US2492970A - Defrosting system - Google Patents

Description

Jan. 3, 1950 H. H. CURRY 2,492,970

DEFROSTING SYSTEM Filed Oct 6, 1943 IN V EN TOR.

HERMAN H. CURRY i Patented Jan. 3, 1950 DEFROSTING SYSTEM Herman H. Curry, Morristown, N. J.

Application October 6, 1943, Serial No. 505,141 6 Claims. (01. 62-4) (Granted under the act of March a, 1883, as amended April 30, 1928; 370 0. G. 757) The present invention relates to improvements in refrigerating machines of the compressorcondenser-evaporator type wherein hot gas or liquid refrigerant is used for defrosting cooling units subject to the collection of frost thereon.

More specifically the invention contemplates the use of the hot refrigerant to supply sufficient heat to defrost the cooling unit in refrigerating machines having a hermetically sealed refrigerant system without resorting to the use of auxiliary valves. It also contemplates the use of the refrigerant collected in the cooling unit during the defrosting process in cooling the said unit during the initial operation of the refrigerating system. It further contemplates controlling operation of the air circulating means until after the temperature of the cooling unit, heated for defrosting, drops to the temperature of the space cooled thereby.

A hermetically sealed refrigerating system is desirable to prevent leakage of gas and to prevent the entrance of moisture into the system. This is particularly true in marine refrigerating systems using Freon as a. refrigerant. Automatic defrosting is also desirable in such systems and especially in quick freezing applications.

In a conventional system, the compressor may be controlled as a function of suction pressure and the amount of liquid refrigerant released to the expansion coil maybe controlled by a thermostatically operated valve as a function of the temperature at the suction end of the expansion coil. These controls each have parts which cannot be serviced or replaced without opening the Freon-containing system. Automatic water defrosting for such systems involves drainage problems and the automatic hot gas defrosting heretofore used requires additional control valves with the attendant possibility of leakage and also necessitates opening the system for servicing the same.

Those refrigerators of the factory-assembled household type using a hermetically sealed system in which an orifice or a capillary tube is used to control the flow of refrigerant to the cooling unit are controlled by means of a thermostatic switch in the compressor motor circuit, said switch being responsive to the temperature of the refrigerated space. This system greatly reduces the probability that the refrigerating machine will require repairs necessitating opening the sealed system. However, this system has not been used in larger field-assembled units because the amount of charge of Freon is critical and must be closely controlled for the particular size and type of system. Moreover, such systems are not capable of defrosting the cooling unit by use of the hot refrigerant without the use of additional auxiliary equipment.

It is the object of this invention to obtain hot gas or liquid defrosting in a hermetically sealed refrigerating system using a capillary tube to control the flow of refrigerant to the cooling unit and not critical as to size of charge within comparatively wide limits.

Another object of this invention is to use hot gas or liquid refrigerant to defrost the cooling unit of a refrigerating system without the use of valves.

- Another object of this invention is to utilize the refrigerant passed into the cooling unit during the defrostng operation to cool the evaporator during the initial operation of the compressor.

Another object of this invention is to reduce the pressure on the pressure side of the compressor to facilitate the starting thereof.

Another object of this invention, is to delay operation of the air circulating means for the cooling unit until after the compressor has had time to reduce the temperature of the cooling unit to that of the refrigerated space.

Another object of this invention is toso mount and house the cooling unit that defrosting is facilitated.

Other objects of the invention will be more fully disclosed in the following specification and claims:

In the drawing, the figure is a diagrammatic illustration of a refrigerating system embodying the invention.

Referring to the drawing, depicting a refrigerating system in which the compressor-condenser unit is, in practice, hermetically sealed the refrigerant compressor I evacuates refrigerant vapor from the cooling unit and discharges it into the condenser 2 where the gas is liquefied. This hot liquid refrigerant is then collected in storage tank 3 from which it is led by means of conduit 14 to an orifice or capillary tube 4 which in turn feeds the liquid refrigerant under reduced pressure to the cooling unit, in a refrigerated space R, where in normal operation sufficient heat is absorbed to vaporize the liquid. This vapor then passes to the compressor inlet by means of conduit I2.

The cooling unit is composed of an expansion coil 5 and a storage chamber 6. The inlet end of said coil is connected to the capillary tube 4 by means of conduit I5 and the outlet end is 3 connected to the chamber I. This chamber may drain through trap II back into the inlet end of coil I. The upper part of chamber 6 is connected with the inlet of the compressor I by means of conduit I2. Defrosting of the cooling unit is facilitated by the use of an approximately horizontal arrangement of the expansion coil 5,

culates air through passage II over the cooling unit.

Compressor motor II and fan I are connected in parallel to a source of electric power and a thermostatic switch I, exposed to the temperature of a space refrigerated by the cooling unit. controls the supply of power thereto. This switch is of a type well known in the art and it is presumed suflicient to represent the same diagrammatically. It may be set to open the circuit at some predetermined low temperature and to close it at a selected higher temperature.

The operation of the system is as follows. Assuming the compressor I is in operation and the temperature of the refrigerated space is approaching the lower temperature setting of thermostatic switch 8 then tank I will contain all excess refrigerant as a hot liquid under considerable pressure. The space above the liquid will be fllled with gaseous refrigerant at a temperature corresponding to the pressure. Chamber 6 will contain only refrigerant vapor at a temperature slightly above that corresponding to the suction pressure of the compressor I. This pressure diflerential will cause a flow of liquid refrigerant through the capillary tube 4. Fan I is circulating air over coil 5.

When the temperature reaches the lower setting of thermostatic switch 8, the switch opens, stopping the motor I3 and fan I. Hot refrigerant continues to flow from tank 3 to coil 5 and the pressure in coil 5, chamber i and tube I2 begins to increase with part of the liquid refrigerant entering coil 8 vaporizing at increasing temperature and pressure until most of the liquid refrigerant has been collected in coil 5 and chamber 6. Heat is carried from tank 3 to co l 5 by hot liquid, or by liquid remaining in tan 3 vaporizing and condensing at lower temperature in coil 5 and as fan 'I is not operating, heat is not carried away fromcoil i but is held by the housing or inclosure 9, resulting in defrosting said coil each time the compressor I stops. As long as both gas and liquid are present on both the hot (compressor) and cold (evaporator) sides of the system, liquid will evaporate on the hot side and vapor will condense at corresponding pressure on the cold side. this process continuing until (1) temperatures equalize, (2) cold side fills with liquid, or (3) all liquid is evaporated from the hot side. Since each operating cycle is perhaps less than one hour long, only a small amount of defrosting will be required. This defrosting operation is expedited by housing 9 which prevents loss of heat from the cooling unit by connection currents. As each cycle of operation will be comparatively short, only a 4 limited amount of moisture will collect as frost on coil 5 and may be effectively melted by the excess liquid refrigerant collected in tank 3 during the operating cycle.

When the temperature in the refrigerated space rises to the upper setting of thermostat 8,

compressor I is started and, as condenser and suction pressures have equalized, operation begins at higher-than-normal capacity, and the pressure against which the compressor must start is materially reduced. As flow through the capillary tube 4 is reduced because of the lower pressure differential, condenser pressure increases and suction pressure decreases. In explanation of this statement, it must be first borne in mind that the capillary tube 4 is proportioned to pass the normal output of the compressor under normal condenser pressure and a normally low evaporator pressure. Thus, in the starting condition assumed, under which there is a lower-thandesigned pressure differential, the flow through the capillary tube will be below normal, and because of the relatively high suction pressure the condenser capacity will be above normal. Therefore, as stated, condenser pressure will increase and, eventually, suction pressure will decrease to normal designed values. Liquid refrigerant in chamber 6 flows back into coil 5 and is vaporized, the vapor compressed, condensed and stored in tank 3 until normal operating conditions are restored.

A time delay relay II, of which there are many suitable types commercially available and so well known in the art that in the present instance it is presumed sufficient to present the same diagrammatically, may be placed in the circuit of the fan I to delay starting the same until after the compressor I operates a sufllcient length of time to insure that the temperature of coil 5 is below that of the refrigerated space before air is circulated therein. The refrigerant collected in chamber 6 during the defrosting operation provides more than normal capacity for a period of time after defrosting for quickly reducing the temperature of the refrigerated space if such temperature is above normal as is customa y after filling the refrigerated space with warm material.

While I have described the preferred form of my invention 1 do not wish to limit myself to the precise details as shown but wish to avail myself of such variations and modifications as may come within the scope of the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. A defrosting refrigerating system including a motor, a compressor driven thereby, a condenser, a storage tank connected to said condenser, a cooling unit and a capillary tube connecting said tank and said unit, said" unit comprising, an expansion coil and a storage chamber positioned above said coil, means connecting each end of said coil to said chamber, said unit receiving hot refrigerant during cessation of operation of said compressor, said unit constituting a reservoir for supplying the system with refrigerant upon resumption of operation of said compressor, and a conduit conducting vapor from said chamber to said compressor.

2. An intermittently operated refrigerating system comprising a motor, a compressor driven to said condenser, a cooling unit, said tank and unit each having a capacity sufllcient to hold all of the refrigerant; a. capillary tube connecting said tank and unit; said unit comprising an expansion coil and a chamber above the same; a substantially U-shaped trap connecting the bottom of said chamber to one end of said coil; said coil being connected at its other end to the bottom of said chamber at a point spaced from said trap; and a conduit connecting the top of said chamber and said compressor, whereby said unit receives hot refrigerant through said tube when the compressor is inoperative thereby defrosting said unit.

3. An automatic defrosting intermittent-cyclically operated refrigerating system comprising a compressor, a condenser connected to said compressor, a tank connected to said condenser, an evaporating coil, flow restricting means connecting said tank and said coil, said means includin a liquid seal at the end of said coil connected to said flow restricting means to prevent bypassing said coil when operating dry; a chamber positioned at a slightly higher elevation than said coil; means connecting said coil to the bottom of said chamber, and a conduit connecting the upper part of said chamber to said compressor, whereby the refrigerant is circulated in said coil when operating flooded.

4. A defrosting mechanical refrigerating system comprising a compressor; a condenser connected thereto, and a storage tank connected to said condenser; a cooling unit; said unit comprising an evaporator coil and a storage chamber above said coil; said coil having an inlet end and an outlet end; flow restricting means connecting said tank and the inlet end of said coil; means connecting the outlet end of said coil to said chamber; said last mentioned means comprising a trap; whereby refrigerant can circulate in'said coil by convection when said unit is flooded. to cause entering liquid and vapor to flow through the coil to insure uniform distribution of refrigerant and a minimum of localized frosting when said unit is operating dry; and means connecting the top of said chamber and said compressor.

5. In a mechanical refrigerating system arranged for automatic defrosting, a refrigerated space, a cooling unit therein; an inclosure for said unit within said space; said inclosure having openings on its lower side arranged to prevent the loss of heat during the defrosting of said unit; means for flooding said cooling unit with hot refrigerant for defrosting said unit; a fan for circulating air over said unit; and means for rendering said fan inoperative during the defrosting of said unit.

6. The refrigerating system of claim 5 that includes means for delaying operation of said fan, for a predetermined period after the end of the defrosting period.

' HERMAN H. CURRY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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