TECHNICAL FIELD

The present invention applies to the art of vapor-compression mechanical refrigeration and more specifically relates to methods and apparatus for using renewable energy sources to reduce the amount of mechanical work required to operate a vapor-compression refrigeration system.

BACKGROUND ART

Before mechanical refrigeration was developed, ancient people such as the Greeks and Romans transported snow and ice from high mountains to their cities. They used snow cellars, insulated cavities dug in the ground to keep the snow, usually packed down as ice for long periods. As late as the 19th and early 20th centuries in Europe and the United States, ice was sawed in large blocks in Northern lakes in the winter and stored for use during summer in ice houses. In India and Egypt, evaporative cooling combined with night radiation to space was long used to manufacture ice. The first man-made refrigeration, cooling produced by the evaporation of ethyl ether into a partial vacuum, was credited to William Cullen at the University of Glasgow in 1748. Although Cullen's procedure involved vapor refrigeration, development of a successful refrigeration machine of this type was not achieved until Jacob Perkin, in 1834, obtained a British patent on a "Volatile- Liquid-Cycle System Using a Compressor". Perkin made at least one successful ice machine but did not actively promote his invention.

In the mid-1800's a U.S. physician, John Gorrie, in Apal- achicola, Florida, developed an "air cycle" machine to provide ice for cooling for his hospital. His machine, which operated success¬ fully, was one similar to a machine proposed, but never constructed, by the inventor Otto Evans in Philadelphia in 180 «5. Gorrie's machine consisted of a compressor that compressed air, which was then cooled by a circulating water bath. As the air reexpanded, it dropped to a sufficiently low temperature to create useful refrigeration for the production of ice or other cooling. The expanded air was then drawn back into the compressor for compression and recirculation.

In 1856 another American, Alexander C. Twinning of Cleve¬ land, produced the first commercial ice machines that used a vapor compression refrigeration system. His first patent was taken out i 1850. James Harrison, who emigrated from Scotland to Australia in 1857, surveyed the machines of Gorrie and Twinning and developed a vapor compression machine using ethyl ether as the refrigerant. Harrison's machine was used commercially for several decades in the brewing industry and for freezing of meat for shipment.

A second type of refrigeration machine was developed in France in the 1850s by Ferdinand Carre. In Carre's system the refrigerant, normally a vapor, is absorbed by a suitable liquid. This solution is heated, driving off the refrigerant as a vapor, which is then condensed. This method is called absorption refriger ation. Carre's first machines employed water as a refrigerant with sulphuric acid as the absorbent. In 1859 Carre introduced ammonia as a refrigerant with ammonia-water as an absorbent. This successful combination was used throughout the world.

In the last half of the 19th century efficient ammonia compressors gradually edged out the air-cycle machine, and vapor compression refrigeration came to predominate. Unfortunately, ammonia stinks. It is also toxic and highly corrosive. In the 1920s a group of synthetic refrigerants known as halogenated hydro¬ carbons was developed. The early halogenated hydrocarbon refrig- erants, which v/ere essentially non-toxic and odorless, were license by one company and carried the trade name, FREON .

As the present application deals only with vapor compres¬ sion refrigeration, the development of absorption refrigeration equipment will not be further discussed. Nor, for similar reasons will the background of thermal electric and other exotic refrig¬ eration techniques be analyzed.

Practical mechanical refrigeration requires that the same refrigerant be repeatedly used for an indefinite period. Three way of doing this are possible: first, vapor compression systems; se- cond, gas expansion cycle systems; and finally, absorption systems. Of these, the vapor compression system is by far the most efficient and predominates the present market.

O.Y. - Wi

A vapor compression refrigeration system comprises three basic elements: an evaporator, a compressor and a condensor.

In the evaporator, the refrigerant boils or evaporates at a temperature low enough to absorb heat from the medium, such as air or water that is being cooled. The boiling point is controlled by the pressure maintained in the evaporator, since the higher the pressure, the higher the boj/ling jDoint. The compressor removes the vapor as it is formed, A-aT* a< ^e at Ae> ^sufficiently rapid to maintain the desired pressure. This vapor is then compressed and delivered to the condensor. The condensor dissipates heat to some heat exchange medium such as water or air. The condensed liquid refrigerant, is then reduced sharply in pressure by passage through an expansion valve. Here, the refrigerant's pressure and temperature drop until they reach the evaporator's pressure and temperature, thus allowing the cycle to be repeated. The process is one in which the refrig¬ erant absorbs heat at a low temperature and then, under the action of mechanical work, the refrigerant is compressed and raised to a sufficiently high temperature to permit rejection of this heat. Mechanical work or energy supplied to the compressor as power is al- ways required to raise the temperature of the system.

One type of mechanical vapor compression refrigeration is referred to commonly as "air conditioning", which is used to produce cooling in public buildings or homes. Air conditioning very often makes use of a central refrigeration plant and distributes cooling to various areas of a house or building, either as air or chilled water.

Reference may be had to Charles Singer, et al., A History of Technology, Volume 5, pages 45-51 (1958), which provides a brief account of refrigeration technology during the period of its most active development. See also, "The History of Refrigeration: 220 Years of Mechanical and Chemical Cold 1748-1968", American Society of Heating, Refrigeration and Air Conditioning Engineering (ASHRAE) Journal, Volume 11, pages 31-39 (July 1969), which chronicles in detail the people and machines which contributed to the modern day refrigeration.

See further, "ASHRAE Handbook of Fundamentals", Chapter 2

(1967), and ASHRAE "Equipment Guide and Data Book" (1969), two volumes that comprise an extensive coverage of current refrigeration practice. One of the problems with mechanical vapor compression refrigeration equipment is that no prior art known to the applicant permits these systems to directly make beneficial use of low-grade heat, such as low-level industrial process heat, hot flue gas from a stove, or the like, or unconcentrated solar energy. It has been im- possible to power a mechanical vapor compression refrigeration sys¬ tem directly with a low technology, solar-thermal collection facil¬ ity. To get high enough temperatures to run a compressor efficiently it has been necessary to use expensive and sophisticated concentrat¬ ing solar collectors. The present invention effectively uses low-level heat for refrigeration applications. It is therefore adaptable to renewable and by-product energy _^ so^r^es. It can use the refrigeration system's own waste heat -β the~ ^* heat of the ambiant air in a hot climate such as is found throughout the Mid-East. The applications and benefits of the present invention are numerous. This invention is especially attractive since it uses energy resources that were previously either not effectively harnessed or were wasted.

The rising costs of primary energy sources, such as oil, coal and gas have steadily driven up the cost of electricity. Re- cent years have seen gas and electricity prices rise even higher, with a further assurance of inflation in the future. In light of this, alternative energy sources and more efficient energy systems become increasingly important.

Renewable resources, such as wood, provide a relatively low-level energy base which is easily and safely produced. Free energy in the form of solar and wind power is available in usable amounts most anywhere. They also produce a broad, low-level energy base for general application. Both renewable and free energy re¬ sources are attractive in that they require no locating costs, entail minimal environmental hazard, and are available indefinitely.

. ^Vi

While available most everywhere and in large volume, these alternative energy sources are of low-level energy potential. There¬ fore, highly efficient machines and systems must be developed to harness and use such energy. Effective use of energy also entails use of waste energy which results from an original process. Examples of this waste energy include low-level industrial process heat, and hot flue gas from stoves or fireplaces. Using this waste energy increases the overall efficiency of the system. The present invention is advantageous since it effectively utilizes both renewable low-level energy sources, such as solar heat or ambiant air heat, and waste heat resulting from industrial pro¬ cesses.

As non-renewable energy prices rise and alternative energy technology improves, alternative energy sources and applications become increasingly cost-efficient. The refrigeration method and apparatus described by the present invention is highly efficient and specifically adaptable to alternative energy sources, for both industrial refrigeration and air-conditioning applications. This refrigeration method also uses industrial waste heat, thereby recovering more usable energy out of the total system. Using such energy, cost-effectiveness is increased, while lessening the burden on primary, non-renewable resources, reducing the resulting costs therefrom. The art of waste heat use is well developed. See for example, U.S. Patent No. 4,053,106, issued October 11, 1977, which discloses a system for utilizing the heat contained in flue gas. Another system of this type used in specific connection with a mechanical heat pump, which is essentially a reversible vapor com- pression refrigeration system, is described in U.S. Patent No. 4,155,505, issued May 22, 1979.

A system for using hot flue gas from a stove or fireplace, such as that shown in U.S. Patent No. 4,143,817, which issued March 13, 1979, for an "Automatic Fireplace Heating System"; and U.S. Patent No. 4,125,148, issued November 14, 1978, for a "Method for Utilization of Waste Energy". All of these prior devices failed to

meet the problem of how to use low-level heat to improve the effi¬ ciency, and thus lower the cost, of a vapor compression refriger¬ ation system.

It is therefore an object of the present invention to provide a method and apparatus for vapor compression refrigeration using relatively low-level heat, such as industrial waste heat, flue gas, solar heat, or ambient air heat.

Yet a further object of the present invention is to provide a vapor compression refrigeration system capable of using solar heat as, for example, heat from solar-thermal collectors. Still another purpose of the present invention is to provide a vapor compression refrigeration system that uses waste hea from flue gas by means of a heat exchange adapted to a stove, fire¬ place, or the like, whereby energy from the combustion of wood, coal or the like decreases or eliminates the conventional external power that would otherwise be required to provide refrigeration of a building or home.

Yet another purpose of the present invention is to provide a vapor compression refrigeration system that can be powered entirel by solar or low-grade thermal energy, i.e. energy that is easily obtained in the developing countries of the third world.

Another purpose of the present invention is to provide an entirely self-contained vapor compression refrigeration system capable of being used in a remote location without the requirement that large amounts of electric power be generated at the remote site Yet still a further purpose of the present invention is to provide an integrated heating and cooling system capable of control¬ ling the thermal environment using only solar or other alterna¬ tive sources of heat.

DISCLOSURE OF INVENTIONS

The present invention is a method and a variety of appar¬ atus for using a renewable heat source to power a vapor compression refrigeration system. The compressible working fluid passing from the system's evaporator is heated prior to being introduced to the compressor. Apparatus embodiments of the present invention include:

1 1. A solar heat/refrigeration system.

2. A wood or coal heat/refrigeration system.

3. An integrated climate control system comprising a wood or coal-burning double-wall stove with appropriate blowers and heat

5 exchangers to either, heat or cool, as required, in conjunction with the vapor compression refrigeration system disclosed by the present invention. The present invention may receive its heat input from solar collectors, flue gases, or any other renewable heat source. It may use the refrigeration system's own waste heat or the heat of

10 the ambient air in a hot climate. A provision may be made whereby these alternative energy sources also provide the mechanical work, either directly or through an electric intermediary means, to com¬ press the system's working fluid.

^} 5 BRIEF DESCRIPTION OF DRAWINGS

FIGURE 1 is a temperature entropy diagram illustrating the thermodynamic operation of a mechanical vapor compression refriger¬ ation apparatus constructed according to teachings of the prior art; FIGURE 2 is a schematic diagram illustrating the major 20 elements of the present invention and their associated thermodynamic values;

FIGURE 3 is a temperature entropy diagram of a vapor heating compression refrigeration apparatus constructed according to the preferred embodiment of the present invention; 25 FIGURE 4 shows the present invention utilizing a hybrid solar thermal/solar electric array to provide thermal and electrical energy to the present invention;

FIGURE 5 is a double-walled stove constructed according to the preferred embodiment of the present invention; 3 ^Q FIGURE 6 shows the present invention operating in syner- gistic interaction with the flue of a stove wherein hot flue gas both preheats the refrigerant and provides mechanical -power for the compressor of the present invention; and

FIGURE 7 is a stove incorporating a means for preheating ³⁵ the refrigerant utilized by the preferred embodiment of the present invention.

BEST MODE OF CARRYING OUT THE ^" INVENTION

FIGURE 1 shows a temperature versus entropy thermodynamic diagram of a vapor compression refrigeration apparatus constructed according to the prior art.

Liquid refrigerant at the condensor temperature is intro¬ duced into an evaporator through a regulating or throttling valve. small portion of the refrigerant evaporates and reduces the temper¬ ature of is shown ant continues at the constant temperature T- , absorbing heat from a working fluid outside the evaporator. This process is shown in FIGURE 1 by line B-C. Vapor is then compressed by a mechanical com¬ pressor along the line C-D in FIGURE 1 to the temperature T ₂ when, by passing the refrigerant through a heat exchange condensor, heat i rejected from the refrigerant at a constant temperature T and the vapor is condensed along the line D-A of FIGURE 1.

FIGURE 2 shows a functional block diagram of an apparatus capable of practicing the method of the present invention.

Structurally, refrigeration system 100 comprises a conden¬ sor heat exchange 102 whose output end 104 is in fluid communication with transfer line 106. The end of transfer line 106 opposite the end connected to condensor heat exchange 102 is connected to the input of control throttling valve 108.

The output of control throttling valve 108 is placed in fluid communication with the input of evaporator 110 by fluid line 112.

The output of evaporator 110 is placed in fluid communi¬ cation with heat exchange 114 by line 116.

The output of heat exchange 114 is placed in fluid communi cation through appropriate valving, not shown, with the low pressure side 118 of compressor 120.

Closing the cycle, the output side 122 _* of compressor 120 i placed in fluid communication through appropriate valving, not shown with the input of condensor 102 by fluid communication line 124. The material used to connect the various parts of the present apparatus is well known to those skilled in the art of

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refrigeration engineering. Specifically, they will be stainless steel or copper tubes weldedj braised, soldered, or otherwise placed in hermetic sealing connection with one another and with the heat exchangers and valves that comprise the invention.

Functionally, a working fluid, i.e. refrigerant, is com¬ pressed by compressor 120 to temperature Tr, . In condensor 102 heat Qu is removed from the refrigerant by heat exchange with air, water, or some other heat exchange medium. As is shown by line A-D on FIGURE 1 this energy exchange is isothermal and results in the

10 condensation of the working fluid. The refrigerant in line 106 is a saturated liquid that passes into and through control valve 108. A portion of this working refrigerant evaporates and changes the tem¬ perature of the remainder of the liquid refrigerant to temperature T, , as shown on FIGURE 1 by line A-B. This liquid and saturated T vapor undergoes isothermal energy exchange in evaporator 110. This energy is represented by Q. in FIGURE 2. The refrigerant, as a saturated vapor, then exits the evaporator, passes through line 116 and enters into heat exchanger 114. At this point in the process, some amount of heat energy Q _c is put into the refrigerant by its

20 passage through heat exchanger 114. The working refrigerant, still as a saturated vapor, exits heat exchanger 114 and passes through line 115 to the input port 118 of compressor 120. In compressor 120 mechanical work is performed to compress the saturated refrigerant vapor until its temperature rises to temperature T ₂ as is shown by

25 line C-D in FIGURE 1.

Results

Example 1 : (Prior art, i.e. no energy input at Cv.)

A textbook case of classical thermodynamics of a vapor com¬ pression refrigeration cycle is found in FUNDAMENTALS OF CLASSICAL

30 THERMODYNAMICS, by Van Wylen and Sonntag, pages 285-286.

In this example (Example 9.6 from the text) an ideal refrig¬ eration cycle using Freon-12 to produce .768 tons, of refrigeration yields a coefficient of performance of 3.55 at an energy cost of

.764 kilowatts. 35

^" BJREΛ^

O.-.I I '

Example 2: (Q _c input sufficient to add 20°F. to refrigeran

For the purpose of this example, heat ( . is considered to be free of cost as would be the case using solar heat.

Assuming that compressor 120 achieves reversible compres- sion and that the throttling valve 108 is operated in an adiabatic manner; further assuming that temperature T is 100° Fahrenheit and that temperature T, is 20° Fahrenheit, that the refrigerant used is Freon-12 and, that the flow rate of the refrigerant in the system is 200 pounds per hour, then the apparatus schematically illustrated in FIGURE 2 will ideally achieve a co-efficient of performance equal to 4.716. This will give a capacity of .768 tons of refrigeration at a power requirement of .7694 horsepower or .574 kilowatts.

Example 3: (Q _c input sufficient to add 30°F. to refrigeran For the purpose of this example, heat Q _c is considered to be free of cost as would be the case using solar heat.

If, however, sufficient energy Q _c is introduced to the refrigerant flowing from line 116 into line 115 such that the tem¬ perature of the saturated vapor in line 115 is raised to 30° Fahren¬ heit then, assuming all other conditions remain the same, the co- efficient of performance of the system is 5.575, the power require¬ ment to achieve the .768 tons of refrigerating capacity drops to .6508 horsepower or .4855 kilowatts.

FIGURE 3 shows a temperature entropy thermodynamic cycle diagram that applicant believes corresponds to the embodiment of the present invention described in connection with FIGURE 2 above. As in FIGURE 1, an initial temperature drop of A-B in FIGURE 3 is caused by the evaporative cooling of the refrigerant. Refrigerant then undergoes isothermal energy exchange along line B-C, which corresponds to the cooling in the evaporator of the present invention. Line segment C-D of FIGURE 3 represents the relatively low-grade heat energy input Q _c to heat exchanger 114 in FIGURE 2. The work done by compressor 120 thus need only be. line segment D-E of FIGURE 3 before condensor 102 can isothermally condense the saturated vapor, which is represented by line E-A of FIGURE.3.

1]

Reasoning by analogy, if a given amount of mechanical work allows compressor 120 to raise the temperature and pressure of the refrigerant from a low evaporation temperature T, to a relatively high temperature T ₂ , then the addition of thermal energy Q _c through heat exchanger 114 will allow the same amount of mechanical work by compressor 120 to raise the working refrigerant to a higher temper¬ ature than T ₂ and to a higher pressure. Since only temperature T ₂ is required by the present system, the amount of work that must be performed by compressor 120 is reduced. FIGURE 4 illustrates a solar powered embodiment of the present invention.

In FIGURE 4 hybrid solar collector 400 has an upper solar thermal collector portion 402 and a lower solar voltaic array 404. The sun 406 is shown providing radiation to hybrid collector 400. In FIGURE 4 the lower portion 408 of solar thermal collec¬ tor 402 is in fluid communication with.the low pressure side of pump 410 by means of fluid conduit 412. The high pressure output end 414 of pump 410 is in fluid communication with the input of condensor 416 by means of fluid line 418; The output of condensor 416 is in fluid communication with the high pressure side of throttling valve 420 by means of fluid communication line 422.

The low pressure or output side of throttling valve 420 is in fluid communication with the input side of evaporator 424 by means of fluid transfer line 426. The output side of evaporator 424 is in fluid communication with the upper input side 428 of solar thermal collector 402 by means of fluid transfer line 430.

Solar voltaic array 404 is electrically connected to electric power transfer line 432. Electric power transfer line 432 is electrically connected by means of compressor connecting line

434 to the electric prime mover of compressor 410. Electric power output line 432 is also electrically connected to-electric prime mover 436 which drives evaporator fan 438 and condensor fan 440.

All of the elements described in FIGURE 4 are standard air conditioning components available from any large supply house such as Thermal Supply in Houston, Texas. All fluid conduits, whether for

vapor or liquid fluids are low pressure copper tubing. The entire system is hermetically sealed and could use, for example, Freon-12 a a refrigerant.

Functionally, solar radiation from the sun 406 strikes hybrid solar array 400. The portion of ^' sunlight falling on solar voltaic array 404 generates electricity by well known means. This electricity is carried through line 432 and 434 to drive the electri prime movers for compressor 410 and motor 436, which is the prime mover for fan 438 and 440. In order to practice the present inven- tion using the arrangement shown in FIGURE 4, it would be necessary to determine the temperature of the evaporator and condensor and to control the electric prime movers for the compressors and fans according to an algorithm derived to yield optimum performance for various input and output temperature levels. These control systems are well known to those skilled in the art of refrigeration engineer¬ ing and have not been included in FIGURE 4 for the sake of simpli¬ city. It should be understood that any desired analog or digital control system can be used in conjunction with the present invention to optimize its performance. The portion of sunlight from sun 406 falling on solar thermal collector 402 provides the Q _c low level heat required to preheat the refrigerant prior to its compression as taught by the present invention. As shown in FIGURE 4, saturated vapor from evapor ator 424 is passed through line 430 into the upper end 428 of col- lector 402. Thermal radiation from the sun heats the refrigerant such that it achieves a, for example, 10 to 30 degree temperature rise by the time it exits the bottom 408 of collector 402 and returns through line 412 to the low pressure end of compressor 410. The refrigerant is then compressed and heat is rejected from it so it condenses to a liquid in condensor 416. The refrigerant, now a liquid, passes through transfer line 422 and through expansion valve 420 into evaporator 424 to complete the cycle.

FIGURE 7 illustrates a stove, which is one method of practicing the present invention using wood or coal as an alternative to electricity or fuel oil.

Stove 700 has an outer firebox 702 equipped with access doors 704 and 706. Firebox 702 has straight-wall sections 708 and an infundibularform flue transition section 710. At the upper end of infundibularfor flue section 710 a flue duct 712 is shown in sche¬ matic cross-section. Flue section 712 has external straight-wall members 714 which are connected at their upper end by welding or any 0 other convenient means to infundibularform stack transistion section 716. Stack transistion section 716 is joined at its upper end by welding or any other convenient means to smoke stack 718, which is in fluid communication with the atmosphere.

The outer wall of stove 700 may be made of steel, brick or 5 any other convenient material sufficiently.refractory to withstand the heat generated by the stove's operation. The interior of the firebox section 708 of stove 700 is preferably lined with firebrick and is provided with a fluid communication to the atmosphere, not shown, by which fresh air may enter to support the combustion pro- o cess.

In the straight portion 714 of flue 712, vertical divider walls 720 and 722 divide flue 712 into three roughly equal flue passageways: left-hand most flue passageway 724, middle flue passage¬ way 726 and right-hand flue passageway 728. 5 Flue passageway 724 is equipped with a damper 730 adapted to controllably open and shut flue section 724. Similarly flue section 726 is fitted with a controllable damper 732 and flue section 728 is fitted with a controllable damper 734. Damper 734 is shown open while dampers 732 and 730 are shov/n closed. 0 Any convenient manual or automatic control means may be used to control these dampers.

A general utility heat exchanger 736 is 'shown operatively inplaced within flue segment 724. A source of cold fluid, such as

5

air or cold water, is placed in fluid communication by input line 738 with the input of utility heat exchanger 736. The output of utility heat exchanger 736 is placed in fluid communication with warm fluid output line 740. Refrigerant heat exchanger 114 from FIGURE 2 is shown operatively inplaced within flue section 728. As in FIGURE 2, refrigerant line 116 is in fluid communication with the input inlet side of heat exchanger 114 which fluid carrying line 115 is connected in fluid communication with heat exchange 114's outlet. Input line 116 comes from the outlet side of evaporator 110 while output line 115 goes to the input side of compressor 120.

Functionally, wood or some other renewable fuel is burned in the firebox 702 of stove 700. As the fire burns, either drawing air in from the room around it or from an outside source to avoid heat loss in the winter, the hot gas at several hundred degrees

Fahrenheit passes up through flue transistion section 710 into any of the flue segments 724, 726 or 728, whose damper is open. If all dampers are open equally, flue gas will flow through flue section 726 preferentially since this section contains no mechanical impedance, i.e. no heat exchanger.

By adjusting the position of dampers 730, 732 and 734, any desired energy flow through a given flue section may be accomplished, subject only to the total availability of heat coming from the fire burning in firebox 702. This relatively low grade flue heat generated by combustion process of wood or some other renewable fuel in the firebox of stove 700 passes in countercurrent heat exchange through exchangers 736, 114 with a cold fluid and refrigerant, respectively. This allows the present invention to be practiced through the use of alternative fuels.

FIGURE 5 is a schematic detail of another embodiment of FIGURE 7 illustrating the use of a double-walled firebox in conjunc¬ tion with the present invention.

As shown in FIGURE 5, a fluid communication passage 502 has one end 504 in fluid communication with the interior of unobstructed

flue 726. Hot gas passageway 502 is in fluid communication at its other end 506 with the low pressure side of blower fan 508.

The high pressure output side of fan 508 is. in fluid communication with hot gas passage 510, which, in turn, is in fluid communication with the annular interior 512 of double-walled firebox 514.

Double-walled firebox 514 has a base 516 joined by welds or any other convenient means to outer wall 518. Outer wall 518 is preferably made of some material such as galvanized steel that is capable of readily transmitting heat from interior 512 to the ex¬ ternal environment.

A layer of insulation 520 insulates base 516 from the interior firebox 522. Annularly, inwardly surrounding, but spaced apart from, wall 518 is an inner wall 524, which is heavily insulated with fiberglass, firebrick and the like. Output fluid duct 526 is in fluid communication with a portion of double-walled firebox interior 512 sufficiently distant from the entry point of inlet duct 510 that flue gas is forced to circulate essentially through the entirety of interior chamber 512 in its passage from inlet duct 510 to outlet duct 526.

The other side of outlet duct 526 penetrates wall 722 in unobstructed flue 726 and is in fluid communication with the flue gas stream in vent 526.

Functionally, when blower 508 is turned off, double-walled firebox 514 is well insulated and cool even if a fire is present in firebox 522. Modern insulating material is capable of maintaining a temperature differential of over 1000° Fahrenheit in the space of only a few inches. One example is the special insulation material developed for the Space Shuttle program, which is now available on the civilian market. The interior of a piece of this insulation may be white hot so that it glows while the other portion of the insul¬ ation may be cool enough to pick up and handle bare-handed without discomfort.

It is anticipated that during the summer months, i.e. when the present invention is being used as an air-conditioning system, the stove shown in FIGURE 5 will be operated in its insulated mode.

This would allow wood or some other renewable fuel to be burned in a house without adversely affecting the system's operation designed to cool the house.

All transition sections, flues and stacks must also be insulated to achieve this result. It is desirable to obtain combus¬ tion air from outside the structure being heated or cooled, rather than using room air, to support the combustion process in the stove shown in FIGURE 5.

In the winter months, when the present invention is not used for air conditioning, a portion of the flue gas exiting flue 426 will be pumped by blower fan 508 through input ducts 502 and 510 to interior, annular space 512 surrounding the interior insulated firebox wall 524. This gas, at a temperature of several hundred degrees Fahrenheit, passes through interior space 512 at a flow rate controlled to heat exterior wall 514 to a useful temperature, i.e. several hundred degrees- Fahrenheit, for heating. Relatively cool flue gas then exits interior space 512 through exit duct 526 and is reinjected into the outlet flue 726.

FIGURE 6 shows the vapor compression refrigeration system illustrated schematically in FIGURE 2 adapted for use with the stove illustrated by FIGURES 7 and 5 above. In FIGURE 6 an additional provision has been made to use flue gas to provide the mechanical work required to drive compressor 120 of the present invention. In FIGURE 6 numbers that are the same as the numbers in FIGURES 2, 5 and 7 illustrate similar structures to the structures shown in the referenced figures.

Structurally, infundibularform transition member 710 and straight flue section 714 contain, in addition to first and second flue dividers 722 and 720, a third interior flue dividing wall 602. The provision of this additional wall creates an additional flue 604 as a companion to flues 728, 726 and 724. Flue 604 is equipped with an annular inverted cone-shaped nozzle 606 beneath and proximate turbine assembly 608, which may be a low-speed Pelton Wheel geared through a gear box 610 to rotate a shaft 612, which penetrates wall 714.

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Rotating shaft 612 is mechanically connected to compressor

120, whereby the hot flue gas flowing through flue 604 provides the mechanical work _p required to accomplish the compression of the working fluid in the present invention. Alternatively, turbine 608 may drive a generator or alter¬ nator and the electricity produced may be used to drive an electric prime mover to provide the work W _p required to operate compressor 120.

Although flue sections 724, 726, 728 and 604 in FIGURE 6 are shown as equal in size for ease of schematic illustration of the present invention, it should be understood that these flues may differ in size as is necessary to obtain the thermal or mechanical energy required to derive the heat exchange or mechanical energy that must be extracted from the flue gas to make the present invention a self-contained device.

Similarly, it should be understood that those skilled in the art will be able to use such expedients as a third heat exchanger driving a turbine which in turn is geared directly to operate com¬ pressor 120, .or which operates a electric generator or alternator, which in turn drives compressor 120 by means of an electric prime mover.

The above description has outlined several specific ways of making and using the present invention. These specific embodiments should not be read to limit the invention. They were included to comply with the United States law that requires an inventor to tell the best way he knows to make and use his invention. It is clear that the present invention is a broad one and can be practiced in many ways by those skilled in the art of refrigeration engineering. Therefore the present invention should not be limited by enabling disclosures given above, but should be limited only by the following claims and their equivalents.