SYSTEM AND METHOD FOR DUAL-CIRCUIT REFRIGERATION USING FLAMMABLE AND NON-FLAMMABLE REFRIGERANTS

Description

TECHNICAL FIELD

This disclosure relates generally to refrigeration systems. More particularly, this disclosure relates to a system and method for dual-circuit refrigeration using flammable and non-flammable refrigerants.

BACKGROUND

Cooling systems are used to cool spaces, such as residential dwellings, commercial buildings, and/or refrigeration units. These systems cycle a refrigerant (also referred to as charge) that is used to cool the spaces.

SUMMARY OF THE DISCLOSURE

Regulations are increasingly requiring manufacturers to transition from traditional refrigerants to low-global warming potential (GWP) refrigerants, particularly mildly flammable (A2L) and highly flammable (A3) types. Currently, there is a need for refrigeration systems specifically designed to accommodate low-GWP refrigerants. For example, propane (R290), an A3 refrigerant, offers a sustainable alternative with an exceptionally low GWP. However, due to its high flammability, regulatory guidelines have set strict limits on the allowable charge for propane, such as approximately 304 grams. This limitation constrains the cooling capacity achievable in a single refrigerant circuit, especially in conventional direct expansion (D-X) systems where one refrigerant is used to absorb heat from the air or material being cooled.

Additionally, some conventional carbon dioxide (CO₂) refrigeration systems, another low-GWP option, may struggle to meet cooling needs in high ambient temperature conditions, such as during summer. When CO₂ reaches its critical point, it enters a supercritical state, which makes it more difficult to condense, which can lead to inefficiencies in providing the required cooling conditioning.

The disclosed system provides a solution to these and other technical problems of conventional refrigeration systems. The disclosed refrigeration system is configured to overcome the cooling limitations seen in the conventional direct expansion (D-X) systems under restricted charge conditions. To this end, the disclosed refrigeration system is configured to utilize CO₂ as a primary refrigerant to provide cooling to target spaces (in a first loop) and propane as a secondary refrigerant to provide cooling to the primary refrigerant (in a second loop). Therefore, the need to increase the charge of propane is reduced. The disclosed refrigeration system further includes a third loop, where propane cools down the CO₂ inside a brazed plate heat exchanger (BPHE). In this process, the cooled CO₂ flows to a tank and is used in the first loop to provide air conditioning to target spaces. Meanwhile, CO₂ in vapor form from the previous conditioning cycle returns to the BPHE, where its heat is transferred to the propane refrigerant. The warmed propane flows to the compressor and subsequently to the outdoor heat exchanger to dissipate heat into the outdoor environment. Therefore, through a multi-loop configuration, the disclosed refrigeration system operates as follows: (1) in the first loop, CO₂ is used as the primary refrigerant to provide conditioning to target spaces; (2) in the second loop, propane is used to cool the CO₂ without exceeding regulatory charge limits for propane; and (3) in the third loop, the warmed propane flows to BPHE, where it transfers heat from vaporized CO₂, which cools the CO₂ down for reuse in the next cycle.

In this manner, the disclosed refrigeration system is configured to integrate components, such as BPHE, that improve the cooling capacity of CO₂ refrigeration systems even in high ambient temperature conditions and enable efficient heat transfer between the propane and CO₂.

In some embodiments, the refrigeration system comprises a first refrigerant circuit and a second refrigerant circuit. The first refrigerant circuit comprises a flash tank configured to store a primary refrigerant. The first refrigerant circuit further comprises a pump positioned downstream of the flash tank, and configured to pump the primary refrigerant received from the flash tank. The first refrigerant circuit further comprises an indoor heat exchanger positioned downstream of the pump, and configured to provide air conditioning to a target space by transferring heat between the primary refrigerant and the target space.

The second refrigerant circuit comprises a compressor positioned downstream of an internal heat exchanger, that is configured to compress a secondary refrigerant received from the internal heat exchanger. The second refrigerant circuit further comprises the internal heat exchanger positioned downstream of an outdoor heat exchanger, which is configured to receive the primary refrigerant in vapor form from the flash tank, condense the primary refrigerant back into liquid by transferring heat from the primary refrigerant to the secondary refrigerant, provide the primary refrigerant in liquid form to the flash tank, and provide the secondary refrigerant to the compressor. The second refrigerant circuit further comprises the outdoor heat exchanger positioned downstream of the compressor, which is configured to condense the secondary refrigerant by releasing heat from the secondary refrigerant to the outdoors.

Certain embodiments of the present disclosure may include some, or none of these advantages. These advantages and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 1 illustrates a diagram of an embodiment of a refrigeration system, according to some embodiments of the present disclosure; and

FIG. 2 illustrates a flowchart of an example method of operating the system of FIG. 1.

DETAILED DESCRIPTION

Embodiments of the present disclosure and its advantages are best understood by referring to FIGS. 1 through 2 of the drawings, like numerals being used for like and corresponding parts of the various drawings.

Regulations are increasingly requiring manufacturers to transition from traditional refrigerants to low-global warming potential (GWP) refrigerants, particularly mildly flammable (A2L) and highly flammable (A3) types. Currently, there is a need for refrigeration systems specifically designed to accommodate low-GWP refrigerants. For example, propane (R290), an A3 refrigerant, offers a sustainable alternative with an exceptionally low GWP. However, due to its high flammability, regulatory guidelines have set strict limits on the allowable charge for propane, such as approximately 304 grams. This limitation constrains the cooling capacity achievable in a single refrigerant circuit, especially in conventional direct expansion (D-X) systems where one refrigerant is used to absorb heat from the air or material being cooled.

Additionally, some conventional carbon dioxide (CO₂) refrigeration systems, another low-GWP option, may struggle to meet cooling needs in high ambient temperature conditions, such as during summer. When CO₂ reaches its critical point, it enters a supercritical state, which makes it more difficult to condense, which can lead to inefficiencies in maintaining required cooling performance.

The disclosed system provides a solution to these and other technical problems of conventional refrigeration systems. The disclosed refrigeration system is configured to overcome the cooling limitations seen in the conventional direct expansion (D-X) systems under restricted charge conditions. To this end, the disclosed refrigeration system is configured to utilize CO₂ as a primary refrigerant to provide cooling to target spaces (in a first loop) and propane as a secondary refrigerant to provide cooling to the primary refrigerant (in a second loop). Therefore, the need to increase the charge of propane is reduced. The disclosed refrigeration system further includes a third loop, where propane cools down the CO₂ inside a brazed plate heat exchanger (BPHE). In this process, the cooled CO₂ flows to a tank and is used in the first loop to provide air conditioning to target spaces. Meanwhile, CO₂ in vapor form from the previous conditioning cycle returns to the BPHE, where its heat is transferred to the propane. The warmed propane flows to the compressor and subsequently to the outdoor heat exchanger to dissipate heat into the outdoor environment. Therefore, through a multi-loop configuration, the disclosed refrigeration system operates as follows: (1) in the first loop, CO₂ is used as the primary refrigerant to provide conditioning to target spaces; (2) in the second loop, propane is used to cool the CO₂ without exceeding regulatory charge limits for propane; and (3) in the third loop, the warmed propane flows to BPHE, where it transfers heat from vaporized CO₂, which cools the CO₂ down for reuse in the next cycle.

In this manner, the disclosed refrigeration system is configured to integrate components, such as BPHE, that improve the cooling capacity of CO₂ refrigeration systems even in high ambient temperature conditions and enable efficient heat transfer between the propane and CO₂.

Refrigeration System

FIG. 1 illustrates an example refrigeration system 100 according to an embodiment of the present disclosure. In general, the refrigeration system 100 is configured to implement a dual-refrigeration circuit using flammable and non-flammable refrigerants. In some embodiments, the refrigeration system 100 comprises refrigerant conduit subsystems 102, a flash tank 112, a pump 114, an expansion valve 116, an indoor heat exchanger 118, a pressure relief valve 120, an internal heat exchanger 122, a compressor 124, an outdoor heat exchanger 126, an expansion valve 128, a thermostat 130, a temperature sensor circuit 136, and a controller 140. In some embodiments, the system 100 comprises a first refrigerant circuit 104 which includes the flash tank 112, the pump 114, the expansion valve 116, the indoor heat exchanger 118, the pressure relief valve 120, and the internal heat exchanger 122. In some embodiments, the system100 further comprises a second refrigerant circuit 106 which includes the compressor 124, the outdoor heat exchanger 126, and the expansion valve 128. The first refrigerant circuit 104 may include indoor units and be configured to circulate a primary refrigerant (e.g., CO₂) that provides cooling to a target space by transferring heat from the target space to the primary refrigerant in the indoor heat exchanger 118. The second refrigerant circuit 106 may include outdoor units and be configured to circulate a secondary refrigerant (e.g., propane) to absorb heat from the primary refrigerant in the internal heat exchanger 122 and reject that heat to the outdoor environment via the outdoor heat exchanger 126.

In some embodiments, the refrigeration system 100 is a transcritical refrigeration system that circulates a non-flammable working fluid, such as a transcritical refrigerant (e.g., CO₂), as a primary refrigerant to provide cooling to target spaces; and circulates at least partially flammable refrigerant, such as propane, as secondary refrigerant, to absorb heat from the CO₂ and facilitate its cooling. The illustrated embodiment of the refrigeration system 100 in FIG. 1 is configured to provide air conditioning to one or more target spaces for one or more applications, such as low-temperature applications (e.g., freezing applications) and medium-temperature applications (e.g., for display cases). In some embodiments, the refrigeration system 100 may include one or more of each of the illustrated components operably coupled to one another. In some embodiments, the refrigeration system 100 may include additional components.

System Components

The refrigerant conduit subsystems 102 facilitate the movement of refrigerants (also referred to herein as working fluids) through a refrigeration cycle such that the working fluid flows as illustrated by arrows in FIG. 1. The refrigerants include a primary refrigerant that is not flammable (e.g. CO₂) and a secondary refrigerant that is at least partially flammable (e.g., propane). The refrigerant conduit subsystem 102 includes any conduit, tubing, and the like that is illustrated in FIG. 1 fluidly connecting components of the refrigeration system 100. In some embodiments, the refrigerant conduit subsystem 102 comprises refrigerant conduit subsystems for circulating a non-flammable refrigerant, such as CO₂, to provide cooling to target spaces, and refrigerant conduit subsystems for circulating a secondary refrigerant, such as propane, to cool down the primary refrigerant within the refrigeration system 100.

The flash tank 112 may generally be a storage component to store primary refrigerant (e.g., CO₂) refrigerant in vapor and liquid forms. The flash tank 112 is fluidly coupled to the refrigerant conduit subsystem 102 and is positioned downstream of the internal heat exchanger 122 (via the second outlet 123b of the internal heat exchanger 122) and the internal heat exchanger 118, and upstream of the internal heat exchanger 122 (via the second inlet 121b of the internal heat exchanger 122) and the pump 114. The flash tank 112 may be configured to separate the primary refrigerant into a vapor refrigerant and a liquid refrigerant. Typically, the vapor refrigerant collects near the top of the flash tank 112 and the liquid refrigerant is collected at the bottom of the flash tank 112. In some embodiments, during providing conditioning according to a conditioning demand, the primary refrigerant in liquid form flows from flash tank 112 toward the indoor heat exchanger 118. Additionally, the primary refrigerant in vapor form (gas) flows from the flash tank 112 toward the internal heat exchanger 122 (at the second inlet 121b) via the pressure relief valve 120 to facilitate heat exchange between the primary refrigerant (CO₂) in vapor form and the secondary refrigerant (e.g., propane), which allows the vapor primary refrigerant to condense and return to the flash tank in liquid form.

The pump 114 may generally be a circulation pump or a refrigerant pump configured to transport the refrigerant through the refrigerant conduit subsystem 102. Examples of pump 114 may include a centrifugal pump, a diaphragm pump, a magnetic drive pump, and a variable-speed pump, among others. The pump 114 is fluidly coupled to the refrigerant conduit subsystem 102, and is positioned downstream of the flash tank 112 and upstream of the indoor heat exchanger 118. The pump 114 may be configured to pump the primary refrigerant (e.g., CO₂) from the flash tank 112 to the indoor heat exchanger 118 (via the expansion valve 116. The pump 114 may operate continuously or intermittently, based on the conditioning demand detected by the controller 140. In some embodiments, the pump 114 is in signal communication with the controller 140 using wired and/or wireless communication. The controller 140 may control the speed and activation of the pump 114 based on the detected cooling demand.

The expansion valve 116 may generally be a flow control valve, a flash gas valve, a solenoid valve, a motorized valve, a check valve, an electronic expansion valve (EEV), a thermal expansion valve (TXV), and the like. The expansion valve 116 may be positioned in the refrigerant conduit subsystem 102 and located in a portion of the refrigerant conduit subsystem 102 that connects the flash tank 112 to the indoor heat exchanger 118. The expansion valve 116 may be fluidly coupled to the refrigerant conduit subsystem 102. The expansion valve 116 is configured to open and close by varying degrees to control the flow of the refrigerant discharged from pump 114 toward the indoor heat exchanger 118 and reduce the temperature of the primary refrigerant before the primary refrigerant enters the indoor heat exchanger 118. The controller 140 may be in signal communication with the expansion valve 116 using wired and/or wireless communication. The controller 140 may control the operation of the expansion valve 116 by sending electronic signals to the expansion valve 116, in the example of EEV valve 116.

The indoor heat exchanger 118 may generally include one or more indoor evaporator coils and fans to move air across the coils. The indoor heat exchanger 118 is fluidly coupled to the refrigerant conduit subsystems 102 and positioned downstream of the flash tank 112 and the valve 116. The indoor heat exchanger 118 is in signal communication with the controller 140 using wired and/or wireless connections. The controller 140 may send control signals to the indoor heat exchanger 118 to control the speed of its fans based on temperature conditions and the cooling demand. The indoor heat exchanger 118 may be configured to receive the primary refrigerant (e.g., CO₂) from the flash tank 112 (via the valve 116 and pump 114) and absorb heat from the target space via the primary refrigerant. The indoor heat exchanger 118 may act as an evaporator. When the primary refrigerant reaches the indoor heat exchanger 118, the primary refrigerant absorbs heat from the surrounding air in the target space and releases cooled or conditioned air into the target space. For example, the primary refrigerant cools metallic components (e.g., metallic coils, plates, and/or tubes) of the indoor heat exchanger 118 as the primary refrigerant passes through them. These metallic components may then cool the air around them. The cooled air may then be circulated such as, for example, by a fan to cool a space such as, for example, a freezer and/or a refrigerated shelf. Therefore, the indoor heat exchanger 118 may provide air conditioning to the target space by transferring heat between the primary refrigerant and the target space.

The pressure relief valve 120 may generally be a check valve, a safety valve, or a pressure-regulating valve configured to allow the flow of the primary refrigerant (e.g., CO₂) in one direction from the flash tank 112 to the internal heat exchanger 122, as shown in FIG. 1. The pressure relief valve 120 is fluidly coupled to the refrigerant conduit subsystem 102 and positioned downstream of the flash tank 112 and upstream of the second inlet 121b of the internal heat exchanger 122. Examples of pressure relief valve 120 may include a spring-loaded relief valve, a diaphragm relief valve, or a check valve, each designed and mechanically calibrated to open when the pressure of the primary refrigerant within the flash tank 112 exceeds a predefined threshold, and close otherwise. In some embodiments, the pressure relief valve 120 may be a passive component, meaning it does not require a control signal to activate. When passive pressure relief valve 120 is implemented, it opens automatically when a threshold pressure is reached within the flash tank 112, and closes otherwise.

The internal heat exchanger 122 may generally be a brazed plate heat exchanger (BPHE), a shell and tube heat exchanger, a coaxial heat exchanger, or a finned-tube heat exchanger, among others. The internal heat exchanger 122 may comprise a first inlet 121a configured to receive the secondary refrigerant from the outdoor heat exchanger 126 (via the expansion valve 128), a first outlet 123a configured to provide the secondary refrigerant in vapor form to the compressor 124, a second outlet 123b configured to provide the primary refrigerant in liquid form to the flash tank 112 (e.g., due to gravity), and a second inlet 121b configured to receive the primary refrigerant in vapor form from the flash tank 112 (via the pressure relief valve 120). The internal heat exchanger 122 is fluidly coupled to the refrigerant conduit subsystem 102 and positioned downstream of the flash tank 112 (at the second inlet 121b) and expansion valve 128 (via the first inlet 121a) and upstream of the flash tank 112 (at the second outlet 123b) and the compressor 124 (via the second outlet 123a). The internal heat exchanger 122 is configured to facilitate heat transfer between the primary refrigerant (e.g., CO₂) in vapor form, which flows from the flash tank 112, and the secondary refrigerant (e.g., propane). To this end, the internal heat exchanger 122 receives the primary refrigerant in vapor form from the flash tank 112, which has a lower temperature due to pressure reduction in the flash tank 112, and circulates it in contact with the secondary refrigerant, e.g., via the blazed plates of BPHE. As the primary refrigerant vapor flows through the internal heat exchanger 122, it transfers heat to the colder secondary refrigerant, which condenses the primary refrigerant back into liquid form by transferring heat from the primary refrigerant to the secondary refrigerant. The internal heat exchanger 122 then provides the primary refrigerant in liquid form to the flash tank 112 and provides the secondary refrigerant to the compressor 124.

The internal heat exchanger 122 may be configured with a surface area (A) and an overall heat transfer coefficient (U) selected from among a plurality of values of A and U, respectively, to increase the heat transfer index between the primary and secondary refrigerants. The heat transfer coefficient (U) may indicate the rate of heat transfer per unit area per unit temperature difference between two mediums (e.g., between the primary refrigerant and the secondary refrigerant). In some embodiments, the internal heat exchanger 122 comprises a surface area (A) that is sufficient to facilitate effective heat transfer for condensing the primary refrigerant to a liquid state within the space constraint of the refrigeration system 100. For example, by simulating various surface areas (A) and the number of the brazed plates within the blazed plate heat exchanger 122, a combination of a particular surface area (A) and a particular number of brazed plates may be identified to accommodate the target heat transfer coefficient while meeting the regulatory refrigerant charge limit and the space constraint. The target heat transfer coefficient may be configured to achieve a heat transfer rate that is required for condensing the primary refrigerant within the temperature and pressure constraints of charge. The surface area (A) may be determined based on simulations where it meets the system size requirement while maintaining the refrigerant charge limit, and the target heat transfer coefficient.

The compressor 124 may be a variable speed compressor or a multiple-stage compressor configured to compress (e.g., increase the pressure of) the secondary refrigerant received from the internal heat exchanger 122. The compressor 124 is generally configured to adjust the cooling capacity by increasing the pressure of the secondary refrigerant to enhance the heat exchange process within the refrigeration system 100. The compressor 124 is fluidly coupled with the refrigerant conduit subsystem 102 and is positioned downstream of the internal heat exchanger 122. The compressor 124 is in signal communication with the controller 140 via wired and/or wireless connections. The controller 140 may transmit electronic signals to adjust the compressor's speed or activate multiple stages to maintain a desired pressure level in the secondary refrigerant circuit. In a variable-speed configuration, the compressor 124 can operate at different speeds to control the pressure and flow rate of the secondary refrigerant. The speed of compressor 124 can be modified to match the cooling demand. In a multi-stage configuration, the controller 140 can activate one or more compressors to adjust cooling capacity based on the cooling demand.

The outdoor heat exchanger 126 may be a high-side heat exchanger, such as a gas cooler or a condenser, and may generally include one or more coils and fans configured to move air across the coils. The outdoor heat exchanger 126 is fluidly coupled to the refrigerant conduit subsystem 102 and is positioned downstream of the compressor 124 and upstream of the expansion valve 128. The outdoor heat exchanger 126 is in signal communication with the controller 140 via wired and/or wireless connections. The controller 140 may send electronic signals to adjust the fan speed based on temperature conditions and cooling demand. The outdoor heat exchanger 126 is configured to transfer heat from the secondary refrigerant (e.g., propane) to the outdoor environment and condense the secondary refrigerant by releasing heat from the secondary refrigerant to the outdoors. When the secondary refrigerant flows through the coils of the outdoor heat exchanger 126, it releases absorbed heat, allowing the refrigerant to cool. When the outdoor heat exchanger 126 operates as a condenser, it cools the secondary refrigerant until it changes from a gaseous to a liquid state. When operating as a gas cooler, the outdoor heat exchanger 126 reduces the temperature of the gaseous refrigerant without changing its state. In certain configurations, the outdoor heat exchanger 126 is positioned such that heat removed from the refrigerant may be discharged into the air in the surrounding environment. For example, the outdoor heat exchanger 126 may be positioned on a rooftop so that heat removed from the refrigerant may be discharged into the air. As another example, the outdoor heat exchanger 126 may be positioned external to a building and/or on the side of a building. This disclosure contemplates any suitable refrigerant (e.g., propane) being used in the disclosed cooling systems. The refrigeration system 100 may include any appropriate number of outdoor heat exchangers 126 with the same or a similar configuration to that shown for the example of the outdoor heat exchanger 126 in FIG. 1.

The expansion valve 128 may be an expansion valve, a high-pressure valve, a motorized valve, a solenoid valve, an electronic expansion valve (EEV), a thermal expansion valve (TXV), or any other suitable valve configured to control the flow of the secondary refrigerant. The expansion valve 128 is fluidly coupled to the refrigerant conduit subsystem 102 and is positioned downstream of the outdoor heat exchanger 126 and upstream of the internal heat exchanger 122. In some embodiments, the expansion valve 128 may be an active component, and in signal communication with the controller 140 using wired and/or wireless connections to allow the controller 140 to send electronic signals to control the opening and closing of the valve. In some embodiments, the expansion valve 128 may be a passive component and may operate without direct control signals from the controller 140. For example, the internal components (e.g., such as a diaphragm or a spring) of the expansion valve 128 may be mechanically calibrated and configured to open and close by varying degrees based on the temperature and pressure of the secondary refrigerant to control the flow rate of the refrigerant. The expansion valve 128 is configured to receive the high-pressured secondary refrigerant discharged from the outdoor heat exchanger 126 and reduce its pressure before it reaches the internal heat exchanger 122. The valve 128 may regulate the pressure of the secondary refrigerant by adjusting its opening to control the flow rate and pressure drop as the refrigerant transitions from the high-pressure side of the outdoor heat exchanger 126 to the lower pressure in the internal heat exchanger 122, and provide a pressure-reduced secondary refrigerant to the internal heat exchanger 122.

The thermostat 130 may be located within the conditioned target space (e.g., a room or building) serviced by the refrigeration system 100. In some embodiments, the controller 140 may be separate from or integrated within the thermostat 130. The thermostat 130 is configured to allow a user to input a desired temperature or baseline setpoint temperature for the conditioned space. In some embodiments, the thermostat 130 includes an interface 132 and display 134 for displaying information related to the operation and/or status of the refrigeration system 100. For example, the interface 132 may communicate with the display 134 to show operational, diagnostic, and/or status messages and provide a visual interface that allows at least one of an installer, a user, a support entity, and a service provider to perform actions with respect to the refrigeration system 100. For example, the interface 132 may communicate with the display 134 to show messages related to the status and/or operation of the refrigeration system 100. The interface 132 may include user interface components to interact with users, e.g., receive a desired temperature for the target space, among others.

The temperature sensor circuit 136 may include one or more temperature sensing circuitries. The temperature sensor circuit 136 may be implemented by a hardware circuit and configured to detect the temperature of the target space that requires conditioning. The temperature sensor circuit 136 may include one or more temperature sensor circuit 136. The temperature sensor circuit 136 may include a thermocouple, a thermistor, a semiconductor-based temperature circuit board, or any other type of temperature sensor. In some examples, the temperature sensor circuit(s) 136 may be positioned upstream and/or downstream of the indoor heat exchanger 118, within the target space, or at any other location. The temperature sensor circuit 136 may be attached to a surface and/or the indoor heat exchanger 118 using any appropriate means (e.g., threaded connections, clamps, adhesives, or the like). The temperature sensor circuit 136 is configured to detect the temperature 162 of the target space periodically (e.g., every second, every minute, etc.) and/or on demand (e.g., in response to a request from a user provided to the controller 140 or a control panel). The temperature sensor circuit 136 is in signal communication with the controller 140 using wired and/or wireless connections. The temperature sensor circuit 136 may provide the detected temperature data 160 (which includes a set of detected temperature 158) to the controller 140. The controller 140 may use the temperature data 160 for evaluating the system conditions. This process is described further below in greater detail in conjunction with the operational flow of the system 100.

The controller 140 is communicatively coupled (e.g., via wired and/or wireless connection) to other components in the refrigeration system 100 and configured to control their operations. In some embodiments, controller 140 can be one or more controllers associated with one or more components of the refrigeration system 100. The controller 140 includes a processor 142 in signal communication with a memory 146 and an input/output (I/O) interface 144. The processor 142 comprises one or more processors. The processor 142 is any electronic circuitry including, but not limited to, state machines, one or more central processing unit (CPU) chips, logic units, cores (e.g., a multi-core processor), field-programmable gate array (FPGAs), application-specific integrated circuits (ASICs), or digital signal processors (DSPs) that communicatively couples to memory 146 and controls the operation of refrigeration system 100. The processor 142 may be a programmable logic device, a microcontroller, a microprocessor, or any suitable combination of the preceding. The processor 142 is communicatively coupled to and in signal communication with the memory 146. The one or more processors are configured to process data and may be implemented in hardware or software. For example, the processor 142 may be 8-bit, 16-bit, 32-bit, 64-bit or of any other suitable architecture. The processor 142 may include an arithmetic logic unit (ALU) for performing arithmetic and logic operations, processor registers that supply operands to the ALU and store the results of ALU operations, and a control unit that fetches instructions from memory 146 and executes them by directing the coordinated operations of the ALU, registers, and other components. The processor 142 may include other hardware and software that operates to process information, control the refrigeration system 100, and perform any of the functions described herein. The processor 142 may be configured to execute software instructions to perform operations of the controller 140. For example, the processor 142 may be configured to execute the software instructions 148 to cause the refrigeration system 100 to perform one or more of its operations described herein. The processor 142 may execute code/software instructions 148 to perform any of its operations. The processor 142 is not limited to a single processing device and may encompass multiple processing devices. The processor 142 may be configured to perform one or more operations of the controller 140 described in FIG. 1 and one or more operations of the method 200 described in FIG. 2.

The memory 146 may be a non-transitory computer-readable medium. The memory 146 includes one or more disks, tape drives, or solid-state drives, and may be used as an overflow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory 146 may be volatile or non-volatile and may comprise a read-only memory (ROM), random-access memory (RAM), ternary content-addressable memory (TCAM), dynamic random-access memory (DRAM), and static random-access memory (SRAM). The memory 146 is operable to store any suitable set of instructions, logic, rules, and/or code for executing the functions described in this disclosure. For example, the memory 146 may store and retrieve information corresponding to software instructions 148, electronic signals 150a-c, temperature data 160, target temperature 164, and/or other data, instructions, and operating parameters for components in the system 100.

The I/O interface 144 is configured to communicate data and signals with other devices. For example, the I/O interface 144 may be configured to communicate electrical signals with the other components of the refrigeration systems 100. The I/O interface 144 may comprise ports and/or terminals for establishing signal communications between the controller 140 and other devices. The I/O interface 144 may be configured to enable wired and/or wireless communications. Connections between various components of the refrigeration system 100 and between components of system 100 may be wired or wireless. For example, conventional cables and contacts may be used to couple the thermostat 130 to the controller 140 and various components of the refrigeration system 100.

In some embodiments, a wireless connection may be employed to provide at least some or all of the connections between components of the refrigeration system 100. In some embodiments, a data bus may couple various components of the refrigeration system 100 together such that data is communicated therebetween. In some embodiments, the data bus may include, for example, any combination of hardware, software embedded in a computer-readable medium, or encoded logic incorporated in hardware or otherwise stored (e.g., firmware) to couple components of the refrigeration system 100 to each other.

As an example and not by way of limitation, the data bus may include an accelerated graphics port (AGP) or other graphics bus, a controller area network (CAN) bus, a front-side bus (FSB), a hypertransport (HT) interconnect, an infiniband interconnect, a low-pin-count (LPC) bus, a memory bus, a micro channel architecture (MCA) bus, a peripheral component interconnect (PCI) bus, a PCI-Express (PCI-X) bus, a serial advanced technology attachment (SATA) bus, a video electronics standards association local (VLB) bus, or any other suitable bus or a combination of two or more of these. In various embodiments, the data bus may include any number, type, or configuration of data buses, where appropriate. In certain embodiments, one or more data buses (which may each include an address bus and a data bus) may couple the controller 140 to other components of the refrigeration system 100.

Operational Flow for Operating the Refrigeration System

In operation, the refrigeration system 100 may provide air conditioning to the target space by circulating the primary and secondary refrigerants through various components, as shown in FIG. 1. The refrigeration system 100 may circulate the primary refrigerant (e.g., CO₂) through the first refrigerant circuit 104 to provide conditioning to the target space, and circulate the secondary refrigerant (e.g., propane) through the second refrigerant circuit 106 to cool the primary refrigerant and reject the heat to the outdoor environment. The operational flow begins when the controller 140 receives a conditioning demand with respect to the target space, such as from the thermostat 130 when a user indicates a desired temperature for the target space. In response to the conditioning demand, the controller 140 activates both the first refrigerant circuit 104 and the second refrigerant circuit 105 until the conditioning demand is met.

The controller 140 may communicate a first electronic signal 150a to activate the compressor 124. The first electronic signal 150a may activate the compressor 124. In response to the compressor 124 being activated, the secondary refrigerant may be circulated through the second refrigerant circuit 106 to reject heat from the secondary refrigerant to the outdoor environment and provide cooling to the primary refrigerant. When the compressor 124 is activated, it compresses the secondary refrigerant, which in turn, increases the pressure and temperature of the secondary refrigerant. The high-pressure, high-temperature secondary refrigerant flows into the outdoor heat exchanger 126, where the secondary refrigerant releases heat to the surrounding outdoor environment. The controller 140 may adjust the speed of fans in the outdoor heat exchanger 126 to increase the heat dissipation as needed based on outdoor temperature conditions and the cooling demand. For example, the controller 140 may communicate a third electronic signal 150c to the outdoor heat exchanger 126 to activate the outdoor heat exchanger 126 and set the fan speed of the outdoor heat exchanger 126 to facilitate heat dissipation into the outdoor environment. After releasing heat, the secondary refrigerant cools and condenses, and exits the outdoor heat exchanger 126 in liquid form.

The secondary refrigerant flows from the outdoor heat exchanger 126 to the expansion valve 128, where the pressure and temperature of the secondary refrigerant are reduced. The expansion valve 128 regulates the flow rate and pressure of the secondary refrigerant before it enters the internal heat exchanger 122 to increase the heat transfer between the primary refrigerant and the secondary refrigerant. In the internal heat exchanger 122, the secondary refrigerant, now at a lower pressure and temperature, absorbs heat from the primary refrigerant, which flows in vapor form from the flash tank 112. This heat transfer condenses the primary refrigerant back into liquid form, which is then directed back to the flash tank 112 for recirculation. Meanwhile, the warmed secondary refrigerant exits the internal heat exchanger 122 and returns to the compressor 124, which completes the second refrigerant circuit 106 cycle. This cycle may continue as long as the compressor 124 remains active to meet the cooling demand.

The controller 140 may communicate a second electronic signal 150b to activate the indoor heat exchanger 118. The second electronic signal 150b may activate the indoor heat exchanger 118. In response to the indoor heat exchanger 118 being activated, the primary refrigerant may be circulated through the first refrigerant circuit 104 to absorb heat from the target space, which in turn, provides conditioning to the target space. In response, the primary refrigerant is circulated through the first refrigerant circuit 104 until the received air conditioning demand is met. As the primary refrigerant flows through the indoor heat exchanger 118, it absorbs heat from the air within the target space, cooling the air and causing the primary refrigerant to evaporate, which transitions from a liquid to a vapor state as it absorbs the heat.

When the vapor pressure in the flash tank 112 exceeds a certain threshold, the pressure relief valve 120 opens to allow the primary refrigerant vapor to flow from the flash tank 112 to the internal heat exchanger 122. This refrigerant flow through the pressure relief valve 120 facilitates efficient heat transfer in the internal heat exchanger 122 by facilitating that the primary refrigerant vapor enters the internal heat exchanger 122 at the appropriate pressure to allow effective condensation by the secondary refrigerant. After absorbing heat in the indoor heat exchanger 118, the primary refrigerant, now in vapor form, flows from the indoor heat exchanger 118 back to the flash tank 112. In the flash tank 112, the primary refrigerant separates into vapor and liquid forms, where the vapor rises to the top of the flash tank 112 and the liquid is collected at the bottom. This allows the primary refrigerant in liquid form to be pumped again by the pump 114 through the first refrigerant circuit 104 to maintain subsequent circulations for cooling the target space.

In the first refrigerant circuit 104, the liquid primary refrigerant stored in the flash tank 112 is pumped by the pump 114 toward the indoor heat exchanger 118. This process continues until the conditioning demand is met. The controller 140 may determine whether the conditioning demand is met by comparing the detected temperature 162 of the primary refrigerant with the target temperature 164 associated with the conditioning demand. During this operational cycle, the controller 140 monitors temperature and pressure conditions within both the first refrigerant circuit 104 and the second refrigerant circuit 106. The controller 140 compares the temperature in the target space (that may correspond to the temperature 162 of the primary refrigerant received from the temperature sensor circuit 136) to the desired temperature 164 set by the cooling demand. If the temperature in the target space deviates from the desired temperature, the controller 140 may adjust the operation of any combination of the components of the system 100 to meet the conditioning demand. In other words, if the detected temperature 162 of the primary refrigerant does not correspond to the target temperature (or is outside an allowed tolerance range from the target temperature), the controller 140 may continue to operate the first refrigerant circuit 104 and the second refrigerant circuit 106 of the refrigeration system 100 to maintain the circulation of the primary refrigerant and secondary refrigerant to meet the cooling demand. For example, if additional cooling is required, the controller 140 may increase the speed of the compressor 124 or modify the opening of the expansion valve 128 to increase the flow rate of the secondary refrigerant, to increase the heat transfer coefficient in the internal heat exchanger 122.

Example Method for Operating a Refrigeration System

FIG. 2 illustrates a flowchart of an example method 200 of operating the system 100 of FIG. 1. The method 200 may be performed by the controller 140 (see FIG. 1) when one or more processors (e.g., processor 142 of FIG. 1) execute software instructions (e.g., software instructions 148) stored in one or more memories (e.g., memory 146 of FIG. 1). The method 200 may include operations 202-216. Modifications, additions, or omissions may be made to method 200. Method 200 may include more, fewer, or other operations. For example, operations may be performed in parallel or in any suitable order.

At operation 202, the controller 140 may receive a conditioning demand with respect to a target space, similar to that described in FIG. 1. The conditioning demand may be associated with the target temperature 164 that is a desired temperature for the target space.

At operation 204, the controller 140 may communicate a first electronic signal 150a to the compressor 124 to activate the compressor 124, similar to that described in FIG. 1. For example, the first electronic signal 150a may activate and set a speed of the compressor 124 to meet the conditioning demand.

At operation 206, the controller 140 may communicate a second electronic signal 150b to the indoor heat exchanger 118 to activate the indoor heat exchanger 118, similar to that described in FIG. 1. For example, the second electronic signal 150b may activate and set the speed of the fans of the indoor heat exchanger 118 to facilitate heat absorption from the target space.

At operation 208, the controller 140 may communicate a third electronic signal 150c to the outdoor heat exchanger 126 to activate the outdoor heat exchanger 126, similar to that described in FIG. 1. For example, the third electronic signal 150c may activate and set the fan speed of the outdoor heat exchanger 126 to facilitate heat dissipation into the outdoor environment.

At operation 210, the controller 140 may receive the temperature 162 of the primary refrigerant from the temperature sensor circuit 136 downstream of the indoor heat exchanger 118. The controller 140 may compare the received temperature 162 with the target temperature 164 associated with the conditioning demand.

At operation 212, the controller 140 may determine whether the received temperature 162 meets is more than the target temperature 164 associated with the conditioning demand. If it is determined that the received temperature 162 is more than the target temperature 164 (“Yes”), the method 200 may proceed to operation 214. Otherwise (“No”), the method 200 may proceed to operation 216.

At operation 214, the controller 140 may adjust the operation of one or more components to reduce the temperature 162 of the primary refrigerant until the conditioning demand is met. For example, the controller 140 may increase the speed of the compressor 124 by communicating an electronic signal to the compressor 124 that causes the speed of the compressor 124 to increase, increase the speed of the fans of the outdoor heat exchanger 126 by communicating an electronic signal to the outdoor heat exchanger 126 that causes the speed of the fans of the outdoor heat exchanger 126 to increase, among others.

At operation 216, the controller 140 may adjust the operation of one or more components to increase the temperature 162 of the primary refrigerant until the conditioning demand is met. For example, the controller 140 may decrease the speed of the compressor 124 by communicating an electronic signal to the compressor 124 that causes the speed of the compressor 124 to decrease, decrease the speed of the fans of the outdoor heat exchanger 126 by communicating an electronic signal to the outdoor heat exchanger 126 that causes the speed of the fans of the outdoor heat exchanger 126 to decrease, among others.

Although this disclosure has been described in terms of certain embodiments, alterations, and permutations of the embodiments will be apparent to those skilled in the art. Accordingly, the above description of the embodiments does not constrain this disclosure. Other changes, substitutions, and alterations are possible without departing from the spirit and scope of this disclosure.

While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated with another system or certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.

To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants note that they do not intend any of the appended claims to invoke 35 U.S.C. § 112(f) as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.