Refrigeration system with reverse flow defrost

Abstract

A refrigeration system including a compressor operable to discharge compressed refrigerant. A first heat exchanger is operable to cool the compressed refrigerant. The first heat exchanger includes a first inlet, an outlet, and a second inlet disposed between the first inlet and the outlet. A second heat exchanger is disposed adjacent a cool space. A valve is movable between a first position to direct the compressed refrigerant to the first inlet and then to the second heat exchanger to cool the second heat exchanger and a second position to direct the compressed refrigerant to the second heat exchanger and then to the second inlet to heat the second heat exchanger.

Description

RELATED APPLICATION DATA

This application claims benefit under 35 U.S.C. Section 119(e) of U.S. Provisional Application No. 60/529,301 filed Dec. 12, 2003.

BACKGROUND

The present invention relates generally to a refrigeration system. More particularly, the present invention relates to a refrigeration system that includes a defrost cycle.

Refrigeration systems cool a space by supplying cold refrigerant to an evaporator. Water vapor in the space being cooled sometimes condenses onto the outer surface of the evaporator and forms layers of ice. These layers of ice reduce the efficiency of the evaporator and make it difficult to maintain the desired temperature within the space.

SUMMARY

In one embodiment, the invention provides a refrigeration system including a compressor operable to discharge compressed refrigerant. A first heat exchanger is operable to cool the compressed refrigerant. The first heat exchanger includes a first inlet, an outlet, and a second inlet disposed between the first inlet and the outlet. A second heat exchanger is disposed adjacent a cool space. A valve is movable between a first position to direct the compressed refrigerant to the first inlet and then to the second heat exchanger to cool the second heat exchanger and a second position to direct the compressed refrigerant to the second heat exchanger and then to the second inlet to heat the second heat exchanger.

In another embodiment, the invention provides a refrigeration system including a plurality of compressors. Each compressor is operable to discharge compressed refrigerant. A first heat exchanger is operable to cool the compressed refrigerant. The first heat exchanger includes a first inlet, an outlet, and a second inlet between the first inlet and the outlet. The system also includes a plurality of evaporators and a receiver in fluid communication with the first heat exchanger and in selective fluid communication with each of the plurality of evaporators. The system further includes a hot gas header and a valve that is movable between a first position to direct the compressed refrigerant to the first inlet and a second position to direct the compressed refrigerant to the hot gas header. A plurality of defrost valves are movable between a first position to place the receiver in fluid communication with one of the plurality of evaporators to cool the evaporator and a second position to place the hot gas header in fluid communication with the one of the plurality of evaporators to heat the evaporator. The evaporator discharges refrigerant to the second inlet when the defrost valve is in the second position.

In yet another embodiment, the invention provides a method of operating a refrigeration system including operating a compressor to deliver compressed refrigerant. The method also includes directing the compressed refrigerant to a first inlet of a first heat exchanger and condensing the compressed refrigerant within the first heat exchanger. The method further includes expanding a portion of the compressed refrigerant and passing the portion of the expanded compressed refrigerant through a second heat exchanger to cool the heat exchanger. The method also includes manipulating a valve to redirect the compressed refrigerant to the second heat exchanger to heat the second heat exchanger and directing the compressed refrigerant to a second inlet of the first heat exchanger. The second inlet is disposed downstream of the first inlet.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the accompanying figures in which:

FIG. 1 is a circuit diagram for a refrigeration system illustrating the flow paths in a refrigeration mode; and

FIG. 2 is a circuit diagram for a refrigeration system illustrating the flow paths in a defrost mode.

DETAILED DESCRIPTION

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 figures. 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.

The basic configuration of a refrigeration system 10 generally includes the conventional components of a vapor-compression or refrigeration cycle (i.e., compressor(s) 15, condenser(s) 20, evaporator(s) 25, a receiver(s) 30, and expansion valve(s) 35). As one of ordinary skill will realize, refrigeration systems may incorporate multiple compressors 15, evaporators 25, and/or condensers 20 in parallel or in series to accomplish the goals of the particular system. As such, the invention should not be limited to systems that include components arranged or numbered as illustrated herein. It should be understood that the invention hereinafter described is not dependent upon the number or size of such components.

Before describing the figures in detail, it should also be noted that the figures have been simplified for the purpose of illustration. Components such as check valves, drain and fill valves, pressure taps, flow meters, sensors, parallel piping, as well as other types of components have been omitted for clarity.

FIGS. 1 and 2 show the basic layout of one arrangement of a refrigeration system 10 incorporating a reverse flow defrost. FIG. 1 shows the flow through a portion of the system when operating in a refrigeration mode and FIG. 2 illustrates the same portion of the system operating in a defrost mode.

With reference to FIG. 1, the flow in refrigeration mode begins when one or more compressors 15 draw superheated refrigerant vapor (e.g., R12, ammonia, CFCs, HCFCs, HFCs, etc.) from a suction header 40. The term “superheated” as used herein includes any refrigerant that contains vapor at or above the saturation temperature for the refrigerant at the particular pressure. The compressor 15 compresses the vapor to produce a flow of superheated, high-pressure refrigerant. The vapor passes through a defrost differential valve 45 that is maintained in an open position when operating in refrigeration mode. From the defrost differential valve 45, the flow passes through the condenser 20, entering through a condenser inlet 50 and exiting through a condenser outlet 55. In the condenser 20, the flow cools and condenses to produce a high-pressure flow of cool liquid refrigerant that is directed into the receiver 30. From the receiver 30, liquid refrigerant is directed to a liquid header 60 that is positioned to supply refrigerant to one, or more than one, of a plurality of cooling paths 65. It should be noted that the term “header” should be read broadly to include structures as simple as a pipe or manifold that are able to deliver or receive a fluid to/from a plurality of flow paths.

For the sake of simplicity, only one complete cooling path 65 is illustrated in FIGS. 1 and 2. The remaining cooling paths 65 are similar to the illustrated path 65. Each cooling path 65 includes an expansion valve 35 and the evaporator 25. The expansion valve 35 expands the flow of vapor to reduce the temperature and pressure of the flow prior to its entry into the evaporator 25. After the flow passes through the evaporator 25, it is returned to the suction header 40 and the cycle repeats.

Each evaporator 25 is positioned to cool a space. Alternatively, multiple evaporators may be used to cool a single space if necessary. The cold refrigerant passes through the evaporator 25 and is heated by the environment in which the evaporator 25 is positioned. Typically, air or another fluid moves across the evaporator 25 and is cooled by the refrigerant as the refrigerant is heated. In some constructions, fans (not shown) are used to move the air across the evaporator 25. The refrigerant is usually heated such that it leaves the evaporator 25 as superheated refrigerant, while the air is cooled and returned to the cool space. Depending on the environment in which the evaporator 25 is positioned, the cold temperature of the evaporator 25 may cause some of the water vapor in the air to condense and freeze onto the evaporator 25. The freezing water forms layers of ice that reduce the efficiency of the heat exchange between the environment being cooled and the refrigerant within the evaporator 25. To improve the evaporator efficiency, the layers of ice generally need to be removed.

To remove the ice, the refrigeration system 10 periodically transitions into a defrost mode. The flows within the refrigeration system 10 when in the defrost mode are illustrated in FIG. 2. A portion of the hot compressed gas exiting the compressors is directed to a hot gas header 70. The defrost differential valve 45 at least partially controls the quantity of hot compressed gas that is directed to the hot gas header 70. For example, when additional hot gas is required in the hot gas header 70, the defrost differential valve is closed slightly or closed completely to reduce the size of the flow path to the condenser 20. The reduced flow path effectively redirects an increased quantity of hot gas to the hot gas header 70. As one of ordinary skill will realize, other constructions could position the defrost differential valve 45 differently. For example, one construction places the defrost differential valve 45 in the flow path to the hot gas header 70. In this position, opening the valve increases the flow to the hot gas header 70.

The hot gas header 70 is selectively connected with each of the cooling paths 65. A defrost valve 72 is positioned within each cooling path 65 to inhibit the flow of refrigerant to the hot gas header 70 when in the cooling mode. In the illustrated construction, a solenoid-operated valve is used as the defrost valve 72 in each cooling path 65. However, other constructions may use other types of valves or other actuation means (e.g., manual) for the defrost valves 72. To transition one of the cooling paths 65 from the refrigeration mode to the defrost mode, the system may close the defrost differential valve 45 to direct additional hot compressed refrigerant to the hot gas header 70 if necessary. The defrost valve 72 corresponding to the cooling path 65 to be heated is opened to direct a flow of hot compressed refrigerant to the evaporator. In addition, an isolation valve 74 is closed to inhibit flow of hot gas from the hot gas header 70 directly to the suction header 40.

As with the refrigeration mode, the defrost cycle begins when the compressor 15 draws superheated refrigerant vapor from the suction header 40. However, with the defrost differential valve 45 reducing or completely preventing flow to the condenser 20, part or all of the flow is redirected to the hot gas header 70. The hot gas header 70 directs the flow of superheated, high-pressure refrigerant vapor through the evaporator 25 in the opposite direction it would flow if in the refrigeration mode. The superheated high-pressure vapor heats the evaporator 25 and melts the accumulated ice. After passing through the evaporator 25, the refrigerant collects in a hot gas return header 75.

The hot gas return header 75 directs the refrigerant to the condenser 20. The flow enters the condenser 20 at a defrost inlet 80 located downstream of the condenser inlet 50. After passing through the condenser 20, the now cooled liquid flows into the receiver tank 30. In an alternative construction, a separate heat exchanger (not shown), having the ability to remove heat (heat removed via air/water or other means) and condense the refrigerant from a vapor to a liquid, receives the flow of refrigerant vapor from the hot gas return header 75 and directs the condensed refrigerant to a reentry point at or after the condenser outlet 55.

As one of ordinary skill will realize, operation in defrost mode directs vapor from the suction header 40 to the hot gas header 70, through the evaporator 25 being defrosted, through the condenser 20, and finally to the receiver tank 30. However, if none of the evaporators 25 in the system are operating in refrigeration mode, none of the refrigerant will be drawn from the receiver tank 30. As such, no refrigerant will flow to the suction header 40, and eventually no refrigerant will be available to the compressors 15. As such, at least one cooling path 65 is generally maintained in the refrigeration mode during a defrost cycle to assure that refrigerant is always available to the compressors 15. With at least one evaporator 25 operating in refrigeration mode, refrigerant is drawn from the receiver tank 30 and returned to the suction header 40, thus completing the defrost cycle.

For the sake of clarity, only one evaporator 25 is illustrated herein. However, it should be understood that multiple evaporators 25 are typically employed in systems of this type. In fact, to operate in the defrost mode for a long duration, one evaporator 25 should be operated in the refrigeration mode as just described to prevent the depletion of the refrigerant. Typically, several evaporators 25 within the system operate in refrigeration mode with the remaining evaporators 25 operating in defrost mode. Of course, all of the evaporators 25 can be operated in refrigeration mode at the same time if desired.

Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of the invention. Thus, the invention provides, among other things, a new and useful system and method of cooling multiple spaces and defrosting the individual evaporators. The constructions of the system and the methods of operation of the system described above and illustrated in the figures are presented by way of example only and are not intended as a limitation upon the concepts and principles of the invention. Various features and advantages of the invention are set forth in the following claims.

Claims

1. A refrigeration system comprising:

a compressor operable to discharge compressed refrigerant;

a first heat exchanger operable to cool the compressed refrigerant, the first heat exchanger including a first inlet, an outlet, and a second inlet disposed between the first inlet and the outlet;

a second heat exchanger disposed adjacent a cool space; and

a valve movable between a first position to direct the compressed refrigerant to the first inlet and then to the second heat exchanger to cool the second heat exchanger and a second position to direct the compressed refrigerant to the second heat exchanger and then to the second inlet to heat the second heat exchanger.

2. The refrigeration system as set forth in claim 1 wherein the compressor comprises an oil-flooded screw compressor.

3. The refrigeration system as set forth in claim 1 wherein the compressor comprises a plurality of compressors, each compressor operable to discharge compressed refrigerant to a common header.

4. The refrigeration system as set forth in claim 1 wherein the second heat exchanger comprises a plurality of evaporators.

5. The refrigeration system as set forth in claim 4 wherein each of the plurality of evaporators is in selective fluid communication with a liquid header and a suction header.

6. The refrigeration system as set forth in claim 4 further comprising a plurality of defrost valves, each defrost valve positioned to provide selective fluid communication between a hot gas header and one of the plurality of evaporators.

7. The refrigeration system as set forth in claim 6 wherein each of the plurality of defrost valves comprises a solenoid-actuated valve.

8. A refrigeration system comprising:

a plurality of compressors, each compressor operable to discharge compressed refrigerant;

a first heat exchanger operable to cool the compressed refrigerant, the first heat exchanger comprising a first inlet, an outlet, and a second inlet between the first inlet and the outlet;

a plurality of evaporators;

a receiver in fluid communication with the first heat exchanger and in selective fluid communication with each of the plurality of evaporators;

a hot gas header;

a valve movable between a first position to direct the compressed refrigerant to the first inlet and a second position to direct the compressed refrigerant to the hot gas header; and

a plurality of defrost valves, each defrost valve movable between a first position to place the receiver in fluid communication with one of the plurality of evaporators to cool the evaporator and a second position to place the hot gas header in fluid communication with the one of the plurality of evaporators to heat the evaporator, the evaporator discharging refrigerant to the second inlet when the defrost valve is in the second position.

9. The refrigeration system as set forth in claim 8 wherein each of the compressors comprises an oil-flooded screw compressor.

10. The refrigeration system as set forth in claim 8 wherein each of the plurality of evaporators is in selective fluid communication with a liquid header and a suction header.

11. The refrigeration system as set forth in claim 8 wherein at least one of the plurality of defrost valves is positioned in the first position when another of the plurality of defrost valves is in the second position.

12. The refrigeration system as set forth in claim 8 wherein each of the plurality of defrost valves comprises a solenoid-actuated valve.

13. A method of operating a refrigeration system comprising:

operating a compressor to deliver compressed refrigerant;

directing the compressed refrigerant to a first inlet of a first heat exchanger;

condensing the compressed refrigerant within the first heat exchanger;

expanding a portion of the compressed refrigerant;

passing the portion of the expanded compressed refrigerant through a second heat exchanger to cool the heat exchanger;

manipulating a valve to redirect the compressed refrigerant to the second heat exchanger to heat the second heat exchanger; and

directing the compressed refrigerant to a second inlet of the first heat exchanger, the second inlet disposed downstream of the first inlet.

14. The method as set forth in claim 13 wherein operating the compressor comprises operating at least one of a plurality of compressors to deliver compressed refrigerant to a common header.

15. The method as set forth in claim 13 wherein the second heat exchanger comprises a plurality of evaporators.

16. The method as set forth in claim 15 wherein at least one of the plurality of evaporators is cooled and at least one of the plurality of evaporators is heated simultaneously.

17. The method as set forth in claim 15 further comprising separating the portion of compressed refrigerant into a plurality of flow streams and expanding each stream.

18. The method as set forth in claim 15 wherein the manipulating step redirects at least a portion of the compressed refrigerant to a hot gas header.

19. The method as set forth in claim 18 further comprising actuating at least one of a plurality of defrost valves to direct compressed refrigerant from the hot gas header to at least one of the evaporators.

20. The method as set forth in claim 13 further comprising directing the compressed refrigerant to the first heat exchanger after passing the compressed refrigerant through the second heat exchanger.