Cooling system

An apparatus includes an ejector, a first load, a second load, a third load, a first compressor, a second compressor, and an accumulator. The ejector directs a refrigerant to a flash tank that stores the refrigerant. The loads use the refrigerant from the flash tank to cool spaces. The first compressor compresses the refrigerant from the first load. During a defrost cycle, the first compressor directs the refrigerant to the third load to defrost the third load, the accumulator separates the refrigerant that defrosted the third load into a second liquid portion and a second vapor portion, the ejector directs the second liquid portion to the flash tank, and the second compressor compresses the second vapor portion.

TECHNICAL FIELD

This disclosure relates generally to a cooling system.

BACKGROUND

Cooling systems may cycle a refrigerant to cool various spaces. For example, a refrigeration system may cycle refrigerant to cool spaces near or around refrigeration loads. After the refrigerant absorbs heat, it can be cycled back to the refrigeration loads to defrost the refrigeration loads.

SUMMARY

Cooling systems cycle refrigerant to cool various spaces. For example, a refrigeration system cycles refrigerant to cool spaces near or around refrigeration loads. These loads include metal components, such as coils, that carry the refrigerant. As the refrigerant passes through these metallic components, frost and/or ice may accumulate on the exterior of these metallic components. The ice and/or frost reduce the efficiency of the load. For example, as frost and/or ice accumulates on a load, it may become more difficult for the refrigerant within the load to absorb heat that is external to the load. Typically, the ice and frost accumulate on loads in a low temperature section of the system (e.g., freezer cases).

In existing systems, one way to address frost and/or ice accumulation on the load is to cycle refrigerant back to the load after the refrigerant has absorbed heat from the load. Usually, discharge from a low temperature compressor is cycled back to a load to defrost that load. In this manner, the heated refrigerant passes over the frost and/or ice accumulation and defrosts the load. This process of cycling hot refrigerant over frosted and/or iced loads is known as hot gas defrost. Existing cooling systems that have a hot gas defrost cycle typically use a stepper valve at the low temperature compressor discharge to increase the pressure of the refrigerant so that the refrigerant can be directed to the flash tank after defrost. However, the pressure difference between the refrigerant at the low temperature compressor and the refrigerant in the flash tank can be small (e.g., 4 bar). As a result, large piping is typically used to limit the pressure drop of the refrigerant during defrost, which can be costly and increase the footprint of the system.

This disclosure contemplates a cooling system that performs hot gas defrost while maintaining a larger pressure differential (e.g., 12 bar). The system includes an accumulator that separates refrigerant into liquid and vapor components. After refrigerant is used to defrost a load, the refrigerant is directed to the accumulator. The accumulator separates this refrigerant into liquid and vapor components. The liquid component is directed to the flash tank through an ejector, and the vapor component is directed to a medium temperature compressor. Because the pressure of the refrigerant at the accumulator is lower than the pressure of the refrigerant at the flash tank, the pressure differential of the refrigerant between the low temperature compressor and the accumulator is increased. As a result, smaller piping may be used, which reduces cost and the footprint of the system. Certain embodiments of the cooling system are described below.

According to an embodiment, an apparatus includes an ejector, a first load, a second load, a third load, a first compressor, a second compressor, and an accumulator. The ejector directs a refrigerant to a flash tank that stores the refrigerant. The first load uses the refrigerant from the flash tank to cool a first space proximate the first load. The second load uses the refrigerant from the flash tank to cool a second space proximate the second load. The first compressor compresses the refrigerant from the first load. The accumulator separates the refrigerant from the second load into a first liquid portion and a first vapor portion and directs the first liquid portion to the ejector. The ejector directs the first liquid portion to the flash tank. The accumulator directs the first vapor portion to the second compressor. The second compressor compresses the first vapor portion. During a first mode of operation, the third load uses the refrigerant from the flash tank to cool a third space proximate the third load, the first compressor compresses the refrigerant from the third load, and the second compressor compresses the refrigerant from the first compressor. During a second mode of operation, the first compressor directs the refrigerant to the third load to defrost the third load, the accumulator separates the refrigerant that defrosted the third load into a second liquid portion and a second vapor portion, the ejector directs the second liquid portion to the flash tank, and the second compressor compresses the second vapor portion.

According to another embodiment, a method includes directing, by an ejector, a refrigerant to a flash tank and storing, by the flash tank, the refrigerant. The method also includes using, by a first load, the refrigerant from the flash tank to cool a first space proximate the first load and using, by a second load, the refrigerant from the flash tank to cool a second space proximate the second load. The method further includes compressing, by a first compressor, the refrigerant from the first load and separating, by an accumulator, the refrigerant from the second load into a first liquid portion and a first vapor portion. The method also includes directing, by the accumulator, the first liquid portion to the ejector, directing, by the ejector, the first liquid portion to the flash tank, directing, by the accumulator, the first vapor portion to a second compressor, and compressing, by the second compressor, the first vapor portion. During a first mode of operation, the method includes using, by a third load, the refrigerant from the flash tank to cool a third space proximate the third load, compressing, by the first compressor, the refrigerant from the third load, and compressing, by the second compressor, the refrigerant from the first compressor. During a second mode of operation, the method includes directing, by the first compressor, the refrigerant to the third load to defrost the third load, separating, by the accumulator, the refrigerant that defrosted the third load into a second liquid portion and a second vapor portion, directing, by the ejector, the second liquid portion to the flash tank, and compressing, by the second compressor, the second vapor portion.

According to yet another embodiment, a system includes a high side heat exchanger, an ejector, a first load, a second load, a third load, a first compressor, a second compressor, and an accumulator. The high side heat exchanger removes heat from a refrigerant. The ejector directs the refrigerant from the high side heat exchanger to a flash tank that stores the refrigerant. The first load uses the refrigerant from the flash tank to cool a first space proximate the first load. The second load uses the refrigerant from the flash tank to cool a second space proximate the second load. The first compressor compresses the refrigerant from the first load. The accumulator separates the refrigerant from the second load into a first liquid portion and a first vapor portion and directs the first liquid portion to the ejector. The ejector directs the first liquid portion to the flash tank. The accumulator directs the first vapor portion to the second compressor. The second compressor compresses the first vapor portion. During a first mode of operation, the third load uses the refrigerant from the flash tank to cool a third space proximate the third load, the first compressor compresses the refrigerant from the third load, and the second compressor compresses the refrigerant from the first compressor. During a second mode of operation, the first compressor directs the refrigerant to the third load to defrost the third load, the accumulator separates the refrigerant that defrosted the third load into a second liquid portion and a second vapor portion, the ejector directs the second liquid portion to the flash tank, and the second compressor compresses the second vapor portion.

Certain embodiments provide one or more technical advantages. For example, an embodiment reduces the size and cost of piping in a cooling system by directing refrigerant used to defrost a load to an accumulator, rather than directly to a flash tank. As another example, an embodiment reduces the amount of refrigerant in a cooling system and the size of a flash tank in the cooling system by directing refrigerant used to defrost a load to an accumulator, rather than directly to a flash tank. Certain embodiments may include none, some, or all of the above technical advantages. One or more other technical advantages may be readily apparent to one skilled in the art from the figures, descriptions, and claims included herein.

DETAILED DESCRIPTION

Embodiments of the present disclosure and its advantages are best understood by referring toFIGS. 1 through 4of the drawings, like numerals being used for like and corresponding parts of the various drawings.

Cooling systems cycle refrigerant to cool various spaces. For example, a refrigeration system cycles refrigerant to cool spaces near or around refrigeration loads. These loads include metal components, such as coils, that carry the refrigerant. As the refrigerant passes through these metallic components, frost and/or ice may accumulate on the exterior of these metallic components. The ice and/or frost reduce the efficiency of the load. For example, as frost and/or ice accumulates on a load, it may become more difficult for the refrigerant within the load to absorb heat that is external to the load. Typically, the ice and frost accumulate on loads in a low temperature section of the system (e.g., freezer cases).

In existing systems, one way to address frost and/or ice accumulation on the load is to cycle refrigerant back to the load after the refrigerant has absorbed heat from the load. Usually, discharge from a low temperature compressor is cycled back to a load to defrost that load. In this manner, the heated refrigerant passes over the frost and/or ice accumulation and defrosts the load. This process of cycling hot refrigerant over frosted and/or iced loads is known as hot gas defrost. Existing cooling systems that have a hot gas defrost cycle typically use a stepper valve at the low temperature compressor discharge to increase the pressure of the refrigerant so that the refrigerant can be directed to the flash tank after defrost. However, the pressure difference between the refrigerant at the low temperature compressor and the refrigerant in the flash tank can be small (e.g., 4 bar). As a result, large piping is typically used to limit the pressure drop of the refrigerant during defrost, which can be costly and increase the footprint of the system.

This disclosure contemplates a cooling system that performs hot gas defrost while maintaining a larger pressure differential (e.g., 12 bar). The system includes an accumulator that separates refrigerant into liquid and vapor components. After refrigerant is used to defrost a load, the refrigerant is directed to the accumulator. The accumulator separates this refrigerant into liquid and vapor components. The liquid component is directed to the flash tank through an ejector, and the vapor component is directed to a medium temperature compressor. Because the pressure of the refrigerant at the accumulator is lower than the pressure of the refrigerant at the flash tank, the pressure differential of the refrigerant between the low temperature compressor and the accumulator is increased. As a result, smaller piping may be used, which reduces cost and the footprint of the system.

In certain embodiments, the size and cost of piping in a cooling system are reduced by directing refrigerant used to defrost a load to an accumulator, rather than directly to a flash tank. In some embodiments, the amount of refrigerant in a cooling system and the size of a flash tank in the cooling system are reduced by directing refrigerant used to defrost a load to an accumulator, rather than directly to a flash tank. The cooling system will be described usingFIGS. 1 through 4.FIG. 1will describe an existing cooling system with hot gas defrost.FIGS. 2 through 4describe the cooling system with an accumulator and ejector.

FIG. 1illustrates an example cooling system100. As shown inFIG. 1, system100includes a high side heat exchanger105, a flash tank110, a medium temperature load115, low temperature loads120A-120D, a medium temperature compressor125, a low temperature compressor130, and a valve135. By operating valve135, system100allows for hot gas to be circulated to a low temperature load120to defrost low temperature load120. After defrosting low temperature load120, the hot gas and/or refrigerant is cycled back to flash tank110. This disclosure contemplates cooling system100or any cooling system described herein including any number of loads, whether low temperature or medium temperature.

High side heat exchanger105removes heat from a refrigerant. When heat is removed from the refrigerant, the refrigerant is cooled. This disclosure contemplates high side heat exchanger105being operated as a condenser and/or a gas cooler. When operating as a condenser, high side heat exchanger105cools the refrigerant such that the state of the refrigerant changes from a gas to a liquid. When operating as a gas cooler, high side heat exchanger105cools gaseous refrigerant and the refrigerant remains a gas. In certain configurations, high side heat exchanger105is positioned such that heat removed from the refrigerant may be discharged into the air. For example, high side heat exchanger105may be positioned on a rooftop so that heat removed from the refrigerant may be discharged into the air. As another example, high side heat exchanger105may be positioned external to a building and/or on the side of a building. This disclosure contemplates any suitable refrigerant (e.g., carbon dioxide) being used in any of the disclosed cooling systems.

Flash tank110stores refrigerant received from high side heat exchanger105. This disclosure contemplates flash tank110storing refrigerant in any state such as, for example, a liquid state and/or a gaseous state. Refrigerant leaving flash tank110is fed to low temperature loads120A-120D and medium temperature load115. In some embodiments, a flash gas and/or a gaseous refrigerant is released from flash tank110. By releasing flash gas, the pressure within flash tank110may be reduced.

System100includes a low temperature portion and a medium temperature portion. The low temperature portion operates at a lower temperature than the medium temperature portion. In some refrigeration systems, the low temperature portion may be a freezer system and the medium temperature system may be a regular refrigeration system. In a grocery store setting, the low temperature portion may include freezers used to hold frozen foods, and the medium temperature portion may include refrigerated shelves used to hold produce. Refrigerant flows from flash tank110to both the low temperature and medium temperature portions of the refrigeration system. For example, the refrigerant flows to low temperature loads120A-120D and medium temperature load115. When the refrigerant reaches low temperature loads120A-120D or medium temperature load115, the refrigerant removes heat from the air around low temperature loads120A-120D or medium temperature load115. As a result, the air is cooled. The cooled air may then be circulated such as, for example, by a fan to cool a space such as, for example, a freezer and/or a refrigerated shelf. As refrigerant passes through low temperature loads120A-120D and medium temperature load115, the refrigerant may change from a liquid state to a gaseous state as it absorbs heat. This disclosure contemplates including any number of low temperature loads120And medium temperature loads115in any of the disclosed cooling systems.

The refrigerant cools metallic components of low temperature loads120A-120D and medium temperature load115as the refrigerant passes through low temperature loads120A-120D and medium temperature load115. For example, metallic coils, plates, parts of low temperature loads120A-120D and medium temperature load115may cool as the refrigerant passes through them. These components may become so cold that vapor in the air external to these components condenses and eventually freeze or frost onto these components. As the ice or frost accumulates on these metallic components, it may become more difficult for the refrigerant in these components to absorb heat from the air external to these components. In essence, the frost and ice acts as a thermal barrier. As a result, the efficiency of cooling system100decreases the more ice and frost that accumulates. Cooling system100may use heated refrigerant to defrost these metallic components.

Refrigerant flows from low temperature loads120A-D and medium temperature load115to compressors125and130. This disclosure contemplates the disclosed cooling systems including any number of low temperature compressors130and medium temperature compressors125. Both the low temperature compressor130and medium temperature compressor125compress refrigerant to increase the pressure of the refrigerant. As a result, the heat in the refrigerant may become concentrated and the refrigerant may become a high-pressure gas. Low temperature compressor130compresses refrigerant from low temperature loads120A-120D and sends the compressed refrigerant to medium temperature compressor125. Medium temperature compressor125compresses a mixture of the refrigerant from low temperature compressor130and medium temperature load115. Medium temperature compressor125then sends the compressed refrigerant to high side heat exchanger105.

Valve135may be opened or closed to cycle refrigerant from low temperature compressor130back to a low temperature load120. The refrigerant may be heated after absorbing heat from the other low temperature loads120and being compressed by low temperature compressor130. The hot refrigerant and/or hot gas is then cycled over the metallic components of the low temperature load120to defrost it. Afterwards, the hot gas and/or refrigerant is cycled back to flash tank110. There may be additional valves between low temperature compressor130and low temperature loads120A-D that control to which load120A-D is defrosted by the refrigerant coming from low temperature compressor130. This process of cycling heated refrigerant over a low temperature load120to defrost it is referred to as a defrost cycle.

Existing cooling systems that have a hot gas defrost cycle typically use a stepper valve at the low temperature compressor discharge to increase the pressure of the refrigerant so that the refrigerant can be directed to the flash tank after defrost. However, the pressure difference between the refrigerant at the low temperature compressor and the refrigerant in the flash tank can be small (e.g., 4 bar). As a result, large piping is typically used to limit the pressure drop of the refrigerant during defrost, which can be costly and increase the footprint of the system.

This disclosure contemplates a cooling system that performs hot gas defrost while maintaining a larger pressure differential (e.g., 12 bar). The system includes an accumulator that separates refrigerant into liquid and vapor components. After refrigerant is used to defrost a load, the refrigerant is directed to the accumulator. The accumulator separates this refrigerant into liquid and vapor components. The liquid component is directed to the flash tank through an ejector, and the vapor component is directed to a medium temperature compressor. Because the pressure of the refrigerant at the accumulator is lower than the pressure of the refrigerant at the flash tank, the pressure differential of the refrigerant between the low temperature compressor and the accumulator is increased. As a result, smaller piping may be used, which reduces cost and the footprint of the system. Embodiments of the cooling system are described below usingFIGS. 2-4. These figures illustrate embodiments that include a certain number of loads and compressors for clarity and readability. However, this disclosure contemplates these embodiments including any suitable number of loads and compressors.

FIG. 2illustrates an example cooling system200. As seen inFIG. 2, cooling system200includes a high side heat exchanger105, an ejector205, a flash tank110, medium temperature loads115A and115B, low temperature loads120A and120B, medium temperature compressor125, low temperature compressor130, valves135A,135B,135C, and135D, an accumulator210, a parallel compressor215, an oil separator220, and valves225A,225B,225C, and225D. Generally, accumulator210separates a refrigerant used to defrost a load into liquid and vapor portions. Accumulator210then directs the liquid portion to ejector205in flash tank110and the vapor portion to medium temperature compressor125. In this manner, the pressure differential between accumulator210and low temperature compressor130is increased relative to the pressure differential between low temperature compressor130and flash tank110, which reduces the cost and size of piping used to contain the refrigerant in certain embodiments.

High side heat exchanger105, flash tank110, medium temperature loads115A and115B, low temperature loads120A and120B, and low temperature compressor130operate similarly in system200as they did in system100. For example, high side heat exchanger105removes heat from a refrigerant. Flash tank110stores the refrigerant. Medium temperature loads115A and115B and low temperature loads120A and120B use the refrigerant from flash tank110to cool spaces proximate those loads. Low temperature compressor130compresses the refrigerant from low temperature loads120A and120B.

Ejector205receives refrigerant from high side heat exchanger105and/or accumulator210. Ejector205then ejects and/or directs this refrigerant to flash tank110. In some systems, the pressure of the ejected refrigerant is controlled and/or adjusted by the pressure of the refrigerant from accumulator110and the shape of ejector205.

Accumulator210separates a received refrigerant into liquid and vapor portions. For examples, accumulator210receives the refrigerant from medium temperature loads115A and115B. Accumulator210then separates the received refrigerant into a liquid portion212and a vapor portion214. Accumulator210then directs some of liquid portion212to ejector205and some of the vapor portion214to medium compressor125. Ejector205directs liquid portion212to flash tank110for storage. Medium temperature compressor125compresses vapor portion214. Some of liquid portion212and vapor portion214may remain in accumulator210instead of being directed to other components of system200. During a defrost cycle, accumulator210receives refrigerant that was used to defrost a load. Accumulator210separates this refrigerant into liquid portion212and vapor portion214. Some of liquid portion212is then directed to ejector205and flash tank110, and some of vapor portion214is directed to medium temperature compressor125.

Parallel compressor215compresses a flash gas from flash tank110. Flash tank110may discharge the flash gas to parallel compressor215. After parallel compressor215compresses the flash gas, parallel compressor215directs the compressed flash gas to oil separator220. By discharging flash gas, the pressure of the refrigerant in flash tank110can be regulated.

Oil separator220separates an oil from received refrigerant. For example, oil separator210may receive refrigerant from parallel compressor215and/or medium temperature compressor125. Oil separator220separates oil from this received refrigerant and directs the refrigerant to high side heat exchanger105. By separating oil from the received refrigerant, oil separator220prevents the oil from flowing to other components of system200. In this manner the oil does not damage other components of system200.

During a first mode of operation (e.g., a regular refrigeration cycle), medium temperature loads115A and115B, and low temperature loads120A and120B use refrigerant from flash tank110to cool spaces proximate those loads. The refrigerant used by low temperature loads120A and120B is directed to low temperature compressor130. The refrigerant used by medium temperature loads115A and115B is directly to accumulator210. Low temperature compressor130compresses the refrigerant from low temperature load from120A and120B and directs the compressed refrigerant to medium temperature compressor125. Accumulator210separates the refrigerant from medium temperature loads115A and115B into liquid portion212and vapor portion214. Accumulator210then directs some of liquid portion212to ejector205and some of vapor portion214to medium temperature compressor125. Medium temperature compressor125then compresses the refrigerant from low temperature compressor130and accumulator210. After compressing the refrigerant, medium temperature compressor125directs the refrigerant to oil separator220and high side heat exchanger105. In this manner, the refrigerant is cycled through system200to cool spaces proximate the loads.

During a defrost cycle, or a second mode of operation, one or more of the loads is defrosted using the refrigerant from low temperature compressor130. Valves135A,135B,135C,135D,225A,225B,225C, and/or225D are controlled to allow refrigerant to flow from low temperature compressor130back to one of the loads to defrost the load. For example, in one defrost cycle, valves135C and225C can open to allow refrigerant to flow from low temperature compressor130through low temperature load120A to defrost low temperature load120A. In another defrost cycle, valve135B and225B can open to allow refrigerant to flow from low temperature compressor130through medium temperature load115B to defrost medium temperature load115B. This disclosure contemplates using refrigerant from low temperature compressor130to defrost any number of loads and any type of loads.

This disclosure contemplates valves135A,135B,135C,135D,225A,225B,225C, and225D being any type of valve. For example, one or more of these valves may be a check valve that allows refrigerant to flow through the valve when the refrigerant has reached a threshold pressure. As another example, one or more of these valves may be a solenoid valve that can be opened or closed by a control. Using a previous example, valve135C may be a solenoid valve and valve225C may be a check valve. In this example, during a defrost cycle, valve135C opens to allow refrigerant to flow from low temperature compressor130to low temperature load120A to defrost low temperature load120A. The pressure of that refrigerant builds until it is high enough to pass through check valve225C and flow to accumulator210. When the defrost cycle ends, valve135C is closed. In another example, both valves135C and225C are solenoid valves. During the defrost cycle, both valves135C and225C are opened to allow refrigerant to flow from low temperature compressor130through low temperature load120A to defrost low temperature load120A. When the defrost cycle ends, valves135C and225C are closed.

After the refrigerant defrosts a load, the refrigerant is directed to accumulator210. Accumulator210separates that refrigerant into liquid portion212and vapor portion214. Accumulator210then directs some of liquid portion212to ejector205and flash tank110and some of vapor portion214to medium temperature compressor125. Ejector205directs liquid portion212to flash tank110for storage. Medium temperature compressor125compresses vapor portion214. Because the pressure of the refrigerant at accumulator210is lower than the pressure of the refrigerant at flash tank110, the pressure differential between low temperature compressor130and accumulator210is greater than the pressure differential between low temperature compressor130and flash tank110. As a result, in certain embodiments, by directing the refrigerant used to defrost the loads to accumulator210, the cost and size of piping used to carry that refrigerant is reduced compared to a system that directs the refrigerant directly to flash tank110after defrost. Additionally, in some embodiments, by directing the refrigerant used to defrost the loads to accumulator210the amount of refrigerant in the system and the size of flash tank110can be reduced without negatively impacting the efficiency of system200.

In certain embodiments, a defrost cycle to defrost a medium temperature load115may be different from a defrost cycle to defrost a low temperature load120. As a result, during a first defrost cycle, or a second mode of operation, a low temperature load120may be defrosted. Then, in a second defrost cycle, or a third mode of operation, a medium temperature load115may be defrosted.

FIG. 3illustrates an example cooling system300. As seen inFIG. 3, system300includes a high side heat exchanger105, an ejector205, a flash tank110, medium temperature loads115A and115B, low temperature loads120A and120B, low temperature compressor130, accumulator210, medium temperature compressor125, parallel compressor215, oil separator220, valves135A,135B,135C, and135D, and valves225A,225B,225C, and225D. Generally, accumulator210separates a refrigerant that was used to defrost a load into a liquid portion212and a vapor portion214. Accumulator210then directs some of the liquid portion212to ejector205and flash tank110and some of the vapor portion214to medium temperature compressor125. Because the pressure of the refrigerant at accumulator210is lower than the pressure of the refrigerant at flash tank110, the pressure differential between low temperature compressor130and accumulator210is greater than the pressure differential between low temperature compressor130and flash tank110. As a result, the size of the piping used to carry the refrigerant may be reduced when the refrigerant used to defrost the loads is directed to accumulator210instead of directly to flash tank110in certain embodiments.

High side heat exchanger105, ejector205, flash tank110, medium temperature loads115A and115B, low temperature loads120A and120B, low temperature compressor130, medium temperature compressor125, accumulator210, parallel compressor215, oil separator220, valves135A,135B,135C and135D, and valves225A,225B,225C and225D operate similarly as they did in system200. For example, high side heat exchanger105removes heat from a refrigerant. Ejector205directs the refrigerant to flash tank110. Flash tank110stores the refrigerant. Medium temperature loads115A and115B and low temperature loads120A and120B use the refrigerant from flash tank110to cool spaces proximate those loads. Low temperature compressor130compresses the refrigerant from low temperature loads120A and120B. Accumulator210separates refrigerant into liquid portion212and vapor portion214. Accumulator210then directs some of liquid portion212to ejector205and flash tank110and some of vapor portion214to medium temperature compressor125. Ejector205directs liquid portion212to flash tank110for storage. Medium temperature compressor125compresses vapor portion214. Parallel compressor215compresses flash gas discharged from flash tank110. Oil separator220separates oil from refrigerant received from parallel compressor215and medium temperature compressor125.

An important difference between system300and system200is that medium temperature loads115A and115B are arranged in series in system300, whereas these loads are arranged in parallel in system200. In other words, in system300, medium temperature load115B uses refrigerant from flash tank110that has passed through medium temperature load115A. After medium temperature load115B uses that refrigerant from medium temperature load115A to cool a space proximate medium temperature load115B, medium temperature load115B directs the refrigerant to accumulator210. Likewise, medium temperature load115A uses refrigerant directly from flash tank110to cool a space proximate medium temperature load115A and then directs that refrigerant to medium temperature load115B. As shown inFIG. 3, it is possible to use accumulator210to increase the pressure differential of the refrigerant even though medium temperature loads115A and115B are arranged in series as opposed to in parallel in system200.

During a first mode of operation, or regular refrigeration cycle, medium temperature loads115A and115B and low temperature loads120A and120B use refrigerant to cool spaces proximate those loads. Low temperature loads120A and120B direct the refrigerant to low temperature compressor130. Medium temperature load115A directs refrigerant to medium temperature load115B. Medium temperature load115B directs the refrigerant to accumulator210. Low temperature compressor130compresses the refrigerant from low temperature loads120A and120B and directs the refrigerant to medium temperature compressor125. Accumulator210separates the refrigerant from medium temperature load115B into a liquid portion212and vapor portion214. Accumulator210then directs some of the liquid portion212to ejector205in flash tank110and some of vapor portion214to medium temperature compressor125. Ejector205directs liquid portion212to flash tank110for storage. Medium temperature compressor125compresses vapor portion214and the refrigerant from low temperature compressor130and directs that refrigerant to oil separator220.

During a second mode of operation, or defrost cycle, low temperature compressor130directs refrigerant back to a load to defrost the load. For example, during a low temperature defrost cycle, low temperature compressor130directs refrigerant back to low temperature load120A. Valves135C and225C can open to allow refrigerant to flow from low temperature compressor130through low temperature load120A to defrost low temperature load120A. As another example, during a medium temperature defrost cycle, valves135A and225A can open to allow refrigerant to flow from low temperature compressor130through medium temperature load115A to defrost medium temperature load115A.

After the refrigerant defrosts the load, the refrigerant is directed to accumulator210. Accumulator210separates the refrigerant into liquid portion212and vapor portion214. Accumulator210then directs some of liquid portion212to ejector205and flash tank110and some of vapor portion214to medium temperature compressor125. Ejector205directs liquid portion212to flash tank110for storage. Medium temperature compressor125compresses vapor portion214. In this manner, the size and cost of piping used to carry the refrigerant is reduced compared to implementations where refrigerant used to defrost the loads flows directly to flash tank110.

FIG. 4is a flowchart illustrating a method400of operating an example cooling system. In certain embodiments, various components of system200or system300perform the steps of method400. By performing method400, the size and cost of piping used to carry refrigerant is reduced in certain embodiments.

In step405, an ejector directs the refrigerant to a flash tank. The flash tank stores the refrigerant in step410. In step415, a first load uses the refrigerant to cool a first space. A second load uses the refrigerant to cool a second space in step420. In step425, a first compressor compresses the refrigerant from the first load. An accumulator separates the refrigerant from the second load into a first liquid portion and a first vapor portion in step430. In step435, the accumulator directs the first liquid portion to the ejector. The ejector directs the first liquid portion to the flash tank in steps440. In step445, the accumulator directs the first vapor portion to a second compressor. The second compressor compresses the first vapor portion in step450.

During a first mode of operation, such as, for example, a regular refrigeration cycle, a third load uses the refrigerant to cool a third space in step455. In step460, the first compressor compresses the refrigerant from the third load. The second compressor compresses the refrigerant from the first compressor in step465.

During a second mode of operation, such as, for example, a defrost cycle, the first compressor directs the refrigerant to the third load to defrost the third load in step470. In step475, the accumulator separates the refrigerant that defrosted the third load into a second liquid portion and a second vapor portion. The ejector directs the second liquid portion to the flash tank in step480. In step485, the second compressor compresses the second vapor portion.

Modifications, additions, or omissions may be made to method400depicted inFIG. 4. Method400may include more, fewer, or other steps. For example, steps may be performed in parallel or in any suitable order. While discussed as systems200and/or300(or components thereof) performing the steps, any suitable component of systems200and/or300may perform one or more steps of the method.

This disclosure may refer to a refrigerant being from a particular component of a system (e.g., the refrigerant from the medium temperature compressor, the refrigerant from the low temperature compressor, the refrigerant from the flash tank, etc.). When such terminology is used, this disclosure is not limiting the described refrigerant to being directly from the particular component. This disclosure contemplates refrigerant being from a particular component (e.g., the high side heat exchanger) even though there may be other intervening components between the particular component and the destination of the refrigerant. For example, the flash tank receives a refrigerant from the accumulator even though there is an ejector between the flash tank and the accumulator.