WO2009142659A1

WO2009142659A1 - Multiple compressor chiller

Info

Publication number: WO2009142659A1
Application number: PCT/US2008/084000
Authority: WO
Inventors: Richard Booth; Duncan E. Hitchcox
Original assignee: Modine Manufacturing Co
Current assignee: Modine Manufacturing Co
Priority date: 2008-05-21
Filing date: 2008-11-19
Publication date: 2009-11-26
Anticipated expiration: 2010-11-21

Abstract

A chiller system operable to cool a flow of chiller fluid includes a first compressor operable to compress a fluid and discharge the compressed fluid to an outlet manifold, a condenser in fluid communication with the outlet manifold and operable to cool the compressed fluid, and an expansion device including an outlet. The expansion device in fluid communication with the condenser and operable to expand the cooled compressed fluid. An evaporator includes an inlet, an evaporator outlet, a first flow path in fluid communication with the expansion device to receive the expanded cooled compressed fluid, and a second flow path through which the chiller fluid flows. The first flow path and the second flow path are arranged in a heat exchange relationship. A load balancing valve is positioned to selectively provide direct fluid communication between the outlet manifold and a point between the outlet of the expansion device and the inlet of the evaporator.

Description

MULTIPLE COMPRESSOR CHILLER

RELATED APPLICATION DATA

[0001] The present application claims the benefit of co-pending provisional patent application Serial No. 61/128,400, filed May 21, 2008, the subject matter of which is hereby fully incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to chillers for generating a supply of cool liquid. More specifically, the present invention relates to a method and apparatus for a chiller having multiple compressors.

SUMMARY

[0003] In some embodiments, the invention provides a chiller system for generating a flow of cooled fluid such as water, the chiller system including a plurality of compressors having inlets and outlets, at least one condenser having an inlet and an outlet, the condenser inlet being in fluid communication with the compressor outlets, an expansion valve having an inlet and an outlet, the inlet being in fluid communication with the condenser outlet, an evaporator having an inlet and an outlet, the inlet being in fluid communication with the expansion valve outlet and the outlet being in fluid communication with the compressor inlets, and a load balancing valve having an inlet and an outlet, the inlet being in fluid communication with the compressor outlets and the outlet being in fluid communication with the expansion valve outlet. In some embodiments, the load balancing valve can shunt excess pressure from the compressor outlets to the expansion valve outlet to reduce the ratio of the compressor outlet pressure to the compressor inlet pressure. Alternatively or in addition, the load balancing valve can shunt pressure from the compressor outlets to upstream of an evaporator inlet to reduce the ratio of the compressor outlet pressure to the compressor inlet pressure. The compressors can be centrifugal compressors operating on magnetic bearings. The chiller system can also include a conduit for flowing the cooled fluid adjacent to the evaporator.

[0004] In some embodiments, the invention provides a method of loading a plurality of compressors of a chiller system for generating a flow of cooled fluid such as water, the chiller having a single circuit of compressors, a condenser, an expansion valve and an evaporator. A first compressor is started and is run at a portion of its total capacity. When a demand on the chiller system exceeds the total capacity of the compressor, the load on the first compressor is reduced and pressure at an outlet of the first and second compressor relative to an inlet of the first and second compressor is reduced to a pre-determined ratio. When the pre-determined outlet to inlet pressure ratio is achieved, the second compressor is started. The pressure at the outlet of the first and second compressor can be reduced by shunting fluid from the outlet to an inlet of the evaporator. The fluid can be shunted by selectively opening a load balancing valve in fluid communication between the compressor outlets and the evaporator inlet.

[0005] In one construction, the invention provides a chiller system operable to cool a flow of chiller fluid. The system includes a first compressor operable to compress a fluid and discharge the compressed fluid to an outlet manifold, a condenser in fluid communication with the outlet manifold and operable to cool the compressed fluid, and an expansion device including an outlet. The expansion device in fluid communication with the condenser and operable to expand the cooled compressed fluid. An evaporator includes an inlet, an evaporator outlet, a first flow path in fluid communication with the expansion device to receive the expanded cooled compressed fluid, and a second flow path through which the chiller fluid flows. The first flow path and the second flow path are arranged in a heat exchange relationship. A load balancing valve is positioned to selectively provide direct fluid communication between the outlet manifold and a point between the outlet of the expansion device and the inlet of the evaporator.

[0006] In another construction, the invention provides a chiller system operable to cool a flow of chiller fluid. The system includes a first compressor operable to compress a fluid and discharge the compressed fluid to an outlet manifold, a second compressor selectively operable to compress a fluid and discharge the compressed fluid to the outlet manifold, and an expansion device including an outlet. The expansion device is in fluid communication with the condenser and is operable to expand the compressed fluid. An evaporator includes an inlet, an evaporator outlet, a first flow path in fluid communication with the expansion device to receive the expanded compressed fluid, and a second flow path through which the chiller fluid flows. The first flow path and the second flow path are arranged in a heat exchange relationship. A sensor is positioned to measure the pressure ratio between the outlet manifold and the evaporator outlet, and a load balancing valve is positioned to provide selective fluid communication between the outlet manifold and a point between the outlet of the expansion device and the inlet of the evaporator. The load balancing valve is operable in response to the measured pressure ratio to maintain the pressure ratio below a predetermined pressure ratio during start-up of the second compressor.

[0007] In yet another construction, the invention provides a method of starting a compressor in a chiller system including a first compressor and a second compressor. The method includes operating the first compressor to draw a fluid from an inlet manifold and to provide a compressed fluid to an outlet manifold, directing the compressed fluid to an evaporator inlet, and passing the compressed fluid through an evaporator to cool a second fluid in the evaporator. The method further includes discharging the compressed fluid from an evaporator outlet to the inlet manifold, measuring a pressure ratio between the outlet manifold and the inlet manifold, and opening a valve in response to the measured pressure ratio being above a predetermined value. The valve is positioned to control fluid flow between the outlet manifold and the evaporator inlet. The method also includes starting the second compressor in response to the pressure ratio falling below the predetermined value, and closing the valve in response to successful start of the second compressor.

[0008] Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Fig. 1 is a perspective view of a chiller system according to some embodiments of the present invention.

[0010] Fig. 2 is a fluid circuit diagram of the chiller system of Fig. 1.

[0011] Fig. 3a is a side view of a portion of the chiller system of Fig. 1.

[0012] Fig. 3b is a top view of the chiller system of Fig. 3 a.

[0013] Fig. 3c is a front end view of the chiller system of Fig. 3 a.

[0014] Fig. 3d is a rear end view of the chiller system of Fig. 3a. [0015] Fig. 4 is a graph illustrating a chiller system operation including a start-up sequence according to an embodiment of the invention.

[0016] Fig. 5 is a graph illustrating a chiller system operation including an alternate startup sequence according to an embodiment of the invention.

DETAILED DESCRIPTION

[0017] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms "mounted," "connected," "supported," and "coupled" and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, "connected" and "coupled" are not restricted to physical or mechanical connections or couplings.

[0018] Figs. l-3d illustrate a chiller system 100 for generating a flow of a cooled fluid, such as water, according to some embodiments of the invention. The chiller system 100 includes a plurality of compressors 104, one or more condensers 108, and an evaporator 112 that together form a closed circuit for circulation of a refrigerant therethrough. The chiller system 100 of the illustrated embodiment of Figs. l-3d is a single circuit system, meaning that refrigerant passes through the compressors 104 once with each circuit through the chiller system 100.

[0019] The compressors 104 are centrifugal-type compressors that each run on magnetic bearings. Referring now to Fig. 2, ball valves 116 are provided at the inlet 105 of each compressor 104 to control the flow of refrigerant into the associated compressor 104. That is, one, two or more of the compressors 104 can be operated simultaneously to increase or decrease the operating capacity of the chiller system 100. The unused compressors 104 can remain inactive until activated to increase the operating capacity of the chiller system 100. [0020] One or more lines 120 fluidly communicate between the outlet, or hot gas side, of each compressor 104 with an inlet of the condensers 108. In the illustrated embodiment, the hot gas lines 120 between each compressor 104 and the condensers 108 are connected in parallel such that the flow of hot gaseous refrigerant from the compressors 104 is evenly distributed among the condensers 108 for condensing. The various pipes operate as a manifold 121 that collects the output from a number of compressors 104 and then distributes that output to the various condensers 108. It should be noted that the number of compressors 104 employed in the system is not related to the number of condensers 108. Thus, the number of compressors 104 employed could equal the number of condensers 108 or could be different as desired.

[0021] A check valve 124 is provided in the hot gas line 120 between each compressor 104 and the condensers 108 to permit hot gas to flow from the compressors 104 to the condensers 108 and to inhibit backflow from the condensers 108 to the compressors 104. A ball valve 128 is provided in each hot gas line 120 between each check valve 124 and the condensers 108 to establish a minimum pressure necessary for hot gas to flow from the compressors 104 to the condensers 108. In addition, a pressure relief valve 132 can be provided in the hot gas line 120 between each check valve 124 and each ball valve 128 to inhibit operation of the system above a maximum pressure between the compressor 104 and the condensers 108.

[0022] The condensers 108 are air-cooled, meaning that ambient air around the condensers 108 receives thermal energy from the hot gaseous refrigerant flowing through the condensers 108. The condensers 108 can be located remotely from the compressors 104 and other components of the chiller system 100. For example, the condensers 108 can be located outdoors, for example, on a roof of a building, while the remainder of the chiller system 100 can be located within the building. In other embodiments, however, such as the embodiment depicted in Fig. 1, the chiller system 100 is assembled as an integrated package for installation in a single location (e.g., outdoors).

[0023] Condenser fans 133 are provided to force ambient air across the condenser 108 to facilitate transfer of heat from the refrigerant within the condenser 108 to the ambient air, thus cooling the refrigerant for condensation. The amount of heat transfer depends upon the volume of air blowing across the condensers 108, which is based on the speed of the condenser fans, and the temperature of the ambient air. The fans can be powered by variable speed motors, such as electronically commutated AC motors so as to have variable speeds for increasing and decreasing the flow rate of the ambient air across the condensers 108 as needed.

[0024] As shown in Fig. 2, a plurality of lines 136 can fluidly communicate between the outlets of the condensers 108 and the inlets of one or more electronic expansion valves 140. Again, the lines 136 are connected in parallel such that the flow of condensed refrigerant from the condensers 108 is evenly distributed among the expansion valves 140 for expansion. Ball valves 142 are provided in the lines 136 to establish a minimum pressure necessary for refrigerant to flow to the expansion valves 140. The piping between the condenser outlets and the expansion valves 140 function as a manifold that collects the condensed fluid from the condensers 108 and evenly distributes the fluid to the expansion valves 140.

[0025] The electronic expansion valves 140 accept the condensed liquid refrigerant from the condensers 108 and expand the liquid refrigerant into a vapor. In the illustrated embodiment, a plurality of expansion lines 144 fluidly communicate between the outlet(s) of the expansion valves 140 and the inlet of the evaporator 112.

[0026] As shown in Fig. 2, the evaporator 112 can be a shell and tube-type evaporator. In other embodiments, the chiller 100 can include one or more evaporators having shell and tube-type constructions, or alternatively, having other constructions, such as, for example, tube and tube-type, plate-type, and the like. Refrigerant vapor and/or vapor-liquid discharged at the electronic expansion valves 140 passes through the evaporator 112. As the vapor and/or vapor-liquid travels through the evaporator 112, any liquid evaporates and the vapor is superheated. A line 152 fluidly communicates between the outlet of the evaporator 112 and the inlets of the compressors 104. This completes the closed circuit that the refrigerant travels through the chiller system 100.

[0027] The evaporator 112 includes a conduit containing a flow of cooled fluid. Cooled fluid flows into an inlet 149 of the conduit, through the conduit in the evaporator 112, and out through an outlet 150. As the refrigerant vapor evaporates within the evaporator, thermal energy is transferred from the cooled fluid through the evaporator 112 to the refrigerant to provide the energy needed to vaporize any refrigerant liquid and to superheat the refrigerant vapor. As energy is transferred from the cooled fluid to the refrigerant, the temperature of the cooled fluid 102 decreases, cooling the cooled fluid. The cooled fluid can be conducted from the outlet 150 elsewhere as needed.

[0028] The chiller system 100 can be operated with a single compressor 104 acting on the refrigerant, or can be operated with two or more compressors 104 acting on the refrigerant to increase the cooling capacity of the chiller system 100. Second and subsequent compressors 104 can be initiated for operation while the first compressor 104 is running to provide additional capacity as needed.

[0029] A compression ratio is calculated based on the measured refrigerant pressure at the compressor outlet 106 and the measured refrigerant pressure at the compressor inlet 105. During normal operation, the compression ratio can vary, depending on the ambient conditions, the demand on the chiller system 100, and the compressor speed. The compression ratio can vary from about 1.5 to about 5.5. However, to initiate start-up of a second compressor 104 while the chiller system 100 is running, a start-up compression ratio must be satisfied. The start-up compression ratio is typically less than the actual compression ratio. If the actual compression ratio exceeds the start-up compression ratio, the compressor can stall. Compressor stall is an aerodynamic condition that occurs when the pressure ratio across a dynamic compressor exceeds a stall limit. During stall, the compressor is unable to compress fluid as the fluid does not flow through the compressor or in some conditions flows in a reverse direction. This means that although the second compressor 104 is running, refrigerant is not being pushed across the compressor 104, reducing the efficiency of the chiller system 100.

[0030] In order to effect changes to the actual compression ratio C during operation of the chiller system 100 in anticipation of a compressor start-up, a bypass line 160 is connected between the hot gas lines 120 at the compressor outlet O and the expansion lines 144 between the expansion valve 140 and the evaporator 112. A load balancing valve 164 is provided in the bypass line 160 to control a supply of gaseous refrigerant from the hot gas line 120 to the expansion lines 144. When the load balancing valve 164 is closed, no gaseous refrigerant flows through the bypass line 160. When the load balancing valve 164 is opened, however, pressurized gas from the hot gas line 120 is shunted to the expansion lines 144. In some embodiments, the load balancing valve 164 can be an electronically modulating valve. [0031] Opening the bypass valve 164 decreases the compressor outlet pressure Po. As the compressor outlet pressure Po is reduced, the compression ratio C is also reduced. Opening the bypass valve 164 can also slightly increase the inlet pressure Pi of the evaporated refrigerant at the compressor inlet, further reducing the compression ratio C.

[0032] Thus, in order to increase capacity of the running chiller system 100, a start-up sequence is initiated in which it is first determined if the actual compression ratio C across the compressors 104 is less than or equal to a desired start-up compression ratio Cs. If the actual compression ratio C is greater than the start-up compression ratio Cs, then the bypass valve 164 is slowly opened (partially or fully) to shunt pressurized refrigerant from the hot gas line 120 to the expansion line 140. The bypass valve 164 is opened slowly so as to avoid rapid pressure changes within the chiller system 100. For example, the bypass valve 164 can be opened approximately 1% per minute over a period of several minutes.

[0033] As the bypass valve 164 is opened, the compression ratio is monitored. When the compression ratio has reduced to a point equal to or less than the start-up compression ratio, the second compressor 104 is started. The desired start-up compression depends upon the specific arrangement of the compressors 104 and the chiller system 100, and the specific arrangement of the compressors 104 themselves. Exemplary start-up compression ratios can be from about 2.0 to about 3.0. In one embodiment, the start-up compression ratio is approximately 2.4.

[0034] Fig. 4 is a chart that illustrates the output of two compressors and the total output of a two compressor system during the start-up sequence of a two-compressor chiller system 100 according to an embodiment of the invention. In this embodiment, in which the start-up compression ratio is 2.4, the first compressor 104 initiated for operation of the chiller system 100 is the compressor having the lowest number of operation hours to date. Before operating the first compressor 104, the system is operating at time A, at which the total system output is zero. This first compressor 104 is started, and is allowed to run loads up to approximately 53% of its maximum output, as shown at time B. The term "load" describes the amount of heat to be removed from the cooled fluid in the chiller. Once a minimum speed, for example, 29,000 rpm, is achieved at the first compressor, the load on the first compressor 104 is reduced to approximately 50% of the maximum output, as illustrated at time C. Once the first compressor 104 has stabilized at approximately 50% for a delay period of, for example, 60 seconds, the load on the first compressor 104 can be adjusted to match the load required by the chiller system 100, as illustrated from time D to time E.

[0035] If the demand on the chiller system 100 meets or exceeds the maximum output of the first compressor 104 (such as is illustrated at time E), a start-up sequence for a second compressor 104 will initiate in which the load on the first compressor 104 is reduced to approximately 50% of its maximum output and the load balancing valve 164 is opened if the compression ratio exceeds the start-up compression ratio, as shown at point F. The first compressor 104 continues operation at approximately 50% of its maximum output until the compression ratio C is equal to or less than the desired start-up compression ratio Cs of 2.4, as illustrated between time F and G. When the actual compression ratio C is equal to or less than the start-up compression ratio Cs, a second compressor 104 is started with a load of approximately 53% of its maximum output, as shown at time H. Once a minimum speed of 29,000 rpm is achieved, the load on the second compressor 104 and the first compressor 104 is reduced or maintained at approximately 50%, as illustrated at time I. After a minimum delay of, for example, 60 seconds, the load on both compressors 104 is adjusted together to satisfy the demand on the chiller system 100, as illustrated between time I and J. In constructions with more than two compressors, the steps from time E to J repeat to initiate the start-up of the third, fourth, fifth, etc. compressors. It should be noted that the illustrated construction shows each of the compressors operating at the same output when they are started. Thus, if 180% of system output is required, each compressor operates at 90%. Other systems may operate differently. For example, one compressor could be maintained at 100% while the second compressor varies its output to match the total system demand.

[0036] Fig. 5 graphically illustrates an alternate start-up sequence for a multi-compressor chiller system 100. The alternate sequence can be used in conjunction with the sequence shown and described with respect to Fig. 4. When a first compressor 104 is in operation and the second compressor 104 is waiting to start (as illustrated at time A), the load balancing valve 164 is opened to achieve the desired compression ratio. These steps can be carried out as described with respect to Fig. 3. If, however, after a maximum delay of, for example, 100 seconds, the desired compression ratio is not achieved, then operation of both compressors 104 is halted as illustrated at time B. When both compressors 104 have completed halting procedures and/or delays, both compressors 104 are started together at loads of approximately 53% of their maximum output as illustrated at time C. Once a minimum operating speed has been achieved, the load is reduced to 50% for both compressors 104 for a delay period as shown at point D. After the delay period, the load for both compressors 104 is adjusted together to meet the demand on the chiller system 100, as illustrated after time D.

[0037] The sequence of Fig. 5 provides a synchronized start-up when a running start-up of a second compressor cannot be carried out.

[0038] Various alternatives to the certain features and elements of the present invention are described with reference to specific embodiments of the present invention. With the exception of features, elements, and manners of operation that are mutually exclusive of or are inconsistent with each embodiment described above, it should be noted that the alternative features, elements, and manners of operation described with reference to one particular embodiment are applicable to the other embodiments.

[0039] For example, while reference is made herein to ball valves 116, 128, check valves 124, and balancing valve 164, in other embodiments other valves, including, but not limited to, any suitable one or multiple-way valves, such as a check valve, ball valve, umbrella valve, duck-bill valve, and the like, can also or alternatively be used to control fluid flow through the various elements of the chiller system 100 or a portion of the chiller system 100.

Claims

CLAIMSWhat is claimed is:

1. A chiller system operable to cool a flow of chiller fluid, the system comprising: a first compressor operable to compress a fluid and discharge the compressed fluid to an outlet manifold; a condenser in fluid communication with the outlet manifold and operable to cool the compressed fluid; an expansion device including an outlet, the expansion device in fluid communication with the condenser and operable to expand the cooled compressed fluid; an evaporator including an inlet, an evaporator outlet, a first flow path in fluid communication with the expansion device to receive the expanded cooled compressed fluid, and a second flow path through which the chiller fluid flows, the first flow path and the second flow path arranged in a heat exchange relationship; and a load balancing valve positioned to selectively provide direct fluid communication between the outlet manifold and a point between the outlet of the expansion device and the inlet of the evaporator.

2. The chiller system of claim 1, further comprising a second compressor selectively operable to compress a fluid and discharge the compressed fluid to the outlet manifold.

3. The chiller system of claim 2, further comprising a sensor positioned adjacent the evaporator to measure a temperature, operation of the second compressor being initiated at least partially in response to the measured temperature.

4. The chiller system of claim 2, further comprising a sensor in fluid communication with the outlet manifold and the evaporator outlet to measure a compression ratio.

5. The chiller system of claim 4, wherein the load balancing valve moves between a closed position and an open position in response to the measured compression ratio exceeding a predetermined value.

6. The chiller system of claim 1 , wherein the first compressor is one of a plurality of compressors each operable to compress a fluid and discharge the compressed fluid to the outlet manifold.

7. The chiller system of claim 1, wherein the condenser includes a plurality of heat exchangers arranged in parallel such that each receives a portion of the compressed fluid from the outlet manifold.

8. The chiller system of claim 1, wherein the expansion device includes a plurality of electronic expansion valves.

9. A chiller system operable to cool a flow of chiller fluid, the system comprising: a first compressor operable to compress a fluid and discharge the compressed fluid to an outlet manifold; a second compressor selectively operable to compress a fluid and discharge the compressed fluid to the outlet manifold; an expansion device including an outlet, the expansion device in fluid communication with the condenser and operable to expand the compressed fluid; an evaporator including an inlet, an evaporator outlet, a first flow path in fluid communication with the expansion device to receive the expanded compressed fluid, and a second flow path through which the chiller fluid flows, the first flow path and the second flow path arranged in a heat exchange relationship; a sensor positioned to measure the pressure ratio between the outlet manifold and the evaporator outlet; and a load balancing valve positioned to provide selective fluid communication between the outlet manifold and a point between the outlet of the expansion device and the inlet of the evaporator, the load balancing valve operable in response to the measured pressure ratio to maintain the pressure ratio below a predetermined pressure ratio during start-up of the second compressor.

10. The chiller system of claim 9, further comprising a second sensor positioned adjacent the evaporator to measure a temperature, operation of the second compressor being initiated at least partially in response to the measured temperature.

11. The chiller system of claim 9, wherein the load balancing valve moves between a closed position and an open position in response to the measured compression ratio exceeding a predetermined value.

12. The chiller system of claim 9, wherein the first compressor and the second compressor are two of a plurality of compressors each operable to compress a fluid and discharge the compressed fluid to the outlet manifold.

13. The chiller system of claim 9, further comprising a condenser in fluid communication with the outlet manifold and operable to cool the compressed fluid.

14. The chiller system of claim 13, wherein the condenser includes a plurality of heat exchangers arranged in parallel such that each receives a portion of the compressed fluid from the outlet manifold.

15. The chiller system of claim 9, wherein the expansion device includes a plurality of electronic expansion valves.

16. The chiller system of claim 9, wherein the first compressor includes a centrifugal compressor and the second compressor includes a centrifugal compressor.

17. A method of starting a compressor in a chiller system including a first compressor and a second compressor, the method comprising: operating the first compressor to draw a fluid from an inlet manifold and to provide a compressed fluid to an outlet manifold; directing the compressed fluid to an evaporator inlet; passing the compressed fluid through an evaporator to cool a second fluid in the evaporator; discharging the compressed fluid from an evaporator outlet to the inlet manifold; measuring a pressure ratio between the outlet manifold and the inlet manifold; opening a valve in response to the measured pressure ratio being above a predetermined value, the valve positioned to control fluid flow between the outlet manifold and the evaporator inlet; starting the second compressor in response to the pressure ratio falling below the predetermined value; and closing the valve in response to successful start of the second compressor.

18. The method of claim 17, further comprising measuring a temperature near the evaporator, and determining that the second compressor should be started at least partially in response to the measured temperature.

19. The method of claim 17, further comprising passing the compressed fluid through a condenser to cool the compressed fluid.

20. The method of claim 17, further comprising passing the compressed fluid through an expansion device to reduce the pressure of the compressed fluid before directing the compressed fluid to the evaporator.