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1. (WO2007000042) REFRIGERATOR OR FREEZER WITH ENHANCED EFFICIENCY
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REFRIGERATOR OR FREEZER WITH ENHANCED EFFICIENCY

CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of prior provisional application serial number 60/694,134, filed June 27, 2005, the contents of which are hereby incorporated herein by reference.

BACKGROUND
[0002] This invention relates to a refrigerator or freezer and to a method of enhancing the efficiency of a refrigerator or freezer.

[0003] Known vapour compression refrigerators, including domestic refrigerators, have a refrigerant filled fluid line which defines a loop incorporating, in fluid flow order, an evaporator, a compressor, a condenser, and an expansion valve. The evaporator is associated with a cavity to be cooled. The condenser has a heat exchanger, typically in the air flow path of a fan, to dissipate heat. The refrigerant may be a low boiling point liquid, such as a hydroflurocarbon. In operation, the compressor draws gaseous refrigerant in the fluid line from the evaporator and pumps the refrigerant toward the condenser. The high pressure in the condenser and the cooling resulting from the heat exchanger and fan liquifies the refrigerant. Cooled liquid refrigerant leaving the condenser passes through the expansion valve and enters the evaporator where it may vaporise by drawing heat from the cavity to be cooled.

[0004] A typical domestic refrigerator consumes 390 to 650 kilowatt hours per year and a typical commercial refrigerator consumes considerably more energy than a domestic refrigerator. These refrigerators throw off waste heat into the room in which they are housed. It would be advantageous to reduce the power consumption of refrigerators.

SUMMARY OF INVENTION
[0005] The primary refrigeration system of a refrigerator or freezer is augmented with a passive refrigeration loop or spur which has a condenser that may be placed outside so that the passive loop or spur cools provides cooling to the primary refrigeration system when the outside temperature is sufficiently low.

[0006] A refrigerator or freezer may have a primary refrigeration circuit with a circuit condenser, a circuit evaporator, a circuit compressor, and a circuit fluid line defining a loop which fluidly connects the circuit evaporator to the circuit condenser through the circuit compressor such that the circuit compressor draws refrigerant in the circuit fluid line from the circuit evaporator and pumps the refrigerant toward the circuit condenser. In an aspect of the invention, a passive refrigeration loop or spur is added. The loop or spur has a loop or spur condenser and a loop or spur line fluidly communicating with a lower portion of the loop or spur condenser. The loop or spur line is associated with the fluid line of the active circuit between an outlet of the circuit evaporator and an inlet of the circuit condenser at a location below the loop or spur condenser.

[0007] According to another aspect of the invention, there is provided a refrigerator or freezer, comprising: a closed primary refrigeration system; a closed secondary, passive, refrigeration circuit; said secondary refrigeration circuit having a heat exchanger in heat exchange relation with said primary refrigeration system, said secondary passive refrigeration circuit being one of a heat pipe loop and a thermosiphon loop.

[0008] According to a further aspect of the invention, there is provided a method of enhancing efficiency of a refrigerator or freezer, comprising: positioning a heat exchanger of a passive refrigeration loop having said heat exchanger and a passive loop condenser in heat exchange relation with waste heat bearing element of a primary refrigeration system of said refrigerator or freezer; positioning said passive loop condenser outside a building housing said refrigerator or freezer such that said passive loop condenser is exposed to ambient temperature, said passive loop condenser positioned above said heat exchanger.

[0009] Other features and advantages will become apparent from a review of the detailed description in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
[0010] In the figures which illustrate example embodiments of the invention,
[0011] FIG. 1 is a schematic view of a refrigerator made in accordance with this invention,
[0012] FIG. 1A is a schematic view of a portion of a refrigerator made in accordance with another embodiment of this invention,
[0013] FIG. 2 is a schematic view of a portion of a refrigerator made in accordance with another embodiment of this invention,
[0014] FIG. 2A is a schematic view of a portion of a refrigerator made in accordance with another embodiment of this invention, and
[0015] FIG. 3 is a schematic view of a portion of a refrigerator made in accordance with another embodiment of this invention.

DETAILED DESCRIPTION
[0016] Turning to FIG. 1, a refrigerator 10 may have a primary refrigeration circuit 11 located inside a building 50 and a secondary (passive) refrigeration loop 15 located at least partially outside building 50. The primary refrigeration circuit 11 may be a vapour compression circuit with a refrigerant filled fluid line 12 which defines a loop incorporating, in fluid flow order, an evaporator 14, a compressor 16, a condenser 18, and an expansion valve 20. The evaporator may be associated with a cavity 22 to be cooled. The circuit's condenser 18 may have a heat exchanger 24 in the air flow path of a fan 26.

[0017] The secondary passive refrigeration loop 15 may have a condenser 30 located outside building 50 coupled in parallel to fluid line 12 through a loop inlet line 32 extending from fluid line 12 (through a wall of the building) to an upper portion of the loop's condenser 30 and a loop outlet line 34 extending from a lower portion of the loop's condenser (through a wall of the building) to fluid line 12. Normally the outlet line will be connected to the lowermost part of the loop's condenser which, in the embodiment of FIG. 1, is the bottom of the loop's condenser. The loop inlet and outlet lines 32, 34 are connected to the fluid line 12 between the outlet 40 of the circuit's compressor 16 and the inlet 38 of the circuit's condenser 18, with the loop outlet line connected to fluid line 12 downstream of the loop inlet line (where the downstream direction D is defined by the direction of refrigerant flow in line 12). The loop outlet line 34 terminates at the fluid line 12 below the level of the loop's condenser. Optionally, the loop's inlet line 32 also terminates at fluid line 12 below the level of the loop's condenser, or at least below the level of the upper portion of the loop's condenser.

[0018] A shield 54 may be disposed around the loop's condenser 30 to shield the heat pipe from the sun.

[0019] The refrigerant may be a low boiling point liquid, such as a hydroflurocarbon. The compressor may be a positive displacement compressor such as a compressor with a piston to draw refrigerant in from the evaporator on a down stroke and expel it toward the compressor on an upstroke.

[0020] In operation, the compressor draws gaseous refrigerant in the fluid line from the evaporator and pumps the refrigerant toward the condenser. Some of the gaseous refrigerant pumped by the compressor travels through loop inlet line 32 to the upper portion of the loop's condenser 30. If the ambient air outside building 50 is sufficiently cold, this refrigerant will condense to liquid which will be gravity fed down the loop's condenser 30 and down the loop outlet line 34 back to the fluid line 12. In consequence, a portion of the refrigerant in the fluid line between the compressor and the condenser is condensed to liquid. This reduces the pressure at the outlet of the compressor, thereby reducing the back pressure on the compressor and, in consequence, the load on the compressor. Hence the power required by the condenser to operate is reduced.

[0021] The cooler refrigerant then enters the condensor. The pressure in the condenser and the cooling resulting from the heat exchanger and fan liquifies remaining gaseous refrigerant. Cooled liquid refrigerant leaving the condenser passes through the expansion valve and enters the evaporator where it may vaporise by drawing heat from the cavity to be cooled.

[0022] Refrigerant will travel through the loop 15 whenever the temperature at the loop condenser 30 is less than the refrigerant temperature at the point where the loop inlet line 32 joins fluid line 12. The refrigerant temperature at the outlet 36 of the circuit evaporator 14 will typically be close to the temperature in cavity 22. Consequently, if the outdoor temperature is expected to be less than the temperature in cavity 22, the loop inlet and outlet lines could join to the fluid line 12 between the outlet 36 of the evaporator and the inlet of the compressor 16. However, the efficiency of the passive refrigeration loop 15 is directly proportional to the differential between the temperature of refrigerant where the loop inlet 32 joins fluid line 12 and the temperature at the loop condenser 30. Thus, while the heat pipe inlet may be positioned anywhere between the outlet of the circuit's evaporator and the inlet of the circuit's condenser, it is advantageously positioned at the outlet of the compressor. This is for the reason that this is the location in fluid line 12 where the refrigerant is the hottest (due to the heat of compression, which is about 500C in a domestic refrigerator) and so cooling such refrigerant maximizes the reduction in the load on the compressor.

[0023] The shield about the loop's condenser reduces solar heating of the loop's condenser.

[0024] If the ambient temperature is too high to allow gaseous refrigerant in the loop's condenser 30 to condense, as more gaseous refrigerant enters the loop's condenser, the vapour pressure in the loop's condenser will rise to the pressure in fluid line 12. At this point, no further gaseous refrigerant will migrate into the loop's condenser and refrigerant in line 12 will simply by-pass the loop's condenser. This situation will continue until the ambient temperature drops to a point where refrigerant begins to condense in the loop's condenser. The result is that the loop's condenser acts as a thermal diode, naturally shutting down when ambient temperatures are too high to allow refrigerant to condense, and naturally turning on again whenever ambient temperatures drop sufficiently to result in refrigerant condensing in the loop's condenser. Of course the lower the ambient temperature, the more quickly refrigerant will condense in the loop's condenser and, hence, the greater the efficiency increase provided by the passive refrigeration loop.

[0025] FIG. 1A illustrates a modification where, rather than having a passive refrigeration loop, a passive refrigeration spur is used. That is, in place of a loop inlet line and outlet line there is simply one loop line 156 which is connected between the bottom of the spur condenser 30 and the fluid line 12 at the outlet 40 of the compressor 16.

[0026] The operation is similar to what has been described in conjunction with FIG. 1 except that gasous refrigerant at the outlet of the compressor flows up into the spur condenser through line 156 and, after condensing in the spur condenser, flows back down line 156 to fluid line 12.

[0027] Turning to FIG. 2, in another embodiment, the loop outlet line is joined to the loop inlet line at fluid line 12 through a heat exchanger/evaporator 260. The condenser 30 of the loop is positioned above the heat exchanger 260. As illustrated in FIG. 2, the heat exchanger may simply be a spiral tube which is wound around the fluid line 12 with one end of the tube joined to the loop outlet line 234 and the other end of the tube joined to the loop inlet line 232. Additionally, the portion of the loop outlet line within the building 50 may be insulated by insulation barrier 258 to avoid unnecessary heating of condensed refrigerant and the portion of the loop inlet line within building 50 may be insulated by insulation barrier 259 to avoid condensation of refrigerant in the upward-sloping loop inlet line, which condensation may present a barrier to the upward flow of refrigerant vapour.

[0028] In this embodiment, the loop inlet line 232, loop condenser 30, heat pipe outlet line 234 and heat exchanger/evaporator 260 form a closed heat pipe loop 211 which is isolated from refrigeration circuit 11. The isolated refrigeration loop 211 may be partially filled with any suitable phase change refrigerant, such as a hydroflurocarbon refrigerant. The refrigerant in circuit 211 may be termed the second refrigerant.

[0029] In operation, hot refrigerant in fluid line 12 at the outlet of compressor passes through heat exchanger/evaporator 260. The cool second refrigerant in heat exchanger/evaporator 260 absorbs heat from the hot refrigerant in the fluid line 12 and, in consequence, is heated. The heating of the second refrigerant causes it to vaporise and migrate into loop condenser 30. In the loop condenser, the second refrigerant is cooled and condenses. The condensed refrigerant flows back down to the heat exchanger 260.

[0030] As is apparent from FIG. 2, the loop outlet line 234, which has the coldest fluid from the passive loop, is joined to the end of the heat exchanger furthest from the compressor 16. In a modification shown in FIG. 2A, it is the loop inlet line 232' which is joined to the end of the heat exchanger 260 furthest from the compressor 16. The set-up of FIG. 2 is believed to be more efficient as the refrigerant leaving the compressor is exposed to increasingly cold temperatures from the coldest heat exchanger of the passive loop.

[0031] Where a closed passive refrigeration loop is employed, rather than partially filling the passive circuit with a liquid phase change refrigerant, the circuit can be completely filled with a liquid refrigerant, which may or may not be a phase change refrigerant. With the circuit completely filled with refrigerant, the circuit acts as a thermosiphon loop rather than as a heat pipe loop. More specifically, when the second refrigerant is heated in heat exchanger 260, it become less dense and convectively flows upwardly along line 232 toward condenser 30. In condenser 30, the refrigerant cools, becomes more dense and flows downwardly along line 234 back to the heat exchanger. An exemplary non-phase change refrigerant is ethanol.

[0032] The condenser 30 of any of the embodiments may simply be a hollow pipe which is vertically oriented, or which declines at an acute angle from the vertical. Alternatively, the hollow pipe condenser, the loop outlet line and the evaporator/heat exchanger may be lined with wicks. In such instance, and where these elements are part of an isolated refrigerant loop (as, for example, in either of the embodiments of FIG. 2 or FIG. 2A), and where the isolated loop acts as a heat pipe loop, another embodiment is available. Specifically, the condenser 30 may be horizontally oriented. This embodiment is illustrated in FIG. 3. Turning to FIG. 3, loop condenser 330 of passive refrigeration loop 311 is a horizontally oriented pipe lined with wicks 370. The loop inlet 332 may communicate to any part of the condenser 330. The loop outlet 334, also lined with wicks, may communicate with the condenser anywhere along its bottom wall. With this embodiment, when gaseous refrigerant enters the condenser 330 and condenses, it is absorbed by the wicks lining the walls of the heat pipe. There is a low pressure in the heat exchanger/evaporator 260 which draws liquid refrigerant along the wicks. The wicks therefore become drier in heat exchanger than elsewhere. The consequence is that liquid refrigerant in the wicks is drawn by capillary action toward the heat exchanger and the process continues.

[0033] To increase the heat transfer rate of the condenser 30 or 330, it could be provided with heat exchange fins.

[0034] With the embodiments of any of FIGs. 2, 2A, or 3, optionally, the mass of heat exchanger 260 may be made sufficiently large so that the heat exchanger is a thermal store. In this instance, whenever the active refrigeration circuit is inactive, the passive refrigeration loop will continue to operate while the temperature of the heat exchanger 260 remains higher than the ambient temperature of the loop condenser 30 (or 330). Over time, this lowers the temperature of the thermal store heat exchanger 260. In consequence, when the active refrigeration circuit turns on, the relatively cold thermal store heat exchanger will act to cool refrigerant in line 12 for a period of time.

[0035] While in the example embodiments the primary refrigeration cycle is a vapour compression cycle, it will be apparent to those skilled in the art that the teachings of this invention have application to refrigeration systems where the primary refrigeration cycle is of some other type. More specifically, the isolated refrigeration loops described in conjunction with FIGs. 2 and 3 may be used to draw heat from a waste heat bearing element in any type of primary refrigeration system And the refrigeration loop and spur of FIGs. 1 and 1A may be used to draw heat from a waste heat bearing fluid line in any primary refrigeration system having such line to tap into provided no non-condensable gas will be trapped. For example, the heat exchanger of the isolated refrigeration loops of FIGs. 2 and 3 could be associated with the condenser or absorber of an absorber refrigeration system, the hot plate of a thermoelectric refrigeration system, or the heat exchanger of a thermo-acoustic refrigeration system. And the refrigeration loop or spur of FIGs. 1 and 1A may be tapped into the condenser of an absorber refrigeration circuit.

[0036] While the example embodiments have been described in conjunction with a refrigerator, equally the refrigerator may be a freezer.

[0037] Other variations will be apparent to those skilled in the art and, therefore, the invention is defined in the claims.