Patent Application
20230408159
This disclosure relates generally to refrigeration systems. More particularly, in certain embodiments, this disclosure relates to hot gas defrost using medium temperature discharge gas.
Refrigeration systems are used to regulate environmental conditions within an enclosed space. Refrigeration systems are used for a variety of applications, such as in supermarkets and warehouses, to cool stored items. For example, refrigeration systems may provide cooling operations for refrigerators and freezers.
During operation of refrigeration systems, ice may build up on evaporators. These evaporators need to be defrosted to remove ice buildup and prevent loss of performance. Previous evaporator defrost processes are limited in terms of their efficiency and effectiveness. For example, using previous technology, defrost processes may take a relatively long time and consume a relatively large amount of energy. In some cases, previous technology may be incapable of providing adequate defrosting, for instance, in cases where a relatively large number of evaporators need to be defrosted in a multiple-evaporator refrigeration system.
This disclosure provides technical solutions to the problems of previous technology, including those described above. For example, a refrigeration system is described that facilitates improved evaporator defrost using medium temperature discharge gas from one or more compressors located downstream of a medium temperature portion of the refrigeration system. While one or a portion of the evaporators of the refrigeration system are operating in a normal refrigeration mode, other evaporator(s) can be operated in a defrost mode using the hot gas produced by the refrigeration process. When defrost operations are complete, evaporators may be operated in a transition mode that protects the system from sudden increases in pressure before the system is returned to normal refrigeration mode operation. Embodiments of this disclosure may provide improved defrost operations to evaporators of refrigeration systems, such as CO2 refrigeration systems. Certain embodiments may include none, some, or all of the above technical advantages. One or more other technical advantages may be readily apparent to one skilled in the art from the figures, descriptions, and claims included herein.
In an embodiment, a refrigeration system includes a plurality of evaporators configured to transfer heat from a space to a refrigerant, one or more medium temperature compressors configured to compress the refrigerant, and a three-way valve positioned downstream from the one or more medium temperature compressors. The three-way valve receives the compressed refrigerant from the one or more medium temperature compressors and is operable to direct flow of the received compressed refrigerant to one or both of (i) a gas cooler and (ii) one or more of the evaporators of the plurality of evaporators based on an operation mode of the plurality of evaporators. A controller is communicatively coupled to the three-way valve. The controller determines that operation of a first evaporator of the plurality of evaporators in a defrost mode is indicated and, after determining that operation of the first evaporator in the defrost mode is indicated, causes the first evaporator to operate in the defrost mode by adjusting the three-way valve to direct a portion of the received compressed refrigerant to the first evaporator.
For a more complete understanding of the present disclosure, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:
Embodiments of the present disclosure and its advantages are best understood by referring to
As described above, prior to this disclosure, defrost operations of refrigeration systems suffered from certain inefficiencies and drawbacks. The refrigeration system of this disclosure provides improvements in defrost performance and energy efficiency. The refrigeration system of this disclosure may be a CO2 refrigeration system. CO2 refrigeration systems may differ from conventional refrigeration systems in that these systems circulate refrigerant that may become a supercritical fluid (i.e., where distinct liquid and gas phases are not present) above the critical point. As an example, the critical point for carbon dioxide (CO2) is 31° C. and 73.8 MPa, and above this point, CO2 becomes a homogenous mixture of vapor and liquid that is called a supercritical fluid. This unique characteristic of transcritical refrigerants is associated with certain operational differences between transcritical and conventional refrigeration systems. For example, transcritical refrigerants are typically associated with discharge temperatures that are higher than their critical temperatures and discharge pressures that are higher than their critical pressures. When a transcritical refrigerant is at or above its critical temperature and/or pressure, the refrigerant may become a “supercritical fluid”—a homogenous mixture of gas and liquid. Supercritical fluid does not undergo phase change process (vapor to liquid) in a gas cooler as occurs in a condenser of a conventional refrigeration system circulating traditional refrigerant. Rather, supercritical fluid cools down to a lower temperature in the gas cooler. Stated differently, the gas cooler in a CO2 transcritical refrigeration system may receive and cool supercritical fluid, and the transcritical refrigerant undergoes a partial state change from gas to liquid as it is discharged from an expansion valve.
Refrigeration system 100 includes one or more MT compressors 102, refrigerant conduit subsystem 104, three-way valve 106, gas cooler 108, flash tank 112, one or more MT evaporators 116 and corresponding valves 114, 118, 120, 122, 124, one or more low-temperature (LT) evaporators 128 and corresponding valves 126, 130, 132, 134, 136, one or more LT compressors 138, a valve 140, a flash-gas bypass valve 142, and controller 150. In some embodiments, refrigeration system 100 is a transcritical refrigeration system that circulates a transcritical refrigerant such as CO2.
The MT compressor(s) 102 are configured to compress refrigerant discharged from the MT evaporator(s) 116 operating in refrigeration mode (as shown in each of
Refrigerant conduit subsystem 104 facilitates the movement of refrigerant (e.g., CO2) through a refrigeration cycle such that the refrigerant flows in the refrigeration mode as illustrated by the arrows in
Three-way valve 106 is generally a motorized or otherwise electronically controllable three-way valve. Three-way valve 106 receives compressed refrigerant from the MT compressor(s) 102 and is adjustable to control the direction of this refrigerant towards the gas cooler 108 to be used to provide refrigeration and/or toward the MT and/or LT evaporators 116, 128 to provide defrost. The controller 150 is in communication with three-way valve 106 and controls its operation.
Gas cooler 108 is generally operable to receive refrigerant (e.g., from three-way valve 106) and apply a cooling stage to the received refrigerant. In some embodiments, gas cooler 108 is a heat exchanger comprising cooler tubes configured to circulate the received refrigerant and coils through which ambient air is forced. Inside gas cooler 108, the coils may absorb heat from the refrigerant, thereby cooling the refrigerant.
Flash tank 112 is configured to receive mixed-state refrigerant and separate the received refrigerant into flash gas and liquid refrigerant. Flash tank 112 may include one or more tanks operable to hold refrigerant at least temporarily. Typically, the flash gas collects near the top of flash tank 112, and the liquid refrigerant is collected in the bottom of flash tank 112. A valve 110 may be disposed at or near an inlet of the flash tank 112 to reduce pressure of refrigerant received by the flash tank 112. When both evaporators 116 and 128 are operated in refrigeration mode (see
When operated in refrigeration mode (see
Each of the one or more MT evaporators 116 has corresponding valves 114, 118, 120, 122, 124 to facilitate operation of the MT evaporator 116 in a refrigeration mode, a defrost mode, and a transition mode. Valve 114 may be an expansion valve. Expansion valve 114 may be configured to receive liquid refrigerant from flash tank 112 and reduce the pressure of the received refrigerant. In some embodiments, this reduction in pressure causes some of the refrigerant to vaporize. Valve 118 may be a motorized orifice valve. Valve 118 at least partially opens when the MT evaporator 116 is operated in a transition mode to direct refrigerant back toward the MT compressor(s) 102, as described in greater detail below. Valves 120, 122, 124 may be any appropriate motorized or electronically controllable valves, such as motorized ball valves, solenoid valves, and/or the like. The controller 150 is in communication with valves 114, 118, 120, 122, 124 and controls their operation.
When the MT evaporator 116 is operated in the refrigeration mode illustrated in
When the MT evaporator 116 is operated in the defrost mode (not shown for conciseness), the three-way valve 106 is adjusted such that at least a portion of compressed refrigerant from the MT compressor(s) 102 is directed towards the MT evaporator 116. The first valve 114 upstream of the evaporator 116 is closed, and the second valve 120 downstream of the evaporator 116 is closed. Third valve 124 and fourth valve 122 are opened to allow flow of compressed refrigerant from the three-way valve 106 toward the MT evaporator 116. The transition-mode valve 118 is closed. In this configuration, heated refrigerant from MT compressor(s) 102 flows through the evaporator 116 and defrosts the evaporator 116. Refrigerant exiting the evaporator 116 flows through the opened valve 124 and to optional pressure-regulating valve 140. Pressure-regulating valve 140, if present, adjusts the pressure of the refrigerant (i.e., decreases or increases pressure of the refrigerant) before it flows back into the flash tank 112.
Once defrost mode operation is complete, the controller 150 may end defrost mode operation and start transition mode operation by at least partially opening valve 118. In some embodiments, the controller 150 may cause defrost mode to end after a predefined period of time included in the instructions 158 and/or schedule 162. In some embodiments, the controller 150 may cause defrost mode operation to end after predefined conditions indicated in the instructions 158 are reached (e.g., after a temperature and/or pressure 160 measured by sensor 144 reaches a threshold 164).
When the MT evaporator 116 is operated in the transition mode (not shown for conciseness), the three-way valve 106 is adjusted such that compressed refrigerant from the MT compressor(s) 102 is no longer provided to the MT evaporator 116. The first valve 114 upstream of the evaporator 116 is closed, and the second valve 120 downstream of the evaporator 116 is closed. Third valve 124 and fourth valve 122 are also closed to stop the flow of compressed refrigerant from the three-way valve 106 toward the MT evaporator 116. The transition-mode valve 118 is opened to allow a controlled flow of refrigerant toward the MT compressor(s) 102. In this configuration, heated refrigerant from the evaporator 116 flows back to the MT compressor(s) 102 at a relatively slow rate determined by the radius of the orifice valve 118. Transition mode operation may continue at least until a pressure of the evaporator 116 is below a threshold value 164. For example, a sensor 144 may measure a pressure and/or temperature 160 of the evaporator 116 that is compared to a threshold 164 in order to end transition mode operation. When transition mode operation is complete, the evaporator 116 returns to refrigeration mode operation.
The LT evaporator 128 is generally similar to the MT evaporator 116 but is configured to operate at lower temperatures (e.g., for deep freezing applications near about −30° C. or the like). When operated in refrigeration mode (see
The LT evaporator 128 includes valves 126, 130, 132, 134, 136 to facilitate operation of the LT evaporator 128 in a refrigeration mode (see
When the LT evaporator 128 is operated in the refrigeration mode illustrated in
When the LT evaporator 128 is operated in the defrost mode of
Once defrost mode operation is complete, the controller 150 may end defrost mode operation and start transition mode operation by at least partially opening valve 130, as shown in the example of
When the LT evaporator 128 is operated in the transition mode of
The temperature and/or pressure sensors 144, 146 may be disposed on, in, or near the corresponding evaporators 116, 128 or refrigerant conduit connected to the evaporators 116, 128. In addition to being used to determine when transition mode operation can be ended, information from sensors 144, 146 may assist in determining when operation in defrost mode is appropriate or should be ended. For example, if the temperature and/or pressure 160 measured by sensors 144, 146 indicates potential freezing of the MT evaporator 116 and/or LT evaporator 128, defrost mode operation may be indicated. In some cases, defrost mode operation is determined to be indicated based on a schedule 162 (e.g., defrost mode operation may be performed at certain predefined time intervals or at certain times).
Valves 114, 118, 120, 122, and 124 for the MT evaporator 116 and valves 126, 130, 132, 134, and 136 for the LT evaporator 128 may be in communication with controller 150, and the controller 150 may provide instructions for adjusting these valves 114, 118, 120, 122, 124, 126, 130, 132, 134, 136 to open or closed positions to achieve the configurations described above for refrigeration mode operation, defrost mode operation, and transition mode operation. For example, instructions 158 implemented by the processor 152 of the controller 150 may determine that operation of the MT evaporator 116 and/or the LT evaporator 128 in a defrost mode is indicated. For example, instructions 158 stored by the controller 150 may indicate that defrost mode operation is needed on a certain schedule 162 or at a certain time. As another example, a temperature and/or pressure 160 of the evaporators 116, 128 may indicate that defrost mode operation is needed (e.g., because the temperature and/or pressure 160 indicates that expected cooling performance or efficiency is not being obtained).
Flash gas bypass valve 142 may be located in refrigerant conduit of the conduit subsystem 104 connecting the flash tank 112 to the MT compressor(s) 102 and configured to open and close to permit or restrict the flow of flash gas discharged from flash tank 112. In some embodiments, controller 150 controls the opening and closing of flash gas bypass valve 142. As depicted in
As described above, controller 150 is in communication with at least three-way valve 106; valves 114, 118, 120, 122, and 124 of the MT evaporator 116; valves 126, 130, 132, 134, and 136 of the LT evaporator 128; and compressors 102, 138. The controller 150 adjusts operation of components of the refrigeration system 100 to operate the evaporators 116, 128 in refrigeration mode, defrost mode, or transition mode as described herein. The controller 150 includes a processor 152, memory 154, and input/output (I/O) interface 156. The processor 152 includes one or more processors operably coupled to the memory 154. The processor 152 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 154 and controls the operation of refrigeration system 100.
The processor 152 may be a programmable logic device, a microcontroller, a microprocessor, or any suitable combination of the preceding. The processor 152 is communicatively coupled to and in signal communication with the memory 154. The one or more processors are configured to process data and may be implemented in hardware or software. For example, the processor 152 may be 8-bit, 16-bit, 32-bit, 64-bit or of any other suitable architecture. The processor 152 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 154 and executes them by directing the coordinated operations of the ALU, registers, and other components. The processor 152 may include other hardware and software that operates to process information, control the refrigeration system 100, and perform any of the functions described herein (e.g., with respect to
The memory 154 includes one or more disks, tape drives, or solid-state drives, and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions 158 and data that are read during program execution. The memory 154 may be volatile or non-volatile and may include ROM, RAM, ternary content-addressable memory (TCAM), dynamic random-access memory (DRAM), and static random-access memory (SRAM). The memory 154 is operable (or configured) to store information used by the controller 150 and/or any other logic and/or instructions for performing the function described in this disclosure.
The I/O interface 156 is configured to communicate data and signals with other devices. For example, the I/O interface 156 may be configured to communicate electrical signals with components of the refrigeration system 100 including valves 106, 114, 118, 120, 122, 124, 126, 130, 132, 134, 136, 140, 142; sensors 144, 146; and compressors 102, 138. The I/O interface 156 may be configured to communicate with other devices and systems. The I/O interface 156 may provide and/or receive, for example, compressor speed signals, compressor on/off signals, valve open/close signals, temperature signals, pressure signals, temperature setpoints, environmental conditions, and an operating mode status for the refrigeration system 100 and send electrical signals to the components of the refrigeration system 100. The I/O interface 156 may include ports or terminals for establishing signal communications between the controller 150 and other devices. The I/O interface 156 may be configured to enable wired and/or wireless communications.
Although this disclosure describes and depicts refrigeration system 100 including certain components, this disclosure recognizes that refrigeration system 100 may include any suitable components. As an example, refrigeration system 100 may include one or more additional sensors configured to detect temperature and/or pressure information.
In an example operation of the refrigeration system 100, the refrigeration system 100 is initially operating with both evaporators 116, 128 in the refrigeration mode, as illustrated in
At some point during operation of the refrigeration system 100, the controller 150 determines that defrost mode operation is needed for the LT evaporator 128. For example, the LT evaporator 128 may be scheduled for defrost at the time that has just been reached. After determining that the defrost mode operation is indicated, the controller 150 causes the LT evaporator 128 to be configured according to
Once defrost of the LT evaporator 128 is complete (e.g., because defrost mode operation has been performed for a predefined period of time and/or a threshold pressure and/or temperature 160 of the LT evaporator 128 has been reached), the controller 150 causes the LT evaporator 128 to operate in the transition mode as illustrated in
At operation 406, the controller 150 causes the evaporator 116, 128 determined at operation 404 to be operated in the defrost mode. For instance, if defrost of the LT evaporator 128 is needed, the controller 150 may cause the three-way valve 106 to allow a portion of refrigerant from the MT compressor(s) 102 to flow towards the LT evaporator 128. First valve 126 and second valve 132 are closed, and third valve 136 and fourth valve 134 are opened. The transition-mode valve 130 remains closed. This achieves the defrost mode configuration of evaporator 128 illustrated in
At operation 408, the controller 150 determines whether defrost mode operation of the evaporator 128 is complete. For example, the controller 150 may determine whether defrost mode operation has been performed for a predefined period of time indicated by schedule 162 and/or if a threshold value 164 is reached for a pressure and/or temperature 160 of the LT evaporator 128. If defrost mode operation is not complete, the controller continues to operate in the defrost mode at operation 406. Once defrost mode operation is complete, the controller 150 proceeds to operation 410
At operation 410, the controller 150 causes the evaporator 128 to operate in the transition mode. For example, the controller 150 may cause third valve 136 and fourth valve 134 to close and may open, at least partially, transition-mode valve 130. At operation 412, the controller determines whether the transition mode operation is complete. For example, the controller 150 may determine whether a temperature and/or pressure 160 of the LT evaporator 128 is less than a threshold value 164 (e.g., of 20 bar). If transition mode operation is not complete, the controller 150 continues to operate the evaporator 128 in the transition mode. However, if transition mode operation is complete, the controller 150 returns to operation 402 and operates the evaporator 128 in the refrigeration mode.
Modifications, additions, or omissions may be made to method 400 depicted in
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 in 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.
