CO2 BOOSTER SYSTEM WITH MEDIUM TEMPERATURE CHILLER

Description

TECHNICAL FIELD

This disclosure relates to cooling systems, particularly cooling systems that use carbon dioxide (CO₂) as a refrigerant.

BACKGROUND

Refrigeration systems are often used to provide cooling to temperature-controlled display devices (e.g., cases, merchandisers, etc.) in supermarkets, cold storage, refrigerated warehouses, process facilities, and other similar facilities. Vapor compression refrigeration systems are a type of refrigeration system that provides such cooling by circulating a fluid refrigerant (e.g., a liquid and/or vapor) through a thermodynamic vapor compression cycle. In a vapor compression cycle, the refrigerant is typically (1) compressed to a high temperature high pressure state (e.g., by a compressor of the refrigeration system), (2) cooled/condensed to a lower temperature state (e.g., in a gas cooler or condenser which absorbs heat from the refrigerant), (3) expanded to a lower pressure (e.g., through an expansion valve), and (4) evaporated to provide cooling by absorbing heat into the refrigerant.

SUMMARY

The present disclosure relates to systems and methods for cooling temperature-controlled devices, and methods of installing and retrofitting cooling systems for temperature-controlled devices.

Implementations of the present disclosure include a system for cooling temperature-controlled devices in a facility that includes a medium temperature subsystem, a low temperature subsystem, and a receiver. The medium temperature subsystem is configured to cool a plurality of medium temperature loads. The medium temperature subsystem includes a chilled fluid heat exchanger, a medium temperature chiller circuit, and one or more medium temperature compressors. The chilled fluid heat exchanger includes a first side and a second side. The medium temperature chiller circuit includes a pump configured to circulate a chiller fluid between at least one of the medium temperature loads and the first side of the chilled fluid heat exchanger. The low temperature subsystem is configured to cool a plurality of low temperature loads. The low temperature subsystem includes one or more low temperature compressors and one or more low temperature evaporators. The receiver is configured to supply CO₂ refrigerant to the second side of the heat exchanger of the medium temperature subsystem and to at least one of the low temperature loads of the low temperature subsystem.

In some implementations, at least one of the medium temperature loads comprises a heat-generating process, and the system is configured to control one or more conditions of the heat-generating process.

In some implementations, at least one of the medium temperature loads comprises heat-generating equipment, and the system is configured to control one or more conditions of the heat-generating equipment.

In some implementations, at least one of the medium temperature loads comprises a comfort cooling system, and the system is configured to control one or more environmental conditions of the facility.

In some implementations, the chilled fluid heat exchanger is configured such that at least a portion of the CO₂ refrigerant evaporates as the passes through the second side of the chilled fluid heat exchanger.

In some implementations, the one or more medium temperature compressors are transcritical compressors. The medium temperature subsystem is configured to circulate a portion of the CO₂ refrigerant through the second side of the chilled fluid heat exchanger to at least one of the one or more transcritical compressors.

In some implementations, the receiver includes a flash gas bypass exit. At least one of the one or more medium temperature compressors is configured to receive a mixture of flash gas passing through the flash gas bypass exit and fluid from the exit of the second side of the chilled fluid heat exchanger.

In some implementations, the one or more low temperature compressors are subcritical compressors.

In some implementations, the chiller fluid includes glycol.

In some implementations, the medium temperature subsystem and the low temperature subsystem are included in a CO₂ transcritical booster system,

In some implementations, the system includes a gas cooler and a gas defrost conduit in fluid communication with the gas cooler. The gas defrost unit is configured to supply hot gas to at least one of the medium temperature loads or at least one of the low temperature loads.

In some implementations, the medium temperature subsystem includes one or more medium temperature evaporators configured to receive CO₂ refrigerant from the receiver and to cool one or more medium temperature loads.

In some implementations, the low temperature subsystem includes a low temperature chiller heat exchanger and a low temperature chiller circuit. The low temperature chiller heat exchanger includes a first side and a second side. The low temperature chiller circuit includes a pump configured to circulate a low temperature chiller fluid between one or more low temperature loads and the first side of the low temperature chiller heat exchanger. The receiver is configured to provide CO₂ refrigerant to the second side of the low temperature chiller heat exchanger.

Other implementations of the present disclosure include a system for cooling temperature-controlled devices that includes a medium temperature chiller system and a CO₂ transcritical booster system. The medium temperature chiller system includes a chilled fluid heat exchanger and a medium temperature chiller circuit. The chilled fluid heat exchanger includes a first side and a second side. The medium temperature chiller circuit is configured to circulate a chiller fluid between one or more medium temperature loads and the first side of the chilled fluid heat exchanger. The CO₂ transcritical booster system includes one or more transcritical compressors, one or more subcritical compressors, and a receiver. The receiver is configured to supply CO₂ refrigerant to the second side of the chilled fluid heat exchanger.

In some implementations, the chilled fluid heat exchanger is configured such that at least a portion of the CO₂ refrigerant evaporates as the CO₂ refrigerant passes through the second side of the chilled fluid heat exchanger.

In some implementations, the CO₂ transcritical booster system is configured to circulate a portion of the CO₂ refrigerant through the second side of the chilled fluid heat exchanger to at least one of the one or more transcritical compressors.

In some implementations, the receiver includes a flash gas bypass exit. At least one of the one or more transcritical compressors is configured to receive a mixture of flash gas passing through the flash gas bypass exit and refrigerant from the exit of the second side of the chilled fluid heat exchanger.

Other implementations of the present disclosure include a method that includes: identifying an existing refrigeration system that includes a medium temperature chiller loop; switching at least one of a plurality of medium temperature loads of the medium temperature chiller loop from the existing refrigeration system to a CO₂ refrigerant transcritical booster system; operating the CO₂ refrigerant transcritical booster system to cool the switched medium temperature loads; and, while the CO₂ refrigerant transcritical booster system is operating to cool the switched medium temperature loads, switching a plurality of direct exchange cooling loads from an existing direct exchange cooling system to the CO₂ refrigerant transcritical booster system.

In some implementations, switching at least one of a plurality of medium temperature loads of the medium temperature chiller loop from an existing refrigeration system to a CO₂ transcritical booster system includes switching the at least one medium temperature load from an existing chiller unit to a new chiller unit coupled to the CO₂ transcritical booster system.

In some implementations, the existing direct exchange cooling system is configured to circulate an HFC refrigerant.

In some implementations, switching the plurality of direct exchange cooling loads includes switching each of at least two of the plurality of direct exchange cooling loads one load at a time.

In some implementations, switching the at least one of the plurality of medium temperature loads of the medium temperature chiller loop includes switching each of at least two of the plurality of medium temperature loads one load at a time.

In some implementations, further including defrosting at least one of the medium temperature loads or the direct exchange cooling loads with a hot gas from the CO₂ transcritical booster system.

In some implementations, at least one of the direct exchange cooling loads is a comfort cooling load.

In some implementations, at least one of the direct exchange cooling loads is a low temperature load.

In some implementations, at least one of the direct exchange cooling loads is a medium temperature load.

Other implementations of the present disclosure include a method of cooling temperature-controlled devices in a facility that includes: fluidly coupling a plurality of medium temperature loads to a medium temperature chiller system; starting up a CO₂ transcritical booster system to provide CO₂ refrigerant to the medium temperature chiller system to remove heat from at least one of the medium temperature loads coupled to the medium temperature chiller system; operating the CO₂ transcritical booster system to cool the at least one medium temperature load coupled to the medium temperature chiller system: while the CO₂ transcritical booster system is operating to cool the at least one medium temperature load coupled to the medium temperature chiller system; starting cooling to one or more direct exchange cooling loads in the facility; and operating the CO₂ transcritical booster system to cool at least one of the direct exchange cooling loads.

In some implementations, starting cooling to the one or more direct exchange cooling loads in the facility includes starting a flow of CO₂ refrigerant from the CO₂ transcritical booster system to one or more evaporators coupled to one or more direct exchange cooling loads in the facility.

In some implementations, starting cooling to the one or more direct exchange cooling loads in the facility includes switching fluid flowing through the evaporators from an HFC refrigerant in an existing cooling system to CO₂ refrigerant in the CO₂ transcritical booster system.

In some implementations, at least one of the one or more evaporators is fluidly coupled to a suction inlet of one or more subcritical compressors of the CO₂ transcritical booster system and cools a low temperature load.

In some implementations, at least one of the one or more evaporators is fluidly coupled to a suction inlet of one or more transcritical compressors of the CO₂ transcritical booster system and cools a medium temperature load.

In some implementations, the one or more evaporators comprise a plurality of evaporators, and starting a flow of CO₂ refrigerant from the CO₂ transcritical booster system to one or more evaporators includes starting a flow to each of two or more subsets of the plurality of evaporators in succession to one another.

In some implementations, starting a flow to each of two or more subsets of the plurality of evaporators includes starting a flow to at least one of the subsets of the plurality of evaporators one evaporator at a time.

Particular implementations of the subject matter described in this specification can be implemented so as to realize one or more of the following advantages.

Implementations of the present disclosure may make modifying existing cooling systems to operate on natural refrigerants easier to accomplish.

Implementations of the present disclosure may allow for minimal disruption to operations during cooling system upgrades by allowing changes to the cooling system to take place in smaller steps, while still operating correctly.

Implementations of the present disclosure may eliminate the need to retrofit large areas of a facility all at once.

Implementations of the present disclosure may allow for retrofit of direct exchange cooling systems to CO₂ refrigerant to be accomplished more smoothly.

Implementations of the present disclosure may allow rack compressors of a booster system to have enough load to operate with no additional connected load.

Implementations of the present disclosure may reduce the amount of high-pressure refrigerants required in a facility.

Implementations of the present disclosure may allow for continued use of existing piping and other components of an existing cooling system.

Implementations of the present disclosure may allow for an instant hot gas defrost operation even with only a small direct exchange load (e.g., with only one direct exchange circuit connected).

The details of one or more implementations of the subject matter of this disclosure are set forth in the accompanying drawings and the description. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a CO₂ transcritical booster system system with a medium temperature chiller according to an illustrative implementation.

FIG. 2 is a block diagram illustrating a retrofit of a cooling system according to an illustrative implementation.

FIG. 3 is a flow diagram of an example process that can be implemented in an existing facility according to some implementations.

FIG. 4 is a flow diagram of an example process that can be implemented in a new facility according to some implementations.

FIG. 5 is a block diagram of a CO₂ transcritical booster system system with a low temperature chiller according to an illustrative implementation.

DETAILED DESCRIPTION

In some implementations, a chilled fluid heat exchanger is used with a CO₂ transcritical booster system to cool products in refrigerated cases and/or cooler boxes. In some implementations, a chiller is included in a CO₂ transcritical booster system when a cooling system is first installed in a facility. In other implementations, a cooling system is retrofitted to include a CO₂ transcritical booster system that provides cooling to a chilled fluid loop. Methods described herein may allow for ease of startup using a medium temperature (MT) chiller coupled to, or incorporated into, the CO₂ transcritical booster system to partially load the system, allowing small additional loads (either medium temperature or low temperature) to be added over time rather than all at once.

In some implementations, a medium temperature chiller is operated as a medium temperature load of a CO₂ transcritical booster system. The chilled fluid in the medium temperature chiller provides cooling to any heat exchangers (including evaporator coils) connected to it for cooling of product in refrigerated cases and/or walk-in cooler boxes. The medium temperature chiller can be incorporated into a CO₂ transcritical booster system or connected to it.

In various implementations, the CO₂ transcritical booster system may or may not have low temperature and/or medium temperature direct expansion loads, as well as a medium temperature chiller to produce chilled fluid for medium temperature applications.

Examples of refrigeration systems that incorporate or are coupled to chillers are described below. Referring generally to the Figures, a CO₂ refrigeration system is shown, according to various exemplary implementations. The CO₂ refrigeration system may be a vapor compression refrigeration system which uses primarily carbon dioxide (i.e., CO₂) as a refrigerant. In some implementations, a CO₂ transcritical booster system is used to provide cooling for temperature-controlled display devices in a supermarket or other similar facility.

FIG. 1 is a block diagram of a CO₂ refrigeration system according to an exemplary implementation. CO₂ refrigeration system 100 may be a vapor compression refrigeration system which uses primarily carbon dioxide (CO₂) as a refrigerant. However, it is contemplated that, in some implementations, other refrigerants can be substituted for CO₂.

CO₂ refrigeration system 100 and is shown to include a system of pipes, conduits, or other fluid channels for transporting the CO₂ refrigerant between various components of CO₂ refrigeration system 100. The thermodynamic components of CO₂ refrigeration system 100 include a gas cooler/condenser 102, a high pressure valve 104, a receiver 106, a gas bypass valve 108, a medium temperature (“MT”) subsystem 110, a low temperature (“LT”) subsystem 112, gas defrost system 114, and a controller 116. Medium temperature (“MT”) subsystem 110 includes medium temperature chiller system 118.

Gas cooler/condenser 102 may be a heat exchanger or other similar device for removing heat from the CO₂ refrigerant. Gas cooler/condenser 102 is shown receiving CO₂ gas from fluid conduit 130. In some implementations, the CO₂ gas in fluid conduit 130 may have a pressure within a range from approximately 45 bar to approximately 100 bar (i.e., about 650 psig to about 1450 psig), depending on ambient temperature and other operating conditions. In some implementations, gas cooler/condenser 102 may partially or fully condense CO₂ gas into liquid CO₂ (e.g., if system operation is in a subcritical region). The condensation process may result in fully saturated CO₂ liquid or a two-phase liquid-vapor mixture (e.g., having a thermodynamic vapor quality between 0 and 1). In other implementations, gas cooler/condenser 102 may cool the CO₂ gas (e.g., by removing superheat) without condensing the CO₂ gas into CO₂ liquid (e.g., if system operation is in a supercritical region). In some implementations, the cooling/condensation process is an isobaric process. Gas cooler/condenser 102 is shown outputting the cooled and/or condensed CO₂ refrigerant into fluid conduit 132.

In some implementations, CO₂ refrigeration system 100 includes a temperature sensor and a pressure sensor configured to measure the temperature and pressure of the CO₂ refrigerant exiting gas cooler/condenser 102. Sensors can be installed along fluid conduit 132, within gas cooler/condenser 102, or otherwise positioned to measure the temperature and pressure of the CO₂ refrigerant exiting gas cooler/condenser 102. In some implementations, CO₂ refrigeration system 100 includes a condenser fan that provides airflow across gas cooler/condenser 102. The speed of the condenser fan can be controlled to increase or decrease the airflow across gas cooler/condenser 102 to modulate the amount of cooling applied to the CO₂ refrigerant within gas cooler/condenser 102. In some implementations, CO₂ refrigeration system 100 also includes a temperature sensor and/or a pressure sensor configured to measure the temperature and/or pressure of the ambient air that flows across gas cooler/condenser 102 to provide cooling for the CO₂ refrigerant contained therein.

High pressure valve 104 receives the cooled and/or condensed CO₂ refrigerant from fluid conduit 132 and outputs the CO₂ refrigerant to fluid conduit 134. High pressure valve 104 may control the pressure of the CO₂ refrigerant in gas cooler/condenser 102 by controlling an amount of CO₂ refrigerant permitted to pass through high pressure valve 104. In some implementations, high pressure valve 104 is a high pressure thermal expansion valve (e.g., if the pressure in fluid conduit 132 is greater than the pressure in fluid conduit 134). In such implementations, high pressure valve 104 may allow the CO₂ refrigerant to expand to a lower pressure state. The expansion process may be an isenthalpic and/or adiabatic expansion process, resulting in a two-phase flash of the high pressure CO₂ refrigerant to a lower pressure, lower temperature state. The expansion process may produce a liquid/vapor mixture (e.g., having a thermodynamic vapor quality between 0 and 1). In some implementations, the CO₂ refrigerant expands to a pressure of approximately 38 bar (e.g., about 550 psig), which corresponds to a temperature of approximately 40° F. The CO₂ refrigerant then flows from fluid conduit 134 into receiver 106. In some implementations, high pressure valve 104 can be eliminated and an ejector can function as both high pressure valve and ejector.

Receiver 106 collects the CO₂ refrigerant from fluid conduit 134. In some implementations, receiver 106 may be a flash tank or other fluid reservoir. Receiver 106 includes a CO₂ liquid portion and a CO₂ vapor portion and may contain a partially saturated mixture of CO₂ liquid and CO₂ vapor. In some implementations, receiver 106 separates the CO₂ liquid from the CO₂ vapor. In one implementation, the receiver operating pressure of receiver 106 is about 60 to 90 bar. In another implementation, the receiver operating pressure of receiver 106 is about 45 to 60 bar, or 45 bar to 90 bar.

CO₂ liquid may exit receiver 106 and pass into conduit 144 and conduit 146. Conduit 144 may be a liquid header leading to MT subsystem 110. Conduit 146 may be a liquid header leading to LT subsystem 112. The CO₂ vapor may exit receiver 106 through conduit 148. Conduit 148 is shown leading the CO₂ vapor to a gas bypass valve 108 (described in greater detail below).

In some implementations, CO₂ refrigeration system 100 includes temperature sensors and/or pressure sensors configured to measure the temperature and pressure within receiver 106. Sensors can be installed in or on receiver 106, or along any of the fluid conduits that contain CO₂ refrigerant at the same temperature and/or pressure as receiver 106, as the case may be.

MT subsystem 110 is shown to include medium temperature chiller system 118 and one or more transcritical compressors 150. Transcritical compressors 150 combine to form a compressor suction group for MT subsystem 110.

Medium temperature chiller system 118 includes chilled fluid heat exchanger 152 and medium temperature chiller circuit 154. Medium temperature chiller circuit 154 includes pump 156. As further described below, pump 156 can be operated to circulate chiller fluid between chilled fluid heat exchanger 152 and medium temperature loads 158 to cool medium temperature loads 158. In some implementations, pump 156 is controlled by controller 116.

Transcritical compressors 150 compress the CO₂ refrigerant into a superheated gas having a pressure within a range of approximately 45 bar to approximately 100 bar. The output pressure from transcritical compressors 150 may vary depending on ambient temperature and other operating conditions. In the example shown in FIG. 1, transcritical compressors 150 operate in a transcritical mode. In operation, the CO₂ discharge gas exits suction group transcritical compressors 150 and flows through conduit 130 into gas cooler/condenser 102.

LT subsystem 112 is shown to include one or more expansion valves 160, one or more LT evaporators 162, and one or more subcritical compressors 164. In various implementations, any number of expansion valves 160, LT evaporators 162, and subcritical compressors 164 may be present. In some implementations, LT subsystem 112 may be omitted and the CO₂ refrigeration system 100 may operate with an AC module interfacing with only MT subsystem 110.

Expansion valves 160 may be electronic expansion valves or other similar expansion valves. Expansion valves 160 are shown receiving liquid CO₂ refrigerant from fluid conduit 146 and outputting the CO₂ refrigerant to LT evaporators 162. Expansion valves 160 may cause the CO₂ refrigerant to undergo a rapid drop in pressure, thereby expanding the CO₂ refrigerant to a lower pressure, lower temperature two-phase state. The expansion process may be an isenthalpic and/or adiabatic expansion process. In certain implementations, expansion valves 160 may expand the CO₂ refrigerant to a lower pressure than expansion valves 160, thereby resulting in a lower temperature CO₂ refrigerant. Accordingly, LT subsystem 112 may be used in conjunction with a freezer system or other lower temperature display cases.

LT evaporators 162 are shown receiving the cooled and expanded CO₂ refrigerant from expansion valves 160. In some implementations, LT evaporators may be associated with display cases/devices (e.g., if CO₂ refrigeration system 100 is implemented in a supermarket setting). LT evaporators 162 may be configured to facilitate the transfer of heat from the display cases/devices into the CO₂ refrigerant. The added heat may cause the CO₂ refrigerant to evaporate partially or completely. In some implementations, the evaporation process may be an isobaric process.

LT evaporators 162 are shown outputting the CO₂ refrigerant via suction line 166, leading to subcritical compressors 164. Subcritical compressors 164 compress the CO₂ refrigerant. In some implementations, subcritical compressors 164 may compress the CO₂ refrigerant to a pressure of approximately 30 bar, having a saturation temperature of approximately 23° F. In this example, subcritical compressors 164 operate in a subcritical mode. Subcritical compressors 164 are shown outputting the CO₂ refrigerant through discharge line 172. Discharge line 172 may be fluidly connected with the suction (e.g., upstream) side of transcritical compressors 150.

CO₂ refrigeration system 100 is shown to include a gas bypass valve 108. Gas bypass valve 108 may receive the CO₂ vapor from fluid conduit 148 and output the CO₂ refrigerant to MT subsystem 110. In some implementations, gas bypass valve 108 is arranged in series with transcritical compressors 150. In other words, CO₂ vapor from receiver 106 may pass through both gas bypass valve 108 and transcritical compressors 150. Transcritical compressors 150 may compress the CO₂ vapor passing through gas bypass valve 108 from a low pressure state (e.g., approximately 30 bar or lower) to a high pressure state (e.g., approximately 45-100 bar).

Gas bypass valve 108 can be operated to control a flow of gas refrigerant from receiver 106 into suction line 159. Gas bypass valve 108 may be operated to regulate or control the pressure within receiver 106 (e.g., by adjusting an amount of CO₂ refrigerant permitted to pass through gas bypass valve 108). For example, gas bypass valve 108 may be adjusted (e.g., variably opened or closed) to adjust the mass flow rate, volume flow rate, or other flow rates of the CO₂ refrigerant through gas bypass valve 108. Gas bypass valve 108 may be opened and closed (e.g., manually, automatically, by a controller, etc.) as needed to regulate the pressure within receiver 106.

In some implementations, gas bypass valve 108 includes a sensor for measuring a flow rate (e.g., mass flow, volume flow, etc.) of the CO₂ refrigerant through gas bypass valve 108. In other implementations, gas bypass valve 108 includes an indicator (e.g., a gauge, a dial, etc.) from which the position of gas bypass valve 108 may be determined. This position may be used to determine the flow rate of CO₂ refrigerant through gas bypass valve 108, as such quantities (e.g., mass flow or volumetric flow or flow rate) may be proportional or otherwise related.

In some implementations, gas bypass valve 108 is a thermal expansion valve. According to one implementation, the pressure within receiver 106 is regulated by gas bypass valve 108 to a pressure of approximately 38 bar.

Chilled fluid heat exchanger 152 can serve as part of a chiller unit for medium temperature loads 158. Chilled fluid heat exchanger 152 includes first side 176 and second side 178. Each of first side 176 and second side 178 can include a coil.

Pump 156 operates to circulate a chiller fluid in medium temperature chiller circuit 154. In one implementation, the chiller fluid is glycol. In some implementations, a portion of the CO₂ refrigerant evaporates as it passes through second side 178 of chilled fluid heat exchanger 152. First side 176 of chilled fluid heat exchanger 152 is in heat transfer communication with second side 178 of chilled fluid heat exchanger 152, such that heat in fluid passing through first side 176 (e.g., glycol) is transferred to fluid passing through second side 178 (e.g., CO₂ refrigerant).

Medium temperature chiller circuit 154 can be a closed-loop circuit for circulating a chilled liquid coolant (e.g., glycol, water, glycol-water mixture, etc.) through one or more medium temperature cases (e.g., refrigerated display cases, etc.), a supply header, a return header, and pump 156. Medium temperature chiller circuit 154 can include valves for controlling the flow of the chilled liquid coolant through medium temperature loads 158.

Thermal components and sensors of system 100 can be communicatively coupled to controller 116. Controller 116 can be operated to control cooling of medium temperature loads and low temperature loads by CO₂ refrigeration system 100. Controller 116 may receive signals from one or more measurement devices (e.g., pressure sensors, temperature sensors, flow sensors, etc.) located within CO₂ refrigeration system 100. Controller 116 may use the input signals to determine appropriate control actions for controllable devices of CO₂ refrigeration system 100 (e.g., compressors, valves, flow diverters, power supplies, etc.)

In some implementations, controller 116 is operated to control switching of cooling by existing refrigeration systems to cooling by CO₂ refrigeration system 100. Switching may be controller in steps or increments (for example, one circuit at a time). In some implementations, switching is based on measured characteristics or conditions of the cooling systems, the loads, or combinations of both. Gas defrost system 114 includes gas defrost unit 180 and gas defrost conduit 182. Gas defrost system 114 may use high temperature discharge gas from CO₂ refrigeration system 100 to melt frost and/or ice.

Gas defrost conduit 182 can carry gas from gas defrost unit 180 to cases or other equipment that produces frost, which may be found in medium temperature loads, low temperature loads, or both. In some examples, gas defrost conduit 182 carries gas to medium temperature and low temperature direct exchange circuits. In some implementations, gas defrost unit 180 includes a three-way valve that can be operated by controller 116 to control the flow of gas through gas defrost conduit 182.

The terms “low temperature” and “medium temperature” are used herein to differentiate between two subsystems of CO₂ refrigeration system 100. Medium temperature subsystem 110 maintains one or more loads, such as cases (e.g. refrigerator cases or other cooled areas) at a temperature lower than the ambient temperature but higher than cases cooled by low temperature subsystem 112. Low temperature subsystem 112 maintains one or more loads, such as freezer display cases or other cooled areas, at a temperature lower than the medium temperature cases. According to one exemplary implementation, medium temperature cases may be maintained at a temperature of approximately 20° F., and low temperature cases may be maintained at a temperature of approximately minus (−) 20° F. Although only two subsystems are shown in the illlustrative implementations described herein, according to other illustrative implementations, CO₂ refrigeration system 100 may include more subsystems that may be selectively cooled.

Applications of systems and processes described in the present disclosure include a commercial supermarket, a cold storage warehouse, and a process cooling facility. In some implementations, a cold storage warehouse or process cooling facility includes refrigeration and air conditioning.

FIG. 2 is a block diagram illustrating a transition from an existing refrigeration system having a medium temperature chiller loop to a system that includes a CO₂ transcritical booster system according to some implementations.

Facility 200 includes medium temperature refrigeration system 202 and low temperature direct exchange refrigeration system 204. Medium temperature refrigeration system 202 and low temperature direct exchange refrigeration system 204 may be existing refrigeration systems in the facility. Medium temperature refrigeration system 202, low temperature direct exchange refrigeration system 204, or both, may use hydroflurocarbon (HFC) refrigerants.

Medium temperature refrigeration system 202 includes chiller unit 205 and medium temperature chiller loop 206. Chiller unit 205 can be operated to circulate a chiller fluid, such as glycol, to cool medium temperature loads 208. Low temperature direct exchange system 204 provides cooling to low temperature loads 210.

CO₂ transcritical booster system 212 may be installed in facility 200 to replace one or more existing refrigeration systems in facility 200, including medium temperature refrigeration system 202 and low temperature direct exchange refrigeration system 204. CO₂ transcritical booster system 212 includes chilled fluid heat exchanger 214, pump 216, and low temperature subsystem 218. Chilled fluid heat exchanger 214 and pump 216 can be coupled to medium temperature loads 208 to form medium temperature chiller loop 206. Pump 216 can be operated to circulate a chiller fluid, such as glycol, in medium temperature chiller loop 206 between chilled fluid heat exchanger 214 and medium temperature loads 208. CO₂ transcritical booster system 212 can be started up to cool medium temperature loads 208.

With CO₂ transcritical booster system 212 operating to cool medium temperature loads 208, low temperature subsystem 218 of CO₂ transcritical booster system 212 can be fluidly coupled to low temperature loads 210. CO₂ transcritical booster system 212 can be operated to cool low temperature loads 210. In some implementations, low temperature loads 210 are switched from low temperature direct exchange system 204 to CO₂ transcritical booster system 212 one evaporator at at time, or one circuit at at time.

FIG. 3 is a flow diagram of an example process that can be implemented in an existing facility according to some implementations.

At the commencement of process 300, an existing refrigeration system that includes a medium temperature chiller loop is identified (302). In one example, the existing refrigeration system includes an HFC chiller unit for medium temperature loads and an HFC direct exchange cooling system for low temperature loads that is are service to provide cooling to a facility, such as the one described above relative to FIG. 2.

Medium temperature loads of the medium temperature chiller loop are switched from the existing refrigeration system to a CO₂ transcritical booster system (304). In some implementations, the loads are switched one circuit at a time. In some implementations, loads are switched one medium temperature load at a time. As the loads are switched, the CO₂ transcritical booster system is operated to cool the switched medium temperature loads (306).

While the CO₂ transcritical booster system is operating to cool the switched medium temperature loads, the direct exchange cooling loads are switched from an existing direct exchange cooling system to the CO₂ transcritical booster system (308). The direct exchange cooling loads can include low temperature loads, medium temperature loads, or both. The direct exchange cooling loads can be switched over time. In some implementations, the direct exchange cooling loads are switched one circuit at a time. In certain implementations, loads are switched one refrigerator case at a time. As the direct exchange cooling loads are switched, the CO₂ transcritical booster system operates to cool the direct exchange cooling loads (310).

In one illustrative implementation, a method is implemented in a supermarket that currently has the medium temperature loads refrigerated using glycol and the low temperature loads refrigerated using HFC direct expansion. A retrofit from existing low temperature to use CO₂ refrigerant may include initially establishing some medium temperature refrigeration load. The existing racks of the refrigeration system may be separated from one another and the low temperature direct exchange and medium temperature chillers independent of one another.

In some implementations, a low temperature direct exchange or medium temperature direct exchange retrofit to CO₂ transcritical booster system is accomplished with a single circuit added at a time. In this case, the medium temperature compressors that are already operating to provide chilled fluid to the medium temperature loads may more easily accept the discharge gas from the low temperature compressors.

In one example of retrofitting a store to a CO₂ transcritical booster system, glycol circuits of an existing system are first switched to the new equipment. In the case where the new equipment is provided with new chillers, a retrofit may include switching the flow of glycol through the new chillers and starting the medium temperature compressors on the new equipment. With the new medium temperature compressors operational, single circuit changes can then take place, allowing the full facility to slowly switch, one circuit at a time, from a HFC type refrigerant system to a CO₂ transcritical booster system.

In some implementations, one or more of the direct exchange circuits of the system use hot gas defrost using CO₂ medium temperature discharge as the source (e.g., transcritical compressor 150 shown in FIG. 1). An instant hot gas defrost operation can be implemented with as little as a single direct exchange circuit connected.

In some implementations, startup of a new facility startup is carried out in a similar manner to that described above for a retrofit. For example, the chilled fluid may be started first to cool medium temperature loads, and then the circuits brought up in stages.

FIG. 4 is a flow diagram of an example process 400 that can be implemented to provide cooling in a new facility according to some implementations.

At the commencement of process 400, medium temperature loads are fluidly coupled to a medium temperature chiller system (402). In one example, the medium temperature chiller system may be part of a new installation of a cooling system at a facility, such as a supermarket.

With the medium temperature loads connected to the medium temperature chiller system, a CO₂ transcritical booster system is started up to provide CO₂ refrigerant to the medium temperature chiller system to remove heat from medium temperature loads coupled to the medium temperature chiller system (404). In some implementations, the loads may be started one circuit at a time. In some implementations, loads are started one medium temperature load at a time. As the loads are started, the CO₂ transcritical booster system is operated to cool the medium temperature loads (406).

While the CO₂ transcritical booster system is operating to cool the medium temperature loads coupled to the medium temperature chiller system, cooling is started to direct exchange cooling loads in the facility (408). The direct exchange cooling loads can include low temperature loads, medium temperature loads, or both. The direct exchange cooling loads can be started over time. In some implementations, the direct exchange cooling loads are started one circuit at a time. In certain implementations, loads are started one refrigerator case at a time. The CO₂ transcritical booster system is operated to cool the direct exchange cooling loads (410).

In some implementations, direct exchange circuits of the new system use a hot gas defrost using CO₂ medium temperature discharge as the source (e.g., transcritical compressor 150 shown in FIG. 1).

In various implementations described above, a cooling system includes a CO₂ refrigeration system with a chiller system that provides cooling for medium temperature loads. A cooling system may, however, in some implementations can a CO₂ refrigeration system with a chiller system that provides cooling for low temperature loads (in addition to, or instead of, medium temperature loads). FIG. 5 is a block diagram of a CO₂ transcritical booster system system with a low temperature chiller according to an illustrative implementation. System 500 includes medium temperature subsystem 502 and low temperature subsystem 504.

Low temperature subsystem 504 includes includes low temperature chiller system 506 and one or more compressors 508. Compressors 508 combine to form a compressor suction group for low temperature subsystem 504.

Low temperature chiller system 506 includes chilled fluid heat exchanger 510 and low temperature chiller circuit 512. Low temperature chiller circuit 512 includes pump 514. Pump 514 can be operated to circulate chiller fluid between chilled fluid heat exchanger 510 and low temperature loads 516 to cool low temperature loads 516. In some implementations, pump 514 is controlled by way of controller 116.

In various examples described above, a facility includes low temperature and medium temperature loads and corresponding low temperature and medium temperature cooling systems. In other implementations, a facility can have only low temperature loads or only medium temperature loads and/or cooling systems.

In various examples described above, a CO₂ refrigeration system is cooled by an adiabatic gas cooler. In other implementations, a CO₂ refrigeration system can be cooled by other systems, such as an air cooled or water cooled device.

In various examples described above, the medium temperature subsystem of a CO₂ booster refrigeration system includes a medium temperature chiller circuit that provides chilled fluid to medium temperature loads. In other implementations, a CO₂ booster refrigeration system can include one or more evaporators that provide direct exchange cooling to medium temperature loads in addition to, or instead of, the chilled fluid cooling systems described above. In various implementations, any number of expansion valves, MT evaporators, and transcritical compressors may be present. The expansion valves may receive liquid CO₂ refrigerant (e.g., from fluid conduit 144) and output the CO₂ refrigerant to the MT evaporators. In some implementations, MT evaporators may be associated with display cases/devices (e.g., if CO₂ refrigeration system 100 is implemented in a supermarket setting).

The present disclosure contemplates methods, systems and program products on memory or other machine-readable media for accomplishing various operations. The described systems, methods, and techniques may be implemented in digital electronic circuitry, computer hardware, firmware, software, or in combinations of these elements. Systems and processes described in the present disclosure, such as controller 116, may be implemented using existing computer processors, or by a special purpose computer processor for an appropriate system, incorporated for this or another purpose, or by a hardwired system. Implementations within the scope of the present disclosure include program products or memory including machine-readable media for carrying or having machine-executable instructions or data structures stored thereon. Such machine-readable media can be any available media that can be accessed by a general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer or other machine with a processor. Combinations of the above are also included within the scope of machine-readable media. Machine-executable instructions include, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing machines to perform a certain function or group of functions.

Particular implementations of the subject matter have been described. Other implementations, alterations, and permutations of the described embodiments are within the scope of the following claims as will be apparent to those skilled in the art. While operations are depicted in the drawings or claims in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed (some operations may be considered optional), to achieve desirable results.

Accordingly, the previously described example implementations do not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure.