US2694904A - Defrosting arrangement for refrigeration systems - Google Patents

Description

Nov. 23, 1954 H. "r. LANGE HAL DEFROSTING ARRANGEMENT FOR REFRIGERATION SYSTEMS Filed Oct. 12, 1951 zzvmvroxs. HAROLD T L-ANGE CHARLES C. GROTE 2/7 United States Patent DEFROSTIN G CEMENT FOR REFRIGERATION .SYSTEMS Harold T. Lange, Webster Groves, Mo. ,.audCharles C. Grote, Dobbs Ferry, :N. Y., assignors'tofsporlan Valve Co., Inc., St. Louis, Mo.,a corporation of Missouri Application'october 12, 195-1, Serlal'No. 251,040

4 Claims. ,(Cl.62--.3)

This invention relates to improvements in defrosting arrangements for refrigeration systems, and more particularly to re-evaporating provisions in the suction line, with controls therefor, in ,a .compressor-ccndenser-evaporator type of system provided with a hot gas evaporatordefrosting circuit.

We :are aware that numerous systems have heretofore been devised for utilizing either directly, hot gases discharged directly by the compressor, or condenser "heat, for the purpose of meltingawaythefrost and ice coating periodically accumulating on and near the usual refrigerant evaporators. However, as far as "has been ascertained after a considerable investigation .of earlier arrangements, none of these .has fully satisfactorily realized its intended purpose, at least without introducing to the system some unsatisfactory and objectionable performance characteristics. Principal among such objections experienced with earlier-arrangements may be .noted a con siderable reduction in efiiciency of the system; atendency under defrosting conditions for .liquid .to slug lover to the compressor and objectionably .or dangerously ,high pressure conditions in parts of the system, sometimes including the compressor, tolmention but. a few .of ,the difficulties heretofore experienced ,and usually accepted as necessary incidents of automatic defrosting. ,It-is accordingly a major objective of the presentimprovements to .obviate each and. all wof-the difficulties noted, and to realize a fully automatic arrangement for periodically freeing the evaporator of frostaccumulation.

A further valuable objective of the present improvements is realized in an arrangement "for vthegeneral purpose noted, and which utilizes .as one of the controls for selectively ,.interposing or excludinga rerevaporator in the suction side of the system, .a thermostaticexpansion valve which is or maybe of some conventional construction, with or withoutminormodifications.

.A further object of the currentfimprovements is realized in an arrangement such .thatthe addition of the controls andfacilities for automatically defrosting. a system which may otherwise be conventional, does notappreciably increase the power requirement of thesystem, does not in- L troduce an excessive pressure-drop ,in the suction side during .the normal refrigerating cycle, and which serves to realize dependablytfrost-iree.evaporator conditions, all without any noteworthy impairment of overall efficiency of the system.

Yet a further and important objective of the present improvements .is .realizedina novel construction and circuit location of a bypass valve unit which functions, coordinately with an auxiliary thermostatic expansion valve in the low side of the system, to effect an automaticselection'between'branches of the'suction line utilized respectively'for vapor return'withminimal pressure drop-during normal refrigeration, and for re-evaporation.

The foregoing and numerous other-objects of themesent improvements will appear from thefollowing detailed description of a presently preferred exemplary arrangement, particularly when "considered in connection with the accompanying drawings thereof, in which:

Fig. 1 isa'schematic or diagrammatic arrangement of elements and tubing constituting'aicompressor condenserevaporator refrigeration-system, includingthe improved defrosting facilities, and

Fig. 2 is'a vertical sectional elevationofa-bypass valve unit utilized forrcontrol-o'fiflow selectively through *the branches of thesuctionlineo'f-the system ofFig.--1.

Referring now by characters of reference :to the'draw- 2,694,904 Patented Nov. 23, 1954 ing, and *fi'rst to Fig. 1, those 'units which are or may be of well known and conventional character and disposition in the fiow'circuit, aredesignated by reference letters, these including a motor driven compressor C, the discharge of'which is supplied to the condenser 'CN, thence to the receiver R, the liquid from which flows through'the liquid line LL to supply'the main evaporator EV. in the line LL and forming a part thereof, is a heat interchanger generally indicated at 10, and shown diagrammatically as including-a jacket portion 11 and an inner flow element 12 forming a part of the suction line, as will appear. From the jacket 11 liquid flow is conducted through a continuationof the line LL to 'a thermostatic expansion valve TEVl. This is or may be of a conventional type and requires no detailed description, it being noted that this unit is thermally responsive to -a fluid charge in its motor system connected to a bulb B1 in thermal exchange relation with the-conduit or tubing at or-near the evaporator outlet.

The evaporator outlet is connected to suction line SHL, a part of which is constituted by the inner circuit 12 of the heat interchanger 10, whence the line ,SL is continued as will hereinafter be described.

The evaporator EV is shown in typical installation with its coils in the line 'offlow of the ail-stream from a propeller fan PF driven by fan motor FM.

As a convenient means forsupplying asource-of heat to the evaporator for purposes of defrosting same, preferably at more or less definite 'yet regulable intervals, there is provided a'hot gas line 13 leading directly from the compressor through a strainer 14 'viaa solenoid valve 15, the line 13 continuing into communication with the evaporator-Etta point 16 which is betweenthe valve T-EVl and the evaporator. The cooled space is shown, merely for completeness-as bounded by walls -W and-shown as preferred, with;the:major operative elements of the system in a mechanical compartment MC. For completeness it may also be noted as desirable to provide, for removal of water resulting from defrosting, a drain line generally indicated at 17.

Although the specific instrumentalities for :periodicity of defrostingconstitute per so .no part of the present improvements, it is noted for completeness'that in the present system there is provided a dcfrosttimer DT, the circuit controlled thereby serving toenergize the solenoidvalve 15 for opening of same to supply the hot gas line 1-3 at predetermined intervals. Although the arrangement shown in the accompanyingdrawing-is merely suggestive and is introduced solely for completeness, the electrical circuits are noted as distinguished by dotted ,lines over the lines of tubing serving to complete the fiow circuit between the several elements of the refrigeration system.

The points of major novelty in the current system'are found in novel items of vcontrol apparatus'and' the arrangementthereof in the low pressure side of the system, sometimes referred to beyond the evaporator, as the suction line. It will be noted that the line SL -is divided -or branched, beginning at point 20. .A first such branch, utilized primarily during the defrostingcycle, is identified with'the line of tubing 21 containing and controlled by a thermostatic expansion valve TEV2, thence proceeding into and through a re-evaporator unit generally-indicated at 22, the coil 23 within whichforms a part of the branch 21 of the suction line. A second propeller fan PF 2 driven by a fan motor FM2 utilizes the usually relatively warm ambient air within the space MC as the heat exchange medium over the coils 23 of the unit'22, with the'eifect of vaporizing any liquid refrigerant which may exist in this portion of the suctionline, thus effectively preventing the return of same to the compressor. A-drain connection 24 is' provided from the re-evaporator'unit 22 to remove any condensatetherefrom.

The branch 21 containing the re-evaporator unit 22is continued thereoeyond to a connection orfitting 25 0f a bypass valve unit generally designated at 26, and hereinafter described in more detail. The final section of suction line SLF between the bypass valve unit 26 and the compressor is shown as connected to the unit 26 through-a single outlet fitting 27.

It will of course be understood that many of the usual control accessories such as a motor starter-MSandadditional valves, all indicated by usual legend, will serve to complete the system and to facilitate usual control operations and servicing of the several elements.

There has thus far been described only one of the dual branches of the suction line SL, namely that which provides for flow through the re-evaporator, primarily under defrosting conditions. It should be noted that the normally used suction line or otherwise expressed, that portion of the suction line which serves to complete the return connection between the evaporator and compressor during normal refrigerant operation, comprises a branch or leg 30 originating at point 20 in line SL, thence continuing into an evaporator inlet fitting 31 directed into the lowermost chamber 32 of the bypass valve unit, as will later be more fully described, it being presently noted that communication between line 30 via chamber 32 and fitting 27 into the final section SLF of the suction line, is under control of a valve element 33 subject to actuation by a fluid-charged bellows 34 in an upper chamber 35 of the unit 26, the valve-opening actuation of bellows 34 being opposed by a valve return spring 36 which is or may be equipped with spring-loading adjustment means (not shown).

Proceeding now to further detail of the preferred form of bypass valve, particularly as shown by Fig. 2, it should first be noted that the suction line SL is of a generous cross section and that the inlet and outlet fittings particularly those designated at 31 and 27 are similarly of ample cross section, so as to realize only a minimum pressure-drop through the unit 26. The valve and valve port of the unit 26 are similarly designed so as to keep at a minimum, any obstruction to normal flow through this unit during the normal operating cycle. The valve unit generally designated at 26 includes in addition to the major elements heretofore designated, a casing which for example, may be of a generally cylindrical form and designated at 37. Presupposing without limitation, a vertical mounting of the bypass valve unit, the casing body or shell will include a bolted sealed upper head 40, and a similar removable bottom closure or head 41. The metallic bellows 34 is located in the upper chamber 35 of the bypass unit, and includes rigid end heads 42 and sealed thereto the metallic bellows structure of expansiblecontractible character shown at 43. A charging tube 44 facilitates introduction of a fluid charge, the tube being sealed off as well known after supplying such fluid. This motor element for actuating the valve 33 is by preference supplied with a predetermined charge which approximates the characteristics of the refrigerant in the system,.and as a matter of usual convenience may consist of a finite quantity of such refrigerant.

A valve stem or push rod indicated at 45 is directly actuated by the lower head 42 of the bellows. It is guidedly constrained to reciprocal movement through a guide element 46 forming a part of a valve cage 47, it being noted that the element 46 may consist merely of a bridge extending diametrally of the cage 47 so as to present virtually no obstruction of freedom of flow between the upper and lower chambers 35 and 32 respectively, when the valve 33 is open. It will appear that the cage 47, threaded into a transverse partition 50, provides along its lower margin a valve seat 51 engaging the valve proper 33.

It is an important feature of the arrangement shown that the valve 33 and the valve port, the latter defined by seat 51, both be of ample dimensions for reasons stated, and it is greatly preferred that the valve 33 be opened under expansion of the bellows, generally indicated at 34, in a direction against the flow from the evaporator to the compressor, or otherwise stated, from inlet fitting 31 via the valve port, to the compressor connection 27.

The function and operation of the several elements and their relation mutually and to the system, will have become at least in part apparent from the structure described; however, it may be noted for completeness that during normal refrigerating operation of the system, line 4 the re-evaporator. However, the much lower pressure" drop through line 30 than line 21, results in a preponderance of flow through leg 30, unit 26 and line SLF.

Defrosting is periodically initiated by timer DT, acting to open valve 15 and the hot gas line 13 to the evaporator relieving same of ice and frost accumulation. Evaporator pressure rises sharply during defrosting, which pressure increase coacts with the spring 36 to close valve 33 against bellows 34, thus closing the bypass branch 30-26. Valve TEV2 being open, the closure of valve 33 compels return flow during defrosting by way of the reevaporator unit 22. During defrosting the superheat decreases, which fact further conduces to closing of valve 33. Since, under these conditions, defrosting return flow occurs solely through the unit 22, wet vapor or liquid acting on bulb B2 throttles valve TEV2, and prevents return of liquid to the compressor. This situation prevails until shortly after the defrost cycle, whereupon the rise in superheat and the decreasing pressure drop across valve 33 again causes full opening of both valves 33 and TEV2. It is noted that the re-evaporator line 2123 is always open into line SLF, through chamber 35 of the valve unit 26. Upon completion of the defrosting cycle and perhaps a short interval thereafter, the relations of the bypass valve and thermostatic expansion valve TEV2 will again be relatively reversed, so as to reestablish the refrigeration cycle upon completion of defrosting. Upon closure of the solenoid valve 15, the normal refrigeration functions of the compressor, condenser and evaporator will of course be resumed.

Experience has shown that during and through a short period following the actual defrosting of the evaportor, liquid from the evaporator returns to the re-evaporator wherein it is vaporized and returned to the compressor. It is of course obviously necessary to prevent the return of liquid to the compressor, either through the bypass line 30-26, or otherwise. It is for the purpose of regulating the amount of liquid refrigerant delivered to the reevaporator that the unit TEV2 is utilized. This is or may be a conventional thermostatic expansion valve as described, under the thermal or sensing control of a bulb B2 which may be and is by preference located in adjacence to the re-evaporator branch line after the outlet of unit 22 and ahead of the bypass valve 26 as shown.

It has been found highly desirable during the normal refrigerating cycle, to bypass the main flow of refrigerant around the re-evaporator line after the defrost cycle has been completed and after the evaporator EV is again normally cooling the load. The bypass valve unit accomplishes this purpose and function, in that it serves to prevent the return of liquid refrigerant to the compressor during the defront cycle. The unit 26 is also specially constructed to provide a portion of the low pressure-drop path between the evaporator EV and the compressor C during the normal refrigerating cycle. Furthermore, the construction and arrangement in the flow circuit of the unit 26, gas-charged to predetermined pressure, is such that it acts to limit the pressure in the compressor crank case to a predetermined maximum, this and the aforesaid results being accomplished fully automatically.

By way of further discussion of operation it may be noted that during and for a short time after the defrosting cycle, when liquid is returning from the evaporator to the re-evaporator, the temperature of the suction line at the point where the bulb B2 is located, will show a superheat corresponding to the setting of the unit TEV2. It should be noted that the spring pressure in the bypass valve 26 should be such that the valve 33 will remain closed so long as superheat is of the order of 5-l0 or whatever range of temperature corresponds to the setting of the unit TEV2.

After the liquid in the suction line has been removed by the re-evaporator, the superheat at the outlet of unit 22 will increase to a value of the order of 15, for example, whereupon the pressure in the motor unit 34 of the bypass valve will overcome the loading of spring 36 which fact and the reduced pressure differential across valve 33 will cause same to open, there being assumed a charge in the unit 34 of the same refrigerant as used in the system. Opening of valve 33 as noted, will reestablish flow through line 30, 31, 33, 27 and SLF to the compressor. In case superheat reduces, for example from 15 to any considerably lower value, the valve 33 will again close.

The provision of a relatively large valve and valve port in the bypass unit 26 assures a low pressure-drop path of flow of generous section fully between the evaporator and the compressor during normal refrigeration operation. Also, by virtue .if the relatively large port or valve seat aperture, there will be realized a highly favorable regulation of the bypass valve due to the relatively higher evaporator pressures obtaining during and perhaps for a minor period of time following the defrost cycle.

Although none of the pressure or temperature values herein stated should be construed as representative of exact conditions but rather as examples or illustrations, they are usually similarly proportioned in different systems. Thus it may be noted that during defrosting operation an evaporator pressure may not unexpectedly attain a value of fifty pounds, and will normally be reduced say to a ten pound value or lower, during the normal refrigeration cycle. By reason of the fact that the flow of refrigerant through the bypass valve is in a valve-closing direction, it will exert a definite valve closing force of the order of 20 p. s. i. during the refrigeration cycle. This valve-closing effect requires extra superheat in the region of the valve motor bellows, and results in balancing of the bypass valve at a superheat higher than During the refrigeration cycle say with a pressure of 10 lbs. in the evaporator, the aforesaid valve-closing force of 10 to p. s. i. will be reduced to a value for example, of the order of 1 p. s. i., which reduction of pressure across the valve disc permits the valve to balance at a lower superheat, causing the valve to open more widely with additional flow area through the port, all of which is desirable in minimizing pressure drop. For reasons stated it will appear as highly desirable that the valve 33 open in a direction against the direction of flow, as shown.

It may be further noted that the arrangement described will act to facilitate pumping out the evaporator when desired. For such purpose the liquid inlet to the evaporator is shut off, resulting in a higher superheat at the outlet end of the re-evaporator, such as quickly and fully to open the bypass valve which facilitates this operation.

It will now have appeared that the novel control apparatus described and the novel arrangement thereof for the purposes noted, will serve fully to realize the several objectives and purposes hereinabove expressly stated, as well as others implied. Although the invention has been described by particularized reference to a single preferred embodiment, the detail of description should be understood solely as instructive rather than as limiting, numerous variants being possible both in structure and arrangement, without departure from the full intended scope of the appended claims.

We claim as our invention:

1. In a refrigerating system including a compressor, a condenser and an evaporator together with means for driving the compressor, and tubing interconnecting the said units in a closed system, a hot gas conduit for defrosting purposes connected directly from the compressor to the evaporator inlet, that portion of the tubing between the evaporator and compressor including a first branch, a re-evaporator in said first branch, a thermostatic expansion valve controlling admission of flow to said first branch and responsive to thermal conditions beyond the re-evaporator, a second or bypass branch connected into the suction line ahead of said thermostatic expansion valve and a bypass valve of thermal responsive character connected to both of said branches and selectively controlling flow therefrom through a remainder of the suction line to the compressor, said bypass valve including a fluid-charged valve motor unit located substantially directly in the line of flow from either of said branches through said remainder of the suction line to the compressor, said bypass valve being actuated by said motor unit in response to thermal conditions and pressure differentials in the first branch beyond the reevaporator and in the bypass branch.

2. In a refrigeration system, a compressor, a condenser, an evaporator, means for driving the compressor, tubing interconnecting the compressor, condenser and evaporator in a closed system, a hot gas conduit for defrosting purposes between the compressor and the evaporator inlet, the tubing between the evaporator and compressor including a first branch, a re-evaporator in and forming a part of said first branch, a thermostatic expansion valve controlling the flow through said first branch and responsive to thermal conditions in the suction side of the system beyond the re-evaporator, a branch serving to bypass a flow around the first said branch, a bypass valve in the by-pass branch, the bypass valve including a fluid-charged expansible motor member and a connected valve element, said motor member being directly in the line of fluid flow from the re-evaporator to the compressor, said valve element being actuated by said motor member in response to thermal conditions and pressure differentials of the first branch and the bypass branch.

3. In a refrigeration system, a compressor, a condenser, an evaporator, tubing interconnecting the said units in a closed system, and means for driving the compressor, a hot gas conduit for defrosting purposes constituting a connection directly between the compressor and evaporator, valve means controlling the hot gas conduit, a thermostatic expansion valve located at the inlet end of the evaporator, the suction line comprised of portions of said tubing beyond the evaporator and including a first branch line, a re-evaporator in said first line, a second thermostatic expansion valve controlling admission of flow to said first line, and a second or bypass branch line, a bypass valve unit of thermal responsive character and including a fluid-charged motor member and a valve element connected to the motor member for actuation thereby, said bypass valve element being in controlling relation to the bypass line, and the bypass unit providing a constantly open portion of the first said branch line, saidvalve element being actuated in response to thermal influences and pressure differentials between the first branch line and the bypass branch line, the bypass line being characterized by a substantially minimal pressure drop therethrough and the re-evaporator line (being characterized by a substantially higher pressure rop.

4. In a refrigeration system, a compressor, a condenser, an evaporator, tubing interconnecting the said units in a closed system, and means for driving the compressor, a hot gas conduit for defrosting purposes constituting a connection directly between the compressor and evaporator, valve means controlling the hot gas conduit, means for periodically actuating said valve means to open the hot gas conduit, a thermostatic expansion valve located at the inlet end of the evaporator, the hot gas conduit having a connection to the evaporator between same and the thermostatic expansion valve, the suction line comprised of portions of said tubing beyond the evaporator and including a first branch line, a re-evaporator in said first line, a second thermostatic expansion valve controlling admission of flow to said first line, and a second or bypass branch line, a bypass valve unit of thermal responsive character and including a fluid-charged motor member and a valve element connected to the motor member for actuation thereby, said bypass valve element being in controlling relation to and urged toward closing position by flow and pressure conditions in the bypass line, and the bypass unit providing a constantly open portion of the first branch line which is connected to the bypass branch line by said bypass valve element, the motor member being so located as to be directly thermally influenced by flow through either of the branch lines, the bypass line being characterized by a substantially minimal pressure drop therethrough and the reevaporator line being characterized by a substantially higher pressure drop.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,326,096 Dillman Aug. 3, 1943 2,342,566 Wofert Feb. 22, 1944 2,520,446 Thrush Aug. 29, 1950 2,526,379 Maseritz Oct. 17, 1950 2,530,440 Nussbaum Nov. 21, 1950

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