US2320265A

US2320265A - Refrigerating apparatus

Info

Publication number: US2320265A
Application number: US314905A
Authority: US
Inventors: Leonard F Clerc
Original assignee: Individual
Current assignee: Individual
Priority date: 1940-01-22
Filing date: 1940-01-22
Publication date: 1943-05-25
Anticipated expiration: 1960-05-25

Description

May z5, 1943.

' F. CLERC REFRI'GERATING APPARATUS Filed Jan. 22, 1940 5 Sheets-Sheet 1 May 25, 1943. LQ F. CLERC l REFRIGERATING A'PARATUS' Filed Jan. 22, 1940 5 Sheets-Sheet-2 Nw fm) May 25, 1943. F. CLERC REFRIGERATING APPARATUS 5 SheetsLSheet 3 Filed Jan. 22, 1940 My 2s, 1943; L. F. CLERC l 2,320,265

REFRIGERATING APPARATUS Filed Jan. 22, 1940 5 Sheets-Sheet 4 May 25 1943- L: F. CLERC REFRIGERATING APPARATUS Filed Jan.v 22, 1940 5. Sheets-Sheet 5 LJ rc www. NNN 0 P u ,T e WF. W ffm? www mNN\\ a. Y W L, mm@ EN WSN Patented May 2 5, l

UNIT-Ep STATES PATENT OFFICE aarmoanarma APPARATUS Leonard F. Clerc, Chicago, Ill. application January zz, 1940, serial No; 314305 s claims. (crea-115) My invention relates generally to refrigerating apparatus,.and more particularly to improvements in refrigeratlng units of the type which may readily beinstalled to cool a refrigerating cabinet, shipping container, or other space which is to be cooled or to be maintained at a low temperature.

-It is an object of my invention to provide anv improved refrigerating apparatus having an improvedl heat exchanger and i having improved means for defrosting the heat exchanger.

A yfurther object is4 to provide a refrigerating unit having improved means for automatically defrosting the evaporator coils at predetermined intervals.

' Ill, which may be formed integrally with an inner end wall I2, the latter having an enlarged flanged inlet opening I4, an aperturedbearing-supporting cup-shaped element I6 being welded or otherwise secured to the inner end wall I2. A suit- A further object is to provide an improved refrigerating unit having a forced air circulating means for transferring'the heat from the article -to be cooled to the evaporator coils of the unit.

A further object is to provide an improved refrigerating unit having means for heating the evaporator coils of the u'nit soas to defrost them readily.

A further object is to provide an improvedY refrigerating unit of the type using' airv as the heat transferring medium, in which means are provided automatically to circulate a limited quantity of air around the evaporator coils of theunit during the operation of rdefrosting.

A further object is to provide a combined evaporator and air blower unit in which the parts are arranged for high eillciency of heat exchange.

A `further object is to provide an improved v form of blower.

A further 'object is to provide improved control means for refrigerating apparatus.

Otherobjects will appear from the following, description, reference being had to-the accompanying"drawings, in which:

i -Figure 1 is a broken sectional view 4oi. the combined evaporator coil and blower unit taken genl erally on the line I--I of- Figure 2:

Figure 2 is a transverse vertical sectional view taken on the line 2-2 of Figure l;

Figure 3 is-a fragmentary sectional view illusl trating the blower construction;

Figure 4 is an enlarged longitudinal vertical sectional viewof the blower portion ofthe unit; Figure 5 is a fragmentary sectional lview of a modied form of heat exchanger;

Figure v6 is a diagrammatic view of a complete cooling system incorporating the invention, showing particularly the electrical controls;

Figure 7- is a developed view illustrative of the coils ol the evaporator; and, Y

ably ribbed outer end Wall l5 of the casing is secured to a flange on the cylindrical wall I0, and has a bearing box I3 welded or otherwise suitably secured at the center thereof. A bearing box 20 is similarly welded or secured to the bearing support I6. Thebearing boxes I8 and 20 contain. suitable antifriction bearings for a shaft 22, which, at its outer. end, carries a pulley 24 driven by a belt 26 from an electric motor 28 (Fig. 8).

. the shaft 22.

A plurality of rotor discs V3l! are secured to hubs 32, which in turn are non-rotatably secured to The'left-most hub 32 (Fig. 4) is illustrated as being-pinned to the shaft, whereas the remaining hubs 32 are provided with keyways to nt over a feather key 34 secured in the shaft Each of the rotor discs 30 carries an annulus 33 which is held in parallel spaced relation with respect to the rotor disc 30 by a plurality of radial blades 38, the latter secured to the'disc 30 and annulus 36 by welding, or, as illustrated, by rivets passing through flanges of the blades. Spaced between the rotors, each composed of a disc 33,

its blades 38, and its annulus 38, is a deilector `-ring 40 having an' annular iiange 42 iitting snugly within the casing Ill, the anges 42 serving as a means to space the defiector rings 4B.

properly. Each of the deector rings 40 is riveted to a partition plate 44, being spaced therefrom by a plurality of radial baiiies 46. The parts 43, 44, and 48 may be riveted together, as illustrated, or may be welded together so as to form a rigid unit. The partitionplates 44 are centrally apertured so as to leave a small amount of clearance around the adjacent hubs 32.

' This is followed by the assembly of another rotor discllwith its associated hub 32 upon the shaft 21, the feather key 34 permitting its hub to slideV l 4, and .5, the blower tute serious air leakage paths.

along the shaft to its proper position adjacent the hub 32 which is pinned to the shaft. Thereafter, another defiector ring and

baille plate assembly

40, 42, 44, 46 may be pressed into `the casing I0, with its flange 42 forming a substantially air-tightseal with the inner wall of the latter, and the parts thus successively assembled, whereupon the outer end wall |5 with its bearing box I8 is secured to the flange' of the casing |0 and the pulley 24 pinned tothe end of the shaft.v The partitions are provided with holes 5|, and the inner end plate with a hole 53, to permit drainage of water from the blower casing. T hese holes are preferably so small that water will be retained therein by surface tension, and upon freezing, seal them. Even though they should not Athus be sealed, they are so small as not to consti- Upon rotation of the shaft 22, air will be drawn into the casing through suitable inlet openings 48 formed in the bearing support I6, and, due to centrifugal action, .be forced outwardly through the spaces between the plates 38 which connect the rotors 30 with their annular plates 36. 'Ihe air thus ejected to the space, around the peripheries of the rotors -will be forcer-i toward the center through the passageways between the baiiles 46, the dellector-ring 40, and partition plate 44, arresting. the rotary motion of the air. The successive rotors will. operate in a similar manner to cause flow of air .under pressure from stage to stage in the vdirection indicated by the arrows in Fig. 4, the air finally being ejected-from the casing through an outlet opening 50.-V

The-blower unit is mounted at one end of an which lead from the unit 80 to an expansion4 valve 86, the latter being connected to the end of the outer coil 88. 'I'he conduit 84 is connected to a suitable controlling thermostat. i

Air is admitted to the left-hand en-d of the inner cylindrical .wall 52 through a fitting 88 having a valve 90 therein. An inlet tting 92 is connected to the valve fitting 88. A conduit 94 leads from the valve fitting 88v to the outlet 14, the` upper end of the conduit 94 being'normally closed by a valve 96. The valve 96 is carried by a valve stem 98,- which has an arm |00 secured thereto, 'the' arm |00 being connected by a link |02 with a, similar arm |04 secured toa shaft I 05, which carries the valve 90. A solenoid |08 has a plunger ||0 which is connected by suitable linkage with an arm ||2 which may be formed integrally with the arm |04. The plunger ||0 is l normally held in its lowermost position by gravity and by a spring |4 so as to hold the valves 90 and 95 inthe positions in which they are shown in full lines in Fig. l. Upon energization of the solenoid |08, the plunger will be swung upwardly,

moving the

valves

90 and 96 to the positions in evaporator coil housing-.shown (Fig. 1) as compr'ising four concentric

cylindrical walls

52, 54, 55,' 58, and end

walls

50 and 82. Suitably l1ocated between the

cylindrical walls

52, 54, 56, 58, are helical evaporator coils 64, 88, and 88,: these coils being connected together, asis clearly shown in Figure 7. These coils fit closely between the cylindrical walls 52-54, 54-'58, 58-58, respecf tively, and successive turns thereof are spaced sumciently to form connected helical air paageways between them. Commencing at the outlet of the blower, this passageway extends between successive turns of the coil 54, through an opening 10 formed in the wall 54, in a reverse direction' (to the right, Fig. l) along the space between the turns of the coil 65, through an opening 12 formedin the wall 56, and thence to the left along the helical passageway between the turns of the coil 68, to an outlet 14. The

walls

52, 54, 56, and 58 have small perforations 51 at their -lowest points to permit drainage -to a trough 59 which has a drain pipe 6| connected thereto.- perforations, like the holes 5| and 53, will usually seal themselves by the formation of ice, as

soon as the unit is `cooled upon recommencement of the refrigerating -portion of the operating cycle.

Within the inner cylindrical wall 52.-are two .additional

evaporator coil sections

18 and 18 which are concentrically arranged. The. lefthand end of lthe coil 18 is connected by a 'suit- -able coupling 19 (Fig. 7) with the left-hand endo'f the coil 64 so that the

coils

15, 18, 64, 56, and

n which they are shown in dotted lines in Fig. 1.

Suitablysecured upon brackets ||6 welded 'to the inner surface of-the end wall is an electrlcalheating unit ||8 mounted in a socket |20.

A conduit |22 is provided for the current supplyconductors |24 leading tothe socket |20.

As diagrammatically illustrated in Fig. 6, the apparatus is connected for maintaining a refrigerating chamber |26 at a predetermined low temperature. The refrigerator cabinet |26 is illustrated as having perforated shelves |28 for supporting articles to be cooled or to be maintained at a low. temperature, and is 'shown as being connected to the outlet 14 by a conduit |30 which leads from said outlet to the upper end of the cabinet |26, thei` air being withdrawn from the cabinet through a return conduit |32, which is connected with the inlet tting 92.

Power is supplied to main conductors |34, |36 from a suitable source of power upon closure of the main control switch |38. Upon closure of this switch, under normal circumstances, the motor of the mechanical refrigeiating unit is supplied with current through normally closed relay contacts |39, 4|. The unit 88 thus commences operating to compress the refrigerating medium withdrawn from the blower and evaporator coils through the conduit 82 and to cause the compressed gas or liquid to flow outwardly 68 form a continuous' length of tubing which serves asv the evaporator coil of a suitable mechanical refrigerating unit, indicated in Fig. 6

Y by the block 80. From this diagrammatic ligure,

it win be noted that the` mechanical refrigeratmg unit has atube 82 leading from the coil 18 to the refrigerating unit, and a pair of conduits 84,

through the conduit 85 to the expansion valve 88.

Closure of the switch |38 also energizes anv electric clock mechanism |31 which is of the program type, having switch mechanism to complete an electric circuit for a predetermined length of time lat selected predetermined intervals. Upon closure of the circuit of the clock switch mechanism, the winding |40 of a relay is energized, causing separation of switch contacts |39|4|, and causing engagement of the armature contact |39 with a fixed contact L42, thereby completing the circuit to the winding of solenoid |08.r

A thermostatic control element |44 is located within the refrigerator chamber |26 at a point at which it is desired to maintain the lowest temperature, this element being adapted to operate a thermostatic switch |46 which is arranged to complete a circuit between the secondary winding of a power supply transformer |48 and the winding of a relay |50,vthe switch |52 of the latter being connectedin series in one of the lines provided for supplying the-motor 28 with power.

the spring ||4, thus completing the operating` positions (Fig.` l). Also, the switch |33|4| will be closedl and the unit l80 thus operating. Under these circumstances, the blower will operate to exhaust air from the cabinet |28 through the conduit |32, drawing this air past the evaporator coils 18, 18, so as to pre-cool the air, and

raise the air pressure by passing it through successive stages of the blower. The air is ejected under pressure through the outlet Bland forced back and forth through the helical passageways formed between the turns of

coils

84, 88. 88, to the outlet 1.4 andv thence through conduit |38 to the cabinet |28. During the course of its flow around the evaporator coils, the air will be cooled emcientlyto substantially the temperature of the outer-most coil `88 (which is at the lowest temperature), so that the air entering the top fof the refrigerator cabinet will be at a suiilciently low temperature that frozen or' frosted foods may readily be stored in the cabinet.

' After a predetermined time interval, selected in the light of past experience with the rate at which the evaporator coils andconnected parts become frosted, the program clock |31 will operthe

valves

80 and 88 will be in their full line cycle of the apparatus'.

Theprogram clock |31 is of such type that it is capable of closing a circuit for a selected period of time at selected intervals. For example, the clock may be set tovenerglze the winding |40 of the relay for a period of seven or eight minutes each twenty-four hours. It is, of course, preferable that the apparatus should not defrost too frequently, but sufficiently often to maintain reasonably high efllciency as a heat exchanger.

Thefrequency with which it should be defrosted will, of course, depend upon the character of the refrigerating load upon the apparatus. If the apparatus is used to cool a chamber containing food in sealed packages, it will be apparent that defrosting will be necessary at very infrequent intervals, possibly only once a week or once .a month, depending upon how often the chamber containing the Vfoods is opened to admit atmospheric air. It will be noted that during the intervalthat defrosting is taking place, the supply of current to the motor ofthe refrigerating unit 80 is cut oi! so that defrosting may -speed in defrosting, the heater I|8 should beof take place with great rapidity. For maximum the highest wattage permitted by the power supply lines, so that the frost. will be melted from the evaporator coils and blower parts as rapidly vas possible, and thus prevent the temperature K in the chamber |28 from rising appreciably. In

order to prevent the heated air which is circulated through the blower and evaporating unit from being circulated through the chamber |28,`

the winding of the solenoid |08 may be controlled by the program clock |31 so as to be energized for a period of a few minutes after the supply of `ate to energize the relay winding closing switches |38-I42 and |38-|83. with consequent energization of solenoid |08, and also connecting. the heater ||8 to the current supply. If the switch |52 happens to be open at this time, the motor 28' will nevertheless be energized because of the completion ofthe parallel circuit through switch |39|53 1 Energization of thesolenoid |08 causes the

valves

90 and 88 to shift `from the positions in which they are shown in full lines in Fig. l to their dotted line positions, whereupon Athe blower unit will merely recirculate the 4air within the evaporator coil casings, past the energized heater H8, since the outlet 14 is connected-directly to the inlet valve fitting`88, and thev ends of the conduits |30 and |82 are closed by the valves.

I --At the same time, the motor of the refrigerating unit 80 is deenergized, because of-the opening of switch |38|4I, so that Adei'rosting will take place rapidly. the frost being melted from the evaporator coils and adjacent casing parts. and dripping through the small perforations 51 in the

cylindrical walls

52, 54, 88, and 88 into the drain trough 58 to which the drain pipe 8| is connected. After the relay |42 4has been energized for a sufllcient length of time to permit complete defrosti'ng of the evaporator and blower unit, the program clock |31 will open the circuit through the winding |40, whereupon the switch |38|4| will close and themotor of the .refrigf erating unit 80 will again be energized. The supply of current to the heating unit ||8 will be interrupted, and the solenoid |08' deenergized to permit the

valves

80, 88 to return to the positions in which they are shownin full lines in Fig. l. under the influence of gravity and the force of current to the heater ||8 has been interrupted at the end of a defrosting operation. By thus delaying the operationl of the

valves

80, 88 for a short time afterthe completion of the defrosting operation. the blower and evaporator coil unit may be brought to a low temperature before the air circulated by the blower is permitted to flow to the chamber |28.

It will be understood that lall of the connecting pipes and conduits which are at a low temperature will be suitably insulated to secure the highest .enlciency.

In Fig. 5, is illustrated a modified form of the large diameter evaporator coils, to take the place of the coils-84, 88, 88. In this figure, the spaces between the shells 'B2-54, 54-58, and 58-58 are each divided into. two helical passageways by a suitably formed generally corrugated sheet |80, one of the helical pasageways conveying the refrigerating medium and serving as a part of the evaporator coil system, while the other passageway serves as an air conduit for conveying air from the blower to the outlet conduit |30.

`The ends of the two passageways may be suitably connected with the corresponding passageways formed between the adjacent shells so that the three pairs of passageways between the four .shells will, in ei'l'ect, form two continuous passageways adjacent each other throughouttheir length. The shell '|80 is preferably seam-welded to the

adiacent shells

52, 54, 88. or 88. and for this purpose it may be desirable to vform the shell with beads |82 so that fluid-tight seals may be obtained by welding.

In Fig. 9, I have shown a modified form of my invention including an improved form of control mechanism and circuits and an improved formy of heat exchanger. In this modied form,

the invention is illustrated as -of general .appli- Y 'A a ductors to the power lines.

' secured thereto five

interrupter cams

230, 28|,

cation, for cooling any type of chamber. -or for air conditioning enclosures.

' v gearing 228 is` arranged to rotate the shaft 224 The heat exchanger shown in Fig. 9 comprises a suitable casing |1| which is provided with a central partition |12 and inwardly proieoting baille walls |14. Baines |18 project inwardly from the casing |1| so as to provide a circuitous air passageway through the casing |1I, as indicated by the arrows. Each section of this passageway has a portion of the conduit |18 extending transversely therethrough, the conduit |18 being representative ofthe evaporator coil of a mechanical refrigerating unit .|80 which is driven by. a motor |82. The portions of the conduit |18 within.v the heat exchanger |10 are provided with radially projecting heat collecting wires |84, or may be provided with the usual heat conducting fins.

Valves

284, 205, 208, lillustrated as of the butterfly type, are arranged to be operated by a solenoid 208 through a suitable linkage, including arms2| 0 connected to the pivoted stems of the valves. A spring 2|| is provided to hold these valves in normal full-line position. 'Ihe valve 204 is adapted to control the now from the conduit |98, to the chamber |88.

while the valve 205 controls the ow from this conduit to the valve chamber 200 and hence to the blower inlet conduit 202. The valve 208 controls the flow from the chamber 88 to bey cooled to the inlet conduit 202 of the blower.

A deflector valve 2|2 is mounted for rotation on a pivot 2|4 and is adapted to be manually operated by means of a handle 2|8. This valve is so arranged that it may, when in the full-line position shown, cause all of the air flowing past thev valve 208 to be drawn from the chamber to be cooled, or when in dotted line position, cause all of the air drawn past the valve 208 to be drawn from the atmosphere. The valve 2I2 and its associated operating mechanism is, ofcourse,

slowly, as for example, one revolution in eight minutes, and upon completion of one revolution,` to permit the shaft to rest for anA extended period,

for example, twenty-four hours, depending upon the frequency with which it is desired to defrost the heat exchanger |10,-as determined by the connected to thevinlet of the blower |88 by a particular refrigerating load to which the apparatus is connected.

The switch 240, upon closure thereof by its cam 280, is adapted to complete a circuit from the power supply line 228 through the winding of solenoid 208, and hence to the power supply conductor 228, i

The switch' 24|,` upon closure thereof by its cam 28|, is adapted to complete a circuit from the conductor 228 through the winding of relay 220 and thermostat 2|8 to the conductor 220,

provided that the thermostat 2|8 is closed.

The switch 242, when closed by its cam 232, is

arranged to complete a cilcuit from the conductor 228 to the switch cont-acts 22| of relay 220 and, providing said .clay is energized, through the blower'motor |80 to the conductor 228.

'Ihe switch 248, upon closure by its cam 288, istadapted to complete acircuit from the conductor 228 through the electrical resistance heater 222 to the conductor 228. j

The switch 244. upon being closed by its cam 284, completes a circuit from the conductor 288 through the refrigerating unit motor |82 to the conductor 228.`

The cams 280 to 234 are shown in the positions they assume when the apparatus is operating normally, i. e., defrosting is not taking place. Upon completion of the interval for normal oper- Aation as an apparatus to cool. the contents of the chamber |88, the shaft 224 `will commerce rotating at a speed which it will be assumed. for

purposes .of illustration, to be at o ne-eighth` of Y arevolution per minute. v

During the rst minute following commencement of the defrosting operationjit will be noted e ln dottedlines because of the energization of solenoid 208. As a result, the blower will draw provided whenever the apparatus is to be used y vair only, or using part recirculated and part fresh air.

Within the chamber |88 is a'thermostat 2|8.

which controls the energization of a relay 220, the switch contacts 22| are in series with the' circuit for energizing the blower motor |80 and are opened wheneverlthe relay is energized.

An electrical heating unit 222 is located in the heating chamber |82 so as to heat the air forced `through this chamber by the blower |88. A synchronous motor, together with a reduction gear-- ing, providing an intermittent drive for a shaft 224- is diagrammatically represented at 228 and is connected to the distributing conductors. 228'* and 228 which are normally supplied with power when a switch 221 is closed to connect these con- 232, 288 and 234 which are adapted to engage The shaft 224 has.

the air directly from the conduit |88 past the open valve 208 and through the inlet conduit 202. 'I'he blower will discharge the air through the heating chamber |82 'to-the exchanger |10. Also,

. during this first minute, the switch `24| will open,

thus d eenergizing the circuit to the thermostat 2| 8 and permitting the relay switch 202 to close, irrespective of the temperature in the chamber |88. Likewise during the rst minute of the deirosting operation, the switch 242 will open, thus deenergizing the circuit for supplying current to the blower motor 88. During this rst minute iof deirosting, the switch 243 will close, energizing the resistance heater 222. Also, during this first minute, the, switch 244 will open, thus deenergizing lthe motor 82 of the refrigerating unit.

, During the second minute of the defrosting operation, the switch 242 will again be closed, thus Venergizing lthe blower motor and causing circulation of air heated by the resistance heater' 222 through the heat exchanger |10.

During the fth'minute of the defrosting operation, the heater will be deenergized and the blower motor deenergized due to the switches 242 and 242. i

During the sixtli minute of the defrosting operation,.the switch 244 will again be closed, causopening of ing the refrigerating unit to. commence oper-- ation through energization of its driving motor |02.

During the eighth minute of 'the defrosting operation, the switch 240 will beropened, deener-A gizing the vrelay 208 and permitting the .spring 2|| to return the

valves

204, 205, and 206 to the positions in which they are shown in full lines. The switch 24| will be closed', thereby establishing a supply circuit for the thermostat 2li, At the same time, the blower motor |90 will be again energized by the closing of switch 242.

From the foregoing, it will appear that during the defros'ting operation, the air will be circulated solely through the heat exchanger |10, and during the first portion of the cycle, will be heated by the heater 222, causing the melting of the frost from the internal surfaces -of the heat exchanger. 'Ihe melted frost may drain through suitable openings formed in the partition '|12 and the bottom of the casing |1| to a suitable drain pipe. After the time has been allowedfor the draining of the-melted frost, the parts are reenergized for normal operation, as above described.

Some of the circuits, particularly -those which supply the motors |82, |90, and heater 222, will in actual practice be completed by relays enerrespectively, so that the latter switches may be of small current carrying capacity, since they will not carry heavy loads. Such relays will pref'- erably be so arranged that they will be. required to be energized only during 'parts' of the relatively short defrosting periods.

Under certain circumstances, particularly where the chamber |86 to be cooled'is a room which is to be air conditioned,'it may not'be necessary to utilize the heater 222 in the circuit, since theair drawn from the chamber will be warm enough to melt the frost from the heat chamber. It will be noted that apertures are provided in all of the horizontal sections of the l asada automatically operable means circulation of air by said blower to flow through gized by the closure of switches 242, 244, and 243 baille wall |12 and in 'the bottom of the casing |69. These apertures permit the melted frost to flow to the .drain pipe. Ordinarily. suillclent water will collect in these small apertures due to capillary attraction so that when the refrigerant is again supplied to the heat exchanger, -the water in these apertures will freeze, thereby sealing them. c

While I yhave shown and described particular v formsI of my invention, it will be apparent yto of a chamber having a space to vbe cooled, a heat exchanger having generally parallel passageways therethrough for the circulation of air and refrigerant in heat exchange relationship, means to supply a refrigerating medium to said heat exchanger, a blower for circulating air .serially through said heat exchanger andsaid chamber, for limiting `the said heat exchanger during a xed interval in `a refrigerating cycle of predetermined length,l and means to heat said heat exchanger'while the 4 air is limited to flow therethrough. a

2. In a refrigerating system,'th e combination of a casing, a plurality of concentric cylindrical shells in said-casing, a plurality of chelical coils of tubing located between said shells and inhe'at conducting relationship therewith, means for circulating a cooling medium through said coils,

and means for circulating air to be cooled through the helical spaces between the turns 'of said coils.` v

3. In a refrigerating'system; the combination of a plurality ofspaced concentric metal cylindrical shells, a length of tubing formed in a plurality of Vconnected concentric helical coils lo`- cated respectively between pairs of said cylin- .drical shells, means for circulating a cooling medium through said tubing, and means for circulating air through the helical passageways formed between the said helical coils and said shells.

4. In an apparatus for maintaining a chamber at a relatively low temperature, the combination of a refrigerating means, electrical means con-V trolling the operation oi said refrigerating means, ablower connected to circulate air past said refrigerating means, electrical means controlling the operation of said blower, means to heat the air supplied to said refrigerating means by said blower, conduits connecting said chamber and refrigerating means, a valve mechanism for con necting said conduits together and cutting off communication between said conduits and said chamber.' electromagnetic means for actuating said valve mechanism, a plurality of switches, a plurality of switch actuators, means to operate said actuators in a predetermined sequence at periodic intervals, and circuits 'connecting said switches and a source of power in series respectively with said electromagnetic means, said means for controlling the operation of said V blower, said heating means, and'said means for controlling the operation of vsaid'refrigerating means.

5. In a system forl maintaining a space at a relatively lowtemperature, the combination of` a heat exchanger, a refrigerating unit connected to said heat exchanger, a motor for driving said refrigerating unit, conduits forrconveying air to 'and from said heat exchanger for cooling by saidrefrigerating unit, air circulating means in one of said conduits, a motor for driving said circulating means, means connecting the end s of f -said conduits respectively to the space to be cooled, valve means'having two operative positions, in one of which said conduits are connected respectively to said space through said last named means and in the other position of which the-ends oi' said conduits are connected together and disconnected from said space, an electrically operated heater. and automatically operable means to move said valves to said second position and to`energize said electrical heater and said motor. wherebyv said air circulating means -Iwill circulate air past said heater and throughv saidheat exchanger without flowing through the `space to be cooled. r 6. In a refrigerating system, the combination of a 'heat exchanger havingv generally parallel passageways separated by heat conducting walls, said passageways having inlets and outlets, one of said passageways serving to. convey a refrigerating medium and the other of said passageways serving to convey air to be cooled, a blower for forcing air through said air passageway, a chamber to be cooled, conduits respectively connecting the inlet and outlet ends of said air passageway with said chamber, a heater located adjacent the inlet to said air passageway, andv time controlled means operable automatically to prevent the flow of airthrough said conduits and to connect the inlet and outlet ends of said air passageway together to form a short-circuit path for the air impelled by said blowerpast said heater.

7. In a reirigerating system, the combination o f a heat exchanger having heat conducting walls forming separate generally parallel passageways,

said passageways having inlet and outlet ends,

one ot said'passageways serving to convey are.

frigerating medium and the other of said passageways serving to convey air to be cooled, means for forcing air through said air passageway, conduits connecting a chamber to be cooled respectively to the inlet and outlet ends of said air passageway, a heater located in saidalrv passageway, time responsive means operablelperaaaaaes y conduits and to connect the inlet and outlet ends of said air passageway together to form a shortcircuit path for the flow oi.'- air impelled by said blower'past said heater, and means for energizing said heater only during the periods that the inlet and outlet ends of said air passageway are Vconnected together.

iodically toprevent the now of air through said 8. In an apparatus for maintaining a refrigerating cabinet at a relatively" low temperature, the combination oi' a refrigerating unit having a cooling element, a blower connected to withdraw air -from said chamber, circulate it past said element and return air tosaid chamber, automatically operable means to prevent the iow ot air to and from said chamber and to cause the air ,impelled bysaid blower to iiowsolely through said refrigerating unit, said last named means being operable during a predeterminedperiod of the operating cycle of the apparatus, means adiacent the blower to-heat the air impelled thereby. and control means to cause energization of said heater for a period commencing simultaneously with the said period of the operating cycle but terminating prior to the termination of said period, whereby said blower will continue to circulate air through said ref rigerating unit for a length of time after said heating means has been deenergized.

LEONARD F. CLERC.