Patent Description:
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.

<CIT> discloses a CO<NUM> refrigeration system according to the preamble of claim <NUM> and a method according to the preamble of claim <NUM> with hot gas defrost, the system comprising an LT system with LT compressors and LT evaporators, and an MT system with MT compressors and MT evaporators, operating in a refrigeration mode and a defrost mode using CO<NUM> hot gas discharge from the MT and/or the LT compressors to defrost the LT evaporators. A CO<NUM> refrigerant circuit directs CO<NUM> refrigerant through the system and has an LT compressor discharge line With a hot gas discharge valve, a CO<NUM> hot gas defrost supply header directing CO<NUM> hot gas discharge from the LT and/or the MT compressors to the LT evaporators, a flash tank supplying CO<NUM> refrigerant to the MT and LT evaporators during the refrigeration mode, and receiving the CO<NUM> hot gas discharge from the LT evaporators during the defrost mode, and a control system directing the CO<NUM> hot gas discharge through the LT evaporators and to the flash tank during the defrost mode.

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).

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. In conventional systems, the hot gas travels very quickly over/through the loads. As a result, heat transfer between the hot gas and the load is limited, which causes the hot gas defrost process to use more hot gas to defrost the load.

In accordance with the invention there is provided an apparatus and method as defined by the appended claims.

This disclosure contemplates an unconventional cooling system that improves heat transfer between the hot gas and the load by increasing the pressure of the hot gas at the load. The system uses a valve (e.g., a regulating valve) that prevents the hot gas at the load from flowing to a receiver (e.g., a flash tank) until a pressure of the hot gas at the load exceeds a threshold. By increasing the pressure of the gas at the load, the hot gas lingers longer in the load, which increases the heat transfer between the hot gas and the load. In some instances, the hot gas even condenses at the load. In this manner, less hot gas (i.e., a decreased mass flow of hot gas) is used to defrost a load. Certain embodiments of the cooling system are described below.

According to an embodiment, an apparatus includes a high side heat exchanger that removes heat from a refrigerant, a flash tank that stores the refrigerant, a first load that uses the refrigerant from the flash tank to cool a first space proximate the first load, a second load, a third load, a first compressor, a second compressor, and a valve. During a first mode of operation: the second load uses the refrigerant from the flash tank to cool a second space proximate the second load, the third load uses the refrigerant from the flash tank to cool a third space proximate the third load, the second compressor compresses the refrigerant from the second load and the third load, and the first compressor compresses the refrigerant from the first load and the second compressor. During a second mode of operation: the second load is configured to use the refrigerant from the flash tank to cool the second space proximate the second load; the second compressor compresses the refrigerant from the second load and directs a portion of the compressed refrigerant to the third load to defrost the third load and directs the portion of the compressed refrigerant after defrosting the third load to the flash tank; the first compressor compresses the refrigerant from the first load and the remaining portion of the refrigerant from the second compressor; and the valve prevents the portion of the refrigerant at the third load from flowing to the flash tank until a pressure of the refrigerant at the third load exceeds a threshold. The valve is a regulating valve and is configured to control the threshold.

According to another embodiment, a method includes removing, by a high side heat exchanger, heat from a refrigerant, storing, by a flash tank, the refrigerant, and using, by a first load, the refrigerant from the flash tank to cool a first space proximate the first load. The method also includes during a first mode of operation: using, by a second load, refrigerant from the flash tank to cool a second space proximate the second load, using, by a third load, the refrigerant from the flash tank to cool a third space proximate the third load, compressing, by a second compressor, the refrigerant from the second load and the third load, and compressing, by a first compressor, the refrigerant from the first load and the second compressor. The method further includes during a second mode of operation: using the refrigerant from the flash tank to cool the second space proximate the second load; compressing, by the second compressor, a portion of the refrigerant from the second load, directing, by the second compressor, the compressed refrigerant to the third load to defrost the third load, and directing the portion of the compressed refrigerant after defrosting the third load to the flash tank; compressing, by the first compressor, the refrigerant from the first load and the remaining portion of the refrigerant from the second compressor; and preventing, by a valve, the portion of the refrigerant at the third load from flowing to the flash tank until a pressure of the refrigerant at the third load exceeds a threshold. The valve is a regulating valve and is configured to control the threshold.

Certain embodiments provide one or more technical advantages. For example, an embodiment increases the heat transfer between hot gas and a load during a defrost cycle by increasing a pressure of the hot gas at the load. 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.

For a more complete understanding of the present disclosure, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:.

Embodiments of the present invention and its advantages are best understood by referring to <FIG> of the drawings, like numerals being used for like and corresponding parts of the various drawings.

This disclosure contemplates an unconventional cooling system that improves heat transfer between the hot gas and the load by increasing the pressure of the hot gas at the load. The system uses a valve (e.g., a regulating valve) that prevents the hot gas at the load from flowing to a receiver (e.g., a flash tank) until a pressure of the hot gas at the load exceeds a threshold. By increasing the pressure of the gas at the load, the hot gas lingers longer in the load, which increases the heat transfer between the hot gas and the load. In some instances, the hot gas even condenses at the load. In this manner, less hot gas (i.e., a decreased mass flow of hot gas) is used to defrost a load. The cooling system will be described using <FIG>.

<FIG> illustrates an example cooling system <NUM>. As shown in <FIG>, system <NUM> includes a high side heat exchanger <NUM>, a flash tank <NUM>, a medium temperature load <NUM>, low temperature loads 120A and 120B, a medium temperature compressor <NUM>, a low temperature compressor <NUM>, a valves 135A-C, a valve <NUM>, and a valve <NUM>. Generally, valve <NUM> prevents hot gas at a low temperature load <NUM> from flowing to flash tank <NUM> until a pressure of the gas at the low temperature load <NUM> exceeds a threshold. This disclosure contemplates cooling system <NUM> or any cooling system described herein including any number of loads, whether low temperature or medium temperature.

High side heat exchanger <NUM> removes heat from a refrigerant. When heat is removed from the refrigerant, the refrigerant is cooled. This disclosure contemplates high side heat exchanger <NUM> being operated as a condenser and/or a gas cooler. When operating as a condenser, high side heat exchanger <NUM> cools 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 exchanger <NUM> cools gaseous refrigerant and the refrigerant remains a gas. In certain configurations, high side heat exchanger <NUM> is positioned such that heat removed from the refrigerant may be discharged into the air. For example, high side heat exchanger <NUM> may be positioned on a rooftop so that heat removed from the refrigerant may be discharged into the air. As another example, high side heat exchanger <NUM> may 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 tank <NUM> stores refrigerant received from high side heat exchanger <NUM>. This disclosure contemplates flash tank <NUM> storing refrigerant in any state such as, for example, a liquid state and/or a gaseous state. Refrigerant leaving flash tank <NUM> is fed to low temperature loads 120A and 120B and medium temperature load <NUM>. In some embodiments, a flash gas and/or a gaseous refrigerant is released from flash tank <NUM>. By releasing flash gas, the pressure within flash tank <NUM> may be reduced.

System <NUM> includes 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 tank <NUM> to both the low temperature and medium temperature portions of the refrigeration system. For example, the refrigerant flows to low temperature loads 120A and 120B and medium temperature load <NUM>. When the refrigerant reaches low temperature loads 120A and 120B or medium temperature load <NUM>, the refrigerant removes heat from the air around low temperature loads 120A and 120B or medium temperature load <NUM>. 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 loads 120A and 120B and medium temperature load <NUM>, 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 loads <NUM> and medium temperature loads <NUM> in any of the disclosed cooling systems.

The refrigerant cools metallic components of low temperature loads 120A and 120B and medium temperature load <NUM> as the refrigerant passes through low temperature loads 120A and 120B and medium temperature load <NUM>. For example, metallic coils, plates, parts of low temperature loads 120A and 120B and medium temperature load <NUM> may 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 system <NUM> decreases the more ice and frost that accumulates. Cooling system <NUM> may use heated refrigerant to defrost these metallic components.

Refrigerant flows from low temperature loads 120A and 120B and medium temperature load <NUM> to compressors <NUM> and <NUM>. This disclosure contemplates the disclosed cooling systems including any number of low temperature compressors <NUM> and medium temperature compressors <NUM>. Both the low temperature compressor <NUM> and medium temperature compressor <NUM> compress 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 compressor <NUM> compresses refrigerant from low temperature loads 120A and 120B and sends the compressed refrigerant to medium temperature compressor <NUM>.

Medium temperature compressor <NUM> compresses a mixture of the refrigerant from low temperature compressor <NUM> and medium temperature load <NUM>. Medium temperature compressor <NUM> then sends the compressed refrigerant to high side heat exchanger <NUM>.

Valves 135A-C may be opened or closed to cycle refrigerant from low temperature compressor <NUM> back to a load (e.g., low temperature load 120A, low temperature load 120B, or medium temperature load <NUM>). The refrigerant may be heated after absorbing heat from other loads and being compressed by low temperature compressor <NUM>. The hot refrigerant and/or hot gas is then cycled over the metallic components of a load to defrost it. Afterwards, the hot gas and/or refrigerant is cycled back to flash tank <NUM>. This process of cycling heated refrigerant over a load to defrost it is referred to as a defrost cycle. In conventional systems, the hot gas travels very quickly over/through the loads. As a result, heat transfer between the hot gas and the load is limited, which causes the hot gas defrost process to use more hot gas to defrost the load.

Cooling system <NUM> improves heat transfer between the hot gas and the load by increasing the pressure of the hot gas at the load. The system <NUM> uses a valve <NUM> (e.g., a regulating valve) that prevents the hot gas at the load from flowing to a receiver (e.g., a flash tank <NUM>) until a pressure of the hot gas at the load exceeds a threshold. By increasing the pressure of the gas at the load, the hot gas lingers longer in the load, which increases the heat transfer between the hot gas and the load. In some instances, the hot gas even condenses at the load. In this manner, less hot gas (i.e., a decreased mass flow of hot gas) is used to defrost a load.

During the defrost cycle, the load that is being defrosted may be turned off. The refrigerant used by the other load(s) supplies the hot gas for the defrost cycle. In the example of <FIG>, valve 135A controls the flow of hot gas to low temperature load 120B, valve 135B controls the flow of hot gas to low temperature load 120A, and valve 135C controls the flow of hot gas to medium temperature load <NUM>. During a defrost cycle, if low temperature load 120B is being defrosted, then valve 135A is open and valves 135B and 135C are closed. Refrigerant from low temperature load 120A is compressed by low temperature compressor <NUM> and directed through valve 135A to low temperature load 120B to defrost low temperature load 120B. If low temperature load 120A is being defrosted, then valve 135B is open and valves 135A and 135C are closed. Refrigerant from low temperature load 120B is compressed by low temperature compressor <NUM> and directed through valve 135B to low temperature load 120A to defrost low temperature load 120A. If medium temperature load <NUM> is being defrosted, then valve 135C is open and valves 135A and 135B are closed.

Refrigerant from low temperature load 120A and/or low temperature load 120B is compressed by low temperature compressor <NUM> and directed through valve 135C to medium temperature load <NUM> to defrost medium temperature load <NUM>.

Valve <NUM> regulates a pressure of the gas at a defrosting load during a hot gas defrost cycle. In certain embodiments, valve <NUM> is a regulating valve. Generally, valve <NUM> prevents hot gas from flowing through valve <NUM> to flash tank <NUM> unless a pressure of the hot gas exceeds a threshold. Valve <NUM> may be selected or adjusted to control this threshold. By using valve <NUM>, hot gas that is defrosting a load does not continue flowing through valve <NUM> to flash tank <NUM> until a pressure of the gas exceeds the threshold. As a result, heat transfer between hot gas and the load is improved. In some instances, so much heat may be transferred that the hot gas condenses at or in the load, and the refrigerant flowing through valve <NUM> to flash tank <NUM> includes a vapor portion and a liquid portion.

Using the previous example, valve <NUM> prevents hot gas from flowing from a defrosting load to flash tank <NUM> until a pressure of the hot gas at load exceeds a threshold. As low temperature compressor <NUM> continues supplying hot gas to the load during the defrost cycle, a pressure of the hot gas at load increases. The hot gas continues to linger at or in the load until the pressure of the hot gas exceeds a threshold controlled by valve <NUM>. As a result, heat transfer between the hot gas and the load is increased. When the pressure of the hot gas exceeds the threshold, the hot gas begins flowing through valve <NUM> to flash tank <NUM>.

In particular embodiments, when hot gas condenses in the defrosting load during a defrost cycle, flash tank <NUM> receives the refrigerant as both a vapor and a liquid. Flash tank <NUM> directs the liquid portion of the refrigerant to other loads, such as low temperature loads <NUM> and/or medium temperature load <NUM>. These loads then use the refrigerant to cool spaces proximate these loads. Flash tank <NUM> directs the vapor portion of the refrigerant to medium temperature compressor <NUM> through valve <NUM>.

Valve <NUM> controls the flow of vapor refrigerant or flash gas from flash tank <NUM> to medium temperature compressor <NUM>. In this manner, valve <NUM> controls an internal pressure of flash tank <NUM>. By opening valve <NUM> more, an internal pressure of flash tank <NUM> may decrease. By closing valve <NUM>, an internal pressure of flash tank <NUM> may increase. Valve <NUM> may be referred to as a flash gas bypass valve. <FIG> illustrates an example cooling system <NUM>. As seen in <FIG>, system <NUM> includes high side heat exchanger <NUM>, flash tank <NUM>, medium temperature load <NUM>, low temperature loads 120A and 120B, medium temperature compressor <NUM>, low temperature compressor <NUM>, valves 135A-C, and valve <NUM>.

Similar to system <NUM>, system <NUM> prevents a hot gas from flowing to flash tank <NUM> during a defrost cycle until a pressure of the hot gas exceeds a threshold. In this manner, heat transfer between the hot gas and a low temperature load <NUM> is increased.

Generally, high side heat exchanger <NUM>, flash tank <NUM>, medium temperature load <NUM>, low temperature loads 120A and 120B, medium temperature compressor <NUM>, low temperature compressor <NUM>, and valve <NUM> function similarly as they did in system <NUM>. For example, high side heat exchanger <NUM> removes heat from a refrigerant. Flash tank <NUM> stores the refrigerant. Medium temperature load <NUM> and low temperature loads 120A and 120B use the refrigerant to cool spaces proximate those loads. Low temperature compressor <NUM> compresses refrigerant from low temperature loads 120A and 120B. Medium temperature compressor <NUM> compresses refrigerant from medium temperature load <NUM> and low temperature compressor <NUM>. Valves 135A-C open and close to control the flow of hot gas to the loads. During the defrost cycle, low temperature compressor <NUM> directs refrigerant through a valve 135A-C to a load to defrost the load.

An important difference between system <NUM> and system <NUM> is the use of valve <NUM> and the absence of valve <NUM>. In system <NUM>, instead of using valve <NUM> to control the flow of hot gas from a load to flash tank <NUM> during the defrost cycle, valve <NUM> is used to control an internal pressure of flash tank <NUM>. The internal pressure of flash tank <NUM> then prevents hot gas from flowing from the defrosting load to flash tank <NUM> until a pressure of the hot gas is greater than the internal pressure of flash tank <NUM>. In this manner, system <NUM> achieves the same result as system <NUM> without using valve <NUM>, which makes system <NUM> cost less than system <NUM> in certain instances. As in system <NUM>, valve <NUM> controls the internal pressure of flash tank <NUM> by allowing a certain amount of flash gas and/or vapor refrigerant to flow from flash tank <NUM> to medium temperature <NUM>.

FIGURE <NUM> is a flow chart illustrating a method <NUM> of operating an example cooling system. In particular embodiments, certain portions of system <NUM> and/or system <NUM> perform the steps of method <NUM>. By performing method <NUM>, the heat transfer between a hot gas and a low temperature load is increased during a defrost cycle.

In step <NUM>, a high side heat exchanger removes heat from a refrigerant. A flash tank stores the refrigerant in step <NUM>. In step <NUM>, it is determined whether the system is in a first mode of operation such as, for example, a regular refrigeration mode. If the system is in the regular refrigeration mode, then a load such as a medium temperature load uses the refrigerant to cool a first space in step <NUM>. In step <NUM>, a second load, such as a low temperature load, uses the refrigerant to cool a second space. A third load, such as another low temperature load, uses the refrigerant to cool a third space in step <NUM>. In step <NUM>, a low temperature compressor compresses the refrigerant from the two low temperature loads. In step <NUM>, a medium temperature compressor compresses the refrigerant from the medium temperature load and the low temperature compressor.

If it is determined in step <NUM> that the system is not in a regular refrigeration cycle and instead is in a second mode of operation such as, for example, a defrost cycle, then the system proceeds to use hot gas to defrost a low temperature load. In step <NUM>, the medium temperature load uses the refrigerant to cool the first space. In step <NUM>, a low temperature load uses the refrigerant to cool the second space. The low temperature compressor compresses the refrigerant from the low temperature load in step <NUM>. The medium temperature compressor compresses the refrigerant from the medium temperature load in step <NUM>. In step <NUM>, the low temperature compressor directs the refrigerant to a third load, such as the low temperature load, to defrost the low temperature load. In step <NUM>, a valve prevents the refrigerant at the third load from flowing to the flash tank until a pressure the refrigerant at the third load exceeds a threshold. In some embodiments, the valve is a regulating valve between the low temperature load being defrosted and the flash tank. In other embodiments, the valve is a flash gas bypass valve positioned between the flash tank and the medium temperature compressor.

Modifications, additions, or omissions may be made to method <NUM> depicted in <FIG>. Method <NUM> may include more, fewer, or other steps. For example, steps may be performed in parallel or in any suitable order. While discussed as systems <NUM> and/or <NUM> (or components thereof) performing the steps, any suitable component of systems <NUM> and/or <NUM> may perform one or more steps of the method.

Modifications, additions, or omissions may be made to the systems and apparatuses described herein without departing from the scope of the disclosure. The components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses may be performed by more, fewer, or other components. Additionally, operations of the systems and apparatuses may be performed using any suitable logic comprising software, hardware, and/or other logic. As used in this document, "each" refers to each member of a set or each member of a subset of a set.

Claim 1:
An apparatus (<NUM>) comprising:
a flash tank (<NUM>) configured to store a refrigerant;
a first load (<NUM>) configured to use the refrigerant from the flash tank (<NUM>) to cool a first space proximate the first load (<NUM>);
a second load (120A);
a third load (120B);
a first compressor (<NUM>);
a second compressor (<NUM>); and
a valve (<NUM>,<NUM>), during a first mode of operation:
the second load (120A) is configured to use the refrigerant from the flash tank (<NUM>) to cool a second space proximate the second load (120A);
the third load (120B) is configured to use the refrigerant from the flash tank (<NUM>) to cool a third space proximate the third load (120B);
the second compressor (<NUM>) is configured to compress the refrigerant from the second load (120A) and the third load (120B); and
the first compressor (<NUM>) is configured to compress the refrigerant from the first load (<NUM>) and the second compressor (<NUM>), and
during a second mode of operation:
the second load (120A) is configured to use the refrigerant from the flash tank (<NUM>) to cool the second space proximate the second load (120A);
the second compressor (<NUM>) is configured to compress the refrigerant from the second load (120A) and to direct a portion of the compressed refrigerant to the third load (120B) to defrost the third load (120B) and to direct the portion of the compressed refrigerant after defrosting the third load (120B) to the flash tank (<NUM>);
the first compressor (<NUM>) is configured to compress the refrigerant from the first load (<NUM>) and the remaining portion of the refrigerant from the second compressor (<NUM>); and
the valve (<NUM>,<NUM>) is configured to prevent the portion of the refrigerant at the third load (120B) from flowing to the flash tank (<NUM>) until a pressure of the refrigerant at the third load (120B) exceeds a threshold;
characterized in that the valve (<NUM>,<NUM>) is a regulating valve and is configured to control the threshold.