US2403818A - Refrigeration system - Google Patents

Description

My 1946- w. L. MOGRATH 2,403,818

' I REFRIGERATION SYSTEM I Filed Aug 26,. 1943 2 Sheets-Sheet 1 Zmbentor Q WILL/HM L. M E /f/U'H Gttorneg Patentecl July 9, 1946 U NIT ED STATES PATENT OFF lC E I BEFRIG'ERATIONSYSTEM William L. McGrath, Syracuse, N. Y., assignor to Minneapolis-Honeywell Regulator Company,.

Minneapolis, Minn., a corporation ofDelaware Application August 26, 1943, Serial No. 500,043

S-Glaims. l The present invention relatesin general tocontrol means for a refrigeration system.

.-A conventional refrigeration system may achieve a measure of control by operating or stopping a compressor in response to a condition of the medium being :cooled .and by using a thermostatic expansion valve to control the fiow of refrigerant to the'ev'aporator. Limit devices comprisin :a cut-out opened by'exce'ssive head pressures and a cut-out opened by abnormallylow suction pressures are sometimes connected in series with the compressor'control means to prevent injury to .the mechanism. The control sys-" tem thus outlined is suificient for some installations, but is not'adequate for other applications, especially under conditions of light load, With light .loads and a throttled flow of refrigerant, the evaporator is pumped down quiter'apidly and short cycling takes place, Attempts have been made to prevent short cycling'by throttling' the suction, but thi's'may cause abnormallylow suction pressure at the compressor and result in mechanical difficulties.

Other attempts-ateontrol hav'e included the use oi'a by-pass:from the hot gas line to the suction line, but this has resulted ingases of excessively high-temperature damaging the compressor. The present system supplements the control exercised by a thermostatic expansion valve over an evaporator by by-passing hot gaseous refrigerant around the condenser and through said-evaporator. 1

It is, therefore, an object of the present invention to improve the control of a refrigerationsystem by by-passing gaseous refrigerant-around the condenser and passing same through the evaporator. I V

It is a further object to control the conditions under which cooling maytake place by preventing the evaporator pressure and temperature from dropping below a predetermined point-said pressure being maintained by 'by-passed gaseous refrigerant. v

The by-pass system of control as "previously known is not :well adapted to multiple fixture operation, for the building up of suction pressureby any one of a pluralit of by-passes'a'fiects' the suction pressure of each of theevaporators. It is thus .a further object of this invention to p'rovide .a system of control utilizing by-passed refrigerant .whichmay be used with multiple fixture installations.

It is aifurther object of this invention to-supplement the control of 1a thermostatic expansion 2 of the refrigerant passed through said thermostatic expansion valve,

The old by-pass system of control, as applied to a refrigeration system, frequently results in over heatedgases being supplied the compressor,

blltihis dilifilil ty is ObViatGd in the presentinstance by passing the Icy-passed refrigerant through the evaporator where said gases are cooled by the-"expanding liquid refrigerant associated therewith. It is, therefore, "an object of this invention to providea system of by-pass controlfor a refrigeration system inwhich'thegases in "the suction means are maintained at a safe temperature.

'I't'is a fur' therdbje'ct of the present invention to supplement the control of .a thermostatic expansion valve bypassing both liquid and gaseous refrigerantthrougha fixed orifice preceding" said expansion valve. Other objects of this invention will become apparent from the following description and from the appended claims.

For a full'disclosure of myinvention, reference is made to the following specification and accompanying drawings, in which:

Figure l'illustrates diagrammatically a multiple fixture refrigeration system embodying the present control system;

Figure 2 shows a modified system similar to thatof Figure l,but using only asingle evaporator "an'da differently located 'by-pass; and

Figure 3-sh'ows asystem somewhat similar to that 'of Figure 2 in which the by-pass incorporates a constant pressure reducing valve.

Referringto Figure LcOmpressor Ill, drivenby motor! l,'di'schargesthrough pipe 12 to condenser 'l3and toby-pass branch M. A liquid line 15 conveys liquified refrigerant from condenser 13 to conduits l9, '2fl,-and 2| which-connect liquid line l5 to evaporators l6, I1, and I8, respectively. Each evaporator is controlled by a thermostatic expansionvalveand an associated by-passevapvalve over an evaporator by varyingiithequality i5 orator it being provided witha thermostatic expansion valve 22 *and bypass -23 evaporator 1 is provided with expansion valve 24 and by-pass while evaporator 1 is equipped with'expansiOn valve 26 and a by-pass 21. Evaporators i6, 11, and 1 8 arec'onnected to main suction mean-s 2 8 163 suction -means '29, 30, and GI, respectively,

Main-'si'ietion means 28 may be provided with, if desired, a throttling'valve 32 controlled by pressure controller 33. -Compre'ssor moto H may be controlled by means "including switch means 34 connected t'o suction means "28 -by tube 35. switch-means 34'is-als0 connected to the highpressure refrigerant line I2 by tube. De-

vice 54 may comprise a conventional low suction pressure cut-out and a high head pressure cutout in series therewith to prevent operation of compressor motor II in the event of an excessive head pressure or extremely low suction pressure. Further, said device 34 may comprise a device such as described in the patent application of Carl G. Kronmiller, Serial No. 371,001, filed December 20, 1940, now Patent No. 2,377,503, issued June 5, 1945.

Hot gas by-pass means 23, 25, and 21 re fitted with modulating valve means 40, 4| and 42, respectively. Valve means 40 is controlled by thermostatic means 43. Thermostatic means 43 comprises a volatile fluid filled bulb 44 and a connected bellows means 45, said bellows operating an arm 45 over potentiometer coil 41. Valve 4| is controlled by thermostatic device 48, similar to 43; and valve 42 is controlled by thermostatic device 49, also similar to 43. The valve means 48, 4| and 42 are each powered by a modulating motor of the sort described in the patent of D. G. Taylor, No. 2,028,110.

If desired, conduits I9, 20, and 2| may be fitted with check valves 50, 5| and 52, respectively, said check valves being located up stream in said conduits above the confluence of the bypassed refrigerant and the liquid refrigerant, said check valves permitting flow only toward their respective evaporators.

Downstream of the confluence of the by-pass 25 and liquid line 20, a fixed orifice 54 may be provided ahead of expansion valve 24. The fixed orifice is proportioned to permit only sufiicient liquid refrigerant to pass therethrough to operate the associated evaporator at full capacity. This orifice supplements the control, in association with a by-pass, of thermostatic expansion valve 24. The introduction of by-passed gaseous refrigerant into the liquid line ahead of said orifice, tends to decrease the density of the refrigerant passin through said orifice and the expansion valve, and thereby results in a lesser flow, by weight, of refrigerant to the associated evaporator, thereby resulting in less refrigeration being possible at said evaporator. Further, the heat of the refrigerant is increased by the admixed hot gases, hence less heat must be added to same to give a predetermined number of degrees of superheat. The orifice also helps to uniformly mix the gaseous and liquid refrigerant. As the thermostatic expansion valve also forms, in effect, an orifice, supplementary orifice means may be used or not as a matter of choice.

The relation and action of the various parts will be further illustrated in the following operation schedule.

Operation of Figure 1 With the switches in device 34 in closed position, motor may be started in any convenient manner such as by closing switch 60, the circuit being: line 6i, wire 62, switch 60, wire 63, switch device 34, wire 64, motor H, wire 65, and line 66.

With motor II and compressor l operating, gaseous refrigerant is discharged through pipe l2 into condenser I3 and to by-pass line I4. Heat is extracted from the refrigerant in condenser l3 in any convenient manner and the refrigerant is thereby liquified. Liquid refrigerant from condenser I3 is led to the evaporators by branch |5, evaporator l6 obtaining its refrigerant from branch I through conduit [9, including check valve 50 and thermostatic expansion valve 22, said refrigerant being exhausted through suction means 29 to main suction means 28. Bellows 45, as shown, is in a fully retracted position due to the satisfied condition of the medium cooled by evaporator l6; bulb 44, connected to bellows 45, being responsive to the temperature of said medium. Arm 46 is therefore at the extreme left of potentiometer coil 41 and has driven motor valve 45, normally closed, to a Wide open position. With valve 43 open, a fiow of gaseous refrigerant enters conduit I9, mixes with. liquid refrigerant from branch l5; and the mixture passes on to feed expansion valve 22, evaporator i5, pipe 29 and main suction means 28. With small flows of hot gas and with sub-cooled liquid refrigerant, the gas will tend to liquify and the amount of sub-cooling will be lessened. At large flows of gaseous refrigerant, where the amount of sub-cooling is insuflicient to liquify said gas, a mixture of gaseous and liquid refrigerant results. Under some conditions, the by-passed gaseous refrigerant may enter conduit 9 at a pressure exceeding that of the refrigerant in pipe I5, thus preventing flow from 5 into l9. However, check valve 5|! prevents the by-pass gases from flowing into l5, thus preventing said by-pass from interfering with the control of other evaporators. The flow of gaseous refrigerant through evaporator l6 prevents that evaporator from being pumped down to a low pressure and temperature. Expansion valve 22 tends to maintain an open position as the by-pass gases are added to the liquid refrigerant, for the higher the percentage of gas entering the evaporator, the less the heat needed to give the required number of degrees of superheat to open said expanslon valve. Under extreme conditions in which hot, gaseous refrigerant only is flowing through the expansionvalve, the valve may remain wide open, the rate of flow being limited by friction and by the restrictions offered by valve 22 and other means. By raising the temperature of the evaporator its cooling effect is lessened, thereby providing temperature control of the medium being cooled. The capacity of each hot gas by-pass may be limited in such manner that the maximum amount of gas passing through same Will be only that necessary to control the associated evaporator. Such limiting means may comprise an orifice or other such restriction in the'gas line or may comprise an adjustment of the electrical means controlling the modulating valve in such manner that the valve can only be opened a desired amount.

Thermostatic bulb H and its associated bellows 72, responsive to the conditions of the medium cooled by evaporato [1, have driven arm 73 to about the mid point of coil 14, thereby driving valve 4| partially open. With valve 4| partially open, hot gas flows through pipe |4,.by-pass line 25 and into conduit 25 where it mixes with liquid refrigerant flowing from branch |5 into said conduit 26. The mixture of gas and liquid refrigerant flows through orifice 54 where it is further mixed, and then through expansion valve 24, evaporator I! and pipe 30 into main suction means 28'. Because the density of the refrigerant passing through orifice 54 ha been lowered by the introduction of gaseous refrigerant the total quantity of refrigerant flowing through expansion valve 24 and evaporator IT, is reduced and the'heat of same is increased, hence comparatively little heat is required to be added through the evaporator to give sufficient superheat to open the expansion valve 24 and raise the pressure and temperaturewithin the evaporator; The capacity of evaporator: is is thereby controllably reducedi- Bulb "I fiandbellows I1 ofthe thermostatic device tit-indicate a condition of maximum demand and arm 78 1s at the: extreme rightof' coil I 9, whereby valve 42 remains in closedv position and no gas" is by-passed; Refrigerant, therefore,

passes through pipe I5, conduit 2 I, thermostatic expan'sion valve 2t, evaporator I 3 and pipe'3-i to main suction means-2'3 in v a conventional manner and evaporator I8 operates at full capacity. If used, the throttling valve ill-introduced in main suction. means I 28 is-control1ed by pressure of gaseous. refrigerant. Under someconditions, however, this control isnot needed for the'power demand of a compressor riseswith increased suction-pressure only-to apredetermined amountand with further rise in suction pressure, power consumption falls off;

Figure 2 In Figure 2; compressor IDI, driven by motor I62; discharges through pipe I53 to condenser IM'and'by-pass line H. Condenser I04 sup- 7 pliesliquidrefrigerant through pipe I05 to thermostatic expansion valve I01 and evaporator Hill, said evaporator being connected by main suction'means' I59 to compressor I'IlI. Compressor IGI= is'protectedby a devicetlw'similar to 34 in the. above example, said. device IIB being connected to suction means IBB'b'y tube II I, and to high'pressure pipe I03 by tube H2. By-pa-ss W5 is fitted'with a normally closed'modul'ating valve II3 under. the control of thermostatic device H4, said'by-pass I95 being, connected'to evaporator lilflimmediatelydown stream of expansion valve I01. Thermostatic expansion valve Ill'imay be of the conventional sort, but preferably has its pressure chamber connected to suction means I09 by equalizer line I15, there being les pressure fluctuation at the exhaust endof evaporator I68 than at the headendwhen the by-passmeans are usedifor control.

' Thermostatic device I14 comprises bellows H6 and an associatedvolatile fluid filled bulb II'I; said bellows .I I6' actuating an arm H8 and movingsa'me over potentiometer coi1II9'.

Operation 0 1 Figure 2 AS in the previous example, compressor IflI and its'motor I92 may be controlled in any. convenient manner such as by manual switch E29, the circuit controlling motor I021 being: current supply wire I2'I, wire I22, switch.l20,.wire. I23, switch device Isl 0, wire. I 24; motor: and current supply :wire. I 26.

With the switches of-"device IIOin closed -po-' II'IZ, wire. I25,

sorIIH.

place; thesystem is operating at f-ulr capacity-.-

With light load and normal control this would means'of 'device III], and thus-'cause-un'duewear. and 'tear on mechanism. In-the present'example" as the demand becomes partially satisfied; arm- II8 is:drawn-across coil I I9 and operates valve I-'I-3*'from' closedto open'positionthereby permit ting by-passing-of refrigerant through pipe I05 In the position shown; arm" to evaporator I08. II8 is about halfway across coil H3, hence, valve" I I3-is partially'open; hot gas is being by.- passed into evaporator I68" where it adds heat and" raises thepressuretherein. As'the pressure within the evaporator is increased, its temperature is likewiseincreased and its cooling effect is "lessened, therebymaking"possible the balancing of therefrigerationsuppliedand 13116102111416 mand" and permitting continuous running of themechanism. When the demand for refrigeration, as determined by thermostatic device I'M, becomes satisfied, arm-"- II 8" isadvanced across coil 9 and" moves-va1ve- H3 toward open position therebyby passingmore gas to said-evaporator.

Anincreasein demand causes an expansion of bellows- H6 and drives I*I8 towardthe left of* I It thereby driving valve II 3 toward closed position and-permittingfull capacity-ofthe system as previously described;

In summary, afc'onventional system, as shown in- Figure 2 may be controlled by varying the pressure Withinthe evaporator by lay-passing gaseous refrigerant thereinto; By increasing thepressure within an" evaporator, the temperature of" same-will automatically be raised, thereby lessening its cooling effects. Further, by action of the thermostatic expansion valve means-,the gas passing from the evaporator has a temperature-* only a predetermined number of degrees above that corresponding to the pressure of the refrigerant within the evaporator and therefore within a safe'limit for inductioninto-compres- F ure 3- re 3, -a's noted, also shows by-passcontrol However, the system of a single evaporator. shown-in thisfigure may beused for plural evaporator ihs-ta'llatibns wherein the lower limit of temperaturedesired for each of the evaporators is the same: v

In: this figure; compressor I5! isdriven by motor- I5'2and' discharges through pipe I53 to condenser I54 'andbyJ-pa'ss pipe I552 Condenser I5'4 supplies'liquid refrigerant through pipe I56 to thermostatic expansion valve I51 and its asso- 'ciatedievaporator I58; said evaporator I58being connected by suction means I59 to compressor I5 I Hot -gas by-pass I includes a pressure re-- ducing valve-of'the constantpressure type, I66; said by-pass=connecting to evaporator I53 just down-stream of expansion valve I51. Motor I52 isprotected against overload" by high pressure cut-out I6I. connected to. line I53 by tube I62.

The operation of. the. motorv is, controlled by thermostatic. device I operating in series with closed and no :by-passin'g :oiirefrigerant taking;

device I619. Thermostatic device IE3 comprises bellows I64 and an associated bulb I65, said bel-. lows ractuating mercury switch means. I68 in such manner that when" a refrigeration demand is satisfied; contact is broken in said switch". When there is: an demand for refrigeration, contactis made;.by;said; switch: The;operatiomofthasys tem thus outlined will be brought out in the following schedule.

Operation of Figure 3 I63 closes a circuit and the compressor is started as follows: current supply wire I10, wir III, mercury switch I66, Wire I12, high pressure cutout IBI, wire Il3, motor I52, wire I14, and current supply wir I15. Assuming that valve ISO in by-pass I55 is closed, refrigeration takes place in a conventional manner. Gaseous refrigerant is compressed in compressor I5I, discharged through pipe I53 into condenser I54, and heat is removed from said refrigerant in said condenser in the usual manner, thus liquifying said refrigerant. Liquid refrigerant from condenser I54 goes through pipe I56 to thermostatic expansion valve I5! which feeds refrigerant into evaporator I58 wherein it is evaporated by heat extracted from the medium being cooled, and the resulting gaseous refrigerant goes through pipe I59 back to compressor I5! to be further compressed and to complete the cycle. Thermostatic expansion valve I5! adjusts the flow of refrigerant to evaporator I58 in such manner that the refrigerant flowing out of evaporator I58 will have a predetermined number of degrees of superheat. Under light loads, with a system functioning in a conventional manner as abov outlined, compressor I 5i will be frequently stopped and started in response to thermostatic device I63. Further, with light loads, the flow of refrigerant through thermostatic expansion valve I51 is considerably reduced and compressor I5I tends to pump evaporator I58 down to very low pressures. Under some conditions of cooling, this is not objectionable; but in other cases the very low suction pressures obtained result in bad running of the compressor and also result in excessive dehumidification of the medium being treated by said evaporator. It is the function of by-pass I55 and its associated valve I68 to provide a lower limit of pressure and temperature for said evaporator I58 to thereby limit the dehumidifying effect of said evaporator and to protect said compressor from unduly low operating pressure.

In practice, the lowest pressure and temperature desired at said evaporator I58 is determined, both from the standpoint of dehumidification and from the effect on the compressing equipment. With a pressure for I58 determined, valve IE8 is set to open at that pressure. In operation, thesystem as thus outlined will operate in a strictly conventional manner until the vaporator pressure reaches the predetermined low limit, at which point valve It!) opens and permits hot gaseous refrigerant to flow through by-pass I55 into said evaporator in sufficient quantities to maintain said predetermined pressure. The minimum pressure of the evaporator being limited, the minimum temperature is also limited and its ability to dehumidify air being treated, or product being cooled, is limited. Obviously, valve I Bil may be set to open at any desired pressure. As before stated, a system of this sort may be used with a multiple evaporator installation if each, of the evaporators has the same lower limit of pressure and temperature.

In the examples of the invention above described, the systems have been controlled by means, responsive to temperature, but this is to be considered as illustrative only and not limiting the scope of the invention. Obviously, other condition responsive means such as humidity sensitive devices may be used instead of the thermostats shown and the present systems may be regulated to govern humidity rather than temperature. In the present case, psychrometric is considered descriptive of both temperature and humidity conditions. The protection means illustrated for the compressor motors is to be considered as illustrative only as these controls may be dispensed with, or any other conventional controls may be substituted therefor.

Many other modifications and adaptations of the present invention are readily apparent to one skilled in the art, hence the scope of the invention is to be determined by the following claims:

I claim as my invention:

1. In a refrigeration system, means controlling the capacity of an evaporator comprising a thermostatic expansion valve for controlling the flow of fluid to said evaporator, means for varying the density of refrigerant supplied to said thermostatic expansion valve means, and orifice means limiting the volume of said variable density refrigerant supplied to said expansion valve.

2. In a refrigerating system, in combination, a source of gaseous refrigerant underpressure, a supply of liquid refrigerant under less pressure, an expansion valve of the superheat responsive type, an evaporator, conduit means connecting said supply of liquid refrigerant to said expansion valve and evaporator, b-y-pass means comprising a valve connecting said source of gaseous refrigerant to said conduit at a point up-stream of the expansion valve, and means responsive to a psychrometric condition in control of said bypass valve.

3. In a refrigerating system, a source of gaseous refrigerant under pressure, a supply of liquid refrigerant under less pressure, a thermostatic expansion valve, an evaporator, conduit means connecting said supply of liquid refrigerant to said expansion valve and evaporator, by-pass means comprising a valve connecting said source of gaseous refrigerant to said conduit at a point up-stream of said expansion valve, means responsive to a psychrometric condition in control of said by-pass valve, and fixed orifice means in said conduit between the junction of said bypass means and conduit means and said expansion valve.

4. In a refrigerating system, a source of gaseous refrigerant under pressure, a supply of liquid refrigerant under less pressure, a plurality of evaporators, expansion valve means for each of said evaporators for controlling refrigerant flow thereto, conduit means connecting said supply of liquid refrigerant to said expansion valve means and said evaporators; and orifice means proportioned to pass suflicient liquid refrigerant to give the desired maximum refrigerating capacity to an associated evaporator, said orifice means being located up-stream from the expansion valve associated with said evaporator.

5. In a refrigerating system, a source of gaseous refrigerant under pressure, a supply of liquid refrigerant under less pressure, a plurality of evaporator means, conduitmeans including a Dlllrality of expansion valve means connecting said supply of liquid refrigerant to said plurality of evaporator means, flow limiting restriction means in said conduit means up-stream of at least one of said expansion valve means, and lay-pass means including valve means connecting said source of gaseous refrigerant to said conduit means up-stream of said expansion valve means and nip-stream of said restriction means.

6. In a refrigerating system, means supplying gaseous refrigerant under pressure, means supplying liquid refrigerant under less pressure, a plurality of evaporators, thermostatic expansion valve means for controlling each of said evaporators, conduit means connecting said liquid refrigerant supply means to said expansion valve means and said evaporators, and means mixing said compressed gaseous refrigerant with said liquid refrigerant up-stream of said expansion valve means to vary the density of the refrigerant passed through the same.

'7. In a refrigerating system, means supplying gaseous refrigerant under pressure, means supplying liquid refrigerant under less pressure, a plurality of evaporators, thermostatic expansion valve means for controlling each of said evaporators, conduit means connecting said liquid refri-gerant supply means to said expansion valve means and said evaporators, a plurality of bylpass means for mixing said gaseous refrigerant with said liquid refrigerant upstream of said expansion valve means to vary the density of the refrigerant passed through the same, and means including condition responsive means for controlling each of said by-pass means.

8. In a, refrigerating system, in combination, a source of gaseous refrigerant under pressure, a supplyof liquid refrigerant under less pressure, evaporator means, an expansion valve means for controlling refrigerant flow through said evaporator means, conduit means connecting said means supplying liquid refrigerant to said expansion valve means and said evaporator means, and bypass means including valve means for mixing said compressed gaseous refrigerant with said liquid refrigerant nip-stream of said expansion valve means for varying the density of the refrigerant passed through said expansion valve means, said by-epass valve means being of the two way sort and controlling the flow of the gaseous refrigerant.

WlLLIAM L. McGRATH.

Images