WO2009135297A1

WO2009135297A1 - Multiple mode refrigeration

Info

Publication number: WO2009135297A1
Application number: PCT/CA2009/000609
Authority: WO
Inventors: Mark A. Fleming
Original assignee: UNIFIED Corp
Current assignee: UNIFIED Corp
Priority date: 2008-05-08
Filing date: 2009-05-07
Publication date: 2009-11-12
Anticipated expiration: 2010-11-08

Abstract

A refrigeration system has a primary refrigeration circuit with an evaporator, a network driver, a condenser, and an expansion valve. These components are connected in series by a primary refrigerant line. The system also has a secondary refrigeration circuit which includes the evaporator, the condenser, and a bypass valve conncted in series by a secondary refrigerant line. The secondary refrigerant line is in fluid communication with the primary refrigerant line and has a network driver bypass line bridging an inlet and an outlet of the network driver. The network driver bypass line incorporates the bypass valve. A controller selectively de-activates the primary refrigeration circuit by de-activating the network driver and activates the secondary refrigeration circuit by opening the bypass valve.

Description

MULTIPLE MODE REFRIGERATION

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims benefit and priority from U.S. provisional patent application No. 61/051 ,465, filed on May 8, 2008, the contents of which are incorporated herein by reference.

BACKGROUND

[0002] This invention relates to a refrigeration system and method of refrigeration.

[0003] Known refrigeration systems include vapour-compression, absorption, thermoelectric and thermo-acoustic systems. These systems, which are used domestically, commercially and industrially, have a refrigerant filled fluid line which defines a loop incorporating, in fluid flow order, an evaporator, a network driver such as compressor, a condenser, and an expansion valve. The evaporator is associated with a compartment to be cooled. The condenser includes a heat exchanger, typically in the air flow path of a fan, to dissipate heat. The refrigerant is a low boiling liquid. In operation, the compressor draws (suction) gaseous refrigerant (cool, low pressure vapourous gas) in the fluid line from the evaporator to the compressor. Hot, high pressure vapour is pumped toward the condenser where it condenses as it passes along the air or fan cooled condenser coil resulting from the heat exchange which liquefies the refrigerant. Cooled liquid refrigerant leaving the condenser passes through the expansion valve (metering device) and enters the evaporator where it may vapourize and change state from a liquid to a gas. During this state change, known as the latent heat of evaporation, heat is drawn out of the cavity to be cooled as it passes along the fan cooled evaporator coil. SUMMARY OF INVENTION

[0004] In accordance with the present invention, there is provided refrigeration system has a primary refrigeration circuit with an evaporator, a network driver, a condenser, and an expansion valve. These components are connected in series by a primary refrigerant line. The system also has a secondary refrigeration circuit which includes the evaporator, the condenser, and a bypass valve connected in series by a secondary refrigerant line. The secondary refrigerant line is in fluid communication with the primary refrigerant line and has a network driver bypass line bridging an inlet and an outlet of the network driver. The network driver bypass line incorporates the bypass valve. A controller selectively de-activates the primary refrigeration circuit by de-activating the network driver and activates the secondary refrigeration circuit by opening the bypass valve.

[0005] In another embodiment, there is provided refrigeration system has a refrigeration circuit with an evaporator, a network driver, a condenser, and an expansion valve. These components are connected in series by a refrigerant line. A fan blows air over the condenser and a duct housing the fan and the condenser may be installed so that the duct inlet extends through a wall or ceiling of a building and the duct outlet extends through the wall or ceiling of the building so that said fan may blow outside air over the condenser.

[0006] Other features and advantages will become apparent from the following description in conjunction with the drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0007] In the figures which illustrate example embodiments of the invention,

[0008] FIG. 1 is a schematic view of a refrigeration system made in accordance with a first embodiment of the invention,

[0009] FIG. 2 is a schematic view of a portion of a refrigeration system made in accordance with a second embodiment of the invention, [0010] FIG. 3 is a schematic view of a portion of a refrigeration system made in accordance with a third embodiment of the invention,

[0011] FIG. 4 is a schematic view of a portion of a refrigeration system made in accordance with a fourth embodiment of the invention,

[0012] FIG. 5 is a schematic view of a portion of a refrigeration system made in accordance with a fifth embodiment of the invention illustrating a first mode of operation,

[0013] FIG. 6 is a schematic view of the refrigeration system of FIG. 5 illustrating a second mode of operation,

[0014] FIG. 7 is a schematic view of a portion of a refrigeration system made in accordance with a further embodiment of the invention,

[0015] FIG. 7A is a detailed schematic view of a portion of the refrigeration system of FIG. 7; and

[0016] FIG. 8 is a schematic view of a portion of a refrigeration system made in accordance with a further embodiment of the invention.

DETAILED DESCRIPTION

[0017] Turning to FIG. 1 , a refrigeration system 10 has an evaporator 12, compressor 14, condenser 16, and expansion valve 18 connected in series by a primary refrigerant line 20. A secondary refrigerant line section 22 bridges the inlet 24 and outlet 26 of the expansion valve. The secondary refrigerant line section 22 is interrupted by an expansion valve bypass valve 28. A secondary refrigerant line section 32 bridges the inlet 34 and outlet 36 of the compressor 14. The secondary refrigerant line section 32 is interrupted by a compressor bypass valve 38. A refrigerant reservoir 40, with an internal wick, connects to refrigerant line 20 downstream of the compressor. A fan 42 is arranged to blow air over the condenser and a second fan 43 is arranged to blow air over the evaporator.

[0018] A controller 50 is input by temperature sensors 44 and 46 and by a manual mode override control 49 and a set point control 51. The controller has a control output to the expansion valve 18, the expansion valve bypass valve 28, the compressor bypass valve 38, the compressor 14, and fans 42 and 43.

[0019] The evaporator 12 is associated with a compartment 52 to be refrigerated. For example, the evaporator could be a sinuous refrigerant line extending along the outside of a wall of the compartment 52 or a refrigerant coil wrapping around walls of the compartment. Temperature sensor 46 is located within the compartment. The condenser 16 and temperature sensor 44 are located on the outside of a wall 54 of a building. The other components of the refrigeration system are on the inside of the building.

[0020] The condenser 16 is positioned vertically higher than the evaporator 12 and the refrigerant line 20 slopes up from the outlet 55 of the evaporator to the inlet 56 of the condenser and down from the outlet 58 of the condenser to the inlet 53 of the evaporator. Thus, the condenser is also vertically higher than secondary refrigeration circuit line sections 22 and 32 and their bypass valves 28 and 38. Further, the inlet 56 of the condenser is located vertically higher than the outlet 58 of the condenser. The condenser may be, for example, a spiral refrigerant line extending between the condenser inlet and outlet in heat transfer relation with heat conductive (e.g., metal) cooling fins.

[0021] A low boiling point refrigerant, such as a hydrocarbon, a hydrofluorocarbon (HFC), or chlorofluorocarbon (CFC) refrigerant is contained within the refrigeration system.

[0022] The expansion valve may be any type of active valve that may be controlled by the controller such as an electronic expansion valve or a thermostatic valve. A thermostatic valve opens or closes responsive to changes in temperature in the evaporator.

[0023] The compressor 14 may be a positive displacement compressor such as a compressor with a piston, scroll or screw, in which refrigerant gases are cyclically evaporated and condensed, absorbing heat from the load to be cooled, and moving that heat to a cold source where it is dissipated. In scroll compressors, refrigerant gas is moved as intake air is compressed between the surfaces of mating involute spirals, one of which is moving to progressively push the evacuated gas out to the exhaust. Scroll compressors are very popular due to their high efficiency, which results from higher compression achieved due to a lower rate of leakage. Screw compressors used in large systems drive the refrigerant vapour between a number screw spindles (usually two). One screw spindle compresses the intake gas, with the intermeshing screw rotating oppositely, creating two axially progressing "chambers", moving the gas from suction to discharge. Multiple spindle compressors function by creating more of these "chambers". Piston or reciprocating compressors use a motor driven crankshaft to drive internal pistons that mechanically reduce gas volume inside the cylinder. When the piston falls, the refrigerant is pulled in through an intake valve, adding pressure. As the piston falls, the now high-pressurized gas is forced out through the exhaust valve and into the system. This style of refrigerant compressors is most often used in high-pressure systems.

[0024] The controller is input with the outdoor temperature sensed by outdoor temperature sensor 44. The controller compares this temperature with a set point temperature for the refrigeration compartment 52 input by an operator through the set point control 51. If the outside temperature is not below the set point temperature by more than a first threshold value (e.g., 1 °C lower), the controller commences a first mode of operation for system 10. To commence this first mode, the controller closes bypass valves 28, 38 and opens expansion valve 18 to establish a primary refrigeration circuit. Thereafter, when the temperature sensed by the temperature sensor 46 inside the refrigeration compartment exceeds the set point temperature, the controller activates compressor 14. This commences a standard vapour-compression cycle in the primary refrigeration circuit where high pressure liquid refrigerant in line 20 is metered through the expansion valve and undergoes an abrupt decrease in pressure, which results in the adiabatic flash evaporation of a portion of the liquid refrigerant. The partially vaporized refrigerant travels through the evaporator 12 where it is completely vaporized as it draws heat from the refrigeration compartment 52. The heated refrigerant vapour is then sucked into the low pressure inlet 34 of the compressor 14 and forced out the high pressure outlet 36 of the compressor. The pressurized heated refrigerant vapour then enters the condenser 16 where it gives up heat and condenses back to a liquid. The high pressure condensed refrigerant is then again metered through expansion valve 18. Once the temperature sensed by temperature sensor 46 drops to a shut-off temperature which is typically somewhat below the operator set point temperature, the controller shuts off the compressor 14. The primary refrigeration circuit then remains quiescent until the temperature in the refrigeration compartment again exceeds the operator set point temperature.

[0025] While the compressor is running, the controller runs fans 42 and 43. In consequence, fan 43 circulates "warm" air in refrigeration compartment 52 over the evaporator while fan 42 moves outside air over the condenser to assist in cooling refrigerant in the condenser.

[0026] If the outside temperature falls below the set point temperature by more than the first threshold value, the temperature is sufficiently cold for the secondary refrigeration mode to operate. However, to avoid oscillation between modes, the controller may only commence the secondary mode of operation if the outside temperature falls below a second threshold value (e.g., 2⁰C below the set point) which represents a larger temperature differential between the outside temperature and the set point than the first threshold value. Thus the controller, once it has commenced the first mode of operation, may continue this first mode of operation while the temperature differential exceeds the first threshold value but remains less than the second threshold value. [0027] To commence the second mode, the controller closes expansion valve 18, disables compressor 14 (which has the effect of shutting off the flow path through the compressor) and opens bypass valves 28 and 38. This completes a secondary refrigeration circuit formed by bypass lines 22 and 32 and the portions of refrigerant line 20 which are not bypassed by lines 22 and 32.

[0028] The temperature differential to operate in the second mode is chosen so that the difference in refrigerant temperature at the outlet of the evaporator and at the outlet of the condenser is sufficient to circulate the refrigerant, as follows. Cooled refrigerant leaving the condenser flows downwardly under the force of gravity through secondary refrigerant line section 22 to the evaporator 12. The evaporator acts as a heat exchanger with the cool refrigerant in the evaporator absorbing heat from the warmer compartment 52. In consequence of being heated, the warmed refrigerant becomes less dense or vaporizes. The less dense or vaporized refrigerant is more buoyant so that it migrates back to the condenser. In the condenser, the refrigerant is again cooled (and condensed where it had vaporized) by exposure to the outdoor temperature.

[0029] Fans 42 and 43 are operated while the refrigeration system operates in the second mode. Where the differential between the outdoor temperature and the set point temperature decreases to less than the second threshold value, the second mode will be maintained provided the differential remains greater than the first threshold value. If this differential is closer to the first threshold value, fan 42 may be operated at a higher speed to increase the heat transfer from the refrigerant in the condenser. If the differential decreases to less than the first threshold value, the first mode is again established.

[0030] Theoretically, refrigerant will travel through the secondary circuit whenever the temperature at the outlet of the condenser is less than the temperature at the outlet of the evaporator. However, if this differential is small, refrigerant flow will be low such that heat transfer is low. It is for this reason that a minimum the first threshold differential is required to operate in the second mode.

[0031] Use of a passive secondary refrigeration loop increases the efficiency of the refrigeration system 10.

[0032] Optionally, the secondary refrigerant circuit may include an auxiliary pump 60. In such case, with smaller temperature differentials between the outlet of the condenser and evaporator, the system may enter a third mode wherein the pump is operated to increase refrigerant flow. Where an auxiliary pump 60 is available, one or more of the components of the refrigeration system inside the building could be located above the condenser. This is not, however, preferred as it increases the power consumed by the refrigeration system and therefore reduces its efficiency.

[0033] The refrigerant reservoir 40 is provided so that the amount of refrigerant in the refrigeration circuit adjusts according to the current mode of operation. More specifically, in the first (vapour-compression) mode where a lesser amount of refrigerant is required, the compressor pushes excess refrigerant in the circuit out into the reservoir. In the second and third modes, the internal wick in the reservoir draws refrigerant from the reservoir back into the refrigeration circuit.

[0034] As described, the refrigeration system provides three modes of operation: a primary, active, refrigeration mode; a secondary, passive, refrigeration mode and a tertiary, circulating, refrigeration mode (where pump 60 is active). An operator may manually override the controller's automatic selection of the current mode for the system using the manual mode override control 49.

[0035] In some instances, it may be possible to place the compressor and bypass line 32, with its bypass valve 38, outside the building.

[0036] Optionally, system 10 may be used with a passive expansion valve, such as a short tube restrictor or a capillary tube, which cannot be opened or closed by the controller. In such instance, a shut-off valve (not shown) is incorporated upstream of the expansion valve which may be closed to effectively close the expansion valve in the second and third modes of operation.

[0037] Optionally, where the expansion valve shuts off whenever the compressor is not running, the controller 50 may not control the expansion valve or the compressor. Instead, the vapour-compression cycle may be controlled in a conventional manner based on the set point and the temperature in compartment 52. In this instance, the controller is modified so that it senses when the compressor is operating and only activates the secondary (or tertiary) mode of refrigeration while the compressor is off. With this operation, the secondary refrigeration mode can increase the length of time the temperature in the refrigeration compartment 52 remains below the set point and, hence, increase the time before the compressor re-activates.

[0038] Turning to FIG. 2, a modified refrigeration system 200 is identical to refrigeration system 10 except that secondary refrigerant line section 22 (FIG. 1 ) and bypass valve 28 (FIG. 1) are omitted. This modification is possible where the expansion valve 18 is of a type (such as an electronic expansion valve) that may be held in the open position when the compressor is off. Thus, in the secondary refrigeration mode, the controller maintains the expansion valve in its open position so that refrigerant may passively flow, as has been described hereinbefore.

[0039] In a modified operation, where the expansion valve 18 is of a type (such as an electronic expansion valve) that may restrict flow to a selected extent, the controller may actively control the degree to which the expansion valve is open in the secondary refrigeration mode in order to control the rate of cooling in this mode.

[0040] Turning to FIG. 3, a modified refrigeration system 300 is identical to refrigeration system 10 except that the condenser 16 is positioned on the inside of wall 54 and is contained in a duct 362 to the outdoors which duct, assisted by fan 42, exposes the condenser to the outside air and, therefore, the outside air temperature. Optionally, rather than duct 362 extending through wall 54 of a building, it could extend through the ceiling of the building.

[0041] The arrangement of FIG. 3 can be used with a standard vapour- compression refrigeration circuit in order to improve its efficiency. Specifically, in cold weather months, duct 362 may be closed over the condenser of a standard vapour-compression refrigeration circuit and the fan 42 may be operated to cool the condenser. This cooling reduces the back pressure of the refrigerant on the compressor thereby reducing the load on the compressor and, therefore, its energy requirements.

[0042] With reference to FIG. 4 wherein like parts to those in FIG. 1 have been identified with like reference numerals, a refrigeration system 400 has a freezer compartment 452 and a cooler compartment 472. There is a port 474 between the two compartments containing a fan 476. A primary, active, refrigeration circuit comprises condenser 16, expansion valve 18, evaporator 12 associated with the freezer compartment 452 and compressor 14, all serially connected by refrigerant line 420. A secondary, passive, refrigeration circuit comprises the condenser 16, evaporator 12 and bypass valve 38, all serially connected by a portion of refrigerant line 420 and by bypass line 432, which bridges the inlet and outlet of the compressor 14 and is interrupted by bypass valve 38. A tertiary, passive, refrigeration circuit comprises the condenser 16, a bypass valve 428, and a heat exchanger 412 extending within cooler compartment 472, all serially connected by a portion of refrigerant line 420 and by tertiary refrigerant line 422.

[0043] Although not shown, refrigeration system 400 also has an outdoor temperature sensor, a cooling compartment temperature sensor, and a freezer compartment temperature sensor, all of which input a controller. The controller also receives an input from a freezer compartment set point control and from a cooler compartment set point control. The controller controls the bypass valves 428, 38, the expansion valve 18, the compressor 14, and the fan 476. [0044] In operation, when the freezer compartment temperature is above its set point, the controller activates the primary refrigeration circuit and maintains the secondary and tertiary refrigeration circuits in an off condition. Once the freezer compartment temperature is brought below the freezer compartment set point temperature, the controller de-activates the primary refrigeration circuit. With the primary circuit de-activated, if the outside temperature is sufficiently below the set point temperature of the freezer compartment to allow the passive secondary refrigerant circuit to maintain the freezer compartment below its set point temperature, the controller activates the secondary refrigeration circuit by holding the expansion valve 18 in an open position and opening bypass valve 38.

[0045] When either the primary circuit or the secondary circuit is in operation, the controller may intermittently operate fan 476 to blow cold air from the freezer compartment and evaporator to the cooler compartment.

[0046] With the primary circuit de-activated, if the outside temperature is not sufficiently below the set point temperature of the freezer compartment 452 for the secondary refrigeration circuit to operate, but is sufficiently below the set point temperature of the cooler compartment 472 to allow the tertiary circuit to maintain the cooler compartment below its set point temperature, the controller leaves expansion valve 18 closed and opens bypass valve 428. Since cold air falls and warm air rises, it is advantageous to have the cooler compartment located above the freezer compartment so that the coolest air from the cooler compartment may descend into the freezer compartment.

[0047] Rather than providing refrigeration system 400 to refrigerate freezer and cooler compartments, refrigeration system 10 of FIG. 1 may be adapted to refrigerate such compartments with the arrangement illustrated in FIG. 5. Turning to FIG. 5, the evaporator 12 of refrigeration system 10 may be positioned within a conduit 580, both ends 581 , 583 of which open to a cooler compartment 572. A fan 582, controlled by the controller (not shown), is interposed in the conduit 580 to one side of the evaporator. The conduit has a one-way valve 584 in its side for allowing air to pass from a freezer compartment 552 to the conduit. One-way valve 584 is located at a side of the evaporator opposite fan 582. A one-way valve 586 is located in a wall 588 between the freezer compartment 552 and cooler compartment 572 at a side of the fan 582 opposite the side at which the evaporator lies. One-way valve 586 allows air to pass from the cooler compartment to the freezer compartment.

[0048] In operation, in the passive refrigeration mode and in the circulating refrigeration mode ~ where pump 60 (FIG. 1) operates ~ when the temperature of the outside air is sufficiently below the set point temperature of the freezer compartment 552, the controller operates the fan in a rotational direction to blow air in the direction shown in FIG. 5. Specifically, air is drawn through conduit 580 from both the cooler compartment 572 (via conduit end 581) and freezer compartment 552 (through one-way valve 584) over evaporator 12. This cools the air. The cooled air is then distributed both to the cooler compartment 572 (through conduit end 583) and the freezer compartment 552 (through one-way valve 586).

[0049] When the temperature of the outside air is sufficient to refrigerate the cooler compartment but insufficient to refrigerate the freezer compartment, the controller operates the fan in an opposite rotational direction to blow air in the direction shown in FIG. 6. Turning to FIG. 6, in this instance, air is drawn through conduit 580 from the cooler compartment 572 via end 583 of the conduit. With the air being drawn through this end of the conduit, one-way valve 586 remains closed. The air then passes over the evaporator 12 and is cooled. It then passes back to the cooler compartment 572 via end 581 of the conduit. With air being blown toward end 581 of the conduit, one-way valve 584 remains closed. Because the one-way valves 584, 586 remain closed, no air circulates through the freezer compartment 552 when the fan is operated in this direction.

[0050] When the refrigeration system is in the passive, or circulating, refrigeration mode where air is circulated only through the cooler compartment, if the temperature in the freezer compartment 552 rises above the freezer compartment set point temperature, the controller switches to active refrigeration mode where the compressor is activated and the direction of rotation of the fan is reversed so that air circulates through both the cooler compartment and the freezer compartment.

[0051] Turning to FIG. 7, wherein like parts to the refrigeration system of FIG. 1 are given like reference numerals, in another embodiment, a refrigeration system 700 has an evaporator 12, compressor 14, condenser 16, shut-off valve 788 and expansion valve 18 connected in series by a primary refrigerant line 20. A refrigerant reservoir 40 connects to refrigerant line 20 downstream of the output of the compressor 14. A heat pipe 790 bridges the evaporator 12 and condenser 16 and acts as a secondary refrigerant line. The heat pipe is interrupted by a heat a shut-off valve 794. The evaporator is associated with a cooler compartment 52 (or a freezer compartment). A fan 43 is positioned to blow air within cooler compartment 52 over the evaporator 12 and another fan 42 is positioned to blow air over the condenser 16. The controller (not shown) supplies control inputs to valves 788 and 794, fans 42 and 43, as well as to the compressor 14. (The controller also receives inputs from an outside temperature sensor, cooler compartment temperature sensor, and cooler set point control, none of which are shown and all of which have been described in conjunction with other embodiments.) As with the previously described embodiments, the condenser is exposed to outside air.

[0052] With reference to FIG. 7A, the evaporating end 792 of the heat pipe 790 connects into the outlet 55 of evaporator 12 as does the portion of line 20 between the evaporator outlet and the compressor. It will also be seen from FIG. 7A that the evaporator comprise a series of coils between its inlet and outlet and these coils surround the outlet 55, such that the outlet is positioned within the evaporator. The condensing end 793 (FIG. 7) of the heat pipe is similarly connected into the inlet of the condenser which is similarly configured to the evaporator.

[0053] Condenser 16 is positioned above the evaporator 12 such that the heat pipe 790 is either vertically oriented or at least sloped toward the vertical. The walls of the heat pipe may have a wick structure to exert a capillary pressure on the liquid phase of the refrigerant to wick it back to the heated end (i.e., at the evaporator) if gravity or pressure is insufficient to overcome surface tension to cause the condensed liquid to flow back to the heated end of the heat pipe.

[0054] In a primary refrigeration mode, shut-off valve 794 is closed, shut-off valve 788 is open, and compressor 14 is active to cyclically initiate a vapour-compression cycle to maintain cooler compartment at its set point temperature.

[0055] If the outside temperature is sufficiently low, the controller establishes a secondary refrigeration mode for refrigeration system 700 in which shut-off valve 794 is open, shut-off valve 788 is closed and the compressor is inactivated. When inactive, the compressor blocks the flow of refrigerant. In the secondary refrigeration mode, refrigerant in the evaporator evaporates by drawing heat from compartment 52 and this refrigerant vapour migrates up the heat pipe 790 and into the condenser where the refrigerant is cooled and condenses. The condensed refrigerant then flows back down the heat pipe and the cycle repeats.

[0056] Optionally, when the heat pipe has a hollow core (for the passage of gaseous refrigerant) surrounded by an annular wick (for the return of liquid refrigerant by capillary action), the secondary refrigeration circuit may operate even with the heat pipe horizontally oriented, or inverted. In such instance, the condenser 16 could be level with, or below, the evaporator 12.

[0057] Turning to FIG. 8, wherein like parts to the refrigeration system of FIG. 7 are given like reference numerals, in another embodiment, a refrigeration system 800 has an evaporator 12, compressor 14, shut-off valve 896, heat pipe 790, shut- off valve 898, condenser 16, pump 60 and expansion valve 18 connected in series by a primary refrigerant line 20. A refrigerant reservoir 40 connects to the heat pipe 790 downstream of the output of the compressor 14. A bypass valve 38 bridges the inlet and outlet of the compressor 14. The evaporator is associated with a cooler compartment (not shown). A fan 43 is positioned to blow air within the cooler compartment over the evaporator 12 and another fan 42 is positioned to blow air over the condenser 16. A controller (not shown) supplies control inputs to valves 38, 896, and 898, fans 42 and 43, as well as to the compressor 14. (The controller also receives inputs from an outside temperature sensor, cooler compartment temperature sensor, and cooler set point control, none of which are shown and all of which have been described in conjunction with other embodiments.) The pump 60 is of type which is open when off. As with the previously described embodiments, the condenser is exposed to outside air.

[0058] As will be apparent from FIG. 8, the coils of the evaporator 12 wrap around the evaporating end 792 of the heat pipe and the coils of the condenser 16 wrap around the condensing end 793 of the heat pipe.

[0059] In the primary mode of refrigeration, the controller maintains compressor bypass valve 38 closed and opens shut-off valves 896 and 898. The compressor is then intermittently activated to pump refrigerant up through the heat pipe 790, through the condenser, and to the expansion valve where the refrigerant is metered through to the evaporator. From the evaporator, the refrigerant returns to the compressor.

[0060] In a passive, secondary, refrigeration mode, the controller shuts off the compressor and closes shut-off valves 896 and 898. This isolates the heat pipe 790 from refrigeration line 20. Thus, refrigerant can flow up and down the heat pipe, but cannot flow out of the heat pipe (other than into reservoir 40). Refrigerant in the heat pipe is warmed at its evaporating end 792 as the refrigerant draws heat from the cooler compartment. The warmed refrigerant migrates to the condensing end 793 of the heat pipe where it is cooled. The cooled refrigerant then returns to the evaporating end where the cycle repeats. Fans 42 and 43 may be operated in the secondary refrigeration mode.

[0061] In a tertiary, circulating, mode, the compressor 14 remains shut off, but the controller opens bypass valve 38 as well as shut-off valves 896 and 898. The controller then activates pump 60 in order to circulate refrigerant in the primary refrigeration circuit, bypassing the compressor.

[0062] As described in connection with the embodiment of FIG. 1 , the primary refrigeration mode may be active when the outdoor temperature exceeds a first threshold. The passive, secondary mode may be established when the outside temperature falls below a lower second threshold. The secondary mode may either remain active while the outside temperature stays below the first threshold or the controller may switch to the third, circulating mode, for outdoor temperatures between the first and second thresholds.

[0063] While the primary mode of refrigeration has been described as a vapour- compression cycle (i.e., a cycle using a compressor), the primary mode of refrigeration could also be any other active refrigeration cycle such as an absorption refrigeration cycle which uses a heat source such as a flame, a thermoelectric refrigeration cycle which uses the Peltier effect, or a thermo-acoustic refrigeration cycle which uses sound waves to compress a column of gas.

[0064] Rather than associating the condenser with outside air, optionally, the condenser could be associated with deep water and use the cool temperature of the water to condense the refrigerant. As another option, the condenser could be associated with the ground temperature below the surface of the ground. This may provide the advantage that the ground temperature is more stable than the air temperature.

[0065] Other modifications will be apparent to those skilled in the art and, therefore, the invention is defined in the claims.

Claims

WHAT IS CLAIMED IS:

1. A refrigeration system comprising: a primary refrigeration circuit comprising an evaporator, a network driver, a condenser, and an expansion valve, said evaporator, said network driver, said condenser, and said expansion valve connected in series by a primary refrigerant line; a secondary refrigeration circuit comprising said evaporator, said condenser, and a bypass valve, said evaporator, said condenser, and said bypass valve connected in series by a secondary refrigerant line, said secondary refrigerant line in fluid communication with said primary refrigerant line and having a network driver bypass line bridging an inlet and an outlet of said network driver, said network driver bypass line incorporating said bypass valve; and a controller for selectively de-activating said primary refrigeration circuit by de-activating said network driver and activating said secondary refrigeration circuit by opening said bypass valve.

2. The refrigeration system of claim 1 wherein said condenser is exposed to outside ambient temperature.

3. The refrigeration system of claim 1 or claim 2 wherein said controller, when activating said secondary refrigeration circuit, also opens said expansion valve.

4. The refrigeration system of claim 1 or claim 2 wherein said bypass valve is a first bypass valve and wherein said secondary refrigeration circuit further comprises a second bypass valve, said secondary refrigerant line having an expansion valve bypass line bridging an inlet and an outlet of said expansion valve, said expansion valve bypass line incorporating said second bypass valve and wherein said controller, when activating said secondary refrigeration circuit, also opens said second bypass valve.

5. The refrigeration system of any one of claim 1 to claim 4 wherein said condenser is positioned above said evaporator and wherein an inlet of said condenser is positioned above an outlet of said condenser.

6. The refrigeration system of any one of claim 1 to claim 5 wherein said secondary refrigeration circuit further includes a circulating pump and wherein said controller, when activating said secondary refrigeration circuit, selectively activates said circulating pump.

7. The refrigeration system of any one of claim 1 to claim 6 wherein said secondary circuit includes a portion of said primary refrigerant line.

8. The refrigeration system of any one of claim 1 to claim 6 wherein said secondary refrigerant line is a heat pipe having an evaporating end connected to an outlet of said evaporator and a condensing end connected to an inlet of said condenser.

9. The refrigeration system of any one of claim 1 to claim 6 further comprising a tertiary refrigeration circuit comprising said condenser, a tertiary circuit bypass valve and a tertiary circuit heat exchanger connected in series by a portion of said primary refrigerant line and by a tertiary refrigerant line, said tertiary refrigerant line bridging an inlet and an outlet of said condenser and incorporating said tertiary circuit bypass valve and said tertiary circuit heat exchanger.

10. The refrigeration system of any one of claim 1 to claim 9 further comprising a temperature sensor exposed to said outside ambient temperature and outputting to said controller.

11. The refrigeration system of any one of claim 1 to claim 10 further comprising a refrigeration compartment, said evaporator being associated with said refrigeration compartment and further comprising a refrigeration compartment temperature sensor outputting to said controller.

12. The refrigeration system of any one of claim 1 to claim 11 further comprising an operator temperature set-point control outputting to said controller.

13. The refrigeration system of any one of claim 1 to claim 12 wherein said network driver is a compressor.

14. A refrigeration system comprising: a primary refrigeration circuit comprising an evaporator, a network driver, a condenser, a first shut-off valve, and an expansion valve, said evaporator, said network driver, said condenser, said first shut-off valve and said expansion valve connected in series nby a primary refrigerant line, said primary refrigerant line connected to an inlet of said evaporator, an outlet of said evaporator, an inlet of said condenser, and an outlet of said condenser; a secondary refrigeration circuit comprising said evaporator, said condenser, a heat pipe and a second shut off valve, said heat pipe connected to said evaporator outlet and said condenser inlet, said heat pipe incorporating said second shut off valve; and a controller for selectively de-activating said primary refrigeration circuit by de-activating said network driver and closing said first shut-off valve and activating said secondary refrigeration circuit by opening said second shut-off valve.

15. A refrigeration system, comprising a refrigeration circuit comprising an evaporator, a network driver, a condenser, and an expansion valve, said evaporator, said network driver, said condenser, and said expansion valve connected in series by a refrigerant line; a fan for blowing air over said condenser; a duct housing said fan and said condenser, said duct having an inlet and an outlet so that said duct can be installed so that said inlet extends through a wall or ceiling of a building and said outlet extends through said wall or said ceiling so that said fan may blow outside air over said condenser.

16. The refrigeration system of claim 15 wherein both said inlet and said outlet face in a first direction.