US2216475A

US2216475A - Air conditioning system

Info

Publication number: US2216475A
Application number: US196682A
Authority: US
Inventors: Ralph H Metcalf
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1938-03-18
Filing date: 1938-03-18
Publication date: 1940-10-01
Anticipated expiration: 1957-10-01

Description

OGL 1, 1940- R. H. METCALF AIR CONDITONING' SYSTEM Filed March 123, 1958 o No :inventor Gttorneg Patented Oct. 1, 1940 AIR CONDITIONING SYSTEM Ralph H. Metcalf, Webster Groves, Mo., assgnor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application March 18, 1938, Serial No'. 196,682

11 Claims.

This invention relates to air conditioning and is more particularly concerned with automatic controls for providing eflicient and economical operation of systems of this character. v

It is an` object of my invention to provide a relatively simple automatic control system for an 'air conditioning installation, which is adapted to operate the Various air conditioning instrumentalities in a manner for maintaining proper operating conditions in summer, in Winter, and during in-between seasons. More specifically, it is an object of my invention to provide an air conditioning control system which provides for three distinct operating sequences for the air condi- 15 tioning apparatus, one for summer, one forA inbetween seasons, and one for winter.

It is a further object of my invention to provide an air conditioning control system for air conditioning apparatus which is especially adapted to handle applications in which the dehumidifying load is quite heavy as compared to the sensible heat or cooling load. More specifically, it is an object of'my invention to provide an air conditioning control 'system which utilizesl fresh air for dehumidifying the space so long as'the condition of the fresh air is suitable for thisl purpose and which uses no more vfresh air than is necessary vfor this purpose to thereby"r`educe the cost of heating this air to a. minimum.

It is a further object to provide a control system for an air conditioning system of the type just described having artificial dehumidifying means, the control system functioning to place this dehmidifying means into operation lonly 'when the dehumidifying action of the freshl air is insufficient for maintaining proper humidity Within the conditioned space.

Still anotherobject of my invention is the provision of a control system which utilizes the dehumidifying eiect of fresh air so long as the condition of the fresh air is suitable for this purpose, but which automatically restricts the ow of fresh air to the space when the fresh air condition becomes unsuitable for this purpose, and which provides for increasing the dehumidifying action of an artificial dehumifying means when the flow of fresh air is so'restricted.

Still another object of my invention is the provision of a system which automatically controls the flow of fresh air into a space in accordance with relative humidity, but which restricts the flow of air to the space irrespective of relative humidity within the space whenever the outdoor temperature falls below a predetermined value.

Further objects consist in the provision of is made t'o the 'following detailed description and the accompanying drawing, the single figure of whichindicates diagrammaticallypan air conditioning control system embodying one form of my invention.

Referring to the drawing, reference character I indicates an air conditioning chamber having a return air inlet duct 2 which may lead from a space being conditioned, and a fresh air inlet duct 3. The discharge end of the conditioning chamber I is connected to a fan 4 which discharges air through a discharge duct 5 to the space being conditioned. Located within the conditioning chamber I is a direct expansion type cooling and dehumidifying coil 6. This cooling coil in turn is connected to a pair -of compressors 1 and 8 which discharge through a conduit 9 into a condenser-receiver I0. receiver is connected by a liquid line II to an expansion valve I2-,located at the inlet of the coil 6. This expansion valve may be of any desired type, and if desired may be of the thermostatic type illustrated, having a bulb |13 attached to the discharge conduit I4 of the cooling coil 6. This discharge conduit in turn is connected to the inlet-s of the compressors 'I and 8. The system just described therefore forms a conventional refrigeration system wherein'operation of the comr pressors 1 and 8 cause chilling of the cooling coil `pass I5 is controlled by means of 4a by-pass damper shown as consisting of a set of dampers I6 which are actuated through a suitable linkage by means of a proportioning motor I1. This proportioningmotor may be of any suitable type and is preferably of the type shown in Patent j 2,028,110 issued to Daniel G. Taylor on January 14, 1936. This proportioning motor is controlled vby means of a space relative humidity controller as will be described hereinafter.

In order to increase the dehumidifying effect of lthe coil 6 there is lprovided a pre-coolingV and reheating circuit A utilizing a heat exchanger I6 which is located in the conditioning chamber on the upstream side of the cooling coil 6 and a secv ond heat exchanger I9 which is located on the The outlet of this condenser-l downstream side of this cooling coil. The upper ends of the heat exchangers I8 and I9 are connected together by means o f a conduit while the lower ends of these heat exchangers are connected together by a conduit 2|, aA circulating pump 22 being interposed in this conduit. This pump 22 may be of any suitable form and may be driven by an electric motor 2,3. Due to the circulation of a heat exchange medium between the heat exchangers I8 and I9, by pump 22, the heat'exchanger |8 will absorb heat from the air passing to the cooling coil 6 and this heat will be delivered up by heat exchanger |9 to the cooled air being discharged from the coolingl coil 6. Due to the pre-cooling action of the heat exchanger |8 the temperature of the air passing to the cooling coil 6 will be reduced to a point nearer its dewpoint than would occur if this precooling action had not taken place. Due to this reduction in temperature of the air, the cooling coil 6 will have less sensible heat to remove from the air before condensation of the moisture in the air begins to take place. The pre-cooling action of the heat exchanger' |8 therefore increases the dehumidifying effect of the cooling coil 6. -In other words, when the circulating pump 22 is in operation, the cooling coil 6 will be caused to perform a larger proportion of dehumidication than will occur when the pump 22 is out of operation.

Referring now to the fresh air inlet duct 3, this duct is provided with a preheating coil 25. This coil extends but part-way across Athe inlet l duct to provide a by-pass 26. The flow of heat- S ing medium to the preheating coll 25 is controlled by means of a valve 28 which maybe actuated by means of a motor 29.4 This motor may be of any suitable two-position type and is herein shown as being of the type utilizing a three-wire control circuit.` The control of this motor will be described later in this specification. The flow of a'ir across the preheating coil 25 may lbe controlled by means of suitable manual dampers 30 for providing a predetermined minimum supply of fresh air to the space at all times. The flow of fresh air through the by-pass 26, however, is controlled by a fresh air damper consisting of a set of dampers 3| which are actuated through a suitable linkage by means of a pro- .portioning motor 32.. This lproportioning motor may be of the type disclosed in the Taylor patent mentioned hereinbefore.y This proportioning motor 32 is controlled by means of a space relative humidity controller as will be described later. Referring to the return air duct 2, this duct may be provided with a set of return air dampers 33 which may be actuated by means of a proportioning motor 34. This proportioning motor is controlled by means of what is termed a dual switch 35 which is actuated by the `fresh airv damper motor 32. This dual switch 35 consists of a potentiometer which is adjusted by the proportioning motor 32. For purposes of illustration, this potentiometer is shown as comprising a slider 36 which is actuated by the shaft of the motor 32, this slider cooperating with a resistance 31. The potentiometer or dual switch is connected to the damper motor 34 in the usual manner. As shown, the controls are arranged in a manner to cause the recirculated air damper to be closed whenever the fresh vair damper 3| is wide open. A's the damper 3| is moved towards closed position, the slider 36 will travel downwardly across resistance 31 which will cause the motor 34to open the damper `33 aproportionate amount.l In this manner the dampers 3| and 33 are controlled tovoperate in unison but in oppositen directions so as to control the relative proportions of fresh and return air being supplied to the conditioning chamber I.

In accordance with my invention, the compressors, the pump 2,2, the valve 28 and the fresh and return air dampers are controlled in part in accordance with outdoor temperature in a manner to provide one type of operation during the heating season, another type of operation during switch carrier carrying a mercury switch 42, a

spring 43 being provided for biasing the switch 42 towards open position. As the outdoor temperature increases, the pressure within the bellows 39 will increase for tilting the mercury switch' 42 towards closed position, against the action of spring 43. This instrument may be so designed and adjusted that when the outdoor temperature is below 35 F. the bellows 39 will becollapsed suiiiciently to allow switch 42 to be opened. When the outdoor temperature is above this value, however, the mercury switch 42 will be tilted to closed position as shown.

The mercury switch 42 is connected to control a pair of relaysgenerally indicated as 44 and 45. The relay 44 may include a relay coil 46 which actuates through a suitable armature (not shown) a pair of switch arms 41 and 48. The switch arms 41 and 48 in turn cooperate with in contacts 49 and,50 respectively, and with out contacts 5| and 52 respectively. When the relay coil 46 is energized the switch arms 41 and 48 will be brought into engagement with the in contacts 49 and 50 while when the coil 46 is deenergized, the switch. arms 41 and 48 will be caused to engage the out contacts 5| and 52 under the action -of gravity or springs (not shown). The relay may be identical with the relay 44 and includes a relay coil 53 and a pair of switch arms 54 and 55 which cooperate with in contacts`56 and 51 and with out" contacts 'thermostat 38. 'Thus when mercury switch 42 is closed, the relay coil 46 will be energized as follows: line wire 60, wire 6|, mercury switch 42, wire 62, relay coil 46, wire 63 and wire 64 to line wire 65. Inasmuch as the relay coil 45 is connected in parallel with the coil 44 as shown, it will be apparent that when the mercury switch 42 is closed,

relay coils

46 and 53 will be energized, while when the mercury switch 42 is open these relay coils will be deenergized.

Reference character 10 indicates generally an outdoor wet bulb temperature responsive thermostat. This thermostat includes a bellows 1| which is connected by a capillary tube 12 to a control bulb 13 in the fresh air duct 2. This control bulb may be provided with a porous cover 14 which may be kept moist in any suitable man- I ner to thereby cause the temperature of the bulb fresh air. The bellows 1| may be arranged to control a mercury switch 15. This instrument may be so designed and adjusted as to cause the mercury switch to be closed whenever the wet bulb vtemperature of the fresh air is above a predetermined value such, for instance, as 55 F., while causing the switch to be open as shown when the wet bulb temperature of the fresh air is -below this value. The mercury switch 15 is arranged to control the relay coil 16 of a relay generally indicated as 11. This relay may be of the same general construction as the relays 44 and 45 and includes a pair of

switch arms

18 and 19. The switch arm 18 cooperates with contacts 80 and 8|, while the switch arm 19 cooperates with a contact 82. .When the mercury switch 15 is closed, the relayv coil 16 will be energized as follows: line wire 60, wire83, mercury switch 15, Wire 84, relay coil 16, wire 85 and wire 64 to line wire 65. It will therefore be seen that when the wet bulb temperature of the fresh air is below F., the relay coil 16 will be deenergized as shown, while when the wet bulb temperature rises above this value the relay coil 16 will be energized. Thefunctions of the relays 44, 45 and 11 will become apparent as this description proceeds.

Referring now to the control of the compressors 1 and 8, these compressors are provided .with

magnetic starters

88 and 89 respectively. These magnetic starters may be of any desired type. The starter 88, for illustration, may comprise a starter coil 90 which actuates switch arms 9|, 92 and 93 which are adapted to connect and disconnect the compressor motor 94 to or from the three-phase line wires 94a. It will be understood that when the coil 90 is energized, the compressor 1 will be placed into operation, while when the coil 95 of starter 89 is energized, the compressor 8 will be placed into operation.

Energization of the coils 90 and 95 may be controlled by means of a step controller 96. This step controller may comprise a proportioning motor 91 which may be of the type shown and described in the Taylor patent. This motor 91 is provided with an operating shaft 98 carrying cams 99 and |00 which actuate mercury switches |0I and |02 respectively. The cams 99 and |00 are arranged in staggered relationship on the shaft 98 as shown. With the arrangement illustrated, as the' shaft 98 is rotated in a clockwise direction the mercury switch |02 will be tilted to closed position. This will energize the starter coil 90 as follows for placing the compressor 1 into operation: line wire |04, wire |05, mercury switch/|02, wire |06, starter coil and wire |01 to line wire |08. Upon further rotation of the shaft 98 in this same direction, the mercury switch |0| will be tilted to closed position -which will energize the starter coil for placing the compressor 8 into operation. It will thereforebe apparent that when the shaft 98 of the step controller is at its extreme counter-clockwise limit of rotation, the mercury switches |0I and |02 will be open and consequently both compressors will be out of operation. As the shaft 98 rotates in a clockwise direction, however, rstthe compressor 1 will be placed into operation and upon further rotation of the shaft 98 the compressor 8 will be placed into operation.

The proportioning motor 91 of the step controller 96 may be controlledin accordance with the load on the system by means of a thermostat I0. This thermostat may comprise a bellows III which is connected by a capillary tube ||2 to a control bulb ||3 which is attached to the cooling coil 6. 'Ihe bulb, tube and bellows contain a suitable volatile fluid for causing the Apressure in the bellows ||I to vary with changes in temperature at the cooling coil 6. The bellows I|| may actuate a bell crank lever having an actuating arm I I4 and a control arm ||5 which cooperates with Va control resistance I|6`to form a control potentiomter. When the coolingr coil temperature is low the bellows III will be contracted by means of a spring I I1 for causing the control arm |I5 to engage the left-hand end of resistance II6 as shown. As the temperature of the cooling coil 6 increases, however, the pressure within bellows III will -increase for causing movement of the control arr'n I I5 to the right across the resistance The motor 91 is provided with a three-wire Acontrol circuit including a,common control wire I I8 and a pair ofcontrol wires I I9 and |20. Upon reference to the Taylor patent, it Will be noted y that the motor 91 is adapted to assume positions depending upon the relative amounts of resistance connected between the common. control wire I|8 and the wire IIS and between the wire ||8 and the wire |20. This adapts the motor 91 for control by a potentiometer such as ||5I|6 of the thermostat I|0. Referring to the wiring between the motor 91 and the thermostat I I0, it will be noted that the common control wire IIB is connected to the switch arm 48 of the relay 44. The in contact 50 in turn is-connected 'by a wire I2I to the control arm or slider I I5 of thermostat IIO. Thus when the outdoor dry bulb temperature is above 35 the relay coil 46 is energizedand this causes the common control wireof motor 91 to be connected to the slider I I5 of thermostat ||0. The control wire ||9 of the motor 91, it will be noted, is connected to the right-hand end of resistance |I6, while the control wire |20 is connected through wire |22 to the left-hand end of resistance ||6. i

, With the slider I I 5 engaging the left-hand end of resistance IIS, the common control wire ||8 is connected directly to the control wire |20 as follows: wire ||8, switch arm 48, contact 50, wire |2|, slider ||5, wire |22 to wire |20. At this same time the entire resistance I I6 is interposed between the Wire ||8 and the wire II9.- This causes the proportioning motor` 91 to assume the extreme counter-clockwise position shown, in which the mercury switches |0| and |02 are' open, thereby-causing the compressors 1 and 8 to be out of operation. As the cooling coil temperature increases, however, the slider ||5 will traverse the resistance |I6 which will interpose part of the resistance I I6 between the control wires ||8 and I I9 while decreasing the portion of this resistance between the control wires I|8 and |20. yThis action will cause the proportioning motor to rotate in a clockwise direction an amount propor- 'tionate to the movement of the slider I5 on resistance I I6. It will thusbe seen that as the temperature of the cooling coil 6 increases, the proportioning motor 91 will be caused to rotate,- this first placing the compressor 1 into operation. As the cooling coil temperature continues to increase, the motor 91 will be rotated further for placing the compressor 8 into operation.

The arrangement just described acts to control the compressors 1 and 8 in accordance with the ation. While I utilize a thermostat responsive to cooling coil temperature for controlling the compressors 1 and 8, other types of control may be utilized. For instance, if desired a suction pressure controller` or other suitable type of control may be substituted in place of the thermostat H0. Also, while the bulb ||3 is shown as attached to the coil 6, it will be understood that this bulb may be attached to the suction line I4, if so desired.

The control action of the thermostat ||0 as above described will occur only when the switch arm 48 of the relay 44 is engaging the contact 50. When the dry bulb temperature of the fresh air falls below F., the relay coil 44 will be deenergized as previously described, this causing the switch arm 48 to disengage contact 50 and to engage the contact 52. This will disconnect the slider I|5 of the thermostat ||0 from the control wire I I8 and will directly connect thev control wire ||8 to the control wire |20, which will have the action'of causing motor 91 to rotate to its extreme counter-clockwise limit of rotation in which the compressorsI 1 and 8 are placed out of operation.l It will therefore be seen that when the outdoor dry bulb temperature is above 35 F., the compressors will be controlled in accordance with the load upon the `cooling coil 6 while when the outdoor temperature is below 35 F., the compressors will be prevented from operating.

As mentioned hereinbefore, the fresh air damper 3| and the by-pass dam-per I6 are controlled in accordance with the relative humidity within the space. This control may be effected by means of a space relative humidity controller |30. This controller may include a humidity responsive device |3I comprising a plurality of strands of hair or other moisture responsive material, this device being secured at oneend to a fixed ,support as shown, while being secured at its other end to an actuating arm |32 of a bell crank lever including a control arm or slider |33. The-slider |33 is arranged to cooperate with a control resistance |34 and a contact strip |35 for forming a control potentiometer. As the spacelrelative humidity decreases, the strands |3| will shrink against the action of a spring |36 for causing the slider |35 to rotate in a clockwise direction.

The control potentiometer formed of slider |33, resistance |34 and contact strip |35, is arranged to control the by-pass damper motor I1. Referring to the wiring, it will be noted that the contact strip |35 is connected directly to one terminal of the motor |1 by a wire |4|, While the resistance |34 is connected to another terminal of the motor I1 by a wire |42. The slider |33, however, is connected by a wire |43 to the in contact 51 of the relay 45. The switch arm 55 of this relay is 4connected to the common control terminal of motor I1 by means of a Wire |44. Thus when the outdoor temperature is above 35 F. the switch arm 55 will engage the contact 51 for placing the humidity controller |30 in control of the by-pass damper motor I1. When the outdoor temperature falls below this value, however,

the relay coil 53 will be deenergized as previously described to cause the switch arm 55 to engage the contact 59. This will disconnect the slider |33 of the humidity controller from the motor I1 while directly connecting the common control v wire |44 of the motor I1 to the control wire |42 through a circuit including contact 59 and wire I42a. This will have the result of causing the motor I1 to run to a position in which the bypass damper I6 is completely closed. 10

The humidity controller potentiometer formed of slider |31, resistance |38 and contact strip |39 controls the fresh air damper motor 32. Referring tothe wiring between this potentiometer and the motor 32, it Will be noted that the slider |31 15 is connected by means of a Wire to the contact 56 of the relay 45. The switch arm 54 of this relay is connected by a wire |5| to contact 8| of relay 11. 'I'he cooperating switch arm 18 in turn is connected by a wire |52 to the com- 2li mon control terminal of the proportioning motor 32. In addition, the resistance 38 is connected to one control terminal of motor 32 by wire |53, and the contact strip |39 is connected to the other motor control terminal by wire |54. the wiring arrangement just described, it will be apparent that when the relay coil 45 is energized and the relay coil 11 is deenergized, the slider |31 will be connected to the common control terminal of motor 32 as follows: slider |31, wire |50, 3Q

contact 56, switch arm 54, wire |5I, contact 8|, switch arm 18 and Wire |52 to the common motor control terminal. Therefore, when the outside temperature is between the limits of 35 F.

dry bulb and F. wet bulb, the relays 45 and 35 11 will be in the positions shown for placing the humidity controller |30 in control of the fresh air damper motor. However, if the outside dry bulb temperature falls below 35 F., the relay coil 53 of relay 45 will be deenergized thus causing the Y switch arm 54to disengage contact '56 and engage contact 58. This will disconnect the slider |31 from the common control terminal of motor 32. Engagement of the switch arm 54 with contact 58 will also directly connect the common control ,f

wire |52 of motor 32 to the control wire |53 as follows: control wire |52, switch arm 18, contact 8|, wire |5I, switch arm 54, contact 58 and wire |56 to wire |53. This short-circuiting of control Wires |52 and |53 will cause the motor 32 to run to a position forcompletely closing the fresh air damper 3|. Also, if the outdoor wet bulb temperature rises above 55 F., the relay coil 16 of relay 11 will be energized thereby causing the switch arm 18 to engage the contact 80. This.,`

when the outdoor temperature is between the t.

limits of 35 F. dry bulb and 55 F. wet bulb, the humidity controller |30 will be placed in controly of the fresh air damper. However, if the outside temperature falls below 35 F. dry bulb or rises above 55 F. Wet bulb, the fresh air damper will be completely closed irrespective of the value of space relative humidity.

Referring again to the humidity controller |30, it will be noted that the sliders |33 and |31 operate sequentially upon their respective con-A trol resistances |34 and |38.` In other words, when the slider |31 engages resistance |38 the slider |33 will ride upon contact l|35, while when the slider |33 engages resistance -|34 the slider |31 will engage contact |39. The purpose of this arrangementis to provide sequential control of the fresh air damper 3| and the bypass damper I6. The advantages of this type of control of the dampers I6 and 3| will be explained more fully under operation In order to provide for heating the space during the heating cycle and for providing the necessary reheat for obtaining dehumidification during the cooling cycle, a pair of reheater-s |60 and |6| may be provided. The ow of heating medium to the reheater |60 may be controlled by Ameans of a valve |62 which is actuated by means of a proportioning motor |63. This proportioning motor in turn may be controlled by means of a return air thermostat |64 which includes a bellows |65 connected by a capillary tube |66 to a control bulb |61 in the return air duct 2. The bellows |65 actuates an actuating arm |68 of a bell crank lever including aconcontrolling the valve motor |63. As the space temperature decreases, the pressure within' bellows |65 will decrease for causing control arm |69 to be shiftedto the right across control resistance |10 which in turn will causethe proportioning motor |63 to'open the valve |62 for placing the reheater |60 in operation.

The ilow of heating medium to the reheater I6| may be controlled by a valve |12 under the control of a proportioning motor |13. This proportioning motor may be controlled by means of a control potentiometer including a slider |14, a resistance |15 and a contact strip |16. With the arrangement shown, it will be apparent that the' valves |62 and |12 will be-controlled in sequence. For example, when the space temperature is high the bellows |66 will be expanded for causing the sliders |69l and |14 to engage the right-handV ends of contact |1| and resistance l|15 respectively. This would cause valves |62 and |12 to be closed. As the space temperature begins, to fall, the slider |14 will move across resistance |15 for causing the valve |12 to be opened. 'At this time, the valve' Operation With the parts in the position shown, the outdoor temperature is above 35 F. dry bulb as indicated by the mercury switch 42 being closed. This has caused the relay coils 46 and 53 to be energized. The resulting engagement of the switch arm 41 with the contact 59 of relay 44 connects the common control wire |80 of the preheater valve motor I|| to the wire |8|, which causes the motor 29 to assume a position in which the valve 28 is closed. The preheater 25 is therefore out of operation. Also, due to the switch arm 48 engaging the contact 50 the thermostat ||0 is placed in control of the step controller 96. The compressors 1 and However, if the 8 are therefore under the control of the load indicating thermostat |I0. At this time also, the switch arm 55 yof relay 45 is Aengaging the contact 51 which places the by-pass damper motor I1 under 'the control of the humidity controller |30. At this time the outside air temperature is below 55 F. wet bulb as indicated by the mercury switch 11 being opened.-v

`the starter coil |82 'for pump motor 23' is de energized which causes the motor 23 'of circulating pump 22 to be deenergized.. The precooler I8 and reheater I9 are therefore not in operation. Also at this time, the space relative humidity is at an intermediate value as indicated by the humidity controller assuming" an intermediate position inA which the sliders |33 and |31 engage the junctions between their .respective resistances and contact strips. 'Due to the slider |33 engaging the right-hand end of resistance |34, the damper motor I1 has assumed a position in which the by-pass damper I6 is wide open. Y Also due tov the slider |31 engaging the left-hand end of resistance |38, the fresh air damper motor 32 has completely opened the fresh air damper 3|. Due to the outdoor temperature being fairly cool a heating load has been placed on the system, this causing the return air controller |64-to assume an intermediate position in which the valve |12 for the reheater? -|6| is open. At this time,

however, the valve |62 for reheater |60 is closed.`

When the outside air temperature is between the limits F. dry bulb and 55 F. wet bulb, it is suitable for dehumidifying thel space. At this time, it will be noted thatdueto the space relative humidity being at an intermediate value, the fresh air damper 3| is wide open for utilizing a maximum amount ofv fresh air for preventing further rise in humidity within thev space. If this fails to prevent the space relative humidity from increasing due, for instance, to the fresh air temperature being of higher humidity than usual, or due to a heavy dehumidifying- This will cause the slider |33 to creases above this value the damper I6 will be closed more and more to increase the amount of dehumidication performed on4 the air supplied to the space. Conversely, as the relative humidity begins falling, the dampers I6 will be opened for decreasing the amount of air passed through the cooling coil. Upon continued fall -of the space relative humidity the by-pass dampers will becomewide open and upon still further fall in humidity the fresh air dampers 3| will begin to be.closed for preventing thel relative humidity from falling too low-within the space.

It will therefore be seen that one feature of my invention is the provision of a sequential cony come closed. In addition, engagement of thel Furthermore, the engagement of the switch arm trol arrangement for the fresh air damper and the cooling and dehumidifying means. This arrangement, it will be noted, utilizes the dehumidifying action of fresh air for controlling the space relative humidity, and only places the artificial dehumidifying means into operation when the fresh air is no longer capable of preventing the space relative humidity from becoming excessive. It will also be apparent that the control apparatus utilizes no more fresh air than necessary for maintaining the properhumidity within the space, thereby conserving on the heat which must be supplied to the air by the reheaters |60 and ISI under the control of the thermostat |64. This thermostat |64, it will be noted, is always operative to prevent the space temperature from falling below the setting of this thermostat. The heaters |60 and I6I therefore provide for reheat during the cooling season and intermediate season and also provide for heating the space during the heating season.

I'f'the outside temperature should fall below 35F. it will be quite low inerelative humidity when heated to the space temperature and the space relative humidity will not become excessive even though only a small amount of fresh air is'supplied. Also, when the outside air falls to this value, considerable heat would be required for heating it to space temperature. It isv therefore desirable to completely close the fresh air damper 3| at this time. Thus when the outside temperature falls below 35 F. the thermostat I8 will deenergize the relays 44 and 45. The resulting engagement of the switch arm 54 with the contact 58 will cause the fresh air damper 3| to become completely closed in the manner previously. described. Also, the resulting engagement of switch arm 55 of relay 45 with the contact 59 will cause the by-pass damper I6 to beswitch arm 48 of the relay 44 with the contact 52 will cause the step controller motor 91 to run to its extreme counterclockwise limit of rotation for preventing operation of the compressors 1 and 8.

41 of relay 54 with the contact -5| will cause the preheater valve motor 29 to open the valve 28 for placing the preheater 25 into operation. It will therefore be seen that when the outdoor temperature is below 35 dry bulb, the fresh air damper is closed, the preheater 25 is placed into operation, the compressors 1 and 8 are prevented from operating, and the by-pass ,damperv I6 is closed. At ythis time the return air thermostat I 64 will control the heaters I6|Land I6 I a manner to maintain the desired space temperature.

On the other hand, if the outdoor temperature rises above 55 wet bulb, it will be of little value for maintaining proper humidity within the4 space. At this time the thermostat 38 will have the relays 44 and 45 energized, which will in the manner previously described cause the preheater valve 28 to be closed and cause the com- -pressor step controller 96 to be placed'under the control of the thermostat II'U. Also at this time the by-pass damper I6 is under the control .of the space relative humidity controller |30. Also, when the outside wet bulb temperature is above 55 F. the relay coil 16 of the relay 11 will be energized. 'I'he resulting engagement of the switch arm 'I8 with the contact.80 will cause the fresh air damper 3| to become completely closed. Also, the engagement of the switch arm 19 with the contact 82 will energize the starter coil |82 of the starter for the pump motor 23. 'I'his will place the pump 22 into operation for causing the precooler I8 and reheater I9 to operate for increasing the dehumidifying action of the cooling coil 6. Therefore, as 'the outdoor air wet bulb temperature rises to a value indicating that the outdoor air is unsuitable for dehumidifying, the

fresh air damper will be closed for preventing entry of fresh air into. the space at this time. Due to the loss of this fresh air at low humidity for dehumidifying the space,v the cooling coil 6 must provide for a greater amount of dehumidification. It will be noted with the present arrangement that at the time that the fresh air becomes unsuitable for dehumidifying the space, the precooler I8 and reheater I9 are placed into operation for increasing the dehumidifying action of the coil 6 for thereby compensating for the loss of fresh air as a dehumidifying medium. At this time, the space relative humidity will continue to be controlled by the humidity controller |38 which will graduatingly position the4 flow through coil 6 as the space relative humidity decreases.'

From the foregoing it will be apparent that I have provided an air conditioning control system for an application in which the dehumidifyin'g load is heavy, this system acting to conserve on operating expenses by utilizing fresh air for dehumidifying the space so long as the fresh air is suitable for this purpose. Also with my improved control system, no more fresh air is taken into the space than is necessary in order to maintain the space at proper humidity, and in addition the artificial dehumidiflcation apparatus is not placed into operation unless the dehumidifying effect of the fresh air is insuiiicient for maintaining proper humidity within the space. In addition, it should be noted that my improved control system acts to restrict the iiow of fresh air to the space whenever the fresh air becomes unsuitable for dehumidifying, and also at this time replaces or compensates for the loss of fresh air as a dehumidifying medium by placing the precooler I8 and reheater I9 into operation for increasing the dehumidifying action of the cooling coil 6. Furthermore, it should be apparent that my control system operates to restrict the supply of fresh air to the space when the outdoor temperature falls to a value indicating Vthat only a small quantity of fresh air is necessary for preventing the space relative humidity from becoming excessive. At this time, the fresh air damper is not only completely closed but also the preheater is placed into operation for preventing possible injury to the air conditioning apparatus due to freezing, and in addition the refrigeration means for the system is placed entirely out of operation.

From the foregoing description it will be noted that mycontrol system provides for three distinct cycles of operation of the air conditioning apparatus, one for the heating season, one for the cooling season, and one for intermediate or in-between seasons. Thus during the heating season the fresh air damper is closed and the preheater is in operation while the refrigeration system is out of operation, this action being caused by the thermostat 38. During the intermediate or in-between season the fresh air as such values will vary for different installa, tions and applications of my invention. Also, lwhile I have shown and described a preferred form of my invention, it Will be apparent that many modifications which are Within the scope of my invention Will occur to those skilled in the art. I therefore desire to be limited only by thescope of the appended claims and the prior art.

I claim as my invention:

1. In an air conditioning system, in combination, a conditioning chamber for conditioning a stream of air being passed to a space to be conditioned, cooling and dehumidifying means inl said chamber, condition responsive means re-A sponsive to a condition indicative of the load on the system for controlling the action of said cooling and dehumidifying' means, a heat transfer circuit for absorbing heat from the air passing to said cooling and dehumidifying means and for returning the absorbed heat to the air after it has passedthrough said cooling and dehumidifying means, means for supplying fresh air to said space, flow control means for varying the flow of fresh air, and thermostatic meansV influencedl by a temperature indicative of the type of load on the system for controlling said heat transfer circuit and said flow control means in -a manner to place said heat transfer `circuit into operation and to decrease the fresh air supply to a minimum when the temperature at said thermostatic means increases to a predetermined value.

2. In an air conditioning system, in combination, a conditioning chamber for conditioning a stream of air being passed to a space vto be conditioned, cooling and dehumidifying means in said chamber, a heat transfer circuit for absorb- Y ing heatfrom the air passing to said cooling and dehumidlfying means and for returning the absorbed heat to the air after it has passed through said cooling and dehumidifyingneans, means for supplying fresh air to said space, flow control means for varying the ow of fresh air, means influenced by the moisture content of air conditioned by the system for sequentially controlling said flow varying means and said cooling and dehumidifying means in a' manner to increase the supply of fresh air and to increase the action of said cooling and dehumidifying means upon increase in humidity, and thermostatic means inuenced by a temperature indicative of the type of load on the system for controlling said heat transfer'circuit and for additionally controlling said flow control means, said thermostatic means being arranged to place said heat transfer circuit into operation and to decrease the fresh air supply to a minimum when the temperature at said thermostatic means increases to a predetermined value.A

3. In an airconditioning system, in combination, a conditioning chamber for conditioning a stream of air being passed to a space to be conditioned, condition changing means in said chammer, actuating means for said condition chang- 'ing means, a by-pass for the air around said condition changing means, by-pass damper means for controlling the relative proportions of the air passed through said condition changing means and through said by-pass, means for supplying fresh air to said space, fresh air damper means for controlling the flow of fresh air, condition responsive means inuenced in accordance with the load on the systemfor controlling said fresh air damper means and said by-pass damper means, and outside temperature influenced thermostatic4 means for substantially closing both of said damper means when the outside temperature varies to a predetermined value.

4. In an air conditioning system, in combination, a conditioning chamber for conditioning a stream of air being passed to a space to be conditioned, condition changing means' in said chamber, actuating means for said condition changing means', a plurality of control devices for said actuating means, motor means for sequentially actuating said control devices, condition responsive means'influenced in accordance with the load on the system for controlling the position assumed by said'motor m'eans to thereby control the operation of said condition .changing means, means for supplying fresh air to said mir space, flow control means for 'varying the flow of fresh air, and outside temperature influencedmeans forv controlling said ow control,A means and for additionally controlling said motor means'in 'a manner to4 reduce the supply of fresh air to a minimum and to place said condition changing means out.of operation when outside temperature varies to a predetermined value.

5. Inv an air conditioning system, in combination, a vconditioning `chamber for conditioning a stream of air being passed to a space to be.y conditioned, condition changing means in said chamber, actuating means for said condition changing means, a plurality of control devices for said .actuating means, motor'means for sequentially actuating said control devices, condition responsive means,responsive to a condition indicative of the load on the system for controlling the position assumed by said motor means to thereby control the operation of said condition changing means, and other condition responsive means influenced by a condition of air passing to said space for additionally controlling said motor means in a manner to cause said motor means to run to a predetermined popassed through said condition changing means and through said by-pass, condition responsive means responsive to a condition indicative of the load on the system for controlling said by-pass damper in accordance with the condition to which said condition-responsive means responds, and outside temperature influenced means for Aadditionally controlling said by-pass damper means and said actuating means, said outside tempera;- ture influenced means being arranged to place said actuating means out of` operation and to ac'- tuate said by-pass damper means to substantially an extreme position when outside tempera- ,ture varies to a predetermined value.

7. In an air conditioning system, in combination, means for cooling a space, means forV supplying fresh air 'to said space, iiow control means for varying the flow of fresh air, psychrometric condition responsive means for controlling said iiow control means and said cooling means, and means including a thermostat inuenced by outside dry bulb temperature and a thermostat iniiuenced by outside wet bulb temperature cooperating therewith for vadditionally controlling said ow control means and said cooling means.

8. In an air conditioning system, in combination, heating means for a space, cooling means for the space, flow control means for varying the supply of fresh air to the space, means responsive to the heat content of the air in the space for controlling said heating and cooling means, changeover relay means for controlling said heating means, said cooling means, and said ow control means, said changeover relay means having three effective positions, a first position. in which the ow control means is actuated to restrict the supply of fresh air, and in which the lcooling means is prevented from operating, a

second position in which the ow control means l is actuated to supply a relatively large quantity of fresh air, and a third position in which the flow control means is actuated for reducing the supply of fresh air and in which the heating means is prevented from operating, and outside temperature influenced means for controlling said changeover relay means.

9. In an air conditioning system, in combination, heating meansfor a space, cooling means for the space, iiow control means for varying the supply of fresh air to the space, changeover relay means for controlling said heating means, said cooling means, and said ow control means, said changeover relay means having three effective positions, a first position in which the iiow control means is actuated to restrict the supply of fresh air, and in which the cooling means is prevented from operating, a second position in which the flow control means is actuated to supply a relatively large quantity of fresh air, and a third position in which the ilow control means is actuated for reducing the supply offresh air and in which the heating means is prevented from operating, and outside temperature influenced means for controllingsaid changeover relay means.

10. In an air conditioning system, in combination, airconditioning apparatus for conditioning a space including heating means, cooling means, and fresh air supplying means, means responsive to the condition of the conditioned air for controlling said heating means and cooling means, changeover relay means for controlling said heating means, said cooling means and said fresh air supplying means, said changeover relay means having threeeifective positions, each of which provides a distinctly different active combination of said air conditioning apparatus, and outside temperature influenced means for controlling said changeover relay means. y

11. In an air conditioning system for a space in a building or enclosure, in combination, a conditioning chamber through which air-is adapted to be passed for a conditioning action, cooling and dehumidifying means in said chamber, condition responsive means influenced by a condition indicative of'the load on the system for controlling theaction of said cooling and dehumidifying means, a heat transfer circuit for absorbing heat from the air passing to said cooling and dehumidifying means and for returning the absorbed heat to the air conditioned bysaid cooling and dehumidifying means, and temperature responsive means influenced by outside temperature for .placing said heat transfer circuit out of opera` tion when outside temperature falls to a predetermined value and for placing said cooling and dehumidifying means out of operation when outside temperature falls to a predetermined lower value.

- RALPH H. ME'IICALF.