US2315517A - Condition control system - Google Patents

Description

April 6, 1943. -r. K. GREENLEE ETAL 2,315,517

CONDITION CONTROL SYSTEM Filed March 7, 1936 2 Sheets-Sheet l INVENTORS v Theodore K. Green/ee, Gerald "(Ba/m, and Cori/0nd N. ODa

BY 46. W/ QAAU IJ ATTORNEYS 4 April 6, 1943. 'r. K. GREENLEE ET AL 2,315,517

CONDITION CONTROL SYSTEM Filed March '7, 1936 2 Sheets-Sheet 2 INVENTORS Theodore K.Gr'en/e, Gerq/d IV. Balm,

ano/ Cori/and N. ODay ATTORNEYS Patented Apr. 6, 1943 CONDITION CONTROL SYSTEM Theodore K. 'Gr'eenlec, Rockford, 111., and Gerald W. Bohn and Cortland N. ODay, Port Washington, N. Y., assignors to Barber-Colman Company, Rockford, 111., a corporation of Illinois Application March 7, 1936, Serial No. 67.612

10 Claims.

This invention relates generally to condition control systems and in some of its aspects has to do more particularly with the control of air conditioning systems of the type in which a mixture of fresh and return or recirculated air is exposed to the action of one or more conditioning units preparatory to being discharged into the space to be conditioned.

The general object of the invention is to provide in a combined heating, cooling, humidifyi'ng and dehumidifying system a new and improved automatic control which is simple in construction, which is positive and reliable in operation, which maintains'the desired condition of the delivered air with a high degree ofaccuracy, which.

insures optimum economy in operation, and which adapts itself quickly and automatically to the requirements of the space being conditioned.

Another object is to provide a novel air cooling system and method of control "therefor in which the air outside of the building is utilized to carry at least apart of the cooling load when its temperature is low enough for that purpose.

A further object is to provide an all weather air conditioning system incorporating a novel cont rol for insuring maintenance of the delivered air at the proper temperature even though it must be pre-cooled, for the purpose of removing excess moisture, to a temperature which would be uncomfortable to the room occupants.

Still another object' is'to provide a novel arrangement for preheating the mixture of 'fresh andreturn air preparatory to conditioning the same. I

It is also an object to provide a novel mechanism for effecting actuation of a condition regulating member under the control of separate condition responsive devices.

The invention also resides-in the novel man'- ner in which the opening and closing of the fresh air inlet is controlled to insure 'a-minimum degree of opening thereof whenever the system is in operation.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection withthe accompanying drawings in which 'Figures 1 and 2, when laid side by side, constitute a schematic view'and wiring diagram of an air conditioning system embodying the novel features of the present invention.

While the invention is susceptible of various modifications and alternative constructions, we have shown in th drawings and will herein describe ln detail the preferred embodiment, but

it is to be understood that we do not thereby intend to limit the invention to the specific form disclosed, but intend to cover all modifications and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.

In the drawings, the invention is embodied for purposes of illustration in a combined ventilating, heating, cooling, humidifying and dehumidifying system for discharging a mixture of fresh' and return or recirculated air into a space 3 within a building having walls 4 and conditioning the mixture thus discharged so as to maintain predetermined conditions of temperature and humidity in the space. A blower 5 induces the flow of fresh and return air through inlet ducts 6 and 1 into a duct 8 having an outlet 9 from which the air is discharged into the space 3. Within the duct 8, the air mixture passes through a filter I 0 and then is exposed to an humidifier II, a cooler l2, and a heater [3 which 'act singly or in combination to condition the air properly. The blower is driven by an electric motor H supplied with current from a high voltag power source l5 under the control of a switch It. 1

The humidifier shown comprises a nozzle ll communicating through a pipe I8 having a valve l9 therein with a source of water under pressure and arranged to discharge a spray of water. into the air current whenever the valve is opened as will be the case when the winding 20 of a solenoid 2! thereof is energized. The humidifier will remain idle when the solenoid is deenergized.

. While any preferred form of artificial refrigeration means may be employed, the cooler l2 shown herein comprises a. coil communicating through pipes 22 with a source 23 of cooling fluid which is circulated through the coil during operation of a pump 24 driven by an electric motor. The motor is excited from the high voltage source whenever the winding 26 of a relay switch 21 is energized.

The heater l 3 selected for illustration comprises a coil extending partially. across the duct 8 and supplied with heating fluid such as steam through a valve 28 arranged a modulating action posed in the by-passage 30 around the heater coil I3 is a damper 3| which is moved progressively to be opened and closed with by an operator 29. Inter- Preferably, though not necessarily, the operator 32 is of the electric type comprising a reversible electric motor 34 operating through appropriate speed reduction gearing to drive a shaft 35 which carries a crank 35 connected by a link 31 to the damper 3|. The motor is of the shaded pole type having a main winding 38 with terminals connected to power conductors 39 and 39" leadin to a low voltage source 40. Mounted on the poles of the motor and arranged in pairs on diametrically opposite sides of the rotor 4| are multiple turn shading coils 42 and 43 which are arranged to be short-circuited selectively to cause the rotor to turn in opposite directions in a manner well understood in the art.

The valve operator 29 is constructed similar to the operator 32 and comprises an electric motor 44 having a main winding connected to the Power conductors 39' and 39" and arranged to drive a shaft 45 carrying a cam 46 by which the member of the valve is reciprocated. When shading coils 41 of the motor are short-circuited with the valve partially open, the rotor turns in a clockwise direction causing the valve to be closed slOWly. Similarly, the valve is opened progressively while shading coils 48 are short-circuited and theooils 41 open-circuited. When both sets of shadin coils are open-circuited, the position of the valve is maintained frictionally.

In the present instance, the position of the valve 28 is shifted to correspond to the heating requirements under different conditions. To this end, the operator 29 is controlled in accordance with the position of the by-pass damper 3|, the arrangement being such that the valve will be moved toward closed position when the by-pass damper reaches the full cooling position shown, will move towardopen position while the damper is disposed in closed or full-heating position, and will be held in fixed position when the damper is in any intermediate position. For the purpose of effecting such control, the circuit for the shading coils 48 is extended from the coils through The terminals of the main winding of the motor 5| are connected to the power conductors 39 and 33a, and the direction of rotation of the operating shaft B2'is determined by selectively short-circuiting pairs of shading coils 55 and 66, the arrangement being such that the fresh air damper will be moved toward open position when the coils 55 are short-circuited and toward closed position when the coils 65 are short-circuited.

In a system'of the above character, the artificial cooling mechanism is the most costly part to operate. The present invention aims toreduce the time and therefore the cost of operation of the cooler |2 to a minimum by utilizing a conductor 50 having therein a limit switch 5| which is closed except when the valve is in fully open position, a switch 52, the conductor 39, and an extension 49 of the conductor 39. A cam 53 on the shaft 35 is shaped to close the switch 52 when the by-pass damper 3| reaches closed position, the coils 48 being thereby short-circuited so that the valve member will be moved away from its seat until it reaches fully open position as evidenced by opening of .the limit switch 5| or until the switch 52 is opened by movement of the by-pass damper away from closed position. Similarly, the short-circuit for the shading coils 41 is controlled by a-limit switch 54 which is closed except in the closed position of the valve 28 and by a switch 55 which is held closed by a cam 56 when the Joy-pass damper 3| is in the open position shown.

The flow of air through the fresh and return inlets is controlled by dampers 51 and 58 dis- I posed in the respective inlets and connected by a link 59 for movement in unison, the fresh air damper being fully closed when the return damper is fully open as shown and vice versa. Progressive movement of the dampers between their limit positions is effected by a power operator 60 which preferably comprises a reversible shaded pole motor 6| geared to a main operating shaft 62 which is connected by a crank 53 and a link 64 to the link 59. The range of movement of the dampers thus corresponds to a half revolution of the shaft 52.

the outside air to carry all or part of the cooling load whenever its temperature is sufliciently low. For ventilating purposes, the invention also contemplates maintenance of the fresh air damper in at least a predetermined partially open position whenever the system is in operation. To these ends, means are provided which operate, when the outside air is below a predetermined useful value, for example 65 degrees F., to control the operator 6!! and cause modulating movment of the damper between the minimum and fully open positions so as to maintain the temperature of the air mixture at a value appreaching that desired for cooling purposes.

In the present instance, such operation is effected by controlling the circuits for the shading coils B5 and 63 by the combined action of switches 61 and B8 of a magnetic relay having a winding 69 which is energized whenever the fan motor I4 is running, by an insertion thermostat 10 responsive to temperatures in the fresh air inlet 6, and by a second thermostat 1| responsive to the temperature of the mixed air and having a thermostatic element which extends substantially across the duct 8 so as to respond to the average temperature of the mixture.

To maintain the fresh air damper open at least to its minimum position irrespective of the condition of the thermostats 10 and 1| whenever the system is in operation, the operating shaft 62 carries a cam 12 which operates switches 13 and 14. When the fresh air damper is in closed position as shown, the switch 13 is held closed and remains closed as the cam turns in a clockwise direction during initial opening of the fresh air damper. As the dwell surface 15 of the cam 'passes beyond the follower 16 as will be the case when the fresh air damper is opened beyond its selected minimum position, the switch 13 is allowed to open and the-switch 14 is allowed to close. As will later appear, the switch 14 acts to limit the position to which the fresh 'air damper may be closed under the action of the thermostats 10 and 1| alone.

Assuming that it is desired, for cooling purposes, to maintain the air delivered to the room at a temperature not lower than 60 degrees, the thermostat 1| would be set so as to close its switch 11 when the mixed air temperature is above 60 degrees and to close the switch 18 when the temperature is below operating range of the thermostat. Since the fresh air should ordinarily be below 65 degrees F., in order to be useful for cooling purposes in the present system, the thermostat 10 is set to close its switch 19 above 65 degrees and to close its switch below this value.

With the thermostats thus set, the fresh and ture is above 60 degrees, and that the system is not operating, the parts being positioned as shown in the drawings. When the fan is started by manual closure of the switch IS, the switch 61 is closed which completes a short circuit for the shading coils 65 of the damper operator 68. This circuit extends from the shading coils through the conductor 39, the switch 6 a conductor 8|, the switch 11 of the thermostat 1|, a conductor 82, the then closed switch 88 damper until the temperature of the mixture falls below 60 degrees whereupon the short circuit for the coils 65 will be broken by opening of the switch 11.

If, at the time the blower is started, the outside temperature is above 65 degrees or the duct temperature is below 60 degrees, the shading coils 65 will nevertheless be short-circuited when the switch 61 is closed, the circuit extending through the conductor 81, the closed switch 13 and either the conductor 86 and the switch 18 or the conductor 89 and the switch 19. Likewise, when the switch 61 is closed, the outdoor air is sufficiently cool to reduce the duct temperature below 60 degrees before the damper 51 reaches its minimum position, the short circuit for the coils 65 will be maintained through the switch 18, the conductor 86, the switch 13 and the conductor 81. In any of the three cases last assumed, the operator will stop when the damper reaches its minimum open position, the switch 13 and either the switch 11 or the switch 18 being then open.

If the temperature of the mixture falls below 60 degrees with the damper 51 opened beyond its minimum position, the switch 18 will be closed, the coils 66 being thereby short-circuited through a circuit extending from the conductor 8| through the thermostat switch 18, the conductor 86, the then closed switch 14, and a conductor 88. The motor 61 then runs in a direction to close the fresh air damper and open the return air duct thereby increasing the temperature of the air mixture until 60 degrees has been attained or the minimum position of the fresh air damper reached. As the temperature-of the mixture rises above 60 degrees, the movement of the damper will be reversed by closure of a short-circuit for the coils 65 through the switch 11, the conductor 82, the thermostat switch 80, and the conductors 83 and 85 and the switch 84.

It will be seen that while the fan is operated and the outside temperature is below 65 degrees, the fresh air damper will be oscillated back and forth under the control of the thermostat 1| between the full open and a predetermined partially open or minimum position thereby maintaining the temperature in the duct 8 at 60 degrees provided the outside temperature is below this value. If the latter is'between 60 and 65 degrees, the fresh air damper will be moved to and remain in fully open position. If, due to a prolonged fall in the air temperature below 60 degrees, the switch 18 remains closed until the fresh air damper reaches its position of minimum opening, the switch 14 will be opened and the closing movement of the damper arrested. When the outside temperature rises above65 degrees as evidenced by opening of the switch and'closure of the switch 19 of the thermostat 18, the-fresh air damper will be moved to its position of minimum opening in spite of the fact that the thermostat 1| will be calling for a lower duct temperature and therefore for more fresh air. Such movement is caused by closure of a circuit extending from the shading coils 66 through the conductor 88, the then closed switch 14, the conductor 86, the conductor 89, the switch 19, the conductor 82, the switch 11, which will then be closed, to the conductor 8|. The operator 68 will thus close the fresh air damper until the minimum position is reached whereupon the switch 14 will be opened by the cam 1.2 thereby opening the shading coil circuit and arresting the closing movement of the fresh air damper.

The fresh air damper is moved to fully closed position independently of the thermostats 10 and II when the fan is stopped and operation of the system discontinued. This is effected by closure of the relay switch 68 which completes a shortcircuit for the shading coils 66 extending from the .coils through the conductor 88, the then closed limit switch 9|, a conductor 98, the switch 65 and the conductor 39. The circuit is broken by opening of the limit switch as the damper becomes fully closed.

From the foregoing, it will be seen that the control by the switches 61 and 68 is superior to that of the thermostats 18 and 1| and that the thermostat 18 is capable of closing the fresh air damper to minimum position while the thermostat 1! is calling for cooler air. Accordingly, the fresh air damper is closed when the system is idle, is always open at least to aminimum position when the system is in operation, is modulated between the minimum and fully open positions when the temperature outside is sufliciently low, that is below 60 degrees, to enable the outdoor air to carry the entire cooling load, remains in fully open position when the outside air is sufficiently cool, that is below 65 degrees, to carry at least a part of the cooling load, and is maintained in the minimum or partially open position when the outside air is above 65 degrees. In this way, the cooler 12 will be called into operation to handle only that portion of the cooling load which cannot be supplied by the outside air under the conditions prevailing at the time. Maximum economy is thus obtained in the operation of the system for cooling purposes, and the service life of the artificial cooling equipment is prolonged.

In systems of the present character, it is desirable to maintain a relative humidity of at least thirty per cent in the space being conditioned. To accomplish this, means is provided for rendering the humidifier operative whenever the relative humidity in the room falls below the desired value. humidostat 93 having an element 94 disposed in the space 3 andarranged to actuate a control switch 95, maintaining the switch open when the relative humidity is above the value for which the humidostat is set and closed when the humidity falls below this value. The switch is arranged in the circuit by which the winding 20 of the solenoid valve 19 is energized and which extends from the power lead 39 through the winding 20,

Herein, this means comprises an 99 and I will be closed respectively when the room temperature is above and below the operating range of the thermostat. A call for heat I which will be evidenced by closure of the switch I00 completes a short-circuit extending from the coils 43 through a conductor IOI, a limit switch I02, which is closed except when the damper 3| is fully closed, a conductor I03, the switch I00, the tongue of the thermostat 98, the conductor 91, and the conductors 49 and 39. With the coils 43 thus short-circuited, the motor 34 rotates in a clockwise direction to close the by-pass damper and thereby increase the amount of heat imparted to the air by the coil I3. If the switch I00 remains closed for a period of time sufficient to enable the damper to reach its fully closed position, then the resulting closure of the switch 52 will initiate operation of the motor 44 to open the steam valve 28 to a greater degree thereby increasing the capacity of the heater I3.

In response to closure of the switch 99 as the room thermostat ceases to call for heat, the shading coils 42 are short-circuited through a circuit which extends through a conductor I04, a limit switch I05 which is closed except when the damper 3I is fully opened, a conductor I06;

a then closed switch I01 of an. insertion thermostat I08 in the duct outlet 3, a conductor I09, the switch 99, and conductors 91, 49 and 39. With the coils 42 thus efiective, the motor 34 runs counter-clockwise to open the by-pass damper 3| and thereby decrease the amount of heat imparted to the air current flowing through the duct 8. In this way, the damper will be oscillated back and forth under the control of the thermostat 98 whereby to cause the conditioned air to be heated to a temperature suffi cient to maintain the desired room temperature. In addition, the operator 29 is controlled in response to the movements of the by-pass damper in a manner such as to adjust the position of the steam valve and throttle the flow of steam to the heating coil I3 so as to establish a rate of flow corresponding approximately to the pre'- vailing heating requirements. The thermostatic control of the damper supplements the steam valve control and enables very accurate regulation of the conditioned air temperature to be obtained. I

When the cooling requirements of the space.

being conditioned cannot be satisfied by supplying fresh air thereto, the cooler I2 is rendered operative underthe control of a thermostat II4 located in the room and adjusted to the temperature which is to be maintained in the room when cooling is required. This temperature will be several degrees above the setting of the heat controlling thermostat 98 and ordinarily will be varied in any well known manner with changes in .the outside temperature.

The thermostat II4 has a switch H5 which becomes closed as the room temperature rises above the value for which the thermostat is set. This switch controls an energizing circuit for the winding 26 of the relay switch 2'! which circuit extends from the power conductor 39 through the winding 26, a conductor IIS, 2. switch III ofa thermostat H8 in the duct outlet 3, a conductor II9, the thermostatic switch II5, the conductors 91 and 49 to the power conductor 39. Thus, when both of the switches H5 and Ill are closed, the relay will be energized starting the pump and causing cooling fluid to be circulated through the coil I2. The cooler continues in operation until the room temperature has risen above the desired value or until the switch III of the duct thermostat is opened.

The latter thermostat is arranged to respond I to changes in the temperature of the air discharged through the outlet 9 and is set to respond to a limit value below which the discharged air would produce objectionable drafts in the room. If the thermostat H8 is set for 62 degrees F., for example, its switch would be opened and the operation of the cooler interrupted whenever the temperature of the conditioned air fallsbelow this temperature even though the cooling requirements of the space as determined by the thermostat II4 have not been satisfied.

Preferably, the air stream thermostat II is adjusted to maintain a temperature of the mixed air slightly below the minimumlimit to which the cooler I2 may reduce the conditioned air as determined by the thermostat IIB. Thus, the artificial cooler is maintained idle by the action of the thermostat II8 so long as the outdoor air is cool enough to carry the entire cooling burden determined by the thermostat II4.

Whenever the relative humidity in the space being conditioned rises above a predetermined maximum value, usually about fifty-five percent, means is provided for operating the cooler I2 irrespective of the condition of the thermostat II4 so as to effect dehumidification of the air being discharged into the room. This means comprises an humidostat I20 in the room set to close a switch I2I whenever the humidity rises above the maximum limit desired. The switch I2I is interposed in a conductor I22 extending between the conductor 91 connected to the power conductor 39 and the conductor II6 leading to the winding 26 so that whenever the switch I2I is closed, the relay' switch 21 will be energized and the flow of cooling medium to the coil I2 initiated.

In the event that the cooling effect of the coil I2 is increased under the independent control of the humidostat I20, to such an extent as to lower the temperature of the conditioned air below that which is desirable from the standpoint of avoiding drafts on the occupants, the heater I3 will be rendered effective to reheat the dehumidified air to the proper temperature. This is accomplished in the present instance by the action of the duct thermostat I08 which is adjusted so that its switch I23 will become closed in response to a minimum limit temperature slightly lower, for example 60 degrees, than the value for which the thermostat H8 is set to respond. When the switch I23 becomes closed, the shading coils 43 will be short-circuited through the conductor I0 I, the then closed switch I02, the conductor I03, a conductor I24, the switch I23, the conductor I09, the then closed thermostat switch 99 and the conductors 91, 49, 39 and 39. As a result, the motor 34 will be started and the by-pass damper 3| moved toward closed position thereby causing heat to be supplied by the coil I3 and the rate of such supply to b increased until the desired minimiun temperature of the'conditioned air, as d v 2,315,517 termined bythethermo'stat I08, has been at tained.

By virtue of this arrangement, the cooler I2 may be employed to perform the additional function of dehumidifying the air, theheater I3 cooperating to prevent air, cooled to a low temperature for the purpose of dehumidification, from being discharged into the room at a temperature below GOdegrees.

dependently operable thermostats I08 and I I8 with the latter set 'torespond to a temperature Such action is made possible in the present instance through the use of the inslightly higher than that for which the thermostat I08 is adjusted.

Under conditions sufficiently severe to prevent the heater I3, when operating at full capacity, from properly tempering the mixture of return air and the minimum amount of fresh air, provision is made for preheating the mixture before it reaches the heater. Preferably, this is accomplished by supplying heat to the return air passing through the inlet 1 by means of a heating coil I supplied with steam or other heating fluid under the control of a regulating valve I26. The position of the latter is controlled by a thermoportion of fresh air admitted to said duct, a power operator for said damper means, a thermostat responsive to the temperature of the mixture of fresh and return air and controlling said operator 'to modulate the position of a damper means between said minimum open position and fully open position and maintain a substantially uniform temperature of the mixture, a thermostat responsive to the temperature of the fresh air exercising control over said operator superior to said first mentioned thermostat and operating to cause movement of said damper means to said minimum open position in responseto a deviation in the fresh air temperature to a predetermined value, and auxiliary control means operable independently of said thermostats to control said operator and cause complete closure of said fresh air inlet from any position in which the damper means is disposed at the time the auxiliary control means is rendered active.

2. In an air conditioning system having an air duct having fresh and recirculated air inlets, a damper controlling the proportion of fresh air admitted to said duct a power operator for movstat I21 responsive to the average temperature of the air in the duct 8 and set to respond to a temperature several degrees, for example five, below the temperature for which the thermostat H is set. .Thus, when the weather is not too severe, the airin the duct 8 will be maintained at 60 degrees under the control of the thermostat 1|,

. while in extremely cold weather, the thermostat I21 will render the heater I25 operative to main- I tain the duct temperature at 55 degrees.

In the present instance, the valve I26 is actuated by an electric operator I28-constructed similar to the' operator 2!! and having shading coils I30 and I3I adapted when short-circuited to cause the valve to be opened and closed respectively.

The circuits for the coils are controlled by limit.

switches I32 and I33 and switches I34 and I35 of the thermostat I21, the latter being closedrespectively when the duct temperature is above and below the value for which the thermostat is set. Location of the preheat coil I25 in the return air duct is especially advantageous in that the coil is not exposed. to the incoming fresh air, and therefore there is no danger of the coil becoming damaged when the outside temperature falls below freezing with the preheat coil inactive.

It will be apparent from the foregoing that the controls above described operate entirely auto-,

matically under all conditions to maintain the desired conditions of temperature and humidity in the space being conditioned and this in spite of the fact that the change from heating to cooling of the air may occur frequently in service. The various control mechanisms are interrelated in a manner such as to operate positively and reliably under all conditions and to enable the amount and complexity of the conditioning units and of the control mechanism itself to be reduced to a minimum. At the same time, the system utilizes whenever possible the cooling effect of the outdoor air thereby providing for optimum economy of operation.

In the appended claims, the terms air condition are used to refer to temperature and humidity conditions only.

We claim as our invention:

ing said damper in opposite directions, a thermostat responsive to the temperature of the air mixture and controlling said operator to modulate the movements of said damper between positions of full and minimum opening of said fresh air inlet to maintain the predetermined minimum temperature of said mixture, a thermostat responsive to the temperature of the fresh air and exercising a control over said operator superior to said first mentioned thermostat and causing movement of said damper toward closed position when the fresh air temperature rises above a predetermined value useful for cooling purposes, and means responsive to movement of the damper and operating to interrupt the closing movement thereof under the control of either 'of said thermostats when the damper reaches said position of minimum inlet opening.

3. In a combined ventilating and cooling system having an air duct'and fresh and return air inlets, damper means controlling the proportiors of fresh and return'air delivered to said duct,

means responsive to the temperature of the air mixture and regulating the movements of said damper means to maintain a substantially uniform temperature of the air mixture, means responsive to the temperature of the fresh air and regulating said damper means independently of said last mentioned means to maintain a fixed minimum proportion of fresh air in the mixture when the fresh air temperature is above a predetermined value useful for cooling purposes, and means controlling said damper means independently of said temperatureresponsive means to effect complete closure of the damper means from any position thereof.

4. In a combined cooling and ventilating system having a duct with fresh and return air in- 1. In an air conditioning System having an air lets, damper means controlling the proportion of fresh air admitted to said duct, a power operator for said damper means, a thermostat controlling said operator to cause opening of the fresh air inlet beyond a minimum degree when the temperature of the mixture of fresh and return air is above a predetermined value whereby the outdoor air may b utilized for cooling purposes, thermostatically controlled means controlling said operator independently of said thermostat to cause movement of the damper and closure of said fresh air inlet to said minimum degree when the temperature of the fresh air rises above a predetermined value, and other means independently controlling said operator to "cause closing movement of said damper means.

5. In an air conditioning system. the combination of means for discharging a current of air into a space to be conditioned, a cooler and a heater each arranged in heat-exchanging relation with respect to said air current, a thermostat in said space controlling the operation of said heater to maintain a uniform temperature in the space when heating of the space is required, 'a second thermostat in said space controlling the operation of a cooler to maintain a predetermined higher temperature in the space when cooling thereof is required, an humidostat in the space adapted'to render said cooler operative independently of said second thermostat when the relative humidity in the space rises above a predetermined value, a third thermostat responsive to changes in the temperature of the conditioned air and controlling said heater to prevent delivery of air to said space at a temperature below a predetermined minimum limit during operation of said cooler under the control of said humid-ostat, and a fourth independently operable thermostat controlling said cooler and operating to limit the temperature to which the conditioned air may be reduced to a value higher than said minimum limit.

6. In a combined ventilating and tempering system having an air duct with fresh and return air inlets, valve means controlling the proportion of fresh and return air admitted to said duct, thermostatic means regulating said valve means to admit varying amounts of fresh air and maintain a substantially uniform temperature of the fresh and return air mixture, thermostatic means exercising a control over said valv means superior to said first mentioned thermostatic means and regulating said valve means to reduce the proportion of fresh air in'said mixture to a predetermined proportion sumcient for ventilating purposes when the prevailingtemperature of the fresh air is such as to render the latter unsuited for tempering'pmposes, and means controllin said valvemeans independently of both of said thermostatic means to cause complete closure of said fresh air inlet from any degree of opening of the valve means.

'7. A control for air conditioning systems having, in combination, valve means controlling a passageway adapted for the flow of a conditioning medium therethrough, a reversible power operator for actuating said valve means, means controlling said operator to cause uninterrupted the further opening of said passageway beyond said predetermined degree of opening, and a-second independently operable temperature responsive device controlling said operator to cause closing of said passageway toward said predetermined amount from any degree of opening beyond such degree.

8. An air condition control having, in combination, a valve controlling a passageway and actuated by a member movable between passageclosed and passage-open positions through a predetermined intermediate position, a reversible power operator for said member including electric motor driving means having valve-closing and valve-opening windings, a first switch which is respectively closed and open when the member is above and below said intermediate position and a second switch which is closed and open when said first switch is open and closed respectively, air condition responsive means having one switch controlling a circuit for said valve opening winding'independently of said switches and another switch controllingsaid opening winding through the medium of said second switch and said closing winding through the medium of said first switch, and an automatic control device having one position in which said air condition responsive means is rendered operative and a second position in which said valveclosing winding is rendered active to cause movement of said member to said closed position independently of said air condition responsive means;

9. An air condition control having, in combination, a valve controlling a passageway and actuated by a member movable between two limit positions through a predetermined intermediate position, a reversible power operator for said member including electric motor driving means having two windings respectively energizable to cause movement of said member in opposite directions, a first switch which is respectively closed and open and a second switch which is respectively open and closed when the member is above and below said intermediate position, air condition responsive means having third and fourth switches respectively closed by opposite movements of a reversibly movable control element, a

circuit for one of said windings including said third switch, a second circuit for said one winding including said second nd fourth switches, and a circuit for the other of said windings including said first and fourth switches.

10. An air condition control having, in combination, a valve controlling a passageway and actuated by a member movable between two limit positions through a predetermined intermediate position, an air condition responsive device having acontrol element movable between two positions, first and second switches respectively closed and open when said member is on one side of said intermediate position and respectively open and closed when the member is disposed on the other side of the. intermediate position, a reversible power operator for said member operable to cause movement of the member from one limit position to said intermediate position independently of said switches when said element is in one of its positions and through the medium of said first switch when the element is in its-other position, said device coacting with said other switch in causing reverse movement of the member when.

CERTIFICATE OF CORRECTION. Patent No. 2,515,517. April 6, 195.

THEODORE K. GREENLEE, ET AL. v

It is hereby certified that error appears in the printed specifieati on of the above numbered patent requiring correction as follows: Page 5,-sec- 0nd column, line 5, for "a damper read sa.1d damper-; line 6, for "said minimum read --a minimum-; page 6, first collimn, line 614., for amount from any degree" read -'-degree from any mount; ahd that the eaid Letters Patent should be read withthiscorrecti on therein that the same may conionnto the record of the case in the Patent Office. I

Signed and sealed this lst day of June, A. D. 19h5.

Henry Van Ar'sd aIe,

'. (Seal) I Acting commissioner'offatents.

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