US3100970A

US3100970A - Thermoelectrically refrigerated apparatus

Info

Publication number: US3100970A
Application number: US95599A
Authority: US
Inventors: Thore Matin Elfving
Original assignee: Individual
Current assignee: Individual
Priority date: 1961-03-14
Filing date: 1961-03-14
Publication date: 1963-08-20
Anticipated expiration: 1980-08-20
Also published as: FR1317639A; DE1401501A1; GB965943A

Description

T. M. ELFVlNG 3,100,970 THERMOELECTRICALLY REFRIGERATED APPARATUS Filed March 14, 1961 4 Sheets-Sheet 1 INVENTOR. More M [/fV/ng.

ATTOEA/f/J.

Aug. 20, 1963 r T. M. ELFVING 3,100,970

THERMOELECTRICALLY REFRIGERATED APPARATUS Filed March 14. 1961 4 Sheets-Sheet 2 V INVENTOR. 7/20/"9 M [A r/ny- 4 Sheets-Sheet 3 Filed March 14, 1961 INVENTOR. Mare M f/f m FIE 7 Aug. 20, 1963 T. M. ELFVING 3,100,970

THERMOELECTRICALLY REFRIGERATED APPARATUS Filed March 14, 1961 9 4 Sheets-Sheet 4 IIE 4 IN VEN TOR. More M [A /m5! United States Patent 3,100,970 TI IERMQELECTRICALLY REFRIGERATED APPARATUS Thore M. Elfving, 433 Fairfax Ave, San Mateo, Calif. Filed Mar. 14, 1961, Ser. No. 95,599 24 Claims. (Cl. 623) The present invention relates to thermoelectrically refrigerated apparatus such as refrigerators or other cooled or refrigerated spaces, compartments and the like, and particularly in which thermoelectric heat pump equipment is used for absorbing heat and lowering the temperature of the refrigerated space.

it is a general object of the present invention to provide improved thermoelectrically refrigerated apparatus, simple in construction and efficient in operation.

Another object of the invention is to provide improved thermoelectrically refrigerated apparatus including a compartment of lower temperature for ice freezing or storage of frozen food or other purposes in connection with such a refrigerated space.

It is still another object of the present invention to provide an improved thermoelectric household refrigerator.

It is a further object of the present invention to provide a thermoelectrically refrigerated apparatus having compartments maintained at different temperatures.

These and other objects of the invention will be understood from the following description when read in connection with the accompanying drawings in which FiGURE 1 is a perspective view partly in section of a thermoelectrically refrigerated apparatus according to the invention;

FIGURE 2 is an enlarged view of the low temperature compartment of FIGURE 1;

FIGURE 3 shows a thermoelectric refrigerator with a freezer compartment below the main refrigerated space with separate thermoelectric heat pumping equipment; and

FIGURE 4 shows another embodiment of a refrigerator with separate freezer compartment and with an improved heat dissipating warming compartment on top of the cabinet.

Referring to FIGURE 1, there is shown a perspective view, partly broken away, of a combined thermoelectric refrigerator and warmer. The refrigerator and warmer include a horizontal assembly of thermoelectric modules 8 with the cold junction side facing downwards and the hot junction side facing upwards. The modules 8 preferably have both sides in thermal contact with anodized and grooved aluminum protective and heat equalizing plates. The plates may be formed and placed in thermal contact in accordance with the teaching in copending application entitled Thermoelectric Heat Pump Assembly, filed February 6, 1%1, Serial No. 87,360, now Patent No. 3,075,360.

The protective and heat equilizing aluminum plates 9 on the cold side are in direct thermal contact with the upper horizontal portion 19 of a double-walled aluminum lining 11. The lining 11 includes spaced aluminum plates or sheets which are bonded or sealed at the edges and include interior bonded areas 13 to form a multitude of gas or liquid passages or channels 12 over the entire lining. The use of such double-walled usually roll bonded, plates or linings in connection with thermoelectric refrigeration is shown in my copending application Serial No. 47,161, filed on August 3, 1960. The inside space of the lining 11 is partly filled with a volatile liquid which serves as a heat transfer medium as described in copending application Serial No. 47,161 above.

The lining 11 can be made by bending a long doublewalled bonded plate in four places as illustrated. The

3,100,970 Patented Aug. 20, 1963 "Ice is directly in contact with another double-walled hermetic system 17 similarly bent to form an enclosed space and provided with gas or liquid passages as illustrated. The double-Walled system 17 is partly filled with a volatile liquid. The double-walled system 17 serves as the heat dissipating surface for the air cooling of the hot junctions of the modules 8. The space enclosed by the plate 17 can be closed off at the rear and provided with a lid or door at the front to form a warmer for various purposes. Preferably, the plate 17 is not insulated on the outside.

It can also be left open, as illustrated in the figure, to form a part of a duct for cold air. For example, it may fonma portion of the air conditioning duct in an automobile. Cold air will then pass over the inside wall surfaces of the double-walled plate 17 whereby the hot junctions of the modules are effectively cooled and the air warmed. The duct is preferably insulated on the outside.

Because of the nature of the heat transfer systems represented by the double-walled plates 11 and 17, both will assume a substantially even temperature over the whole of their surfaces. The temperature of plate 11 will be close to the cold junction temperature, whereas the temperature of the plate 17 will be close to the hot junction temperature of the modules 8. The doublewalled plates 11 and 17 can be expanded on both sides or on one side only, preferably being smooth on the side in thermal contact with the

protective aluminum plates

9 and 16.

The modules ll are provided with direct current by the lead 1 8. The power may be obtained from a direct current power supply connected to a source of A.-C. power; The current is regulated by the variable resistor 19.

Referring to FIGURE 1, there is provided a low tempeuature compartment 20 with an ice tray 21. The lining 2,2 of the low temperature compartment is cooled by thermoelectric modules 23 having their cold junctions in direct thermal but not electrical contact with the lining 22. The hot junctions are in thermal contact with the upper portion of the double-walled lining 11 through the heat equalizing and protective aluminum plate 24.

The modules 23 form a first stage heat pumping system indirectly cooled by the modules 8 which in relation to the modules 23 constitute a second stage heat pumping system. Thus, according to the invention, the thermoelectric modules 8 are used both as a single stage heat pump for absorbing heat from the compartment 14 and as second stage heat pumping means in combination with a first stage heat pump for creating temperatures below freezing in the low temperature compartment 20. The first stage modules 23 can be supplied with direct current parallel with the modules 8 over a separate variable resistor 25.

FIGURE 2 shows in sectional view the low temperature compartment 20. The ice tray 21 is placed on the metal lining 22 which in the ceiling is in direct thermal contact with the cold junctions of the modules 23. The metal lining 22 of this compartment can be of plain sheet metal, preferably of copper or aluminum. It can also be of the double-walled type and filled with a heat transfer medium for equalizing the temperature all over the lining. The

modules 23 are on their hot junction side provided with a heat equalizing, preferably anodized and grooved, plate 24 which is glued to'the uneven underside of the horizontal portion ll) of the lining 11, where the channels 12 are at least partly'filled with volatile liquid condensate. The heat from the hot junctions of the modules 23 will evaporate the volatile liquid and the heat from V the first stage modules will be delivered over the whole area of the plate 9 and the cold junction side of the modules 8. The ice freezing or low temperature compartment 20 can, according to the invention, be provided with a suitable insulation 26 as shown in the drawing. In FIGURE 2 is also shown a filling valve 27 which serves to aid in filling the double-walled'lining 11 with a volatile liquid.

The firststage modules 23 are in the figure placed in thermal contact with the upper portion of the lining 11, in other words in contact with the heat dissipating portion of the hermetic heat transfer system attached to the cold junctions of the modules 8. The first stage modules 23 can, according to the invention, also be placed at the lower portion of said heat transfer system, for instance, on the floor portion of the lining '11. In both cases the heat from the hot junctions of'the first stage thermoelectric heat pump is carried to the cold side of the modules 8 as in an ordinary cascade coupling with the dilference, however, that the second stage modules 8, ac-

, cording to the invention, have a much larger pumping capacity than needed for the first stage heat pump only and therefore can serve also as directcooling means for the refrigerator itself.

The energy supplied to the second stage modules 8 is, according to the invention, several times greater than the energy supplied to the first stage heat pump =23. A ratio of between '10 and 12 to l or more is representative of normal conditions in a household refrigerator where only ordinary ice freezing is wanted. In a refrigerator where also a low temperature compartment for the keeping of frozen food is provided, an energy ratio of between 4 and 8 to 1 is suitable, depending uponthe relative size of the compartments for medium and low temperatures. The total energy necessary is naturally dependent upon the size of the cabinet, its insulation and the prevalent ambient temperature as well asupon the factor of merit (Z-factor) of the thermoelectric material used, and the number and size of the thermocouples. The second walled panel with a great multitude of interconnected cavities or hollow spaces evenly dispersed over the whole lining which forms the side walls and ceiling and door in the refrigerator commodity compartment. The edges 35 of the lining 33 are firmly bonded together without any outlet except for a filling valve 36 for filling the cavities in the double-walled lining 33 partly with a heat transfer medium like Freon.

The upper horizontal portion or ceiling of the lining 33 is on its overside in thermal contact with the cold junction side of the thermoelectric couple assemblies 38 supplied with 11-0 current from a power supply 39 through the leads all over the thermostat 41, which can be of the intermittent operating type, with a sensitive bulb 42 placed in the commodity space 31. The thermostat acts upon the A.-C. input leads to the rectifier 39 as de-,

scribed in .my previously mentioned copending application Serial No. 47,161. The hot junction sides of the thermoelectric assemblies 3?, are in contact with a heat dissipating fin radiator 43 with forced air circulation by the fan 44. The fan and the radiator are provided with a protective cover 45. The heat dissipating means in contact with the hot junctions 38 can be of any type, for

- figure is shown metal tray shelves 48, preferably of anodized grooved aluminum, in thermal contact with the cold junctions and serving as radiators for ice freezing trays 49. The space 5% under the ice freezers serves as storage 2 room for frozen food or similar purposes.

stage? thermocouples with the double function of providing medium temperature cooling means for the direct cooling of the main refrigerator space and of second stage heat pump in an indirect cascade system has to operate with a relatively high temperature difference between the cold and the. hot junctions, say a At of 35-45 C.

The thermoelectric couple assemblies 47 may be supplied with D.-C. current separately from a smal rectifier '51 through the leads 52 over the smal variable resistor 53.

As'previously mentioned, an automatic temperature control of the described system is carried out by means of a thermostat for intermittent energization of the main heat pump, represented by the modules 38, with the sensitive bulb 42 of the thermostat placed in the compartment 31. Because of the small ratio of energy supplied to the first stage heat pump, it can, according to the invention, stay on all the time in order to keep a constant temperature in the freezer compartment. The firststage thermocouples will operate normally also when the energy supply to the second stage heat pump is tempoin an air cooled application. The corresponding coeiilcapacity is adequate for ice freezing and a low temperature storage place in a medium size refrigerator. The arrangement of a thermoelectric first stage heat pump indirectly connected to the main heat pump equipment, according to the invention, has proven very efficient and economical with a minimum of losses.

' FIGURE 3 shows another embodiment of a refrigerator according to the invention with separate thermoelectric heat pumps for a commodity space above freezing and for a freezer compartment. The commodity space 31 with shelves 32 has a double-Walled metal lining 33 with a multitude of bonds 34 between the two Walls in the form of small round patches, spots or joined surfaces of any configuration forming a pressure resistant doublerarily shut ofll as long as the temperature of the heat transfer system represented by the lining 33 is not raised more than a few degrees. The temperature of the lining 33 will be kept fairly constant by the accumulative efiect of the content in the refrigerated space and shorter cutoff intervals of the main heat pump will, therefore, not.

afiect the refrigeration of the freezer compartment which is an important feature of the present invention. In combination with the automatic temperature control of the food compartment 3 1, the low temperature compartment temperature is preferably provided with a hand regulated temperature control comprising the small variable resistor 53 in series with the first stage thermocouples which, thus, are permanently but variably energized. When the invention is applied to a refrigerator for an automobile or boat, also the main heat pump can be provided with a variable resistor in series with the thermocouples to adjust the heat pumping capacity according to the ambient requirements, as illustrated in FIGURE 1. I

The thermoelectric assembly 47 dissipating the heat from its hot junctions to the bottom portion of the doublewalled-lining 33 operates with a small temperature difference between the hot and the cold junctions. Under junctions.

normal operating conditions, the hot junctions can be kept at a temperature of '|-10 C. or lower and can produce freezing temperatures of C. or lower with a At of only C., which for a Z-factor of 3 means a corresponding COP close to 2 and a refrigerating efiect twice as large as the energy input. The coupling of the low temperature first stage thermocouple assemblies indirectly to the main heat pump assembly over the lining 33 creates very favorable conditions with a minimum of losses to the first stage low temperature junctions. The indirect coupling of the two stages, according to the invention, thus offers maximum efliciency, simplicity and flexibility.

The thermoelectric freezer compartment design illustrated by FIGURE 3 can, according to the invention, also be used in combination with other refrigeration processes, such as compressor refrigeration or absorption refrigeration. Bothcompressor refrigeration and absorption refrigeration rapidly lose in efliciency at lower evaporator temperatures. The loss is due mainly to the expansion of the refrigerant gases at lower temperatures. Thermoelectric refrigeration is independent of this physical law but is instead sensitive for large temperature differences between the cold and the hot junctions. It is, therefore, technically and economically advantageous to combine, for instance, compressor refrigeration at medium temperature operation with a thermoelectric heat pump for refrigeration effects at lower temperatures.

A refrigerator with two compartments of difierent temperatures, as described in FIGURE 3, offers an example of such a combination of two different refrigeration processes. The double-walled lining 33 in FIGURE 3 can, according to the present invention, be connected at each of the edges 35 with the low pressure side of a compressor so that the lining 33 forms an evaporator with an expansion valve at one end and a suction line at the other. The compressor can be operated at a back pressure corresponding to the desired temperature of the main commodity space, say at an evaporator temperature of +1 to 2 C. The double-walled lining 33 is as before partly filled with refrigerant. The thermoelectric heat pump equipment for the freezer compartment 46 can be arranged in exactly the same way as previously described. In this way, the compressor can operate at a high back pressure with maximum efficiency while the thermoelectric heat pump takes the temperature down to say 20 C. The heat exchange between the thermoelectric heat pump 47 and the double-walled lining 33 will take place in the same way regardless if the lining 33 is cooled thermoelectrically or by a compressor. The temperature of the compartment 31 can in both cases be regulated by a thermostat connected to the A.-C. lead to intermittently energize the associated D.-C current supply or motor as the case may be. The freezer compartment heat pump stays on all the time except for defrosting and other similar interruptions. The freezer compartment can be defrosted by switching the D.-C. current to the thermoelectric heat pump 47 so that the cold junctions become hot This defrosting operation can be hand regulated or automatic in any known way.

The combination of a medium temperature Freon system in the form of a double-walled lining or plate evaporator with a thermoelectric heat pump in thermal con tact with said lining and plate on its hot junction side, according to the invention, can be given a multitude of forms. The double function of the volatile liquid system to provide direct medium temperature cooling of a refrigerated space and to serve as a heat sink for a low temperature thermoelectric heat pump system is characteristic of the present invention. The invention can be applied to all types of refrigerators or similar devices where more than one working temperature is desired.

In FIGURE 4 is shown a household refrigerator with a freezer compartment as in FIGURE 3 but with another type of final heat dissipating surface in the form of a semi-closed warming compartment. The main thermocouple assembly 61 is as before placed with its cold side against the upper horizontal portion of the double-walled lining 62 which encircles the medium temperature refrigerator compartment 63 as previously described. A preferably anodized and grooved aluminum plate 64 placed between the lining 62 and the thermocouple assembly 61 serves to establish the thermal contact between the cold junctions and the lining. Under the floor of the compartment 63 is arranged a freezer compartment 65 cooled by the first stage thermoelectric modules 66 dissipating their heat on the hot junction side to the lining 62 as described in connection with FIGURE 3.

The main thermoelectric assembly 6; is on its hot junction side in thermal contact, over another equalizing plate 67, with the heat absorbing portion 68 a double-walled heat transfer lining 69, partly filled with volatile liquid forming a semi-closed heat dissipating warming chamber 70 as illustrated by the figure. The lower heat absorbing part 68 is placed in a hole or cut out in the ceiling insulation 71 and has approximately the same area as the thermocouple assembly 61. "In this way, full insulation thickness can be provided between the cold lining 62 and the warm heat dissipating lining 69 except for the contact area of the thermocouple assembly. The cold lining 62 can preferably be insulated from the compartment 63 in the ceiling portion thereof by means of an insulation layer 72 which serves to prevent drippage of condensate from the ceiling and also reduces losses when the thermoelectric assembly 61 is deenergized and the temperature between the cold and hot junctions is equalized. The

' void formed in the floor of the chamber 76! by the protruding portion 68 of the lining 69 is covered by a screen 73. The floor and the screen 73 can preferably be covered by a suitable floor rack, not shown in the figure, to prevent direct contact between warm objects and the lining 69.

Instead of the heat dissipating linings shown above for air cooling of the refrigerator, one can provide simple double-walled plates in contact with the hot junctions of the main thermocouple assembly for water cooling of the heat pump. Such an arrangement would be especially suitable for shipboard refrigeration.

I claim:

1. A refrigerator comprising a first refrigerating chamber, a second refrigerating chamber of a higher temperature than said first refrigerating chamber, at least a first and at least a second thermocouple assembly, each having hot and cold junctions, a one-way heat transfer system comprising, a double-Walled member partly filled with a refrigerant, said double walled member having a heat absorbing evaporator portion and a heat dissipating condenser portion at a higher level than the evaporator portion, said condenser portion being in direct thermal contact with the cold junctions of said second thermocouple assembly, said evaporator being in heat exchange rela .tion to said second refrigerating chamber, the hot junctions of said first thermocouple assembly being in direct thermal contact with said double walled member, the cold junction side of said first thermocouple assembly being in heat exchange relation with said first refrigerating chamber for cooling the same, means for dissipating heat from the hot junction side of said second thermocouple assembly, and means for supplying said first and second 3. A refrigerator as in claim 1 wherein the first refrigerating chamber is located directly under the second refrigerating chamber with the double-walled member forming the floor of the second refrigerating chamber and the ceiling of the first refrigerating chamber.

4. A refrigerator as in claim 1 wherein said first refrigeration chamber is within the second refrigeration chamber.

5. A refrigerator as in claim 2 additionally including separate second power supply means for supplying direct current energy to said first thermocouple assembly.

6. A refrigerator as in claim 1 wherein said means for dissipating heat from the hot junction side of said second thermocouple assembly comprises a double-walled lining, partly filled witha refrigerant.

7. A refrigerator comprising a first refrigerating chamber, a second refrigerating chamber of a higher temperature than-said first refrigerating chamber, a double-walled member forming ceiling, floor and at least one wall of said second refrigerating chamber, a refrigerant heat transfer medium inside said double-walled member, the

'floor and wall portions of said double walled member comprising the heat absorbing portion of a one-way heat transfer system, the ceiling comprising the heat dissipating portion of said one-way heat transfer system, first and second thermocouple assemblies each having hot and cold junctions, the hot junctions of said first thermocouple assembly in direct thermal contact with the heat absorbing portion of said double-walled member, the cold junction side of said first thermocouple assembly in heat exchange relation to said first refrigerating chamber, the cold junction side of said second thermocouple assembly in heat exchange relation to said heat dissipation portion of said double-walled member, means for dissipating heat from the hot junction side of said second thermocouple assembly, and means for supplying electric energy to said first and second thermocouple assemblies.

8. A refrigerator as in claim 7 additionally including power supply means for supplying electric energy in the form of direct current to said second thermocouple assem bly, means for supplying alternating current power to said power supply, and means for sensing the temperature within said second refrigerating chamber comprising a thermostat, said thermostat being connected to intermittently apply alternating current to said power supply to thereby maintain a predetermined temperature within said second refrigerating chamber.

9. A refrigerator as in claim 7 wherein the first refrigerating chamber is located directly under the second refrigerating chamber with the double-walled lining forming the floor of the second refrigerating chamber and the ceiling of the first refrigerating chamber.

10. A refrigerator as in claim 7 wherein said first thermocouple assembly has its hot junctions in thermal contact with said double-walled ceiling of the second refriger-ating chamber and the first refrigeration chamber is Within the second refrigeration chamber.

11. A refrigerator as in claim 7 wherein said means for dissipating heat from the hot junction side of said second thermocouple assembly comprises a double-walled lining, partly filled with a refrigerant.

12. A thermoelectric system for pumping heat from at least two different temperature levels comprising first and second thermocouple assemblies, a first refrigerated space in heat exchange with the cold junction side of said first thermocouple assembly and being cooled thereby, a second refrigerated space of higher temperature than said first refrigerated space, a hermetic one-way heat transfer system comprising a heat absorbing portion in thermal contact with the hot junction side of said first thermocouple assembly and in heat exchange relationship with said second refrigerated space and cooling the same, and

a heat dissipating portion at a higher level in direct thermal contact with the cold junction side of said second thermocouple assembly, the second thermocouple assembly having a double function of pumping heat from both said second refrigerated space of higher temperature and from the hot junction side of said first thermocouple assembly, and means for supplying said first and second thermocouple assemblies with electrical energy.

13. A thermoelectric system as in claim 12 wherein the heat pumping capacity of the second thermocouple assembly is substantially larger than the heat dissipation from the hot junction side of said first thermocouple assembly.

14. A thermoelectric system as in claim 12 wherein the hot junction side of the second thermocouple assembly is in thermal contact with an air-cooled heat dissipating fin radiator.

15. A thermoelectric system as in claim 12 wherein the hot junction side of the second thermocouple assembly is cooled by a second hermetic heat transfer system comprising a heat absorbing portion in direct thermal contact with said hot junction of said second thermocouple assembly and a heat dissipating portion exposed to the surrounding air. 1 V

16. A thermoelectric system as in claim 12 wherein the hermetic heat transfer comprises -a double-walled member with the walls bonded in spots to form a multitude of gas and liquid passages.

17. A thermoelectric system as in claim 16 wherein the heat dissipating portion of said double-walled hermetic heat transfer system is substantially horizontal.

18. A thermoelectric system as in claim 17 wherein said first thermocouple assembly has its hot junctions in thermal contact With the underside of said horizontal heat dissipating portion of said hermetic heat transfer system, whereby said, horizontal portion acts as both a heat absorbing and heat dissipating portion of the hermetic heat transfer system.

19. A thermoelectric system as in claim 16 wherein the heat absorbing portion of said double-walled hermetic heat transfer system is at least in part substantially horizontal and wherein the hot junctions of said first thermocouple assembly are in thermal contact with said horizontal part of the heat absorbing portion.

20. A refrigerator comprising a low temperature refrigeration region and a refrigeration chamber of a higher temperature, refrigeration means including an evaporator in heat exchange relationship with said refrigeration chamber for cooling the same, a thermocouple assembly having hot and cold junctions with the hot junctions in direct thermal contact with said evaporator and having its cold junction disposed to absorb heat from the low temperature refrigeration region.

21. A refrigerator as in claim 20 wherein said low temperature. refrigenation region is within said second refrigerating chamber.

22. A refrigerator as in claim 20 wherein said low ing in thermal contact with said member, the cold junction side of said first thermocouple assembly being in heat exchange relation with said first refrigerating chamber for cooling the same, means for dissipating heat from the hot junction of said second thermocouple assembly having an area in thermal contact therewith which is substantially the same as the area of the hot junctions, and insulationmeans insulating the remainder of said heat dissipating means from the double-walled member.

24. A refrigerator comprising a first refrigerating chamber, a second refirigerating chamber of a higher temperature than said first refrigerating chamber, at least a f st and at least a second thermocouple assembly, each having hot and cold junctions, a doublewallerl member partly filled with a liquid heat transfer medium, said member being in thermal contact with the cold junctions of said second thermocouple assembly and in heat exchange relation to said second refrigerating chamber, the hot junctions of said first thermocouple assembly being in thermal contact With said member, the cold junction side of said first thermocouple assembly being in heat exchange relation with said first refrigerating chamber for cooling the same, a double-Walled lining part-1y filled with refrigerant in thermal contact with the hot junction side of said second thermocouple assembly, said double-Walled References (Jited in the file of this patent UNITED STATES PATENTS Lindcnblad June 12, 1956 Gaysowski MW 30, 1961

Claims

1. A REFRIGERATOR COMPRISING A FIRST REFRIGERATING CHAMBER, A SECOND REFRIGERATING CHAMBER OF A HIGHER TEMPERATURE THAN SAID FIRST REFRIGERATING CHAMBER, AT LEAST A FIRST AND AT LEAST A SECOND THERMOCOUPLE ASSEMBLY, EACH HAVING HOT AND COLD JUNCTIONS, A ONE-WAY HEAT TRANSFER SYSTEM COMPRISING, A DOUBLE-WALLED MEMBER PARTLY FILLED WITH A REFRIGERANT, SAID DOUBLE WALLED MEMBER HAVING A HEAT ABSORBING EVAPORATOR PORTION AND A HEAT DISSIPATING CONDENSER PORTION AT A HIGHER LEVEL THAN THE EVAPORATOR PORTION, SAID CONDENSER PORTION BEING IN DIRECT THERMAL CONTACT WITH THE COLD JUNCTIONS OF SAID SECOND THERMOCOUPLE ASSEMBLY, SAID EVAPORATOR BEING IN HEAT EXCHANGE RELATION TO SAID SECOND REFRIGERATING CHAMBER, THE HOT JUNCTIONS OF SAID FIRST THERMOCOUPLE ASSEMBLY BEING IN DIRECT THERMAL CONTACT WITH SAID DOUBLE WALLED MEMBER, THE COLD JUNCTION SIDE OF SAID FIRST THERMOCOUPLE ASSEMBLY BEING IN HEAT EXCHANGE RELATION WITH SAID FIRST REFRIGERATING CHAMBER FOR COOLING THE SAME, MEANS FOR DISSIPATING HEAT FROM THE HOT JUNCTION SIDE OF SAID SECOND THERMOCOUPLE ASSEMBLY, AND MEANS FOR SUPPLYING SAID FIRST AND SECOND THERMOCOUPLE ASSEMBLY WITH ELECTRIC ENERGY.