Patent Description:
Cooling systems may cycle a refrigerant (e.g., carbon dioxide refrigerant) to cool various spaces.

<CIT> discloses a refrigerant circulating system designed for incorporation in the refrigeration system of an industrial plant such as may operate with multi-stages of compression and with evaporators discharging to the high stage compressor suction as well as to the booster compression suction. The apparatus disclosed in <FIG> of <CIT> comprises a system comprising: a first low side heat exchanger configured to use refrigerant to cool a first space proximate the first low side heat exchanger wherein the refrigerant discharged by the first low side heat exchanger comprises a liquid portion and a gaseous portion; a second low side heat exchanger configured to use refrigerant to cool a second space proximate the second low side heat exchanger wherein the refrigerant discharged by the second low side heat exchanger comprises a liquid portion and a gaseous portion; an accumulator configured to collect the refrigerant discharged by the first and second low side heat exchangers; a first compressor configured to compress the refrigerant from the accumulator; and a second compressor configured to compress the refrigerant discharged by the first compressor.

<CIT> discloses a refrigeration cycle apparatus including: a main circuit comprising an evaporator, a first compressor, an intercooler, a second compressor and a condenser which are connected in this order; and an evaporation-side circulation path that allows a refrigerant liquid retained in the evaporator to circulate via a heat exchanger for heat absorption.

<CIT> discloses a refrigeration system with an economizer for transcritical operation, in which a refrigeration circuit has a compressor operating at least on three pressure levels: section pressure on the compressor suction side; intermediate pressure at an economizer connection; and discharge pressure on a discharge side.

<CIT> discloses a refrigeration cycle constituting an air conditioner, comprising: a compressor; a radiator; an accumulator; an expansion device; an evaporator; a turbine pump arranged in the accumulator and having a turbine rotated by refrigerant introduced from the radiator releasing the refrigerant into the accumulator, and a pump rotating together with the turbine to thereby compress refrigerant introduced from the evaporator and release this refrigerant into the accumulator.

<CIT> discloses a flash tank of a two-stage compression heat pump system that can perform cooling and heating with a separate type intercooler and a high-stage compressor protection device.

Cooling systems may cycle a refrigerant (e.g., carbon dioxide refrigerant) to cool various spaces. One type of cooling system is a refrigeration and/or freezing system (e.g., refrigeration shelves and freezers in a grocery store). These systems typically include a medium temperature section (e.g., refrigeration shelves) and a low temperature section (e.g., freezers). The refrigerant from the low temperature section is fed into the medium temperature section to stabilize the medium temperature section (e.g., a medium temperature compressor). Some installations, however, do not include a complete medium temperature section. For example, these installations may be lacking medium temperature low side heat exchangers (e.g., refrigeration shelves). As a result, the medium temperature compressor compresses mostly refrigerant from the low temperature section. This refrigerant has a high temperature, which causes the efficiency of the medium temperature compressor to drop.

This disclosure contemplates an unconventional cooling system that floods the low temperature low side heat exchangers (e.g., freezers) in the system. An accumulator is positioned between the low temperature low side heat exchangers and the low temperature compressor. The accumulator collects the refrigerant (both liquid and vapor) from the flooded low temperature low side heat exchangers. Refrigerant discharged by the low temperature compressor is fed through the accumulator so that heat can be transferred to the refrigerant collected in the accumulator. As a result, the temperature of the refrigerant discharged by the low temperature compressor drops before that refrigerant reaches the medium temperature compressor. In this manner, the temperature of the refrigerant at the medium temperature compressor reduced, which improves the efficiency of the medium temperature compressor. Embodiments of this cooling system are described below.

According to the invention there is provided a system and a method as defined by the appended claims.

Certain embodiments provide one or more technical advantages. For example, an embodiment according to the invention transfers heat from refrigerant from a low temperature compressor to refrigerant discharged by low temperature low side heat exchangers to reduce the temperature of the refrigerant from the low temperature compressor before that refrigerant reaches a medium temperature compressor. As a result, the efficiency of the medium temperature compressor improves. 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 disclosure 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 floods the low temperature low side heat exchangers (e.g., freezers) in the system. An accumulator is positioned between the low temperature low side heat exchangers and the low temperature compressor. The accumulator collects the refrigerant (both liquid and vapor) from the flooded low temperature low side heat exchangers. Refrigerant discharged by the low temperature compressor is fed through the accumulator so that heat can be transferred to the refrigerant collected in the accumulator. As a result, the temperature of the refrigerant discharged by the low temperature compressor drops before that refrigerant reaches the medium temperature compressor. In this manner, the temperature of the refrigerant at the medium temperature compressor is reduced, which improves the efficiency of the medium temperature compressor. The cooling system will be described using <FIG>. <FIG> will describe an existing cooling system. <FIG> describe the cooling system that floods low temperature low side heat exchangers.

<FIG> illustrates an example cooling system <NUM>. As shown in <FIG>, system <NUM> includes a high side heat exchanger <NUM>, a flash tank <NUM>, low temperature low side heat exchangers 106A and 106B, a low temperature compressor <NUM>, a medium temperature compressor <NUM>, an oil separator <NUM>, and a valve <NUM>. Generally, system <NUM> cycles a refrigerant to cool spaces proximate the low side heat exchangers 106A and 106B. Cooling system <NUM> or any cooling system described herein may include any number of low side heat exchangers.

High side heat exchanger <NUM> removes heat from a refrigerant. When heat is removed from the refrigerant, the refrigerant is cooled. High side heat exchanger <NUM> may be 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 low side heat exchanger <NUM> and medium temperature low side heat exchanger <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 low side heat exchangers 106A and 106B and medium temperature compressor <NUM>.

When the refrigerant reaches low temperature low side heat exchangers 106A and 106B, the refrigerant removes heat from the air around low temperature low side heat exchangers 106A and 106B. For example, the refrigerant cools metallic components (e.g., metallic coils, plates, and/or tubes) of low temperature low side heat exchangers 106A and 106B as the refrigerant passes through low temperature low side heat exchangers 106A and 106B. These metallic components may then cool the air around them. 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 low side heat exchangers 106A and 106B, the refrigerant may change from a liquid state to a gaseous state as it absorbs heat. Any number of low temperature low side heat exchangers <NUM> may be included in any of the disclosed cooling systems.

Refrigerant flows from low temperature low side heat exchangers 106A and 106B to compressors <NUM> and <NUM>. The disclosed cooling systems may include 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 highpressure gas. Low temperature compressor <NUM> compresses refrigerant from low temperature low side heat exchangers 106A and 106B and sends the compressed refrigerant to medium temperature compressor <NUM>. Medium temperature compressor <NUM> compresses the refrigerant from low temperature compressor <NUM>.

Oil separator <NUM> separates an oil from the refrigerant before the refrigerant enters high side heat exchanger <NUM>. The oil may be introduced by certain components of system <NUM>, such as low temperature compressor <NUM> and/or medium temperature compressor <NUM>. By separating out the oil, the efficiency of high side heat exchanger <NUM> is maintained. If oil separator <NUM> is not present, then the oil may clog high side heat exchanger <NUM> and/or low temperature low side heat exchangers 106A and 106B, which may reduce the heat transfer efficiency of system <NUM>, high side heat exchanger <NUM>, and/or low temperature low side heat exchangers 106A and 106B.

Valve <NUM> controls a flow of flash gas from flash tank <NUM>. When valve <NUM> is closed, flash tank <NUM> may not discharge flash gas through valve <NUM>. When valve <NUM> is opened, flash tank <NUM> may discharge flash gas through valve <NUM>. In this manner, valve <NUM> may also control an internal pressure of flash tank <NUM>. Valve <NUM> directs flash gas to medium temperature compressor <NUM>. Medium temperature compressor <NUM> compresses the flash gas along with refrigerant from low temperature compressor <NUM>. Valve <NUM> may also be referred to as a flash gas bypass valve.

As seen in <FIG>, system <NUM> does not include medium temperature low side heat exchangers (e.g., refrigerated shelves in a grocery setting). These medium temperature low side heat exchangers typically discharge a refrigerant that mixes with and cools the refrigerant from low temperature compressor <NUM> before that refrigerant reaches medium temperature compressor <NUM>. Due to their absence from system <NUM>, the refrigerant that reaches medium temperature compressor <NUM> includes mostly the hot refrigerant from low temperature compressor <NUM>. The increased temperature of the refrigerant reaching medium temperature compressor <NUM> results in a degradation of the efficiency of medium temperature compressor <NUM>.

This disclosure contemplates an unconventional cooling system that floods low temperature low side heat exchangers 106A and 106B (e.g., freezers) in system <NUM>. An accumulator is positioned between low temperature low side heat exchangers 106A and 106B and low temperature compressor <NUM>. The accumulator collects the refrigerant (both liquid and vapor) from the flooded low temperature low side heat exchangers 106A and 106B. Refrigerant discharged by low temperature compressor <NUM> is fed through the accumulator so that heat can be transferred to the refrigerant collected in the accumulator. As a result, the temperature of the refrigerant discharged by low temperature compressor <NUM> drops before that refrigerant reaches medium temperature compressor <NUM>. In this manner, the temperature of the refrigerant at medium temperature compressor <NUM> is reduced, which improves the efficiency of medium temperature compressor <NUM>. Embodiments of the cooling system are described below using <FIG>. These figures illustrate embodiments that include a certain number of low side heat exchangers and compressors for clarity and readability. These embodiments may include any suitable number of low side heat exchangers and compressors.

<FIG> illustrates a cooling system <NUM>. As seen in <FIG>, system <NUM> includes a high side heat exchanger <NUM>, a flash tank <NUM>, low temperature load side heat exchangers 106A and 106B, a low temperature compressor <NUM>, a medium temperature compressor <NUM>, an oil separator <NUM>, a valve <NUM>, an accumulator <NUM>, and a valve <NUM>. Generally, system <NUM> floods low temperature low side heat exchanger 106A and 106B such that the discharge from low temperature low side heat exchangers 106A and 106B include a liquid portion and a vapor portion. Accumulator <NUM> collects the refrigerant discharged from low temperature low side heat exchangers 106A and 106B and transfers heat from the discharge from low temperature compressor <NUM> to the collected refrigerant. As a result the refrigerant discharged by low temperature compressor <NUM> is cooled before reaching medium temperature compressor <NUM>, which improves the efficiency of medium temperature compressor <NUM>.

Several of the components of system <NUM> operate similarly as they did in system <NUM>. High side heat exchanger <NUM> removes heat from a refrigerant. Flash tank <NUM> stores refrigerant. Low temperature low side heat exchangers 106A and 106B use refrigerant from flash tank <NUM> to cool spaces proximate low temperature low side heat exchangers 106A and 106B. Low temperature compressor <NUM> compresses refrigerant. Medium temperature compressor <NUM> compresses refrigerant from low temperature compressor <NUM> and flash tank <NUM>. Oil separator <NUM> separates an oil from refrigerant. Valve <NUM> controls a flow of flash gas from flash tank <NUM> to medium temperature compressor <NUM>.

As discussed above, the lack of medium temperature low side heat exchangers in many cooling systems may cause medium temperature compressor <NUM> to compress mostly refrigerant from low temperature compressor <NUM>. Because this refrigerant is very hot, the efficiency of medium temperature compressor <NUM> suffers. System <NUM> improves the efficiency in medium temperature compressor <NUM> over other cooling systems by flooding low temperature low side heat exchangers 106A and 106B and by transferring heat from the discharge of low temperature compressor <NUM> to the refrigerant discharged by low temperature low side heat exchangers 106A and 106B, in certain embodiments.

Low temperature low side heat exchangers 106A and 106B are flooded in system <NUM>. Generally, to flood low temperature low side heat exchangers 106A and 106B, more refrigerant than low temperature low side heat exchangers 106A and 106B can evaporate is directed to low temperature low side heat exchangers 106A and 106B. As a result, not all of the refrigerant that is directed to low temperature low side heat exchangers 106A and 106B is evaporated within low temperature low side heat exchangers 106A and 106B. As a result, the refrigerant discharges by low temperature low side heat exchangers 106A and 106B will include a vapor portion and a liquid portion. The discharged refrigerant is directed to accumulator <NUM>.

Accumulator <NUM> collects the refrigerant discharged by low temperature low side heat exchangers 106A and 106B. Refrigerant may enter accumulator <NUM> through inlet <NUM>. Inlet <NUM> may be a pipe or a tube that directs refrigerant into the body of accumulator <NUM>. Inlet <NUM> may be positioned at a top surface of accumulator <NUM>. Because the refrigerant discharged from low temperature low side heat exchangers 106A and 106B include both a liquid portion and a vapor portion, the refrigerant entering accumulator <NUM> also includes a liquid portion <NUM> and a vapor portion <NUM>. Liquid portion <NUM> drops to and collects at the bottom of accumulator <NUM>. Vapor portion <NUM> collects in the space above liquid portion <NUM>. As more refrigerant is collected by accumulator <NUM>, a level <NUM> of liquid portion <NUM> in accumulator <NUM> rises.

Accumulator <NUM> discharges refrigerant through outlet <NUM>. Outlet <NUM> may be a pipe or a tube that directs refrigerant out of accumulator <NUM> and to low temperature compressor <NUM>. Outlet <NUM> may have a U-shaped curvature that exits accumulator <NUM> at a top surface of accumulator <NUM>. As a result, a first end of outlet <NUM> is contained within accumulator <NUM> at a position that is vertically higher than level <NUM>. A second end of outlet <NUM> is outside accumulator <NUM>. Vapor portion <NUM> enters the first end of outlet <NUM> and is carried out of accumulator <NUM> through the second end of outlet <NUM>. Due to the shape of outlet <NUM>, vapor portion <NUM> of refrigerant in accumulator <NUM> may enter outlet <NUM>. Liquid portion <NUM> of refrigerant in accumulator <NUM> may not enter outlet <NUM> unless liquid portion <NUM> rises above the point at which vapor portion <NUM> enters outlet <NUM>. Certain safeguards discussed below may be implemented to control level <NUM> to prevent liquid portion <NUM> from entering outlet <NUM>. As a result, liquid refrigerant is prevented from entering low temperature compressor <NUM>, which protects low temperature compressor <NUM> from liquid slugging.

Discharge from low temperature compressor <NUM> is directed into accumulator <NUM> via piping <NUM>. Piping <NUM> carries refrigerant from low temperature compressor <NUM> into accumulator <NUM>. Piping <NUM> may coil or wind within accumulator <NUM> to increase the heat transfer area as the refrigerant from low temperature compressor <NUM> flows through accumulator <NUM>. Piping <NUM> then directs the refrigerant to medium temperature compressor <NUM>.

As discussed previously, the refrigerant from low temperature compressor <NUM> has a high temperature. As that refrigerant flows through accumulator <NUM>, the heat in that refrigerant is transferred to the refrigerant collected in accumulator <NUM>. The heat may be transferred to both the liquid portion <NUM> and the vapor portion <NUM>. As a result, the refrigerant discharged by low temperature compressor <NUM> is cooled before that refrigerant is directed to medium temperature compressor <NUM>. As liquid portion <NUM> absorbs heat from the refrigerant in piping <NUM>, liquid portion <NUM> may evaporate. The evaporated refrigerant may then drift upwards in accumulator <NUM> and enter outlet <NUM>. As a result, the level <NUM> of liquid portion <NUM> may drop as heat from the discharge of low temperature compressor <NUM> is transferred to liquid portion <NUM>.

Sight glasses <NUM> are coupled to accumulator <NUM>. Sight glasses <NUM> allow visibility into the interior of accumulator <NUM>. Importantly, through sight glasses <NUM>, an operator can see the level <NUM> of liquid portion <NUM>. If the level <NUM> is too high, the operator may determine that more heat should be transferred to liquid portion <NUM> to evaporate liquid portion <NUM>. If the level <NUM> is too low, the operator may determine that less heat should be transferred to liquid portion <NUM> to allow more liquid refrigerant to collect in accumulator <NUM>.

Valve <NUM> controls a flow of refrigerant from low temperature compressor <NUM> to medium compressor <NUM>. Generally, valve <NUM> allows refrigerant from low temperature compressor <NUM> to bypass accumulator <NUM>. When valve <NUM> is closed, the refrigerant from low temperature compressor <NUM> flows through accumulator <NUM> to medium temperature compressor <NUM>. When valve <NUM> is partially open or fully open, some or all of the refrigerant discharged by low temperature compressor <NUM> bypasses accumulator <NUM> enroute to medium temperature compressor <NUM>. Valve <NUM> may open or close based on the level <NUM> of liquid portion <NUM> in accumulator <NUM>. For example, when level <NUM> is high, valve <NUM> may close to direct more refrigerant from low temperature compressor <NUM> to accumulator <NUM> to increase heat transfer. When level <NUM> is low, valve <NUM> may open to allow refrigerant from low temperature compressor <NUM> to bypass accumulator <NUM>, so that additional liquid refrigerant can collect in accumulator <NUM>.

Sensor <NUM> may detect level <NUM> of liquid portion <NUM> in accumulator <NUM>. In certain embodiments, sensor <NUM> may determine when level <NUM> exceeds or falls below a threshold. If level <NUM> exceeds the threshold, sensor <NUM> may cause valve <NUM> to close. As a result, more refrigerant from low temperature compressor <NUM> flows into accumulator <NUM>, increasing heat transfer to evaporate liquid portion <NUM>. Level <NUM> may then drop below the threshold. When sensor <NUM> detects that level <NUM> is below the threshold, sensor <NUM> may cause valve <NUM> to open. Some or all of the refrigerant from low temperature compressor <NUM> may then flow through valve <NUM> to medium temperature compressor <NUM>, bypassing accumulator <NUM>. As a result, less heat transfer occurs within accumulator <NUM> and level <NUM> may increase. In this manner, the amount of liquid portion <NUM> in accumulator <NUM> may be controlled.

<FIG> is a flowchart illustrating a method <NUM> of operating the cooling system <NUM> of <FIG>. Generally, one or more components of system <NUM> perform the steps of method <NUM>. In particular embodiments, by performing method <NUM>, the efficiency of medium temperature compressor <NUM> is improved.

In step <NUM>, flash tank <NUM> stores a refrigerant. Low temperature low side heat exchanger 106A uses the refrigerant to cool a space in step <NUM>. Low temperature low side heat exchanger 106B uses the refrigerant to cool a space in step <NUM>. Both low temperature low side heat exchangers 106A and 106B are flooded such that the discharge of low temperature low side heat exchangers 106A and 106B includes both a liquid portion and a vapor portion.

Accumulator <NUM> collects the refrigerant from low temperature low side heat exchangers 106A and 106B in step <NUM>. The collected refrigerant includes both a liquid portion <NUM> and a vapor portion <NUM>. Liquid portion <NUM> collects at the bottom of accumulator <NUM>. Vapor portion <NUM> is discharged from accumulator <NUM>. Low temperature compressor <NUM> compresses the refrigerant from accumulator <NUM>. The compressed refrigerant may then be directed back to accumulator <NUM>, so that heat within the compressed refrigerant may be transferred to the refrigerant collecting in accumulator <NUM>. In step <NUM>, accumulator <NUM> transfers heat from the refrigerant from low temperature compressor <NUM> to the refrigerant collecting within accumulator <NUM>. As a result, the refrigerant from low temperature compressor <NUM> is cooled before reaching the medium temperature compressor <NUM>. Additionally, liquid portion <NUM> may experience some evaporation, and the evaporated refrigerant may be directed out of accumulator <NUM>.

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 system <NUM>(or components thereof) performing the steps, any suitable component of systems <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 invention. The components of the systems and apparatuses may be integrated or separated. 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.

This disclosure may refer to a refrigerant being from a particular component of a system (e.g., 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 low temperature low side heat exchanger) even though there may be other intervening components between the particular component and the destination of the refrigerant. For example, the low temperature compressor receives a refrigerant from the low temperature low side heat exchanger even though there is an accumulator between the low temperature low side heat exchanger and the low temperature compressor.

Claim 1:
A system (<NUM>) comprising:
a first low side heat exchanger (106A) configured to use refrigerant to cool a first space proximate the first low side heat exchanger, the refrigerant discharged by the first low side heat exchanger comprises a liquid portion and a gaseous portion;
a second low side heat exchanger (106B) configured to use refrigerant to cool a second space proximate the second low side heat exchanger, the refrigerant discharged by the second low side heat exchanger comprises a liquid portion and a gaseous portion;
an accumulator (<NUM>) configured to collect the refrigerant discharged by the first and second low side heat exchangers (106A, 106B);
a first compressor (<NUM>) configured to compress the refrigerant from the accumulator (<NUM>);
a second compressor (<NUM>) configured to compress the refrigerant discharged by the first compressor (<NUM>),
wherein the accumulator (<NUM>) comprises piping (<NUM>) configured to carry refrigerant from the first compressor (<NUM>) into the accumulator (<NUM>) to transfer heat from the refrigerant discharged by the first compressor (<NUM>) to the refrigerant collected by the accumulator (<NUM>) from the first and second low side heat exchangers (106A, 106B), the piping (<NUM>) directing the refrigerant to the second compressor (<NUM>),
the system (<NUM>) further comprising a valve (<NUM>) configured to control a flow of the refrigerant discharged by the first compressor (<NUM>), such that the refrigerant discharged by the first compressor (<NUM>) flows through the valve (<NUM>) and to the second compressor (<NUM>) bypassing the accumulator (<NUM>) when the valve (<NUM>) is open, and the refrigerant discharged by the first compressor (<NUM>) flows through the accumulator (<NUM>) and to the second compressor (<NUM>) when the valve (<NUM>) is closed.