Air conditioning apparatus having reheat means

Oct. 1, 1963 _L w. atchison 3,105,366

AIR CONDITIONING APPARATUS HAVING REHEAT MEANS Filed May 16, 1962

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FIG. 2

INVENTOR. LEONARD W. ATCHISON

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HIS ATTORNEY

United States Patent Office 3,105,366 __________________ Patented Oct. 1, 1963

3,105,366

AIR CONDITIONING APPARATUS HAVING . REHEAT MEANS

Leonard W. Atchison, Louisville, I£y., assignor to General Electric Company, a corporation of New York

Filed May 16,1962, Ser. No. 195,163

Claim. (CI. 62—173)

The present invention relates to and has for its principal ' object the provision of an air conditioning apparatus having an improved arrangement for cooling and dell humidifying air from ‘an enclosure.

In. accordance with the present invention there is provided an air conditioner having a refrigeration system including a compressor, condenser, expansion means and an evaporator connected in refrigerant flow relationship. Means are provided for circulating an air stream from the enclosure over the evaporator of the air conditioner for cooling the air and removing moisture therefrom prior to discharging the air stream back into the enclosure. In order to provide improved dehumidification of this air stream without unduly cooling the air within the enclosure there is provided a reheat coil arranged on. the downstream side of the evaporator. The reheat coil has an inlet connecting with the refrigeration system between the compressor and the condenser for receiving hot discharge gas from the compressor and an outlet connecting with refrigeration system between the condenser and the expansion means for returning refrigerant to the system. The hot gas flow into the reheat coil is controlled by a solenoid valve which is energized to open the valve when the temperature of the enclosure is a predetermined number of degrees above that required to satisfy the thermostat and to de-energize the refrigeration system. A check valve is provided adjacent the outlet end of the reheat coil for preventing flow of refrigerant from the condenser into the outlet end of the coil when the solenoid valve is closed.

For a better understanding of the invention reference may be had to the accompanying drawing in which:

FIGURn, 1 is a cross-sectional view of an air conditioner incorporating the arrangement of the present invention;

FIGURE 2 is a line diagram illustrating in schematic form the refrigeration system of the present invention and a thermostat arrangement for energizing the valve controlling the reheat coil to provide dehumidification of the air without substantial cooling thereof; and

FIGURE 3 illustrates a modification of the system shown in FIGURE 2.

Referring now to FIGURE 1 there is shown an air conditioning unit comprising a metallic case 2 which is divided by a barrier 3 into two separate compartments designated the condenser or outer compartment 4 and an evaporator or inner compartment 6. A condenser 7 is positioned, within the outer compartment and an evaporator 8 is disposed across the end of the evaporator compartment 6. The evaporator 8 and condenser 7 are connected in refrigerant flow relationship with a compressor 9 which is also located in the outer compartment 4. Suitable means, such as a capillary tube (shown only in FIGURE 2), is connected between the condenser 7 and the evaporator 8 for expanding liquid refrigerant from condenser pressure to evaporator pressure in order to promote vaporization of liquid refrigerant flowing between these heat exchangers thereby cooling the evaporator of the system. Other means such as an expansion valve may be incorporated for this purpose.

Means are provided for circulating air from within the enclosure through the inner or evaporator compartment 6 for cooling and removing moisture from the enclosure air. . More specifically, a fan 11 is provided in the lower portion of the evaporator compartment for pulling an air stream through the inlet opening 12 .and through the evaporator 8. This air stream passes to the rear of the 5 compartment 6 where it is diverted by the barrier 3 into the upper portions of the compartment to be discharged back into the enclosure through the outlet opening 13. Outdoor air is drawn into the condenser compartment 4 by a condenser fan 14 through the inlet opening 16 and 10 circulated through the condenser compartment 4 where it passes in heat exchange relationship with the condenser 7 prior to being discharged to the outdoors again through outlet openings (not shown) in the condenser compartment. Fans 11 and 14 are both driven in the conven15 tional manner by a motor 17 mounted on the barrier 3 which separates the two compartments.

When a unit of this type is employed for cooling an enclosure, the evaporator 8 extracts heat from the air circulated through the evaporator compartment 6 from 20 within the room or enclosure and the condenser discharges the heat taken up by the refrigerant flowing through the system to the outdoor air being circulated through the outer compartment 4. The outdoor air cools the condenser 7, thereby condensing the high pressure, high 25 temperature refrigerant flowing into it from the compressor. As the air stream flows over the evaporator 8 from the enclosure, the evaporator removes moisture -from this air stream as well as cooling it. That is, moisture in the. air stream condenses out onto the evaporator coils 30 which are usually below the dew point temperature of the air stream, thereby dehumidifying it as it passes over the evaporator coils. This moisture or condensate water is collected in a drip tray 18 and delivered through an insulated conduit 19 to the outdoor compartment 4 where 43 it is drained or otherwise disposed of by means located in the condenser compartment.

It is well recognized that excessive humidity in an enclosure usually creates uncomfortable living conditions even though the air temperature within the enclosure may not be very high. Under these circumstances, it is desirable to remove moisture from the air without lowering the enclosure temperature to any great extent. Inasmuch as the evaporator of an air conditioning unit necessarily 45 ™^U-^St 5°°^{1 the air before ii;} removes moisture therefrom, it is desirable to again heat the air after it leaves the evaporator before it is discharged into the enclosure In order to perform this function in the air conditioner ot the present invention, a reheat coil 21 is mounted in ₅₀ the evaporator compartment 6 downstream from the evaporator 8 for heating the air stream leaving the evaporator “unng certain periods of the conditioning operation as will be hereinafter explained.

In the disclosed embodiment, the reheat coil 21 forms 55 a second heat exchanger lying closely adjacent the evaporator 8 through which the air stream flowing through the compartment 6 must pass prior to being circulated by the fan 11 into the upper portions of the case to be discharged out the opening 13. As may be seen in FIGURE 2 60 ^the,^{reheat c}°il ^actuaI1Y comprises a second condensing coil arranged in parallel with the condensing coil 7. That is, the inlet end 21α of the reheat coil 21 is connected into the system between the compressor 9 and the condenser 7 so that at least a part of the gas flowing from the com65 ^press% ^{9 may enter th}e reheat coil 21 where its heat may be utilized to heat the air stream flowing through the evaporator compartment 6. The other or outlet end 216 of the reheat coil 21 is connected into the system again between the condenser 7 and the expansion means or 70 capillary 10 so that all of the refrigerant flowing through the reheat coil 21 passes through the expansion means 10 prior to being returned to the compressor 9. Thus, all

3,105,366 of the refrigerant, which is condensed in the reheat coil 21 by the cold air stream flowing thereover, enters the capillary 1® and is expanded to evaporator pressure, to further aid the cooling of the evaporator before flowing into the compressor 9.

As may be seen in FIGURE 2, means is provided in the form of a solenoid operated valve 22 for opening and closing the inlet to the reheat coil 21 in order to control the reheat function of this coil during the operation of the air conditioner. Solenoid valve 22 may be any,of the well known types of solenoid valves now on the marset which may be operated to open and close a passage therethrough when energized and de-energized respectively by an electrical current. It is preferable that the valve be normally closed and moved to the open position when the solenoid coil is energized. Valves of this type are well known in the field of air conditioning and a further description thereof is not deemed necessary for a full understanding of the invention.

At the opposite or outlet end of the reheat coil 21, adjacent the connecting point between the condenser 7 and the capillary 10, there is provided a check valve 24 which opens to permit flow of refrigerant back into the system from the reheat coil but prevents refrigerant from the condenser 7 from flowing into, the reheat coil. Thus during operation of the air conditioner for strictly cooling purposes, i.e. without the heating operation of the reheat coil, the check valve 24 eliminates flow of refrigerant into the reheat coil from the condenser 7 and thereby prevents refrigerant from condensing out of the system in the reheat coil. This increases the efficiency of the system and eliminates the possibility that it may operate with an undercharge of refrigerant.

Means are provided in the present invention for energizing the solenoid valve 22 whenever the temperature of the air stream entering the unit from the enclosure drops to a predetermined temperature and for de-energizing the solenoid valve when the temperature of the air stream rises above the predetermined temperature. More specifically, the air conditioner is provided a thermostat 23 which senses the incoming air temperature, and controls the operation of the refrigeration system within the unit. Thermostat 23 contains a temperature sensing member adapted to energize switches for controlling the operation of the compressor 9 and the solenoid valve 22 whenever the temperature of die enclosure 'air rises above or goes below predetermined temperatures. In the illustrated embodiment, the thermostat 23 contains a sensing means, such as the bimetal member 26, adapted to energize the compressor 9 whenever the temperature rises above a predetermined temperature, such as 75° F. or any other temperature assumed desirable by the occupants of the enclosure. As may be seen in FIGURE 1 this temperature may be adjusted by means of a manual control knob 25 on the front of the unit which, in a manner well known in the 'art, may be employed to adjust the switch to close at any desired temperature. Thus, whenever the temperature of the enclosure air rises above the predetermined temperature, such as the aforementioned 75 F., the bimetal or temperature sensing means 26 closes its contacts to connect line power through lines LI and L2 to the compressor 9. In the illustrated ^arrangement, the thermostat is provided with a second sensing means, such as the second bimetal switch 27 arranged in series with the first bimetal switch and adapted to close and thereby energize a second circuit whenever the temperature of the enclosure 'air is below a second predetermined temperature such as 78° F. The second circuit includes the solenoid coil 22α which, as will be obvious from FIGURE 2 is energized when both bimetal switches 26 and 27 are closed. Thus, switch 27 closes its contacts whenever the temperature of the enclosure -air is below the predetermined temperature, such as -the aforementioned 78° and energizes the solenoid 22α to open the valve 22 thereby permitting passage of hot compressed gas from the compressor into the reheat coil 21 whenever, the temperature of the enclosure is below this predetermined temperature. As the temperature of the enclosure rises sensing means or bimetal switch 27 opens thereby de-energizing solenoid valve 22 and closing off the inlet ίο the reheat coil 21. This stops flow into the reheat coil 21 and forces all of the discharge gas to flow into the condenser 7. The air conditioning unit then operates to cool the air flowing through the evaporator 8 without the heat of the reheat coil.

Manual control knob 25 also adjusts the temperature at which bimetal switch 27 opens and closes to maintain the range of temperatures at which dehumidification or reheat occurs. Thus, when the occupant lowers the temperature at which switch 26 closes to, for example, 73° F., then switch 27 is also adjusted to operate at 76° F.

It should be noted that the above arrangement causes the unit to cool the enclosure air at all temperatures above the second predetermined temperature set for operation of the switch 27, such as the aforementioned temperature of 78° F. At temperatures between those set for operation of the switch 26 and switch 27 (such as, for example, 75° F. ’and 78° F. respectively) the air conditioner operates to cool the air stream and remove moisture therefrom as well as to reheat the air stream, so that.the air stream is not too greatly cooled by the unit. This tends to make the unit operate for a ’greater period of time wi1hout substantially lowering the room temperature, while removing larger amounts of moisture from the air stream than is possible merely by means of a cooling operation. It is understood, of course, that when the temperature of the incoming 'air drops below the first predetermined temperature (75° F.), the temperature .responsive switch 26 disconnects the compressor thereby interrupting the cooling cycle as well as the dehumidification cycle.

At times it may be desirable for the operator to utilize the air conditioner for cooling only under conditions which might otherwise cause the second bimetal switch 27 to energize the solenoid valve 22 thereby shunting a portion of the discharge gas into the reheat coil 21. In order to permit the operator of the unit to operate, the conditioner on cooling only, there is preferably, provided a switch 29 in the circuit leading to the solenoid 22α of valve 22 which may be manually operated to interrupt the current flow to the solenoid 22α. Means, such as the knob 28 on the front of the unit, is provided for manually opening or closing the switch 29, thereby, making it possible to operate the air conditioner to provide cooling with&gt; out reheat under those conditions when the unit would normally operate on reheat, such as when the enclosure temperature was between the aforementioned 75 F. to 78° F. temperature interval.

Referring now to FIGURE 3, there is shown a second arrangement of the refrigeration circuit adapted to provide reheat operation. Instead of the check valve adjacent the outlet end 21δ of the reheat coil 21, there is provided a reverse bend 31 of tubing at the outlet end which rises above the latter portions of the reheat coil 21 to form a liquid trap therein. Thus, upwardly turned loop 31 rises above the portion 21c of the reheat coil and creates a liquid trap in the portion 21c of the reheat coil 21. In this arrangement, it will be necessary to charge the system with a greater volume of refrigerant, in order for the system to operate at greatest efficiency. When the valve 22 closes, all of the gas in the reheat coil 21 is cooled to its condensing temperature and is effectively removed from the system and because the end 21Z&gt; of the reheat coil is open (i.e. is not provided with a check valve) the entire volume of the reheat coil may fill with liquid or condensed refrigerant. Once the refrigerant liquid fills the volume of the reheat coil, it no longer has any effect on the system. _ .

At times, when the condenser 7 is running low on liquid, it is possible to have gaseous refrigerant in the end 7α

3,105,366 of the condenser 7 leading to the capillary. The liquid trap created by the upwardly formed loop 31 prevents gaseous refrigerant from replacing the liquid refrigerant in the reheat coil 21, thereby reducing the efficiency of the system for cooling. Liquid refrigerant fills the entire 5 volume of the tube in the lower portion 21c of the reheat coil,, thereby preventing the high pressure gas from flowing into the coil 21 and preventing the liquid refrigerant from draining out of the coil. This effectively prevents continuous condensing of the refrigerant in reheat coil 10 21 during the cooling operation which would, of course, add heat to the air flowing over the reheat coil and thereby reduce the cooling effect on the air stream in the evaporator or indoor compartment 6 of the air conditioner.

While in accordance with the patent statutes there has 15 been described what at present is considered to be the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is, therefore, the aim of the appended 20 claim to cover all such changes and modifications as fall within the true spirit and scope of the invention.