US2327536A - Gas fired air conditioning system - Google Patents

Description

Aug. 24, 1943. J. 5. LocKE GAS. FIRED AIR CONDITIONING SYSTEM F'iled'Dec. 11, 1941 INVENTOR- -J=unms 5.1506102 ATTORNEY Patented Aug. 24, 1943 2,327,536 GAS FIRED AIR. CONDITIONING YSTEM James S. Locke,

Park Ridge, 111., assignor to Minneapolis-Honeywell Regulator Company,

Minneapolis, Minn., a corporation of Delaware Application December 11, 1941, Serial No. 422,513

13 Claims.

The present invention relates to air conditioning systems and control arrangements therefor.

The primary object of the invention is to provide an improved control arrangement for conditioning apparatus employing a gas fired heater or the like wherein the volume of air being treated is modulatingly controlled in accordance with the temperature in a space being served, and the flow of gas or other corresponding medium is modulatingly controlled in accordance with the discharge temperature of the air, that is the temperature of the air passing over the heater.

Anotherobject of the invention is to provide an arrangement comprising a gas fired heater having face and by-pass dampers associated therewith, with a space thermostat controlling th dampers and a' discharge thermostat controlling the fiow of gas to the heater.

Another object of the invention is to provide a control arrangement in an air conditioning system embodying fresh and return air dampers, a conditioning device having face and by-pass dampers associated therewith controlled by a space thermostat, and means for adjusting the fresh air damper in response to a discharge tem-- perature controller after the face damper has been moved to a minimum position by the space thermostat.

Numerous other objects and advantages of 'my invention will become apparent from the following detailed description and annexed drawing.

Referring to the drawing, numeral I designates an air conditioning duct of the type as conventionally employed in air conditioning systems. The right end of the duct is connected to the inlet of a circulating fan H drivenby an electric motor I2, the fan discharging into a duct l 3 which communicates with a room or space to be conditioned I4. Fresh air from outdoors can be admitted through the left end of the duct l0 and return air from the room or space is admitted to the duct l0 through a return air duct I5 so that the fresh and return air can mixin the duct Ill. The proportions of fresh and return air which are mixed in the duct H] are controlled by a fresh air damper l6 and return air damper l1, both of these dampers being operated in a manner well known in the art by means of a proportioning type damper motor 20. The proportioning motor 20 comprises a reversible electric motor, this motor being of the type shown in detail in the proportiom'ng control system disclosed in the patent to D. G. Taylor No. 2,028,110. The damper motor 20 has a shaft which operates a crank-arm 21 which through a link 22 and a link 23 connecting the two sets of dampers operates both sets of dampers at the same time. Power is supplied to the motor 20 through wires 24 and 25 which may be connected to any suitable source of power. The operation of the fresh and return air dampers and the controls for the damper motor will be described more in detail hereafter.

Disposed in the duct I3 is a partition member 30 which separates the flow of air in the duct 13 So that it follows two paths, one on either side of the partition member. On one side of the partition is a gas fired heater designated by the numeral 3 I. This heater may be of any well known type of gas fired heater common in the art. Gas is supplied to the heater through a pipe 32 and interposed in the pipe 32 is a control valve generally designated by the numeral 33. As shown, this control valve is a schematic representation of the gas control valve shown in detail in the patent of C. G. Kronmiller, No. 2,214,558. As disclosed, the gas valve comprises a body portion 34 having the usual partition member therein having an openin therethrough forming a valve seat with which cooperates a valve member 35. The valve member 35 is connected to a valve stem 36 which extends through a packing gland 31 and which is normally biased in an upward direction toward open position of the valve, by a coil spring-38 interposed between the packing nut of the packing gland and a collar 39 on the valve stem. Numeral 40 designates a bell-crank lever pivoted at 4|, one arm of which normally engages a pin 42 on the upper part of the valve stem 36 and the other arm of which normally bears against the operating stem of an expansible and contractible bellows 43 forming part of a thermostatic controller 44. The thermostatic controller includes a thermal bulb 45 disposed in the path of air which passes over the heater 3|, the thermal bulb being connected to the bellows 43 by a capillary tube 46. The thermal bulb 45 contains a volatile liquid which vaporizes and develops a pressure in the thermostatic controller, dependingvupon the temperature of the air passing over the bulb 45. The bellows 43 expands and contracts in accordance with the said temperature and through the bell-crank lever 40 urges the valve stem 36 downwardly when the bellows expands and permits it to move upwardly under the influence of spring 38 when the bellows contracts. In other words, the thermostatic controller 44 operates to throttle the position of the valve 33, depending upon the temperature of the air passing over the heater. The parts of the thermostatic controller are so adjusted that it has been throttled to a minimum position. This is a common way of operating gas valves and is well known in the art as shown in the Kronmiller patent.

In addition to the thermostatic controller ll, the valve 39 may be closed by means of an electric motor driven mechanism 59. This mechanism includes an electric motor which operates a plunger 5| which moves up and down under the influence of the motor and a biasing spring, the plunger 5| moving down and engaging the upper end of the valve stem-36 and fully closing the valve when the motor of the device 59 is deenergized. When the motor of the device 59 is energized, the plunger 5| is retracted to the position as shown in the drawing and in this position the valve 93 can open under the influence of the biasing spring 29. As mentioned above, the valve 33 may include mechanism for causing it to immediately close after it has been throttled to a minimum position, and this mechanism may takethe form of electrical contacts which deenergize the motor of device 59 when the valve has reached a minimum position. The details of this arrangement are shown in the Kronmiller patent.

Within the duct l9, associated with the parti-' tion 39 and the heater 9| are a set of face and by-pass dampers 55 including face dampers 56 and by-pass dampers 51. These dampers are operated by means of an operating arm 58 connected to the crank-arm 59 of a proportioning type damper motor 69 which is of the same type as the damper motor 29. Power is supplied to the damper motor59 through wires 6| and 92 which may be connected to any suitable source of power, not shown.

The controls for the system include a proportioning type space thermostat 65 which controls the damper motor 69. The thermostat 65 comprises a coiled bimetallic element 66 which has attached thereto a blade 61 forming a slider adapted to be moved over a slide wire resistance 68 when the temperature afiecting the bimetal element 69 rises and then falls. The bimetal element 66 is connected to the proportioning motor 69 by a wire 69 and the ends of the slide wire resistance are connected to the proportioning motor by wires I9 and II, respectively. When the temperature afiecting the thermostat falls the slider 91 is moved to the left along resistance 69 and when the temperature rises. the slider 61 is moved to the right along resistance 69. Thisoperation is well known in the art in connection with .proportioning control systems and. is the same as set forth in detail in the Taylor patent. The controller 95 may operate over a range of from '10 to 72, for example, the

slider being at the midpointbf resistance 68' when the temperature is 71. With the parts in the position shown, the slider is at the midpoint of resistance 99 and the dampers are in an intermediate position. When the temperature falls, the 'damper motor 69 operates the dampers so as to increase the amount of air passing over the heater 9| and to decrease the amount going through thcby-pass. when the temperature afiecting controller 99 rises, the dampers are operated in the Opposite manner.

The damper motor 99 has associated therewith two auxiliary switches designated by the numerals 1s and 1s. The auxiliary switch 15 includes a cam 11 mounted on the shaft of the proportioning motor 99, the cam 11 having a single dwell, as shown, and being arranged to operate a pivoted switch carrying lever 19 carrying a double-ended mercury switch 19. Normally, the electrodes at the right end of the mercury switch 19 are bridged by the mercury and as the temperature'in the space rises and the controller 95 operates the dampers 55 to cause less air to pass over the heater II, the cam 11 is rotated in a clockwise direction, and as will presently appear more clearly, when the dampers 95 reach a predetermined position the cam II will actuate the mercury switch I9 to cause the electrodes at its left end to be bridged. This occurs alter the gas valve 93 has been closed and only a small quantity of air is being passed over the heater II.

The auxiliary switch 19 includes a cam 9| similar to cam 11 and having a single dwell. The cam 9| is arranged to actuate a pivoted switch carrying lever 92 carrying a mercury switch 92 having electrodes at its right end. As pointed out above, when the damper motor 99 is operated in a direction to cause less air to pass over the heater 3|, the shaft of the motor rotates in a clockwise direction and as cam 8| rotates, its dwell will lift the lever 92 and open the mercury switch when the face dampers 99 have reached a minimum position-wherein a minimum amount of air is passing over the heater II. This minimum position is of course determined by the adjustment of cam 9| with respect to the drive shaft of motor 99. As will be presently pointed-out, the mercury switch 99 controls the motor of the device 99 forming part of valve 93, and the mercury switch causes closure of the valve when the face dampers '99 have reached 'a minimum position. Mercury switch 19 is tilted slightly after mercury switch 99, that is, after the temperatures has risen slightly higher. This operation will be referred to more in detail hereinafter.

The controls for the fresh and return air damper motor 29,include a proportioning type discharge air temperature controller 99. The controller 99 includes a slide wire resistance 9| cooperating with which is a pivoted slider 92 which is movable about its pivot by an expansible and contractible bellows 93, the movable end of which carries a stem bearing against the slider 92. The slider is normally urged against the stem of the bellows 93 by a coil spring 94. The interiorof the bellows 93 is connected to a thermal bulb 95 by acapillary tube 99. The thermal bulb 99 is disposedin the path of the air being discharged by the fan I| so that the cgntroiler 99 is responsive to the temperature of the'disch arge air from the fan. The controller 99 is not normally in control of the motor 29 but it may be placed in control thereof by the mercury switch II. The circuits whereby the controller 99 controls the motor 29 will be described in the complete description of the operation of the system as a whole hereinafter.

when the controller 99 is not controlling the motor 29, .the fresh air damper I9 is normally in a minimum position admitting a minimum quantity of fresh air and the return air dampers I1 of the fresh air damper, that is the position of motor 20 establishing the minimum position of the fresh air damper I6 is determined by a manually adjustable rheostat 99 comprising a resistance IOI and a manually adjustable contact I02. The circuits whereby the rheostat 99 controls the minimum position of the fresh air damper will be traced presently.

When the fresh and return air dampers are unfder control of the discharge controller 90, the

outdoor air temperature may rise to a relatively high value at which it is not desired that any more than a minimum. amount of fresh air be admitted because the air is then too warm to. effect any cooling in the spaces. In my arrangement, under these circumstances, if the damper motor 20 is under control of the controller 90, the control is taken away from the controller 90 and returned to the rheostat 99 which returns the dampers to minimum position of the fresh air damper. This function is produced by an outdoor temperature responsive controller I05 comprising an expansible and contractible bellows 06 connectd to athermal bulb I01 located in the left end of the duct I by means of a capillary tube I00. The bulb I01 responds to outdoor temperature and it contains a volatile liquid which vaporizes and develops a pressure in bellows I06, depending upon outdoor temperature, the bellows I 06 expanding and contracting accordingly. The movable end of bellows I06 carries a stem which engages a pivoted switch carrying lever I09 carrying a double ended mercury switch IIO, the lever I09 normally being biased in a counterclockwise direction by a coil spring I I I. The mercury switch IIO has electrodes at its left end which are normally bridged when the temperature affecting the controller I05 is below a predetermined value. When the outdoor temperature rises to a predetermined value ,the bellows I06 expands rotating lever I09 in a clockwise direction to cause the mercury to move to the right end of switch IIO bridging the electrodes at the right end. The controller I05 may be so adjusted that this occurs at a temperature of "77", for example. In addition to the controls as so far described, the controls include a relay desighated by the numeral II5, this relay comprising a winding IIB having an armature associated therewith attached to movable switch blade H1 which moves to the left into engagement with a fixed contact H8 when the relay is deenergized and which is moved to the right into engagement with a fixed contact 9' by the armature when turns. Power is supplied to the primary winding 'I3I through line conductors I33 and I34 which may-be connected to any suitable. source of power, not shown. The winding I2I of relay I20 is controlled by a manual switch including a manually movable switch blade I35 which normally engages a fixed electrical contact I361 The operation of the system as a whole will now be described. With the parts in the position shown, the valve 33 is in an open position so that the gas is being supplied to the heater 3I and the controller is substantially in a satisfied position. The motor of the device 50 is energized so that the plunger 5I is retracted, the fan II is in operation, and the damper motor 20 is in minimum position of the fresh air damper I6. As mentioned above, the relays I I5 and I20 are normally energized. The energizing circuit for relay I 20 is as followszfrom secondary I32 of transformer I30 through wire I4I, switch blade I35, contact I36, wire I42, winding I2I and wire I43 back to the secondary I32. The energizing circuit for relay H5 is as follows: from line conductor I34 through wire I44, contact I25, blade I22, wire I45, winding H6 and wire I46 back to line conductor I33. The circuit for fan motor I2 is as follows: from line conductor I34 through wire I40, contact I26, blade I23; wire I49, the fan motor, and wire I50 back to line conductor I33. The circuit for the motor of device 50 is as follows: from line conductor I34 through wire I53, contact I21, blade I24, wire I54, the motor of device 50, wire I55, mercury switch 83, and wire I56 back to line conductor I33.

With the parts in the position shown, the controller is not in control of the damper motor 20 because the slider 92 is not connected to the damper motor inasmuch as the electrodes at the left end of mercury switch 19 are unbridged.

The damper motor 20 has three control terminals designated I51, I58 and I59. As is well known with this type of motor if terminals I51 and I58 are shunted the motor operates to one extreme position, and if the terminals I 58 and I59 are shunted the motor operates to its other extreme position. The motor is so arrangedthat when terminals I51 and I58 are shunted, the motor will operate to an extreme position wherein the fresh air damper is fully closed and the return air damper is wide open. With the parts in the position shown, the terminals I51 and I58 are partly shunted through the rheostat 99 so that the motor has operated toward an extreme position stopping with the fresh air dampers in a minimum position determined by the adjustment of the rheostat 99. The circuit whereby terminals I51 and I58 are partly shunted is as follows: from terminal I58 through wire I60, blade II1 of relay II5, contact II9, wire IBI, the left end of mercury switch I I 0, wire I62,.the right end of mercury switch 19, wire I63, wire I64, wire I65, contact I02, part of resistance IDI, wire I66, and wire I61 back to terminal I51.

As the system now operates, the controlled 65 will position the dampers 55 to control the relative volumes of air passing over the heater 3| so as to maintain the desired temperature in the space, the controller 65 as pointed out above, on a fall in temperature causing more air to pass over the heater 3I and upon a rise in temperature causing less air to-pass over the heater 3|. -When the temperature in the space tends to become satisfled, that is, as the temperature therein rises, the controller 65 will position the dampers 55 so as to cause less air to pass over the heater 3|, that is, as the temperature rises towards 72 wherein the slider 61 approaches the right end of resistance 68. As the amount of air passing over the heater 3| is reduced, its temperature will 'of course rise and as it rises towards the controller 44 will begin throttling the valve 33 towards closed position. If the temperature at the bulb 45 reaches 110 before the face damper 56 has reached its minimum position, the gas valve 33 will be fully closed, as pointed out above. The purpose of the controller 44 is of course to prevent the heater 3| from being operated at excessively high temperatures. Normally, however, the controller 65 will cause the damper 56 to be positioned to a minimum position before the controller M closes valve 33, and when the damper 56 has reached this minimum flow position, cam 8| will open mercury switch 83 which will interrupt the circuit of the motor of device 59 and thereupon the plunger 5| will immediately move downwardly engaging the upper end of valve stem 36, closing the valve 33. When this occurs, heating of the air is of course discontinued. If the weather conditions are such that the temperature affecting controller 65 continues to rise, the dampers 55 will be positioned to cause still less air to pass over the heater 3| and cam 11 will now tilt mercury switch 19 so that the electrodes at its right end are unbridged and the electrodes at its left end are bridged. When this occurs, the rheostat 99 will be deprived of full control of the motor 29 and control of motor 29 will be placed under command of the controller 99. The upper end of slide wire resistance 9| of controller 99 is connected to terminal I51 of the damper motor 29 by the following connection: wire I64, wire I65, contact I92, a portion of resistance I9I', wire I66, and wire I61. The lower end of resistance 9| is connected to terminal I59 of motor 29 by'wire I19. The slider 92 is now connected to the terminal I58 of motor 29 by the following connection: from slider 92 through wire "I, the left end of mercury switch 19, wire I62, the left end of mercury switch II9, wire I61, contact 9, blade H1 and wire I69 to terminal I58. Thus the controller 99 is now in control of the motor 29 and the rheostat 99 is not in full control because the circuit whereby rheostat 99 had full control is interrupted due to unbridging of the electrodes at the right end of mercury switch 19. Rheostat 99 prevents the dampers from being moved to fully closed position of the fresh air damper I6 whencontroller 99 is in controL'. The fresh and return air dampers will nowmove out of minimum position of the fresh air'damper because there is less resistance between terminals I59 and I59 than between terminals I51 and I58. The damper motor 29 will now be positioned in accordance with the demands of the thermostatic controller 99, and as the temperature affecting thermal bulb 95 rises bellows 93 will expand, moving slider 92 downwardly over resistance 9| tending to shunt the terminals I58 and I59 so as to move the fresh and return air dampers into a wider open position of the fresh air damper. In other words, as the discharge temperature of the air from the fan rises, the dampers are operated to admit more and more fresh air. Conversely, as the temperature affecting bulb 95 falls, slider, 92 moves upwardly along resistance 9I' so as to cause motor 29 to operate in the opposite direction to move the fresh and return dampers to- Wards minimum position of the fresh air damper.

In the event that the outdoor temperature should rise to 77, for example, such that the fresh air is not suitable for cooling of the spaces, the controller.,|95 will respond in the manner described above and tilt mercury switch II9 so as to unbridge the electrodes at its left end and to bridge the electrodes at its right end. When this occurs, the controller 99 is deprived of control of the motor 29 because the connection from.

the slider 92 to the terminal I58 is interrupted. When this occurs, the rheostat 99 is again placed in control of the damper motor 29 so that it again assumes its 'position wherein the fresh air 5 damper is in minimum position. Terminals I51 and I58 of motor 29 are now again partly shunted by rheostat 99, the connections being as follows: from terminal I58 through wire I69, blade II1, contact H9, wire IBI, the right end of mercury switch II9, wire I15, wire I65, contact I92, a portion of resistance I9I, wire I66, and wire I61. back to the terminal I51.

Upon falling temperatures in the space, cams 11 and 8| will tilt their mercury switches back into the positions shown wherein the fresh air damper is in minimum position and the motor of device 59 is energized to permit opening of the gas valve 33. The controller 65 will modulate the dampers 55 as before.

Whenever the fan I is to be manually stopped, the manual switch blade I35 is moved away from contact I36. This deenergizes the relay I29 and switch blades I22, I23, and I24 move away from their associated contacts. When this occurs, the 25 circuit of fan motor I2 is of course interrupted,

the circuit of the motor of device 59 is interrupted, and the circuit of relay I I5 is opened so as to deenergize the relay 5. When relay H5 is deenergized, blade I I1 moves away from contact I I9 and into engagement with contact II8. When this occurs, terminals I51. and shunted so as to cause motor 29 to operate to an extreme position wherein the fresh air dampers are fully closed and the return air damper is wide open. The connections whereby terminals I51 and I58 are shunted are as follows: from terminal I58 through wire I69, blade II1, contactl I8, wire I16, and wire I61.to terminal I51. Thus when-- ever the fan is stopped, the fresh air damper is moved to closed position and the gas valve is I closed if it was open at the time.

From the foregoing those skilled in the art will appreciate the advantages of my invention and the economies which may be gained by utilization thereof. By reason of my particular arrangement of controls associated with the gas fired heater, modulating control of the space temperature is provide for and also modulatin control of the flow of gas to the heater- The thermostatic controller 44, by acting as a limiting device prevents the heater from being operated at excessive temperatures. The arrangement whereby the fresh air damper will be moved out of minimum position and controlled by the discharge temperature controller 99 provides an economizer control feature which is automatically brought into use in response to the space controller 65. By reason of this arrangement, the best advantage is taken of outdoor air by utilizing it for improving the conditions of the space without treatment of the air.

If desired artificial cooling means may also be provided for cooling the air in warm weather.

The single embodiment of my invention which I have disclosed is representative of its preferred form. Numerous variations and modifications of the invention will occur to those skilled in the art, and therefore the invention is to be interpretedin the light of the disclosure, the disclosure being illustrative rather than limiting upon the invention. The invention is to be limited only in accordance with the scope of the claims appended hereto.

I claim as my invention:

1. In an air treating system, in combination,

I58 are fully temperature changing means of a type wherein the temperature is varied by regulating the flow of a fluid medium, means for passing air in heat exchange relationship with said means, means for regulating the amount of air being treated by the first means, said regulating means comprising a device responsive to a condition representative of the amount of temperature changing eifect necessary to maintain the temperature of the treated air at a desired value, means responsive to the temperature of air passing the temperature changing means for modulatingly adjusting the temperature changing effect thereof, said temperature responsive means comprising a fluid flow control valve controlling a fluid medium associated with said temperature changing means; and means for causing said valve to close when said air regulating means has assumed a position wherein a minimum volume of air passes the temperature changing means.

2. In an air treating system, in combination, temperature changing means of a type wherein the temperature is varied by regulating the flow of a fluid medium, means for passing air in heat exchange relationship with said means, means for regulating the amount of air being treated by the first means, said regulating means com prising a device responsive to a condition representative of the amount of temperature changing efiect necessary to maintain the temperature of the treated air at a desired value, means responsive to the temperature of air passing the temperature changing means for modulatingly adjusting the temperature changing eiTect thereof, means for admitting outdoor air into said system, and means for automatically adjusting said last mentioned means when said air regulating means reaches a position indicative of a minimum demand for temperature change of the air.

3. In an air treating system, in combination, temperature changing means of a type wherein the temperature is varied by regulating the flow of a fluid medium, means for passing air in heat exchange relationship with said means, means for regulating the amount of air being treated by the first means, said regulating means comprising a device responsive to a condition representative of the amount of temperature changing effect necessary to maintain the temperature of the treated air at a desired value, means responsive to the temperature of air passing the temperature changing means for modulatingly adjusting the temperature changing effect thereof, means'for admitting outdoor air into said system, means for automatically adjusting said last mentioned means when said air regulating means reaches a position indicative of a minimum demand for temperature change of the air, and means responsive to outdoor air temperature for causing said outdoor air admitting means to assume a minimum position when the temperature of the outdoor air reaches a predetermined value.

4. In an air conditioning system, in combination, means forming an air conditioning duct, a gas fired heater in said duct, valve means controlling a flow of gas to the heater, face and bypass dampers associated with said heater, means responsive to a condition representative of heating requirements of a space controlling said dampers, means responsive to temperature of air passing the heater arranged to modulatingly control the valve means, and means for causing the valve means to fully cut off the flow of gas when the dampers have been positioned to a position causing a minimum amount of air to pass over the heater.

5. In an air conditioning system, in combination, means forming an air conditioning duct, 2. gas fired heater in said duct, valve means controlling a flow of gas to the heater, face and bypass dampers associated with said heater, means responsive to a condition representative of heating requirements of a space controlling said dampers, means responsive to temperature of air passing the heater arranged to modulatingly control the valve means, means for admitting outdoor air to said duct, damper means controlling the amount of outdoor air admitted', and means for automatically adjusting said last damper means from a minimum air admission position to a wider open position when said face damper reaches a position causing a minimum flow of air over said heater.

6. In an air conditioning system, in combination, means forming an air conditioning duct, a gas fired heater in said duct, valve means controlling a flow of gas to the heater, face and by-pass dampers associated with said heater, means responsive to a condition representative of heating requirements of a space controlling said dampers, means responsive to temperature of air passing the heater arranged to modulatingly control the valve means, means for admitting outdoor air to said duct, damper means controlling the amount of outdoor air admitted, and means for automatically adjusting said last damper means from a minimum 'air admission position to a wider open position when said face damper reaches a position causing a minimum flow of air over said heater, said automatic means for adjusting the outdoor air damper means comprising a device responsive to the temperature of air passing through the duct.

7. In-an air conditioning system, in combination, means forming an air conditioning duct, 9. gas fired heater in said duct, valve means controlling a flow of gas "to the heater, face and Icy-pass dampers associated with said heater, means responsive to a condition representative of heating requirements of a space controlling said dampers, means responsive to temperature of air passing-the heater arranged to modulatingly control the valve means, means for admitting outdoor ,air to said duct, damper means controlling the amount of outdoor air admitted, means for automatically adjusting said last damper means from a minimum air admission position to a wider open position when said face damper reaches a position causing a minimum flow, of air over said heater, and

means responsive to the temperature of outdoor air forgcausing said outdoor air damper means to assume a minimum air flow position when the temperature of the outdoor air reaches a predetermined value.

8. In an air conditioning system, in combination, means forming an air conditioning duct,

. a gas fired heater in said duct, valve means controlling a flow of gas to the heater, face and bypass dampers associated with said heater, means responsive to a condition representative of heating requirements of a space controlling said dampers, means responsive to temperature of air passing the heaterarranged to modulatingly control the valve means, means for admitting outdoor air to said duct, damper means controlling the amount of outdoor air admitted, means for automatically adjusting said last damper means from a minimum air admission position to a...

wider open position when said face damper reaches a position causing a minimum flow of air over said heater, said automatic means for ad- Justing the outdoor air damper means comprising a device responsive to the temperature of air passing through the duct, and means responsive to the temperature of outdoor air for causing said outdoor air damper means to assume a minimum air flow position when the temperature of the outdoor air reaches a predetermined value.

9. In an air conditioning system, in combination, means forming an air conditioning duct, a gas fired heater in said duct, valve means controlling a flow of gas to the heater, face and by-pass dampers associated with said heater,

a position causing a minimum flow of air over the heating mean thevalve means are moved to fully closed position, and means whereby upon said face damper reaching substantially said position said outdoor air damper means are moved from a minimum position to a wider open position.

10. In an air conditioning system, in combination, means forming an air conditioning duct, a gas fired heater in said duct, valve means controlling a flow of gas to the heater, face and bypass dampers associated with said heater, means responsive to a condition representative of heating requirements of aspace controlling said dampers, means responsive to temperature of air temperature responsive means in control of said temperature control means for regulating the temperature in said space, a fresh air damper, means for causing said fresh air damper to move to its minimum open position when said temperature control means is operative, and means for positioning said fresh air damper in accordance with the temperature of the air discharged to said space when said temperature control means is inoperative.

'12. In an air treating system, in combination, a. fresh air 'duct, a return air duct, 9. third duct connected to said other ducts for conducting the mixture of fresh and return air back to a space passing the heater arranged to modulatingly control the valve means, means for admitting outdoor air to said duct, damper means controlling the, amount of outdoor air admitted, means whereby upon said face damper reaching a position causing a minimum flow of air over the' heating means the valve means are moved to fully closed position, and means whereby upon said face damper'reaching substantially said position said outdoor air damper means are moved from a minimum position to a wider open position, and means responsive to temperature in said duct for automatically adjusting said outdoor air damper means.

11. In an air treating system, in combination, a fresh air duct, a return air duct, a third duct connected to said other ducts for conducting the mixture of fresh and return air back to a space to be conditioned, temperature control means including a heat exchanger in one of said ducts,

tobe conditioned, temperature control means including a heat exchanger in one of said ducts, temperature responsive means in control of said temperature control means for regulating the temperature in said space, a fresh air damper, means. for causing said fresh air damper to move to its minimum open position when said temperature control means is operative, means for positioning said fresh air damper in accordance with the temperature of the air discharged to said space when said temperature control means is inoperative, and means causing said fresh air damper to move toits minimum open position when the temperature of the fresh air is such that it is not suitable for mixture with return air for maintaining the temperature of the air discharged to said space at a proper value.

13. In an air treating system, in combination, a fresh air duct, 9. returnair duct, a third duct connected to said other ducts for conducting the mixture of fresh and return air back to a space to be conditioned, temperature control means including a heat exchanger in one of said ducts, temperature responsive means in control. of said temperature, control means for regulating the temperature in said space, a fresh air damper, means for causing said fresh air damper to move to its minimum open position when said temperature control means is operative, means for positioning said fresh air damper in'accordance with the temperature of the air discharged .to said space when said temperature control means is inoperative, means causing said fresh air damper to move to its minimum open position when the temperature of the fresh air i such that it is not suitable for mixture with return air for maintaining the temperature of the air discharged to said space at a proper value,'fan means for causing a flow of air throughsaid ducts, an energizing circuit for said fan means and means for closing said fresh air damper and rendering said temperature control means inoperative when said fan means is deenergized.

JAMES S. LOCKE.

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