US2195781A - Air conditioning - Google Patents

Description

April 1940- A. B. NEWTON 2,195,781

AIR CONDITIONING Filed Sept. 29, 1936 2 Sheets-Sheet 1 mi %& db:

Gttomegs Patented Apr. 2, 1940 UNITED STATES PATENT. OFFICE AIR CONDITIONING poration of Delaware Application September 29, 1936, Serial No. 103,209

26 Claims.

This invention relates to air conditioning and more particularly to cooling and dehumidifica- "tion under summer conditions.

Prior to my invention it has been proposed to pass the air to be conditioned successively over two refrigerative evaporators from which refrigerant is drawn by a constant speed compressor and to which refrigerant is admitted through automatic expansion valves of the superheat control type. When there is demand for cooling, or for dehumidification'or both, the compressor is kept in operation, but whenever the demand is for dehumidification alone one of the evaporators is cut out of the refrigerative circuit. The effect is to evaporate less refrigerant, but at a lower-suction pressure, so that not only is the total cooling effect on the air less than when both evaporators operate, but more moisture is" condensed from the air because the single evaporator operates at a lower temperature. In other words, the sensible cooling diminishes not only because of the reduction of total refrigerant evaporated, but also because a larger proportion of the refrigeration then effective is devoted to the extraction of latent heat from the water vapor carried by the air.

Regulation of this sort is commercially satisfactory but has the disadvantage that some sensible cooling is a necessary incident to dehumidification, whereas it is preferable to secure dehumidification without sensible cooling when humidity alone is high.

According to the present invention, the air preferably contacts the evaporators serially andv in such case the second evaporator is the one cut out during simple dehumidification. At such times the second evaporator is temporarily converted into a condenser for at least a part of the refrigerant compressed by thecompressor. While it so operates it serves as a reheater for the air cooled by the first evaporator, and restores to the air at least a part of the heat extracted by the first evaporator. The air thus is first cooled and then reheated, the temperature dip serving to remove moisture without substantial final change in sensible heat, or at any rate with lessfreduction than is had with the described prior art arrangements. H in the present invention the use of a constant 50 speed compressor is preferred because it is the simplest way known to applicant, to reduce evaporator temperature and increase the dehumidifying effect when evaporative capacity is redguiced. Other functionally equivalent means for r noing evaporative temperature are known and may be substituted, within the scope of this invention. Moreover, since some dehumidification is secured at normal evaporator temperature, reduction of evaporator temperature is not essential to practice of the invention in its broadest aspectl.

While the principal feature of novelty is that above described, there are ancillary features, particularly as to the arrangement of the automatic expansion valve, the control connections, etc., which will be appreciated as the detailed description proceeds.

The system is also favorably constituted for the inclusion in. the installation of means for heating and humidifying under winter conditions, and can be made to operate with success between seasons when conditions shift back and forth between heating and cooling requirements; Such an arrangement will be disclosed as a modified embodiment.

In the drawings,

Fig. 1 is a diagram of a very simple embodiment of the invention intended solely for conditioning in summer.

Fig. 2 is a diagram of a similar system including means for conditioning in winter, and controls which will operate between seasons to select and regulate the action of the system according to demand.

Fig. 3 is a section of an automatic expansion valve used in both embodiments above described.

For simplicity the invention will be described as embodied in a system in which air withdrawn from the room is conditioned and returned to the room, but nothing in the invention precludes its use with air circuits in which all or any part of the air supplied to the conditioner is fresh air. In other words, these various well known arrangements are equivalents, so far as the invention is concerned.

Similarly, the controls responsive to room condition are shown located in the room, but their location at any point at which they would respond to room conditions, for example in the return air duct, falls within the scope of the invention.

Further, while particular electrical controls will be described in some detail, temperature and humidity control systems different in structure but essentially similar in effect are well known andsubstitution is possible. For example, thermostats of the pneumatic type are highly developed and can be arranged to parallel the functions of the electrical type chosen for illustration. Since the inventioniresides in the way the controls are applied so as to be properly coordinated, and not in the mechanics of the control devices themselves, applicant is entitled to a considerable range of equivalents.

In the embodiments shown the air passes serially over the two evaporators, and this arrangement is preferred, because when dehumidifying without substantial ultimate cooling substantially all the air is first dehumidified and then substantially all is reheated so that the desired effects are secured in the maximum degree. It should be understood, however, that a useful result may be secured without adhering to this arrangement, for if one stream is cooled and dried and another heated, mixture of the streams in the fan 'results in reheating of the first stream after moisture has been rejected.

Referring now to Fig. 1.

The Walls 6 enclose a room or other space to be conditioned. The return air duct 8 leads from the room to the intake end of the conditioner housing 9, from which a total volume fan driven by motor l2, draws air and returns it to the room through the duct l3. Mounted in the housing 9 are two coils l4 and I5, conventionally represented as sinuous coils. It is immaterial to the invention what particular type of coil is used. In the air conditioning art it is customary to use finned tubes so asto get a large heat transfer surface,

The suction line N5 of a refrigerative circuit, leads to the suction of compressor I! which is driven through a belt l8 by an electric motor |9. This motor is started and stopped by an electrically controlled starting switch, diagrammatically indicated at 2|. The compressor discharges through the pipe 22 and branch pipe 23 to a combined condenser and receiver 24, from which the liquid line 25 leads. The fittings indicated at 26 are normally-open stop valves.

Branch pipe 2'! leads from the discharge pipe 22. The discharge end of the coil I4 is permanently connected with the suction line I6. The dischargeend of the coil l5 leads to a T or junction 28 which is selectively connectedwith the suction line I6 or with the high pressure branch line 21 by valves 29 and 3|, so arranged that when one is opened the other is closed. The valve 29 is actuated by the energization and deenergization of a winding 32, while the valve 3| is similarly actuated by a winding 33. The valves are each biased in closing direction and each is opened only when its related coil is energized. The two windings 32 and 33 are selectively energized by a switch mechanism, hereinafter described.

When the valve 29 is open and the valve 3| is closed, coil I5 is connected to suction line |6, but when the valve 3| is opened and the valve 29 is closed coil I5 is connected to the high pressure branch pipe 21. The liquid line 25 leads to two automatic expansion valves, 34 which controls the supply of refrigerant to the coil H, and 35 which controls supply of refrigerant to the coil |5. Since these two valves are structurally identical it will suffice to describe the valve as illustrated in section in Fig, 3, and then describe its connections, the connections for the two valves being different.

Liquid refrigerant is supplied through line 25 tothe connection 36 and is delivered to the connected evaporator coil through the connection 31.

,Flow from connection 36 to connection 31 is controlled by a. poppet valve 38 which seats in the direction of flow. This valve is connected to a stem 39 and is urged in a valve closing direction,

by a coil compression spring 4|. The stress on this spring is adjustable by means of nut 42 which is threaded on a portion of the housing, as clearly shown in Fig. 3. The stem 39 is in thrust relation with a flexible diaphragm 43 which is subject on its lower face to fluid pressure in the chamber 44. The chamber 44 is isolated from the discharge connection 37, a packing gland being arranged to seal the stem 39, as clearly indicated in the drawings.

The chamber 44 is subject to pressure arriving through a pressure connection 45. The space above the diaphragm 43 is subject to fluid pressure arriving through the connection 46, the temperature connection.

Reverting now to Fig. 1, it will be observed as to the valve 34 that a pipe 41 leads from the pressure connection 45 to the discharge of coil l4, so that the chamber 44 in valve 34 is always subject to suction pressure. The pipe 48 leads from the temperature connection 46 to a thermostatic bulb 49 in thermal conducting relation with the outlet of the coil I4. It will be observed, therefore, that the valve 34 functionsv in response to superheat at the outlet of the coil I4.

The connections for the valve 35 are slightly different. A pipe 5| leads from the pressure connection 45 to the outlet of the coil I5, from which it results that if valve 29 is opened and valve 3| closed, the chamber 44 of valve 35 is at the suction pressure in the system, but if valve 3| is opened and valve 29 is closed, the chamber 44 is subject to the discharge pressure in the system, with the result that valve 38 then will be held continuously closed. Pipe 52 leads from the temperature connection 46 of valve 35 to a thermostatic bulb 53 which is not placed adjacent the discharge of coil l5 but is in thermal conducting relation with the suction line l6 beyond thevalve 29. The purpose of this is to locate the thermostatic bulb 53 where it will be subjected to the suction temperature of the system and never subjected to the much higher discharge temperature. It will be observed, however, that when valve 29 is opened and valve 3| closed, the flow resistance between the point of connection of the pipe 5| and the location of the thermostatic bulb 53, is negligible so that when the valve 35 is operative to supply liquid refrigerant to the coil l5 the control will be substantially in response to superheat at the outlet of the coil.

The arrangement described protects the thermostatic bulb against overheating, prevents it from tending to open the expansion valve 35 when the valve 29 is closed, while the location of the connection of the pipe 5| insures that the expansion valve 35 will be maintained closed when the suction connection valve 29 is closed.

With the compressor running and the valve 29 closed and valve 3| opened, coil I5 serves as a condenser. Refrigerant then liquefied in the coil I5 is fed to the coil H by way of the high side float valve 54 and the check valve 55.

Leads 56 and 51 from any suitable current source provide electric current for operating the electrically actuated valves 29 and 3| and the motor control switch 2| which starts and stops motor l9.

Lead 51 is connected with a terminal of the control switch 2| and with one terminal of each of the windings 32 and 33. Lead 56 is connected to the right hand contact of the thermostatic mercury tube switch 56 which tilts clockwise to close when dry bulb temperature rises above a chosen value assumed for discussion to be F.

arcane;

assumed when temperature is below 80 and humidity is above The other terminals of switches 58 and 59 are connected to line 60 which leads to the second terminal of control switch 2| which therefore runs motor l9 unless both switches 58 and 53 are open.

Valves 29 and 3| are biased to closed position and open only if their respective windings 32 or 33 be energized. The tilting thermostatic mercury tube switch 6! energizes these windings selectively, but only when line 60 is energized by the closure of at least one of the switches 58 or 59. Line 60 is connected to the middle contact of switch Bl, winding 32 to the lefthand contact and winding 33 to the righthand contact. Thermostaticswitch 6| is set to a control point not above, and preferably a few degrees below the control point of thermostatic switch 58. For discussion 74 is assumed as the control point of switch 6| Below this temperature it tilts clockwise to energize winding 33 and deenergize 32 as shown in Fig. 1, while above this temperature it tilts counterclockwise and reverses this effect.

Assuming that the thermostats and the humidostats are set for the values mentioned, which values are merely illustrative, and that dry bulb temperature is above 80, the compressor will run and will run whether or not humidity is above or below 50%. Inasmuch as'the dry bulb temperature is above the setting of the thermostat 6|, valve 29 is opened and valve 3| is closed. Consequently both coils are connected to the suction line and both operate at a normal suction pressure to cool the air passing through the housing 9. The amount of dehumidificatlon which will occur will depend on humidity conditions in the room,

but under these conditions both cooling and humidification will occur.

Suppose now the dry bulb temperature in the room-falls below 80"v while-the relative humidity is above 50%.- This amounts to saying that thermostatic switch 58 opens but humidostatic switch 59 remains closed. The compressor will continue a to run and the conditioning effect will be unchanged. This action, however, can continue only until dry bulb temperature falls to the setting of the thermostatic switch 6|, 1. e., 74". If at this time the relative humidity is still above 50% so that the humidostatic switch 53. is still closed, thecompressor will continue in action, and the thermostatic switch 6| will shift to close the valve 29 and open valve 3i. This disconnects coil I5 from suction line it and connects it with the discharge line 21. Warm high pressure refrigerant from the compressor I! will thenfiow through valve 3| to the coil IS in which it is condensed. The highpressure thus established in coil 15 will be transmitted through pipe I to chamber 44 of expansion valve 35,- and will hold valve 38 to its seat preventing the supply of liquid refrigerant through liquid line to coil.

I5. The thermostatic bulb 53 will not interfere with this action because it is still subject to temperature in the suction line. Liquid refrigerant condensed in the coil IE will flow through the expansion valve 54 and'the check valve 55 to 0011- II, but the refrigerant so flowing will be insuflicient to supply all the refrigerant required by'the coil ll. Consequently the expansion valve 34 will supply the remainder under the control of the superheat at or near the bulb 49.

Thus both coils will operate to cool the air and to an extent to dehumidify' the air when dry bulb temperature is high. If dry bulb temperature falls to normal value and the system is keptin operation because humidity is high, the dry bulb temperature can be only slightly reduced before low-limit thermostat 6| responds and converts the second coil l5 from an evaporator coil to a condenser coil. When this occurs the suction pressure in the systemdrops because the compressor operates at constant speed and the total amount of refrigerant fed through the coil I l is less than the amount of refrigerant fed through both coils l4 and I5 when they were both operating as evaporators. Consequently less heat is abstracted from theair but it is abstracted at a lower temperature so that more latent heat and less sensible heat is' abstracted.

This intensifies the dehumidifying effect and diminishes, but does not eliminate, the cooling effect of the coil l4. However, the sensible cooling caused by the coil I4 is counteracted by the reheating effect of the coil l5 which operates as a condenser and consequently rejects heat into the air stream.

The above operative sequences are mentioned ous to recount in detail will occur from time to I time. Such control cycles can be readily deduced and will conform to the requirementsv imposed.

An important point is that the system can operate to dehumidify without substantial reduction in dry bulb temperature. This results in important economies. The humidity control is in response to relative humidity which is a function of dry bulb temperature. To secure the desired relative humidity, but at a lower dry bulb temperature entails an unnecessary and wasteful removal of atmospheric moisture for it does not improve comfort conditions. Hence, maintenance of the dry bulb temperature, reduces the latent heat load and improves the operative' efllciency as compared to a system in which relative humidity is held constant and dry bulb temperature is reduced as an incident to dehumidiflcation.

A further development of. this idea by the use of a modifying control subject to outdoor ternperatures to secure the maximum practicable economy under varying summer conditions, is a feature of the elaborated embodiment shown in Fi 2. s v

Fig. 2 shows all the components of Fig. 1 with certain additions and refinements particularly in the automatic controls.

,Identical parts in Fig. 2 are given the same reference numerals as in Fig. 1. Modified control elements are given the same number with 'the letter a. New components are distinctively motor Bld. The operating range of Bic may be from' a low limit approximating the lowest outdoor temperature at which cooling is needed, to Y a high summer temperature. The resulting adjustment of the control point is from a low value, say 74 when outdoor temperature is low, to a value slightly below the control point of thermostat 58, say 79 when outdoor temperature is high.

Thus on hot days the controls are set to take the utmost practicable advantage of the economy secured by limiting dehumidification to that essential for comfort, while on cooler days cooling and dehumidification are allowed to continue to lower values of temperature. The readjustment can, of course, be made manually, if preferred.

At the entrance end of conditioner housing 9 spray heads 62 are added. These are supplied with water under pressure through connection 63 under control of valve 64 which is biased to closed position and opened by energizing winding 65, one of whose terminals is connected to lead 51. The other terminal of the winding is connected with the middle terminal of the low limit humidostat mercury tube switch 66, whose left-hand terminal is connected with lead 56. The control point of humidostat 66 is low, say 40% relative humidity, below which value the switch shifts from the position shown in Fig. 2, counterclockwise to close a circuit from 56 to 51 through winding 65 thus opening valve 64 and operating the spray heads.

The humidostat 59a. differs from humidostat 59 of Fig. 1 only in that it has a third (left-hand) contact which is connected to the right hand contact of low limit humidostatic switch 66. Thus if temperature is high, so that switch 58 energizes line 60 and humidity is low so that switch 590. is tilted counterclockwise, there will be a circuit from 56 to 60 (via switch 58) through left contact of switch 59a to right contact of switch 66 through winding 65 to line 57. This operates the sprays whenever they would perform adiabatic cooling because of high air temperature and low relative humidity.

Eliminators 61 are used to remove entrained water droplets from the air stream. A heater coil 68 is mounted in the exit end of housing 9. It might be of any controllable type, but is assumed to be a steam coil controlled by the normally closed valve 69 fed with steam by line H and opened by energizing winding I2. One terminal of this winding is connected with lead 51, the other with the right hand contact of thermostatic mercury tube switch 13 whose other contact is connectedwith lead 56. This switch closes the circuit and admits steam to coil 68 if temperaturefalls below a chosen point,

say 70 F.

The system disclosed in Fig. 2 has the same functions as the system of Fig. 1 and certain added functions in addition to the readjustment feature above discussed. The thermostat 13 controls heating means. The low limit humidostat 66 operates the sprays 62 whenever humidity falls below a chosen low value, or whenever thermostat 58 calls for cooling and humidostat 59 does not call for dehumidification. Thus some adiabatic sensible cooling is secured by the use of the sprays during the cooling season whenever dehumidification is notrequired. The same sprays maintain a minimum relative humidity during the heating season.

Two specific embodiments have been described and others within the scope of the invention can be evolved by the exercise of mechanical skill.

The valves 29 and 3| conjointly perform the function of a three-way valve arranged to connect the discharge of coil I5 selectively with lines l6 and 21, as will be obvious to those skilled in the art.

What is claimed is:

1. The method of controlling an air conditioning plant of the refrigerative circuit type in which air to be conditioned exchanges heat with two surface heat exchangers connected in said circuit, which comprises operating both exchangers as evaporators when cooling is chiefly required, and when dehumidification is chiefly required operating one exchanger as an evaporator and the other as a. condenser.

'2. The method of controlling an air conditioning plant of the refrigerative circuit type in which air to be conditioned exchanges heat with a first surface heat exchanger and then with a second surface heat exchanger both connected in said circuit, which comprises operating both exchangers as evaporators when cooling is chiefly required, and when dehumidification is chiefly required operating said first exchanger as an evaporator and said second exchanger as a condenser.

3. The method of controlling an air conditioning plant of the refrigerative circuit type in which air to be conditioned exchanges heat with two surface heat exchangers capable of operating as evaporators, which comprises operating both exchangers as evaporators at a normal suction pressure when cooling is chiefly required, and when dehumidification is chiefly required operating one exchanger as an evaporator at a lower suction pressure than said normal and at the same time operating the other heat exchanger as a condenser.

4. The method of controlling an air conditioning plant of the refrigerative circuit type in which air to be conditioned exchanges heat with two surface heat exchangers serially, both said exchangers being capable of operating as evaporators, which comprises operating both exchangers as evaporators at a normal suction pressure when cooling is chiefly required, and when dehumidification is chiefly required operating the exchanger first affecting the air as an evaporator at a lower suction pressure than said normal, and the other exchanger as a condenser.

5. The method of controlling an air conditioning plant of the refrigerative circuit type in which air to be conditioned exchanges heat with two surface heat exchangers capable of operating .as evaporators, which comprises operating both exchangers as evaporators when cooling is chiefly required, and when dehumidification is chiefly required operatirg one exchanger as an evaporator and at the same time operating the other heat exchanger as a condenser, and supplying refrigerant so condensed to the exchanger which operates as an evaporator.

6. The method of controlling an air conditioning plant of the refrigerative circuit type in which air to be conditioned exchanges heat with two surface heat exchangers serially, the exchangers forming parts of said circuits, which comprises operating both exchangers as evaporators when cooling is required; when temperature in the conditioned space is depressed below normal and humidity in the conditioned space is above normal, operating the exchanger first affecting the air as an evaporator and the other exchanger as a condenser; and adjusting the permissible depression of temperature below normal according to outdoor temperature.

7. In an air conditioning system, the combination of a refrigerating circuit having evaposive to temperature and to humidity for, keeping said circuit in operation when temperature or humidity or both exceed chosen values; and temperature responsive means controlling the operative characteristics of said circuit and effective at a limiting temperature below the above named chosen value, to reduce the temperature of at least a portion of said evaporator and cause the circuit to reject heat to the conditioned air.

8. In an air conditioning system', the combination of a refrigerating circuit having an evapo rator, and means for circulating air to be conditioned thereover, said circuit serving to absorb heat from air being conditioned through said evaporator and reject said heat; means responsive to temperature and to humidity for keeping said circuit in operation when temperature or humidity or both exceed chosen values; temperature responsive means controlling the operative characteristics of said circuit and effective at a limiting temperature below the above named chosen value, to reduce the temperature of at means for circulating air to be conditioned; a

refrigerative circuit including a heat exchanger in the path of circulating air; converting means means for circulating air to be conditioned; a

refrigerative, circuit including a heat exchanger .in the path of circulating air; converting means for selectively establishing two operative conditions in one of which the exchangerserves as a refrigerative evaporator to abstract heat and in the other of which a portionof the exchanger serves as a refrigerative evaporator to abstract heat, and another portion serves as a condenser to reject heat to-the circulating air; means responsive to the temperature of conditioned air for controlling said converting means; and means responsive to outdoor temperature serving to vary the temperature at which the last-named means actuates said converting means.

11. In an airconditioner, the combination of two surface heat exchangers; means for circulating air to be conditioned in heat exchange rela- 1 tion with said exchangers; a constant speed compressor; a condenser; and means for connecting said exchangers in circuit with said compressor and condenser, in two relations, in one of which both exchangers operate as, evaporators, and 'in theother of which one operates as an evaporator and the other as a condenser.

12. In an air conditioner, the combination of two surface heat exchangers; means for circulating air to be conditioned in 'heat exchanging relation with one of said conditioners and then with the other thereof; a constant speed compressor;

changers in circuit with said .compressor and condenser in two relations, in one of which both exchangers operate as evaporators, and in the other of which the exchanger which first afiects the air operates as an evaporator and the other exchanger operates as a condenser.

13. man air conditioner, the combination of two surface heat exchangers; means for circulating air to be conditioned in heat exchange relation with said. exchangers; a constant speed compressor; a condenser; means for connecting said exchangers in circuit with said compressor and condenser in two elations, in one of which both exchangers operate as evaporators, and in the other of which one operates as an evaporator and the other as a condenser; and means for supplying refrigerant condensed in the last-named exchanger to the other exchanger. Y

14. In an air conditioner, the combination of two surface heat exchangers; means for circulating air to beconditioned in heat exchange relation with said exchangers; a compressor; a condenser into which said compressor discharges; a suction line connecting one of said exchangers with the suction of the compressor; valve means for selectively connecting the other of said exchangers with the suction and with the discharge of said compressor; and two automatic expansion valves arranged to feed liquid refrigerant from said condenser to respective exchangers, said expansion valves including temperature responsive means subject to temperature in the suction line and pressure responsive means subject to pressure in the respective related exchangers.

15. In an air conditioner, the combination of two surface heat exchangers; means for circulating air to be conditioned in heat exchange relation with said exchangers; a constant speed compressor; a condenser into which said compressor discharges; a suction line connecting one of said exchangers with the suction of the compressor; valve means for selectively connecting the other of said exchangers with the suction and with the discharge of said compressor; two automatic expansion valves arranged to feed liquid refrigerant from said condenser to respective exchangers, said expansion valves including temperature responsive means subject to temperature in the suction line and pressure responsive means subject to pressure in the respective related exchangers; and means for feeding liquid refrigerant from said other exchanger to the flrstnamed exchanger. 1

16. In an air conditioner) the combination of two surface heat exchangers; means for circulating air to be conditioned in heat exchange relationwith said exchangers; a compressor; a cona condenser; and means for connecting said exdenser into which said compressor -discharges; a

pansion valves including temperature responsive means subject to temperature in the suction line and pressure responsive means subject to pres-.

lating air to be conditioned in heat exchange relation with said exchangers; a compressor; a condenser; means for connecting said exchangers in circuit with said compressor and condenser in two relations, in one of which both exchangers operate as evaporators and in the other of which one operates as an evaporator and the other as a condenser; controlling means responsive to temperature and to humidity, arranged to stop said compressor when humidity and temperature are both normal and to run said compressor when either or both humidity and temperature are high; and temperature responsive means functionally related to said controlling means and in conjunction therewith controlling the means for connecting the exchangers to establish the second-named relation when humidity is high and temperature concurrently falls below normal and to establish the first-named relation at other times.

18. In an air conditioner, the combination of two surface heat exchangers; means for circulating air to be conditioned in heat exchange relation with said exchangers; a constant speed compressor; a condenser; means for connecting said exchangers in circuit with said compressor and condenser in two relations, in one of which both exchangers operate as evaporators and in the other of which one operates as an evaporator and the other as a condenser; controlling means responsive to temperature and to humidity, arranged to stop said compressor when humidity and temperature are both normal and to run said compressor when either or both humidity and temperature are high; and temperature responsive means functionally related to said controlling means and in conjunction therewith controlling the means for connecting the exchangers to establish the second-named relation when humidity is high and temperature concurrently falls below normal and to establish the firstnamed relation at other times. i 19. In an air conditioner, the combination of two surface heat exchangers; means for circulating air to be conditionedin heat exchange relation with said exchangers; a compressor; a condenser; means for connecting said exchangers in circuit with said compressor and condenser in two relations, in one of which both exchangers operate as evaporators and in the other of which one operates as an evaporator and the other as a condenser; controlling means responsive to temperature and to humidity, arranged to stop said compressor when humidity and temperature are both normal and to run said compressor when either or both humidity and temperature are high; temperature responsive means functionally related to said controlling means and in conjunction therewith controlling the means for connecting the exchangers to establish the second-named relation when humidity is high and temperature concurrently falls below normal and to establish the first-named relation at other times; and means responsive to outdoor temperature, and serving to adjust the control point of the last-named temperature responsive means.

20. In an air conditioner, the combination of two surface heat exchangers; means for circulating air to be conditioned in heat exchange relation with said exchangers; a compressor; a

condenser; means for connecting said exchangersa condenser; controlling means responsive to temperature and to humidity, arranged to stop said compressor when both humidity and tem perature do not exceed normal and to run said compressor at other times; temperature responsive means functionally related to said controlling means .and in conjunction therewith controlling the means for connecting the exchangers to establish the second-named relation when humidity is above normal and temperature concurrently is below normal and to establish the first-named relation at other times at least when the compressor runs; normally inactive means for spraying water into the air approaching said heat exchangers; and means responsive to humidity and serving when humidity is abnormally low to cause said spraying means to operate.

21. In an air conditioner, the combination of two surface heat exchangers; means for circulating air to be conditioned in heat exchange relation with said exchangers; a compressor; a condenser; means for connecting said exchangers in circuit with said compressor and condenser in two relations, in one of which both exchangers operate as evaporators and in the other of which one operates as an evaporator and the other as a condenser; controlling means responsive to temperature and to humidity, arranged to stop said compressor when both humidity and temperature do not exceed normal and to run said compressor at other times; temperature responsive means functionally related to said controlling means and in conjunction therewith controlling the means for connecting the exchangers to establish the second-named relation when humidity is above normal and temperature concurrently is below normal and to establish the first-named relation at other times at least when the compressor runs; normally inactive means for spraying water into the air approaching said exchangers; and means responsive to humidity and operatively related to said controlling means for operating said sprays when humidity is abnormally low and also when humidity is normal and temperature is high.

22., In an air conditioner, the combination of two surface heat exchangers; means for circulating air to be conditioned in heat exchange relation with said exchangers; a compressor; a condenser; means for connecting said exchangers in circuit with said compressor and condenser in two relations, in one of which both exchangers operate as evaporators and in the other of which one operates as an evaporator and the other as a condenser; controlling means responsive to temperature and to humidity, arranged to stop said compressor when both humidity and temperature do not exceed normal and to run said compressor at other times; temperature responsive means functionally related to said controlling means and in conjunction therewith controlling the means for connecting the exchangers to establish the second-named relation when humidity is above normal and temperature concurrently is below normal and to establish the first-named relation at other times at least whenthe compressor runs; normally inactive means for supplying heat to the circulating air; and means responsive to an abnormally low temperature for rendering the last-named means active.

23. In an air conditioner, the combination of two surface heat exchangers; means for circulating air to be conditioned in' heat exchange relation with said exchangers; a compressor; a condenser; means for connecting said exchangers in circuit with said compressor and condenser in two relations, in one of which both exchangers operate as evaporators and in the other of which one operates as an evaporator and the other as a condenser; controlling means responsive to temperature and to humidity, arranged to stop said compressor when both humidity and temperature do not exceed normal and to run said compressor at other times; temperature responsive means functionally related to said controlling means and in conjunction therewith controlling the means for connecting the exchangers to establish the second-named relation when humidity is above normal and temperature concurrently is below normal and to establish the first-named relation at other times at least when the compressor runs; normally inactive means for spraying water into the air approaching said heat exchangers; means responsive to humidity and serving when humidity is abnormally low to cause said sprays to operate; normally inactive means for supplying heat to the circulating air; and means responsive to an abnormally low temperature for rendering the last-named means active.

24. In an air conditioning system, the combination of a refrigerating circuit including a compressor operated at substantially uniform capacity, an evaporator and means for circulating air to be conditioned thereover, said circuit serving to absorb heat from the air being conditioned through said evaporator and reject said heat; means responsive to relative humidity arranged to cause and suspend the operation of said circuit as relative humiditypasses above and below a chosen value; means operable to limit the total liquid refrigerant supplied to said evaporator, whereby at least a portion of the evaporator will be caused to operate at an abnormally low suction pressure; and means responsive to reduction of temperature of the conditioned air below a limiting temperature serving to cause the circuit to deliver rejected heat to the air after its heat exchange with the evaporator, and serving also to operate said liquid refrigerant supply limiting means.

25. In an air conditioning system the combination of a refrigerating circuit including a compressor operated at substantially uniform capacity, an evaporator and means for circulating air to be conditioned thereover, said circuit serving to absorb heat from the air being conditioned through said evaporator and reject said heat; means responsive to temperature and to relative humidity arranged to cause operation of said circuit when temperature or relative humidity or both exceed chosen values and to suspend the operation of said .circuit when both are below such values; means operable to limit the total liquid refrigerant supplied to said evaporator, whereby at least a portion of the evaporator will be caused to operate at an abnormally low suction pressure; and means responsive to reduction of temperature of the conditioned air below a chosen temperature lower than the above-named temperature value to cause the circuit to deliver rejected heat to the conditioned air and serving also to operate said liquid refrigerant supply limiting means.

lable operating means for Withdrawing refrigerant'from said evaporator and delivering it at higher pressure to said condensing means; means operable to cause said evaporator to operate at an abnormally low pressure and to cause said exchanger to deliver. heat to the air; control means responsive to conditions in said space and comprising temperature responsive and humidity responsive means: and connections whereby said control means controls the operating means for the refrigerating system and also controls the

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