BOTTLE COOLER DEFROSTER AND METHODS
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Benefit is claimed of U.S. Patent Application Ser. No. 60/663,961, filed March 18, 2005, and entitled "BOTTLE COOLER DEFROSTER AND METHODS", the disclosure of which is incorporated by reference herein as if set forth at length. Copending application docket 05-258-WO, entitled HIGH SIDE PRESSURE REGULATION FOR TRANSCRITICAL VAPOR COMPRESSION SYSTEM and filed on even date herewith, discloses prior art and inventive cooler systems. The disclosure of said application is incorporated by reference herein as if set forth at length. The present application discloses possible modifications to such systems.
BACKGROUND OF THE INVENTION [0002] The invention relates to refrigeration. More particularly, the invention relates to beverage coolers.
[0003] The CO2 bottle cooler utilizes a compressor, a gas cooler, an expansion device, and an evaporator to transfer heat energy from a low temperature energy reservoir to a high temperature energy sink. This transfer is achieved with the aid of electrical energy input at the compressor. A temperature difference between the outdoor air and the refrigerant drives the thermal energy transfer from the interior air to the refrigerant as it passes through the lower temperature heat exchanger (e.g., evaporator). The fan continues to move fresh air across the evaporator surface, maintaining the temperature difference, and evaporating the refrigerant. If the surface temperature of the evaporator is below the dew-point temperature of the moist air stream, water will condense onto the fins. When the surface of the evaporator is below freezing, water droplets that condense on the surface can freeze. Frost crystals then grow from the frozen droplets and begin to block the airflow passage through the evaporator fins. The blockage increases the pressure drop through the evaporator, which reduces the airflow. As a result of the insulating effect of frost and blockage of airflow, the refrigerant temperature in the evaporator decreases, which ultimately causes degradation in the bottle cooler performance and reduction of the cooling capacity and COP. Eventually, a defrost cycle must be initiated.
[0004] The existing method is to shut off the compressor and higher temperature (at least in a normal mode) heat exchanger (e.g., condenser) fan while still keep the evaporator fan running. By circulating the air inside the bottle cooler cabinet through the evaporator, the
frostWffie'tJ'b'il c&belaBstddi. Since the temperature of the air in the cabinet (nominally
3.3°C (38°F), more broadly 2-4°C (36-390F)) is very close to the temperature of the frost (O0C (320F)), the defrost process usually takes a long time.
[0005] If the bottle cooler is installed outdoors, an electric heater is usually needed to heat the air inside the cabinet to keep the beverage from freezing. Because the efficiency of the electric heater is at most 100%, the costs of heating the air in winter is quite significant.
SUMMARY OF THE INVENTION
[0006] A bottle cooler system includes means for switching the system to a second mode of operation wherein refrigerant in the evaporator defrosts an ice buildup on the evaporator. The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a schematic of a first CO2 bottle cooler.
[0008] FIG. 2 is a schematic of a first alternate CO2 bottle cooler.
[0009] FIG 3 is a pressure-enthalpy diagram of the defrost cycle of the CO2 bottle cooler of FIG. 2 in a defrost mode. [0010] FIG. 4 is a schematic of a second alternate CO2 bottle cooler in a cooling mode.
[0011] FIG. 5 is a schematic of the CO2 bottle cooler of FIG. 4 in a defrost mode.
[0012] FIG. 6 is a side schematic view of a display case bottle cooler including a refrigeration and air management cassette.
[0013] FIG. 7 is a view of a refrigeration and air management cassette. [0014] Like reference numbers and designations in the various drawings indicate like elements.
DETAILED DESCRIPTION
[0015] FIG. 1 schematically shows a transcritical vapor compression system 20 of a bottle cooler. The system comprises a compressor 22, a first heat exchanger 24, an expansion device 26, and a second heat exchanger 28. An accumulator 30 may also be located in a suction line portion of the refrigerant flowpath 32 between the outlet of the second heat exchanger 28 and the inlet 34 of the compressor 22. A discharge line of the flowpath 32 extends from the outlet 36 of the compressor to the inlet of the first heat exchanger 24. Additional lines connect the first heat exchanger outlet to the expansion device inlet and the expansion device outlet to the second heat exchanger inlet. An exemplary expansion device 26 is an electronic expansion device. Alternative devices are disclosed in the Docket 05-258-WO application identified above.
[0016] The heat exchangers 24 and 28 may each take the form of a refrigerant-to-air heat exchanger. Air flows across one or both of these heat exchangers may be forced. For example, one or more fans 40 and 42 may drive respective air flows 44 and 46 across the coils of the two heat exchangers. The system may include a controller 50 which may be coupled to one or both of the expansion device 26 and compressor 22 to control their respective operations. The controller 50 may be configured to accept user input and/or may be configured to accept input from one or more sensors (e.g., temperature or pressure sensors). FIG. 1 shows an exemplary pair of temperature sensors 52 and 54 (e.g., thermocouples). The first temperature sensor 52 is positioned to measure a temperature of the coil of the second heat exchanger 28 (advantageously positioned to measure the air temperature entering or exiting the heat exchanger or to measure the saturation temperature refrigerant in the heat exchanger). The second temperature sensor 54 is positioned to measure a temperature of refrigerant in the suction line. [0017] The first heat exchanger 24 may be positioned external to the refrigerated volume of the bottle cooler. The second heat exchanger 28 may be positioned internal to such volume or along a recirculating air flowpath to/from that volume.
[0018] In a first mode of operation (e.g., a normal cooling mode) the compressor is on and the fans 40 and 42 drive their respective air flows 44 and 46. The first heat exchanger 24 acts as a gas cooler discharging heat to the air flow 44 to cool the refrigerant passing through the first heat exchanger. This refrigerant is expanded passing through the expansion device 26 so that its temperature further drops. The second heat exchanger 28 acts as an evaporator, cooling the air flow 46 and thus the refrigerated volume of the bottle cooler. During normal operation, frost may accumulate on the coils of the second heat exchanger 28.
IUU19] In a sec'ond'tδfefrό'st) mode of operation the first fan 40 is shut-off, decreasing the heat extraction from the refrigerant in the first heat exchanger 24. As a result, the refrigerant entering the second heat exchanger 28 may be above O0C. Thus, this refrigerant may be effective to defrost the second heat exchanger. Additionally, the fan 42 may continue to operate. To the extent that the air within the beverage cooler is above 00C, the air flow 46 will further facilitate defrosting of the second heat exchanger 28. While in defrost mode, if the expansion device 26 is controllable, the expansion device may be opened to provide a larger opening size to prevent over pressurization within the high pressure portion of the system. [0020] The need to defrost may be determined in a variety of ways. In one example, a timer is used (e.g., included in the controller) and the system switches to the defrost mode after a predetermined period of time has elapsed. If a more complicated controller is used, a temperature sensor or combination of temperature sensors can be used. For example, when both (1) a first temperature measured by the temperature sensor 52 is below a first predetermined value (thus indicating a potential for frosting by distinguishing a potential frosting condition from a pulldown condition; e.g.,40°F for air temperature or 33°F for a coil temperature); and (2) the difference between a second temperature measured by the temperature sensor 54 and the first temperature is above a second value, the evaporator may be assumed to be frosted and a defrost mode can be entered. [0021] The system may shift back to the cooling mode from the defrost mode in similar fashion. A fixed time is one example. A sensed condition (e.g., when the output of one of the temperature sensor 52 and the temperature sensor 54 exceeds a third predetermined value; e.g.,40°F for air temperature or 350F for coil temperature). [0022] FIG. 2 shows an alternate system 70 having a refrigerant flowpath 72 with first and second segments/branches 74 and 76 between the compressor outlet 36 and the inlet of the second heat exchanger 28. The first branch 74 may contain the first heat exchanger 24 and the expansion device 26 in a similar fashion to the first system 20. The second branch 76 contains a switching valve 78. The switching valve 78 may also be controlled by the controller 50 (not shown for this and the remaining embodiments). [0023] In a first (cooling) mode of operation, the switching valve 78 is closed and operation is similar to the first mode of the system 20. In the second (defrost) mode, the switching valve 78 is open, causing at least a portion of the compressed refrigerant to bypass the first branch 74 and, thereby, lack the cooling otherwise provided by the first heat exchanger 24 (even with its fan 40 off) and expansion device 26. There may still be some
tlow through the first Bfancri'74. However, the first heat exchanger 24 and the expansion device 26 may be relatively restrictive so that a majority of the system flow passes along the second branch 76.
[0024] Because of the refrigerant bypass along the second branch 76, the net resulting temperature of refrigerant entering the second heat exchanger 28 in the system 70 defrost mode may be higher than for the defrost mode of the system 20. [0025] The heating capacity of the system during the defrost mode will essentially be the same as the input power to the compressor. The input power to the compressor is a function
C of the discharge pressure of the compressor. To maximize the heating capacity, the input power should be maximized and thus the discharge pressure should be as high as possible without producing overpressurization. In this way, the power input, and thus the heating capacity is maximized, which minimizes the defrost time. Minimizing the defrost time allows the system to exit the defrost mode and return to the cooling mode quickly, which minimizes disturbances to the temperature of the product stored in the cooler. [0026] FIG. 3 is a pressure-enthalpy diagram of the defrost cycle of the system 70. The refrigerant flowpath includes a first leg 90 through the compressor. During this leg 90, both the pressure and enthalpy increase to a point 91 due to the input of mechanical energy. A second leg 92 is associated with the second branch 76 and refrigerant passage through the switching valve 78. The switching valve 78 acts as an expansion device so that the second leg 92 is preferably close to isenthalpic ending at a reduced pressure point 93. From the reduced pressure point 93, a third leg 94 represents essentially constant pressure passage through the second heat exchanger 28, giving up heat to melt the frost accumulation. The exemplary third leg 94 returns to a reduced enthalpy origin 95 from which the first leg 90 resumes. In the exemplary illustration, the origin 95 (minimum enthalpy and pressure point) is at or near the saturated vapor line 96 separating the mixed liquid-vapor region 97 ("vapor dome") from the vapor region 98. In alternative situations, the cycle may occur entirely within the vapor region 98 remote of the vapor dome. In yet other possible situations, a portion of the cycle may be along or within the vapor dome. [0027] Another alternative is to add a flow reversing valve (e.g., a four-way valve). This may be particularly useful for bottle coolers that will be installed outdoors. During the summer when cooling is needed, the CO2 bottle cooler operates as a cooling device, lowering the temperature of the air inside the cabinet. In winter, by activating the four-way valve, the flow is reversed and the bottle cooler operates as a heat pump, providing heat to the air inside the cabinet. Because the efficiency (or COP) of a heat pump is always much higher than
100%, the""όperatiόn"costl!fόrJneating the air is significantly reduced. This heat pump operation mode can also be used to defrost the evaporator coil.
[0028] FIG. 4 shows a system 100 having a flow reversing valve 102 having a flow reversing valve element 104 with two distinct flowpaths. An exemplary element is a rotary element. FIG. 4 shows the valve element 104 oriented in a first (cooling) mode.
[0029] FIG. 5 shows the valve element 104 oriented to provide a second (defrost or heat pump) mode. The valve 102 links a compressor loop 110 of the refrigerant flowpath to a main loop 112. The heat exchangers 24 and 28 and expansion device 26 are positioned along the main loop 112. In both modes, flow along the compressor loop 110 is in the same direction. The valve serves to reverse flow along the main loop 112. In the defrost mode, the second heat exchanger 28 acts as a gas cooler. The hot refrigerant gas passing through the second heat exchanger 28 may be particularly effective to melt frost. The first heat exchanger 24 may act as an evaporator. In the defrost mode, the expansion device 26 regulates pressure in the second heat exchanger 28. [0030] A particular area for implementation of the invention is in bottle coolers, including those which may be positioned outdoors or must have the capability to be outdoors (presenting large variations in ambient temperature). FIG. 6 shows an exemplary cooler 200 having a removable cassette 202 containing the refrigerant and air handling systems. The exemplary cassette 202 is mounted in a compartment of a base 204 of a housing. The housing has an interior volume 206 between left and right side walls, a rear wall/duct 216, a top wall/duct 218, a front door 220, and the base compartment. The interior contains a vertical array of shelves 222 holding beverage containers 224.
[0031] The exemplary cassette 202 draws the air flow 44 through a front grille in the base 224 and discharges the air flow 44 from a rear of the base. The cassette may be extractable through the base front by removing or opening the grille. The exemplary cassette drives the air flow 46 on a recirculating flow path through the interior 206 via the rear duct 210 and top duct 218.
[0032] FIG. 7 shows further details of an exemplary cassette 202. The heat exchanger 28 is positioned in a well 240 defined by an insulated wall 242. The heat exchanger 28 is shown positioned mostly in an upper rear quadrant of the cassette and oriented to pass the air flow 46 generally rearwardly, with an upturn after exiting the heat exchanger so as to discharge from a rear portion o the cassette upper end. a drain 250 may extend through a bottom of the wall 242 to pass water condensed from the flow 46 to a drain pan 252. A water accumulation 254 is shown in the pan 252. The pan 252 is along an air duct 256 passing the flow 44
dowristreanfof the"heat"eicti:ahger 24. Exposure of the accumulation 254 to the heated air in the flow 44 may encourage evaporation.
[0033] One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, when implemented as a remanufacturing of an existing system or reengineering of an existing system configuration, details of the existing configuration may influence details of the implementation. Accordingly, other embodiments are within the scope of the following claims.