CO2 REFRIGERATION SYSTEM WITH MULTIPLE RECEIVERS

A refrigeration system having a primary receiver, a secondary receiver, a first gas bypass valve, and second gas bypass valve, a feed control valve, and a controller. The primary receiver has a primary receiver operating pressure and is configured to collect a refrigerant circulated by the refrigeration system. The secondary receiver includes a liquid refrigerant inlet fluidly coupled to a primary receiver liquid refrigerant outlet. The feed control valve is coupled between the primary receiver liquid outlet and the secondary receiver liquid refrigerant inlet. The controller operates the feed control valve to control a flow of a liquid refrigerant from the primary receiver to the secondary receiver.

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 which 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 that 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.

Implementations of the present disclosure include a refrigeration system having a primary receiver, a secondary receiver, a first gas bypass valve, and second gas bypass valve, a feed control valve, and a controller. The primary receiver has a primary receiver operating pressure and is configured to collect a refrigerant circulated by the refrigeration system. The primary receiver includes a primary receiver inlet through which refrigerant enters the primary receiver, a primary receiver gas outlet through which gas refrigerant exits the primary receiver, and a primary receiver liquid refrigerant outlet through which liquid refrigerant exits the primary receiver. The secondary receiver has a secondary receiver operating pressure that is less than the primary receiver operating pressure. The secondary receiver includes a liquid refrigerant inlet fluidly coupled to the primary receiver liquid refrigerant outlet and configured to receive liquid refrigerant from the primary receiver, and a secondary receiver gas outlet through which gas refrigerant exits the secondary receiver. The first gas bypass valve is fluidly coupled to the primary receiver gas outlet and is operable to control a flow of the gas refrigerant from the primary receiver through the first gas bypass valve. The second gas bypass valve is fluidly coupled to the secondary receiver gas outlet and is operable to control a flow of the gas refrigerant from the secondary receiver through the second gas bypass valve. The feed control valve is coupled between the primary receiver liquid outlet and the secondary receiver liquid refrigerant inlet. The controller is configured to operate the feed control valve to control a flow of a liquid refrigerant from the primary receiver to the secondary receiver.

In some implementations, the receiver operating pressure in the primary receiver is between about 60 bar and about 90 bar, and the receiver operating pressure in the secondary receiver is less than about 60 bar.

In some implementations, the controller is configured to operate the feed control valve to maintain a level of liquid refrigerant in the secondary receiver at a setpoint.

In some implementations, the controller is configured to operate the feed control valve to maintain a level of liquid refrigerant in the secondary receiver within a predetermined range.

In some implementations, the controller is configured to maintain a level of liquid refrigerant in the primary receiver at or above a minimum level.

In some implementations, the controller is configured to maintain a level of liquid refrigerant in the primary receiver at or above a minimum level and a level of liquid refrigerant in the secondary receiver at or above a minimum level.

In some implementations, the feed control valve includes a pressure regulator valve.

In some implementations, the feed control valve includes a solenoid valve.

In some implementations, the refrigeration system further includes a first set of one or more compressors fluidly coupled to the primary receiver gas outlet; and a second set of one or more compressors fluidly coupled to the secondary receiver gas outlet.

In some implementations, the refrigeration system includes a first subsystem and a second subsystem, wherein the first subsystem receives liquid refrigerant from the primary receiver, wherein the second subsystem receives liquid refrigerant from the secondary receiver.

In some implementations, the refrigeration system further includes a medium temperature (MT) subsystem configured to receive liquid refrigerant from the secondary receiver. The MT subsystem includes one or more MT compressors configured to operate in a transcritical state, one or more MT evaporators, and one or more MT expansion valves.

In some implementations, the refrigeration system further includes a low temperature (LT) subsystem configured to receive liquid refrigerant from the primary receiver.

The LT subsystem includes one or more LT compressors configured to operate in a subcritical state, one or more LT evaporators, and one or more LT expansion valves

In some implementations, the refrigeration system further includes: an LT subsystem and an MT subsystem each configured to receive liquid refrigerant from the secondary receiver; and a primary subsystem configured to receive liquid refrigerant from the primary receiver.

In some implementations, the primary subsystem includes an air-conditioning system.

In some implementations, the primary subsystem includes a process cooling loop.

In some implementations, an ejector fluidly coupled between a gas cooler of the refrigeration system and the first receiver.

In some implementations, a parallel compressor coupled between an outlet of the first receiver and an outlet of one or more MT subsystem compressors.

In some implementations, an additional receiver configured to receive liquid refrigerant from the secondary receiver.

In some implementations, the refrigerant is carbon dioxide.

Further implementations of the present disclosure include a refrigeration system having two or more receivers, a liquid refrigerant feed line, one or more feed control valves, and a controller. The two or more receivers are configured to collect refrigerant circulated by the refrigeration system. The liquid refrigerant feed line is between a liquid refrigerant outlet of a first one of the receivers and a liquid refrigerant inlet of a second one of the receivers having a receiver operating pressure lower than the receiver operating pressure of the first one of the receivers. The one or more feed control valves are in the liquid refrigerant feed line. The controller is configured to operate the one or more feed control valves to control a level of liquid refrigerant in at least the second one of the receivers.

In some implementations, the two or more receivers include a primary receiver, a secondary receiver, and a tertiary receiver. The secondary receiver receives a flow of liquid refrigerant from the primary receiver and has a secondary receiver operating pressure that is lower than the primary receiver operating pressure. The tertiary receiver receives a flow of liquid refrigerant from the secondary receiver and has a tertiary receiver operating pressure that is lower than the secondary receiver operating pressure.

Further implementations of the present disclosure include a method for operating a refrigeration system including: collecting a refrigerant circulated by the refrigeration system within a primary receiver having a primary receiver operating pressure, the primary receiver comprising a liquid refrigerant outlet through which the refrigerant exits the receiver; providing liquid refrigerant from the primary receiver to a secondary receiver having a secondary receiver operating pressure that is lower than the primary operating pressure; operating a first gas bypass valve fluidly coupled to the primary receiver gas outlet of the to control to control a flow of the gas refrigerant from the primary receiver through the first gas bypass valve; operating a second gas bypass valve fluidly coupled to the secondary receiver gas outlet to control a flow of the gas refrigerant from the secondary receiver through the second gas bypass valve; and operating a feed control valve to control a flow of a liquid refrigerant from the primary receiver to the secondary receiver.

In some implementations, operating the feed control valve to control a flow of liquid refrigerant from the receiver to the secondary receiver includes maintaining a liquid level in the secondary receiver within a particular operating range.

In some implementations, the method further includes monitoring a liquid refrigerant level in the primary receiver, and maintaining the liquid refrigerant level in the primary receiver at or above a predetermined minimum level.

Further implementations of the present disclosure include a method for operating a refrigeration system including collecting a gas refrigerant circulated by the refrigeration system within a primary receiver having a primary operating pressure, the receiver comprising a liquid refrigerant outlet through which liquid refrigerant exits the receiver; providing liquid refrigerant from the primary receiver to a secondary receiver having a secondary receiver operating pressure that is less than the primary receiver operating pressure; and operating a feed control valve to control a flow of a liquid refrigerant from the primary receiver to the secondary receiver to maintain a level of liquid refrigerant in the secondary receiver within a particular operating range.

In some implementations, the method further includes monitoring a liquid refrigerant level in the primary receiver, and maintaining the liquid refrigerant level in the primary receiver at or above a predetermined minimum level.

In some implementations, the method further includes receiving liquid refrigerant from the secondary receiver into a tertiary receiver; and operating a feed control valve to control a flow of a liquid refrigerant from the secondary receiver to the tertiary receiver to maintain a level of liquid refrigerant in the tertiary receiver within a particular operating range.

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 allow a system to operate more efficiently with varying environmental conditions.

Implementations of the present disclosure may help to balance the charge of a system for winter and summer operating conditions.

Implementations of the present disclosure may allow a portion of a refrigeration system to use lower pressure piping, lower pressure valves, and other lower pressure fluid components.

DETAILED DESCRIPTION

In various implementations, a cooling system has two or more receivers. Each of the receivers may be in the form of a flash tank. In some implementations of a two-receiver system, a gas cooler outlet for a refrigeration system is connected to the higher pressure receiver (primary receiver) (for example, 60 bar or 90 bar) via a high pressure valve. A high-pressure valve maintains gas cooler pressure. The primary receiver supplies liquid to high pressure evaporators, which can be, for example, a display case, a walk-in cooler evaporator, or air conditioning evaporator (e.g., MT suction group 1). The operating pressure of the primary receiver can be controlled by another pressure regulating valve or flash gas bypass valve which is connected to a suction group. A liquid level sensor/switch in the primary receiver/flash tank can ensure a minimum liquid level in the tank.

A secondary receiver is connected to primary receiver through a feed control valve. The primary receiver supplies liquid to secondary receiver. The secondary receiver's operating pressure can be maintained/controlled by another pressure regulating valve which is connected to another suction group (e.g., MT suction group 2 an LT suction group).

A liquid level sensor is installed in a secondary receiver/flash tank. The liquid level sensor measures the liquid level in the secondary receiver. The liquid level sensor is coupled to a controller that uses the liquid level sensor to control the liquid level in the secondary receiver. For example, the controller can send a signal to the liquid feed to open when the level in the secondary receiver goes low and send a signal to the liquid feed valve to close when the liquid level in the secondary receiver goes high. The liquid level sensor can also ensure a minimum liquid level in the secondary receiver. The secondary receiver may operate at intermediate pressure (for example, 45 bar or 60 bar).

Further examples of multiple receiver systems are described below. Referring generally to the Figures, a CO2refrigeration system is shown, according to various exemplary implementations. The CO2refrigeration system may be a vapor compression refrigeration system which uses primarily carbon dioxide (i.e., CO2) as a refrigerant. In some implementations, a CO2booster system is used to provide cooling for temperature controlled display devices in a supermarket or other similar facility.

FIG.1is a block diagram of a CO2refrigeration system according to an exemplary implementation. CO2refrigeration system100may be a vapor compression refrigeration system which uses primarily carbon dioxide (CO2) as a refrigerant. However, it is contemplated that other refrigerants can be substituted for CO2without departing from the teachings of the present disclosure.

CO2refrigeration system100and is shown to include a system of pipes, conduits, or other fluid channels for transporting the CO2refrigerant between various components of CO2refrigeration system100. The thermodynamic components of CO2refrigeration system100include a gas cooler/condenser102, a high pressure valve104, a primary receiver106, and secondary receiver108, a primary gas bypass valve110, secondary gas bypass valve112, feed control valve114, a medium-temperature (“MT”) subsystem116, a low-temperature (“LT”) subsystem118, a primary subsystem120, and controller122. (In this example, the primary subsystem can also be referred to as an MT subsystem.)

Gas cooler/condenser102may be a heat exchanger or other similar device for removing heat from the CO2refrigerant. Gas cooler/condenser102is shown receiving CO2gas from fluid conduit130. Refrigerant passes through oil separator131before flowing to gas cooler/condenser102. In some implementations, the CO2gas in fluid conduit130may 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/condenser102may partially or fully condense CO2gas into liquid CO2(e.g., if system operation is in a subcritical region). The condensation process may result in fully saturated CO2liquid or a two-phase liquid-vapor mixture (e.g., having a thermodynamic vapor quality between 0 and 1). In other implementations, gas cooler/condenser102may cool the CO2gas (e.g., by removing superheat) without condensing the CO2gas into CO2liquid (e.g., if system operation is in a supercritical region). In some implementations, the cooling/condensation process is an isobaric process. Gas cooler/condenser102is shown outputting the cooled and/or condensed CO2refrigerant into fluid conduit132.

In some implementations, CO2refrigeration system100includes a temperature sensor and a pressure sensor configured to measure the temperature and pressure of the CO2refrigerant exiting gas cooler/condenser102. Sensors can be installed along fluid conduit132, within gas cooler/condenser102, or otherwise positioned to measure the temperature and pressure of the CO2refrigerant exiting gas cooler/condenser102. In some implementations, CO2refrigeration system100includes a condenser fan that provides airflow across gas cooler/condenser102. The speed of the condenser fan can be controlled to increase or decrease the airflow across gas cooler/condenser102to modulate the amount of cooling applied to the CO 2 refrigerant within gas cooler/condenser102. In some implementations, CO2refrigeration system100also 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/condenser102to provide cooling for the CO2refrigerant contained therein.

High pressure valve104receives the cooled and/or condensed CO2refrigerant from fluid conduit132and outputs the CO2refrigerant to fluid conduit134. High pressure valve104may control the pressure of the CO2refrigerant in gas cooler/condenser102by controlling an amount of CO2refrigerant permitted to pass through high pressure valve104. In some implementations, high pressure valve104is a high pressure thermal expansion valve (e.g., if the pressure in fluid conduit132is greater than the pressure in fluid conduit134). In such implementations, high pressure valve104may allow the CO2refrigerant 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 CO2refrigerant 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 CO2refrigerant expands to a pressure of approximately 38 bar (e.g., about 550 psig), which corresponds to a temperature of approximately 40° F. The CO2refrigerant then flows from fluid conduit134into primary receiver106.

Primary receiver106collects the CO 2 refrigerant from fluid conduit134. In some implementations, primary receiver106may be a flash tank or other fluid reservoir. Primary receiver106includes a CO2liquid portion and a CO2vapor portion and may contain a partially saturated mixture of CO2liquid and CO2vapor. In some implementations, primary receiver106separates the CO2liquid from the CO2vapor.

Secondary receiver108is fluidly coupled to primary receiver106by way of feed conduit136. A portion of liquid refrigerant exiting primary receiver106can be received in secondary receiver108. Feed control valve114controls a flow of a liquid refrigerant from primary receiver106to secondary receiver108. Examples of a feed control valve114include a pressure regulating valve, a solenoid valve, a flow meter, or a motorized ‘liquid feed’ valve. Feed control valve114can be operated (e.g., by way of controller122) to control a liquid level in secondary receiver108and/or primary receiver106.

The receiver operating pressure of secondary receiver108is lower than receiver operating pressure of primary receiver106. In one implementation, the receiver operating pressure of primary receiver106is about 90 bar, and the receiver operating pressure of secondary receiver108is about 60 bar. In another implementation, the receiver pressure of primary receiver106is about 60 bar, and the receiver operating pressure of secondary receiver108is about 45 bar.

Each of primary receiver106and secondary receiver108include liquid level-measuring devices. The liquid level-measuring devices can be, for example, a level switch or a level sensor. The liquid level measuring device can be coupled to controller122. In one example, primary receiver106includes a level switch138and secondary receiver108includes a level sensor140. Level sensor140may provide a signal corresponding to the level of liquid refrigerant in secondary receiver108.

Information from level sensor140can be used by controller122to control a liquid level in secondary receiver108. The liquid level in the secondary receiver108can be maintained within a pre-determined range. As examples, controller122can maintain a liquid level in secondary receiver108between 40 and 60% full, between 50 and 60% full, or at least 50% full.

In certain implementations, feed control valve114is operated to control pressure in one or more receivers. For example, if the pressure drops to below a desired level in secondary receiver108, feed control valve114can be opened to raise the liquid level in secondary receiver108to correct for the pressure drop.

CO2liquid may exit primary receiver106through feed conduit136and conduit142. Conduit142may be a liquid header leading to primary subsystem120. The CO2vapor may exit primary receiver108through flash gas line143. Conduit143is shown leading the CO2vapor to a primary gas bypass valve110(described in greater detail below).

CO2liquid may exit secondary receiver108and pass into conduit144and conduit146. Conduit146may be a liquid header leading to MT subsystem116. Conduit144may be a liquid header leading to LT subsystem118. The CO2vapor may exit secondary receiver108through flash gas line148. Flash gas line148is shown leading the CO2vapor to a secondary gas bypass valve112(described in greater detail below).

In some implementations, CO2refrigeration system100includes temperature sensors and/or pressure sensors configured to measure the temperature and pressure within primary receiver106, secondary receiver108, or both. Sensors can be installed in or on primary receiver106, in or on secondary receiver108, or along any of the fluid conduits that contain CO2refrigerant at the same temperature and/or pressure as primary receiver106or secondary receiver108, as the case may be.

MT subsystem116is shown to include one or more expansion valves150, one or more MT evaporators152, and one or more secondary group transcritical compressors154. In various implementations, any number of expansion valves150, MT evaporators152, and secondary group transcritical compressors154may be present. Expansion valves150may be electronic expansion valves or other similar expansion valves. Expansion valves150are shown receiving liquid CO 2 refrigerant from fluid conduit146and outputting the CO2refrigerant to MT evaporators152. Expansion valves150may cause the CO2refrigerant to undergo a rapid drop in pressure, thereby expanding the CO2refrigerant to a lower pressure, lower temperature two-phase state. In some implementations, expansion valves150may expand the CO2refrigerant to a pressure of approximately 20 bar to 25 bar. The expansion process may be an isenthalpic and/or adiabatic expansion process.

MT evaporators152are shown receiving the cooled and expanded CO2refrigerant from expansion valves150. In some implementations, MT evaporators152may be associated with display cases/devices (e.g., if CO2refrigeration system100is implemented in a supermarket setting). MT evaporators152may be configured to facilitate the transfer of heat from the display cases/devices into the CO2refrigerant. The added heat may cause the CO2refrigerant to evaporate partially or completely. According to one implementation, the CO 2 refrigerant is fully evaporated in MT evaporators152. In some implementations, the evaporation process may be an isobaric process. MT evaporators152are shown outputting the CO2refrigerant via suction line156, leading to secondary group transcritical compressors154.

Secondary group transcritical compressors154compress the CO2refrigerant into a superheated gas having a pressure within a range of approximately 45 bar to approximately 100 bar. The output pressure from secondary group transcritical compressors154may vary depending on ambient temperature and other operating conditions. In the example shown inFIG.1, secondary group transcritical compressors154operate in a transcritical mode. In operation, the CO2discharge gas exits secondary group transcritical compressors154and flows through conduit130into gas cooler/condenser102.

LT subsystem118is shown to include one or more expansion valves160, one or more LT evaporators162, and one or more subcritical compressors164. In various implementations, any number of expansion valves160, LT evaporators162, and subcritical compressors164may be present. In some implementations, LT subsystem118may be omitted and the CO2refrigeration system100may operate with an AC module interfacing with only MT subsystem116.

Expansion valves160may be electronic expansion valves or other similar expansion valves. Expansion valves160are shown receiving liquid CO 2 refrigerant from fluid conduit146and outputting the CO2refrigerant to LT evaporators162. Expansion valves160may cause the CO2refrigerant to undergo a rapid drop in pressure, thereby expanding the CO2refrigerant 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 valves160may expand the CO2refrigerant to a lower pressure than expansion valves160, thereby resulting in a lower temperature CO2refrigerant. Accordingly, LT subsystem118may be used in conjunction with a freezer system or other lower temperature display cases.

LT evaporators162are shown receiving the cooled and expanded CO2refrigerant from expansion valves160. In some implementations, LT evaporators may be associated with display cases/devices (e.g., if CO2refrigeration system100is implemented in a supermarket setting). LT evaporators162may be configured to facilitate the transfer of heat from the display cases/devices into the CO2refrigerant. The added heat may cause the CO2refrigerant to evaporate partially or completely. In some implementations, the evaporation process may be an isobaric process.

LT evaporators162are shown outputting the CO2refrigerant via suction line166, leading to subcritical compressors164. In this example, before reaching subcritical compressors164, the refrigerant passes through heat exchanger168in secondary receiver108and to accumulator170.

Subcritical compressors164compress the CO2refrigerant. In some implementations, subcritical compressors164may compress the CO2refrigerant to a pressure of approximately 30 bar, having a saturation temperature of approximately 23° F. In this example, subcritical compressors164operate in a subcritical mode. Subcritical compressors164are shown outputting the CO2refrigerant through discharge line172. Discharge line172may be fluidly connected with the suction (e.g., upstream) side of secondary group transcritical compressors154.

Primary subsystem120is shown to include one or more expansion valves180, one or more evaporators182, and one or more primary group transcritical compressors184. In various implementations, any number of expansion valves180, evaporators182, and primary group transcritical compressors184may be present.

In the context of this example, “primary subsystem” refers to the loop receiving its refrigerant from a primary receiver (in this case, primary receiver106). In some implementations, the primary subsystem operates a high pressure cooling loop. As one example, the primary receiver106may have a pressure between approximately 60 bar and approximately 90 bar. In one implementation, primary system120includes display case evaporators for display cases. In another implementation, primary system120includes evaporators for air conditioning. In still another implementation, primary system120includes evaporators for process cooling. In certain implementations, primary system120provides cooling for two or more types of evaporators (e.g., air conditioning and display cases).

Expansion valves180may be electronic expansion valves or other similar expansion valves. Expansion valves180are shown receiving liquid CO 2 refrigerant from fluid conduit142and outputting the CO2refrigerant to MT evaporators182. Expansion valves180may cause the CO2refrigerant to undergo a rapid drop in pressure, thereby expanding the CO2refrigerant to a lower pressure, lower temperature two-phase state. In some implementations, expansion valves180may expand the CO2refrigerant to a pressure of approximately 20 bar to 25 bar (or higher). The expansion process may be an isenthalpic and/or adiabatic expansion process.

Evaporators182are shown receiving the cooled and expanded CO2refrigerant from expansion valves180. In some implementations, MT evaporators may be associated with display cases/devices (e.g., if CO2refrigeration system100is implemented in a supermarket setting). Evaporators182may be configured to facilitate the transfer of heat from the display cases/devices into the CO2refrigerant. The added heat may cause the CO2refrigerant to evaporate partially or completely. According to one implementation, the CO 2 refrigerant is fully evaporated in evaporators182. In some implementations, the evaporation process may be an isobaric process. Evaporators182are shown outputting the CO2refrigerant via suction line188, leading to primary group transcritical compressors184.

Primary group transcritical compressors184compress the CO2refrigerant into a superheated gas having a pressure within a range of approximately 45 bar to approximately 100 bar. The output pressure from primary group transcritical compressors184may vary depending on ambient temperature and other operating conditions. In the example shown inFIG.1, primary group transcritical compressors184operate in a transcritical mode. In operation, the CO2discharge gas exits primary group transcritical compressors184and flows through conduit130into gas cooler/condenser102.

CO2refrigeration system100is shown to include a primary gas bypass valve110. Primary gas bypass valve110may receive the CO2vapor from fluid conduit143and output the CO2refrigerant to primary subsystem120. In some implementations, primary gas bypass valve110is arranged in series with primary group transcritical compressors184. In other words, CO2vapor from primary receiver106may pass through both primary gas bypass valve110and primary group transcritical compressors184. Primary group transcritical compressors184may compress the CO2vapor passing through primary gas bypass valve110from a low pressure state (e.g., approximately 30 bar or lower or higher) to a high pressure state (e.g., 45-100 bar).

Primary gas bypass valve110can be operated to control a flow of gas refrigerant from fluid conduit143into suction line188. Primary gas bypass valve110may be operated to regulate or control the pressure within primary receiver106(e.g., by adjusting an amount of CO2refrigerant permitted to pass through primary gas bypass valve110). For example, primary gas bypass valve110may be adjusted (e.g., variably opened or closed) to adjust the mass flow rate, volume flow rate, or other flow rates of the CO2refrigerant through primary gas bypass valve110. Primary gas bypass valve110may be opened and closed (e.g., manually, automatically, by a controller, etc.) as needed to regulate the pressure within primary receiver106.

In some implementations, primary gas bypass valve110includes a sensor for measuring a flow rate (e.g., mass flow, volume flow, etc.) of the CO2refrigerant through primary gas bypass valve110. In other implementations, primary gas bypass valve110includes an indicator (e.g., a gauge, a dial, etc.) from which the position of primary gas bypass valve110may be determined. This position may be used to determine the flow rate of CO2refrigerant through primary gas bypass valve110, as such quantities may be proportional or otherwise related.

In some implementations, primary gas bypass valve110may be a thermal expansion valve. According to one implementation, the pressure within primary receiver106is regulated by primary gas bypass valve110to a pressure of approximately 60 bar.

CO2refrigeration system100is shown to include a secondary gas bypass valve112. Secondary gas bypass valve112may receive the CO2vapor from fluid conduit190and output the CO2refrigerant toward secondary group transcritical compressors154. In some implementations, secondary gas bypass valve112is arranged in series with secondary group transcritical compressors154. In other words, CO2vapor from primary receiver106may pass through both primary gas bypass valve110and secondary group transcritical compressors154. Secondary group transcritical compressors154may compress the CO2vapor passing through secondary gas bypass valve112from a low pressure state (e.g., approximately 30 bar or lower or higher) to a high pressure state (e.g., approximately 45-100 bar).

Secondary gas bypass valve112can be operated to control a flow of gas refrigerant from secondary receiver108into suction line156. Secondary gas bypass valve112may be operated to regulate or control the pressure within secondary receiver108(e.g., by adjusting an amount of CO2refrigerant permitted to pass through secondary gas bypass valve112). For example, secondary gas bypass valve112may be adjusted (e.g., variably opened or closed) to adjust the mass flow rate, volume flow rate, or other flow rates of the CO2refrigerant through secondary gas bypass valve112. Secondary gas bypass valve112may be opened and closed (e.g., manually, automatically, by a controller, etc.) as needed to regulate the pressure within secondary receiver108.

In some implementations, secondary gas bypass valve112includes a sensor for measuring a flow rate (e.g., mass flow, volume flow, etc.) of the CO2refrigerant through primary gas bypass valve110. In other implementations, secondary gas bypass valve112includes an indicator (e.g., a gauge, a dial, etc.) from which the position of secondary gas bypass valve112may be determined. This position may be used to determine the flow rate of CO2refrigerant through secondary gas bypass valve112, as such quantities may be proportional or otherwise related.

In some implementations, secondary gas bypass valve112may be a thermal expansion valve. According to one implementation, the pressure within secondary receiver108is regulated by secondary gas bypass valve112to a pressure of approximately 38 bar (or lower or higher).

Applications of systems and processes described in the present disclosure include a commercial supermarket, a cold storage warehouse, and a process cooling facility.

In one implementation, a commercial supermarket has two sets of evaporators, for example, 60 bar and 45 bar medium temp evaporators. The 60 bar evaporator uses high pressure piping. The 45 bar medium temp evaporator uses low pressure piping.

In other implementation, a cold storage/refrigerated warehouse or processing cooling facility has two evaporator ratings, for example, a 90 bar evaporator and a 60 bar evaporator, or 90 bar evaporator and a 45 bar evaporator. In some implementations, a cold storage warehouse or process cooling facility includes refrigeration and air conditioning.

FIG.2is a block diagram illustrating controller122in greater detail according to an exemplary implementation. Controller122may receive signals from one or more measurement devices (e.g., pressure sensors, temperature sensors, flow sensors, etc.) located within CO2refrigeration system100. For example, controller122is shown receiving measurements from level sensor140. Controller122may use the input signals to determine appropriate control actions for controllable devices of CO2refrigeration system100(e.g., compressors, valves, flow diverters, power supplies, etc.). For example, controller122is shown providing control signals to primary gas bypass valve110, secondary gas bypass valve112, and feed control valve114.

In some implementations, controller122is configured to operate feed control valve114at a desired setpoint or within a desired range. Controller122also operates primary gas bypass valve110and secondary gas bypass valve112to control pressure in primary receiver106and secondary receiver108, respectively. In certain implementations, controller122uses a valve position of primary gas bypass valve110as a proxy for CO2refrigerant flow rate. In some implementations, controller122operates high pressure valve104and expansion valves of MT subsystem116, LT subsystem118, and primary subsystem120to regulate the flow of refrigerant in system100and various sub-systems of system100.

Controller122may include feedback control functionality for adaptively operating the various components of CO2refrigeration system100. For example, controller122may receive a setpoint (e.g., a level setpoint, a temperature setpoint, a pressure setpoint, a flow rate setpoint, a power usage setpoint, etc.) and operate one or more components of system100to achieve the setpoint. The setpoint may be specified by a user (e.g., via a user input device, a graphical user interface, a local interface, a remote interface, etc.) or automatically determined by controller122based on a history of data measurements. In some implementations, controller122receives a setpoint for a liquid level of one or more of the receivers in CO2refrigeration system100.

Controller122may be a proportional-integral (PI) controller, a proportional-integral-derivative (PID) controller, a pattern recognition adaptive controller (PRAC), a model recognition adaptive controller (MRAC), a model predictive controller (MPC), or any other type of controller employing any type of control functionality. In some implementations, controller122is a local controller for CO2refrigeration system100. In other implementations, controller122is a supervisory controller for a plurality of controlled subsystems (e.g., a refrigeration system, an AC system, a lighting system, a security system, etc.). For example, controller122may be a controller for a comprehensive building management system incorporating CO2refrigeration system100. Controller122may be implemented locally, remotely, or as part of a cloud-hosted suite of building management applications.

Controller122includes a processing circuit202. Processing circuit202is shown to include a processor204and memory206. Processor204can be implemented as a general purpose processor, an application specific integrated circuit (ASIC), one or more field programmable gate arrays (FPGAs), a group of processing components, a microcontroller, or other suitable electronic processing components. Memory206(e.g., memory device, memory unit, storage device, etc.) may be one or more devices (e.g., RAM, ROM, solid state memory, hard disk storage, etc.) for storing data and/or computer code for completing or facilitating the various processes, layers and modules described in the present application. Memory206may be or include volatile memory or non-volatile memory. Memory206may include database components, object code components, script components, or any other type of information structure for supporting the various activities and information structures described in the present application. According to an exemplary implementation, memory206is communicably connected to processor204via processing circuit202and includes computer code for executing (e.g., by processing circuit202and/or processor204) one or more processes or control features described herein.

Controller122includes a communications interface208. Communications interface208can be or include wired or wireless interfaces (e.g., jacks, antennas, transmitters, receivers, transceivers, wire terminals, etc.) for conducting electronic data communications. Data communications may be conducted via a direct connection (e.g., a wired connection, an ad-hoc wireless connection, etc.) or a network connection (e.g., an Internet connection, a LAN, WAN, or WLAN connection, etc.). For example, communications interface208can include an Ethernet card and port for sending and receiving data via an Ethernet-based communications link or network. In another example, communications interface208can include a Wi-Fi transceiver or a cellular or mobile phone transceiver for communicating via a wireless communications network.

FIG.3is a flow diagram of an example process300that can be implemented on a multiple receiver refrigeration system according to some implementations.

The refrigeration system (e.g., CO2refrigeration system100) can initially be charged (302) to a total liquid charge required for the system (304). The total charge can include an estimated liquid charge required for primary receiver and systems downstream and an estimated charge required for the secondary receiver and systems downstream. The total charge can include an estimate(s) for summer operation, winter operation, or both.

During operation, the liquid level in primary receiver and secondary receiver are measured (306). A determination is made of whether the liquid level in the secondary receiver is above a set level (308). The set level can be, for example, 50% of receiver volume, or 60% of receiver volume.

If the liquid level in the secondary receiver is above the set level, the timer is reset (310). The system can continue to measure primary and secondary receiver levels.

If the liquid level in the secondary receiver is not above the set level (ex: 50% of receiver volume), the liquid feed valve between the primary receiver and the secondary receiver is opened (e.g., liquid control valve114) (312).

Based on one or more additional measurements, a determination is made whether the primary receiver and secondary receiver liquid level are both above the minimum level (314). If the total liquid level of primary receiver and liquid receiver is above the minimum level, the timer is reset (316). If the total liquid level of primary receiver and liquid receiver is not above the minimum level, one or more components of the system is recharged (302). For example, refrigerant can be added to a primary receiver, a secondary receiver, or both.

In the example shown inFIG.1, a CO2refrigeration system100has two receivers. A system may, however, include any number of receivers providing refrigerant to any number of cooling subsystems.

FIG.4is a block diagram illustrating an example of a system having three receivers. System400includes primary receiver402, secondary receiver404, and tertiary receiver406. Primary receiver402provides refrigerant to primary subsystem408. Secondary receiver404provides refrigerant to secondary subsystem410. Tertiary receiver406provides refrigerant to LT sub-system412and MT subsystem414.

System400includes primary gas bypass valve416, secondary gas bypass valve418, tertiary gas bypass valve420. Each of the gas bypass valves can control a pressure level in one of the respective receivers. Feed control valve422between primary receiver402and secondary receiver404can be operated to control a liquid level in secondary receiver404. Feed control valve424between secondary receiver404and secondary receiver406can be operated to control a liquid level in tertiary receiver404. Level sensors426and428provide sensor data that can be used by controller122to control liquid levels in secondary receiver404and tertiary receiver406.

In the example shown inFIG.4, tertiary receiver406provides refrigerant to an LT subsystem and an MT subsystem. Other arrangements of multiple receivers and subsystems can be included in various implementations. For example, a secondary receiver can be dedicated to provide refrigerant solely to an LT subsystem, while a tertiary receiver can be dedicated to provide refrigerant only to an MT subsystem. Other examples include arrangements in which a primary receiver provides refrigerant to one of the following: (a) an MT subsystem; (b) an LT subsystem; (c) an MT and a LT system; (d) an air conditioning system; (e) an MT subsystem and an air conditioning system; (f) an air conditioning system and an LT subsystem; and (g) an air conditioning system, an MT system, and an LT subsystem. In addition, any combination of the above can be applied to secondary and tertiary receivers.

In one implementation, a primary receiver and a secondary receiver provide refrigerant to MT subsystems at different evaporating temperatures. In another implementation, a secondary receiver and a tertiary receiver provide refrigerant to LT subsystems at different temperatures. In still another implementation, a primary receiver provides refrigerant to an air conditioning system, a secondary receiver provides refrigerant to an MT subsystem, and a tertiary receiver provides refrigerant to an LT subsystem.

In some implementations, a CO2refrigeration system having multiple receivers includes an ejector, flash gas heat exchanger, heat reclamation, parallel compression, or combinations thereof. Examples of ejectors that can be employed include: liquid ejectors, high-pressure ejectors, low-pressure ejectors, and combination ejectors.FIG.5is a block diagram of a CO2refrigeration system according to some implementations. System500includes primary receiver502, secondary receiver504, parallel compressor506, ejector508, and heat recovery unit510. In this example, a gas cooler intercooler evaporator512is coupled to condenser514. Parallel compressor506is configured to receive a flow from of gas refrigerant from primary receiver502. Primary receiver502and secondary receiver504provide liquid refrigerant to various heat load subsystems. Liquid feed valve516can be operated to control a liquid level in secondary receiver504. Pressure control of receivers and control of the heat load subsystems can be similar to that described above with respect toFIGS.1through4.

FIG.6is a block diagram illustrating a portion of a CO2refrigeration system including an ejector and flash gas heat exchanger according to some implementations. CO2refrigeration system600includes heat exchanger602, heat exchanger 3-way valve604, ejector606, and high pressure valve608. Heat exchanger602includes coil610and coil612. Coil610is in heat transfer communication with coil612, such that heat in fluid passing through coil610is transferred to fluid passing through coil612.

Heat exchanger602receives a flow of refrigerant from a gas cooler (such as gas cooler102shown inFIG.1) via conduit614. Refrigerant passes to one or more receivers via conduit616. Conduit618can be fluidly coupled to the suction side of one or more parallel compressors (such as parallel compressor506shown inFIG.5). Conduit620can be coupled to a flash gas outlet of one or more receivers. Conduit622can receive refrigerant from the the output of one or more evaporators of a cooling subsystem (such as MT subsystem116shown inFIG.1). In various implementations, ejector606can be a high pressure ejector, a low pressure lift ejector, or a combination ejector. In certain implementations, conduit622receives refrigerant from a liquid accumulator of an MT subsystem.

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 and medium temperatures loads and/or cooling systems.

In various examples described above, a CO2refrigeration system is cooled by an adiabatic gas cooler. In other implementations, a CO2refrigeration system can be cooled by other systems, such as an air cooled or water cooled device.

Particular embodiments of the subject matter have been described. Other embodiments, 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 embodiments 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.