US3367131A

US3367131A - Defrost means for refrigeration unit

Info

Publication number: US3367131A
Application number: US551445A
Authority: US
Inventors: John K Foessl
Original assignee: Galt Equipment Ltd
Current assignee: Galt Equipment Ltd
Priority date: 1966-05-19
Filing date: 1966-05-19
Publication date: 1968-02-06
Anticipated expiration: 1985-02-06

Description

Feb, 6, 1968 J. K. FoEssL 3,367,131

DEFROST MEANS FOR REFRIGERATION UNIT Filed May 19, 1966 4 Sheets-Sheet l P2555 sw/rc# F 7 INVENTOR J. K. FOESSL mm f5? A TTORNE YS Feb. 6, 1968 J. K. FoEssL. 3,367,131

DEFROST MEANS FOR REFRIGERATION UNIT Filed May 19, 1966 4 Sheets-Sheet 2 NVE/YTOR J. K. FUESSL l y /Qr/v l'TUR/VEYS Feb. 6, 1968 J. K. Fos-:SSL 3,367,131

DEFROST MEANS FOR REFRIGERATION UNIT Filed May 19, 1966 4 Sheets-Sheet o 9/ H07 5mm/yr GAS l 8 *I l INI/ENTOR /28 J. K. FoEssL ATTORNEYS Feb. 6, 1968 J. K. Foi-:SSL

DEFROST MEANS FOR REFRIGERATION UNIT 4 Sheets-Sheet 4 Filed May 19, 1966 IIIII mi l HIIIIII INVENTOR J. K. FOESSL I ifm f5? United States Patent O 3,367,131 DEFROST MEANS FOR REFRIGERATION UNIT .lohn K. Foessl, Candiac, Montreal, Quebec, Canada, as-

signer to Galt Equipment Limited, Montreal, Quebec, Canada Filed May 19, 1966, Ser. No. 551,445 Claims. (Ci. 62-238) This invention relates to refrigeration equipment and, particularly, to a self-contained refrigeration unit of the vapor compression type which embodies an improved and separate automatic defrosting system. Such a self-contained refrigeration unit is particularly adaptable for fitting into a cargo container for maintaining the interior of the container within a specified temperature range.

Most refrigeration units of the vapor compression type at present in use are powered by electric generators driven by diesel or gas engines. The electric power from the generator is used to drive the compressors, fans, control circuits, and to provide electrical heat for defrosting the evaporators, or for heating the interiors of the cargo Containers, as required.

Such presently used units have many disadvantages, some of which are as follows:

(a) The operators of the units, who are usually in the business of moving freight, are forced to carry both eleci trical generators and engines for driving the generators, both of which are very heavy pieces of equipment and must be transported by the carrier as dead load, thereby reducing the amount of revenue producing load which can be carried.

(b) Using an engine to drive a generator means that the engine must run continually at design or full load speed, during all stages of the unit operation, in order to maintain a supply of current to power the compressor and fans, or the defrost heater, etc;

(c) The total loss of etiiciency, through the use of both a motor and a generator, represents a large factor in the overall cost of operating the unit.

(d) The complexity of a system embodying both driving motor and generator results in high initial manufacturing and purchasing costs, and increased servicing and maintenance problems;

Thus, in such presently used systems, the use of a generator is essential in order to provide a source of controlled electrical heat for evaporator defrosting and heating purposes.

The present invention overcomes the aforementioned disadvantages by providing a simplified refrigeration unit in which an internal combustion engine is used primarily for driving a compressor and in which the hot exhaust gases from the engine are utilized for evaporator defrosting and heating purposes. Such an improved unit enables the engine to run at idling speed during the defrost cycle when the compressor is not running, and thus enables the unit to operate for longer periods without refueling, or to carry a reduced fuel load with lighter fuel tanks and consequent increased revenue load carrying capacity. Such an improved unit also reduces overall unit weight, again resulting in increased revenue load carrying capacity, and also reduces the initial manufacturing costs, together with reduced servicing and maintenance problems.

It is, therefore, the main object of this invention to provide an improved refrigeration unit of the vapor compression type, in which the compressor is driven by an internal combustion engine and in which hot gases from the engine exhaust are utilized for evaporator defrosting and other heating purposes.

Another object is to provide a refrigeration unit of the vapor compression type in which an internal combustion engine is provided for driving the compressor, and in which a heat storage bank is provided for storing the engine exhaust heat.

3,367,13l Patented Feb. 6, 1968 ICC Another object is to provide an improved refrigeration unit which eliminates the need for an electrical generator, thus providing a unit of lower initial cost and overall weight, together with reduced servicing and maintenance problems, than conventional units of similar capacity.

A further object is to provide an improved refrigeration unit in which the compressor driving engine is able to run at idling speed during evaporator defrosting, and is thus able to carry lighter fuel loads than conventional refrigeration units which require the engine to run at a constant speed for driving an electrical generator.

These and other objects will be further apparent by referring to the following detailed description and figures, in which:

FIG. l is a perspective view of a typical cargo container illustrating a refrigeration unit, in accordance with this invention, positioned at one end thereof.

FIG. 2 is a side view, partly cut-away, and to an enlarged scale, of the refrigeration unit according to this invention and as shown in FIG. 1.

FIG. 3 is a section on 3 3 in FIG. 2.

FIG. 4 is a section on 4 4 in FIG. 2.

FIG. 5 is a schematic diagram of the refrigeration circuit.

FIG. 6 is a Schematic diagram of the defrost fluid circuit.

FIG. 7 is a schematic wiring diagram of the complete refrigeration unit (shown on the same sheet as FIG. l).

FIG. 8 is a plan view of the condenser coils, to a further enlarged scale.

FIG. 9 is a side view of the condenser coils.

FIG. 10 is an end View of the condenser coils.

FIG. ll is a plan view of the evaporator and heater coils, to a further enlarged scale.

FIG. 12 is a side view of the evaporator and heater coils.

FIG. 13 is an end view of the evaporator and heater coils.

FIG. 1 illustrates a perspective view of a typical SXSXZO cargo container 20 in which the refrigeration unit 22 is positioned in one end thereof. Arrow 24 indicates air iiowing into the unit to the condenser through louvered panel 26. Arrow 28 indicates cooling air iiowing out from the diesel engine compartment through louvered panel 30. Arrow 32 indicates air flowing out generally from the unit. The unit control panel is indicated at 34 and is covered by hinged door panel 36.

Referring now to FIGS. 2 to 4 which show details of refrigeration unit 22, and to FIG. 5 which is a schematic diagram of the refrigeration circuit, the unit is assembled in a frame structure 38 which includes an upstanding rear flange 40 for attachment to the cargo container 20.

Frame structure 38 and the unit casing are constructed from aluminum alloy, for reduction of weight and corrosion problems, and all connections are Argon welded.

An air cooled single cylinder diesel engine 42 is provided for driving a reciprocating compressor 44 through a centrifugal clutch 46. A typical example of such a diesel engine 42 includes an electrical starting system and a two-speed governor providing an engine idling speed of 900 r.p.m. and a full load operating speed of 2700 r.p.m. at which the engine will develop 8 B.H.P. at the shaft. Full power take-olf at cam shaft at half engine speed for direct coupled compressor drive and full speed drive from the fly wheel by belt drive for driving condenser and evaporator fans, as will be described later. Diesel engine 42 is attached to frame 38 through vibration absorbing mounts 38. A typical example of compressor 44 provides a capacity of 14,100 B.t.u./hr. at minus 20 F. saturated suction temperature, F. condensing temperature, 3.2 B.H.P., and operates with refrigerant 22. Centrifugal clutch 46 is designed so that compressor 44 will not be driven when engine 42 idles at 900 r.p.rn., and provides smooth and gradual load transmission from the engine to the compressor, and additionally provides a safety feature by preventing damage to compressor 44 through the accidental introduction of liquid into the compressor cylinders.

The refrigeration circuit, shown schematically in FIG. 5, is basically a conventional vapor compression type system. A typical example of such a system may have a gross cooling capacity of 14,000 B.t.u./hr. at minus 20 F. suction temperature, 110 F. condensing temperature, when air entering the condenser is 90 F. Net capacity available for removal of heat from the container and product may be 11,500 B.t.u./hr.

Refrigerant, in the form of vapor, is compressed within compressor 44 to such pressure that it can be easily liquitied by the following condenser. Thus, vapor at high temperature and pressure leaves compressor 44, passes through vibration eliminator 50 and check valve 52and enters condenser 54. Check valve 52 is provided to prevent back flow and a pressure relief valve 56 is provided between check valve 52 and condenser 54. The hot vapor is liquified within condenser 54 by removal of the latent heat therefrom.

A typical example of such a condenser is shown in FIGS. 8 to 10, which comprises a

copper condenser coil

56, 4 rows deep, with copper fins 58 for air cooling. Condenser 54 is electrotinned for maximum corrosion resistance. An axial flow condenser fan 60 (see FIG. 2) is provided for forcing cooling air over coil 56 and ns 58. Condenser fan 60 is driven by fan shaft 62 through angle gear box64. Fan shaft 62 is driven, by belt drive 66, at full engine speed from the iiy wheel. An adjustment 68 is provided for obtaining correct belt tension.

Refrigerant in liquid form, and at a high temperature and pressure, leaves condenser 54 and enters liquid receiver 70, then flows through shut-olf valve 72, drier 74, sight glass 76, and shut-off valve 78, and into heat exchanger 80. The hot liquid is precooled within heat exchanger 80, then ows into expansion valve 82.

The refrigerant, which is still at a high temperature and pressure, is allowed to expand within expansion valve 82 and, in so doing, the temperature and pressure drops. The cold low pressure liquid then enters distributor 84 where a further expansion and cooling takes place and the refrigerant becomes a cold wet vapor which passes,y

through individual distributor tubes 86, into evaporator S8.

Evaporator 88 is exposed to the interior of container 20 and thus the cold wet vapor owing through the evaporator will take up heat from the interior of the container and, in so doing, will evaporate and become completely saturated.

A typical example `of such an evaporator is shown in FIGS. 11 to 13. However, FIGS. 11 to 13 show an assembly 89 which also includes lower and upper heater coils 90 and 91 which are positioned, respectively, below and above the evaporator coils 88 and will be described later. Evaporator 88 comprises a plurality of separate side-by-side coils, each coil 6 rows deep and being fed by an individual distributor tube 86, such that refrigerant will flow downwardly therethrough. The outlet of each coil feeds into a common evaporator header 92 which discharges to suction tube 94. The assembly 89, of evaporator coils S8 and defrost

heater coils

90 and 91, is constructed of copper tubes and common aluminum tins 96. An axial ow evaporator fan 98 (see FIG. 2) is provided for circulating air through the assembly 89. Evaporator fan 9S is driven by fan shaft 100 through angle gear box 102. Fan shaft 100 is driven by fan shaft 62 through electro-magnetic clutch 104.

Refrigerant, in the form of warm saturatedvapor, then passes through suction tube 94 into heat exchanger 80 where it is preheated and then returns, through vibration eliminator 106, to the suction side of compressor 44, under the influence of suction pressure, and again becomes compressed to a high temperature and pressure, and the cycle repeats.

Low pressure gauge 108 is positioned on control panel 34 and indicates the suction inlet pressure of compressor 44. High pressure gauge 110 is positioned on control panel 34 and indicates the discharge pressure of compressor 44. Shut-off valves 109 and 111 are provided in the links to pressure gauges 108 and 110, respectively. High pressure control 112 is positioned on control panel 34 and controls the discharge dessure of compressor 44.

Refer now to FIG. 6 which is a schematic diagram of the defrost fluid circuit. In this automatic circuit the hot exhaust gases from diesel engine 42 are utilized for defrosting evaporator coils 88 and for heating the container when required. A muHier-heat exchanger assembly 114 is located adjacent diesel engine 42 and all exhaust gases are passed directly thereinto from the engine exhaust manifold. Muffler-heat exchanger 114 comprises a housing 116 having a spiral coil 118 of prime surface positioned therein and exposed to the hot exhaust gases. A heat bank 120 is adapted to absorb and store up to 95% of the exhaust heat during the whole operating time of diesel engine 42. Heat bank 120 provides a large amount of heat for rapid evaporator defrosting to prevent the interior temperature of container 20 from rising excessively. The defrost heating medium is a silicone Huid which circulates throughoutthe defrost circuit. The preferred characteristics of the silicone fluid are 200 viscosity at 77 F., flash point 600 F., pour point minus 63 F., boiling point 392 F.

Heat bank 120 is constructed of aluminum or like material and comprises two separate compartments, an outer closed jacket 122 which provides a reservoir for the defrost uid, and an inner closed container 124 which contains a wax having a high latent heat factor and a fusion point well above that of water. Heat transfer coil 126 is positioned within the wax in inner` container 124. Exhaust outlet 128 is connected to mutllerheat exchanger assembly 114 and passes directly through heat bank 120. Thus, when diesel engine 42 is running, hat exhaust gases owng through exhaust outlet 128 will melt the wax in inner container 124 and maintain it at a high temperature. The characteristics of the wax will enable it to build up to a high temperature and the high latent heat factor will enable it to maintain the high temperature for long periods of time.

The defrost uid is forced circulated within a closed circuit by a positive displacement gear pump 132. Heat transfer coil 126 is included in the closed circuit and thus the defrost fluid therein will be heated by heat transfer from the hot wax. Hot defrost fluid is drawn from the lower portion of outer jacket 122, through gear pump 132 and up to a prime surface continuous coil 134 positioned in the evaporator drip pan 136. Thus, the drip pan will always be warm and ice-free and will allow defrost water to immediately drain through drain tube 138 (see FIG. 2). Gear pump 132 is driven directly by diesel engine 42 through a belt drive 140 and an electro-magnetic clutch. The pressure of the defrost iiuid is indicated by pressure gauge 142 positioned on control panel 34 (see FIG. 5 A shut-ott valve 143 is provided in the line to pressure gauge 142. The hot defrost tiuid then circulates through

heater coils

90 and 91 where it loses heat and returns, via coil 118, in muier-heat exchanger assembly 114 where the uid is preheated, to heat transfer coil 126. The defrost uid is again heated in heat transfer coil 126 and then ows into outer jacket 122 for recirculation. Pressure relief orifice 144 is provided across pump 132 to relieve the load on idling diesel engine 42 when pump 132 is started. Pressure relief orifice 146 is provided in the feed line between heat transfer coil 126 and outer jacket 122.

Evaporator fan 98 forces air downwardly through evaporator coils 88 and defrost

heater coils

90 and 91, which are connected together by common fins 96, evaporator coils 88 being sandwiched between lower and upper defrost coils 90 and 91. This particular arrangement provides improved defrosting of evaporator coils 88, as follows:

(a) When the unit is on defrost cycle, and the cooling cycle is off, warm defrost iluid is circulated through drip pan coils 134 and then enters lower defrost heater coils 90, and melts the ice on the lower half of evaporator coils S8 by radiation, conductance through the common fins 96 and by slow convection. The warm liquid, now slightly cooler, then enters upper defrost coils 91 and melts the ice on the upper half of evaporator coils 88 by radiation and conductance through the common tins 96. Circulation is maintained until evaporator coils 88 are completely free from ice. Evaporator fan 98 is stopped during the defrost cycle and the unique construction of the sandwiched evaporator and defrost coils assembly 89 ensures that no air convection currents will ow through during defrost, thus reducing the heat input to the cold interior of container 20. FIG. 13 illustrates this phenomenon. The lower half of evaporator coils 88 will be heated by the lower defrost heater coils 90 and will cause upward air convection currents, as indicated by arrow A. The upper half of evaporator coils 88 will be heated by the upper defrost heater coils 91 and will cause downward air convection currents, as indicated by arrow B. These currents will meet approximately at line C and will thus form an effective barrier against through convection air flow.

A thermostatically controlled evaporator fan delay switch is fitted to ensure that evaporator fan 98 does not start after the defrost cycle has terminated until the cooling cycle has cooled the evaporator and evaporator space to a temperature at least equal to that of the interior of container 20. This prevents a quantity of cold air being drawn through a warm evapora-tor and rapidly heated, which could cause a pneumatic pressure to be built up in the container with possible ensuing damage. The defrost cycle is commenced when air flow through evaporator 88 reaches a predetermined static pressure, due to the ice build-up on the coils. The cooling cycle starts again when the evaporator rises to a predetermined temperature during defrosting.

The condenser fan 69 runs at all times, thus ensuring the lowest possible compressor discharge pressures on compressor start-up, which allows selection of smaller driving engines with all the resultant savings.

Muler-heat exchanger assembly 114 is adapted to be self-draining when the engine is running at full speed and the defrost uid is not being circulated. This prevents any possible damage to the defrost fluid by decomposition and also prevents any thermal stresses on the piping arrangement.

Final discharge of the exhaust gas is through outlets 130 which pass under the crankcase of compressor 44 and maintain the crankcase at a temperature suicien-tly elevated to prevent the condensing of refrigerant into a liquid therein, which would dilute the compressor lubricating oil and cause it to lose its lubricating qualities, or to foam when the compressor is started, causing it to leave the compressor through the cylinder in excessive quantities. Additionally, the compressor could become filled with liquid to the extent that mechanical damage would occur when the compressor was rotated.

The evaporator and defrost heater coils assembly 89 and fan section are insulated with polyurethane slab insulation 4" thick, and polyurethane slab insulation 2 thick is placed between the condenser coils and connection end.

The necessary unit control instruments are located in a waterproof cabinet as shown in FIG. 4, and are indicated by control panel 34. The control instruments include a 7 day recording temperature controller minus 30 F. to 170 F. 8 chart, a remote bulb thermometer, compressor pressure gauges, system master control switch, controllers for diesel engine 42, and instruments for remote electric start-up of diesel engine 42. A conventional 12-volt engine driven generator and battery 14S (see FIG. 2) is provided for engine start-up and to provide the necessary power for the control circuits.

Static pressure defrost control and evaporator fan delay thermostat are located inside the evaporator fan housing.

The arrangement for driving evaporator fan 98, from diesel engine 42 through electromagnetic clutch 104, provides further advantages, as follows:

(a) When the interior of container 20 has reached the desired temperature diesel engine 42, and thus fan 98, revert to idling speed, thus reducing the B.t.u. input.

(b) The mechanical drive eliminates the usual requirement for an electric fan motor. Thus, only mechanical heat is added, rather than the heat given up by an electric motor, plus mechanical heat.

(c) A conventional electrically driven fan gives off more heat during the off-cycle of the cooling system, thus speeding up the temperature rise of the container which results in the cooling system cycling more often with resultant increased cost and wear on machinery.

FIG. 7 is a schematic wiring diagram showing the electrical connections of the complete refrigeration unit, including the following components: temperature recorder 150, defrost switch 152, fan delay thermostat 154, electromagnetic evaporator fan clutch 104, surge condensers 156, regulator 158, ignition switch 160, pre-heat and starting switch 162, resistors 164, heater 166, high pressure switch 168, oil pressure control light 170, control light 172 (indicates control circuit is energized), a generator control light 174, diesel oil pressure switch 176, D.C. generator 178, engine starter motor 180, 12 V. battery 182, glow plug 184, solenoid operated dual-speed control for diesel 186, and electromagnetic pump clutch 188.

The operation of the refrigeration unit, in accordance with this invention, is as follows:

Diesel engine 42 is started, in accordance with normal engine starting procedures, and is then allowed to idle approximately at 900 r.p.m. until normal operating ternperature is reached. During this warm-up period, the engine only drives condenser fan 60 at idle speed, which draws less than 1A H.P. The desired temperature, for the interior of container 20, is selected on the controller and the system switch put to ON position.

Electromagnetic clutch 104 now engages and transmits power to evaporator fan 98. On demand for cooling, controller 150 will operate the solenoid operated dual-speed control 186 for diesel engine 42 and the engine speed will increase to the full operating speed of approximately 2,700 r.p.m. The centrifugal clutch 46 will engage and start compressor 44, fans 60 and 98 will run at full speed, and the cooling cycle will commence. When the required Itemperature is reached, controller 150 will switch the engine to idle speed, disconnecting compressor 44 and only idling the fans to maintain air circulation with minimum heat gain due to mechanical energy input.

When evaporator defrosting is required, a circuit automatic defrostat (not shown) will override the thermostat and switch the engine to idle speed, thus stopping the cooling system and also deenergizing electromagnetic clutch 104 to stop evaporator fan 98 and to stop all air circulation within container 20. The electromagnetic pump clutch 188 for pump 132 is energized and hot defrost fluid is circulated within the defrost circuit, for defrosting the evaporator coils. The defrostat is reset automatically when the temperature of the evaporator coils reaches 40 F and the cooling cycle then resumes. If the temperature within container 2O drops more than 2 F. below the set point on the control, heating is automatically provided by means of circulation of hot defrost uid within the defrost 7 circuit and with both fans operating at idle speed for the gentle circulation of warm air within container 20.

The entire unit is designed for the utmost simplicity and fuel economy. It is calculated that for a total unit weight not exceeding, for example, 1650 lbs., the fuel tank needs only to hold 50 imperial gallons and tank with fuel would not weigh more than 500 lbs. based on days continuous operation at full load engine speed.

It is thus seen that a refrigeration unit, according to this invention, provides many advantages over conventional units, some of which are as follows:

Exhaust heat from the driving engine, instead of being wasted as usual, is utilized as a source of heat for defrosting the evaporator, as a source of heat for heating the container, and as a source of heat for maintaining the compressor crank case at a temperature sufficient to prevent the condensing of refrigerant into a liquid therein.

The engine only runs at full speed when the controller calls for cooling and further different from conventional units, it does not have to drive a large electric generator to supply power for heating, or evaporator defrosting, or compressor crank case heating. Thus, when not required to supply power for the cooling cycle, the engine runs at idle speed, with resultant reduction in fuel consumption, extension of operating range, and increase in the life of the engine.

What I claim is:

1. A vapor compression type refrigeration unit including a compressor, condenser coils, evaporator coils, an expansion valve, interconnecting conduit means therefor forming a complete closed refrigeration circuit and having refrigerant therein, an internal combustion engine for driving `said compressor, and a separate system for defrosting said evaporator coils, said system including heat storage means, duct means for conducting hot exhaust gases from said engine through said heat storage means for transfer of heat thereinto, defrost piping forming a closed circuit and having a defrost fluid therein, a portion of said defrost piping extending into said heat storage means for transfer of heat to said defrost fluid, another portion of said defrost piping positioned adjacent said evaporator coils for supplying heat thereto, and pump means for circulating said fluid within said defrost piping circuit.

2. A refrigeration unit as set forth in claim 1 including separate fan means for directing air over said condenser and evaporator coils, said fan means being driven from said engine.

3. A refrigeration unit as set forth in claim 2 in which said fan means for directing air over said evaporator coils is driven from said engine through an electromagnetic clutch.

4. A refrigeration unit as set forth in claim 1 in which said defrost fluid is a silicone fluid having a viscosty of 200 at 77 F., a flash pont of 600 F., a pour point of minus 63 F., and a boiling point of 392 F.

5. A refrigeration unit as set forth in claim 1 including an exhaust gas heatexchanger positioned in said exhaust gas duct means, the hot exhaust gases from said engine passing through said exchanger and then to said heat storage means, a further portion of said defrost piping extending through said heat exchanger for preheating the defrost fluid therein after leaving said portion adjacent said evaporator coils.

6. A refrigeration unit as set forth in claim 1 in which said heat storage means comprises a closed inner compartment containing a wax having a high latent heat factor and a fusion point substantially above that of water, and a closed outer compartment formed around said inner compartment, said defrost piping extending within the wax in said inner compartment and the defrost fluid therein discharging into said outer compartment which provides a reservoir therefor and forms part of said closed circuit, said exhaust duct means extending through said inner and outer compartments.

7. A refrigeration unit as set forth in claim 1 in which said defrost piping adjacent said evaporator coils comprises lower and upper defrost piping coils positioned below and above said evaporator coils and series connected within said defrost piping circuit, said fluid circulating through said lower coils before circulating through said upper coils.

8. A refrigeration unit as set forth in claim 7 including a drip pan positioned below said evaporator coils and a further portion of said defrost piping yforming coils adjacent said drip pan and series connected in said defrost piping circuit such that fluid Iwill flow therethrough and heat said drip pan before flowing into said lower and upper defrost coils.

9. A refrigeration unit as set forth in claim 1 in which said exhaust gas duct means extends adjacent the crank case of said compressor after passing through said heat storage means, the exhaust gases flowing through said duct means and supplying heat to said compressor crank case before discharging into atmosphere.

10. A refrigeration unit as set forth in claim 1 including an exhaust gas heat exchanger positioned in said exhaust gas duct means and adjacent said engine, the hot exhaust gases from said engine passing through said exchanger and then to said heat storage means, and in which said heat storage means comprises a closed inner cornpartment containing a wax having a high latent heat factor with a fusion point substantially above that of water and a closed outer compartment formed around said inner compartment, and in which said defrost piping adjacent said evaporator coils comprises lower and upper defrost piping coils positioned below and above said evaporator coils, said defrost piping forming a coil within the wax in said inner heat storage compartment, the defrost fluid therein discharging into said outer compartment which provides a reservoir for said fluid and forms part of said closed circuit,y said closed defrost circuit including in series connection said outer reservoir compartment, said pump means, said lower defrost coil, said upper defrost coil, coil means positioned within said exhaust heat exchanger, and said coil in said inner compartment, said fluid being circulated by said pump in the direction of the aforementioned circuit components, said exhaust duct means extending through said inner and outer compartments of said heat storage means.

References Cited UNITED STATES PATENTS 2,384,210 9/1945 Sunday 62--238 XR 2,440,146 4/1948 Kramer -s 62-277XR 2,546,723 3/1951 Clark 62-238 XR 2,693,682 11/1954 Winger 62-277 MEYER PERLN, Primary Examiner.

Claims

1. A VAPOR COMPRESSION TYPE REFRIGERATION UNIT INCLUDING A COMPRESSOR, CONDENSER COILS, EVAPORATOR COILS, AN EXPANSION VALVE, INTERCONNECTING CONDUIT MEANS THEREFOR FORMING A COMPLETE CLOSED REFRIGERATION CIRCUIT AND HAVING REFRIGERANT THEREIN, AN INTERNAL COMBUSTION ENGINE FOR DRIVING SAID COMPRESSOR, AND A SEPARATE SYSTEM FOR DEFROSTING SAID EVAPORATOR COILS, SAID SYSTEM INCLUDING HEAT STORAGE MEANS, DUCT MEANS FOR CONDUCTING HOT EXHAUST GASES FROM SAID ENGINE THROUGH SAID HEAT STORAGE MEANS FOR TRANSFER OF HEAT THEREINTO, DEFROST PIPING FORMING A CLOSED CIRCUIT AND HAVING A DEFROST FLUID THEREIN, A PORTION OF SAID DEFROST PIPING EXTENDING INTO SAID HEAT STORAGE MEANS FOR TRANSFER OF HEAT TO SAID DEFROST FLUID, ANOTHER PORTION OF SAID DEFROST PIPING POSITIONED ADJACENT SAID EVAPORATOR COILS FOR SUPPLYING HEAT THEREO, AND PUMP MEANS FOR CIRCULATING SAID FLUID WITHIN SAID DEFROST PIPING CIRCUIT.