US2805555A - Hot gas defrost system - Google Patents

Description

Sept. 10, 1957 F. A. SCHUMACHER HOT GAS DEFROST SYSTEM Filed July 11, 1956 INVENTOR.

' FRANK A. SCHUMACHER HIS ATTORNEY United States Patent HOT GAS DEFROST SYSTEM Frank A. Schumacher, Louisville, Ky., assignor to General Electric Company, a corporation of New York Application July 11, 1956, Serial No. 597,222

3 Claims. ((31.62-4) The present invention relates to refrigerating system including means for the hot gas defrosting of an evaporator component of the system. It is more particularly concerned with a plural temperature refrigerating system including a high temperature evaporator and a low temperature evaporator in series connection in a refrigerating system and improved means for introducing hot gas into the low temperature evaporator for the defrosting of that evaporator.

An object of the invention is to provide a refrigerating system including a refrigerant line bypassing the conenser for periodically introducing into the evaporator hot compressed refrigerant for the defrosting of the evaporator and means in the defrosting circuit for increasing the load on the compressor and thereby increasing the amount of heat available for defrosting purposes.

Another object of the invention is to provide a plural temperature refrigerating system including in series connection an automatically defrosting high temperature evaporator and a low temperature or freezer evaporator, the system including a defrosting circuit for introducing hot compressed refrigerant directly from the compressor into the low temperature or freezer evaporator and means in that circuit for increasing the load on the compressor in the form of a flow restricting means in heat exchange relationship with the freezer evaporator.

Further objects and advantages of the invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In carrying out the objects of the present invention there is provided a refrigerating system comprising a compressor, a condenser, a flow restricting element and an evaporator connected in series refrigerating circuit. For defrosting the evaporator there is included a valve controlled conduit bypassing the condenser and the flow restricting means or elements connected to the condenser so that hot compressed refrigerant can be conducted directly from'the compressor to the evaporator for defrosting purposes. The defrosting circuit also includes a fixed restrictor ahead of the evaporator being defrosted for increasing the load on the compressor and thereby increasing the heat available for defrosting purposes. In the preferred modification of the present invention the refrigerating system includes a high temperature selfdefrosting evaporator and a low temperature or freezer evaporator including a flow restriction between the two evaporators, this flow restriction comprising part of the defrosting circuit as means for providing the desired load on the compressor during the defrosting cycle.

For a better understanding of the invention reference may be had to the accompanying drawing in which:

Fig. 1 is a view of a portion of a refi'igerator incorporating an embodiment of the present invention, and

Fig. 2 is a schematic illustration of a refrigerating system employed in the refrigerator of Fig. 1.

Patented Sept. 10, 1957 Referring to the drawing there is shown a two-temperature refrigerator which includes a frozen food compartment 2 and a fresh food compartment 3. The refrigerating system employed to maintain these two compartments at their proper operating temperatures is shown schematically in Fig. 2. This system includes a hermetically sealed motor-compressor unit 5 and a condenser 6. The system further includes a high temperature evaporator 7 which is disposed-within the fresh food compartment 3 for cooling this compartment and a low temperature evaporator 10 for cooling the freezer compartment. The low temperature evaporator of the flooded type comprises tubing arranged in generally serpentine form connected to a header 13 and secured, in a manner well known in the art, to the exterior of the liner 11 forming the freezer compartment 2. During the normal refrigerating cycle, refrigerant is supplied from the condenser 6 through a capillary tube 12 to the high temperature evaporator 7. From the'high temperature evaporator 7 the refrigerant flows through a restricted conduit 14 and an injector 15 into one of the lower passes 16 of the serpentine freezer evaporator 10. If desired, a Weighted valve 18 may be included to maintain normal pressure differential between the evaporators. The restricted tubing 14 and the injector 15 (and the weighted valve 18 if used) serve to maintain an operating pressure differential between the high temperature evaporator 7 and the low temperature evaporator 10 and the restricted tubing 14 is brazed or otherwise secured to the bottom wall of the liner 11 for the purpose of accelerating the rate of freezing of water in freezing trays placed in this portion of the liner as is more fully described and claimed in my prior Patent 2,728,198, issued December 27, 1955, and assigned to the same assignee as the present invention. Vaporized refrigerant is returned to the compressor 5 from the header 13 through suction line 17, thus completing a normal series refrigerating circuit.

The normal operation of the system is controlled by the switch 19 which is adapted to engage contacts 20 in a line 21 through which power is supplied to the motor compressor unit 5. The switch 19 is actuated by a bellows 22 in response to the temperature of the high temperature evaporator 7 by means of a thermostatic bulb 23 positioned in contact with the evaporator 7. Accordingly the normal or refrigerating operation of the system is controlled hy the temperature of the high temperature evaporator 7. To prevent the accumulation of frost on the high temperature evaporator 7 disposed within the fresh food compartment 3, the switch 19 is arranged to'energize the compressor unit 5 only after the high temperature evaporator 7 has attained a temperature above freezing to assure the melting of any frost which has collected on this evaporator and to de-energize the compressor unit 5 when this high temperature evaporator 7 has reached a subfreezing temperature in the neighborhood of or close to that sought to be maintained in the freezer compartment 11.

Due to the fact that the freezer compartment 2 is separate and insulated from the fresh food compartment 3 the temperature of that compartment will fluctuate only a few degrees during the on and off cycles of the compressor unit 5 even though the high temperature evaporator 7 subjected to the higher temperatures in the fresh food compartment 3 will exhibit a temperature change over range from approximately 0 degrees F. to 35 to 37 degrees F. Since the freezer evaporator 10 continuously operates well below freezing temperatures there is a gradual accumulation of frost within the freezer compartment 2 or more specifically on the walls of the a liner 11 forming this compartment. As this layer of frost has an insulating eifect reducing the efliciency of the evaporator 10, it is necessary to remove this frost from time to time in order to prevent too serious a reduction in the operating efiiciency of the system. In accordance with the present invention means are provided for periodically introducing into the freezer evaporator hot compressed refrigerant directly from the compressorin order that this low temperature evaporator can be heated by the hot gas to defrosting temperatures. Since it is desirable that the defrosting of the low temperature evaporator 10 take place as quickly as possible in order to prevent damage to the contents of the freezer compartment z, there is provided in accordance with the present invention means for increasing the load on the compressor unit 5 during the defrosting operation and thereby iucreasingth'e amount of heat available in the hot gas for defrosting purposes. r r V 'l'n order to introduce hot compressed refrigerant into the low temperature evaporator 10.. there provided a conduit 27-bypassing the condenser 6, the flow restricting element -12Han d-the high temperature evaporator 7 and connectingthe outlet of the compressor 5 to the line leadi-ng from the high temperature evaporator 7 to the low temperature evaporator 10. A solenoid operated valve 28 is. provided in the bypass line '27 and this valve is normally closed so that during the operation of the refrigerating system on the refrigerating cycle, the flow of refrigerant from the compressor 5 is through the condenser -6 to the evaporators in series.

The operation of .the solenoid valve 28 is controlled by a switch 30 which also by means'of lines 31 energizes the compressor unit -5 whenever the solenoid valve 28 is energized and open. The switch 30 may be of any suitable type. For example it may be a manually controlled switch whereby the user of the refrigerator manually effects the defrosting operation of the refrigerating system. Alternatively it may be a timer control switch so that the refrigerating system is operated ,on the defrosting cycle periodically as for example once a day.

Whenever theswitch 30 energizes the solenoid valve v 28 to open this valve, the energization of the compressor unit 5 ,causes hot compressed refrigerant gas to. flow through the bypass line 27 directly to the frozen food or low temperature evaporator 10; By including the restrictions 14 and 15 in the hot gas .circuit, the restriction increases the pressure against which the compressor unit 5 must pump and thereby increases the watt input to the compressor motor .cooled by the circulating refrigerant substantially over the input in the case where a nonrestricted hot gas flow is employed. This increased wattage results in more energy being transmitted to the circulating refrigerant, speeding up thedefrosting of the frozen food evaporator 10 or in other words decreasing .the time necessary for frost removal.

As an example of the manner in which the present inventionmay be :put into .eifect, the restriction in thebypass pr defrost circuit formed by the restricted conduit 14 in heat exchange relationship with the bottom of the liner 11 and ,by the injector 1 5 effected an increase in the motor running watts from 300 to 337 watts at the start of the defrost cycle and from 360 to 450 watts at the end of the de os ope ation when the ubes .comp the p rator 10 were approximately 40 F. The restriction in this case was formed by the injector consisting .of 5 /2 inches of .095 inside diameter tubing and by the tubing 14 which .was .171)" inside diameter and approximately seven f e i lengt r It be'noted that during the defrosting operatien no valve means are provided to prevent flow of refrigerant thrqughthe normal. circuit that ,is through the condenser 15, therestrictor 12 and the high temperature evaporator -7 -;F o r that reason the restriction provided in the defrost circuit up .to the point where the conduit 27 connects to the system between the high temperature evaporator and the low temperature evaporator is lrept at a although if desired a restriction 35 having a low restrictive value may be introduced into the line 27. While such a 4 restriction will add to the total restrictive value provided by the line 14 and the injector 15, it is necessary that the restrictive value of the restrictor 35 be kept below that which will cause a substantial portion of the refrigerant to flow through the condenser 6. For that reason there is preferably employed only the restricting means forming part of the normal refrigerating circuit since the presence of these restricting means in the defrosting circuit does not affect the restrictive balance between the normal and defrosting circuits or in other words will load the compressor unit Without causing an excessiveam'ount of the compressed refrigerant .to flow through the condenser 6 instead of the bypass line 27. While there has been shown and described a specific embodiment of the present invention, it is not desired that the invention be 'limited to the particular construction shown and described. For example the use of restriction in the hot gas bypass line is not necessarily confined to the defrosting of a low temperature evaporator in a plural evaporator circuit although the invention is particularly advantageous as applied to such systems andspecifically to systems such as that disclosed in which the low temperature evaporator is of the flooded type and includes an injector such as injector 15. With such an arrangement it has been found that the hot gas introduced into the What, I claim as new and desire to secure by Letters Patent .of the United States is:

l. A refrigerating system comprising a compressor, a pondenser, a'florv restricting element, a hightemperature evaporator for cooling .a fresh food compartment, a low temperature evaporator for maintaining a frozen food compartment at subrfreezing temperatures, said compressor, condenser, flow restricting element, high temperature evaporator and low temperature evaporator being connected in series in a closed refrigerating .circuit, control means responsive to thejcemperature .of said high temperatureevaporator for startingsaidnompressor only vwhen said high temperature evaporator has attained a temperature above freezing to assure defrosting of said high temperavtpreevaporator prior to energization of saidscompressor and means for periodically .defrosting said low temperatureevaporator including a .conduit bypassing said condenser, flow restricting .element and high temperature evaporator and connecting said compressor directly to the inlet to said loyv temperature evaporator for the introduction of -hot gas into .said .low temperature evaporator, a valve in said .cpnduitrcontrolling the flow of refrigerant therethgough, control meaps for controlling the pperation of said valve and energizing .said compressor ,when said valve is open, and a restrictor having a lower restn'gtive value than said flow restricting element for increasing the amount .of heat available in the hot low temperature evaporator. V

2. A refrigerating system comprising a compressor, a condenser, afirst flow restricting elemenha high temperature evaporator fgr cooling ,9. fresh food compartment, a second flow restricting element, a low temperature evaporator for maintaining a frozen food compartment at subfreezingotemperatures, said compressor, condenser, first gas for defrosting said flow restricting element, high temperature evaporator,

second flowrestricting .element andv low temperature .evaporatorheing connected in series in a closed refrigeratns c cui goon-91 m ans respon iv to the temperature of sa s lhi h tep nra g e evaporate: o st. ins said q pressor rl vt e sa d .h sh em er t re-sac um ha attained a te erature above freezing to assure defrosting of'said high temperature evaporator prior to energization 9 sa d compresso and mean f r p fiqd s v ros said low perature evaperator including ,a condpit by- Pa sin sad e t m n fi s flew r st ic in el m n and high tmperawr'e Wanderers renew n s i wows sor to the inlet to said second flow restricting element for the introduction of hot gas through said second element into said low temperature evaporator, a valve in said conduit controlling the flow of refrigerant therethrough, control means for controlling the operation of said valve and energizing said compressor when said valve is open, said second element placing a load on said compressor and thereby increasing the amount of heat available in the hot gas for defrosting said low temperature evaporator, said second element being in heat exchange relationship with at least a portion of said low temperature evaporator.

3. A refrigerating system comprising a compressor, a condenser, a first flow restricting element, a high temperature evaporator for cooling a fresh food compartment, a second flow restricting element having a lesser restrictive value than said first element, a flooded low temperature evaporator for maintaining a frozen food compartment at sub-freezing temperatures, said compressor, condenser, first flow restricting element, high temperature evaporator, second flow restricting element and low temperature evaporator being connected in series in a closed refrigerating circuit, control means responsive to the temperature of said high evaporator has attained a temperature above freezing to assure defrosting of said high temperature evaporator prior to energization of said compressor and means for periodically defrosting said low temperature evaporator including a conduit bypassing said condenser, first flow restricting element and high temperature evaporator and connecting said compressor to the inlet to said second element for the introduction of hot gas into said low temperature evaporator, said second element including an injector for effecting circulation of refrigerant in said flooded low temperature evaporator, a valve in said conduit controlling the flow of refrigerant through said conduit, control means for controlling the operation of said valve and energizing said compressor when said valve is open, said second restrictive element having restrictive valve sufficient to load said compressor and thereby increase the amount of heat available in the hot gas for defrosting said low temperature evaporator.

References Cited in the file of this patent UNITED STATES PATENTS 2,458,589 Groat Jan. 11, 1949 2,765,633 Mufiiy Oct. 9, 1956

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