US2984083A - Refrigerating and defrosting system - Google Patents

Description

May 16, 1961 F. P. CROTSER ETAL 2,984,083

REFRIGERATING AND DEFROSTING SYSTEM Filed March 5, 1959 3 Sheets-Sheet 1 INVENTORS FRANK F. CROTSER CARL E. BROWN h I d, ATTOQNEYS V y 16, 1961 F. P. CROTSER ETAL 2,984,083

REFRIGERATING AND DEFROSTING SYSTEM Filed March 5, 1959 3 Sheets-Sheet 2 INVENTORS FRANK P. CROTSER BY CARL E. BROWN ATTORNEYS May 16, 1961 F. P. cRoTsER ET AL 2,934,083

REFRIGERATING AND DEFROSTING SYSTEM 5 Sheets-Sheet 3 Filed March 5, 1959 1 L 3 was INVENTORS FRANK P- CROTSER CARL E. BROWN BY a; @My

ATTORNEYS 2,984,083 REFRIGERATING AND DEFROSTINGSYSTEM P. Crot ser Carl E. Brown, Adrian, Mich., asslgnors to 'Revco, Inc., Deerfield, Mich., a corporation of Michigan Filed Mar. 5, 1959, Ser. No. 791,497

. f 7 Claims. (Cl. 62-234) This invention relates to a refrigerating system having an evaporator that requires periodic defrosting, and more particularly to an improved system for periodic defrosting ofsuchevaporator.

- The evaporator of a refrigerating system is used to absorbv heat from a space to be refrigerated, and such absorption of heat is accomplished by introducing into the evaporator a liquefied refrigerant which vaporizes in the evaporator to produce the required cooling effect. The refrigerating cycle is completed by the use of a compressor which withdraws vaporized refrigerant from the evaporator, compresses the vaporized refrigerant and passes thecompressed refrigerant into a condenser in which it is cooled and thus reliquefied and from which it flows through a restricted passage into the evaporator. By virtue of this restricted passage, the pressure is much higher in the condenser than in the evaporator, so that the refrigerant will be liquefied in the condenser and will be evaporated in the evaporator.

In a completely automatic refrigerating system, it is necessary periodically to melt the frost that accumulates onthe exterior of the evaporator. Such defrosting of the evaporator can be accomplished by shutting off the refrigerating system until the frost has melted, but it is preferable to accomplish defrosting by supplying heat to the evaporator so as to melt the frost quickly and thus reduce the time during which refrigeration is discontinue'd. i

' One method which has been widely used for heating an evaporatorperiodically to defrost it is the hot gas method -of defrosting. That method has been accomplished heretofore by providing a bypass line which leads from the discharge side of the compressor directly to the evaporatorandwhich contains a valve that is open duringthe'defrostingoperation and is closed at other times. Durin'g a'hot' gasdefrosting operation as practiced heretofore, the evaporator is heated by running the Patented May 16, 1961 domestic refrigerating system is designed to move large,

. volumes of gasat low pressures and tends to overheat if there is a substantial increase in the pressure and thus in the density-of the gas entering the compressor. Such a compressor, when electrically .driven, is usually connected in series with a safety switch that opens thecircuit to stop the compressor when an overload is encountered and then recloses' to restart the compressor. Even though the opening and closing of such a safety switch may permit a hot gas defrosting operation to be completed in spite of the tendency of the refrigerant pressure to become excessive, the defrosting operation is then unduly prolonged and the starting and stopping of the compressor near the end of the defrosting operation may cause a housewife to become alarmed and to call a Serviceman.

The principal object of the invention is to provide an I improved refrigerating and defrosting system that obviintended to disclose and illustrate the invention but not ates the disadvantages of the hot gas defrosting systems heretofore known. More specific objects and advantages are apparent from the following description, which is to limit its scope.

Fig. I of the drawings is a diagram showing a pre- Fig. II is a fragmentary sectional view taken along the line I-III of Fig. I.

Fig; III is a fragmentary sectional view showing an alternative construction that may be used in place of the construction shown in Fig. II.'

Fig. IV is a graph showing the variation during the defrosting operation of the pressure at three points in the system of Fig. I.

Fig. V is a diagram showing a modified system embodying the invention. In the system of Fig. I, a compressor 10 is provided with a discharge line 11 which is connected both to a condenser 12 and to a bypass 13. The condenser '12 in turn is connected to a capillary tube 14 which may consist, for example, of 13 feet of tubing having an internal diameter of .031 inch. The capillary tube 14 leads to an evaporator 15, which is shown in Fig. I in the form of a serpentine tube. At the end'of the evaporator 15 is an enlarged section forming an accumulator 16 in which liquefied refrigerant may collect. The accumulator 16 is connected to a suction line 17 that leads compfessor while the valve is open in the bypass leading from the discharge side ofthe compressor to the evaporator, so that the hot gas leaving the compressor passes directlyjthroughthetevaporator and back to the compressor; and thus heats the evaporator to melt.the

frost thereon. .It iscustomary to control such a hot gas defrosting. operation .by meansv of a timer or other controldevicefwhich starts'the defrosting operation after the .refrigeratinglsysjtem has been operating .for a sufl'i cient period .of to 'cause a substantial accumulation of frost'onthe evaporator. The control device holds back to the compressor 10. I 1

The bypass 13 includes a solenoid valve 18 which is open during the defrosting operation. A novel feature of the system illustrated in Fig. Iis that the bypass 13 does not lead directly to the evaporator 15, but instead leads toa defrosting'tube 19 which runs parallel and adjacent to the tubing that forms the evaporator 15. Preferably, the defrosting tube 19 and the evaporator tube 15 consist of asingle extruded section that is composed of two tubular portions 15 and 19 and a connecting fin 20, The evaporator tube 15 may be provided with an additionalfin 20' (shown only in Fig. II) to increase the 5111' face area through which heat is absorbed during the re-. frigerating operation. The evaporator tube. 15 and the defrosting tube 19 are not necessarily of equal diameter,

. and it is often advantageous to use a smaller defrosting One diflicuIt'y' thatisencountered in the operation of hot g'asf'defrosting" systemsheretofore known, which is obviated*by tliepresent"invention, is that the pressure hf tlie -i'efrigerant entering the compressor rises .to an weaver/awe near the=end of a defrosting oper'ation. rhe iype'pr cempressor that is ordinarily used in a tube (for example, a defrosting tube having an internal diameter of 4 inch when the evaporator tube has an internal diameter of inch). The defrosting tube 19 pref erably leads to a reheating tube 21, .which' may be heated, for example, by passingthrough'the-compressor 10- as illustrated in Fig. I. 'A compressor manufactured for use in household refrigerators or freezers often provided with a passage known as an oil-cooler 10011,? and;such passage is commonly. connected in series with the cop denser so that the refrigerant flows through such passage after being partially cooled in the condenser. The compressor illustratedin Fig. I embodies such as passage, but in this case the passage is not connected in series with the condenser but instead forms part of the reheating tube 21.

' Also provided in the system illustrated in Fig. I is a restriction 22; which-preferably follows the reheating tube 21, and may consist, for example, of 1 foot of tubing having an internal diameter of .07 inch. The restriction 22 leads into the suction line 17.

The dashed line 23 indicates what portions of the system are enclosed in the compartment or cabinet to be refrigerated.

In many domestic refrigerators the evaporator, instead of consisting of a serpentine tube, is a rolled forged aluminum structure. Fig. III illustrates the use, in the system of Fig. I, of a rolled forged aluminum structure in which the defrosting tube 19a and the evaporator tube are arranged side by side.

The electrical system illustrated in Fig. I includes line wires 24 and. 25, one side of the compressor 10 being permanently connected to the line wire 24 by means of a conductor 26, and one side of the solenoid valve 18 being permanently connected to the line wire 24 by means of a conductor 27. Connected to the other line wire 25 by means of a conductor 28 is a thermostatic element 29 which is illustrated in Fig. I as a bi-metallic switch. The thermostatic element 29 is so located that it is responsive to the temperature in the refrigerated compartment indicated by the dashed line 23. Whenever the temperature in the refrigerated compartment is above a predetermined upper limit, the thermostatic element 29 is in its left-hand position as illustrated in Fig. I. In this position, the thermostatic element completes a circuit from the conductor 28 to a conductor 30 so as to connect the compressor 10' across the line wires 24 and 25 to keep the compressor running.

During the normal refrigerating cycle of the system illustratedin Fig. I, the compressor 10 runs until the evaporation of the refrigeration in the evaporator tube 15 has reduced the temperature in the refrigerated compartment toa, predetermined lower limit. When the temperature falls to such lower limit, the thermostatic element 29 moves to the right so as to open the circuit between the conductors 28 and 30. While this circuit is open, the compressor 10 remains at rest, and the temperature in the refrigerated compartment gradually rises as the supply of liquefied refrigerant in the evaporator tube 15 and the accumulator 16 is exhausted by continued evaporation. Then when the temperature reaches the predetermined upper limit hereinbefore mentioned, the thermostatic element 2 9-moves to its left-hand position, and a new refrigerating cycle begins.

In the system of Fig. I a switch '31 is provided to energize and thus open the solenoid valve 18 while the compressor 10 is running. When closed, the switch 31 completes a circuit from the conductor 30' through conductors 32 and 33 to the solenoid valve 18. A control device is used to hold the switch 31 closed during each defrosting operation. Such a control device may be operated in any desired manner to close the switch 31 when a substantial layer of frost has accumulated on the evaporator 15, and then to reopen the switch 31 when the layer of frost has melted. The control device may operate by temperature sensing to detect the accumulation of a substantial layer of frost on theevaporator tube and to detect the disappearance of frost by melting, but for the sake of simplicity Fig. I shows a simple timer motor 34 which is permanently connected across the line wires 24 and 25 and therefore runs continuously, and which drives a timing cam.35 The timing; of the defrostingoperation may be 'varied to meet different operating conditions, but in 4 v speed that the switch 31 alternately remains. closed. fol: approximately 20 minutes and remains open for several hours. Another advantageous feature of the system of Fig. I is the presence of a conductor 36 which, through the conductor 33, connects the solenoid valve 18 to a contact 37 associated withthe thermostatic element 29. Whenever the thermostatic element 29 is in its right-hand position, it completes a circuit from the conductor 28 through the contact 37 and the conductors 36, and 33 to. the solenoid valve 18. Thus, the solenoid-valve 18. not" only remains open during the defrosting operation but also remains open whenever the compressor 10 is not running. If the thermostatic element 29 happens to be in its right-hand position, with the solenoid valve 18 open, at the moment when the switch 31 is closed by the timing cam 35, the closing of the switch 31 starts the compressor running by energizing the compressor through the conductors 36, 32, and 30. The significance of this feature is as follows:

The presence of the contact 37 in the conductor 36 becomes important in case the thermostatic element 29 happens to be in its right-hand position at the moment when switch 31 is closed by the timing contact 35. Irr that case, if the contact 37 and the conductor 36 were not present, the defrosting operation would not begin until a thermostatic element 29 had moved to its left-hand position, and thedefrosting interval provided by the timing cam 35 would have to be long enough to permit defrosting to be completed. In the absence of the. contact 37 and the conductor 36, two extreme conditions could occur. One such extreme condition would occur if the thermostatic element had moved to its right-hand position just before the switch 31 was closed by the timing cam 35, and the other such extreme condition would occur if the thermostatic element had moved to its left-hand position just before the switch 31 was closed. As a practical matter it would be necessary'under such circumstances to design the timing cam 35 to provide a relatively long defrosting interval so as to permit defrosting to be completed in case the thermostatic element had moved to its right-hand position just before the switch 31 was closed by the timing cam.

Thus, if the contact 37 and the conductor 36- were not present the timing cam 35 would have to be designed to provide a relatively long defrosting interval that would prove to be excessive whenever the switch 31- happened to v be closed by the timing cam just after the thermostatic element had moved to its left-hand position. Whenever the defrosting interval thus proved to be successive spoilage of food products under refrigeration would be liable to occur, particularly if the refrigeration system. were being used with a home freezer, whichis intended to'keep its contents in a frozen condition.

The operation of the system illustrated in Fig. I may be summarized as follows:

After the switch 31 is closed by the timing cam 35,

- both the compressor 10 and the solenoid valve 18 are energized, so that the compressor 10 is running and the solenoid valve 18 is open. The defrosting operation then proceeds as the compressor forces the. hot compressed refrigerant-through the bypass 1-3 to the defrosting tube 19. Heat is. conducted from the defrosting tube 19 to the evaporatortube 15 to melt the layer of frost, and the timing cam 35 keeps the switch- 31 closed for a period just long enough to complete the melting of the'layer of frost. The requiredperiod is always the same because the compressor 10 is running and the solenoid-valve 18 is open immediately 'afterthe switch 31 closes.

' The restriction 22 performs an important function in the operation of the system shown in Fig; I. If it were not for the restriction;22, the-pressure:of-the-refrigerant would tendto rise. to an; excessive value near theend of atypical case the timingcam- 35 may-operate-atsucha 76 theidefrostingoperationpsoas;tqcause.theoverloading of itsrqstma san.ahic ecpmm n y dif q tih meth dsti g-1 h: d fr s n pera r duc n Pr ate 9f. t e f i c a t kes pla e 1 as t reduce h suction. line and" thusv avoid overloading of seem s v I sh uldxbe n rh w v rt a es t tio 2', :ash r inb fQ edesc b d, c is f a reduction in -;the pressure of .the refrigerant passing;

through the restriction is moderated toreduce the refrig 'eratingreifectofsuch reduction in pressure, so as to avoid chilling.,the-;suction line 17; substantiallybelow room temperature., If the reduction in. pressure of the refrigerant 'passingithrough the restriction 22 were sufficientto causethewsuction line to be chilled substantially below room temperatureiexcessive sweating; or frosting of the suction line: would :occur during ..the.;defrosting operation.

Asrafurtheri precaution against chilling of thejsuction line during therdefrostingioperatiom'the refrigerant that passes through the restriction 22 is heated in the system illustrated'in Fig'. I. Ithas been discovered that much better results are: obtained during the-' defrosting operation ,if therefrigerant is heated beforeitpasses through thelrestriction 22thanifit is heated after it passeslthrough the 'et 22." If'in a'systehr su chasthat illustrated in Fig. therefrigerant'were' nOtTeheatedbefOre it passed through thejrestriction 22 during the defrosting operation, thje,p'res s ure of the refrigerant entering the restriction 22 would be relatively lowduring'all but'thelast part of the defrostingpperation, because of the chilling action'of the layer of frost, so that the 'rate 'offfiow' of the refrigerant througliithejrestriction 22' would be very low andthe Idefrqsting',therefore'would'bevery slow, In the .systemof Fig; I, the reheating'of the" refrigerant just before it enters the restriction 2'2 causes the pressure of the refrigerant entering the restriction to be considerably higher and causes the defrosting to take place considerably faster than would be the case in the absence of such reheating.

Fig. IV is a graph showing how the pressure of the refrigerant varies during a typical defrosting operation, at three points in the system of Fig. I, time being plotted on the horizontal axis and pressure being plotted on the vertical axis. The upper curve 38 shows the pressure in the discharge line 11; the intermediate curve 39 shows the pressure of the refrigerant entering the restriction 22; and the lower curve 40 shows the pressure in the suction line 17. The curves 38 and 39 represent substantial gauge pressures ranging as high as several atmospheres, and the curves 3'8 and 39 are plotted on the same scale of pressure. The suction line pressure represented by the curve 40 is a relatively slight pressure and is plotted on a scale that is substantially larger than the scale of pressure on which the curves 38 and 39 are plotted.

At the start of the defrosting operation plotted in Fig. IV, the compressor is running so that the discharge line pressure 38 is relatively high and the suction line pressure 40 is relatively low. As the solenoid valve 18 opens, the discharge line pressure 38 drops sharply because of rapid condensation of the refrigerant in the de-.

frosting tube 19. The suction line pressure 40 drops also as the pressure in the condenser 12 falls while the refrigerant expands from the condenser into the defrosting tube 19. As the defrosting operation proceeds, all three of the pressures rise. It should be noted that each of the three pressure curves turns upward at an intermediate point in the rising portion of the curve. Such upturn in each curve may be due to the fact that the frost melts away from direct contact with the evaporator tube 15 and the defrosting tube 19.

The important point brought out in Fig.v IV is that all .aAs-the refr erant; pas e -t r a .fl i ic ibn 2;

tubi gi hat sub ant ly-i s o e a b se striction 22 1as hereinbefore} described. "Thesystem illustrated-in Fig. V 'ffers from the sys;

temofFigrI in the following respects: 7 a

The bypass the system fof "Fig.1.. A solenoid valve 41 is interposed not in positionto pl'joc iuc ev a defrosting operation.

, The operation of the system illustrated in Fig. ay.

be summarized as follows:

Thesolenoid valve 41-ha's'no'function when the compresser {10 is not running, but whenever the compressor is running during a normal refrigerating cycle the solenoid valve'is open, becausefit'isenergized through the conduc tor28, the thermostatic element 29,. t'he ,conductors30 and- .32, I the, switch. .31 ,and; the conductors 43 and 44'; durin'g' ,a 'norm'al refrigerating 'cycle the system of F 'g; ;V'. functions linthe same manner'as the sy'stemflof During a defrosting operation, the timing cam 35 holds the-switch 31in such a position that-the solenoid valve 41;

is Qenejrgiz'ed, and closed, so that'the hot gasflowing through 'thebypass 13pa'sses through the evaporatortube 15, the accumulator 1'6 and the reheating tube 21 and.

thereafter follows thesame pathlas in the system of Fig.1. I"Ihe distinction between the system" of Fig; I and th'e' system of FigtV resides in the factthat' in the system of- Fig.. I a separate defrosting tube l 9.is provided to con-' duct the hot refrigerant in heat exchange relationship with the evaporator tube "duringfthe defrosting operation, whereas in the syster'n'o'f FiggVthe"hotrefrigerant, dur ing the defrosting operation, is led through the evaporator tube itself. At the same time, it is necessary that the hot refrigerant, during the defrosting operation, pass through the restriction 22 before entering the suction line 17. Since the refrigerant cannot be caused to pass through such a restriction during the normal refrigerating cycle, it is necessary in the system of Fig. V to provide a bypass in the form of the solenoid valve 41 which is open during a normal refrigerating cycle, and is closed during a defrosting operation to cause the hot refrigerant to pass through the restriction 22. Various other embodiments of the invention may be devised to meet various requirements.

We claim:

1. In a refrigerating and defrost system, in combination, a compressor, a condenser, a refrigeration restriction, and an evaporator operatively connected for circulating refrigerant; by-pass means for selectively applying hot refrigerant from said compressor in heat exchange relationship with said evaporator; means for reheating said bypass refrigerant after said heat exchange operation; and second restriction means returning said reheated bypass refrigerant to said compressor.

2. In a refrigerating and defrost system, in combination, a compressor, a condenser, a refrigeration restriction, and an evaporator operatively connected for circulating refrigerant; bypass means for selectively applying hot refrigerant from said compressor in heat exchange relationship with said evaporator; means for reheating said bypass refrigerant after said heat exchange opera- .tion; and second restriction means returning said reheated bypass refrigerant to said compressor; said bypass means comprising a defrost coil adjacent said evaporator and bypass valve means controlling the flow of refrigerant to said defrost coil.

3. In a refrigerating and defrost system, in combinapressor; Such leveling bfliisidfie to the act; "of the A v I connected directly to the evaporator; tube 15, .an'd there is no separate defrosting tube-as in,

tion, a compressor, a condenser, a' refrigeration restric:

tion,- and anevaporator operativelyconnected for circulating refrigerant; bypass means for selectively applying liot refrigerant-from said' compressor in heat exchange relationship with said evaporator; means. for reheating said bypass refrigerant after said heat exchange operation; and second restriction means returning said reheated bypass refrigerant to said compressor; said bypass means comprising a defrost, coil adjacent said evaporator and bypass valve means controlling the flow of refrigerant to said defrost coil; said bypass valve being selectively opened by a timing control means;

4. In a refrigerating and defrost system, in combination, a compressor, a condenser, a refrigeration restric-' tion, and an evaporator operatively connected for circulating refrigerant; bypass means for selectively applying hot refrigerant from said compressor in heat exchange relationship with said evaporator; meansfor reheating said bypass refrigerant after said heat exchange operation; and second restriction means returning said reheated bypass refrigerant to said compressor;.said bypass means ineluding a bypass valve selectively opened and closed by a timing control means;

5. In a refrigerating and defrost system, in combina-. tion, a compressor, a condenser, a refrigeration. restric-.

tion, and an evaporator operatively'connected for circulating refrigerant; bypass means for selectively applying hot refrigerant from said compressor in heat exchange relationship with said evaporator; means for reheating.

said bypass refrigerant, after said heat exchange operation; and second restriction means returning said reheated bypass refrigerant to said compressor; said reheating means including means disposing said refrigerant in heat exchange relationship with the heat dissipated by said compressor. a

6. In a refrigerating and defrost system, in'combination, a compressor, a condenser,- a refrigeration restriction, and an evaporator operatively connected for circulating refrigerant; bypass means for 1 selectively applying hot refrigerant from said compressor in heat exchange relationship with said evaporator; means for reheating said bypass refrigerant after said heatexchange operation; and secondrestn'ction means returning said reheated bypass refrigerant to said compressor; said bypass means comprising a defrost coil adjacent said evaporator and bypass valve means controlling the flow of refrigerant to said defrost'coil; said reheating means including means disposing said refrigerant in heat exchange relationship with the heat dissipated by said compressor.

7. In a refrigerating and defrost system in combination, a compressor, a condenser, a refrigeration restriction, and an evaporator operatively connected for circulatingrefrigerant; bypass means for selectively applying hot refrigerant from said compressor in heat exchange relationship with said evaporator; means for heating said bypass refrigerant after said heat exchange operation; and second restriction means returning said heated bypass refrigerant to said compressor; said second restriction means being of larger internal diameter and thus offeringless resistance to the flow of refrigerant therethrough than said first-mentioned restriction means.

Nonamaque Mar, 15, 1960

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