US3559421A - Refrigeration defrost system with receiver heat source - Google Patents

Abstract

A COMPRESSION-TYPE REFRIGERATION SYSTEM IS DISCLOSED WHICH UTILIZES THE CONVENTIONAL SUCTION LINE OF SUCH A SYSTEM AS A DEFROST CONDUIT AT PERIODIC INTERVALS AND FURTHER INCLUDES MEANS TO HEAT THE LIQUID REFRIGERANT IN THE RECEIVER OF THE SYSTEM TO MAINTAIN THE REFRIGERANT AT SUFFICIENT PRESSURE AND TEMPERATURE TO SERVE AS A SOURCE OF HEAT DURING A DEFROST CYCLE.

Description

Feb. 2, 1971 Quussa u 3,559,421

REFRIGERATION DEFROST SYSTEM WITH RECEIVER HEAT SOURCE Filed Feb. '7. 1969 THE-.1-

TIMER I SOLE/VOID I 37 com MCI DE F R057 80L E NO/D 38a fiTHREE-WAYSOLENO/D LL I W %4/ RECEIVER HEATER Alla/nay 54 L l/WE/VTOR 3 V 52 arm .1: NUSSBAUM United States Patent 3,559,421 REFRIGERATION DEFROST SYSTEM WITH RECEIVER HEAT SOURCE Otto J. Nussbaum, Monroeville, Pa., assignor to Halstead & Mitchell Co., Zelienople, Pa., a corporation of Pennsylvania Filed Feb. 7, 1969, Ser. No. 797,392 Int. Cl. F25b 41/00 US. Cl. 62--196 7 Claims ABSTRACT OF THE DISCLOSURE A compression-type refrigeration system is disclosed which utilizes the conventional suction line of such a system as a defrost conduit at periodic intervals and further includes means to heat the liquid refrigerant in the receiver of the system to maintain the refrigerant at sufficient pressure and temperature to serve as a source of heat during a defrost cycle.

BACKGROUND OF THE INVENTION (1) Field of the invention The present invention relates to refrigerating systems and particularly to a compression-type reversible refrigeration system having a normal refrigeration cycle and a hot gas defrost cycle.

(2) Description of the prior art It may be explained that mechanical refrigeration systems of the compression type generally comprise a condensing unit including a motor driven compressor, an air or liquid cooled condenser for liquefying the compressed refrigerant, a pressure reducing device and an evaporating unit in which the refrigerant is caused to evaporate at a lower pressure, thereby producing a cooling elfect. Low temperature systems are commonly designed to serve a space to be maintained at a temperature below 32 F. such as, for instance, a frozen food storage room or an environmental test chamber.

It is well known that the surface of the evaporator tends to accumulate frost thereon. This is due to the fact that when the surface temperature of the evaporator drops below 32 F., any moisture condensed out of the air flowing over the evaporator will freeze on the surface of the evaporator. Any buildup of frost or ice on the evaporator surface acts as an insulator, decreasing the rate of heat transfer through the evaporator and substantially minimizing the efiiciency of the refrigeration cycle and may eventually render it ineffective.

Therefore, the most important aspect of low temperature refrigeration is reliable defrost of the evaporator which should be automatic and rapid so as to have the least possible effect on the temperature of the refrigerated space. At the same time, the energy required to heat the evaporator surface for'defrosting should preferably be generated within the refrigeration system rather than originate from external sources.

In a conventional refrigeration system, the heat energy removed from the cooled space is normally rejected at developed to a point of acceptable reliability and automation, but they require a great deal of additional and often costly installations.

SUMMARY OF THE INVENTION The present invention provides a hot gas defrost system which combines the advantages of the two basic aproaches used heretofore, while eliminating the need for the cumbersome reversing mechanisms as well as for additional defrost conduits and auxiliary evaporators.

Briefly, the present invention comprises the usual components of a mechanical refrigeration system of the compression type but has additional means to utilize the conventional suction line of the system as a defrost conduit at periodic intervals, and further has means to heat the liquid refrigerant in the receiver of the system to maintain the refrigerant at sufiicient pressure and temperature to serve as a source of heat during a defrost cycle.

The advantages and capabilities of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings illustrating the preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a refrigeration and hot gas defrosting system embodying the present invention; and

FIG. 2 is a schematic wiring diagram of an electrical control circuit which may be used with the system of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings wherein like reference characters refer to like parts, and particularly to FIG. 1, there is schematically shown a refrigeration circuit embodying the present invention usable as a refrigeration system having hot gas defrosting features. This refrigeration system comprises a compressor 10 of conventional construction, having a suction intake or low side 12 and a discharge or high side 14. The compressor discharge is connected through a discharge line or con duit 16 to the inlet side of an air cooled condenser 18 for discharging compressed refrigerant vapor into the condenser 18. The condenser outlet is connected through a check valve 20 and a first conduit or drain line 22 to a liquid refrigerant receiver 24. The receiver 24 is connected through a dip tube 26, a shutoff valve 28, a liquid solenoid valve 30, an expansion device 32 and a second conduit comprising a liquid line 34 to'the inlet side of an evaporator 36 having a motor driven fan 37. The evaporator 36 is of conventional construction. The expansion device 32 may be any suitable refrigerant control device such as, for example a thermostatic or constant pressure expansion valve or the like.

The outlet side of evaporator 36 is connected through a suction line 42, a three-Way valve 38, a suction pressure regulating valve 40 which may, for example, be a holdback valve or a thermostatic control valve, to the suction side- 12 of the compressor 10. Aswill be more fully explained hereinafter, the three-way valve 38, during a normal refrigeration cycle, is in a first predetermined position which permits flow of refrigerant in the suction line 42 from the evaporator outlet through valve 40 t0 the compressor suction side 12.

A first by-pass conduit 44 is coupled into the circuit and to the liquid line 34 in by-passing relation to valve 30 and expansion device 32. A check valve 46 is provided in conduit 44 to prevent refrigerant toflow through conduit 44 during a normal refrigeration cycle. A second by-pass conduit 47 is coupled into the circuit and is connected be tween the discharge line 16 and the three-way valve 38 which, during a normal refrigeration cycle, prevents flow of refrigerant through by-pass conduit 47.

A third conduit 48 having a defrost solenold valve 50 therein is connected between the receiver 24 and suction line 42 at a position between the three-way valve 38 and holdback valve 40 and thus to the suction side of the compressor 10. The valve 50 prevents flow of refrigerant through conduit 48 from the receiver 24 to the suction side 12 of the compressor during a normal refrigeration cycle.

As is known to those skilled in the art, the evaporator 36 can be quickly and efficiently defrosted by the delivery of hot gas periodically thereto to internally heat the evaporator. To this end, means are associated with the receiver 24 for heating liquid refrigerant therein to maintain the refrigerant at sufficient pressure and temperature, which temperature may typically be 65 F. to 85 F., so that the refrigerant may serve as a source of heat during a defrost cycle in the system.

As shown schematically in FIG. 1, an electric insert heater 52 is disposed within the receiver 24 and the heater 52 provides the source of heat for the receiver 24. While the source of heat for the receiver 24 has been shown as an electric insert heater this is not to be taken in a limiting sense as the receiver may, for example, be provided with a surrounding water jacket supplied with warm water from a water cooled condenser when this latter type of condenser is utilized, or the receiver 24 may contain coils supplied with hot discharge gas from the compressor during the normal refrigeration cycle.

In operation, the flow of refrigerant in the above-described system during a normal refrigeration cycle is from the compressor 10 by way of discharge line 16 to the condenser 18; from condenser 18 through drain line 22 and check valve 20 to receiver 24. With the defrost solenoid operated valve 50 closed during the refrigeration cycle, liquid refrigerant is then delivered through dip tube 26, shut-off valve 28, liquid line 34, and open solenoid valve 30 to the expansion valve 32 which feeds liquid refrigerant to the evaporator 36. From the outlet side of evaporator 36, vaporized refrigerant is returned through suction line 42, three-way valve 38 and suction pressure regulating valve 40 to the suction intake of compressor 10, completing the cycle.

To initiate a defrost-cycle in the system, the liquid or control solenoid valve 30 and three-way valve 40 are merely shifted to close valve 30 and move the three-way valve 40 to a second predetermined position which allows refrigerant flow in the second by-pass conduit 47 and which disconnects the suction line 42 from the suction side 12 of the compressor 10. The refrigerant flow during the defrost cycle is from the receiver 24, through third conduit 48 and defrost solenoid valve 50 which is opened concurrently with the closing of valve 30 and the moving of three-way valve 38 to its second position, into the suction side of the compressor 10. Then the refrigerant passes through the compressor 10, through by-pass line 47, then into suction line 42. Flow by way of discharge line 16 to the condenser 18 is minimized since the latter is at a relatively high pressure by comparison to the evaporator 36. By-pass line 47 is thus connected in lay-passing relation to the condenser 18. Continuing with the refrigerant flow in the defrost cycle, the refrigerant flow is then through the suction line 42 into the outlet side of the evaporator 36 and thus through the evaporator 36 in a direction opposite that of the normal refrigeration cycle such that the evaporator functions as a condenser rejecting heat to frost formed on the evaporator, thereby melting such frost. Condensed liquid from evaporator 36 leaves by way of check valve 46, bypassing the expansion valve 32 and control valve 30, through by-pass line 44, and returns to the liquid receiver 24 through liquid line 34 and shut-off valve 28. The liquid returned to the receiver 24 1s partially evaporated due to the heat supplied by the a g means 52 which is automatically controlled by either a temperature or pressure responsive de 54 to maintain the boiling point of the liquid in receiver 24 at the required level. In cold climates or outdoor installation, the liquid receiver 24 may be suitably insulat d t preserve its heat.

At the end of the defrost cycle, the circuit is shifted to a post-defrost condition for a short interval immediately following defrost. During the post-defrost cycle, defrost solenoid valve 50 is closed and three-way valve 38 1s returned to its first position permitting flow of refrigerant in the suction line from the evaporator outlet through valve 40 to the compressor suction side. The fan motor 37 on the evaporator 36, which is stopped during defrost, remains deenergized and the liquid solenoid valve 30 remains closed while the condenser fan motor 19, which is also stopped during defrost, is restarted until the pressure in evaporator 36 is reduced to the normal refrigeration level. At the same time, pressure regulating valve 40 at the suction side of the compressor 10 throttles to prevent overloading of the compressor 10 that may otherwise be caused by the elevated pressure in the evaporator 37. At the termination of post defrost, that is, when the evaporator pressure is reduced to normal, the evaporator fan motor 37 is restarted and liquid solenoid 'valve 30 is opened, thereby resuming the normal refrigeration cycle.

FIG. 2 is a schematic wiring diagram of a typical control circuit which may be used to control the system of FIG. 1. As shown in FIG. 2, the compressor 10 is connected in series with the usual low pressure and high pressure cutout switches designated LP and HP, respectively. A timer motor 60 is connected in series with the contacts of a thermostat T1, which is the thermostat monitoring the space to be conditioned. The contacts of thermostat T1 are closed during cooling so that the timer motor 60 operates only when the thermostat T1 calls for cooling. At the start of defrost, timer 60, opens normally closed switch 62 and closes normally open switch 64. The opening of switch 62 stops the fan motor 37 of evaporator 36 and deenergizes relay CR2. With relay CR2 deenergized, the normally open contacts 1CR2 close energizing control solenoid 30a closing valve 30. The closing of switch 64 energizes defrost solenoid 50a opening valve 50, energizes the three-way solenoid 38a shifting valve 38 to its second or defrost position, and energizes relay CR1. With relay CR1 energized, normally closed contacts 1CR1 open deenergizing the fan motor 19 of condenser 18. The system is now in the defrost cycle and the refrigerant flow is as described above.

A timer release solenoid 66 is mechanically coupled to the switches 62 and 64 to return the switches to the position they occupy before defrost, and is connected electrically to a hot contact of a defrost terminating thermostat 68 having its remote bulb attached to the coldest point of the evaporator 36. During the normal refrigeration cycle, the thermostat switch 68 is in a position indicated as cold maintaining the fan motor 37 of evaporator 36 running and relay CR2 energized. During defrost, the temperature sensed by the feeler element of thermostatic switch 68 gradually rises until it reaches the level to cause the switch to shift to the position indicated as hot whereupon the switch 68 energizes the timer release solenoid 66 which returns the timer switches 62 and 64 to their refrigeration position, and this deenergizes solenoids 50a and 38a, which effects movement of valve 50 to its closed position, shifts three-way valve 38 back to its first or refrigeration position, and deenergizes relay CR1 causing contacts 1CR1 to return to their normally closed position re starting the fan motor 19 of condenser 18. However, during this post-defrost condition, with switch 68 shifted to the position indicated hot, the fan motor 37 of evaporator 36 remains deenergized and valve 30 remains closed because relay CR2 remains deenergized and contacts 1CR2 remain closed. While the pressure in the evaporator 37 is being reduced, as described above, the evaporator temperature is gradually reduced and the defrost termination thermostat 68 returns to the cold position restarting the evaporator fan motor 37 and energizingrelay CR2 thereby opening the contacts IORZ and thus energizing control solenoid 30a which opens control solenoid valve 30. The normal refrigeration cycle is thus resumed with the flow of refrigerant in the normal refrigeration cycle as above described. F I

While one preferred embodiment of the present invention has been particularly shown and described, it is apparent that various modifications may be made therein within the spirit and scope of the invention, and it is desired, therefore, that only such limitations be placed on the invention as-are imposed by the prior art andset forth in the appended claims.

I claim as my invention:

1. In a reversible refrigeration system comprising a compressor having discharge and suction sides, a condenser, a liquid refrigerant receiver, an expansion means and evaporator means, and wherein said components of the system are interconnected by conduit means in a closed circuit to provide a normal refrigeration cycle, the improvement comprising:

valve means in said circuit shiftable to selected positions for terminating said normal refrigeration cycle and for causing heated refrigerant to fiow through the entirety of said evaporator means in the system to effect a defrost cycle,

heating means associated with said receiver for heating liquid refrigerant therein to maintain the refrigerant at sufiicient pressure and temperature so that the heated refrigerant may serve as a source of heat during said defrost cycle, and

means for preventing refrigerant from passing from said receiver into said condenser during a defrost cycle.

2. In a reversible refrigerations system as defined in claim 1, including means for interconnecting said receiver with the suction side of said compressor during said defrost cycle, and by-pass means coupled with said conduit means of said closed circuit in by-passing relation to said condenser such that flow of refrigerant in said defrost cycle is from said receiver, through said compressor and then through said evaporator in a direction opposite that of the normal refrigeration cycle whereby the evaporator functions as a condenser which rejects heat to frost formed on the evaporator thereby melting such frost.

3. In a reversible refrigeration system comprising a compressor having discharge and suction sides, a condenser, a liquid refrigerant receiver, an expansion means and an evaporator interconnected by conduit means in a closed circuit to provide a normal refrigeration cycle wherein flow of refrigerant is from the discharge side of the compressor, through the *condenser, then to the receiver, then through the expansion means, then through the evaporator and thereupon through the compressor, the improvement comprising:

valve means in said conduit shiftable to selected positions for connecting the suction side of said compressor to said receiver and for causing refrigerant from said receiver to be pumped through said compressor to said evaporator to effect in said system a defrost cycle,

means associated with said receiver for heating liquid refrigerant therein to maintain the refrigerant at sufficient pressure and temperature so that the heated refrigerant may serve as a source of heat during said defrost cycle, and

means for preventing refrigerant from passing from said receiver directly into said condenser during a defrost cycle.

4. In a reversible refrigeration system as defined in claim 3, including first and second by-pass conduit means coupled with said conduit means of said closed circuit with said first by-pass conduit being in by-passing relation to said expansion means during said defrost cycle and with said second by-pass conduit being in by-passing relation to said condenser during said defrost cycle. 5. In a reversible refrigeration system as defined in claim.4 including means for interconnecting said receiver with the suction side of said compressor during said defrost cycle such that during said defrost cycle flow of refrigerant is from the receiver, through the compressor, then through said first by-pass conduit, and then through said evaporator in a direction opposite that of the normal refrigeration cycle whereby the evaporator functions as a condenser rejecting heat to frost formed on the evaporator thereby melting such frost. 6. In a reversible refrigeration system as defined in claim 5 wherein after passing through said evaporator, refrigerant flow during said defrost cycle is then through said second by-pass conduit and thereupon to said receiver. 7. In a reversible refrigeration system comprising a compressor having discharge and suction sides, a condenser having inlet and outlet sides, a discharge line connected between said compressor discharge side and said condenser inlet side, a receiver, a first conduit comprising a drain line connected between the outlet side of said condenser and said receiver, an evaporator having inlet and outlet sides, a second conduit comprising a liquid line connected between said receiver and the inlet side of said evaporator and having an expansion means therein adjacent said inlet side of said evaporator, and a suction line connected between the outlet of said evaporator and the suction side of said compressor and wherein the fiow of refrigerant in said system during a normal refrigeration cycle is from the discharge side of the compressor through the discharge line into and through the condenser, then through said drain line into the receiver, then from the receiver through said liquid line into and through said expansion means, then into and through the evaporator, then through the suction line into and through the com- 40 pressor, the improvement comprising a control solenoid valve disposed in said liquid line, said control solenoid being open during said normal refrigeration cycle to permit flow of refrigerant in said liquid line from the receiver into said expansion means, a three-way solenoid valve disposed in said suction line, said three-way valve being in a first predetermined position during said normal refrigeration cycle to permit flow of refrigerant in said suction line from said evaporator outlet to said compressor suction s1 e, first by-pass conduit coupled to said liquid line in by-passing relation to said control solenoid valve and said expansion valve and having check valve means therein preventing refrigerant flow in said first by-pass conduit during said normal refrigeration cycle, a third conduit means having a defrost solenoid valve therein connected between said receiver and said suction line and being connected to said suction line between said three-way valve and the suction side of said compressor, said defrost solenoid valve preventing flow of refrigerant through said third conduit from the receiver to the suction side of said compressor during a normal refrigeration cycle, second by-pass conduit connected between said discharge line and said three-way valve in by-passing relation to said condenser, said three-way valve in said first predetermined position preventing refrigerant flow through said second by-pass conduit during said normal refrigeration cycle, means associated with said receiver for heating liquid refrigerant therein to maintain the refrigerant at suificient pressure and temperature so that the refrigerant may serve as a source of heat during a defrost cycle in said system,

first means responsive to a predetermined condition in said system for initiating a defrost cycle in said system, and

second means which upon receiving a signal from said first means (a) shifts said three-way valve to a second predetermined position permitting flow of fluid in said second by-pass conduit and disconnects said suction line from the suction side of said compressor, (b) closes said control solenoid valve permitting flow of fiuid in said first by-pass conduit and (0) opens said defrost solenoid valve permitting flow of fluid in said third conduit from the receiver to said suction line and thus to the suction side of said compressor, the flow of refrigerant in said defrost cycle being from the receiver through said third conduit into the suction side of said compressor, then through the compressor, then through the second by-pass line, then through the three-way valve into References Cited UNITED STATES PATENTS 2,807,145 9/1957 Henderson 62-496 3,23 8,737 3/ 1966 Shrader 62196 3,358,469 12/1967 Quick 62l96 3,427,819 2/ 1969 Seghetti 62-278 MEYER PERLIN, Primary Examiner US. Cl. X.R. 62-278

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