Demand Flow provides an added benefit of preventing the formation of these droplets by maintaining or increasing the overheating of the refrigerant to properly vaporize the refrigerant before it reaches the compressor.
[000155] In one or more modalities, the operational strategy maintains refrigerant overheating by controlling chilled water pumps according to a Delta T line. In this way, the refrigerant overheating can be kept close to or equal to the design conditions, regardless of evaporator charge. When compared to the operation of a traditional cooler operating at low Delta T, the overheating of the refrigerant is typically much greater under the operational strategy.
[000156] To illustrate, with reference to figure 1, the primary chilled water pump 116 of a primary circuit 104 can be controlled according to a Delta T line as described above. In this way, a Delta T can be maintained in chiller 112. As can be seen from figure 5, this maintains the Delta T of chilled water in the evaporator of chiller 508 which is connected to the primary circuit by one or more chilled water ducts 532. As a result of keeping Delta T of chilled water in the 508 evaporator, the refrigerant overheating can be maintained close to or equal to the design condition in the evaporator.
[000157] As can be seen, a synergy is developed between the condenser cooling and pumping water subsystems as a result of maintaining Delta T according to the operational strategy. For example, controlling the condenser water inlet temperature, condenser water outlet temperature, and condenser pump flow rate provides a synergistic effect on the chiller energy, condenser pump energy, and cooling tower efficiency. . It will be understood that optimal power combinations of condenser pump, chiller and cooling tower fan can be discovered during installation or configuration of the operational strategy. IV. DEMAND FLOW ENERGY USE
[000158] As shown above, chilled water plant control systems / schemes can positively or negatively influence the capacity and energy use of a chilled water plant. In general, traditional control schemes focus almost entirely on Delta P therefore resulting in artificial capacity reductions and overuse of energy for a given load. Demand Flow reduces energy use and maximizes the capacity of the chilled water plant, regardless of load.
[000159] The following are the reductions in energy use provided by Demand Flow in the chilled water plant subsystems, including chilled water pumps, condenser water pumps, compressors, cooling tower fans, and fans on the air side. A. chilled water pumps
[000160] The fundamental premise behind chilled water variable flow applications is best understood through the Affinity Laws. The Affinity Laws determine that system load (tones) and flow (GPM) are linear, system flow and pressure drop (TDH) is a quadratic function and system flow and energy is a cubic function. So when the system load is reduced the amount of chilled water flow is reduced proportionally but the energy is reduced exponentially.
[000161] As previously discovered in this narrative, traditional pumping water algorithms based on Delta P can reduce flow but not enough to avoid systems with Low Delta T syndrome. When the building load falls from the design conditions the relationship between load (Tones) and flow (GPM) of the system is described by the equation
a Delta T value equal to or close to the design parameters through the Demand Flow operational strategy optimizes the flow (GPM) close to the original specifications and selection criteria of the system equipment thereby optimizing both work and pumping energy. Also, the optimal flow rates provided by the Demand Flow reduce power usage exponentially as seen through the Affinity Laws.
[000162] As previously described, using the chilled water pump to control for the Delta T system design has the double effect of optimizing the chiller energy through overheating as well as the chilling water pump energy. Also, as will be described below, air side capacity will also be increased and fan energy reduced as a direct result of the Demand Flow operational strategy. B. Condenser water pumps
[000163] The Affinity Laws also apply to the side of capacitor energy. When the building load falls from the design conditions the relationship between system load (Tones) and condenser water flow (GPM) is as described by the Affinity Laws as well. Keeping a Delta T equal to or close to the design parameters through Demand Flow control algorithms optimizes the flow (GPM) close to the original system equipment selection criteria thereby optimizing both work and pumping energy. Similar to chilled water pumps, the energy use of condenser water pumps (as well as other pumps) decreases exponentially with reduced flow rate.
[000164] As previously discovered in this narrative, traditional strategies for pumping condenser water based on constant volume result in very low Delta T operation through the condenser, minimizing the ability to reduce compressor energy by subcooling the refrigerant. . Using the operational strategy in condenser water pumps has the triple effect of optimizing pump energy, cooling tower efficiency, and managing the minimum elevation requirements in the chiller, even at very low condenser water inlet temperatures. . As will be further proven later in this narrative, the efficiency of the cooling tower will also be increased and fan energy as a direct result of this Demand Flow control strategy.
[000165] Shifts in the energy usage of the Demand Flow condenser water pump can be determined in the same way as the chilled water pumping energy. It is observed that in the unusual case, as the condenser water pumps are small (for example, low power) relative to the nominal tonnage of the chiller, operate the condenser water system in the design Delta T or near under load conditions high under Demand Flow can in some cases cause the chilled water plant to use slightly higher energy than operating under low Delta T condenser water. However, operating in this manner under Demand Flow maintains an adequate elevation in the condenser even when operating the very low condenser water inlet temperature. This maximizes sub-cooling, which typically more than compensates for any increase caused by operating close to or outside the design Delta T under higher load conditions. The optimal operating Delta T will typically be determined during the installation or configuration process through field tests. C. Compressors
[000166] Reductions in compressor energy derived through the application of an operational Demand Flow strategy are best quantified by calculating the associated displacement in the Refrigerant Performance Coefficient (COPR). COPR is the measure of efficiency in the refrigeration cycle based on the amount of energy absorbed in the evaporator when compared to the amount of energy spent in the compression cycle. The two factors that determine COPR are the cooling effect and the compression heat. Compression heat is the heat energy equivalent to the work performed during the compression cycle. The compression heat is quantified as the difference in enthalpy between the refrigerant entering and leaving the compressor. This relationship can be expressed as
, where RE is the cooling effect and HC is the compression heat. For optimal COPR, the refrigerant overheat should be as high as possible and the refrigerant subcooling should be as low as possible.
[000167] Using chilled water pumping, condenser water pumping, and cooling tower fan subsystems to achieve optimal COPR is unique in the industry and critical to Demand Flow Technology.
[000168] Compressor power shifts under Demand Flow will be further explained now. The design COPR is calculated from known chiller performance data, while operating the COPR is a design adjustment based on the current cooling and compression heat effect.
[000169] For example, the chart in table 4 contains design refrigerant properties and measurements for a Carrier cooler (Carrier Corporation Trade Mark) before and after an actual Demand Flow renewal. Table 4

[000170] The top line of this spreadsheet shows the design efficiency to be 0.7 KW / Ton and the design COPR to be 8.33. The second line is the measured operating parameters of the chilled water system before the Demand Flow implementation. The third line is the measured operating parameters of the chilled water system with Demand Flow applied. The fourth line is the efficiency that the chiller is able to obtain in the best operating conditions. It should be noted that the change in tonnage and nominal efficiency obtained in this cooler improving the cooling effect. Tonnage is increased by 30% while efficiency is improved by over 50%
[000171] These data are now applied to the pressure enthalpy diagram in figure 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, comparing the graph before 2004 and the graph after Demand Flow 2008 there is an increased cooling effect and reduced elevation (without accumulation) under Demand Flow. As can also be seen, the Demand Flow application has increased 2012 sub-cooling as well as 2016 refrigerant overheating. D. Cooling Tower Fans
[000172] Demand Flow cooling tower fan energy is approximately linear to the load in a well-maintained operating system with collection temperatures obtainable under current environmental conditions. The condenser water inlet temperature or cooling tower fan setpoints can be set equal to the design wet bulb temperature + wet tower collection temperature approach for wet bulb. Shifts in the cooling tower fan energy can be based on the actual condenser water inlet temperature, nominal in-line tonnage, measured tonnage and actual in-line cooling tower fan power.
[000173] A graph of a system in operation with the Demand Flow operational strategy applied is shown in table 5.Table 5

[000174] In this case study, the cooling tower fan setpoint has been reduced from 83 degrees to 61 degrees to demonstrate the shift in energy between the subsystems when the condenser water inlet temperature drops. The graph is read from right to. left E. Air side fans
[000175] Energy and fan capacity on the side of the air are directly affected by the Low Delta T Syndrome and mix deviation in the plant. For example, a 2 degree rise in chilled water temperature can increase the fan energy of the air handling unit of variable air volume by 30% under design load conditions. This loss of efficiency can be directly quantified using basic heat exchanger calculations. It is observed that work and energy on the air side are affected by the Low Delta T Syndrome in the same way as other heat exchanger systems with a loss of supply capacity and increased energy consumption.
[000176] The heat transfer equation Q = U - A - LMTD, where Q is the global heat transferred, U is the global heat transfer coefficient of the heat exchanger material, A is the surface area of the heat exchanger , and LMTD is the record of average temperature difference, it is a way to observe the effects of the Low Delta T Syndrome in the cold water coils of the air handler. In cold water coils the LMTD describes the relationship between the inlet / outlet on the air side and the inlet / outlet on the water side. In the context of Demand Flow systems where chilled water moves more slowly (higher Delta T), there are some discussions that the global heat transfer coefficient, U, is reduced, resulting in less efficient coil performance. While it may be true that U is reduced, this is more than offset by the effects of the supply of cooler chilled water in a Demand Flow system, which is reflected in the higher LMTD. In fact, the larger LMTD more than makes up for any theoretical U-shaped reduction as seen in the following example.
[000177] More specifically, the LMTD analysis shows that reducing CHWS for the coil by decreasing cooler set points or eliminating mixing in the plant bypass can dramatically improve the coil's performance. The graph in table 6 provides an LMTD analysis that details the potential displacements of airside coil capacity in Demand Flow. With the exemplary data in Table 6, a 25% increase in capacity is obtained. Table 6

[000178] Table 7 A illustrates the relationship between chilled water flow and Delta T in a system with Low Delta T Syndrome. Table 7B illustrates a Demand Flow System coil with decreased chilled water supply temperatures and GPM associated with constant temperature and return load of chilled water. Table 7C illustrates the increased serpentine potential in chilled water flows with decreased chilled water supply temperatures. This example illustrates the flexibility of the Demand Flow operational strategy to overcome particular problems in a given system.

[000179] Table 8 is a graph that illustrates energy shifts on the air side under Demand Flow in an exemplary chilled water plant. Table 8

[000180] The total cooling load on the air side is calculated by the equation Q <= 4.5-CAM- (A, -A,), where entaipia of incoming air is hl and enthalpy of outgoing air is h2. For example, based on this formula and on the following premises, the energy use of the ventilator after the Demand Flow is applied can be calculated / quantified. - The monthly average load (Qt) of the air handling unit (AHU) is known from previous analyzes. - AHU CFM is linear to load. - The enthalpy (hi) of air entering the AHU is known from the design information or direct measurement.
[000181] Based on the above, the monthly average CFM of AHU can be determined by the equation,
where Qtavg is the monthly average of Qt of AHU and Qtmax is the maximum Qt of AHU. The monthly mean of enthalpy of outgoing air can be determined by the equation,
, where Qtavg is the monthly average of Qt of AHU and CFMavg is the monthly average of CFM of AHU. It is observed that the value 4.5 is a constant that can be adjusted for the location of the environment based on the density of the air.
[000182] The sample data in figure 24 illustrate the results of these calculations and assumptions for a system that has a maximum connected load of 1000 Tons to 315,000 CFM.
[000183] The minimum CFM on the air side is 35% and the minimum AHU SAT is as shown. As can be seen, the Demand Flow provides several advantages. V. SPECIFIC ADVANTAGES UNIQUE TO THE FLOW OF DEMAND
[000184] As can be seen from the above, the Demand Flow provides a unique operational strategy in the HVA / C industry. Additionally, the Demand Flow and its operational strategy is the first that specifically: 1. Uses external control operations in production subsystems for pumping chilled water to optimize the overheating of evaporator refrigerant, or enthalpy of refrigerant that leaves the evaporator in this way. beneficially influencing the mass flow component of the compressor's energy use. Controlling chilled water pumps, such as via VFDs, to close to or equal to the Delta T of the manufacturer-designed evaporator (eg, Delta T design) using Demand Flow chilled water pumping operations controls refrigerant overheating to the design conditions of the chiller manufacturer regardless of the percentage of charge in a chiller at any time. This optimizes the enthalpy of the refrigerant leaving the evaporator and reduces the energy of the chiller compressor when compared to a chiller operation less than the design Delta T (ie low Delta T).
[000185] Demand Flow also uses external control operations in chilled water distribution pumping subsystems to obtain design Delta T regardless of load conditions at the chilled water plant, thereby eliminating the Low Delta T Syndrome in the subsystem of water from the chiller. 2. Uses external control operations in condenser water pumping and cooling tower fan subsystems to optimize the subcooling of condenser refrigerant, or enthalpy of the refrigerant leaving the condenser (and entering the evaporator), In this way, the mass flow component of the compressor's energy equation, as described above, is beneficially influenced. Demand Flow control operations in condenser water pumping and cooling tower fan subsystems generally determine the saturated pressure / final operating temperature differential between the evaporator and condenser in the chiller (ie elevation). This beneficially influences the mass flow components and elevation of the compressor's energy equation, discussed above.
[000186] As explained, the saturated pressure of the evaporator can be considered a relative constant because the conditions of entry and exit of chilled water are kept constant. However, the temperatures and pressures of water entering the condenser, when using constant volume condenser water pumps, will vary according to environmental and load conditions. Therefore, condenser saturated pressure conditions can be manipulated, through the condenser water outlet temperature, to control the minimum pressure differential required by the chiller manufacturer. Demand Flow Constant Delta T variable flow operations control condenser water pumps, such as through VFDs, to maintain the manufacturer's minimum differential pressure (ie elevation) between the evaporator and condenser at all times.
[000187] The Demand Flow also matches the condenser water flow to the chiller load in this way reducing the flow of condenser water through the cooling tower under all partial load conditions. As explained, partial load conditions exist in most of the ice water plants 90% of the time. When the flow of condenser water is reduced to the cooling tower collection temperature approach for wet bulb it is reduced equally. This is an almost linear relationship to approximately half the temperature of the original design approach of the cooling tower. This produces lower cooling tower collection temperatures at any given partial load on the same cooling tower fan energy. In turn, lower cooling tower collection temperatures result in lower condenser water inlet temperatures in the condenser providing sub-cooling for the refrigerant in the condenser.
[000188] Additionally, Demand Flow uses external control operations in a condenser water pumping subsystem to obtain Delta T close to or equal to the design for a condenser regardless of chiller load conditions, thereby eliminating the Low Down Syndrome Delta T in the condenser water subsystem. 3. Uses external collaboration control operations between production and distribution circuits in order to balance the flow between the circuits, minimizing or eliminating the excess flow and diversion mix that contribute to the Low Delta T Syndrome, such as in the decoupled ice water. This produces the best delivery capacity on the air side at any given flow rate of chilled water. This also allows the primary circuit pumping or production loop pumping to meet varying load conditions of the distribution pumping system. Under Demand Flow, Low Delta Syndrome is reduced to its lowest possible level, if not effectively eliminated. 4. Uses critical zone reconfigurations to meet increased cooling demand while controlling chilled water pumping according to a Delta T line. Critical zone reconfigurations can also be used to decrease the cooling output by reconfiguring the Delta T line. 5. Operates the chilled water plants and their components at minimal partial pumping pressures to minimize chilled water valve bypass and the resulting overcooling, thereby decreasing the system load. 6. Produces a synergistic reduction in the energy use of the chilled water plant as well as an increase in the supply capacity by synchronizing chilled water pumping, condenser water pumping, compressor operation, cooling tower operation, and side operation donate.
[000189] Although various modalities of the invention have been described, it will be apparent to those skilled in the art that many additional modalities and implementations are possible and are within the scope of this invention.

权利要求:
Claims (11)
[0001]
1. Method for efficient operation of a chilled water plant, characterized by the fact that it comprises, adjusting a chilled water Delta T that comprises a chilled water inlet temperature and an chilled water outlet temperature in one or more components of the chilled water plant; control the flow rate of chilled water through one or more components to maintain the Delta T of chilled water through one or more components, the flow rate of chilled water being controlled by one or more chilled water pumps (116 , 120, 204); and perform a critical zone readjustment to adjust the chilled water Delta T when one or more trigger events occur, one or more of the trigger events comprising at least one of the group consisting of the opening of a chilled water valve of a air handling unit (124) beyond a particular limit, an increase in the temperature of the chilled water at a diversion (128) of the chilled water plant, a decrease in the temperature of the chilled water at a deviation (128) of the water plant chilled water and a change in the flow rate of a tertiary pump (204) beyond a particular limit, the chilled water Delta T being readjusted by an action selected from the group consisting of adjusting the chilled water inlet temperature and adjust the chilled water outlet temperature; the control of the chilled water flow rate through one or more components to maintain the chilled water Delta T reduces the Low Delta T Syndrome in the chilled water plant.
[0002]
2. Method according to claim 1, characterized by the fact that the Delta T of chilled water in one or more components of the chilled water plant is maintained by increasing the flow rate of the chilled water to reduce the Delta T of ice water and decrease the flow rate of ice water to increase the Delta T of ice water.
[0003]
3. Method according to claim 1, characterized by the fact that it additionally comprises establishing a Delta T of the condenser water comprising a low condenser water inlet temperature and a condenser water outlet temperature in a condenser (508), with the condenser (508) using the low water inlet temperature of the condenser to provide cooling subcooling; and maintaining the Delta T of the condenser water by adjusting the flow rate of the condenser water through the condenser (508), the flow rate of the condenser water being adjusted through one or more condenser water pumps ( 516).
[0004]
Method according to any one of the preceding claims, for operating one or more pumps (116, 120, 204) of a chilled water plant comprising, pumping water at a first flow rate through a chiller (112) with a first pump (116); adjust the first flow rate to maintain a first Delta T through the chiller (112), the first Delta T comprising a chiller inlet temperature (112) and a chiller outlet temperature that provides superheat in an evaporator (512) of the chiller (112) independent of the load conditions of the chilled water plant; pump the water at a second flow rate through an air handling unit (AHU) with a second pump (120); adjust the second flow rate to maintain a second Delta T through the air handling unit (AHU), the second Delta T comprising an inlet temperature of the air handling unit (AHU) and an outlet temperature of the unit air handler (AHU) that provides the desired cooling output in the air handler unit (AHU) regardless of the load conditions of the chilled water plant; the first Delta T and the second Delta T are similar to balance the first flow rate and the second flow rate and reduce the bypass mixture (128) in a bypass (128) of the chilled water plant.
[0005]
5. Method according to claim 4, characterized by the fact that the first Delta T and the second Delta T are the same.
[0006]
6. Method according to claim 4, characterized in that it additionally comprises increasing the second flow rate by readjusting the second Delta T when a water valve of the air handling unit (124) opens beyond a particular limit, and the increase in the second flow rate increases the cooling output in the air handler (124).
[0007]
Method according to claim 4, characterized in that it additionally comprises pumping water through a distribution loop from the chilled water plant to the second pump (120) at a third flow rate with a third pump (204); adjust the third flow rate to maintain a third Delta T; increase the third flow rate by readjusting the third Delta T when the second flow rate provided by the second pump (120) is beyond a particular limit, and increasing the third flow rate increases the cooling capacity in the user of air (124).
[0008]
Method according to claim 4, characterized in that it additionally comprises, pumping water from the condenser at a fourth flow rate through a capacitor (508) of the chiller (112) with a fourth pump; and adjusting the fourth flow rate to maintain a fourth Delta T in the condenser (508), the fourth Delta T comprising an inlet water temperature of the condenser and an outlet water of the condenser which provides refrigerant subcooling and prevents refrigerant stacking regardless of load conditions of the chilled water plant.
[0009]
9. Controller (1004) to control one or more pumps (116, 120, 204) of a chilled water plant, characterized by the fact that it comprises an input (1020) configured to receive sensor information from one or more sensors (1028); a processor (1004) configured to control a flow rate provided by one or more pumps (116, 120, 204) to maintain a Delta T through a component of the chilled water plant, with the processor (1004) increasing or decreasing the flow rate to maintain Delta T based on sensor information and generates one or more signals to control the flow rate provided by one or more pumps (116, 120, 204), with Delta T comprising a temperature of inlet and outlet temperature; an output (1024) configured to send one or more signals to one or more pumps (116, 120, 204), with the processor (1004) being configured to perform a critical zone reset to adjust the Delta T of chilled water when one or more of the trigger events occurs, one or more of the trigger events comprising at least one of the group consisting of the opening of a chilled water valve of an air handling unit (124) in addition to a particular limit, an increase in chilled water temperature in a diversion (128) of the chilled water plant, a decrease in chilled water temperature in a diversion (128) of the chilled water plant and a change in the flow rate of a pump tertiary (204) beyond a particular limit.
[0010]
10. Controller, according to claim 9, characterized by the fact that the processor is configured to perform a critical zone readjustment by decreasing the Delta T in response to sensor information that indicates that additional cooling capacity is desired in the component.
[0011]
11. Controller, according to claim 9, characterized by the fact that the processor (1004) is configured to maintain Delta T by controlling the Delta T's outlet temperature, the outlet temperature being controlled by adjusting the flow rate through the chilled water plant component.

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同族专利:

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公开号 | 公开日

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IN2012DN00637A|2015-08-21|

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CA2768736A1|2011-01-27|

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KR20120038515A|2012-04-23|

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AU2010275035A1|2012-02-09|

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US8660704B2|2014-02-25|

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CN102498352A|2012-06-13|

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US20130047643A1|2013-02-28|

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CA2768736C|2017-10-03|

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HK1205240A1|2015-12-11|

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EP2457037A4|2017-12-13|

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KR101642542B1|2016-07-25|

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CN102498352B|2015-07-22|

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WO2011011033A1|2011-01-27|

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ES2726430T3|2019-10-04|

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BR112012001358A2|2016-03-15|

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EP2457037B1|2019-02-13|

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US20110022236A1|2011-01-27|

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DK2457037T3|2019-05-06|

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SG178053A1|2012-03-29|

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MX2012001015A|2012-02-28|

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CN104215006B|2017-05-03|

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US8275483B2|2012-09-25|

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CN104215006A|2014-12-17|

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AU2010275035B2|2014-10-16|

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EP2457037A1|2012-05-30|

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HK1171805A1|2013-04-05|

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法律状态:
2019-01-15| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|

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2019-09-03| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|

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2020-05-19| B06A| Notification to applicant to reply to the report for non-patentability or inadequacy of the application [chapter 6.1 patent gazette]|

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2020-09-01| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|

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2020-12-08| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 10 (DEZ) ANOS CONTADOS A PARTIR DE 08/12/2020, OBSERVADAS AS CONDICOES LEGAIS. |

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