US2372839A - Air conditioning system - Google Patents

Description

3, 1945. w, McGRATH 2,372,839

' AIR CONDITIONING SYSTEM 7 1 Filed Dec. 6, 1941 s Shets-Sheet 1 new A". V

v INVENTOR. William. L. M? Grand.

April 3, 1945. w. L. McGRATH AIR CONDITIONING SYSTEM Filed Dec. 6, 1941 3 Sheets- -Sheet 2 FRESH AlR I 4 ll 'INVENTOR. Wi11ia1n I4. Mic-NHL April 3, 1945. w, McGRATH 2,372,839

-AIR CONDITIONING SYSTEM Filed Dec. 6, 1941 3 Sheets-Sheet 3 TO OTHER ZONES AIR SUPPLY saw COOLER FRESH RETURN AIR AIR FLg. a

INVENTOR. Wi11iawg. Ia. M5 C hfih...

Allorneyf' I Patented A r. .3, 1945 AIR CONDITIONING SYSTEM William L. McGrath, Philadelphia, ,Pa., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application December 6, 1941, SerialNo, 421,867

18 Claims.

This invention relates in general to a year around air conditioning system for a zone, or

for a plurality of zones, and in particular to a system of the type in whichv the supply of conditioned air for each of a pluralit of zones is furnished by individually varying the relative proportions of air simultaneously admitted to each zone from separate supplies of cool and warm air which serve as common sources of supply for each of the zones. The invention particularly relates to a novel and improved humidiflcation con-.

trol employed in conjunction with a system of the ype in which each of the zones is conditioned by regulating the proportions of air simultaneously supplied from a warm air duct and cool air duct. Thus my invention embodies new and novel improvements in conditioning systems of the type disclosed in the patent to G. D. Guler, No. 2,238,- 688.

One object of the invention is to control the humidity in a forced air system employing a warm air duct and a cool air duct by dehumidifying and cooling the air supplied to the cool air duct and diverting a regulated portion. of the dehumidified and cooled air for mixture with the air supplied to the warm air duct under the con i trol' of a humidity responsive means. 7

A further object of the invention is the provision of means for preventing draft efiects in a zone, or zones, due to-the zone controller requiring the admission of air from a cool air duct during periods when the cool air duct temperatures would normally be relatively very low. Thising conditioned and avoiding duplication of heatdicative of a condition existing in either one of the volumes of air, or in a zone being conditioned. -The zone conditioning is accomplished by regulating the proportionate amounts of these separate volumes of air simultaneously admitted to a zone or to each of the zones and may be under the control of means responsive to or indicative of a condition existing in a zone, or in each of the zones being conditioned. In accordance with my invention the humidity is controlled by cooling and dehumidiiying. one volume of air admitted .to a cool air duct and diverting a portion of the dehumidified and cooled air into a warm air duct for mixing with a second volume of air prior to treatment thereof by a heat exchanger in the warm air duct. The heat exchanger may operate to maintain a predetermined temperature in the warm air duct and a temperature responsive means for controlling the operation of this heat exchanger may be modified in operation by means responsive to outdoor temperature.

For the prevention of draft efiects being conditioned during periods when the teming means. One particular object is to prevent treated volumes is in varying proportions diverted,

to and mixed with the air of a second volume to either treat or assist in the treatment of the second volume of air. The proportion of air diverted from the first to the second volume is controlled by a condition responsive means inperature in a cool air duct would otherwise be sulilciently low to produce .such effects a first volume of air in the conditioner is heated for maintaining the air in the warm air duct at a predetermined high temperature and a second volume v A porsure the existence of a temperature that is sufflciently high to avoid the'production of the draft effects. In this manner the diverted warm air may be employed to maintain a predetermined minimum temperature in the cool air duct and this temperature is sufiiciently high that draft eiiects will be avoided.

A particular object of the invention is the provision of a double duct type of .air conditioning system in which the volume of air in a first duct is maintained at af predetermined temperature that is lower than that maintained in the second duct. A regulated mixture of fresh and recirculated air is admitted to the conditioner. A controlled heat exchange cooling and dehumidifying means is maintained for the air admitted to the first volume. r A portion of the cooled and dehumidified air is mixed with the air supply for the second volume of air under the control of a humldity'responsive means to provide for any re-- quired dehumidification of the two volumes of air and the humidity responsive means likewise conthus controlled for humidity is subjected to a conin a zonetrolled heating means which heats and maintains this volume at a predetermined temperature.

A portion of the heated volume of air is mixed with the cooledand dehumidified air of the first volume under the control of thermostatic means for the purpose of treating and maintaining the volume in the cool air duct at the desired value of temperature lower than that maintained in the second duct. The thermostatic controller means is likewise employed to control the means for regulating the mixture of fresh and recirculated air which is admitted to the conditioner. This controller may be compensated for outdoor conditions. A plurality of zones, or a single zone may be conditioned in accordance with the individual zone requirements of humidity and temperature by admitting thereto a-mixture of the two treated volumes of'air. A means for reguthe temperature in the zones upon increase in outdoor temperatures when the system is operating on the summer cycle and to maintain a conthe winter cycle.

stant temperature control during operation on The outdoor temperatureresponsive bulb 30 is employed to regulate these compensating controllers 3|, 32 and 33, in a manner more fully described hereinafter.

Therefrigeration machine 40 is operated durlug the cooling season to make effective the coollating the mixture of the two treated volumes may be provided and this means is preferably controlled by individual zone temperature condition responsive means, although various type of condition responsive means including humidity responsive means may be employed. My invention provides year around air conditioning in which a plurality of zones may be individually conditioned and wherein certain of the zones may require heating and others simultaneously require cooling.

Other objects and advantages of my invention will be apparent from the embodiments thereof described below and illustrated in the drawings.

Figure 1 is a schematic diagram of one form of my air condition system.

Figure 2 is a schematic diagram of a modifica-l tion ofmy invention as illustrated in Figure 1 and i-elating particularl to a system which provides for the elimination of draft effects in the zones being conditioned.

Figure 3 is a schematic diagram of a preferred form of my invention which as illustrated employs pneumatic controls.

Referring to Figure 1, the fan I supplies air to a plenum chamber II from which it is fed to the warm air duct l2 and they coolair duct 13. A heater I5 is located in the warm air duct and is regulated by a motor operated valve [6 in accordance with the temperature in the warm air duct. The valve motor is controlled-bythe temperature responsive bulb l1 and this control may be modified in accordance with outdoor temperature under the control of the temperature responsive bulb IS in such a manner that for winter operation as the outside temperature decreases a higher warm air temperature is maintained. The valve operating motor may be of the type illustrated in Patent No. 2,028,110 issued to D. G. Taylor on January 14, 1936.

ing and dehumidifying means IS. The refrigerant compressor is operated in a conventional manner by acontrol 34 responsive to the return line refrigerant pressure and this control may in turn be regulated by aswitching device 35 controlled by the outdoor temperatureresponsive bulb 36. Anexpansion valve 38 in the refrigerant supply line for thecooling means 19 may be of a well known type that is influenced by the evaporator outlet temperatures under the control of thebulb 39.

A motor operated refrigerant return line pressure control means 4|, of which theterminals 42 and 43 are connected to any. suitable source of power, is employed to operate a by-pass reduction valve in a known manner for varying the compressor capacity. The several pressure responsive control means acting in conjunction with the expansion valve control means serve to operate the cooling means 19 to establish a desired temperature in the cool air duct.

A humidifyingspray device 45 controlled bysolenoid valve 45 is provided for supplying moisture to the air during operation on the winter cycle. This spray device is illustrated as being. located in the fan plenum chamber but may ,eral zones. The spray is further controlled by The air admitted to the cold air duct I: is

cooled and dehumidifled by the cooling means i9 of a system which may be operated to dehumidify employed to proportion the air admitted to each of the respective zones from the warm and cold air ducts. Themotors 26, 21 and 28 may be of a switch 50 which is actuated bya connection with a summer and winter operatingcycle changeover switch 5|, which in turn is controlled by an outdoor temperature responsive bulb 52. This switch may be adjusted to close at a temperature of, for example, 65 F. 1

Fresh and returnair dampers 56 and 51 are of the reverse acting and proportioning type and are positioned'by a.motor 58 of the type illustrated in the patent to D. G. Taylor referred to above. For the operation of these dampers the' temperature responsive bulb 52 located in the air plenum chamber is employed to maintain the temperature therein at a predetermined value of, for example, 65 F., or above.

For operating the fresh and return air damp- 'ers 56 and 51 an economizer humidityresponsive control 10 is provided which serves to. improve the operating characteristics of the system. The outdoor humidityresponsive device 10 is placed in control of the fresh and return air dampers when the outdoor temperature responsive device 52 actuates bellows 15 to operate switch The switch 5I is actuated at a predetermined temperature of, for example, 75 4 F. to place outdoor humidity responsive device III in control of the fresh and return air dampers for the purposeof closing thefresh air damper 56. The fresh and return air dampers are also operated in accordance with outdoor humidity to maintain as nearly as possible a relative humidity of or lower. During those periods when the outdoor humidity is excessively high including such periods during whichit is raining, the fresh air damper will be moved to a closed position when the relative humidity ex.-

ceeds the desired value and thus decrease the dehumidification requirements of the sytsem. The humidity responsive device I0 is employed to actuate a switch I98 which ,serves to close thefresh air damper 56 when the outside air rises to a value of, for example, 60 degrees relative humidity or above. .The dampers are normally controlled in a modulating manner by thethermostat 62 to maintain a desired value of, for example, 65 F. in theplenum chamber 62. The control of the fresh and return air dampers is further described below.

An improved temperature and humidity control is provided by dehumidifying and cooling a first volume of air which flows from the fan amount of air supplied from the fan plenum.-

direction for a given position of the master controller. In other words,-thedevice 95 effectively adjusts the range X to raise or lower the control range of the master control 90 in accordance with variations in outdoor temperature.

In operation on the winter cycle the relative humidity is normally low with the result that the humidity responsive control 81 operates themotor 84 to close the by-pass damper 82. The master potentiometer controller 94 for positioning thedamper 83 is accordingly positioned at. one end of its effective control range on thepotentiometer resistances 92 and 93. The

' ,damper motor as is then'regulated to throttle volume ofair circulated in the air conditioning system is decreased in a manner proportional with decreasing outdoor temperatures.

The operation of the system is as follows: The

' fan I0 may be operated in a continuous or other chamber II and that which is diverted from the the direct control of a humidity responsive element 81 which may be located in the zone or otherwise positioned to respond to humidity conditions representative of those existing in the zones.

Themotor 85 for positioning thedamper 83 is regulated primarily by a master potentiometer controller 90. The potentiometer controller -is actuated by a. shaft 9| in accordance with the positioning ofmotor 84 and the shaft positions aslider arm 92 with respect to acenter tap resistance 93 and the. potentiometer resist-1 ance 94. 'Ihe operation of this controller is such that as the slider arm is moved a distance X, themotor 85 is actuated between positions for fully opening and closing thedamper 83.

In the winter operating cycle when outdoor tem peratures are relatively'low it is desirable to decrease the volume of air circulated in the conditioning system.' In order to restrict the air flow, the control for thedamper 83 is compensated by an outdoor temperatureresponsive device 95. The outdoor temperatureresponsive device 95 actuates the bellows 96 to position a pivoted and biasedpotentiometer slider arm 91 with respect to thepotentiometer resistance 98. The operation of this potentiometer serves to vary the control asserted by the master con-' troller. 90 in such a manner that as theslider arm 91 moves to the left upon decrease in temperature the-dampers are operated in a closing the air in the system.

well known manner, not shown, for circulating The heater I5 in the warm air duct is regulated by the motor operated valve Ii for which current is supplied by the leads I20 and I2I. This motor is controlled by the temperature responsive capsule I I located in the warm air duct which actuates the bellows I88 for positioning a potentiometer slider arm I09 with respect to the center tap resistance H0 and a potentiometer resistance II I. Movement of the potentiometer slide arm serves to vary the resistance inserted between the common wire II2 of the potentiometer motor control circuit'and the wires I I3 and I I4 of the motor control circuit with a resultant operation of the motor. Upon a decrease in the temperature in the warm air duct, the potentiometer slider arm I89 is moved to the right and the valve motor-is correspondingly operated in an opening direction for mainperature maintained in the warm air duct within the predetermined temperature range and to in-. crease the temperature maintained in the warm air duct as the outdoor temperature decreases below a predeterminedvalue of, for example, 60 F. The compensating temperature responsive capsule I8 actuates .a bellows I25 to operate the biased and pivoted potentiometer slider arm I 29 with respect to the potentiometer resistance I21. The potentiometer slider arm I26 is connectedto the common wire I I2 of the heater valve motor control circuit.- The wire H3 of the motor control circuit is connected to the left end of the potentiometer resistance I21 and the wire H4 or this control circuit is connected to the right end of the potentiometer resistance I21. During operation on the winter-cycle when the heating demands on the system are at a maximum, the

fresh air responsive compensating device I8 will operatepotentiometer slide arm 12! to the right in response to a decrease in temperature. This serves to operate the motor, for further opening the valve and for increasing the temperature by varying the control range of the master controller I09. In this manner the temperature in the warm air duct is maintained at a temperature of 80 F. when the outdoor temperature is above 60 F. and within a temperature range of from 80 to 100 during the winter operating cycle at a particular temperature determined by the outdoor temperatureresponsive means 18.

Therefrigeration system 40 is of a type well known in the art and includes a compressor I38 operated by a motor ISI for suppling refrigerant to a condenser I32. The refrigerant is in turn supplied to the dehumidifying and air cooling means, l9 under the control of a well known type ofexpansion valve 38. Theexpansion valve 38 is of a type that responds to the refrigerant return line temperature under the control of the temperatureresponsive means 38. The refrigeration control valve operates to maintain a desired temperature for the cooling means I8. The return line pressure responsive control and by-pass reduction valve 4! serve to vary the compressor capacity and in conjunction with thevalve 38 controls the temperature in the cool air duct.

The cooling and dehumidifying system is made effective for operation on the summer cycle by I 2,372,839 I maintained within the range of 80 F. to roo s.

mitting a greater proportion of fresh air. In this manner the fresh and return air dampers are so regulated as to maintain the predetermined temperature in the fan plenum chamber when posan outdoor temperatureresponsive capsule 36 operating through a bellows for actuating the pivotally mounted andbiased mercury switch 35 to complete a circuit which permits operation of the refrigerant compressor from the line wires 288 and 2M. Theswitch 35 is adjusted topermit operation of the refrigerant compressor motor for the summer cooling 'cycle at a desired temperature at, for example, 65 F. The operation of the compressor motor I3! is additionally regulated in order to maintain a desired pressure in the refrigerant return line. For this purpose a refrigerant return line pressureresponsive cutoff device 34 operates through a bellows to actuate the pivotally mounted and biased mercury switch in control of the compressor motor.

The fresh and returnair dampers 58 and 51 are operated in a proportioning manner and also in a manner to serve as a conditioning "economizer. To serve this further economizer purpose thedamper motor 58 is operated to close thefresh air damper 58 if the outdoor temperature exceedsa? predetermined value and also if the outdoor humidityexceeds a predetermined value as mentioned above. With theswitch 5| in the position illustrated, the temperature responsive means 62 located in the fan plenum chamber then operates to control the positioning of the fresh and return airdamper actuating motor 58. The temperature responsive means 82 actuates a bellows for positioning a pivotally' mounted and biasedpotentiometer slider arm 220 with respect to the potentiometer resistance MI. The potentiometer slider am 228 is connected to the center or common wire of the balanced motor control circuit. The ends of thepotentiometer resistance 22! are connected bywires 224 and 225 to the outer terminals of themotor 58 to complete the motor control circuit. Movement of thepotentiometer slider arm 22!! to the left along thepotentiometer resistance 22! resulting from an increase in temperature in'the fan plenum chamber decreases the resistance in the motor control circuit which includes thewires 224 and 225 while increasing the resistance in the circuit which includes thewires 223 and 225 with the result that motor 58 is operated to position the fresh and return airdampers for adsible by reason of existingoutdoor and return air temperatures.

When the outside temperature exceeds the predetermined value of 75 F., the temperature responsive capsule 52 operates thebellows 15 to close theswitch 5| and complete a circuit to thedamper motor 58 which serves to shunt the external resistance from the portion of the motor control-circuit which includes thewires 223 and 225. This accordingly unbalances the motor control circuit and actuates the motor to close thefresh air damper 58 to minimize the cooling demands on the system.

Should the outdoor relative humidity rise to exceed the predetermined value of 60 per cent the humidityresponsive device 10 operates to close switch I68 and likewise complete a circuit to thedamper motor 58 to shunt the resistance in the portion of the control circuit that includes thewires 223 and 225. This switch I60 also accordingly serves to actuate themotor 58 in a manner to close thefresh air damper 58 This control or the fresh air damper serves to reduce the dehumidification requirements of the system to a minimum particularly in summer when the outdoor humidity is frequently very high.

During operation on both the summer and 1 cehumidification is normally required and operation of the cooling means I9 is necessary for both cooling the air supplied to the cool air duct and for dehumidification purposes. The air supplied to thewarm air duct 12 through thedampers 82 and 83 is primarily controlled by the humidity responsive element 81; The humidity responsive device 81 positions the pivoted and biasedpotentiometer slider arm 88, and this aim is connected to the center or common contro1 wire 25I of thedamper operating motor 84. Thepotentiometer resistance 89 is connected by thewires 252 and 253 to themotor 84. Energy is supplied to the motor from theline wires 258 and 251. The position of theslider arm 88 is varied in accordance with the humidity as the element 81 expands and contracts and serves to vary the resistance in themotor control circuit 25I and 253 with respect to that in the circuit25l and 252 to thus unbalance the circuit and actuatemotor 84 to correspondingly position the damper 82. The damper 82 is controlled entirely by the humidity responsive element 81 and as the humidity increases this damper will be operated to admit a larger proportion of dehumidified and cooled air to the warm air duct. Thereverse acting damper 83 is positioned bymotor 85 and for summerv operation this motor is also controlled primarily by the humidity responsive device 81 in keeping with the operation of themotor 84.

-Thedamper motor 84 operates a linkage 8| to position theslider arm 92 of the master potentiometer for effecting the control of thedamper motor 85. Theslider arm 92 is positioned with respect to the center tappedresistance 93 and the resistance 94 of the potentiometer. The center tapped potentiometer resistance is connected by a wire 2 to the common wire 214 of the motor control circuit and the potentiometer resistance 94 is connected by wires 218 and 212 to the outer wires 215 and 218, respectively, of the motor control circuit. Power is supplied tomotor 85 from the supply lines 218 and 219. Operation of thedamper motor 84 to vary the position of theslider arm 92 results in varying the resistance in the motor controlcircuit including wires 218 and 21| with respect to the resistance in the motor controlcircuit including wires 21| and 212 and themotor 85 is operated to position thedamper 83 an amount corresponding to the movement of thepotentiometer slider arm 92. Movement of the slider arm 92 a distance X will operate thedamper 83 between thefully open and fully closed positions. Thedamper 83 is in this manner operated in a closing direction upon movement of the damper 82 in an opening direction in response to an increase in humidity. Thedampers 82 and 83 are positioned under the control of the humidity responsive means 81 to maintain a desired value of relative humidity of, for example, 55% in the summer.

The warm airdamper regulating motor 85 is further controlled by the fresh air temperature responsive means 95, although this is so adjusted as to exert a controlling action primarily when the system is operating on the winter cycle for causing a throttling operation of thedamper 83 as the outdoor temperature decreases below a predetermined temperature of, 60 F.

During the winter operating cycle when dehumidiflcation no longer is normally required, the humidity responsive means 81 will operatemotor 84 to maintain the damper 82 in a closed position. Themotor 84 in turn positions theslider arm 92 ofpotentiometer 98 to open thedamper 83 so that substantially all of the air supplied to the warm for example,

'air duct must pass through thedamper 83. In

motor control circuit by the wires 215 and 218.

When in response to decreasing outdoor temperatures the Slider arm is moved to the left across thepotentiometer resistance 98 the resistance in the circuit including wires 214 and 215 is decreased with respect to that in the circuit including the wires 214 and 218. This unbalancing of the motor control circuit results in operating themotor 85 for positioning thedamper 83 in a closing direction. During. operation on.the winter cycle as the outdoor temperature decreases to relatively low values from a predetermined temperature of, for example, 60, thedamper 83 is throttled to decrease the total flow of air in the system.

The humidifying spray means 45 controlled by 9,889 I 288 and 28|, themercury switch 88, and the pivot-.

ally mounted and biased mercury switch-48 which is actuated by the humidityresponsive device 49.

23 for zone B; and 24, 25 for zone C may be actutiometer slider 29| of a master potentiometer with respect to thecentertapped resistance 292 and thepotentiometer resistance 293. The center tapped resistance is connected throughwire 294 to thecommon wire 291 of the control circuit fordamper motor 28. The ends of thepotentiometer resistance 293 are connected through.

thewires 295 and 298 to thewires 299 and 298 of the motor control circuit. Movement of the slider arm 29| across theresistances 292 and 293 a distance X varies the resistance in thecircuit including wires 294 and 295 with respect to that including thewires 294 and 298 to produce an unbalan'cing of the motor control circuit and result in the operation ofthe damper.motor 28 to actuate thedampers 28 an 2| between fully openand fully closed positions.

In this manner, thedampers 28 and 2| are positioned to control thefiow of warm and cool air and maintain a selected temperature for which each zone ther- "mostat is adjusted. The thermostat T for the zones .3 and C operate in a similar manner and areillustrated diagrammatically in the drawings.

Control of the conditioning by the zone thermostats T may be compensated for relatively high outdoor temperatures in a manner to increase the temperature maintained in each zone as the outdoor temperature increases above a predetermined value of, for example, 75 F; For this purpose the outdoor,temperature responsive'means 38 is employed to operate a series of zone compensating potentiometercontrollers 3|, 32 and 33. e v

motor control circuit, the right-hand end of the potentiometer resistance is connected bywire 298 of the motor control circuit and the left hand end of the conductor secured to the potentiometer thesolenoid valve 48 is operable under the control of the' humidity responsive means 49 for humidifying the air when the system is operated on the winter cycle. The pivotally mountedmercury switch 58 is operated through a linkage 219 which is connected to theswitch 5|. The solenoid valve for regulating the humidifying spray is operated through a circuit including the lines resistance 381 is connected-tothe wire 299 of the motor control circuit. For temperatures lower than .75" F., the slider arm of the potentiometer controller 3| is positioned by the bellows 385 along a conductor connected to the potentiometer resistance 381 and no compensating action is produced by the potentiometer. However, as the temperature varies between F. and F. the

slider arm is positioned along thepotentiometer resistance 301 to vary the resistance betweenwires 291 and 299 with respect to that inserted betweenwires 291 and 238 of the control circuit formotor 26. Thedamper motor 26 is accord-- inglyactu'ated in response to the unbalancing of the compensating potentiometer control circuit in a manner to increase the temperature of the conditioned air admitted to the zone upon anincrease in relatively high outdoor temperatures. In eilect, the compensating controller 3| serves to vary thecontrol point of the master potentiomand a cool air duct is treated and tempered inaccordance with variously compensated controls and wherein the treatment of the air for one duct is aided by mixing therewith controlled portions of the air as treated for use in the other duct. The air as conditioned for use in the warm and cool air ducts is employed for conditioning each zone in accordance with the compensated requirements of the individual zones.

In Figure 2 of the drawings there is disclosed a, modification of the system illustrated in Figure 1. In this modification the flowof air from the warm and cool air ducts is controllably proportioned for COmiitiOIliXlg the plurality of zones A, B, and C in accordance with the individual zone requirements as shown in Figure 1. The modification shown in Figure 2 discloses a system in which a substantially constant air flow is maintained and in which draft effects are eliminated during periods of relatively low outdoor temperatures. Referring to Figure 2, a fan I supplies air to a plenum chamber I I from which it is fed to awarm air duct 400 and a cool air duct 40I. A heat exchange means is employed for heating the air supplied to the warm air duct and also a portion of the air supplied to the cool air duct. The heating medium supply is regulated by a motor operated valve 6 controlled by the temperature responsive means 4" located in the warm air duct. The temperature responsive means 4I1 through bellows'4l8 positions a pivotally mounted and biased potentiometer slider arm 4 I 9 with respect to thepotentiometer resistance 420 for controlling the motor op-i erated valve M6. The potentiometer slider arm M9 is connected to thecommon wire 423 of the motor control circuit and the ends of thepotentiometer resistance 420 are connected to wires 42I and 4220f the motor control circuit. Movement of the potentiometer slider arm 9 by the temperature responsive means 1 varies the resistance in the circuit which includes thewires 42I and 423 with respect to the resistance in the circuit including the wires 42I and 422. This unbalancing of the motor control ,circuit results inv operation of the motor actuated valve' H3 in a graduating manner corresponding to the movement of the potentiometer slider arm. The temperature responsive device 4" is adjusted to maintain a desired temperature in the warm air duct of, for example, 140 F. In order to maintain a substantially constant air flow without the production of objectionable draft effects during periods of relatively low outdoor temperatures, the air admitted to the cold air duct is maintained at a predetermined temperature of,

for example, 65 F. In order to maintain the tem- 5 perature of the air in the cool air duct at a temperature of 65 F. this volume of air is made up of a mixture of air from the fan plenum. chamber I I and air diverted to the cool air duct from the volume which is conditioned in the warm air duct. Thereverse operating dampers 404 and 405 are operated by themotor 405 under the control of the temperature responsive means 425 located in the cool air duct for maintaining the temperature of the air supplied to the cool air duct at 65 F. The temperature responsive means 425 throughbellows 426 actuates the potentiometel:slider arm 421 with respect to the 'p0tentiometer resistance 428 for controlling thedamper operating motor 400.. The potentiometer slider 2arm 421 is connected by thecommon wire 400 of the motor control circuit, and the ends of thepotentiometer resistance 423 are connected to the wires 0 and 4 of the motor control circuit. Movement of the potentiometer slider arm with respect to theresistance 420 causes an unbalancing of the motor control circuit which results in the operation of the motor for adjusting the position of the reverse acting dampers. Power for operating the motor 406 is obtained from thesupply lines 401 and 403.

Reverse acting fresh and return air dampers 453 and 451 for proportioning the flow of 7 fresh and return air are positioned by a. motor 450 and their operation may be controlled by the temperature (responsive device 425 located in the cool air duct for operation of thedampers 404 and 405. The potentiometer controller for the dam-per motor is actuated by thebellows 426 through a linkage 492 that cooperates with the 40slider arm 421 to position the slider arm with respect to the potentiometer resistance 43I. Thepotentiometer slider arm 430 is connected to thecommon wire 434 of the damper motor control circuit and the ends of the potentiometer re- 40 sistance 43I are connected towires 435 and 430 I of the motor control circuit. Power for operating the motor 450 is supplied from thelines 431 and 438 which are connected to a suitable source,

not shown. Movement of the potentiometer slider arm to the left across the full length of the potentiometer resistance 43I in response to an increased demand for heated air in the cool air duct results in unbalancing the motor control circuit and operation of the fresh air damper from a fully open to a fully closed position.

A minimum open position for the fresh air damper may be required for ventilation purposes regardless of the existence of low outdoor temperatures. A resistance 432 is inserted in thewire 436 of the motor control circuit to prevent operation of the damper motor beyond a minimum open position for the fresh air damper. The resistance 432 may be adjusted by the conevent of a relatively low internal heat load.

tact 433 to maintain any desired minimum open- I The system described in Figure 2 providesfor advantageous operation of a double duct type of conditioning system during thewinter. The temperature of the air in the cool air duct is controlled by diverting and mixing therewith a porgiont of the treated air supply from the warm air uc located in the cool air duct is employed to control the temperature of the air admitted thereto for the prevention of drafts in the zones being conditioned during low outdoor temperatures. The cool air temperature responsive control means is also employed to operate a damper motor for positioning the fresh and return air dampers and manually adjustable means are incorporated in the control circuit to prevent the proportioning operation of the fresh and return air dampers beyond a minimum open position for the fresh air damper upon increased demands for heating of the air supplied to the cool air duct which normally accompanies decreasing outdoor temperatures. As referred to above. the cool and warm air ducts shown in Figure 2 may be employed to condition a zone or zones under the control of zone mixing dampers of the type illustrated in Figure 1.

The preferred form of my invention as illustrated in Figure 3 embodies features in addition to certain of those incorporated in the forms of my invention illustrated in Figures 1 and 2 as .will become apparent from the following description.

In this embodiment of my invention a dual plenum type of conditioning system is employed to provide summer and winter individual zone control. The conditioning for both temperature and humidity is partly regulated by a controlled diversion of various quantities of air between the warm and cold air plenums and means are provided for controlling the mixture of air from the plenums in accordance with the individual zone requirements.

A double cage type offan 500 is employed to circulate air to the cool air duct 5M and the warm air duct 582. Fresh air is supplied through theduct 503 to that side of the dual fan which is con nected to the cool air duct 5M and return air is supplied through theduct 504 to that side of the dual fan which is connected to thewarm air duct 502. In this manner the fresh air admitted to the system will for the most pai'tbe supplied to the cool air duct. In the summer thefresh air will accordingly be subjected to cooling and dehumidification in the cool air duct. In winter operation the fresh air will most effectively serve to maintain the temperature of the cool air duct at the desired value, and during this time the return air which is for the most part admitted to the warm air duct 'will require a minimum of heating.

Reverse acting dampers 585 and 50B positionedby themotors 501 and 508, respectively, are emj ployed to control in a proportioning manner the fresh and return air admitted to thesystem.

Thecooler 5|0 located in the cool air duct is regulated by the joint action of anexpansion valve 5| l and the solenoid valve5l2 for the pur-' be of any suitable type and as illustrated is regu- A single temperature responsive means cool air duct for mixture with the supply of air lated by a valve in to maintain a desired ntemperature at the outlet of the warm air duct.

The reverse acting and 'proportioning dampers 520 and 52l are actuated by amotor 522 and serve to divert cooled and dehumidified air from the that is to be'heated in the warm air duct. Thereverse acting dampers 523 and 524 are actuated by amotor 525 and serve to divert heated air from the warm air duct to thecooi air duct for mixture with the cool air in order to maintain the desired temperature of the cool air duct outlet supply. A back pressure regulating valve or other known means for regulating the capacity control of the refrigeration compressor, not

shown, may preferably also-be employed to prevent freezing of the coil uponfvariation in the duct outlets, respectively, and these dampers are The flow of condi-' actuated by themotor 534. tioned air to each zone is regulated in a similar manner.

The'system is schematically illustrated in Fi ure 3 asbeing controlled pneumatically and-various well known forms of pneumatic control means might be employed. It will be apparent that the system may be operatedby electrical control means or by a combination of electric andpneumatic controllers. In the form illustrated thesolenoid valve 512 for the cooler is controlled by a switch and relay device 538,which is actuated pneumatically by varying the pressure from theair supply'linc 539. The motor is connected by theline 539 to a suitable source of air supply, not shown, such which'is positioned with respect to a nozzle in thesupply line 539 to vary the pressure therein. Thethermostat 540 is actuated by a tempera ture responsive capsule 54! located in the fresh air plenum. The switch 538 serves to control a circuit which includes any suitable source of power, not shown, for operation of the solenoid valve 5l2 to in turn control the cooling medium supply for the cooler. The valve '5l2 is actuated in conjunction with thevalve 5 to control the cooler 510 in a known manner in order to maintain a desired temperature of the air subjected thereto and this temperature may be of a value that is sufficiently low as to produce dehumidification. A

The heater 5H5 is operated by the motor actuated valve 5H which is connected to anair line 543 that is supplied from any suitable source.

Themaster thermostat 540, operatedby the capsule'54l in response to outdoor or fresh air plenum-chamber temperature, serve in conjunction with thesubmas'ter thermostat 544, which is actuated by thecapsule 545 located near the outlet of .the warm air duct, to control the operation of the heater. For this purpose the motor and flapper of thethermostat 544 serve to vary the bleed of air from theline 543 for actuating the heater valve 5H. Also, themaster thermostat 540 isconnected through thelines 539 and 548 to apressure motor 550 which serves to position the nozzle of theline 543 with respect to that of the flapper of thesubmaster thermostat 544 to vary the pressure inline 543 and to thus modify the control of the heater by thethermostat 544. The pressur motor 550 is illustrated as being of a type that operates through a flexible connection 55l in theline 543 to position the nozzle of theline 543 with reference to the flapper of thesubmaster thermostat 544 through the operation of a biased bellows operated member or motor connected to theline 548. Accordingly as the master thermostat varies the pressure inline 548 the nozzle ofth line 543 is varied in position with respect to the flapper of thesubmaster thermostat 544 to decrease the control point of saidsubmaster thermostat 544 upon rise in outdoor temperature. The heater is thus operated to maintain a warm air outlet duct tem-.

perature within a range of from 75 .F. to 100 F. as the fresh air temperature decreases from a value of 70 F. to F. and a predetermined temperature is maintained in the warm air duct for a given temperature in the fresh air plenum.

The motorized valve I4 in control of the spray humidifying means is operated by aline 555 which is connected to a suitable source of air supply, not shown, and controlled by the hu- .midity responsive means HI. The humidity responsive means located in the return air plenum serves to position the pivoted and biased flapper for varying the pressure in theline 555 to operate the spray to maintain a desired value of'humidity of the air in the system.-

Themotor 522 in control of thereverse acting dampers 520 and 52! i operated by air supplied through theline 551 from a suitable source, not shown. Th humidity responsive control device H2 is illustrated as being located in the return air duct, but might, if desired, be located in the discharge of the warm air duct, and this device serves. to position a flapper element for varying the pressure in theline 551 for operation of themotor of the mixing dampers. On a rise in relative humidity thedampers 520 and 52l will be positioned in a manner to divert an increased amount of cold, dehumidified air from the cool air duct for mixture with the supply for the warm air duct. The" cool, dehumidified air will if necessary be reheated in the warm airduct. The humidity responsive means H2 thus serves to v ry the volume of air subjected to cooling and dehumidification and to maintain the desired conditions of humidity for the system.

Athermostat 560 operated by a temperature responsive capsule 56l located in the cool air duct and thereverse acting thermostat 562 operated by a temperature responsive capsule 553 which is responsive to outdoor, or fresh air plenum chamber' temperatures, serve jointly to control themotors 525, 501 and 508 for the reverse acting warm to cool airduct mixing dampers 523 and 524 and the fresh and returnair dampers 505 and 505. Each of the motors are connected for operation to aline 566 which is supplied with air from any suitable source. The duct diverting dampers and the fresh and return air dampers are preferably operated in the sequential manner hereinafter described. Thethermostat 560 actuates a flapper element'for controlling the pressure in the line 565 for actuating the mixing damper motor to normally maintain a cool air duct outlet temperature of 60 F. The mixing damper motor 525is adJusted, in a known manner, for operation between the closed and open damper positions upon a variation of pressure in the line 556 of, for example, between 3 and 8 pounds. Upon a decrease in temperature in the cool air duct thethermostat 560 accordingly actuatesmotor 525 and the mixing dampers to increase the flow of air diverted from the warm air duct and to cor-. respondingly decrease the flow of cooled air. Themotor 501 normally maintains the fresh air damper in a closed or in a predetermined minimum opened position. The reverse acting fresh and return air damper' motors are adjusted for operation between their full open and fully closed positions as the pressure in theline 566 varies between, for example, 8 pounds and 13 pounds. Upon a suiiicient rise in temperature in the cool air duct thethermostat 560 operates to increase the pressure in line 556 to within the range of 8 pounds and 13 pounds for actuation of themotor 501 and 506 to increase the supply of fresh air to the system and to correspondingly decrease the supply of return air. Upon a temperature drop in the cool air duct thethermostat 560 will actuate the fresh and return air dampers to decrease the flow of fresh air and subsequently actuate the mixingdampers 523 and 524 to increase the amount of heated air diverted from the warm air duct. Thereverse acting thermostat 562 is adjusted for operation as the outdoor temperature rises above F. to modify the pressure theline 566 for operating the fresh air damper in a closing direction and'the return air damper in an opening direction in order to prevent the use of large quantities of outside air when the outside temperature is relatively high. Thisthermostat 562 will have no effect upon the damper motors as the temperature decreases below a value of 75 F. g

Thethermostat 510 is located in the zone, or in other desired position by virtue of which it is capable of controlling both-the humidity and temperature which it is desired to maintain in the zone to be conditioned. This thermostat serves to control the reverse acting warm and coolair duct dampers 532 and 533 for varying in a graduated manner the flow of conditioned air from the warm and cool air ducts to theparticular zone beingserved thereby. Thedamper operating motor 534 is connected with the line 5'" which is supplied from any suitable air supply source, not shown, and the temperature responsive bellows of thethermostat 510 positions the flapper valve to regulate the pressure maintained in the air supply line for actuating the damper motor.

Upon an increase in the zone temperature thethermostat 510 positions the flapper in a manner to decrease the flow or air permitted to escape from line 5' and to accordingly increase the pressure in the line for actuating thedamper motor 534 to move the coolair duct damper 532 in an opening direction and to correspondingly move the warmair duct damper 533 in a closing direc- Control elements similar to the thermostat 515 may be employed in association with each individual zone of the system for operation of the and both economical and eificient in operation.

In the operation of the system the fresh and return an dampers and the warm and cool air duct diverting dampers cooperate with a single heating means and a single cooling means to economically condition the air in the warm and cool air ducts with respect to both humidity and temperature for the year around. In the winter the humidity of the system is maintained'at a desired value by the humidifying means in the warm air duct and since thehumidity and temperature requirements are generally proportional at this time, the zone thermostats proportion the warm and humidified air to the zones in accordance with inchange means in said first duct to saidsecond duct for mixture with the air directly circulated thereto, humidity responsive means for controlling the said regulating means for diverting dividual requirements. In the winter the fresh air admitted to the system largely maintains the if necessary in order to maintain the desired cool air duct outlet temperature.

In the summer operation of the system the fresh air admitted to the system forms the large est portion of the volume circulated and most of this air will be admitted to the cooling coil. A

portion of this cooled and dehumidified air is subsequently diverted into the warm air duct as required. If the cooling and dehumidifying requirements are relatively high the dehumidified air diverted to the warm air duct will be heated and a portion of air from the warm air duct is subsequently diverted to the cool air duct to maintain the desired conditions therein. The

zone thermostats will in the summer control air flow from the two volumes of air to the individual zones to maintain the desired zone temperature,

air to said second duct, zone damper means in said first and second ducts for proportioning the flow of air issuing simultaneously from said ducts for conditioning each of said zones, and temperature responsive means in each of said plurality of zones for individually regulating the zone conditioning air flow proportioning means.

2-. In an air conditioning system for a plurality of zones, the combination comprising, a conditioning unit including a plurality of separate ducts, heat exchange means in each of said ducts, means for forcing .air through the ducts, means for regulating the heat exchange means in one of said ducts for dehumidifying and cooling the air, means for regulating. a fiow of the said and by reason of the particular dehumidification treatment of the two volumes of air the humidity refiquirements of the zones are simultaneously satis ed.

It will be noted that the system of my invention is operative to provide year around air conditioning for a. single zone or for a plurality of zones in accordance with the individual zone requirements and although certain of the zones require heating at a time when other zones demand cooling.

dehumidified and cooled air from the said one duct to a second duct for mixture with the fiow of air therein andprior to treatment by the heat exchange means in the said second duct, humidity responsive means for controlling the air fiow regulating means, means for regulating the proportions of air admitted to each of the plurality of zones from said plurality of ducts, and temperature responsive means for controlling the'means for regulating the proportions oi air admitted to each of the zones.

3. An air conditioning system for a plurality of zones, in combination comprising, a conditioning chamber containing a first volume of air and a second separate volume oi air and means to supply air therefor, heat exchange means for cooling and dehumidiiying said first volume of air, regulating means for diverting a portion of said first volume of cool and dehumidified air to said second volume of air for admixture therewith, heat exchange means for said second volume of air including the portion diverted from the first volume and means including temperature responsive means for maintaining the sec- Ineach of the above described systems of my invention, provision may readily be made for shutting ofi the conditioning of one or more zones of the system. In order to insure a constant pressure fiow of air to each zone, volume dampers controlled by static pressure in the system might be employed in a manner well known in the art and the cross-sectional area of the warm and cool air ducts leading to each zone outlet may be so designed as to insure a proper distribution of the conditioned air to the duct outlet for each zone. It is' obvious that the systems illustrated may lie-modified in various forms within the scopev of my invention and that the systems are capable of application various fields, accordingly the embodiments disclosed are merely illustrative and the invention is to be limited only as determined by the appended claims.

. I claim as my invention:

1. In an air conditioning system for a plurality of zones, the combination comprising,.a first duct and a second duct, means for circulating air through said ducts, heat exchange means in said first duct, regulating means for diverting a portion of the air which has passed in heat exchange relation with said heat exand volume at a predetermined temperature, means for proportioning the flow of air from said first volume and from said second volume for admission to each oi said zones to be conditioned,

humidity responsive means for controlling the said regulating means for diverting a portion of said first volume of air to said second volume, and temperature responsive means for regulating the said means for proportioning the flow oi air for admission to each zone of the plurality of zones to be conditioned.

4. An air conditioning system in combination comprising, a conditioning chamber containing a first volume of air, a second volume of air, and

means to supply air therefor, heat exchange means for each of said volumes of air and means for regulating the heat exchange means, damper means for diverting a portion of said first volume of air after contact with said heat exchange means to said second volume of air for admixture therewith, zone damper means operated by motor means for proportioning' the flow of air from said first'volume and. from said second volume for admission to a zone to be conditioned, humidity responsive means for controlling the said damper means-in a graduating manner for diverting a. portion of said first volume of air to said-second volume and temperature responsive means for controlling the regulating means proportioning the fiow of air admitted to a zone to be conditioned.

5. In an air conditioning system ,for a pluraldamper in a closing direction, heat exchange means in said first duct, regulating means for diverting a portion of the air which has passed in heat exchange relation with said heat exchange means in said first duct to said second duct for mixture with the air directly circulated thereto, heat exchange means for said second duct for treating said mixture of air therein, humidity responsive means for controlling the said regulating means for diverting air to said second duct, zone damper means in said first and second ducts for proportioning the flow of -air issuing simultaneously from said ducts for conditioning each of said zones, and temperature responsive means in each of said plurality of zones for individually regulating the zone conditioning air fiow proportioning means.

6. In an air conditioning system, the combination comprising, a first duct'and a second duct, means for circulating air through said ducts; heat exchange means in said firstduct and in said second duct, regulating means for controlling the fiow of air to said second duct in a graduating manner including damper means for the control of air admitted directly thereto and damper means for diverting treated air from said first duct, humidity responsive means for controlling the said regulating means to increase the proportion of air diverted to said second duct upon increase in humidity above a predetermined value while maintaining the volume of air circulated thereto substantially constant, and means responsive to temperature for additionally controlling the said regulating mean for decreasing the total fiow of air to said duct upon decreasing temperature from a predetermined temperature.

7. A system in combination comprising, a con- I ditioning unit including a first outlet and a second outlet, means for circulating a medium through said unit and for separating the flow to each of said outlets, means in said unit for conditioning the flow of medium to the said first outlet including temperature responsive means and heating means for maintaining a predeter mined temperature of the medium flow to the first of said outlets, damper means for diverting,

' a flow of the medium ,at said predetermined temperature for said first outlet to the fiow of medium for said second outlet, damper means for regulating a flow of fresh and recirculated 'medium to the inlet of said-unit, and condition re-, sponsive means subject to the flow 'of medium for said second outlet for controlling both the said means for regulating the flow of fresh and recirculated medium and the said flow divertin means.

8. A system in combination comprising, a conditioning unit including a first outlet and a second outlet means for circulating a medium through said unit and for separating the flow to each of said outlets, means in said unit for conditioning the fiow of medium to'the said first outlet including temperature responsive means and a heat exchanger for maintaining a predetenmined temperature of the medium fiow to the first of said outlets, damper means for diverting a flow of the medium at said predetermined temperature for said first outlet to the flow of medium for said second outlet, damper means for regulating a flow of fresh and recirculated medium to the inlet of said unit, temperature responsive means subject to the flow of medium for said second outlet for controlling both the said means for regulating the flow of. fresh and recirculated medium and the said flow diverting means, damper means for proportioning the fiow of air issuing simultaneously from each of said outlets, and zone condition responsive means for controlling the positioning of said fiow proportioning outlet damper means.

9. .An air conditioning system in combination comprising, regulating means for admitting fresh and return air to a conditioner and for circulating the air therethrough, partition mean for separating the air flow to maintain a first and a second volume of untreated air iii-the conditioner, cooling means for the said first volume of air, damper means for mixing 'air from the second volume with the cooled air of the first volume, and temperature responsive means for controlling said mixing damper means and said fresh and return air regulating means in such manner that the proportion of fresh air to return air is a maximum within a predetermined temperature range and is a minimum at a temperature above said range.

10. A conditioning system in combination comprising, a first and a second medium conditioner, means for circulating a medium through said conditioners, a first heat exchange means for cooling and dehumidifying the medium fiow to the said first conditioner, temperature responsive means for controlling the first heat exchange means to maintain the medium subjected thereto at a first predetermined temperature, means for regulatingv a fiowof medium to the second conditionerincluding means for admittin 'medium thereto at said first predetermined temperature from said first conditioner, humidifying means in said second conditioner, heat exchange and temperature responsive means in said second conditioner for maintaining the flow of medium to the outlet thereof at a second predetermined temperature, means for regulating a supply of medium to the outlet of the first conditioner including means for regulating and mixing a fiow of medium at said first predetermined temperature with a flow of medium from said second conditioner at said second predetermined temperature, temperature responsive means for controlling said mixing and regulating means to maintain a predetermined temperature of the medium flow to the outlet of said first conditioner, and humidity responsive mean for controlling the said humidifyin means and the said means for regulating the fiow of medium at the first predetermined temperature for admission to the second conditioner.

11. A year around conditioning system for a plurality of zones in combination comprising, a

first and a second medium conditioner, means for circulating a medium through said conditioners, a

'first heat exchange means for cooling and dehumidifying the medium flow to the said first IO-conditioner, temperature responsive means for thereto and for admitting medium thereto at said first predetermined temperature from said first conditioner, humidifying means in said second conditioner, heating means and temperature responsive means in said second conditioner for ,maintaining the flow of medium to the outlet thereof at a second predetermined temperature, means for regulating a supply of medium to the outlet of the first conditioner including means for regulating and mixing a flow of medium at said flrst predetermined temperature with aflow' of medium from said second conditioner at said secondpredetermined temperature, temperature -re-' sponsive means for controlling said mixing and regulating means to maintain a predetermined temperature of the medium flow to the outlet of said first conditioner, humidity responsive means for controlling the said humidiiying means and the said means for regulating the flow of medium' at the first predetermined temperature for admission to the second conditionendamper means for regulating the air supply from each of sa d means and through said ducts into said zones,

means for varying the percentage of air flowing across each heat exchange means while mainperature of the air in said cool air duct forcausing some of the heated air from said warm' air duct to flow into said cool air duct in order to prevent the temperature ofthe air in said cool air duct from dropping below a predetermined value, and temperature responsive means in each zone for regulating the proportion of air from each outlet flowing into said zone for maintaining the temperature therein constant.

15. In an air conditioning system, the combination including a plurality of separate ducts, heat exchange means in each of said ducts, means for iorcingair through the ducts, means for regulating the heat exchange means in one of said ducts for dehumidifying and cooling the air,

means for regulating a flow of said dehumidified.

and cooled air-from the said one duct to a second duct for mixture with the flow of air therein and prior to treatment by the heat exchange meansin the said second duct, humidity responsive means for controlling the air flow regulating means, and means for regulating the flow of air from said ducts.

16. In an air conditioning system, the combination comprising, a first duct and a second duct,

an air supply, means for-circulating air through said ducts, heating means in said first duct and.

cooling means in said second duct, means for diverting air from said second duct into said taining the total flow of air substantially constant by diverting a portion of the air flowing through one duct after it has passed over its heat exchange means and causing it to fiow into said other duct,

. means influenced by a psychrometric condition of the air in one of said ducts for controlling said last mentioned meansin a manner tending to maintain said psychrometric condition substantially' constant, and temperature responsive means in each zone for regulating the proportion of air from each outlet flowing into said zone for maintaining the temperature therein constant.

13. In an air conditioning system for a plurality of zones, in combination, warm and cool air ducts, each of said ducts having an outlet connected to each of said zones for regulating the temperature and humidity therein, means caus- 5 ing a flow of air through said ducts and into said zones, cooling means in said cool air duct for I cooling and dehumidifying the air flowing therethrough, and, means including means responsive to an increase in the relative humidity in said zones for causing an increase in the percentage of air flowing across said cooling means by causing some of said'cooled and dehumidified air to flow into said warm air, duct, and means responsive to the temperature in said zones for regulating the air flowing from the outlets of saidducts. a

first duct, humidity responsive means for con- I trolling said diverting means, other means for controlling the flow of air into said first duct,

means responsive to thetemp'erature of the air supply and influenced by said humidity responsive means to regulate said other means, and means to control the flow of air from said ducts.

17. In an air conditioning system, in combination, a warm air duct, a cool air duct, each duct having anoutlet, heating means in said warm air duct, means causing a flow of fresh and return air through said ducts and said outlets,

means responsive to the temperature of the air in said cool air duct for causing some of the heated air fromsaid warm air duct to flow intosaid cool air duct to prevent the temperature of the air in said cool air duct from dropping below a predetermined value, and means for regulating the proportion of fresh air to return air in'respouse to said means responsive to the temperature of air in said cool air duct.

18. A system in combination comprising, a conditioning unit including a first outlet and a second outlet, means for circulating a medium through said outlets, means in said unit including a heat exchanger for maintaining a prede-' termined temperature of the medium flow to the first-of said outlets, means for diverting afiow of the medium at saidpredetermined temperature for the first outlet to the flow oi-medium for. said second outlet to maintain a predetermined temperature of the medium fiow to said second outlet, means for regulatin a. fiow or 14. In an air conditioningsystem fora plural-,

ity. of zones, in combination, a warm air duct, 2.

cool air duct, each duct having an outlet for each zone, heating mean in said warm air duct,

1 means causing a flow of fresh and return air through said ducts and into said zones, means,

controlling-the proportions of said fresh and re: turn air in-response to the air'temperature in said cool air. duct, means responsive to the temfresh and recirculated medium to the inlet of said unit. and means responsive to the temperature of the air flowing to said second outlet for sequentially controlling both the said mean for regulating the flow of fresh and recirculated medium and the. said fiowdiverting mean in such manner that the fresh air flow is first minimized and then air is diverted .in increasing amounts as the temperature of the air flowing to-the second outlet drops below --a predetermined value.

' WIILIAM L. McGRA'IH.

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