WO2006049883A2

WO2006049883A2 - Refrigerant cycle with tandem compressors for multi-level cooling

Info

Publication number: WO2006049883A2
Application number: PCT/US2005/037692
Authority: WO
Inventors: Alexander Lifson; Michael F. Taras
Original assignee: Carrier Corporation
Priority date: 2004-10-28
Filing date: 2005-10-21
Publication date: 2006-05-11
Also published as: WO2006049883A3; EP1805462A4; JP2008518194A; EP1805462A2; US20060090505A1

Abstract

A tandem compressor cycle is utilized that delivers compressed refrigerant to a common discharge manifold, and then to a common condenser. From the common condenser, the refrigerant passes to a plurality of evaporators, with each of the evaporators being associated with a separate environment to be conditioned. Each of the evaporators is associated with one of the plurality of compressors. By utilizing the common condenser, yet a plurality of evaporators, the ability to independently condition a number of environments is achieved without the requirement of having a dedicated circuit with multiple additional components. Thus, the overall system cost can be greatly reduced. In embodiments, one or more of the plurality of compressors can be provided by a compressor bank having its own plurality of compressors.

Description

REFRIGERANT CYCLE WITH TANDEM COMPRESSORS FOR MULTI-LEVEL COOLING

BACKGROUND OF THE INVENTION

[0001] This application relates to a refrigerant cycle utilizing tandem compressors sharing a common condenser, but having separate evaporators.

[0002] Refrigerant cycles are utilized in applications to change the temperature and humidity or otherwise condition the environment. In a standard refrigerant system, a compressor delivers a compressed refrigerant to an outdoor heat exchanger, known as a condenser. From the condenser, the refrigerant passes through an expansion device, and then to an indoor heat exchanger, known as an evaporator. In the evaporator, moisture may be removed from the air, and the temperature of air blown over the evaporator coil is lowered. From the evaporator, the refrigerant returns to the compressor. Of course, basic refrigerant cycles are utilized in combination with many configuration variations and optional features. However, the above provides a brief understanding of the fundamental concept.

[0003] In more advanced refrigerant cycles, a capacity of the air conditioning system can be controlled by the implementation of so-called tandem compressors. The tandem compressors are normally connected together via common suction and common discharge manifolds. From a single common evaporator, the refrigerant is returned through a suction manifold, and then distributed to each of the tandem compressors. From the individual compressors the refrigerant is delivered into a common discharge manifold and then into a common single condenser. The tandem compressors are also separately controlled and can be started and shut off independently of each other such that one or both compressors may be operated at a time. By controlling which compressor is running, control over the capacity of the combined system is achieved. Often, the two compressors are selected to have different sizes, such that even better capacity control is provided. Also, tandem compressors may have shutoff valves to isolate some of the compressors from the active refrigerant circuit, when they are shutdown. Moreover, to improve compressor lubrication, pressure equalization and oil equalization lines are frequently employed.

[0004] One advantage of the tandem compressor is that better capacity control is provided, without the requirement of having each of the compressors operating on a dedicated circuit. This reduces the overall system cost.

[0005] However, certain applications require cooling at various temperature levels. For example, low temperature (refrigeration) cooling can be provided to a refrigeration case by one of the evaporators connected to one compressor and intermediate temperature (perishable) cooling can be supplied by another evaporator connected to another compressor. In another example, a computer room and a conventional room would also require cooling loads provided at different temperature levels, which can be supplied by the proposed multi-temp system as desired. However, the cooling at different levels will not work with application of a conventional tandem compressor configuration, because a separate evaporator for each cooling level would be required. Thus, non-tandem independent compressors must be used in a dedicated circuit for each cooling level. Furthermore, each circuit must be equipped with a dedicated compressor, dedicated evaporator, dedicated condenser, and dedicated condenser fans. This arrangement having a dedicated circuitry for each temperature level would be very expensive.

[0006] This invention offers a solution to this problem where tandem compressors can be used for operating a refrigerant system at multiple distinct temperature levels. SUMMARY OF THE INVENTION

[0007] In this invention, as opposed to the conventional tandem system, there is no suction manifold connecting the tandem compressors together. Each of the tandem compressors is connected to its own evaporator, while both compressors are still connected to a common discharge manifold and a single condenser. Consequently, for such tandem compressor system configurations, additional temperature levels of cooling, associated with each evaporator, become available. An amount of refrigerant flo^~wing through each evaporator can be regulated by flow control devices placed at the compressor suction ports as well as by controlling related expansion devices or utilizing other control means such as evaporator airflow.

[0008] In a disclosed embodiment of this invention, precise control of various sub-sections of the environment can be achieved by utilizing distinct evaporators for each separate area. Each of the evaporators communicates with a separate compressor, while the compressors send compressed refrigerant through a common discharge manifold to a common condenser. In this manner, a separate environmental control in each of the cooling zones is achieved, and there is no necessity of providing a complete set of the components of two individual refrigerant circuits (such as an additional condenser and additional condenser fans).

[0009] It should be understood that if more than two tandem compressors are connected together, then the system can operate at each additional temperature level associated with the added compressor. For example, with three tandem compressors, operation at three temperature levels can be achieved by connecting each of the three compressors to a dedicated evaporator. In another arrangement two out of the three compressors can operate with common suction and discharge manifold and be connected to the same evaporator, while the third compressor can be connected to a separate evaporator. Of course, the tandem application can be extended in an analogous manner to more than three compressors.

[0010] These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 shows the prior art. [0012] Figure 2 is a first schematic. [0013] Figure 3 is a second schematic.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0014] Referring to Figurel, a conventional prior art multi-level (bi-level in this case) system 10 is shown to include two separate circuits 11 to serve subsections of the environment at different temperature levels. Each basic circuit 11 includes a dedicated evaporator 17, condenser 15, compressor 13, expansion device 14, condenser fan 16, evaporator fan 18 and associated piping. As known, each circuit can be controlled to maintain a desired evaporator temperature by various means and thus provide multi-level cooling to the environment. As mentioned above, such conventional approach is cumbersome and requires a significantly higher cost for system manufacturing and operation. [0015] A refrigerant cycle 20 is illustrated in Figure 2 having a pair of compressors 22 and 23 that are operating generally as tandem compressors. Optional valves 26 are positioned downstream on a discharge line associated with each of the compressors 22 and 23. These valves can be controlled to prevent backflow of refrigerant to either of the compressors 22 or 23 should only one of the compressors b>e operational. That is, if for instance compressor 22 is operational with compressor 23 stopped, then the valve 26 associated with compressor 23 will be closed to prevent flow of refrigerant from the compressor 22 back to the compressor 23. The two compressors communicate with a discharge manifold 29 leading to a common condenser 28.

[0016] From the condenser 28, the refrigerant continues downstream and is split into two flows, each heading through an expansion device 30. From the expansion device 30, one of the flows passes through a first evaporator 32 for conditioning a sub-environment B. The refrigerant passing through the evaporator 32 passes through an optional suction modulation valve 34, and is returned to the compressor 22. The second refrigerant flow passes through an evaporator 36 that is conditioning a sub-errvironment A. This refrigerant also passes through an optional suction modulation valve 34 and is returned to the compressor 23.

[0017] A control 40 for the refrigerant cycle 20 is operably connected to control the compressors 22 and 23, the expansion valves 30, suction modulation valves 34 and valves 26. By properly controlling each of these elements in combination, the conditions at each evaporator 32 and 36 can be controlled as necessary for the sub-environments A and B. The exact controls necessary are as known in the art, and will not be explained here. However, the use of the tandem compressors 22 and 23 utilizing a common condenser 28 reduces the number of components necessary for providing the independent control for the sub- environments A and B, and thus is an improvement over the prior art.

[0018] Figure 3 shows a more complicated refrigerant cycle 50 for conditioning three sub-environments A, B and C. As shown, a single condenser 52 communicates with a discharge manifold 51. A first compressor 54 also communicates with the discharge manifold 51. A second compressor bank 56, communicating with the same discharge manifold 51, includes two tandem compressors which each communicating with a suction manifold 65.

[0019] A third compressor bank 58, once again, communicating with the discharge manifold 51, includes three compressors all operating in tandem and communicating with a suction manifold 67. The control of the compressor banks 56 and 58 may be as known in the art of tandem compressors. As mentioned above, by utilizing the compressor banks 56 and 58, a control over the temperature in each of the sub-environments B and C is provided.

[0020] From the condenser 52, the refrigerant passes through separate expansion devices 60, and to separate evaporators 62, 64 and 66. As is shown, evaporator 62 conditions the air heading into a sub-environment A, evaporator 64 conditions the air heading into a sub- environment B, and evaporator 66 conditions the air heading into a sub-environment C. Optional suction modulation valves 70 are positioned on each of the suction lines returning to the compressors 54, 56 and 58. Again, a control 72 is provided that controls each of the elements to achieve the conditions within each of the sub-environments A, B, and C. The individual control steps taken for each of the sub-environments would be known. It is the provision of the combined multi-level system utilizing a common condenser and tandem compressors that is inventive here.

[0021] Of course, other multiples of compressors and compressor banks at various multiple temperature levels can be utilized within the scope of this invention.

[0022] Although preferred embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Claims

CLAIMSWhat is claimed is:

1. A refrigerant cycle comprising: a plurality of compressors, where at least two of said compressors deliver a refrigerant to a discharge manifold leading to a common condenser, refrigerant passing through said common condenser, and then expanding into a plurality of evaporators, said plurality of evaporators associated with said plurality of said compressors, where said at least two compressors connected to separate evaporators.

2. The refrigerant cycle as set forth in claim 1, wherein at least one of said plurality of compressors is a compressor bank having its own plurality of compressors receiving refrigerant from a common evaporator.

3. The refrigerant cycle as set forth in claim 1, wherein a suction modulation valve is positioned between at least one of said evaporators and at least one of associated compressors.

4. The refrigerant cycle as set forth in claim 1, wherein a shut-off valve is positioned on a discharge line downstream of at least one of said compressors, but upstream of said discharge manifold.

5. The refrigerant cycle as set forth in claim 1, wherein a separate expansion device is positioned to receive refrigerant heading to at least one of said evaporators.

6. The refrigerant cycle as set forth in claim 1, wherein said plurality of compressors includes at least three compressors.

7. The refrigerant cycle as set forth in claim 6, wherein at least one of said plurality of compressors is a compressor bank having its own plurality of compressors receiving refrigerant from a common suction manifold leading from a common evaporator.

8. A method of operating a refrigerant cycle comprising the steps of:

1) providing a refrigerant cycle including a plurality of compressors where at least two of said compressors delivering refrigerant to a common condenser through a discharge manifold, refrigerant passing from said common condenser to a plurality of evaporators, with each of said evaporator delivering refrigerant to one of said plurality of compressors; and

2) operating said refrigerant cycle by independently controlling refrigerant flow to each of said evaporators to achieve a desired condition for an environment conditioned by each of said evaporators.

9. The method as set forth in claim 8, wherein at least one of said plurality of compressors includes a compressor bank including its own plurality of compressors, and said compressor bank being controlled to achieve desired conditions within an associated environment.

10. The method as set forth in claim 8, wherein suction modulation valves are provided to control the flow of refrigerant from some of said plurality of evaporators to some of said plurality of compressors.

11. The method as set forth in claim 8, wherein discharge shutoff valves are provided to prevent the backflow of refrigerant to some of said plurality of compressors.