US20080184715A1

US20080184715A1 - Bottle Cooler Defroster And Methods

Info

Publication number: US20080184715A1
Application number: US11/908,623
Authority: US
Inventors: Yu Chen; Tobias H. Sienel; Parmesh Verma; Hans-Joachim Huff
Original assignee: Carrier Comercial Refrigeration Inc
Current assignee: Taylor Commercial FoodService LLC
Priority date: 2005-03-18
Filing date: 2005-12-30
Publication date: 2008-08-07
Also published as: JP2008533429A; CN101142454A; EP1859211A4; WO2006101567A1; EP1859211A1

Abstract

A bottle cooler system (20, 70, 100) includes a compressor (22), a first heat exchanger (24) and a second heat exchanger (28). In a cooling mode of operation, the second heat exchanger is downstream of the first heat exchanger and upstream of the compressor to cool contents of an interior volume. In a defrost mode of operation, refrigerant in the second heat exchanger is used to defrost an ice build-up on the second heat exchanger.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

Benefit is claimed of U.S. Patent Application Ser. No. 60/663,961, filed Mar. 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

The invention relates to refrigeration. More particularly, the invention relates to beverage coolers.
The CO₂bottle 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.
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 frost on the coil can be heated. Since the temperature of the air in the cabinet (nominally 3.3° C. (38° F.), more broadly 2-4° C. (36-39° F.)) is very close to the temperature of the frost (0° C. (32° F.)), the defrost process usually takes a long time.
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

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

FIG. 1 is a schematic of a first CO₂bottle cooler.

FIG. 2 is a schematic of a first alternate CO₂bottle cooler.

FIG. 3 is a pressure-enthalpy diagram of the defrost cycle of the CO₂bottle cooler of FIG. 2 in a defrost mode.

FIG. 4 is a schematic of a second alternate CO₂bottle cooler in a cooling mode.

FIG. 5 is a schematic of the CO₂bottle cooler of FIG. 4 in a defrost mode.

FIG. 6 is a side schematic view of a display case bottle cooler including a refrigeration and air management cassette.

FIG. 7 is a view of a refrigeration and air management cassette.

Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

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.
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.
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.
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.
In a second (defrost) 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 0° C. 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 0° C., 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.
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.
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 35° F. for coil temperature).
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).
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 flow through the first branch 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.
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.
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, 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.
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.
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 CO₂bottle 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 operation cost for heating the air is significantly reduced. This heat pump operation mode can also be used to defrost the evaporator coil.
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.
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.
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.
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.
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 to 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 downstream of the heat exchanger 24. Exposure of the accumulation 254 to the heated air in the flow 44 may encourage evaporation.
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.

Claims

1. A cooler system (20; 70; 100) comprising:

a compressor (22) for driving a refrigerant along a flowpath (32; 72; 100, 112) in at least a first mode of system operation;

a first heat exchanger (24) along the flowpath (32; 72; 100, 112) downstream of the compressor (22) in the first mode;

a second heat exchanger (28) along the flowpath (32; 72; 100, 112) upstream of the compressor (22) in the first mode to cool contents of an interior volume of the system; and

means (50; 78; 102) for defrosting an ice buildup on the second heat exchanger using refrigerant in the second heat exchanger.

2. The system of claim 1 wherein the means comprises:

a controller (50) programmed or configured to run a first fan (40) to drive a first air flow (44) across the first heat exchanger in the first mode and, in a second mode, shut the first fan (40) off to increase a temperature of the refrigerant passing through the second heat exchanger to defrost the build-up.

3. The system (70) of claim 1 wherein the means comprises:

a valve (78) along a bypass flowpath from a first location along the flowpath between the compressor and the first heat exchanger to a second location between an expansion device and the second heat exchanger, the valve openable to switch the system into a bypass mode where at least a portion of a compressor outlet flow passes along the bypass flowpath and to the second heat exchanger and is in sufficient quantity to heat the second heat exchanger to defrost the ice buildup.

4. The system (100) of claim 1 wherein the means comprises:

a reversing valve (102) actuatable to put the system in a second mode wherein flow through the first (24) and second (28) heat exchangers is reversed.

5. The system of claim 1 wherein the means further is means for heating the cooler interior volume to prevent freezing of the contents when an outside temperature falls below a threshold.

6. The system of claim 1 being a self-contained externally electrically powered beverage cooler positioned outdoors.

7. The system of claim 1 wherein:

the first (24) and second (28) heat exchangers and compressor (22) are removable from a housing of the system as a unit without need to previously empty contents of the system.

8. The system of claim 1 wherein:

the refrigerant comprises, in major mass part, CO₂; and

the first (24) and second (28) heat exchangers are refrigerant-air heat exchangers.

9. The system of claim 1 wherein:

the refrigerant consists essentially of CO₂; and

the first (24) and second (28) heat exchangers are refrigerant-air heat exchangers each having an associated fan (40, 42), a first mode air flow (44) across the first heat exchanger (24) being an external flow and a first mode airflow (46) across the second heat exchanger (28) being a recirculating internal airflow.

10. The system of claim 1 in combination with said contents which include:

a plurality of beverage containers in a 0.3-4.0 liter size range.

11. The system of claim 10 being selected from the group consisting of:

a cash-operated vending machine;

a transparent door front, closed back, display case; and

a top access cooler chest.

12. A method for operating a cooler system (20; 70; 100) comprising:

in at least a first mode of system operation, operating a compressor (22) to compress and drive a refrigerant along a flowpath (32; 72; 100, 112);

in the first mode, rejecting heat from the refrigerant in a first heat exchanger (24) along the flowpath (32; 72; 100, 112) downstream of the compressor (22);

in the first mode, absorbing heat to the refrigerant in a second heat exchanger (28) along the flowpath (32; 72; 100, 112) upstream of the compressor (22) to cool contents of an interior volume of the system; and

in a second mode of operation, means defrosting an ice buildup on the second heat exchanger using refrigerant in the second heat exchanger.

13. The method of claim 12 wherein a transition between the first mode and the second mode is performed by:

a controller (50) programmed or configured to run a first fan (40) to drive a first air flow (44) across the first heat exchanger in the first mode and, in the second mode, shut the first fan (40) off to increase a temperature of the refrigerant passing through the second heat exchanger to defrost the build-up.

14. The method of claim 12 wherein a transition between the first mode and the second mode is performed by:

a valve (78) along a bypass flowpath from a first location along the flowpath between the compressor and the first heat exchanger to a second location between an expansion device and the second heat exchanger, and wherein the valve is opened to switch the system into said second mode where at least a portion of a compressor outlet flow passes along the bypass flowpath and to the second heat exchanger and is in sufficient quantity to heat the second heat exchanger to defrost the ice buildup.

15. The method of claim 12 wherein a transition between the first mode and the second mode is performed by:

a reversing valve (102) actuated to put the system into the second mode wherein flow through the first (24) and second (28) heat exchangers is reversed.