US2350408A - Direct expansion air conditioning control system - Google Patents

Description

June 6, 1944. w MCGRATH 2,350,408

DIRECT EXPANSION AIR CONDITIONING CONTROL SYSTEM Filed May 28, 1941 I 15 1 EF- 2 Sheet-Sheet 1 Aifornay" June 6,1944. w MCGRATH 2,350,408

DIRECT EXPANSION AIR CONDITIONING CONTROL SYSTEM Filed May 28, 1941. 2 Sheets-Sheet .2

3221 l I l l I I l l l I EVAPORATOR.

DIRECT ALI-me 2m 22? 2o; I 206 zoq EVAPORATOR.

AIR SUPPLY w u 0 m n 7 U z u- 2 L H 0 uluu. HMI V QH H u 89 u. 0 00 g 5 I L "1V7 I I m m m w. 9 l h u w u- 7 m w .I a 3 o m. T 1 ml o% P A V E a 0 u DIRECT ACTING I nvcnflor William. 11. M9 Graflu Patented June 6, 1944 UNITED "STATES PATENT FFICE DIRECT EXPANSION AIR CONDITIONING CONTROL SYSTEM William L. McGrath, Philadelphia, Pa., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application May 28, 1941, Serial No. 395,584

22 Claims.

This invention relates to control of direct expansion refrigerating apparatus, particularly" arrangements have heretofore been used to control such systems in attempting to maintain desired temperature and/or humidity conditions.

The desideratum to be fulfilled is that of controlling the amount of refrigeration produced while maintaining proper operating .conditions in the evaporator as respects the relative portions of the evaporator containing unevaporated refrigerant and dry gas and at the same time controlling the evaporator temperature so as to maintain the proper dehumidifying effect. The primary object of my invention is to fulfill the said desideratum in an improved and more ellicacious manner.

In the types of systems in question the amount of refrigeration produced is frequently varied by providing a. plurality of compressors feeding a common evaporator. "In the past it has been proposed to control the evaporator temperature by controlling the amount of refrigeration effected, that is, by controlling the operation of the com pressors in response to evaporator pressure.

However, to thus control the compressors insequence in response to evaporator pressure the pressure controller must have a relatively wide differential to prevent short cycling of the compressors from one step of operation to another and when the controller has such a wide diflerential undesirable variations in suction pressure,

that is, evaporator pressure, takes place. Ac-

cording to my invention, I control the evaporator pressure by controlling the admission of refrigerant through the expansion valve and this may be smoothly and uniformly done.

Specifically an object of my invention is to provide a control arrangement for direct expansion type refrigerating apparatus used for conditioning air wherein the amount of refrigerant circulated through the evaporator is varied and admission of refrigerant to the evaporator is controlled by a superheat type expansion valve having means whereby the valve is adjustable by evaporator pressure to maintain the evaporator pressure within limits nece sary for proper dehumidification.

Anotherobject is to control the amount of refrigerant circulated through the evaporator and to simultaneously control the pressure by one valve, and the superheat at the evaporator outlet I by another valve.

.Another object of my invention is to control the amount of refrigerant circulated in response to temperature requirements and to adjust the pressure maintained by the valve in response to humidity requirements.

Other objects of my invention and its numerous advantages will become apparent as the following specification is read in the light of the accompanying drawings, in which,

Figure 1 represents diagrammatically an air' conditioning system employing direct expansion refrigerating apparatus having one form of my invention embodied therein,

v Figure 2 diagrammatically represents a portion of the complete system shown in Figure 1 and culated through a duct llv which is connected to the inlet of a fan I! which may be driven by a motor or other suitable means. The fan discharges through a duct l3 into the room the air of which is to be treated. The duct H has a portion H through which outdoor air, that is,

- fresh air is admitted, and the duct H has a branch portion l5 communicating with theroom or other space through which air from the room or space is retumedto the duct 'H to be recirculated. All fresh air, or all return air, may be used, or a mixture thereof may be automatically controlled in any of the usual manners.

Disposed in the duct H where the mixture of return and outdoor air may be passed over it is a coil or evaporator l1 forming part of a direct expansion refrigerating apparatus. The refrigcrating apparatus includes four compressors I8,

I9, 20 and 2|. The compressors have discharge conduits 22, 23, 24 and 25 respectively, which are connected to a common discharge header 26. The

header 26 is connected to a condenser 27 by means of a pipe 28 and the condenser 21 is connected to an expansion valve 29 by means of a pipe'30. The outlet of the expansion valve 29 is connected to the evaporator II by means of a pipe 3|. The suction side of the four compressors are connected to a common suction header 33 by means of pipes 34, 35, 35 and 31 respectively. The outlet of the evaporator I1 is connected to the suction header 33 by means of a pipe 38. From the foregoing it is apparent that the compressors 8, I3; 28 and 2| are connected in parallel to the evaporator ll of the refrigerating apparatus.

The expansion valve 23 is of a type which maintains a predetermined degree of superheat at the outlet of the evaporator. This particular expansion valve is disclosed in detail in an application of Alwln B. Newton, Serlal No. 286,594, filed July 26, 1939. The valve 29 has a body having a longitudinal throat 4| therein forming a seat for a valve head 42. Numeral 43- designates a valve stem which extends upwardly into a chamber 44 in the upper part of the body of the valve, the valve stem being connected to a flexible diaphragm 45. The upper part of the throat 4| is slightly enlarged and in the enlarged portion is disposed packing material 48 around the valve stem 43 to prevent leakage around the valve stem, the packing being held in place by a ring 41. The dlaphragm'45 is secured between a flange at the upper part of the body of the valve 23 and a corresponding'flange' on a dome shapedcap member 48 which may be secured to the body of the valve in any suitable manner. Attached to the valve stem 43 is a disc 43 and disposed between this disc and the bottom of the chamber 44 is a coil spring 58 which normally urges the valve into closed position. The space within the cap member48is connected to a. thermal bulb 5| by means of a capillary tube 52, the thermal bulb 5| being disposed adjacent the pipe 38 which connects the evaporator with the suction side of the various compressors. The bulb 5| is charged with a vaporizable liquid which vaporizes and produces a pressure in the bulb 5|, tube 52, and

within the cap 48, the pressure depending upon the temperature of the refrigerant in the pipe 38 adjacent to the evaporator I1.

Means are provided to form an equalizer connection between the chamber 44 of the valve 23 and the suction pipe 38. The purpose of the equalizer connection as well knownin theart, is to render the diaphragm 45 responsive to pressure at the outlet of the evaporator. Numeral 55 designates a valve disposed in the equalizer connection, the purpose of which is to vary the eflfect of evaporator outlet pressure on the diaphragni 45. The valve 55 has an internal partition having an opening extending therethrough which forms a seat 58 for a valve Head 51. Nu-

through the pipe 83 into the chamber 44 andv maintains the valve 23 fully closed. When the valve 55 is open, refrigerant which is bled into the channel 83 and into the chamber 44 through the pipe 83 may be bled off to the suction pipe 38 through the valve 55' and the pipe 84. The pressure in the chamber 44 andpipe 83 then of course depends upon the rate at which refrigerant is bled through'the valve 55.

The stem 58 of valve 55 is connected to a crank 18 which is engaged upon" an eccentric 1| driven by the proportioning motor 12. The proportioning motor is controlled by a pressure controller 13 which is connected to the suction pipe 38 by means of a pipe 14 and by a compensating humidity responsive controller 15. The proportioning motor 12 and the controllers l3 and 15 by which it is controlled correspond to similar contentiometer type of controller operated in response to variations in humidity in the space wherein "the air is being treated. The connections. between the controllers l3 and I5 and the proportioning motor I2 are substantially the same as those' shown in the Haines patent. The controller 13 corresponds to the controller 2| of Haines and the controller 15,- which acts as a compensator, corresponds to the controller3| of Haines. to its controllers is the same as that described in the Haines patent. The proportioning motor 12 rotates the eccentric II in one directionor the other and when the eccentric is thus rotated, the crank 18 is moved substantially in a vertical direction either upwardly or downwardly so as to thereby move the valve stem 58 in a manner to move the valve head 51 towards closed position meral 58 designates a valve stem connected to V the head 51 and extending externally of the valve through asealing bellows 53, one end of which is attached to the; body of the valve 55 and the other end of which is attached to the stem 58. The lowerpcrtion of valve 55 has a vertical channel 88 therein which communicates with the valve chamber and with a chamber 6| at the lower partof the valve body. At the lower end of channel 38 is an orifice member having an orifice providing communication between chamber Gland channel 88. The equalizer connection above referred to. comprises a pipe 83 connecting the chamber 44 with the channel 68, and a pipe 54 providing communlcation between the chamher in the upper part of the valve body, thatis, on the. discharge side the valve 55 and the suction pipe 38. Communication is therefore pmor away from closed position.

The compressors i8, |3,'28 and 2| arecon- 'trolled by a step controller 11 which comprises a reversible motor 18 which drives a shaft I3 upon which are mounted cams 88, 8|, 82 and 33. The motor I8 is controlled by a temperature responsive controller 84 whichcomprises a potentiometer type controller operated responsively to temperature in the return air duct l5, the con-- troller including a thermal bulb 85 disposed in the air stream and connected to the controller by means of a capillary tube 88, The details of the controller 84 and motor 18 are the same as those of the Haines patent referred to above.

Each of the cams 88, 8|, 82 and 83 has a dwell, the dwells being angularly spaced about the shaft 13 and the dwells being operable, to actuate a movable blade of switches 83, 83, 38 and 3| respectively. Upon a temperature rise affecting the controller 84, the motor 13 rotates the shaft 13 in the direction indicated by arrow 32 and the cams sequentially close their respective switches, the switch 83 closing first and the other switches closing afterwards upon a progressive The operation of motor l2'in response opened in sequence in the reverse order. The switches 88, 89, 98 and 9| control the compressors -|8, I9, 28 and 2| respectively, as will presently appear.

With the parts in the positions shown, the

temperature and humidity conditions in the space are satisfactory. All of the switches 88, 89, 98-

- 88 may have an operating range of from 74 F.

to 80 F. for example. That is, upon a rise in temperature of the return air-from 74 F. to

closure of switch 88 and energization of.com-

80 F., the controller 88 will operate motor'l8 an amount suflicient to close all of the switches 88, 89, 98 and 9|. In other words, when the return air temperature rises from 74 F. to 80 F. all four of the compressors will be energized as will presently appear.

The function of. the valve 29 is normally to maintain a predetermined degree of superheat at the outlet of the evaporator. In operation, the coil cools as well as'dehumidifies the air which passes thereover. At times, particularly when only one or two compressors, for example, are in operation the evaporator pressure may tend to rise to such a high value that the temperature of the evaporator would not be low enough to provide for the proper amount of dehumidification of the air. To prevent .the temperature of the evaporator from thus rising to a higher than desired value, I have provided the controller 13 in connection withthe valve 55. The function of the controller 13 as will presently appear, is to maintain the evaporator pressure at substantially a predetermined value. g

If in a system of the type disclosed, Freon 12" is the refrigerant used in the refrigerating apparatus, proper dehumidification will be obtained if the evaporator pressure does not rise above 45 pounds. Thus the controller l3'may be set so as to prevent the evaporator pressure from rising above 45 pounds when it would otherwise tend to' do so. The controller 13 has an operating differential which may be relatively narrow as respects its total differential or range. Its'operating difierentialmay be two pounds for example, that ism the controller I3 will control the valve 55 so as to move it between fully opened and fully closed position when the pressure affecting controller 13 deviates through an amount of two pounds; For example, with the parts in the position shown, the valve 55 is fully closed an the pressure in the suction pipe 38 and thus the pressure affecting the controller .13 is about 45 pounds. When the pressure afi'ecting controller 13 is reduced to 45 pounds, thevalve 55 will begin to open and will be fully opened when the pressure has fallen to 43 pounds.

The humidity-controller 15 may have. a fairly narrow differential and normally will tend to maintain the humidity at a desired value of 50%. Should the humidity rise above the desired value, the controller 18 will be reset to maintain a lower suction pressure and conversely if the humidity falls below the desired value, the controller .13 will be reset to maintain a higher suction pressure.

With the parts in the position shown, should the temperature in the return air duct l5 rise above 74, the motor I8 will be operated to cause pressor l8 through the following circuit: from line conductor 95 through wire 96, switch 88.

wire 91, the motor of compressor |8,and wire.

98 to line conductor 99, the line conductors 95 and 99 being connected to any suitable source of power not shown. -When the compressor I8 is started, the pressure in evaporator I1 and suction pipe 88 will be reduced. As soon as the pressure in suction line 38 has been reduced into the operating range of controller '|3, that is,

to 45 pounds, for example, the controller 18 will operate motor 12 in a manner to crack the valve 55 open. When valve 55 is thus opened refrigerant will be permitted to bleed from chamber 88 underneath diaphragm 85 through pipe 58, channel 88 and through valve 55 and pipe 88 to the suction pipe 38. This will permit valve 29 to open, theamount of opening of course depending upon the pressures on opposite sides of diaphragm 85, the pressure above the diaphragm depending upon the temperature at the outlet of the evaporator affecting thermal bulb 5| and the pressure below the diaphragm in chamber '88 depending. upon the amount of opening of valve 55 and the pressure in'the suction pipe 88. The valve 29 will nowadmit refrigerant to the evaporator and a relatively large number-of degrees of superheat will be maintained at the outlet of the evaporator, perhaps 30 F. or F. Upon a further rise in temperature in ,the return air duct |5 affecting the controller 88'- the motor 18 will be operated to cause cam 8| to close switch 89 energizing compressor |9 through the following circuit: fromline wire 95 through a wire I88, switch 89, wire IN, the motor of compressor l9,.and wire, I82 to line conductor 99. When compressor |9 starts there 'will be a greater suction taken on evaporator 1 tending to reduce the pressure therein. The controller '13 will respond to the increased suction in the suction pipe 38 and the reduction in pressure will cause the controller to operate motor 12 in a direction to move valve 55 to a wider'open position; This will permit bleeding of refrigerant from the chamber 88 at a greater rate and valve 29 will move toward a wider open position, that is, permitting a lower number of degrees of super-heat to be maintained at the outlet of evaporator H. In other'words, the amount of efi'ective surface of evaporator ll: will be increased when compressor I9 is started but the controller 13 will maintain the pressure in the evaporator at substantially the same value. It is to be understood that if the equalizer connections were connected directly to the suction pipe 38 without the valve 55 and controller 13 being provided, with compressors l8 and I9 operating or only'compressor l8 operating, the valve 29 -would operate normally to maintain the usual number of degrees of superheat at the outlet of the. evaporator H which would be perhaps 10. Under these circumstances the pressure in the evaporator would very likely be considerably above pounds which with the type of refrigerant "T12," above re ferred to, would be too high for proper dehumidification of the air. It is to be seen therefore that the controller 13 and valve operate to prevent the evaporator pressure from rising above 'desired'values when only one or two compressors are operating.

If the temperature in the return air duct |5 affecting controller 88 continues to rise the motor 18 will be operated sufliciently to cause cam 82 to close switch 98 energizing compressor 28 by means of the following circuit: from line con-' ductor 99. When compressor 20 is started, there will be a further increased suction effect in suc-' tion pipe 38 which will be sensed by the controller I3. The increased suction effect produced by starting of compressor 20 will be sufficient to cause controller 13 to move to the limit of its operating differential, that is, to cause the valve 55 to move. to fully open position. If so, the chamber 44 underneath diaphragm 45 will now be in unrestricted communication with the suction pipe 38, and the valve 55 will have no effect upon the number of degrees of superheat maintained at the outlet of the evaporator by the valve 29. That is, the starting of compressor 20 may now reduce the, evaporator pressure below 43' pounds, controller 13 having no further control effect On the system. The valve 29 willnow operate normally to maintain superheat, for example, at the outlet of the evaporator which is the number of degrees of superheat usually maintained by .superheat type of expansion valves. It is to be seen therefore that the effect of controller 13 is to increase the number of degrees of superheat maintained at the outlet of the evaporator and to thereby prevent the pressure in the evaporator from rising above a given value, controller I3 normally maintaining the evaporator pressure substantially constant.

Upon a further rise in temperature affecting the controller 84 the motor I8 will be operated to cause cam 19 to close switch 9| energizing compressor 2| by'means of a circuit as follows: from line conductor 95 to, wire )5, switch 9|,

wire I01, the motor of compressor 2| and wire |||8 to line conductor 99. Starting of compressor 2| will produce an increased suction effect in suction pipe 38 tending to further reduce the pressure in evaporator H. ,The valve 29 will continue to maintain 10 of superheat at the outlet of the evaporator. By reason of all four compressors now being in operation the maximum amount of refrigeration will be taking place in evaporator l1 and the pressure will be at a relatively low value.

25 towards closed position, thus restricting or throttling the admission of refrigerant to evaporator In other words, a higher number of bf superheat than normal will now be degrees maintained at the outlet of evaporator l1. By thus throttling the admission of refrigerant to the evaporator and increasing the amount of superheat maintained at the outlet the pressure .therein is prevented from rising above the setting of controller I3. As the temperature affecting controller 84 continues to decrease, the switch 89 will next be opened causing the compressor i9 to stop. Upon stopping of compressor l9 there will be a further reduced suction effect in suction pipe 38 which will be sensed by controller 13, that is, there will be a rise of pressure in pipe 38 and controller 13 will respond moving valve 55 further towards closed position. This will further restrict the bleed from chamber 44 and the resulting increased pressure therein will tend to cause valve 29 to move further in a throttling direction causing the number of degrees of superheat maintained at the outlet of the evaporator to be further increased. Thus again by throttling the flow of regrlgerant to the evaporator and increasing the amount of superheat maintained at the outlet, the pressure therein is prevented from rising above the setting of con- 'troller I3.

When the temperature in the return air duct has fallen to the desired valuev of 74, motor 18 will be operated to cause cam 8|] to open switch *8! and the last compressor, that is, compressor |8 will be stopped.

When compressor I8 is stopped, there will be no further suction effect in pipe 38 and the evaporator pressure and the The temperature in the return air duct I5 and I affecting controller 84 shouldn'ow begin to fall,

and as it falls below 80 the switches 88, 86, 90 and 9| will be sequentially opened, the switch 3| opening first. When switch 9| opens compressor 2| will be stopped and the amount of refrigerant circulated through evaporator will of: course be reduced. Due-to stopping of compressor 2|, the evaporator pressure will rise but it will not rise'sufficiently to cause controller 13 to move into its operating range and there will be no change in the amount of superheat maintained at the outlet of evaporator As the temperature affecting controller 84 continues to fall switch 90 will be opened next stopping compressor 20. When compressor 20 stops, the reduction of suction effect in pipe. 38 will be sufilcient to cause controller 13 to move into its operating range, that is, the pressure in pipe 38 will rise above 43 pounds causing controller 13 to again effectively control motor "l2 and valve 55. When controller 13 thus moves into its operating range, the valve will be moved towards closed position tending to restrictthe bleed from chamber 44 through valve 55 and to the suction pipe 38. Due to the restriction, thatis, the reduced rate of bleed, the pressure within chamber 44 will be slightly increased tending to move valve pressure in pipe 38 will'rise and the rise in pressure will cause controller 13 to move to the limit of its operating range causing valve 55 to move to a fully closed position. Refrigerant will not now be permitted to bleed from chamber 44 and high pressure refrigerant from pipe 65 will be communicated through restricted orifice 62, channel 60 and pipe 63 into chamber 44, and the resulting pressure therein will maintain valve 29 in fully closed position.

From ,theforegoing, it is to be seen that when only one or two compressors are operating, so that with the usual type of control the evaporator pressure would be relatively high, too high for proper dehumidification of the air, the control arrangement of my invention provides for limiting the, pressure in the evaporator so that it does not rise, above a value at which proper dehumidification will be obtained, the arrangement normally maintaining. the evaporator pressure constant. After the valve 55 has been fully opened, as is apparent, it has no further effect upon the number of degrees of superheat maintained at the outlet of the evaporator by valve 28. Further reduction in evaporator pressure is then of course .dependent upon the relat onship between the total compressor capacity and the capacity of evaporator II. It is to be understood that the operating differential of controller 13 might be so related to the compressors and evaporator used that the controller 13 would As pointed out above, the controller 13 has a relatively wide total differential which may be 40 pounds pressure, for example. At any time when one or more compressors are operating if the relative humidity in the space being served should rise above the desired value of 50% relative humidity, the compensating controller 15 will act to reset the control point of controller 13. That is, if the humidity rises above 50%, for example, the control point of controller 13 will be lowered to a value below 45 pounds, for example, the control point of controller 13 might be reduced to 39 pounds. The operating differential of controller 13 would remain the same, that is, two pounds, for example, and it would now move the valve 55 between fully closedand fully opened positions when the pressure affecting controller 13 changed between 40 pounds and 38 pounds, for example. Under these circumstances, the controller 13 would operate ina similar manner to that described above to maintain the evaporator pressure between 38 and 40 pounds, that is, the evaporator pressure would not be permitted to rise above 40 pounds. The lower evaporator pressure and corresponding evaporator temperature would cause increased dehumidification which would cause the humidity an arrangement wherein the pressure in the evaporator is controlled by means of a separate valve responsive to evaporator pressure. In Fig.

2, numeral 20! represents an evaporator of the direct expansion type. If desired, this evaporator may be used in a system the same as the one disclosed in detail in Fig. 1 including a plurality of compressors sequentially controlled in response to temperature requirements. In Fig. 2, numeral 202 represents a liquid refrigerant line through which refrigerant is supplied from a source of supply. Interposed in the line 202 is a first valve 203 which is of a conventional type arranged to respond to pressure so as to maintain the pressure beyond the valve at a constant value.

ing material 205 to prevent the leakage of refrigerant past the stem into the upper part .01

the valve body. The valve stem is connected to a flexible diaphragm 206 which forms a chamber underneath the diaphragm and this chamber is connected to the discharge pipe 201 of the evaporator by a tube 208. The pressure underneath the diaphragm urges the valve in closing direction against the force of a coil spring 200 which may be adjusted by means of an adjusting knob M0. The valve 203 is normally open, and when the pressure communicated through the tube 208 rises to a predetermined value determined by the.

setting of knob 2I0, the diaphragm. 206 moves the valve toward closed position sufllciently to maintain the pressure at' the said predetermined value. v

Interposed in the liquid line 202 beyond the valve 203 is a second valve 2|6 which isof the conventional type adapted to maintain a prede- The valve has a stem 200 which passes through packof a pressure chamber above the diaphragm. This chamber is connected to a thermal bulb 2l8 by means'of a tube 2l0, the thermal bulb 2I8 being disposed in heat exchange relationship with the discharge pipe 201 of the evaporator. The bulb 2! is filled with anexpansible liquid which vaporizes and develops a pressure termined degree of superheat at the outlet of above the diaphragm 2 depending upon the temperature affecting the bulb. The diaphragm 2 is normally urged upwardly by a coil spring 220 this spring thus urging the valve in closing direction. The valve stem passes through packing material 22l to prevent leakage of refrigerant past the valve stem and the chamber underneath the diaphragm 2 is connected to the tube 200 by a tube 222 so that pressure from the discharge pipe 201 of the evaporator is communicated to a chamber underneath the diaphragm. The pressures on opposite sides of the diaphragm 2 I 1 normally maintain the valve 2!! in a balanced position dependently upon the amount of superheat existing in the discharge pipe 201. In other words, if the number of degrees of superheat increases, the pressure above the diaphragm tends to preponderate over that below the diaphragm and the valve is moved slightly in openingdirection until rebalance is brought about.

Disposed in the discharge pipe 201 is a motorized valve 225 driven by an electric motor 226 which is controlled by a thermostat 221 responsi've to the temperature of medium cooled by the evaporator. The thermostat 221 and valve 225 may be of the type disclosed in detail in the patent of D. G. Taylor, No. 2,028,110. Upon a rise in temperature the thermostat 221 opens the valve 225 to permit a greater amount of refrigerant to be circulated through the evaporator, and i culated through the evaporator.

In normal operation the valve .225 controls the amount of refrigerant circulated through the evaporator and the valve 203 controls the admission of refrigerant to the evaporator to maintam a predetermined pressure in the evaporator. As pointed out above, the valve 203 operates to malntaina predetermined pressure on the downstream side or the valve, that is, in the evaporator. In other words, the thermostat 221 controls the refrigerative capacity, that is the amount of refrigerant which is circulated while the valv 203 maintains the pressure in the evaporator constant. The valve-2|5 is normally in a relatively wide open position, but in the event that liquid refrigerant tends to pass over into the discharge pipe 201 of the evaporator, the temperature afr'ecting bulb 2 will be so reduced that the reduction in pressure above diaphragm 2 will permit spring 220 in conjunction with the pressure underneatnthe diaphragm to move valve zl'5 towards closed position so as to reduce the rate of admission of refrigerant to the evaporator so as to prevent liquid from passing into the discharge pipe. Thus, the systemv operates to vary the amount of refrigerant circulated while its pressure is maintained constant, the valve 5 acting to prevent liquid from passing into the suction line. g

Figure 3 shows a different form of my invention wherein a single valve is used in the liquid line, this valve being operative in response both to the amount of superheat in the discharge pipe pending upon the adjustment; of spring 325.

6. of the evaporator and also to pressure in the evaporator. The arrangement of Fig. 3 may be used" with the multiple compressor-arrangement of Fig. 1 or the suction line valve of Fig. 2 may the discharge pipe 301 of the evaporator by a tube 308. The-valve stem 300 is connected to a floating lever M0, the left end of which is connected to an expansible and contra'ctible bellows 3 by a stem 312.. The bellows 3H isdisposed in a portion 313 of housing 304 forming a bellows chamber, the stem 3|2 passing through an annular member 3l5 forming a stop limiting contraction of the bellows 3| 1. The bellows is normally urged into an expandedposition by a coil spring 316 inside of the bellows. The chamber outside the bellows is connected to a thermal is an air pressure operated co iitrol valve 403 of the well known direct acting type which has a pressure chamber including an expansible wall which acts to close the valve upon an increase in pressure in the pressure chamber.

Numeral 404 designates the discharge pipe of the evaporatori Numeral 405 designates a supply pipe from a source of air pressure such as is conventionally used in pneumatic control systems, the supply of air pressure usually being at fifteen pounds. Numeral v406 designates a fixed restriction through. which the air must pass before being communicated to the control device. The restriction 406 is connected to the expansible chamber of the valve 403 by a tube 401. Numeral 408 designates a first branch pipe communicat- ,ing with pipe 401, the branch pipe having afittirig at its end, 409, with a bleed orifice thereon. Numeral 4l0 designates a second branch pipe communicating with pipe 401 having a fitting 4 with a bleed orifice therein. Associated with the orifice m the fitting 40a is a flapper m bulb 3I1,.by means of'a tube in, the bulb an I being disposed in heat exchange relation with the discharge pipe 301 of the evaporator.

The right end of lever 310 is connected to an expansible and contractible bellows 320 disposed within a portion 32! 'of' housing 304 forming a chamber forthe bellows. The stem 322 passes through an annular member 323 forming a stop limiting contraction of the bellows 320. Numeral 325 designates a coil spring which normally urges the bellows 320 into compressed position, the spring 325 being adjustable bymeans of a manual knob 326 outside of the housing 304. Numerals 321 and 323 designate stops within the connected to the flapper member 2 so as to portion 321 of housing 304 which limit the ex-.

pansion of bellows 320. The bulb 3" is filled with expansible liquid which vaporlzes and thus the pressure exterior of'the bellows 3 depends upon the temperature in the discharge pipe 301.

In operation, the valve 303 is normally: adjusted primarily by the bellows 320 responsive only to pressure in the pipe 301. Upon an increase in pressure the bellows 320 tends to expand moving the right end or lever 310 and'the valve upwardly toward closed position. Thus, f

the valve will normally be positioned dependently upon the pressure in the evaporator and the pressure will be maintained at a value ties;

The bellows 3|! will normally assume a balancedposition dependently upon the pressure within the bellows and the pressureon the outside of the bellows communicated through tube 3l8 from the bulb 311. As in the previous embodiment, if liquid refrigerant should tend to pass into the dischargepipe 301, the temperature-within bulb 3|] and consequently the pressurearound the outside of bellows ill will be so reduced that thebellows will be expanded by means of the spring'3l0 acting in conjunction with the pressure within the bellows to move the left endof lever M0 and the valve upwardly to= wards closed position. This movement of the valve will reduce the admission of refrigerant to the evaporator sufliciently to prevent any liquid frombeing carried over into the discharge pip'e-301.

In Fig. 4, I have shown an arrangement simiarranged to control the rate of bleed from the orifice. The flapper H2 is pivoted at M3 and .it is normally biased in a clockwise direction by a coil spring 4. An expansible bellows 415 is urge it toward the fitting 409 when the bellows expands, the bellows 5 being connected to the heat exchange relation with the discharge pipe .404 by a tube 9. The bellows 4I1 expandsand contracts in accordance with the temperature in the discharge pipe 404. From the foregoing, it is to be seen that the operating means for the. flapper 412 respond to the amount of superheat in the discharge pipe 404 inasmuch as the pressure in the said pipe acting through bellows 4l5 opposes the temperature of the discharge pipe acting through the bellows ,4I1.

Numeral 425 designates a flapper disposed adjacent the orifice in fitting 4i i, flapper 425 being pivoted at 426 and having an arm 421 which is normally in engagement with an operating stem connected to an expansible and contractible bellows 428'. The bellows 420 is connected to the discharge pipe 404 by a tube 423. The flapper 425 is normally urged away from the fitting 4 by a coil spring 430 connected to the am 421. Upon an increase in pressure the bellows 420 expandsmoving the flapper 425 toward fitting is suchthat the rate of bleed through each of these orifices is less than through the restriction lar to that. of the previous figures but whereinv I the valve is operated by pneumatic control devices. In Flg. 4, the evaporator is designated by the numeral 40! and the liquid line is designated by the numeral 402. Disposed in the liquid line 406. Thus if the orifice in either of the fittings 403or-4l| is completely obstructed, the pressure will build up in pipe 401 to a value sufi'iciently high to completely close the valve 403. In normal operation the superheatin the discharge pipe 404 is great enough so that the pressure in bellows 4|1 preponderates over the pressure in bellows 5 and the flapper 4 l2 is held in aposi- .tion away from fitting 403 so as not to obstruct 4 so as to control the pressure acting on the a valve 403 to cause a predetermined evaporator pressure to be maintained; Thus, when bellows sure in pipe 401 affecting the valve is increased.

Thus, upon the increase in pressure the valve 403 is moved towards closed position to reduce the pressure in the evaporator. Upon a decrease in pressure within bellows 428, the pressure in pipe dill is similarly decreased, and valve E03 moves in opening direction to increase the evaporator pressure. That is, the evaporator pressure is normally maintained at a constant value in response to the bellows 428. In the event that liquid refrigerant should tend to pass into the discharge pipe 604, the temperature afiecting bellows 4M will be reduced and the corresponding pressure in bellows M5 will preponderate over the pressure in bellows 4H.- Ihe flapper M2 will be moved towards the fitting 409 to reducethe rate of. bleed therefrom. Correspondingly, the pressure in pipe Ml affecting valve 403 will be increased so as to move the valve 403 towards closed position to reduce the rate of admission. of refrigerant to the evaporator and thereby prevent liquid from passing over into the discharge pipe 404. 7

From the foregoing, those skilled in the art will readilyappreciable that I have provided a very unique control arrangement for refrigerating apparatus wherein the evaporator pressure is maintained constant and also liquid refrigerant circulated through the evaporator may be varied to meet loaddemands while the pressure is kept at a desired value and the evaporator is operated under efiicient conditions. The embodiments of my invention which I have disclosed are representative of its previous forms. Various modifications and changes may be made by those skilled in the art and it is to be understood that my invention is to be limited not by my disclosure but only in. accordance with the claims appended hereto.

I claim as my invention: v

1. In an air conditioning system, in combination, a direct expansion type refrigerating apparatus including an evaporator, means comprising a plurality of compressors whereby the amount of refrigeration produced by the apparatus may be varied, means for passing air to be conditioned over the evaporator whereby the air is cooled and dehumidified, means responsive to a condition of the air being treated for controlling said tion produced by the refrigerating apparatus, and means including a valve controlling the supply of refrigerant to the evaporator, said last means being responsive to evaporator pressure and arranged to control the admission of refrigerant to the evaporator in a manner to maintain the evaporator pressure substantially constant while the amount of refrigeration produced by the refrigerating apparatus is varied.

2. In an air conditioning system, in combination, refrigerating apparatus including an evaporator and a variable capacity source of refrigerant supply connected to the evaporator, means responsive to a condition of air being treated for controlling the capacity of the source of refrigerant supply, and means including a valve controlling the supply of refrigerant to the evaporator. said last means being responsive to evaporator Pressure and a n ed to control the admission compressors to control the amount of refrigerav of refrigerant to the evaporator to maintain a constant evaporator pressure when the capacity of the source of supply is varied.

3. In an air conditioning system, in combination, a direct expansion type refrigerating apparatus including an evaporator, means whereby the amount of refrigeration produced by the apparatus may be varied, means for passing air to be conditioned over the evaporator whereby the air is cooled and dehumidified, means responsive to a condition of the air being treated for controlling the amount of refrigeration produced by the refrigerating apparatus, means including a valve of the type responsive to superheat at the outlet of the evaporator controlling the admission of refrigerant to the evaporator, and means responsive to evaporator pressure for additionally controlling the position of said valve in accordance with variations in evaporator pressure for maintaining said pressure at avalue at which it is ca-' pable of dehumidifying the air passing over said evaporator.

4. In an air conditioning system, in combination, a direct expansion type refrigerating apparatus including an evaporator, means whereby the amount of refrigeration produced by the apparatus may be varied, means for passing air to be conditioned over the evaporator whereby the air is cooledand dehumidified, means responsive to acondition of the air being treated for controlling the amount of refrigeration produced by the refrigerating apparatus, means including a valve controlling the supply of refrigerant to the evaporator, said last means being responsive to evaporator pressure and arranged to control the admission of refrigerant to the evaporator in a manner to maintain'the evaporator pressure substantially constant while the amount of refrigeration produced by the refrigerating apparatus is condition of the air being treated for controlling the capacity of the source of refrigerant supply, means including a valve controllingthe supply of refrigerant to the evaporator, said last means being responsive to evaporator pressure and arranged to control the admissionof refrigerant to the evaporator to prevent the evaporator pressure from rising above a predetermined value when the capacity of the source of supply is reduced, and humidity responsive ineans associated with said last-named means and operable to vary the evaporator pressure maintained and correspondingly the evaporator temperature in order to preserve proper humidity conditions.

6. In a refrigerating system, in combination, a compressor, a condenser, and an evaporator, a valve of the superheat responsive type controlling the admission of refrigerant to the evaporator,

constant while the amount'of refrigerant circulated through the evaporator is varied.

7. In a refrigerating system, in combination, a compressor, a condenser and an evaporator, valve means of thesuperheat responsive type controlling the admission of refrigerant to the evaporator, means for varying the amount of refrigerant circulated through the evaporator tending to cause the evaporator pressure to vary, said valve means including an expansible chamber, means providing communication between said chamber and the outlet of the evaporator, the pressure in said chamber affecting the valve means to govern the number of degrees of superheat maintained at the evaporator outlet, valve means controlling said means of communication and means responsive to evaporator pressure controlling said last valve means whereby said first f valve meansi controlled in a manner to norma ly maintain a substantially constant evaporator pressure while the amount of refrigerant circulated through the'evaporator is varied.

8. In an air conditioning system, in combination, a direct expansion type refrigerating apparatus including an evaporator,'means for'passing air to be conditioned over the evaporator whereby the air is cooled and dehumidifled, means whereby the amount of, refrigeration produced by the apparatus may be varied, means responsive to load requirements controlling said last means,

means including a valve of the type responsive to su-perheat at the outlet .of the evaporator controlling the admission of refrigerant to the evaporator, and means responsive to evaporator pressure for additionally controlling the position of said valve for maintaining said evaporator pressure substantially constant while the amount of refrigeration produced by the refrigeratinglappa ratus is varied.

9. In an air conditioning system, in combina tion,'a direct expansion type refrigerating apparatus including an evaporator, means comprising a plurality of compressors whereby the amount the amount of refrigeration produced by the refrigerating apparatus is varied, said valve means having a pressure chamber connected to the evaporator outlet and a controlling valve interposed in the connection between the said pressure chamber and evaporator outlet for varying the pressure in said chamber.

of refrigeration produced by the apparatus may be varied, means for passing air to be conditioned over the evaporator whereby the air is cooled and .dehumidified; means responsive to the temperature of the treated air whereby said compressors are started and stopped insequence depending on the temperature of theair, and means including a valve controlling the supply of refrigerant to the evaporator, said last means bein a responsive to evaporator pressure and arranged to control the admission of refrigerant to the evaporator in a manner to maintain the evaporator pressure substantially constant while the amount of refrigeration produced by the reins-- erating apparatus :is varied.

10. In an air conditioning system, in combination, a direct expansion type refrigerating apparatus including an evaporator, means comprising a plurality of compressors whereby the amount of refrigerant to the evaporator, saidlast means being responsive to evaporator pressure and arranged to control the admission of refrigerant to 11. In a refrigerating system, in combination, a compressor, a condenser and an evaporator, valve means of the superheat responsive type controlling the admission of refrigerant to the evaporator, means for varying the amount of refrigerant circulated through the evaporator tending to cause the evaporator pressure to vary, said valve means including an expansible chamber, means providing communication between said chamber and the outlet of the evaporator, the pressure in said chamber affecting the valve means to govern the number of degrees of superheat maintained at the evaporator outlet, valve means controlling said means of communication, means responsive to evaporator pressure controlling said last valve means whereby said first valve means is 'controlledin a manner to maintain a substantially constant evaporator pressure, and means responsive to the humidity of the treated air cooperating with said evaporator pressure responsive means for varying the pressure maintained in the evaporator so as to preserve proper humidity conditions.

' 12. ,In an air conditioning system, in combination, direct expansion refrigerating apparatus including an evaporator, means for passing air over the evaporator for cooling and dehumidifying the air, a plurality of compressors connected to said evaporator for circulating refrigerant therethrough, means responsive to the temperature of the treated air controlling the compressors whereby the compressors are started and stopped depending on the air temperature, means comprising an expansion valve controlling the admission of refrigerant to the evaporator, said" valve meansembodying mechanism to maintain the evaporator pressure at a substantially constant value when the number of compressors in operation is varied, said mechanism comprising a pressure chamber and means providing communication between said chamber and the outlet of the evaporator, the pressure in said chamber goveming the amount of opening of the expansion valve, a control valve interposed in said means to evaporator pressure controlling said control I the evaporator in a manner to maintain the evaporator pressure substantially constant while 76 providing communication, and means responsive valve to maintain a substantially constant evaporator pressure. Y

13. In an air conditioning system, in combinati0% direct expansion refrigerating apparatus inclu mg an evaporator, means for passing air over the evaporator for cooling and dehumidifying the air, a plurality of compressors connected'to said evaporator for circulating refrigerant therethrough, means responsive to the temperature of the treated air controlling, the compressors stant value'when the number of compressors in operation is varied, said mechanism comprising a pressure chamber "and means providing communication betweensaid chamber and the outlet of the evaporator, the pressure in said chamber governing the amount or opening of the expanasrogos r 9 sion valve, a control valve interposed in said means providing communication, means responsive to evaporator pressure controlling said control valve to maintains substantially constant evaporator pressure, and means responsive to humidity of the treated air associated with said pressure responsive means for varying the evapo-. rator pressure maintained to preserve proper humidity conditions.

14. In a refrigerating system, in combination, means comprising a source of refrigerant supply, an evaporator, meanscontroliing the supp y of refrigerant to the evaporator comprising a valve, said valve including mechanical means responsive to pressure in the evaporator and to temperature at the outlet ofthe evaporator for adjusting the valve in accordance with the amount of superheat at the evaporator outlet, and mechanical means responsive to evaporator pressure for adjusting the valve to maintain a constant evapora-tor pressure.

15. In a refrigerating system, in combination,

means comprising a source of refrigerant, an

evaporator, means controlling the flow of refrigerant to the evaporator comprising a valve, said valve including a bodily movable lever member for actuating the valve, means responsive to evaporator pressure and to temperature at the outlet of the evaporator for actuating said member whereby the valve is adJusted to control the amount of superheat .at the outlet of the evaporator, and another means responsive to evaporator pressure for. actuating said member whereby said valve is adjusted in a manner to control the evaporator pressure.

' 16. In a refrigerating system, in combination, means forming a source of refrigerant, an evaporator connected to said source, means comprising a valve controlling the flow of refrigerant to the evaporator, said valve being of the type adapted to control the amount or superheat at the outlet of the evaporator, a second valve controlling the flow of refrigerant through the evaporator, said valve having means whereby it is responsive to evaporator pressure so as to control the evaporator pressure to maintain it constant, and means for varying the amount of remeans forming a source of refrigerant, an evaporator, means for circulating refrigerant through the evaporator, means for varying the amount of refrigerant circulatedsoas to tend to cause the evaporator pressure to vary, means responsive to a condition of air being treated controlling 'said last means, means for maintaining a concooled and dehumidifled over said evaporator.

means for supplying said evaporator with liquid refrigerant, means controlling the amount of refrigerant delivered to the evaporator in accordance. with the temperature of the conditioned air, a constant superheat expansion valve in con: troi of said evaporator tending to maintain a relatively high pressure in said evaporator when the temperature of said conditioned air is relatively low, and means maintaining said pressure relatively low for purposes of dehumidiflcation of the air passing over said evaporator.

20. In an air conditioning system, in combination, an evaporator, means passing air to be cooled and dehumidified over said evaporator, means for supplying said evaporator with liquid refrigerant, means controlling the amount of refrigerant delivered to the evaporator in accordtaining means tends to maintain.

fregerant circulatedthrough the evaporator while the pressure is maintained at a constant value.

17. In a refrigerating system, in combination, means forming a smrrce of refrigerant. an evaporator connected to said source, means comprising a valve controlling'the flow of refrigerant to a refrigerant circulated throughthe evaporator while the pressure is maintained at 'a constant value, said last means comprising another valve responsive to a condition of medium being treated b the system.

18. In a reii'iserating system, in combination,

21. In an airconditioning system, in combination, a source of liquid refrigerant, an evaporator for said refrigerant for cooling a fluid medium, means for causing a. flow of refrigerant from said source to said evaporator, a first valve for varying said flow in accordance with the ternperature of said medium, a second valve in controLof said flow of refrigerant, and means responsive to evaporator pressure in control of said second valve for maintaining said pressure constant.

22. In anair conditioning system, in combination, a source of liquid refrigerant, an evaporator for said refrigerant for coolingv a fluid medium, means for causing a flow of refrigerant from said source. to said evaporator, a first valve for varying said flow in accordance with the temperature of said medium, a second valve in control of said flow of refrigerant, means responsive to evaporator pressure in control of said second valve for g said pressure constant, and means including a third valve for maintaining a constant degree of superheat at the outlet of said evaporator. WILLIAM L. McGRa'i'B.

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