US2828614A - Air conditioner - Google Patents

Description

' :UETMW April 1, 1958 L. R. SMITH 2,828,614

AIR CONDITIONER Filed Jan. 19, 1954 INVENTOR Lewis 1i. Smi z AIR CGNDETIONER Lewis R. Smith, Auburn, N. Y., assignor to Remington Corporation, Auburn, N. Y., a corporation of Delaware Application January 19, 1954, scrim No. 4ii4,897

3 Claims. (Cl. 623) This invention relates to refrigeration and air conditioning, and more in particular to controlling the refrigerating capacity of a refrigeration system having a fixed refrigerant charge.

With refrigeration systems, particularly of the type using a fixed restrictor, such as a capillary tube, the refrigerant flow is dependent to a degree upon the amount that the liquid is sub-cooled below its vapor1zat1on temperature prior to its entrance to that fixed restrictor. The rate of liquid flow through a capillary tube increases substantially as the liquid is sub-cooled below its vaporization temperature, and the rate of flow is decreasedwhen the sub-cooling is reduced. When the refrigerant temperature at the entrance to a fixed restrictor 18 such that there is refrigerant vapor present, the rate of flow is substantially reduced from what it would be if the refrigerant were entirely in the liquid phase; at or below its saturation temperature, i. .e. saturated or sub-cooled. Furthermore, each pound of refrigerant circulated has ahigheraverage calorific value as it enters the evaporator thereby increasing the overall refrigerating. effect of the system.

With the mass production of refrigeration systems, such as are used in room air conditioning units for cooling and dehumidifying the air, there has arisen a .need for more accurate manual and automatic control upon the refrigerating effect of a particular unit. Further- ''more, when units are made with a fixed restrictor and with afixed refrigerant charge, the range of operating conditions .through which the system can operate with a highdegree of efiiciency is limited. When units of identical construction .are mass produced, the fixed restrictor and fixed refrigerant charge are determined for specific operating conditions assumed to be those .most frequently encountered at which high efficiency is desired. It 'is 'anzobjectofthe present invention to provide refrigeration :systemsand modes of manual and automatic control of the operation thereof which will adapt the system to many varying conditions of operationand many different types of installation.

It is a further object to provide an arrangement for avoiding certain of the difficulties which have been encountered in the past with refrigeration systems of .fixed;charge type. It is a stillfurther object to permit freedom of design and use with respect to refrigeration systems .as discussed above. It isa further object to pro ride for the above with structure which is simple and relatively inexpensive, and yet which is sturdy and is dependable in use. These and other objects will be in part obvious and in part pointed out below.

The-single figure of the drawing is'a schematic representation of one ebodimen-t of the invention.

Referring to the drawing, a refrigeration system is disclosed which performs the cooling and dehumidifying operations in'a unit air conditioner. This system includes a-compressor 2 driven by an electric motor and auto maticaily controlled, a coil and'fin condenser d which ice is cooled by air directed through it by fan 6, and a coil and fin evaporator 8. Evaporator 8 is surrounded by a shell or casing 10 within which there is a fan (not shown) which draws the air through the evaporator from the near side in the drawing, thus to cool and dehumidify the air. The air is directed upwardly through an outlet 12, from which it is delivered through a grill (not shown) into the conditioned room or space. The air drawn through the evaporator maybe partially fresh air, and the remainder is air drawn from the room and thus recirculated.

The elements of the refrigeration system are interconnected, with there being a suction gas line 14 extending from the evaporator to the compressor; a highpressure gas line 16 extending from the compressor to the condenser; and, a liquid line 18 extending from the condenser and supplying the liquid refrigerant through a pair of capillary tubes 20 to the evaporator.

The system is also provided with an auxiliary refrigerant container 22 which is connected through a small diameter tube 24 to the lower portion of the condenser at 26. As is explained below, tube 24 has a U- bend which prevents free flow of refrigerant. The connection of tube 24 at 26 is into the condenser coil directly above the second row of coil tubes, the bottom or first row of coil tubes being in'horizontal alignment with the liquidline .18. Container 22 is provided with an electric heater 28 which receives current through a manually adjustable resistance unit 30 from a transformer 32, which is connected to a source of power by a switch 33. This resistance unit 30 may be shunted by the closing of the switch of a thermostat 34 which has its bulb 36 in the path of the air flowing to the evaporator. This thermostat may be rendered ineffective at the operating temperatures by a manual adjustment (not shown), or it may be adjusted so as to open and close its switch in accordance with predetermined variations in the temperature of the air flowing to'the evaporator. The usual safety and manual controls are provided for the sys tem to prevent improper operation, and to operate the system as desired.

The functions of the system can best be understood by first outlining the normal mode of operation. Assume that switch 23 is closed, and that the adjustable resistor 39 is set to provide a predetermined heating effect from heater 28 to container 22. If this heating effect is of such a small magnitude that the heat being added to container 22 is less than that required to raise the refrigerant temperature within the container up to or above its saturation temperature, as determined by the pressure of the refrigerant in the condenser to which the container is connected, the container will become or remain filled with liquid refrigerant.

If the heating effect becomes such that heat is added to the container fast enough to raise the temperature of the container and its contents above the refrigerant saturation temperature, the liquid refrigerant will tend to evaporate and any that is evaporated will move to the top of the container. Because; of its greater volume, the vaporous refrigerant so produced will force the remaining liquid refrigerant from the bottom of the container through tube 24 into the condenser Assume that the system contains suflicient refrigerant to operate with. refrigerant being condensed and sub cooledfin the condenser, that liquidrefrigerant and liquid only is entering the capillary tubesltl and through which the refrigerant is expanding into the evaporator 8 Where it is evaporated and from which it returns tothe compressor. Also assume that the container 22 is empty of liquid refrigerant and that switch 33 ,is closed so that the heater f2'8fis Ibeing" energized at its maximum heating rate. The system is now'op'erating with substantubes 20 at a more rapid rate.

9 7 Q? tially the entire refrigerant charge circulating in the principal elements of the refrigeration system.

If however, the switch of thermostat 34 opens, heater 28 will be energized at a minimum rate and if that heatingrate is insufficient to maintain container 22 and its contents at'a temperature at or above the refrigerant saturation temperature, as determined by the refrigerant pressure in the condenser to which container 22 is consufficiently great to overcome the cooling effect of the air surrounding the container and to maintain the container and its contents at a temperature slightly above the refrigerant saturation temperature as determined by the refrigerant pressure in the condenser. Under these conditions, a drop in the air temperature surrounding container 22' will increase the cooling efiect on the container which will tend to reduce the refrigerant temperature below its saturation temperature and thereby cause the container to become filled with liquid refrigerant which will in turn reduce the efiective refrigerating capacity of the system. This causes a reduction in the cooling effect on the air passing to the conditioned space, and raises the temperature in the conditioned space. This tends to increase the return air temperature; i. e., that of air surrounding container 22. Thus, the temperature of the conditioned space is controlled, and the control effect is satisfied.

The control temperature point is adjusted by means of resistance element 30, but is also dependent upon the condensing pressure. The condensing pressure is dependent, in an air cooled system, to a large extent upon the prevailing outdoor air temperature; that is, an increase in the outdoor temperature tends to increase the condensing pressure and thereby increase the saturation temperature of the refrigerant in container 22. For example, if the container is filled with refrigerant vapor at a temperature only slightly above that of saturation prior to an increase in condensing pressure, that increase tends to produce condensation of the refrigerant in container 22, and this reduces the cooling effect. Therefore, an increase in outside air temperature increases the control temperature point. is desirable to provide in comfort air conditioning; that is, a higher inside air temperature is maintained with higher outside air temperatures so as to prevent excessive temperature differences.

For most conditions of operation, a decrease in amount of refrigerant which is circulated through the system will cause a decrease in the refrigeration effect of the system. In many systems, the greatest cooling effect occurs when there is sufficient refrigerant present to permit the last tube or tubes of the condenser as the refrigerant leaves that condenser to be filled with liquid refrigerant. This sub-cools the liquid refrigerant thoroughly so that it passes from the condenser at a lower temperature and therefore is available to absorb more heat in the evaporator. This sub-cooling of the liquid refrigerant also causes it to flow through the capillary Hence, the evaporator receives liquid refrigerant at a higher rate and the air is additionally cooled by the additional refrigerant which is thus supplied. This additional flow of refrigerant through the capillary tubes is the effect referred to above is connection with the discussion of sub-cooling the liquid refrigerant. A more extreme change in the rate at which the refrigerant flows through the capillary'tubes is observed by comparing the condition of where some gas is In general, this is the eflcct which it the H present in the liquid refrigerant with the condition where only liquid is present.

Considering now the operation of the system, assume that switch 33 is closed and heater 28 is energized, the heating efiect is controlled by changing the adjustment of the contact on resistor unit 30. Furthermore, the maximum heating effect is obtained by closing the contacts of thermostat 34. Hence, for any given conditions of operation with heater 28 producing less than maximum amount of heat, the closing of the thermostat switch increases the heating and this tends to increase the amount of refrigerant in the system. Therefore, assuming that the system is operating and that the air passing over the thermostat bulb 36 is at an excessively high temperature, and that the thermostat is adjusted to close its switch at that temperature. Then resistor unit 30 is shunted and the heating eifect of heater 28 is increased. This drives liquid refrigerant into condenser 4 and thereby increases the amount of refrigerant which is being circulated. This increase in the amount of refrigerant being circulated causes the system to operate to produce a greater refrigeration effect. Assume then that there is a drop in the temperature of the air passing bulb 36 sutficient to open the thermostat switch, the heating effect of heater 23 is immediately reduced. The container 22 is therefore permitted to cool, and gas refrigerant is condensed therein so that liquid refrigerant is drawn from the condenser into the container. This immediately reduces the refrigerating effect.

A somewhat similar mode of operation may be carried on somewhat manually by setting the thermostat so that its switch remains open throughout the entire range of normal operation, and then manually adjusting the contact, on resistor unit 30. In this way, the refrigerating effect of the system may be manually controlled, with the operation changing gradually from a minimum refrigeratingefiect to a maximum refrigerating eifect.

It has been indicated above that the flow of liquid refrigerant to and from container 22 also depends upon the refrigerant pressure in condenser 4, and this in turn depends upon the cooling etfect of the air passing through the condenser. Accordingly, if the condenser is being cooled by outside air, and the outside temperature rises, there is a gradual rise in the refrigerant pressure inthe condenser, and this tends to cause refrigerant to be condensed in container 22 so that liquid refrigerant is withdrawn from the condenser. This effect causes an automatic reduction in the refrigeration effect under some conditions of operation, so that there is a tendency forthe temperature within the conditioned room or space'to be cooled less as the outside temperature rises. In other words, assuming any general conditions of operation, a lower outside temperature will tend to cause the system to cool the inside air to a lower temperature and, conversely, a rise in the outside temperature will tend to cause the system to maintain the inside air at a higher temperature. Of course, this effect is somewhat due to the fact that container 22 is subjected to the cooling effect of the recirculated air.

It is possible and in many cases desirable to locate container 22 in other places than where shown. For example, it may be located physically beside the condenser or made integral with the condenser.

It is to be understood that under some circumstances a thermostat can be placed in series in either the primary vor secondary circuit of transformer 32 supplying power to the electric heater 28 instead of shunting the resistance element 30. I

With this system the desired control upon the refrigeration effect is obtained with a small consumption of electrical power, and the control parts are simple and sturdy, and they are relatively inexpensive. The container 22 which is open to the refrigerant circuit is hermetically sealed in the usual manner, and the electrical parts are of standard construction. Under some circumstances.

the container 22 may be of another form, or it may be differently positioned. For example, it may be positioned so as to be responsive to the air which has passed through the evaporator and certain of the advantages of the invention will still be obtained. In the illustrative embodiment, the U-bend at 24 forms a liquid trap so that refrigerant does not circulate by a vapor-lift action. This insures the mode of operation described above. Under some circumstances, the connection with chamber 22 could be arranged in a different manner, for example at the top of the chamber, so that refrigerant gas tends to flow to and from the condenser. This tends to give a relatively slow response, but certain of the advantages of the invention are attained.

I claim:

1. In an air conditioning unit, the combination of, a refrigeration system having an air cooled condenser which is subjected to change in ambient temperatures and a compressor which delivers compressed refrigerant thereto and having an evaporator and capillary tube restrictor means through which refrigerant flows from said condenser to said evaporator, means for flowing air through said evaporator, a refrigerant chamber positioned in the path of the air flowing through said evaporator and subjected to the cooling action of said air, tube means connecting said refrigerant chamber to the lower portion of said condenser, an electric heater positioned in heat exchange relationship with said chamber and a thermostatic controller responsive to the temperature of said air stream controlling said heater.

2. In an air conditioning unit, the combination of, a refrigeration system having an air cooled condenser, a compressor which delivers compressed refrigerant to said condenser, capillary tube restrictor means through which refrigerant flows from said condenser to said evaporator, means for flowing a stream of air in heat exchange relationship with said condenser, means for flowing a stream of air to be cooled in heat exchange relationship with said evaporator, a refrigerant chamber positioned in one of said air streams within which the refrigerant is subjected to the cooling action of said air, tube means connecting said refrigerant chamber to said condenser, an electric heater positioned in heat exchange relationship with said chamber, a manual controller for initially adjusting the amount of heat supplied by said heater, and a thermostatic controller responsive to the temperature of one of said air streams to change the amount of heat supplied by said heater.

3. In an air conditioning unit, the combination of, a refrigerant system having an air cooled condenser which is subjected to changes in ambient temperatures and a compressor which delivers compressed refrigerant thereto, said system also having an evaporator and capillary tube restrictor means through which refrigerant flows from said condenser to said evaporator, means for flowing a stream of air through said evaporator, a refrigerant chamber positioned in the path of the air flowing through said evaporator and subjected to the cooling action of said air, tube means connecting said refrigerant chamber to the lower part of said condenser, an electric heater positioned in heat exchange relationship with said chamber, a manual controller for adjusting the heat supplied by said electric heater to said chamber, and a thermostatic controller responsive to the temperature of said air stream for increasing the heat supplied by said heater.

References Cited in the file of this patent UNITED STATES PATENTS 2,183,343 Alsing Dec. 12, 1939 2,183,346 Buchanan Dec. 12, 1939 2,359,595 Urban Oct. 3, 1944 2,453,131 Hubbard Nov. 9, 1948 2,524,813 Lathrop Oct. 10, 1950

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