REFRIGERATION SYSTEM WITH FLUID DEFROST
A refrigeration system having a refrigerant circuit including a condenser, a flow control device, an evaporator, and a compressor connected in series. The compressor is configured to circulate a cooling fluid through the refrigerant circuit. The refrigerant circuit has an inlet line fluidly connecting the condenser to the evaporator and a suction line fluidly connecting the evaporator to the compressor. A heater is positioned to heat the cooling fluid during a defrost mode, and a pressure control is coupled to the refrigerant circuit downstream of the evaporator. In the defrost mode, the pressure control apparatus is configured to increase system pressure during the defrost mode to maintain flow of refrigerant into the evaporator and to control flow of cooling fluid to the compressor.
This application claims priority to and is a continuation-in-part of U.S. patent application Ser. No. 15/093,346, filed Apr. 7, 2016, the entire contents of which are incorporated by reference herein.
BACKGROUNDThe present invention relates to refrigeration systems and, more particularly, to fluid defrost of heat exchangers in refrigeration systems.
Refrigeration systems are well known and widely used in supermarkets, warehouses, and elsewhere to refrigerate product that is supported in a refrigerated space. Conventional refrigeration systems include a heat exchanger or evaporator, a compressor, and a condenser. The evaporator provides heat transfer between a refrigerant flowing within the evaporator and a fluid (e.g., water, air, etc.) passing over or through the evaporator. The evaporator transfers heat from the fluid to the refrigerant to cool the fluid. The refrigerant absorbs the heat from the fluid and evaporates in a refrigeration mode, during which the compressor mechanically compresses the evaporated refrigerant from the evaporator and feeds the superheated refrigerant to the condenser, which cools the refrigerant. From the condenser, the cooled refrigerant is typically fed through an expansion valve to reduce the temperature and pressure of the refrigerant, and then the refrigerant is directed through the evaporator.
Some evaporators operate at evaporating refrigerant temperatures that are near or lower than the freezing point of water (i.e., 32 degrees Fahrenheit). Over time, water vapor from the fluid freezes on the evaporator (e.g., on the coils) and generates frost. Accumulation of frost decreases the efficiency of heat transfer between the evaporator and the fluid passing over the evaporator, which causes the temperature of the refrigerated space to increase above a desired level. Maintaining the correct temperature of the refrigerated space is important to maintain the quality of the stored product. To do this, evaporators must be regularly defrosted to reestablish efficiency and proper operation. Many existing refrigeration systems use electric heaters that are placed underneath the evaporator to defrost the evaporator using convection heat. Other existing systems re-route hot gaseous refrigerant from the compressor directly to the evaporator so that heat from the hot refrigerant melts the frost on the evaporator (i.e. reverse hot gas defrost).
SUMMARYIn one aspect, the present invention provides a refrigeration system having a refrigerant circuit including a condenser, a flow control device, an evaporator, and a compressor connected in series. The compressor is configured to circulate a cooling fluid through the refrigerant circuit. The refrigerant circuit has an inlet line fluidly connecting the condenser to the evaporator and a suction line fluidly connecting the evaporator to the compressor. A heater is positioned to heat the cooling fluid during a defrost mode, and a pressure control is coupled to the refrigerant circuit downstream of the evaporator. In the defrost mode, the pressure control apparatus is configured to increase system pressure during the defrost mode to maintain flow of refrigerant into the evaporator and to control flow of cooling fluid to the compressor.
In another aspect, the present invention provides a refrigeration system having a refrigerant circuit including a condenser, a flow control device, an evaporator, and a compressor connected in series. The compressor is configured to circulate a refrigerant through the refrigerant circuit. The refrigerant circuit has an inlet line fluidly connecting the condenser to the evaporator and a suction line fluidly connecting the evaporator to the compressor. A refrigeration mode directs the refrigerant through the evaporator in a first direction via the inlet line. A defrost mode directs refrigerant though the evaporator in the first direction via the inlet line. A first heater is coupled to the inlet line and configured to heat the refrigerant during the defrost mode. A pressure control apparatus is coupled to the refrigerant circuit downstream of the evaporator and configured to increase system pressure to maintain flow of refrigerant into the evaporator during the defrost mode.
In another aspect, the present invention provides a method of defrosting a refrigeration system having a refrigeration mode and a defrost mode. The method includes circulating refrigerant in the refrigeration mode through a condenser, a flow control device, an evaporator, and a compressor of the refrigeration system. The method also includes circulating refrigerant in the defrost mode through the evaporator in the same direction as the refrigeration mode. The method also includes heating the refrigerant in the defrost mode and increasing the system pressure in the defrost mode to maintain flow of refrigerant into the evaporator during the defrost mode.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.
DETAILED DESCRIPTIONWith reference to
The refrigeration system 45 has a refrigeration mode during which the evaporator 60 conditions an airflow (e.g., the air flowing through passageway 70 in the merchandiser 10) based on heat transfer between the refrigerant in the evaporator 60 and the air passing over the evaporator 60. The refrigeration system also has a defrost mode during which frost buildup on the evaporator 60 is reduced or removed.
Although the invention is described with reference to its application in the refrigerated merchandiser 10, it will be appreciated that the refrigeration system 45 and method for defrosting the refrigeration system 45 described in detail below will have other applications.
As shown in
In the defrost mode, the controller 100 activates the heater 75, which begins heating the refrigerant flowing to the evaporator 60. The flow control device 55 regulates (e.g., maintains, increases, or decreases) the flow of refrigerant to the evaporator 60 during the defrost mode, and ensures that refrigerant continues to flow to the evaporator 60 in the defrost mode. The pressure control apparatus 80 is configured to increase system pressure during the defrost mode to maintain flow of refrigerant into the evaporator 60 and to control flow of refrigerant to the compressor 65. As illustrated in
The defrost mode is deactivated by the controller 100 in response to the sensor 95 detecting a refrigerant temperature at or above a predetermined temperature threshold, and the refrigeration system 45 returns to the refrigeration mode. The heater 75 is turned off at this transition between modes, and the controller 100 can control the pressure control apparatus 80 to regulate how much refrigerant flows to the compressor 65.
The pressure control apparatus 80 for the refrigeration system 145 includes a first pressure regulator 105 that is disposed in the suction line 90, and a solenoid valve 120 and a second pressure regulator 115 that are disposed in a bypass line 110 that bypasses the first pressure regulator 105. The first pressure regulator 105 (e.g., an evaporator pressure regulator valve) has a first pressure setpoint (e.g., 30 psi) and the second pressure regulator 115 (e.g., an evaporator pressure regulator valve) has a second pressure setpoint (e.g., 78 psi, 130 psi) that is higher than the first pressure setpoint.
The solenoid valve 120 controls the flow of refrigerant in the bypass line 110 and to the second pressure regulator 115. The solenoid valve 120 is closed during the refrigeration mode (not shown) for the refrigeration system 145. During the defrost mode, the solenoid valve 120 is open and the first and second pressure regulators 105, 115 restrict or prevent flow of refrigerant to the compressor 65 to build pressure in the system 145 and maximize the amount of refrigerant in the evaporator 60. When the system pressure exceeds the first pressure setpoint, refrigerant begins to flow to the compressor 65 through the first pressure regulator 105 and the suction line 90. Between the first pressure setpoint and the second pressure setpoint, refrigerant does not flow through the bypass line 110 to the compressor 65. Refrigerant only flows through the bypass line 110 when the system pressure exceeds the second pressure setpoint. The defrost mode is terminated when the sensor 95 detects an evaporator temperature that exceeds the predetermined threshold.
The solenoid valve 235 controls the flow of refrigerant in the suction line 90 by permitting or inhibiting refrigerant flow. During the refrigeration mode (not shown) for refrigeration system 245, the solenoid valve 235 is open. During the defrost mode, the solenoid valve 235 is closed and builds pressure in the system 245 to maximize the amount of refrigerant in the evaporator 60. If the pressure of refrigerant in the system 245 exceeds a safety pressure setpoint (e.g., 130 psi), the controller 100 opens the solenoid valve 235 and refrigerant begins to flow to the compressor 65 through the suction line 90. The defrost mode is terminated when the sensor 95 detects an evaporator temperature that exceeds the predetermined threshold.
The electronic pressure regulator 340 controls the flow of refrigerant in the suction line 90. During the refrigeration mode (not shown) for refrigeration system 345, the electronic pressure regulator 340 is open. During the defrost mode, the electronic pressure regulator 340 is controlled to build pressure in the system 345 to maximize the amount of refrigerant in the evaporator 60. When a predetermined pressure setpoint or threshold (e.g., 30 psi, 78 psi, 130 psi, etc.) is exceeded, the electronic pressure regulator 340 at least partially opens and releases refrigerant to the compressor 65 through the suction line 90 to relieve pressure in the system 345. The defrost mode is terminated when the sensor 95 detects an evaporator temperature that exceeds the predetermined threshold.
The solenoid valve 420 controls the flow of refrigerant in the bypass line 410 and to the second pressure regulator 415. During the refrigeration mode (not shown) for the refrigeration system 445, the solenoid valve 420 is closed. During the defrost mode, the solenoid valve 420 is open and the first and second pressure regulators 405, 415 build pressure in the system 445 to maximize the amount of refrigerant in the evaporator 60. When the system pressure exceeds the first pressure setpoint, refrigerant begins to flow to the compressor 65 through the first pressure regulator 405 and the suction line 90. Between the first pressure setpoint and the second pressure setpoint, refrigerant does not flow through the bypass line 410 to the compressor 65 due to the higher pressure setpoint of the second pressure regulator 415. Refrigerant only flows through the bypass line 410 when the system pressure exceeds the second pressure setpoint. The defrost mode is terminated when the sensor 95 detects an evaporator temperature that exceeds the predetermined threshold.
The solenoid valve 535 controls the flow of refrigerant in the suction line 90. During the refrigeration mode (not shown) for the refrigeration system 545, the solenoid valve 535 is open. During the defrost mode, the solenoid valve 535 is closed and builds pressure in the system 545 to maximize the amount of refrigerant in the evaporator 60. If the pressure of refrigerant in the system 545 exceeds a safety pressure setpoint (e.g., 130 psi), the controller 100 opens the solenoid valve 535 and refrigerant begins to flow to the compressor 65 through the suction line 90. The defrost mode is terminated when the sensor 95 detects an evaporator temperature that exceeds the predetermined threshold.
The electronic pressure regulator 640 controls the flow of refrigerant in the suction line 90. During the refrigeration mode (not shown) for refrigeration system 645, the electronic pressure regulator 640 is open. During the defrost mode, the electronic pressure regulator 640 is controlled by the controller 100 to build pressure in the system 645 to maximize the amount of refrigerant in the evaporator 60. The electronic pressure regulator 640 releases refrigerant through the suction line 90 to the compressor 65 to relieve pressure in the system 645 based on the pressure setpoint of the pressure regulator 640. The defrost mode is terminated when the sensor 95 detects an evaporator temperature that exceeds the predetermined threshold.
As illustrated in
In general, the pressure control apparatus 80 described with regard to
The release pressure for the apparatus 80 is refrigerant-specific due to each refrigerant having a different phase change pressure at 32 degrees Fahrenheit (the melting point of water that has frozen on the evaporator). For example, refrigerant R404 has a phase change pressure of approximately 72 psi that corresponds to 32 degrees Fahrenheit, so setting the phase change pressure of the apparatus 80 to approximately 78 psi will maximize defrost (i.e. completely, or nearly completely eliminate frost on the evaporator 60) and minimize excess heat in the refrigeration system.
With reference to
In the exemplary systems described with regard to
In the defrost mode of the systems 845, 945, the controller 100 activates the heater 875, 975 which begins heating the refrigerant within the evaporator 60. The heater 875, 975 defrosts the coils of the evaporator 60 mostly through convection and radiation and with conduction occurring in some locations of the evaporator 60 based on the location of the heater 875, 975 within the evaporator 60. The flow control device 55 regulates the flow of refrigerant to the evaporator 60 during the defrost mode and ensures that refrigerant continues to flow to the evaporator 60 in the defrost mode. The pressure regulator 80 controls the system pressure during defrost mode to maintain flow to the evaporator 60 and to control flow to the flow of refrigerant to the compressor 65. The defrost mode in the refrigeration system 845 is deactivated by the controller 100 in response to a signal from the sensor 95. The sensor 95 can coupled to the evaporator 60 or to the suction line 90 to detect the buildup of frost on the evaporator 60 based on the temperature of refrigerant exiting the evaporator 60. In some constructions, the controller 100 can automatically initiate the defrost mode at preset time periods (e.g., every two hours) or preset times (e.g., 2 A.M., 10 A.M., 3 P.M., 10 P.M.). The defrost mode is then deactivated by the controller 100 in response to the sensor 95 detecting a refrigerant temperature at or above a predetermined temperature threshold, and the refrigeration system 845, 945 returns to the refrigeration mode. The heater 875, 975 is turned off at the transition between defrost and refrigeration modes, and the controller 100 can control the pressure control apparatus 80 to regulate how much refrigerant flows to the compressor 65 during defrost.
Various features and advantages of the invention are set forth in the following claims.
Claims
1. A refrigeration system comprising:
- a refrigerant circuit including a condenser, a flow control device, an evaporator, and a compressor connected in series, the compressor configured to circulate a cooling fluid through the refrigerant circuit, and the refrigerant circuit having an inlet line fluidly connecting the condenser to the evaporator and a suction line fluidly connecting the evaporator to the compressor;
- a heater positioned to heat the cooling fluid during a defrost mode; and
- pressure control apparatus coupled to the refrigerant circuit downstream of the evaporator,
- wherein, in the defrost mode, the pressure control apparatus is configured to increase system pressure during the defrost mode to maintain flow of refrigerant into the evaporator and to control flow of cooling fluid to the compressor.
2. The refrigeration system of claim 1, wherein the heater is positioned downstream of the flow control device.
3. The refrigeration system of claim 1, wherein the pressure control apparatus includes a solenoid valve or a pressure regulator.
4. The refrigeration system of claim 1, wherein the pressure control apparatus includes a first pressure regulator coupled to the suction line, the refrigerant circuit further including a bypass line that bypasses the first pressure regulator and that has a second pressure regulator, and wherein the first pressure regulator has a first pressure setpoint and the second pressure regulator has a second pressure setpoint that is higher than the first pressure setpoint.
5. The refrigeration system of claim 4, wherein the first pressure regulator includes an evaporator pressure regulator valve and the second pressure regulator includes a solenoid valve.
6. The refrigeration system of claim 1, wherein the heater includes a first heater, the refrigeration system further comprising a second heater in communication with the flow control device, wherein the second heater is configured to control the flow control apparatus to selectively permit or restrict flow of cooling fluid to the evaporator during the defrost mode.
7. The refrigeration system of claim 1, further comprising a sensor coupled to the evaporator and configured to detect a temperature of the evaporator, and a controller in communication with the heater to activate the heater in response to buildup of frost on the evaporator, wherein the controller is configured to terminate the defrost mode by deactivating the heater in response to the sensor detecting a cooling fluid temperature at or above a predetermined temperature threshold.
8. The refrigeration system of claim 7, wherein the temperature of the evaporator detected by the sensor includes a temperature of the cooling fluid in or exiting the evaporator.
9. The refrigeration system of claim 7, wherein the controller is further in communication with the pressure control apparatus to regulate a position of the pressure control apparatus between an open position and a closed position.
10. The refrigeration system of claim 1, wherein the refrigeration circuit further includes a recirculation line fluidly connected between the suction line and the inlet line, wherein the recirculation line is configured to recirculate cooling fluid exiting the evaporator to the inlet line upstream of the heater.
11. The refrigeration system of claim 1, wherein the heater is positioned in and coupled to the evaporator.
12. The refrigeration system of claim 1, wherein the heater is positioned directly below the evaporator.
13. A refrigeration system comprising:
- a refrigerant circuit including a condenser, a flow control device, an evaporator, and a compressor connected in series, the compressor configured to circulate a refrigerant through the refrigerant circuit, and the refrigerant circuit having an inlet line fluidly connecting the condenser to the evaporator and a suction line fluidly connecting the evaporator to the compressor;
- a refrigeration mode in which refrigerant is directed through the evaporator in a first direction via the inlet line;
- a defrost mode in which refrigerant is directed through the evaporator in the first direction via the inlet line;
- a first heater coupled to the inlet line and configured to heat the refrigerant during the defrost mode; and
- a pressure control apparatus coupled to the refrigerant circuit downstream of the evaporator and configured to increase system pressure to maintain flow of refrigerant into the evaporator during the defrost mode.
14. The refrigeration system of claim 13, wherein the heater is positioned downstream of the flow control device.
15. The refrigeration system of claim 11, wherein the pressure control apparatus includes a solenoid valve or a pressure regulator.
16. The refrigeration system of claim 11, wherein the pressure control apparatus includes a first pressure regulator coupled to the suction line, the refrigerant circuit further including a bypass line that bypasses the first pressure regulator and that has a second pressure regulator, and wherein the first pressure regulator has a first pressure setpoint and the second pressure regulator has a second pressure setpoint that is higher than the first pressure setpoint.
17. The refrigeration system of claim 14, wherein the first pressure regulator includes an evaporator pressure regulator valve and the second pressure regulator includes a solenoid valve.
18. The refrigeration system of claim 11, wherein the heater includes a first heater, the refrigeration system further comprising a second heater in communication with the flow control device, wherein the second heater is configured to control the flow control apparatus to permit flow of cooling fluid to the evaporator during the defrost mode.
19. The refrigeration system of claim 11, further comprising a sensor coupled to the evaporator and configured to detect a temperature of the evaporator, and a controller in communication with the heater to activate the heater in response to buildup of frost on the evaporator, wherein the controller is configured to terminate the defrost mode by deactivating the heater in response to the sensor detecting a cooling fluid temperature at or above a predetermined temperature threshold.
20. The refrigeration system of claim 17, wherein the controller is further in communication with the pressure control apparatus to regulate a position of the pressure control apparatus between an open position and a closed position.
21. The refrigeration system of claim 11, wherein the refrigeration circuit further includes a recirculation line fluidly connected between the suction line and the inlet line, wherein the recirculation line is configured to recirculate cooling fluid exiting the evaporator to the inlet line upstream of the heater.
22. A method of defrosting a refrigeration system having a refrigeration mode and a defrost mode, the method comprising:
- circulating refrigerant in the refrigeration mode through a condenser, a flow control device, an evaporator, and a compressor of the refrigeration system;
- circulating refrigerant in the defrost mode through the evaporator in the same direction as the refrigeration mode;
- heating the refrigerant in the defrost mode; and
- increasing system pressure in the defrost mode to maintain flow of refrigerant into the evaporator during the defrost mode.
23. The method of claim 22, further comprising deactivating the defrost mode based on a temperature of refrigerant exiting the evaporator meeting or exceeding a temperature threshold.
24. The method of claim 22, further comprising heating the refrigerant upstream of the evaporator.
25. The method of claim 22, further comprising heating the refrigerant within the evaporator.
Type: Application
Filed: Oct 3, 2016
Publication Date: Oct 12, 2017
Inventors: Tobey D. Fowler (St. Charles, MO), Sean M. Hanlon (O'Fallon, MO), Paul R. Laurentius (Saint Charles, MO)
Application Number: 15/283,809