HK1135168A - Tandem compressors with pulse width modulation suction valve - Google Patents

Description

Tandem compressor with pulse width modulation suction valve

Technical Field

The invention relates to a refrigeration system comprising tandem compressors and a pulse width modulation control on a suction line leading to at least one of the tandem compressors.

Background

Refrigeration HVAC & R systems typically include a compressor that delivers compressed refrigerant from a compressor discharge to a condenser, from which the refrigerant is then delivered to an expansion device, an evaporator, and finally back to the compressor suction through a closed loop. The heat load requirements of a refrigeration system can vary and are generally dependent upon the operating environment inside and outside the room, the heat load generated within the conditioned space, and the requirements of the fresh air cycle. Sometimes, a higher system cooling capacity is required, and therefore a greater refrigerant flow is required to circulate throughout the refrigeration system. Sometimes, a lower cooling capacity and a smaller refrigerant flow may be sufficient to maintain the conditioned space within a desirable range. To provide an efficient means of controlling refrigerant flow, some refrigeration systems utilize tandem compressors to provide unloading capability by disconnecting one of the tandem compressors to match the system capacity to the thermal load in the conditioned space. In such systems, two or more compressors may simultaneously deliver compressed refrigerant to a downstream heat exchanger, such as a condenser. Typically, a single discharge line communicates with the discharge of the tandem compressors. These discharge lines then converge into a single discharge manifold connected to the condenser. Likewise, a single suction line communicates with the suction inlet of the tandem compressor. These suction lines emerge from a single suction manifold connected to a line extending from the evaporator outlet. On the other hand, tandem compressor systems are known in which a separate condenser is associated with each compressor, while the compressors are still connected to the same evaporator. Similarly, tandem compressor systems may be connected to separate evaporators and still communicate with the same condenser. The latter two configurations are typically used when the compressor or evaporator is associated with separate indoor and outdoor environments, which may have different operating characteristics.

The control of a typical tandem compressor system operates one or more compressors depending on the system heat load. Thus, the compressor can be controlled to provide discrete stages in system capacity. Also, as is known, tandem compressor arrangements may include pressure and oil balancing lines to prevent oil from draining from the compressor and to improve reliability.

One method of better controlling the capacity of a refrigeration system is to control the compressor of the refrigeration system using a pulse width modulation control. With such control, the suction pulse width modulation valve cycles between open and closed positions at a predetermined rate to prevent and then allow refrigerant to flow to the compressor. This virtually eliminates throttling or any other losses as the valve cycles between the open and closed positions. In this way, the amount of refrigerant compressed by the compressor can be accurately adjusted to the required capacity while maintaining efficient operation of the system. Although pulse width modulation controls are known in refrigerant systems, they are not incorporated into tandem compressor systems.

Disclosure of Invention

In a disclosed embodiment of the invention, two or more tandem compressors are operated in a refrigeration system. The suction line leading to at least one of the two compressors is equipped with a suction valve with a pulse width modulation control. The capacity provided by the compressor can then be accurately adjusted to the heat load requirements in the environment to be conditioned. In one embodiment, only one compressor is equipped with such a suction valve controlled by pulse width modulation. In another embodiment, a suction pulse width modulation valve is provided on the manifold to each compressor.

In various embodiments, the compressor delivers refrigerant to a separate condenser, but is still associated with a single evaporator; or receive refrigerant from a separate evaporator, but still deliver compressed refrigerant to a single condenser. In other embodiments, tandem compressor refrigeration systems may be equipped with economizer cycle devices and/or bypass features to achieve more flexible control over supply capacity.

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.

Drawings

FIG. 1 shows a first illustrative refrigeration system.

Fig. 2 shows a second schematic.

Fig. 3 shows a third schematic.

Fig. 4 shows a fourth schematic.

Fig. 5 shows a capacity map of the schematic of fig. 1.

Fig. 6 shows a fifth schematic.

Fig. 7 shows a sixth schematic.

Detailed Description

Fig. 1 shows a refrigerant system 20 having two compressors 22 and 24, the two compressors 22 and 24 operating in series to compress and deliver refrigerant to a common discharge manifold 28. A single condenser 30 receives refrigerant from the common discharge manifold 28 and delivers the refrigerant to an expansion device 32. An evaporator 34 is positioned downstream of the expansion device 32. Refrigerant from the evaporator 34 enters the common suction manifold 26 and returns to the compressors 22 and 24. as is known in the art, a control 38 of the system operates to drive one or both of the compressors 22 and 24 to provide the desired capacity to the refrigeration system 20. The compressors 22 and 24 may be the same size or may be different sizes. The control and operation of tandem compressor refrigerant systems is well known in the art and further description is not necessary. The novelty lies in the provision of the suction valve 36 with a pulse width modulation control controlled by a control device 38 or a dedicated controller. Thus, as is known, the control 38 cycles the valve 36 between open (normally fully open position) and closed (normally fully closed or nearly fully closed position) positions at a predetermined rate to control the flow of refrigerant to the compressors 22 and 24. In this way, the amount of refrigerant delivered to the compressors 22 and 24 can be precisely adjusted to obtain a precise capacity value, regardless of how many compressors are operating at a particular time. Since the pulse width modulation valve 36 cycles between the open and closed positions, there is minimal throttling or other losses associated with the valve 36. The cycle rate and time interval at which the valve 36 is in the open position is determined by the capacity delivered to the conditioned environment, reliability requirements, allowable comfort range parameter variations, and refrigerant system thermal inertia. Although two tandem compressors are shown, refrigeration systems having three, four, or even more tandem compressors are also known. The present invention thus provides a useful and effective means to obtain precisely adjusted refrigerant system capacity from a tandem compressor configuration while minimizing temperature and humidity variations in the conditioned space, improving user comfort and reducing power consumption.

Fig. 2 shows another embodiment 220 in which the tandem compressors 122 and 124 again deliver refrigerant to the common discharge manifold 28 and downstream condenser 30. The system configuration differs in that the refrigerant is tapped into two separate expansion devices 132, and two separate evaporators 134A and 134B. Such an arrangement is typically provided when the evaporators are used in different conditioned/refrigerated areas and have different operating characteristics. Thus, there is no common suction manifold delivering refrigerant to each of the compressors 122 and 124. In this embodiment, there is only one compressor, compressor 122, having a suction pulse width modulation valve 136, the suction pulse width modulation valve 136 being mounted on the suction line leading to the compressor and controlled by a pulse width modulation control 138. As described above, the control 138 may be a stand-alone control or integrated into a system control of the refrigeration system 220. In addition, when precise adjustments to the delivery capacity of the refrigerant system 220 (and particularly the evaporator 134A) are required, the compressor 122 will operate because it is capable of providing precise refrigerant flow control through the associated pulse width modulated suction valve 136. Also, while only two tandem compressors are shown in FIG. 2, only one of which has an associated pulse width modulation valve, more tandem compressors and many of which have an associated pulse width modulation valve are within the scope of the present invention.

Fig. 3 also shows another embodiment 221 in which each compressor 22 and 24 delivers refrigerant to a separate condenser 230 and 232, but still receives refrigerant from the same evaporator 34. Such an arrangement is typically employed when the condenser discharges heat to different environments (e.g., indoor and outdoor) and has different operating characteristics. The condensers 230 and 232 deliver refrigerant to a separate expansion device 233, and the refrigerants then combine before returning to the evaporator 34 and the common suction manifold 26. In addition, a pulse width modulation valve 36 is installed on the suction line to the tandem compressors 22 and 24 and controls the flow of refrigerant through the refrigeration system 221 regardless of how many compressors are in operation. Similar to the fig. 2 embodiment, a pulse width modulation valve 36 is associated with only one of the compressors 22 or 24 and controls the flow of refrigerant through that particular compressor and associated condenser, if desired (see further explanation below). Again, this embodiment can be extended to any number of tandem compressors.

Fig. 4 shows a refrigeration system 222. This system is somewhat similar to the system of FIG. 1; however, the pulse width modulation valve 136 is located downstream of the common suction manifold 26 and on the suction line that delivers refrigerant only to the compressor 122. With this arrangement, it is desirable to operate only one of the compressors 122 and 124 at any one time because the compressor oil sumps of the two compressors 122 and 124 will have a substantial pressure differential when the pulse width modulation control for the valve 136 is activated. Otherwise, inter-compressor cross leakage, oil evacuation and reliability problems can occur. In addition, the compressor 122 is able to precisely control the capacity of the refrigeration system 222. Any number of tandem compressors may also include an associated pulse width modulation valve with this arrangement.

The capacity of the refrigeration system as adjusted by the pulse width modulation valve in fig. 1 is shown in fig. 5. As shown in this figure, if full capacity is required, the two tandem compressors are run together and the pulse width modulation valve is fully open. When the capacity demand decreases, the pulse width modulation valve will cycle between open and closed positions. When further capacity reduction is required, the valve is in the closed position for a longer period of time than in the open position. When the capacity demand is low enough, one of the tandem compressors is turned off and the pulse width modulation valve cycle is again changed to the open position for most of the time. When the capacity demand is reduced even further, the system continues to operate with one compressor off and the pulse width modulation valve cycle period is adjusted so that the pulse width modulation valve is in the closed position for an extended period of time. The most appropriate time for the controller to shut down a compressor is determined and based primarily on system capacity requirements, while further adjustments may be made to account for system availability and reliability. While fig. 5 illustrates the adjustment of the position of the pulse width modulation valve in the schematic of fig. 1, it is also applicable in a similar manner to the other embodiments of the invention illustrated in the other figures.

Fig. 6 illustrates improved features of the system 300 that can be incorporated into any of the schematic diagrams described above. Tandem compressors 302 and 304 are similar to the embodiments described above, and compressor 302 includes an associated pulse width modulation valve 303 with a pulse width modulation control 305. However, the present arrangement provides more flexibility in capacity control. The condenser 306 receives refrigerant from the tandem compressors 302 and 304 and delivers it to the liquid line. A portion of the refrigerant is tapped from the liquid line downstream of the condenser 306 and the tapped refrigerant is passed through an economizer expansion device 310 (where the refrigerant is expanded to a lower pressure and temperature) and flows into an economizer heat exchanger 312 for heat transfer interaction with the refrigerant circulating in the main circuit. As is known, the refrigerant passing through the tap line 308 subcools the refrigerant flowing in the liquid line 314 into a main expansion device (not shown). This provides a greater thermal potential to the refrigerant entering the evaporator (also not shown) and thereby increases the cooling capacity and/or efficiency of the refrigeration system. Such economizer cycle devices are known in the art. Although the flows from the tap line 308 and the liquid line 314 are shown passing through the economizer heat exchanger 312 in the same direction, this is for simplicity of illustration only. In practice, they preferably flow in a counter-current arrangement. The refrigerant from the tap line 308 then flows through a return line 316 with a shutoff valve 318 and a vapor injection line 320. A vapor injection line 320 injects the refrigerant returning from line 316 to an intermediate compression point of the economizer compressor 302, as is known in the art. It should be noted that the shutoff valve 318 is not necessary if the economizer expansion device 310 is equipped with a shutoff capability.

Further, as shown in fig. 5, if the compressor 304 is also energy efficient, a return line 330, indicated by hatching, can also return refrigerant to the second compressor 304. It should be noted that the compressors 302 and 304 need not share the same economizer branch component (e.g., economizer heat exchanger 312) and economizer expansion device 310.

A bypass valve 322 may be opened to selectively bypass at least a portion of the partially compressed refrigerant from the compressor 302, through the vapor injection line 320 and a bypass line 324, and back to the suction line. Normally (not always), the bypass function is used in the non-economized mode of operation. Also, the compressor 304 may be equipped with a bypass function. Furthermore, the use of a bypass for compressor unloading is known in the art. However, adding a bypass and/or economizer function to a tandem compressor system comprising at least one compressor with a pulse width modulation control allows for more flexible control of the capacity provided. Since the economized and bypass functions provide two additional discrete stages of capacity control, the pulse width modulation technique provides precise control for operation of the refrigeration system during the economized stage (when the economizer circuit is engaged) and the bypass stage (when the bypass function is activated). Thereby providing highly accurate control of the conditioned space and achieving improved operating efficiency of the refrigerant system. Also, multiple tandem compressors can be equipped with economizer and bypass features (whether or not economizer branch components such as economizer heat exchangers and economizer expansion devices are shared) and associated with pulse width modulation control. Also, the energy saving and bypass functions need not be combined with each other. For example, only the economizer feature or only the bypass feature can be associated with a particular compressor. Furthermore, as is known in the art, it may be desirable to provide a small leak through the pulse width modulation valve (or a small bypass around the valve) when the valve is in a closed position to prevent the compressor from operating under vacuum.

It should be noted that although the present invention is described with only two tandem compressors, more than two tandem compressors can be connected together in a tandem configuration, as is known in the art. Moreover, each of the compressors shown in the above figures can represent a group of compressors connected together in series and having a nested arrangement. In this nested arrangement, any compressor can be equipped with a pulse width modulation valve. For example, a two-stage nested tandem compressor system, incorporating two compressor banks 422 and 424 and a suction modulation valve 436, is shown in fig. 7. It should also be noted that, in general, the pulse width modulation valve can be associated with any compressor or any type of compressor in the system, such as a scroll compressor, a rotary compressor, a reciprocating compressor, a screw compressor, and the like. Further, the refrigeration system can be part of a single circuit configuration or a multi-circuit arrangement. In a multi-circuit configuration, only a single circuit is equipped with multiple tandem compressors with suction pulse width modulation valves, or multiple circuits contain tandem compressors and associated suction pulse width modulation valves.

Although a preferred embodiment of this invention has 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 (39)

1. A refrigeration system comprising:

at least two compressors operating in parallel to compress and deliver refrigerant downstream to at least one condenser, at least one expansion device disposed downstream of the at least one condenser, and at least one evaporator disposed downstream of the at least one expansion device; and

refrigerant is returned from the at least one evaporator to the at least two compressors through at least one suction line, a suction valve is provided between the evaporator and at least one of the at least two compressors, the suction valve being equipped with a pulse width modulation control to control the amount of refrigerant delivered to the at least one of the at least two compressors.

2. The refrigeration system of claim 1, wherein at least two of the at least two compressors have at least one common manifold.

3. The refrigerant system as set forth in claim 2, wherein said at least one common manifold is a suction manifold.

4. The refrigerant system as set forth in claim 2, wherein said at least one common manifold is a discharge manifold.

5. The refrigeration system of claim 1, wherein at least two of the at least two compressors deliver refrigerant to a single condenser.

6. The refrigeration system of claim 1, wherein a single expansion device receives refrigerant from at least two of the at least two compressors.

7. The refrigeration system of claim 1, wherein a single evaporator delivers refrigerant to a suction manifold that returns refrigerant to at least two of the at least two compressors.

8. The refrigeration system of claim 7, wherein the suction valve is disposed on the suction manifold to regulate a flow of refrigerant to at least two of the at least two compressors.

9. The refrigeration system of claim 7, wherein the suction valve is positioned downstream of the suction manifold and on a line delivering refrigerant to at least one of the at least two compressors.

10. The refrigeration system of claim 1, wherein at least two of the condensers separately receive refrigerant from the at least two compressors.

11. The refrigeration system of claim 10, wherein each of the at least two compressors is equipped with a separate expansion device.

12. The refrigeration system of claim 1, wherein there are at least two evaporators separately returning refrigerant to the at least two compressors.

13. The refrigeration system of claim 12, wherein at least two expansion devices are provided and separately deliver refrigerant to the at least two evaporators.

14. The refrigeration system of claim 1, wherein at least one of the at least two compressors is equipped with a bypass function.

15. The refrigeration system of claim 14, wherein at least one of the at least two compressors is equipped with a bypass function and the at least one compressor is associated with the suction valve.

16. The refrigerant system as set forth in claim 1, wherein at least one of said at least two compressors is equipped with an economizer cycle.

17. The refrigerant system as set forth in claim 16, wherein at least one of said at least two compressors is equipped with an economizer cycle and said at least one compressor is associated with said suction valve.

18. The refrigerant system as set forth in claim 16, wherein more than one of said at least two compressors is provided with an economizer cycle and these economizer compressors share at least one of the economizer branch components.

19. The refrigeration system of claim 1, wherein at least one of the at least two compressors is a bank of compressors, and the suction valve is associated with at least one compressor in the bank.

20. The refrigeration system of claim 1, wherein at least one of the at least two compressors is selected from the group consisting of a scroll compressor, a rotary compressor, a screw compressor, and a reciprocating compressor.

21. A method of operating a refrigeration system comprising the steps of:

providing at least two compressors operating in parallel to compress and deliver refrigerant downstream to at least one condenser, at least one expansion device downstream of the at least one condenser;

providing at least one evaporator downstream of said at least one expansion device; and is

Returning refrigerant from the at least one evaporator to the at least two compressors through at least one suction line, a suction valve disposed between the evaporator and at least one of the at least two compressors and utilizing a pulse width modulation control on the suction valve to control the amount of refrigerant delivered to the at least one of the at least two compressors.

22. The method of claim 21, wherein at least two of said at least two compressors have at least one common manifold.

23. The method of claim 22, wherein the at least one common manifold is a suction manifold.

24. The method of claim 22, wherein at least one common manifold is an exhaust manifold.

25. The method of claim 21, wherein at least two of the at least two compressors deliver refrigerant to a single condenser.

26. The method of claim 21, wherein a single expansion device receives refrigerant from at least two of the two compressors.

27. The method of claim 21, wherein a single evaporator delivers refrigerant to a suction manifold that returns refrigerant to at least two of the at least two compressors.

28. The method of claim 27, wherein said suction valve is disposed on said suction manifold to regulate refrigerant flow to at least two of said at least two compressors.

29. The method of claim 27, wherein the suction valve is disposed downstream of the suction manifold and on a line delivering refrigerant to at least one of the at least two compressors.

30. The method of claim 21, wherein at least two of the condensers separately receive refrigerant from at least the at least two compressors.

31. The method of claim 30, wherein each of the at least two compressors is equipped with a separate expansion device.

32. The method of claim 31, wherein there are at least two evaporators separately returning refrigerant to the at least two compressors.

33. A method according to claim 32, wherein at least two expansion devices are provided to separately deliver refrigerant to said at least two evaporators.

34. The method of claim 21, wherein at least one of the at least two compressors is equipped with a bypass function.

35. The method of claim 34, wherein at least one of the at least two compressors is equipped with a bypass function and the at least one compressor is associated with the suction valve.

36. The method of claim 21, wherein at least one of the at least two compressors is equipped with an economizer cycle.

37. The method of claim 36, wherein at least one of the at least two compressors is equipped with an economizer cycle and the at least one compressor is associated with the suction valve.

38. The method as set forth in claim 36, wherein more than one of said at least two compressors is provided with an economizer cycle and these economizer compressors share at least one of the associated economizer branch components.

39. The method of claim 21, wherein at least one of the at least two compressors is a bank of compressors and the suction valve is associated with at least one compressor in the bank.