US2978877A - Hot gas defrosting system with gravity liquid return for refrigeration systems - Google Patents

Description

April 11, 1961 J. N. LONG 2,978,877

HOT GAS DEFROSTING SYSTEM WITH GRAVITY LIQUID RETURN FOR REFRIGERATION SYSTEMS Filed Aug. 4, 1958 I9 25 f o 25 W 3 39 11. z /4 /9 EVAPORATOR l9 EVAPORATOR /7 F /5 76 4 /5 30 27 "1" 30 f //9 E 34 I L27 2 6 J5 1 l TRANSFER DRUM OIL 9 l 36 29 comp. SEP. 2 38/ 7 CONDENSER RECEIVER 39 INVENTOR. I FUSEPH N .LoNq- M, M ME -77 ftorneys are conventional systems.

United States Patent nor GAS DEFROSTING'SYSTEMGRAWTY RETURN FOR REFRIGERATION SYS- This invention relatesgenerally. to -refrige-r ation cyatems and more articularly roan improved s stem ot hot gas defrosting for theevaporator's. s r

'lninefrigeration systems, a considerable amount of ice builds up on the evaporator units and prevents 'prope-r heat transfer, and to insure elfioient operation of the cvaporators, this ice. :buiId-upymustbe removed periodically. i

The principle of using hot gas from the compressor to defrost the evaporators is well known 'and has been used with considerable success. Serious problems have arisen in such defrosting system's, however, the principal one. of which is efiiciently disposing of the-large quantity of liquidaformed in the evaporators by condensation' of the hot gas. Stated otherwise, the heat given off 'hy the gaseous refrigerant in athe storage room causes the refrigerant to condense, and. although the evaporator coil or air units have thus been defrosted, aconsiderable quantity ofliquid refrigerantiis formed in the evaporator; whichis-highly undesirable. Y i I The problem of liquid formation in the evaporators hasbeen a troublesome one to the refrigeration industry for many years; Various attempts have been made, both from experimental ,andn commercially useful viewpoints, to-dispose; of thisn-l-iquidin ran deficient mannen The liquid cannot be returned totheasuctiori "line because of consequent damage to ithe co'mpre'ssor.

In accordance with the present invention, a refrigeration system is provided-having a hotgasdefrosting system in which the liquid thatyis condensed. in "the evaporator unit: during the defrostingperiodis returned through a transfer drum :and then directly to thereceiver "by gravity. By means of. thisi-nvention, the necessity of re-evaporating. the liquid asitcomes from thexevaporators andureturning it to the compressor. is eliminated: :Instead, the

' liquid is returned-more directly-to the receiverandin its useful liquid state. ASAHJI'CSU'HI, a hot gas def-rosting are rangement for a-refrigerating: system. is provided which is more economical both-to produce and to-operate. than More specifically, the invention provides a defrosting system of the above typefor use with a plurality ofvevaporator units andwherein an automaticfltimer is used to determine the defrost time for each evaporator unit or load, so that the'defrosting thereof; is accomplished in sequence, one load at a time; 1,

Another more specific-object ofthe present invention is to provide a novel electrical control circuiizfor a defrost system of. the above typein which th e operation of the evaporator unit or units is controlled by their respective temperature controller to maintain room, tempera:

ture under normal operations. The defrosting operation is initiated by. an automatictimer which takes over control of its evaporator from the temperature controller during the defrosting operation. This automatic, timer actuates other valves to cause-defrosting of the evaporator and in sequence if a plurality or evaporators ateus ed in thesystem. l

' 'These and other objects and advantages of the present invention will appear later as this disclosure progresses, reference being had to the accompanying drawings, 'in which:

Figure its a schematic diagram of one typical' refrigeration system embodying the improved hot gas defrosting system in accordance with the present invention; and

Figure 2 is an electrical Wiring diagram showing the "electrical apparatusand connections involvedin the system of Figure l, the components being in the normal position as when not energized. V

While the invention has been illustrated and described herein as being advantageously applicable to a system utilizing two evaporator units; it is not desired or intended to thereby limit the scope or utility of the invention to any particular number or type of evaporator's. Conventional air un -s 'or pipe gravity coils may be used,

"for example, as well as-any combination thereof. It is also contemplated that descriptive terms employed herein will he given the broadest: possible interpretation consi'stent wit'lpthe disclosure. l i i 2 Referring "in greater detail-to the drawings, the improved refrigeration system includes a conventional compresso'r: 5 having a discharge line 6 which conducts the hot vaporized refrigerant through the oil separator 7, check valve 8 andinto the condenser 9. Theli'quid refriger-ant then leaves the condenser via conduitil'fi which contains a hand Valve 1 1 and enters the high pressure liquid-receiver .12. The high pressure liquid then is dis?- charged firorh the, receiver through :conduit 13, solenoid valves 14. and through the conventional thermostatic expansion valves 15 where it expands into the evapo ratorslo. and 17. The compressor, oil separator, condenser, receiiver andeva'porators are conventional and it will be. understood certain conventional check valves and shut-off valves havebeen omitted, such asha'nd valves or: each side of the compressor, for the sake of clarity and as their use is Well-known to those skilled in theant. I As thecontrol valves and switches are the same for each evaporator unit, only one set will, be specifically referredfto but similar reference numerals will be 'used for similar elements. p t

,During normal operation, liquid refrigerant is admitted tothe evaporators when solenoid valves 14 areopehed. After the liquid refrigerant expands in the evaporator to thereby create the desired cooling effect in the area. where it' is located, the vaporized refrigerant is then permitted tonleave the evaporators via the suction line 19, when the solenoid valves 20 therein are; opened, and is returned'to the compressor 5. i p

Solenoid valves 14 and 20 are thus normally operated by the conventional thermostat, temperature, controller, 22 (Fig. 2) to open and close the liquid line 13 and suction linepl9 to maintain a predetermined: temperature ofthe refrigeratedarea. i

Duringthis normal operation ofthe refrigeration systern, a considerable amount of ice will build up. on the evaporator units and this icemust be; periodically removed to ,insure good heat transferand efiicient operationof the units. Prior practice has involved the; peri odic passing ofthe hot gas from. the compressordirectly into the evaporators for the purpose ofmelting the ice formed thereon. This practice, howevenwhile Sewing to effectively melt the ice, resulted in a large amount of liquid refrigerant beingformed in 'the evaporators, and'the eflicient disposal of this liquid refrigerant has been a source of concerrr tothisjihdustry for many'years. It has been a widespread practice to re-evaporate this liquid in one manner or another, asby 'me'ans o f 'vari ous h'eat eiichangers', and then ultimately returnthe ya:

' Inaccordance with the present invention, to initiate a defrost cycle, the hot vaporized refrigerant, or gas, is introduced through conduit 24, which is connected to the compressordiseharge line 6, into' the evaporators when the solenoid valve 25 in line 24 is opened. At the time this hot gas valve.25 is opened, the-supplyline valve 15 and suction line valve 19 are closed.

A liquid return line 27 places the evaporator in communication with a transfer drum or tank 29 when the combination relief and solenoid stop valve 30 in line 27 is open. Valve 30 is set to open at a predetermined pressure in the evaporators, such as for example, 60 psi.

The valve 30 remains closed during the defrosting period untilthe hot gas in the evaporators causes the pressure therein to rise above the predetermined pressure relief setting of the valve. The normal pressure setting (say about 60 psi.) for valve 30, is sufficient to maintain enough heat in the evaporator to cause defrosting.

After approximately 60pounds of pressure has developed in the evaporator, the relief valve 30 opens and this pressure is sufficient, to .force the liquid into the transfer drum, veven if the latter is installedin a location above the level of the evaporator. a Venting means'are provided for the drum 29 throng solenoid valve 34 in conduit 35, which'conduit connects the upper portion of the drum to the suction line 19.

During'the defrosting cycle, the solenoid valves 14, 20 are controlled by the defrosting timer 32 rather than by the temperature controller 22. Valves-'25 and 34 are controlledby the timer only and are both open during the defrosting period as will appear more fully later.

An equalizer line 36 has a solenoid valve 37 therein and places the upper portion of the drum in communication with the condenser. A drain line 38 places the cycle, thereby separating the drum from the high pressure side of the system and the drum is placed under suction 'line pressure by line 35 and open valve 34. Valves 37 and 39 are also controlled only by the defrosting timer 32, as will appear.

After the defrost period has elapsed, as determined by the timer 32, the latter returns all of the solenoid valves to their normal position. In other words, the liquid valve 15 and suction valve 19 revert back to control by the thermostat controller 22; hot gas valve 25 and the drain-relief valve 30 are both closed; equalizing valve 34 to suction is closed; drain valve 39 and equalizing valve 37 are opened. Under these conditions, the drum is isolated fromthe low pressure side of the system and communicates with the high pressure side throughvalves 37 and 39. vAsa result, the pressure then builds up in t conventional type and are actuated by their timer 32;

is a combination control that opens the circuit to shut down the system in the event the system pressure either exceeds or falls below the predetermined operating range. The oil pressure control OPC acts to stop the compressor if its oil pressure fails. The low pressure control LPC is an automatic control that cuts the compressor in and outdepending on the suction pressure v A manually operated selector switch SS when moved to the H position acts to bypass the LPC switch and the system can then be operated by hand or manually. When the selector switch is moved to the A position, the system operates automatically'under the influence of the LPC which turns the compressor on and off in accordance with'the suction pressure.

The conventional automatic starter S is connected to the three-phase supply line's bywires50, 51 and 53; to the selector switch SS by wire 54 and to the com- .pressor motor CM by wires 55, 56 and'57. j

By means of the present invention, the evaporator units are periodically and alternately defrosted by hot gas from the compressor. During the ,defrost period for one ,of the units, all of the various solenoid valves for that unit are controlled by their defrost timer rather than some of them being controlled by the thermostat control. The liquid formed in the evaporators is released therefrom by the relief' valve, and this liquid is forced under pressure into the transfer drum, which drum is,

at that time blocked from the high pressure side ofv the system and is vented to the suction line thereof- After the defrost period is finished, the timer returns the solenoid valves to their normal position; that is,.the hot gas is shutoff from the evaporator; the liquid and suction valves revert back. to control by the thermostat Controller; the transfer drum is placed in communication with the. high pressure side of the system, more specifically, with the condenser and receiveryand the drum is closed to the low pressure or .suction side of the system. The transfer drum is then pressurized andthe'liq uid refrigerant therein drains by gravity into the high'pres sure receiver, ready for reuse. I

Variousmodes of carrying out'the invention are contemplated as being within the scope of the following erant through a condenser and-receiver and into an These relays have the normally openswitch 41 which,

when closed, energizes valves 37 and 39. The normally closed switch 42, when closed, causes valves 30 and 34 to be energized and open. The normally closed switch 43 is connected to the compressor circuit so that when a unit is to be defrosted and its corresponding compressor is 'not'operating, the relay cuts the compressor back into the circuit to furnish hot gas for the defrosting process.

The defrost timers 32 actuate their respective relays 40, control the valves 25, 34, 37 and 39, and in addition,

during the defrost cycle only, control the solenoid valves Other. conventional controlling devices are shown in Fignrcjand include a dualpressure control DPC which evaporator, and also having a suction linefor returning evaporated refrigerant back to the compressor, a liquid transfer drum connected between said evaporator and said receiver for returning liquid refrigerant to said 'receiver, a'hot "gas line between the compressor and said evaporator, and temperature responsive electrical control means including a defrost timer and valves for regulating refrigerant flow in said systemand adapted to close said pressure and suction lines and open said hot gas line to thereby permit hot gas to enter and defrost said evaporator, said control means also adapted to block communication between said drum and receiver and permit liquid refrigerant to pass underpressure from saidevap orator to. said drum when pressure in said evaporator exceeds a predetermined amount; and atthe end of the defrost-cycle'said control means being adapted to place said drum in communication with said receiver and isolate a said drum from the suction side of said system whereby liquid refrigerant jcan drain by gravity from the drum to the receiver. r i 1 V,

2. A refrigeration system comprising a compressor having a high pressure refrigerant line for passing refrigerant through a condenser and receiver and into an evaporator, and also having a' suction' line for returning evapdjra ted refrigerant back to the compressor, a liquidtransfer drum connected between said evaporator and said receiver: for

returning liquid refrigerant to said receiver, a vent conduit placing said drum in communication with the suction side of the system, a hot gas line between the compressor and said evaporator, and temperature responsive electrical control means including a defrost timer and valves for regulating refrigerant flow in said system and adapted to (1) close said pressure and suction lines and open said hot gas line to thereby permit hot gas to enter and defrost said evaporator, (2) block communication between said drum and receiver and open said vent line, (3) permit liquid refrigerant to pass from said evaporator to said drum when pressure in said evaporator exceeds a predetermined amount, and at the end of the defrost cycle said control being adapted to close said vent line and place said drum in communication with said receiver whereby liquid refrigerant can drain by gravity from the drum to the receiver.

3. In a refrigeration system, the combination comprising a compressor, a condenser, a liquid receiver, an evaporator, a liquid conduit for connecting said compressor to said evaporator through said condenser and receiver, a suction conduit connecting said evaporator to said compressor for returning refrigerant to said cornpressor, a valve in each of said liquid and suction conduits, a liquid transfer drum, conduit means between said evaporator and said drum and having a combination electrically operated and pressure relief valve therein, a drain conduit between said drum and said receiver and including a valve therein, a vent conduit between said drum and the suction side of the system and having a valve therein, a hot gas line between the compressor and said evaporator and having a valve therein, and electrical control means adapted at the beginning of a defrosting cycle to close said liquid, suction and drain conduit valves, and open said hot gas line valve to thereby permit hot gas to enter and defrost said evaporator, said relief valve being adapted to open when pressure in said evaporator exceeds a predetermined amount to thereby permit liquid refrigerant to pass from said evaporator to said drum, said control means also adapted at the end of the defrost cycle to place said drum in communication with said receiver whereby liquid refrigerant can drain by gravity from the drum to the receiver.

4. A refrigeration system comprising a compressor, a condenser, a liquid receiver, an evaporator, a liquid conduit for connecting said compressor to said evaporator through said condenser and receiver, a suction conduit connecting said evaporator to said compressor for returning refrigerant to said compressor, a valve in each of said liquid and suction conduits, a temperature controller for actuating said liquid and suction conduit valves to thereby control said evaporator during normal operation, a liquid transfer drum, conduit means between said evaporator and said drum and having a combination electrically operated and pressure relief valve therein, a drain conduit between said drum and said receiver, an equalizer conduit between said drum and said condenser, said drain and equalizer conduits each having a valve therein, a vent conduit between said drum and the suction side of the system and having a valve therein, a hot gas line between the compressor and said evaporator and having a valve therein, and electrical control means for actuating said valves and adapted to initiate a defrosting cycle by (1) closing said liquid and suction conduit valves, (2) closing said drain and equalizer conduit valves, and (3) opening said hot gas line valve to thereby permit hot gas to enter and defrost said evaporator, said relief valve being adapted to open When pressure in said evaporator exceeds a predetermined amount to thereby permit liquid.

refrigerant to pass from said evaporator to said drum, said control means also being adapted at the end of the defrost cycle to isolate said drum from the suction side of the system and place said drum in communication with said receiver whereby liquid refrigerant can drain by gravity from the drum to the receiver.

5. A refrigeration system comprising a compressor, a condenser, a liquid receiver, an evaporator, a liquid conduit for connecting said compressor to said evaporator through said condenser and receiver, a suction conduit connecting said evaporator to said compressor for returning refrigerant to said compressor, a valve in each of said liquid and suction conduits, a temperature controller for actuating said liquid and suction conduit valves to thereby control said evaporator during normal refrigerating operation, a liquid transfer drum, conduit means between said evaporator and said drum and having a combination electrically operated and pressure relief valve therein, a drain conduit between said drum and said receiver, an equalizer conduit between said drum and said condenser, said drain and equalizer conduits each having a valve therein, a vent conduit between said drum and the suction side of the system and having a valve therein, a hot gas line between the compressor and said evaporator and having a valve therein, and electrical control means for actuating said valves for a defrosting cycle and adapted to (1) close said liquid and suction conduit valves, (2) close said drain and equalizer conduit Vales, (3) open said vent conduit valve and (4) open said hot gas line valve to thereby permit hot gas to enter and defrost said evaporator and place said drum in communication with the suction side of the system, said relief valve being adapted to open when pressure in said evaporator exceeds a predetermined amount to thereby permit liquid refrigerant to pass from said evaporator to said drum, said control means also adapted at the end of the defrost cycle to close said vent conduit valve and open said valves in said drain and equalizer conduits, to thereby place said drum in communication with said condenser and receiver and isolate said drum from the suction side of said system whereby liquid refrigerant can drain by gravity from the drum to the receiver.

References Cited in the file of this patent UNITED STATES PATENTS 2,525,560 Pabst Oct. 10, 1950 2,729,950 Toothman Jan. 10, 1956 2,770,104 Sweynor Nov. 13, 1956 2,778,195 Christensen J an. 22, 1956 2,841,962 Richards July 8, 1958

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