US 3453838 A
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y 19.69 A. s. DECKER ETAL 3,
REFRIGERATION SYSTEM Filed March 10, 1967 EVAPORATOR COMPRESSOR CONDENSER RECEIVER INVENTORS ALAN S. DECKER BY HANS P. PETERSON ATTORNEYS United States Patent 3,453,838 REFRIGERATION SYSTEM Alan S. Decker, Farmington, and Hans P. Peterson, Simsbury, Conn., assignors to Dunham-Bush, Inc., West Hartford, Conn., a corporation of Connecticut Filed Mar. 10, 1967, Ser. No. 622,143 Int. Cl. F25d 21/06, 21/04 US. Cl. 62-155 7 Claims ABSTRACT OF THE DISCLOSURE A refrigeration system is disclosed having means to defrost the evaporator utilizing the hot, compressed refrig- Defrosting the evaporator of a refrigeration system simply and efficiently is a constant problem. In some systems, a defrosting cycle is carried out by which hot refrigerant gas is circulated through the evaporator to melt the accumulated ice or frost. Often such arrangements are complicated and expensive, or they are undependable or otherwise unsatisfactory. A common problem is that during the defrosting cycle, liquid refrigerant tends to return to the compressor, causing various difiiculties, e.g., oil dilution, impaired operation, and actual damage to the parts. Another problem is that excessive time is needed to defrost the evaporator. A further problem with some systems is that the compressor is starved of refrigerant so that it does not deliver compressed gas at a sufficiently high rate to defrost the evaporator rapidly and efiiciently, and that may cause an unacceptable temperature rise in the refrigerated space.
It is an object of the present invention to provide an improved and dependable hot gas defrosting arrangement for refrigeration systems. A further object is to provide for defrosting a refrigeration system in a manner which avoids the past problems and difficulties. A specific object is to provide a refrigeration system with hot gas defrosting means with assurance that liquid refrigerant does not return to the compressor. A further object is to provide for the above with a hot gas defrosting arrangement which is extremely simple and efficient, and which may be readily adjusted to meet the specific conditions encountered in use.
In the drawing, the single figure is a schematic representation of a system embodying the invention.
Referring to the drawing, a compressor 2 has an outlet discharge line 4 and an inlet or suction line 6. During the normal refrigeration operation, compressed gas flows through line 4 to a condenser 8, where it liquifies, and the liquid refrigerant passes to a receiver 10. The liquid refrigerant flows from the receiver through a liquid line 12, having therein a normally-open solenoid valve 16 and a thermostatic expansion valve 18, to the evaporator which is located within a refrigerated space. In the evaporator, the refrigerant vaporizes, cooling air moved through the evaporator by a fan 22 and thereby maintaining the refrigerated space at a temperature within a range which may be relatively narrow. The refrigerant gas returns from the evaporator to the compressor through line 6. Expansion valve 18 has a control bulb 19 which is positioned to sense the temperature of the refrigerant gas passing through line 6 so that the valve controls the supply of liquid to the evaporator accordingly.
The refrigeration system includes a defrosting system which comprises: a T-coupling 5 in line 4 between the compressor and the condenser; 21 hot gas line 24 connected to line 4 at T-coupling 5 and extending from line 4 to line 12 and connected thereto by a. T-coupling 25 at the inlet to the evaporator; a normally-closed solenoid valve 27 in line 24; a T-coupling 29 in line 24; a by-pass line 26 connected to line 24 by T-coupling 29; line 24 has a by-pass control valve 28 therein and extends to line 6, to which it is connected by a T-coupling 31; a one-way check valve 30 in line 24 beyond T-coupling 29, which permits gas flow in line 24 only toward line 12; and, a condensate water-collection pan and drain pipe unit 40 located below the evaporator 20 and having hot gas line 24 in heat-exchange contact with it. There is also a timer control unit 42 which has temperature-sensing bulbs 43 and 44 positioned, respectively, to sense the temperature of the refrigerant flowing from the evaporator, and the temperature at the external fins of the evaporator. Control unit 42 controls solenoid valves 27 and 16, and it also acts to stop the fan 22 during the defrosting operation. During the refrigeration cycle, the defrosting system is inoperative, and line 24 is isolated by the closed valve 27 and check valve 30.
The defrosting operation is initiated when desirable by control unit 42, for example, every 4, 6 12 or 24 hours. With any particular refrigeration system, the required frequency for defrosting is determined, depending upon the rate at which frost or ice accumulates on the evaporator, and also upon the desired and expected mode of operation and demands upon the system. When that has been determined, timer unit 42 is then set and the entire operation proceeds automatically. The refrigeration system has standard safety controls and operating controls which start and stop the compressor to maintain the desired temperature conditions. This normal operation is interrupted periodically by the defrosting control unit 42.
At the beginning of a defrosting cycle, solenoid valve 16 is closed so as to stop the flow of liquid refrigerant through the expansion valve to the evaporator. The compressor continues to run so that there is a pump-down period during which all of the liquid refrigerant in the evaporator is evaporated. The suction pressure then drops and the compressor is stopped either by low-pressure control or by the corresponding drop in the temperature sensed by bulb 43. Control unit 42 responds to that sensing of the temperature drop and turns oif fan 22, and it also opens the hot gas solenoid valve 27. The opening of valve 27 causes hot gas to flow through line 24. Also, a portion of the hot gas flows from line 24 through the bypass line 26 to the suction line 6. The compressor is restarted, and it continues to operate throughout the remainder of the defrosting cycle.
The continued fiow of hot gas through. line 24 heats the pan and drain unit 40, and then flows onto the evaporator and also through the bypass line to suction line 6. Initially, the hot gas entering the evaporator tends to condense because of the low evaporator temperature, and the accumulated ice and frost tend to maintain that condition. Hence, at that stage of the defrosting cycle, the hot gas entering the evaporator does not constitute an adequate supply of gas to the suction side of the compressor. Accordingly, considering only the portion of the hot gas passing to the evaporator, the compressor would tend to stop under its low-pressure control. However, the hot gas which is bypassed from line 24 through line 26 is sufficient to maintain a satisfactory suction pressure condition at the compressor, and the compressor continues to operate.
The hot gas in evaporator 20 raises the tube and fin temperatures so as to start melting the ice, and the resultant water is collected and discharged through pan and drain unit 40. The cooled refrigerant gas tends to condense and flow toward the compressor in suction line 6. However, the adjustment of valve 28 is such that sufficient hot gas is bypassed to line 6 to cause re-evaporation of all liquid refrigerant which passes from the evaporator back toward the compressor. The operation continues, with the hot gas maintaining the pan and drain unit 40 to a sufficiently high temperature to insure that the condensate is discharged without being blocked by refreezing. As the melting of the ice continues, there is a general rise in the levels of the pressures and temperature within the system. However, at all times the conditions are such as to prevent liquid refrigerant from reaching the compressor, and the suction pressure does not drop sufficiently to stop the compressor.
When substantially all of the ice has melted, the evaporator surface temperature sensed by bulb 44 causes control unit 42 to close valve 27 and to open valve 16, thus discontinuing the defrosting operation and returning the system to the normal refrigeration cycle. However, the melting and draining may continue because of the residual heat. Fan 22 is not restarted until the temperature of the evaporator drops again to a predetermined sub-freezing value as sensed by bulb 44, and that prevents the fan from blowing condensate and water vapor into the refrigerated space. Control unit 42 then starts fan 22, and the refrigeration system continues under its standard temperature controls. Control unit 42 includes a timer which provides an overall time limit on the duration of each defrosting cycle. The normal defrosting operation is carried on in a relatively short period of time, during which the temperature in the refrigerated space does not rise beyond an acceptable amount. The maximum period permitted by the timer for each defrosting cycle is greater than that which is normally required, but it is still short enough to avoid an objectionable rise in the refrigerated space temperature. Hence, if there is an abnormally heavy accumulation of frost or ice on the evaporator because of unusual operating conditions, the defrosting cycle may be stopped prior to complete removal, and the remainder will be removed during the next defrosting cycle. The timer ha the additional function of discontinuing the defrosting cycle if there is malfunctioning of the defrosting control elements.
Illustratively, the pump-down period is of the order of three minutes and may be a timed operation. However, as indicated, it may be terminated by a low-pressure control or by suction temperature, for example, at a temperature of the order of 20 F. below the normal operating suction temperature for the refrigeration cycle. The timer is adapted to provide an overall maximum duration for each defrosting cycle, with a maximum of sixty minutes but normally of the order of thirty minutes,
Valve 28 is adjusted manually to provide the proper balance between the relative amounts of hot refrigerant flowing to the evaporator and directly to the suction line. The minimum amount of hot gas bypassed directly to the suction line is that amount which will satisfy the compressor and provide continued operation of the compressor, particularly during the initial portion of the deforsting operation. Operating conditions may require changes in the setting of this valve.
The system of the present invention is simple and highly efiicient, and it requires a relatively small number of components other than those constituting the basic refrigeration system. The normal protective controls may be relied upon to provide complete protection against excessive refrigerant pressure conditions.
What is claimed is:
1. In refrigeration apparatus, the combination of z a refrigeration system having a compressor with a compressed gas discharge line and a suction gas line and an evaporator having a refrigerant inlet to which liquid refrigerant is supplied during the refrigeration operation and a refrigerant outlet from which gas refrigerant flows to said suction line during the refrigeration operation; and defrosting means for said refrigeration system comprising means forming a compressed gas flow path from said compressed gas dis 5 charge line directly to said inlet of said evaporator and a flow path from said gas discharge line directly to said suction line, valve means which is closed to block the flow of compressed refrigerant along said flow paths, flow regulating means to regulate the rate of flow of compressed gas along said flow path to said suction line to re-evaporate condensed refrigerant flowing from said evaporator, and control means to control defrosting.
2. Refrigeration apparatus as described in claim 1 wherein said refrigeration system includes a liquid supply line extending to the inlet of said evaporator, and wherein said defrosting means includes a supply to the evaporator in the liquid line which is open during the refrigeration operation and is closed during the defrosting operation.
3. Refrigeration apparatus as described in claim 1 which includes a condensate pan and drain unit, and wherein said flow paths extend in heat exchange relationship with said pan and drain unit.
4. Refrigeration apparatus as described in claim 1 which includes a check valve which prevents the flow of refrigerant along said flow paths away from said evaporator inlet.
5. In refrigeration apparatus, the combination of: a refrigeration system having a compressor with a compressed gas discharge line and a suction line and having an evaporator with surfaces upon which ice or frost forms; and defrosting means including a defrosting-gas line extending from said compressed gas discharge line to said evaporator thereby to deliver compressed gas to said evaporator, a bypass line extending from said defrostinggas line to said suction line, means to control the relative amounts of compressed gas delivered through said defrosting-gas line respectively to said evaporator and through said bypass line to said suction line, whereby said suction line receives gas from said bypass line to re-evaporate condensed refrigerant passing from the evaporator during the defrosting operation.
'6. Refrigeration apparatus as described in claim 5 which includes, a defrost control unit to control the initiation and termination of the defrosting operations including: temperature sensing means to sense the temperature of surfaces of said evaporator, fan means to cool air by passing it into heat-exchange relationship with said evaporator, said control means including means to stop said fan at the start of each defrosting operation and to restart the fan at the end of each defrosting operation in response to a drop in temperature sensed by said temperature sensing means.
7. Refrigeration apparatus as described in claim 5 which includes, a defrost control unit to control the initiation and termination of the defrosting operations including: timing means to initiate the defrosting operations at predetermined time intervals.
References Cited UNITED STATES PATENTS 2,281,770 5/1942 Hoesel 6281 2,688,850 9/1954 White 62-234 2,713,249 7/1955 Schordine 62155 65 3,071,935 1/1963 Kapeker 62-155 3,213,637 10/1965 Halls 62-81 2,892,318 6/1959 Makkotf 62196 2,978,877 4/1961 Long 62-196 7 WILLIAM J. WY'E, Primary Examiner.
US. Cl. X.R. 62-496, 197, 234