US3332251A - Refrigeration defrosting system - Google Patents

Description

July 25, 1967 J. E. WATKINS 3,332,251

REFRIGERATION DEFROSTING SYSTEM Filed Oct. 24, 1965 JOHN E. WATKINS 45 MJMMAAJM ATTYS,

United States Patent 3,332,251 REFRIGERATION DEFRDSTING SYSTEM John E. Watkins, 9 N. 3rd Ave.,

Maywood, Ill. 60153 7 Filed Oct. 24, 1965, Ser. No. 504,550 9 Claims. (Cl. 62-81) ABSTRACT OF THE DISCLOSURE A defrosting system for refrigeration equipment is disclosed in which hot gas from the compressor is directed into the coils of the evaporator for defrosting purposes without having passed through the condenser or receiver. This is accomplished through a system of by-pass lines and valves which make use of a single heat exchanger which serves to prevent the entrance of unvaporized slugs of liquid refrigerant into the compressor inlet during both refrigerating and defrosting operations.

This invention relates generally to refrigerating systems and more particularly to the removal of frost accumulating on the cooling elements of compressive process type refrigerating systems.

When the cooling surfaces of refrigerating systems of the type used to cool freezers or storage compartments are maintained at a temperature less than the freezing point of water, moisture in the air condenses on the surfaces and eventually freezes to form a coating of frost which has an insulating effect and which should be removed in order to obtain eflicient refrigerating operation. The removal of this frost coating, called defrosting, is periodically required to again restore the refrigerating system to efiicient operation.

A relatively simple and successful technique for defrosting refrigerating system cooling surfaces has been the use in a defrost cycle of the refrigerating fluid itself for warming the cooling surfaces to melt and remove the accumulated frost. Using such a defrost cycle offers the advantages of eflicient heat transfer to melt the frost on the cooling surfaces without the requirement of fans, ducts, spray devices, or other additional equipment in the region of the cooling surfaces. Moreover, these systems are adaptable to automatic control with their operation governed by many of the same devices used to control the system during the refrigeration cycle.

When the working fluid of a compressive process refrigerating system is used to warm and thereby defrost the cooling surfaces of the system, problems arise in controlling the flow of refrigerant gas to obtain efiicient defrosting operation. To obtain faster defrosting, higher flow rates of superheated refrigerant gas are required. At higher flow rates, however, the condensation of this gas may cause slugs of liquid refrigerant to accumulate in the suction line of the system. If these slugs of liquid reach the suction side of the compressor, the compressor may be damaged.

It is a primary object of this invention to provide a defrosting system which utilizes the heat of compression of compressed refrigerating gas for defrosting the cooling coils.

Another object is to provide a hot gas defrosting system supplying to the coils being defrosted substantially all of the heat added by the compressor without the risk of liquid slugs being passed from the evaporator into the compressor suction line.

A related object is to provide a method of using a heat exchanger for suction gas superheating during both refrigeration and defrosting, in which the rate of heat fed to the evaporator is regulated by the system itself so as to eliminate the need for special controls.

A further related object is to provide a method for defrosting the evaporator of a refrigerating system which utilizes refrigerant gas superheated by the heat of compression from the compressor and employs a dualfunction heat exchanger for adding heat to the refrigerant entering the suction side of the compressor to eliminate liqqid slugs during both the refrigerating and defrosting cyc e.

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawing, in which the invention is illustrated in connection with a conventional compressive process refrigerating system.

FIGURE 1 is a diagrammatic view of a preferred compressive process refrigerating system incorporating the present invention.

FIG. 2 is a sectional view of the bypass valve indicated in FIG. 1.

While the invention will be described in connection with a preferred embodiment, it will be understood that I do not intend to limit the invention to that embodiment, but intend to cover all alternative constructions, modifications or equivalents as may be included within the spirit and scope of the invention as defined by the claims.

Referring to FIG. 1, there is shown a receiver 11, which serves as a source of liquid refrigerant for the system. In the course of normal refrigerating operation, this liquid refrigerant is maintained at a relatively high pressure by a compressor 12. The normal flow of refrigerant during refrigerating operation is indicated by solid arrows. From the receiver 11, the refrigerant flows through a heat exchanger 13 where a portion of its heat energy is given up to gaseous refrigerant returning from an evaporator 14 as will be hereinafter described. From the heat exchanger 13, the liquid refrigerant flows through supply lines to a feed valve 15, here shown as a thermostatic expansion valve, which has a throttling action and causes the liquid refrigerant to drop to a lower temperature and pressure, as is well known in the refrigerating art. From the feed valve 15, the cold refrigerant passes to the evaporator 14, which is constructed to provide a refrigerant flow path having a relatively large amount of surface area so as to facilitate the transfer of heat. In the preferred embodiment, this is accomplished by means of a plurality of cooling coils and transverse fins, as described in my Patent No. 2,998,712, issued Sept. 5, 1961. The coils and fins of the evaporator 14 thus serve as cooling surfaces for removal of heat from the air or other medium which is in turn circulated through the space to be cooled. It is when this air or other medium contains moisture that the problem of condensation and frost formation arises.

From the evaporator 14, the refrigerant passes again to the heat exchanger 13, through a path of flow separate from that taken by the liquid refrigerant as it passed from the receiver 11 to the supply valve 15. The refrigerant from the evaporator 14, whether superheated or saturated or carrying some excess unevaporated liquid, is considerably colder than the liquid refrigerant entering the heat exchanger 13 from the receiver 11. Heat energy is therefore transferred from the warmer fluid to the cooler, in this case the cooler fluid being that which is returning from the evaporator 14. During normal refrigerating operation, the function of the heat exchanger 13 is to supply suflicient heat energy to the refrigerant returning to the compressor 12 so that no slugs of liquid refrigerant remain which might damage the compressor. In the preferred embodiment, the heat exchanger is constructed so that its outer shell, through which the refrigerant passes from the evaporator 14 to the compressor 12, contains a trap (not shown) in which liquid refrigerant is caught should it not be vaporized by passing through the heat exchanger. In addition, oil returning from the evaporator will also accumulate in this trap with the liquid and may be drained slowly to the compressor suction through a leak tube or equivalent, at a rate not harmful to the compressor.

From the heat exchanger 13, the returning gaseous refrigerant enters the suction inlet of the power driven compressor 12. The refrigerant gas is then compressed by the compressor 12 to a relatively high pressure and temperature so that heat energy can be dissipated as the refrigerant passes through a condenser 16.

The condenser 16 is constructed in a manner similar to the evaporator 14, having a refrigerant flow path adapted to transfer heat energy from the condensed refrigerant to a cooling medium which passes over its outer surface. This cooling medium may be air, water or any suitable medium, circulated by any suitable means. In the condenser 16, the heats of evaporation and compression are removed from the compressed refrigerant vapor causing liquid refrigerant to be precipitated upon the inner walls of the condenser 16 and the resulting flow of liquid refrigerant is then transferred into the receiver 11, from which point the process again begins and continues as has been heretofore described.

Control of the supply valve 15 in the preferred embodiment is accomplished thermally, with the operating power being obtained from a temperature-sensitive element 17 located so as to sense the superheat of the spent refrigerant flowing from the evaporator 14.

In accordance with the invention, frost which has accumulated on the evaporator outer surfaces is removed through the use of the relatively hot pressurized refrigerant gas supplied at the outlet of the compressor 12. The flow of this hot gas is carried through a hot gas supply line 21 from the compressor outlet to a point where the flow of hot gas may enter the path of normal refrigerant flow just upstream of the heat exchanger 13. The flow of refrigerant during defrosting operation is shown by dashed arrows. This diversion of compressor outlet flow, which serves to bypass both condenser 16 and receiver 11, is accomplished by means of a shutoff valve 22 and a pressure-operated throttling valve 23. The shutoff valve 22 is normally open to allow liquid refrigerant to flow from the receiver 11 to the heat exchanger 13 during normal refrigeration. The pressure-operated valve 23 prevents reverse flow from the heat exchanger 13 into the outlet line of the compressor 12, and is preferably constructed with spring biasing means to provide the throttling effect.

Further in accordance with the invention, to avoid the throttling and consequent reduction in pressure and temperature which take place in the supply valve 15 during normal refrigerating operation, a bypass line 24 including a bypass valve 25 is provided to allow relatively large quantities of warm refrigerant to pass from the compressor 12 through the heat exchanger 13 to the evaporator 14 by a path which circumvents the supply valve 15. For refrigerating operation the bypass valve 25 is normally closed but has an alternate open position for defrosting. The electrically actuated bypass function of the valve 25 may alternatively be combined in one valve with the modulating effect of the supply valve 15. Although the valves are herein shown separately for purposes of description, a dual-function valve can be used.

Pursuant to the invention, defrosting of the evaporator 14 by hot refrigerant is carried out by merely closing the shutoff valve 22, thereby causing an immediate pressure drop in a downstream supply line 26, and opening the bypass valve 25. The result of these operations is to direct the flow of relatively hot refrigerant from the compressor 12 through the pressure-operated throttling valve 23 which opens as the compressor outlet pressure begins to exceed the pressure downstream of the shutoff valve 22 by an amount equal to the spring biasing force in the valve 23, through the heat exchanger 13 to the bypass line 24 and thence into the evaporator 14. This flow of hot refrigerant is at a higher temperature and pressure than that present in the evaporator 14 during normal refrigerating operation because in defrosting operation it has not passed through the condenser 16, receiver 11, or supply valve 15, after having left the compressor 12. Defrosting is thereby effected by the transfer by condensation of some of the heat energy from the hot gaseous refrigerant to the liquid refrigerant returning from the evaporator 14, in amounts suflicient to vaporize it, the balance of the heat energy passing on to the evaporator in a mixture of liquid and gas which becomes warm enough to melt away any accumulated frost. From the evaporator 14, the flow of refrigerant continues through the heat exchanger 13 and into the compressor 12 as in normal refrigerating operation, except that conditions of temperature and pressure in the heat exchanger are somewhat different from those during normal refrigerating operation. The function of heat exchanger 13 during defrosting is the same as that during refrigerating: to prevent slugs of liquid refrigerant from entering the compressor inlet and to serve as a trap for liquid refrigerant and for oil which may have accumulated in the system. But because of the different mode of operation, the heat exchanger 13 has a dual function, since the heat transfer to refrigerant leaving the evaporator 14 during defrosting takes place at a higher temperature and pressure than that during normal refrigerating operation. The effect is to transfer latent heats from one stream to the other, leaving the heat of compression for defrosting the evaporator.

A controlled amount of throttling of the compressor outlet flow is done as it passes through the pressureoperated throttling valve 23 and through the hot gas supply line 21. The hot gas is throttled for the purpose of reducing the refrigerant pressure in the system downstream of the valve 23 while still allowing the compressor 12 a substantial pressure differential to work against. The higher the pressure differential, the more work can be supplied to the hot gas flow by the compressor 12, and the more energy is available for the removal of frost from the evaporator 14. In the preferred embodiment, the pressure-operated throttling valve 23 is of a construction which will be familiar to those skilled in the refrigerating art, having a spring biasing means adapted to prevent flow from the compressor 12 through the hot gas supply line 21 while the shutoff valve 22 is in its normal open position. For the purpose of preventing flow in the reverse direction, the biasing means in the valve 23 need only be strong enough to resist the frictional pressure drop caused by the normal flow of refrigerant through the condenser 16, receiver 11 and associated piping. In practice, however, the spring biasing means is chosen to provide a biasing force somewhat in excess of that required to overcome this pressure drop. This is done to provide the advantages of a controlled amount of throttling which allows the compressor 12 to work against a greater pressure head and results in warmer refrigerant being supplied to the evaporator 14 during defrosting.

It is a feature of the invention that the flow of hot refrigerant through the evaporator 14 is at a temperature and pressure considerably higher during normal refrigerating operation. These conditions give rise to the additional advantage of being able to purge from the evaporator 14 any oil which may have accumulated there. Any such oil will be swept by the flow of hot refrigerant into the shell of the heat exchanger 13 where it will be trapped as has been previously mentioned and bled to the compressor.

In the preferred embodiment, defrosting is initiated by closing the shutoff valve 22. The bypass valve 25, while it may be opened simultaneously with the closing of the shutoff valve 22, is preferably not actuated until the pressure in the supply line 26 has reduced so as to prevent a sudden surge of pressure that would otherwise carry over through the bypass valve 25 into the evaporator 14, blowing liquid ahead of it which might possibly carry back into the compressor 12. Delayed operation has been accomplished in the preferred embodiment by constructing the bypass valve 25 so that it will not open in response to its actuating signal until the pressure differential across its openings has decreased to less than a predetermined value. For this purpose the bypass valve 25 is similar to the conventional pilot-operated solenoid valves which are commonly used in the refrigeration art, but differs from these valves in that the normal pilot passage is omitted. Thus, in the preferred form of the bypass valve 25, shown in FIG. 1 an inlet port 27 and an outlet port 28 are separated by a web 29 having a chamfered opening 31 which serves as a seat for a tulip-shaped valve plug 32. The lower portion of valve plug 32 seats against the opening 31, while the upper portion forms a piston which is slidably received in a bore 33. The port 34 and the bleed port 35 are provided in the plug 32 to permit pressure from the inlet port 27 to be communicated back to a pressure cavity 36 which is formed behind the pistonlike upper end of the plug 32. Thus, the pres-sures surrounding the plug 32 are equalized except for the pressure differential across the plug at the opening 31, which tends to urge the plug 32 against the seat of the opening 31, thereby sealing it. A pin 38 which is resiliently urged downwardly by a spring 39 is loosely fitted in a retainer 40, and extends upward through a perforated spacer 41 into engagement with a solenoid plunger 42. Actuation of the pin 38 is provided by energizing a solenoid coil 43 disposed above the plunger 42, which draws the plunger 42 upward into engagement with the pin 38.

Conventional pilot-operated valves are constructed with a pilot passage located in the valve plug 32, which opens into the outlet port 28 and is sealed by the tip of the pin 38. In conventional valves, the pilot passage permits the valve to be opened against a considerable pressure differential, but to insure a delay in the operation of the valve 25 sufficient to allow pressure in the supply line 26 to reduce to safe levels, the pilot passage is omitted so that the valve 25 will not open on energization of the solenoid coil 43 until the pressure differential across the opening 31 is sufiiciently low so that the force urging the plug 32 onto its seat in the opening 31 may be overcome by the relatively small lifting force provided by the action of the solenoid coil 43 on the plunger 42 and transmitted by the spring 39 to the plug 32. The resulting effect is that the valve 25 will not open in response to its actuating signal until the pressure differential across its opening has decreased to a value determined by the area of the opening 31 and the lifting force available from the solenoid 43.

Automatic operation is facilitated in the preferred embodiment by the incorporation of electrical solenoid operating means in the shutoff valve 22 and the bypass valve 25. Such electrically-operated solenoid valves are commercially available and are regularly used in the refrigerating system art. Any suitable system of automatic operation may then be used to effect defrosting such as a timing mechanism.

I claim-as my invention:

1. In a refrigerating system having a compressor provided with an inlet and an outlet, an evaporator, a condenser, and means operable in a refrigerating cycle for conveying hot refrigerant gas from said compressor outlet to said condenser and for conveying liquid refrigerant from said condenser to said evaporator, the combination of means operable in a defrost cycle for bypassing hot refrigerant gas from said compressor outlet around said condenser and for conveying said hot refrigerant gas to said evaporator, and a dual-function heat exchanger for adding heat to refrigerant returned to said compressor inlet from said evaporator, the heat being derived from said liquid refrigerant during the refrigerating cycle and from said hot refrigerant gas during the defrost cycle.

2. A refrigerating system having a source of liquid refrigerant, a compressor having an outlet and an inlet, a

dual-function supply valve, an evaporator, a condenser discharging refrigerant into said source, a heat exchanger adapted to exchange heat between a first path of flow connecting the compressor outlet and the supply valve and a second path of flow connecting the evaporator and the compressor inlet, a hot gas supply line including a throttling means and a normally closed pressure-operated valve allowing refrigerant from the compressor outlet to by-pass the condenser and source, a normally open shut-off valve adapted to interrupt flow of refrigerant from the source, said valves in their normal positions effecting refrigeration by supplying refrigerant through the supply valve to the evaporator, which refrigerant has been condensed by passage through the condenser, and said valves in their alternate positions effecting defrosting by supplying refrigerant from the compressor to the evaporator by way of the hot gas supply line in relatively larger quantities without the refrigerant having been cooled by passage through the condenser.

3. In a refrigerating system having a source of liquid refrigerant, a compressor having an outlet and an inlet, a normally open supply valve, an evaporator, a condenser discharging refrigerant into said source, and a heat exchanger adapted to exchange heat between a first path of flow connecting the compressor outlet and the supply valve and a second path of flow connecting the evaporator and the compressor inlet, the improvement comprising a by-pass line including -a normally closed by-pass valve allowing refrigerant to by-pass the supply valve, a hot gas supply line connecting said compressor outlet and said first path of flow including a normally closed valve allowing refrigerant from the compressor outlet to by-pass the condenser and source, a normally open shutoff valve adapted to interrupt flow of refrigerant from the source, said valves in their normal positions effecting refrigeration by supplying refrigerant to the supply valve and evaporator, which refrigerant has been condensed by passage through the condenser, and said valves in their alternate positions effecting defrosting by supplying refrigerant from the compressor to the evaporator by way of the hot gas supply line without the refrigerant having been cooled by passage through the condenser.

4. The refrigerating system of claim 3 in which a throttling means is incorporated into one of the normally closed valves, said one valve including spring biasing means.

5. The refrigerating system of claim 3 in which said bypass valve includes opening means responsive to a reduction of differential refrigerant pressure across said by-pass valve below a predetermined value.

6. In a refrigerating system having a source of liquid refrigerant, a compressor having an inlet and an outlet, a normally open supply valve, an evaporator, a condenser discharging into said source, and a heat exchanger adapted to exchange heat between a first path of flow between said source and the supply valve and a second path of flow between the evaporator and the compressor inlet, the method of defrosting the evaporator comprising the steps of interrupting the flow of liquid refrigerant from said source, and directing the flow of relatively warm compressed gaseous refrigerant from the outlet of said compressor into said heat exchanger through said first flow path without passing through said supply valve.

7. In a refrigerating system having a source of liquid refrigerant, a compressor having an inlet and an outlet, a normally open supply valve, an evaporator, a condenser discharging into said source, and a heat exchanger adapted to exchange heat between a first path of flow between said source and the supply valve and a second path of flow between the evaporator and the compressor inlet, the method of defrosting the evaporator comprising the steps of interrupting the flow of liquid refrigerant from said source, directing the flow of relatively warm compressed gaseous refrigerant from the outlet of said compressor into said heat exchanger through said first flow path without having passed through said condenser or said source, throttling said flow through said first flow path, and directing said flow from the outlet of said first flow path from said heat exchanger into said evaporator without passing through said supply valve.

8. In a refrigerating system having a source of liquid refrigerant, a compressor having an inlet and an outlet, a normally open supply valve, an evaporator, a condenser discharging into said source, and a heat exchanger adapted to exchange heat between a first path of flow between said source and the supply valve and a second path of flow between the evaporator and the compressor inlet, the method of defrosting the evaporator comprising the steps of interrupting the flow of liquid refrigerant from said source, directing the flow of relatively warm compressed gaseous refrigerant from the outlet of said compressor through a throttling valve into said heat exchanger through said first flow path without having passed through said condenser or said source, and directing said flow from the outlet of said first flow path from said heat exchanger into said evaporator without passing through said supply valve.

9. In a refrigerating system having a source of liquid refrigerant, a compressor having an inlet and an outlet,

a normally open supply valve, an evaporator, a condenser discharging into said source, and a heat exchanger adapted to exchange heat between a first path of flow between said source and the supply valve and a second path of flow between the evaporator and the compressor inlet, the method of defrosting the evaporator comprising the steps of interrupting the flow of liquid refrigerant from said source, directing the flow of relatively warm compressed gaseous refrigerant from the outlet of said compressor into said heat exchanger through said first flow path Without having passed through said condenser or said source, and when the pressure differential between refrigerant pressure in said evaporator and in the first flow path through said heat exchanger is less than a predetermined value, directing said fiow from the outlet of said first flow path from said heat exchanger into said evaporator without passing through said supply valve.

References Cited UNITED STATES PATENTS 3,022,639 2/1962 Brown 62278 X 3,195,321 7/1965 Decker 62-278 MEYER 'PERLIN, Primary Examiner.

Claims (1)

1. IN A REFRIGERATING SYSTEM HAVING A COMPRESSOR PROVIDED WITH AN INLET AND AN OUTLET, AN EVAPORATOR, A CONDENSER, AND MEANS OPERABLE IN A REFRIGERATING CYCLE FOR CONVEYING HOT REFRIGERANT GAS FROM SAID COMPRESSOR OUTLET TO SAID CONDENSER AND FOR CONVEYING LIQUID REFRIGERANT FROM SAID CONDENSER TO SAID EVAPORATOR, THE COMBINATION OF MEANS OPERABLE IN A DEFROST CYCLE FOR BYPASSING HOT REFRIGERANT GAS FROM SAID COMPRESSOR OUTLET AROUND SAID CONDENSER AND FOR CONVEYING SAID HOT REFRIGERANT GAS TO SAID EVAPORATOR, AND A DUAL-FUNCTION HEAT EXCHANGER FOR ADDING HEAT TO REFRIGERANT RETURNED TO SAID COMPRESSOR INLET FROM SAID EVAPORATOR, THE HEAT BEING DERIVED FROM SAID LIQUID REFRIGERANT DURING THE REFRIGERATING CYCLE AND FROM SAID HOT REFRIGERANT GAS DURING THE DEFROST CYCLE.

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