US 3189085 A
Description (OCR text may contain errors)
J1me 15, 1965 A. H. EBERHART 3,
AIR CONDITIONING APPARATUS Filed Sept. 13, 1960 HEAT COOL l7 7 l8 2 i INDOOR I I l. III I C U aw nvvnv TOR ARTHUR H EBERIZART ATTORNEY United States Patent Ofiice 3,189,985 Patented June 15, 1965 3,189,085 APR CONDITKONING APPARATUS Arthur H. Eberhart, Hilliard, Ohio, assignor to Westing-' house Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Sept. 13, 1960, Ser. No. 55,794 5 Claims. (Cl. 165-12) This invention relates to air conditioning apparatus and more particularly to an improved system for removing frost from the heat exchangers of such apparatus.
Many present day self-contained air conditioning units employed to cool the air in a room or other enclosure are equipped with, so-called, reversible heat pumping systems which also permit the unit to be-usedto extract heat from outdoor air and add this heat to indoor air for room heating purposes. Such units are usually used for heating purposes under mild weather conditions in which the outdoor temperature is generally above 30 degrees F. I It has become increasingly desirable, however, to extend the lower limit of the range of outdoor air temperatures in which these units are usable. A serious factor limiting the use of air conditioning units in removing heat from lower temperature outdoor air is the accumulation of excessive frost on the outdoor heat exchanger. of the unit when that heat, exchanger is operating below 32 degrees F.
Air conditioning units can be employed to heat indoor air from an outdoor air heat source of relatively low temperature provided the outdoor heat exchanger is periodicaliy warmed to above 32 degrees F. to limit excessive accumulations of frost thereon. It is an object of this invention to provide improved means for effecting this frost removal.
It has been proposed that the outdoor heat exchanger of the air conditioning unit be defrosted by the periodic application of heat from an electric heating element lo cated on the heat exchanger or in the stream of air flowing through the heat exchanger. The latter arrangement is considered the more desirable of the two because'it insures even distribution of heat over the entire heat exchanger and enables heat to be applied directly to the frost on the heat exchanger. With such heated air defrosting systems as have been proposed heretofore an excessively large heating element is required to warm the cold outdoor air sufiiciently to make it effective to defrost the outdoor heat exchanger. Such systems frequently have been deficient in requiring an excessively lng period of time to defrost the outdoor heat exchanger.
In accordance with this invention the air conditioning unit is equipped with means for effecting a reduction in the rate at which outdoor air is conveyed over the heater element and the heat exchanger during defrosting so that a heating element of reasonable heat output is capable of warming the reduced quantity of air to a temperature sufliciently high for rapid defrosting purposes. In the preferred embodiment of the invention, hereinafter deiscribed in detail, air flow through the outdoor heat exghanger is reduced during defrosting by reducing the rate if energization of an electric motor driving the fan or either means circulating air over that heat exchanger. A very substantial reduction in air flow is accomplished by supplying electric current to this motor in short pulses under control of a, so-called, cycling switch, which is placed in the circuit of the fan motor during defrosting. A further object of this invention, then, is the provision of improved means for supplying electrically heated air to the outdoor heat exchanger of an air conditioning unit to effect defrosting of the heat exchanger.
Another object of the invention is to provide improved means for reducing the electrical power input to the means for circulating air over the outdoor heat exchanger to facilitate heating the air to a temperature sufficient to effect rapid defrosting of the outdoor heat exchanger.
Other objects, advantages and features of the invention will appear from the following detailed description of the invention wherein reference is made to the accompanying drawing in which the single figure of the drawing is a schematic illustration of air conditioning apparatus embodying the invention.
The air conditioning apparatus illustrated includes a conventional compression refrigeration system including an indoor, or inside, heat exchanger 11, an outdoor, or outside, heat exchanger 12 and a compressor 13 for circulating a heat transfer fluid through the two heat exchangers. The fluid circuit further includes a reversing valve 14 which is connected to the compressor inlet and outlet by means of a suction line 15 and a hot gas line 16, respectively. The fluid circuit between heat exchangers 11 and 12 is completed by an expansion device 19, in the form of a long, small bore tube, commonly termed a capillary tube. Reversing valve 14 is adapted to direct hot gaseous refrigerant through a conduit 17 to indoor heat exchanger 11 and direct to the compressor inlet cold vaporous refrigerant returning from outdoor coil 12 'via another conduit 18, as indicated by the solid line arrows, or to reverse the direction of refrigerant flow and direct warm vaporous refrigerant to outdoor heat exchanger 12 and direct to the compressor inlet cool re frigerant from indoor heat exchanger 11, as indicated by the dotted line arrows.
As is well understood, heat is absorbed by whichever of the two heat exchangers, 11 and 12, is having refrigerant withdrawn therefrom by compressor 13, and heat is dissipated by the other heat exchanger-that heat exchanger to which warm vaporous fluid is being pumped by the compressor 13. The legends Heat and Cool appearing adjacent reversing valve 14 refer to the condition of operation of indoor heat exchanger 11 and they indicate that the system is conditioned either to heat indoor air or to cool indoor air.
The indoor heat exchanger 11 has associated therewith means for propelling indoor air thereover, including a fan 21 which is driven by an electric motor 22. Similarly, outdoor air is circulated over outdoor heat exchanger 12 by means of another fan 23, which is driven by another electric motor 24. The two fan motors 22 and 24, as well as compressor 13, are energized by electrical current from a common supply system illustrated in the drawing as lines L1 and L2.
All of the above described components of the air conditioning apparatus are commonly employed in so-called reversible air conditioning units and are normally housed in a casing (not shown) which includes suitable partitions, or baflles, for directing and separating indoor and outdoor air.
Outdoor heat exchanger 12 operates as an evaporator to absorb heat from outdoor air propelled thereover by fan 23 when the system is functioning to heat indoor air. Quite naturally, when conditions are such as to make it desirable to warm the air in an enclosure the outdoor temperature is relatively lower and often near the freezing temperature of water. In order to absorb heat, heat exchanger 12 must operate at a still lower temperature and, consequently, it is likely that frost will form on the outdoor heat exchanger. Should this frost accumulation become excessive it detrimentally affects operation of the system because thefrost insulates the heat exchanger, preventing it from effectively absorbing heat from the outdoor air, and also chokes the air flow passages through the heat exchanger, further reducing the ability of the heat exchanger to absorb heat. Consequently, it is necessary to periodically raise the temperature of the outdoor heat exchanger 12 to some temperature above 32 degrees F. to effect removal of frost.
In accordance with this invention, defrosting is accomplished by introducing heat into the stream of air flowing through the outdoor heat exchanger 12 by means of an electric heating element 26. This heating element is preferably located, as shown, between the outdoor air fan 23 and the air inlet face of the outdoor heat exchanger 12. In order to reduce the time required to melt frost from the outdoor heat exchanger 12 it is desirable to deenergize compressor 13 during defrosting to prevent heat transfer fluid from being circulated through the system. With the system shut down it is also desirable to deenergize motor 22 driving indoor air fan 21 because, during this period, indoor heat exchanger 11 is not effective to warm indoor air. In accordance with this invention, motor 24 driving outdoor air fan 23 remains energized to circulate outdoor air over heating element 26 and onto outdoor heat exchanger 12, but electrical energy is supplied to motor 24 at a reduced rate so as to substantially reduce the rate at which outdoor air is conveyed to outdoor heat exchanger 12.
Control of the supply of electrical energy to compressor 13 and to fan motors 22 and 24 to initiate and terminate a defrosting operation is exercised by means of a defrost switch, indicated generally by the numeral 27, and comprising a movable blade 28 adapted to carry current supplied by line L2. When the air conditioning system is operating to either heat or cool indoor air, switch blade 28 is in engagement with a fixed contact 29 for supplying current from line L1 through conductors 31 and 32 to compressor 13 and indoor fan motor 22. This is the solid line position of switch blade 28 illustrated in the drawing. When blade 28 is in this position it is also in engagement with a second stationary contact 33 for supplying electric current to outdoor fan motor 24 via conductors 34 and 35. Line L1 is connected directly to motors 22 and 24 and compressor 13 by return conductors 37. Electric heating element 26 is also connected to line L1 by means of conductor 37, but is not energized until it becomes desirable to defrost outdoor coil 12.
A defrosting operation for outdoor coil 12 is initiated by switch blade 28 moving from its solid line position to the dot and dash line position thereof, by virtue of which movement it becomes separated from contacts 29 and 33 to break the electrical circuits to motors 22 and 24 and compressor 13 and engages a third stationary contact 38 to establish another electrical circuit to outdoor fan motor 24 and complete a circuit through heating element 26. The latter circuit includes conductor 39 running between contact 38 and heating element 26. The new circuit to outdoor fan motor 24 includes a device, indicated generally at 41, which is adapted to effect a reduction in the rate at which fan motor 24 is energized and cause fan 23 to operate at a lower speed, so as to substantially reduce the rate at which air is supplied to outdoor heat exchanger 12 during defrosting.
In its preferred form, device 41 is a cycling, or flasher, switch which periodically makes and breaks the electrical circuit to fan motor 24. Such switches generally include a resistance heating element 42 for applying heat to a thermally responsive member 43 for actuating a pair of contacts 44 in series with heater 42 and the circuit to be controlled, in this case the circuit through fan motor 24, including conductors 46, 36 and 37. Thermally responsive member 43 is adapted to close contacts 44 when it is within a normal range of ambient temperatures and is adapted to open contacts 44 when heated to a predetermined higher temperature by heater 42. Separation of contacts 44 deenergizes heater 42, allowing thermally responsive member 43 to cool and reclose contacts 44. Switch 41, thus, cycles as its thermally responsive member 43 is alternately heated and cooled to supply current in pulses to outdoor fan motor 24.
It is preferable to use a flasher switch to reduce the rate of energization of outdoor fan motor 24 during defrosting because this system makes it possible to operate motor 24 at a much lower speed than could be achieved through the use of current or voltage limiting devices. Intermittently energizing motor 24 at substantially full line voltage provides sufiicient torque within the motor to overcome friction and prevent stalling. The slower speed of fan 23 thus obtainable results in low air flow over defrosting heater 26 so that a smaller heater may be employed in this application and yet achieve sufficient temperature rise in the outdoor air to insure defrosting of outdoor heat exchanger 12. As can be readily understood, the speed of fan 23 is directly proportional to the percentage of time that switch contacts 44 are closed with respect to total cycling time. The desired fan speed can be predetermined by proper selection of heater 42 and thermally responsive member 43 to produce appropriate cycling of the switch.
Actuation of defrost switch 27 can be accomplished by any suitable means for detecting an excessive accumulation of frost on outdoor heat exchanger 12. The control system illustrated in the drawings and preferred for this application is a temperature responsive system including two bellows 48 and 49 communicating respectively with elongated blind tubes 50 and 51, which bellows are linked to switch blade 28 in such a manner that the bellows oppose each other. Bellows 48 and 49 and the tubes communicating therewith are charged with a volatile fluid. An increase or a decrease in the temperature to which each tube 50 and 51 is subjected is reflected in a tendency toward expansion or contraction, respectively, of the bellows associated therewith. Tube 50 has a portion thereof in contact with out-door heat exchanger 12 to sense the temperature of a fluid carrying portion of the heat exchanger. Tube 51 has a portion thereof exposed to outdoor air flowing over heat exchanger 12 for sensing outdoor air temperature. When the system is functioning properly and outdoor heat exchanger 12 is relatively free of frost tube 50 will sense a temperature below that sensed by tube 51 and the difference between the two temperatures will fall Within a limited, predictable range. So long .as the difference between these two temperatures falls within this range the pressure in bellows 49 is balanced by the pressure in bellows 48 and switch blade 28 remains in the full line position illustrated.
In the event outdoor heat exchanger 12 acquires an excessive covering of frost the temperature of fluid carryring portions of the heat exchanger drops because the frost insulates the heat exchanger and reduces the rate at which it can obtain heat from the outdoor air. This results in a substantial increase in the difference between the temperature sensed by tubes 50 and 51, respectively, enabling bellows 49 to overcome the opposition of bellows 48 and move switch blade 28 into engagement with contact 38 to initiate defrosting. Subsequent warming of tube 50, upon removal of frost from heat exchanger 12, causes bellows 48 to expand, moving switch blade 28 back into engagement with contacts 29 and 33 system to heating operation.
'From the foregoing it can be appreciated that this in-,' vention constitutes a novel approach to defrosting the outdoor heat exchanger of an air conditioning system opera ing to warm a room, or enclosure. The concept of rteducing the quantity of outdoor air flowing over an electric defrosting heater and the outdoor heat exchanger to insure rapid defrosting with a heating element of reasonable size enables the air conditioning unit to be operated at lower outdoor temperatures than prior units not equipped with means for reducing this air flow. Moreover, the use of a flasher switch to reduce the rate of energization of the outdoor fan motor insures that a substantial reduction in the fan speed, and consequently in air flow, can be achieved without incurring a stalling condition of fan motor operation which could result in failure of the defrost system to function properly.
and returning the While the invention has been shown in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modiiications without departing from the spirit thereof.
What is claimed is:
1. Apparatus for conditioning the air of an enclosure comprising a heat exchanger subject to the accumulation of frost, an electric heater arranged to defrost said heat exchanger by heating air flowing to said heat exchanger, means for propelling air over said heater and through said heat exchanger, an electric motor for driving said air propelling means, and an electrical supply circuit for said motor, a device for effecting energization of said motor at a reduced rate to cause air to be propelled oversaid electric heater and through said heat exchanger at a reduced rate, and control means responsive to an excessive accumulation of frost on said heat exchanger for simultaneously effecting energization of said heater and connecting said device in said circuit.
2. Apparatus for conditioning the air of an enclosure comprising a heat exchanger subject to the accumulation of frost, an electric heater arranged to defrost said heat exchanger by heating air flowing to said heat exchanger, means for propelling air over said heater and through said heat exchanger, an electric motor for driving said air propelling means, and an electrical supply circuit for said motor, a cycling switch adapted to effect periodic current flow in said circuit thereby to provide reduced energization of said motor and reduced flow or" air propelled over said heater and through said heat exchanger, and control means responsive to an excessive accumulation of tfirost on said heat exchanger for simultaneously efl'ecting energization of said heater and connecting said cycling switch in said circuit.
"3. In an air conditioning system for heating an enclosure, a pair of interconnected heat exchangers one inside and one outside said enclosure, a compressor for circulating a heat trans-fer fluid through said heat exchangers to absorb heat at said outside heat exchanger and dissipate heat at said inside heat exchanger, an electric heater arranged to defrost said outside heat exchanger by heating air to be circulated over said outside heat exchanger, electric motor driven means for circulating outside air over said electric heater and through said outside heat exchanger, control means for energizing said electric heater in response to conditions indicative of accumulation of excessive frost on said outside heat exchanger, and means energized simultaneously with said electric heater ior modifying operationor" said air circulating means to cause the air to be circulated over said heater and through said outside heat exchanger at a reduced rate when said heater is energized.
4. In an air conditioning system for heating an enclosure, a pair of interconnected heat exchangers one inside and one outside said enclosure, a compressor for circulating a heat transfer fluid through said heat exchangers a a 6 r to absorb heat at said out-side heat exchanger and dissipate heat at said inside heat exchanger, an electric heater arranged to defrost said outside heat exchanger by heating air to be circulated over said outside heat exchanger, means for circulating outside air over said electric heater and said outside heat exchanger, an electric motor for driving said air circulating means, control means including a switch mo-vahle from a first position to a second position in response to conditions indicative of accumulation of excessive frost on said outside heat exchanger, said switch in its first position conditioning a first electrical circuit for energizing said compressor and said motor, said switch in its second position conditioning a second electrical circuit excluding said compressor and including said motor and said heater, and means in said second circuit for eifecting energization of said motor at a reduced rate to cause air to be circulated over said heater and through said outdoor heat exchanger at a reduced rate when said heater is energized.
5. In an air conditioning system for heating an enclosure, a pair of interconnected heat exchangers one inside and one outside said enclosure, a compressor for circulating a heat transfer fluid through said heat exchangers to absorb heat at said outside heat exchanger and dissipate heat at said inside heat exchanger, an electric heater arranged to defrost said outside heat exchanger by heating air to be circulated over said outside heat exchanger, means for circulating outside air over said electric heater and said outside heat exchanger, an electric motor for driving said air circulating means, control means including a switch movable from a first position to a second position in response to conditions indicative of accumulation of excessive frost on said outside heat exchanger, said switch in its first position conditioning a first electrical circuit for energizing said compressor and said motor, said switch when in its second position energizing said heater and conditioning another electrical circuit excluding said compressor and including said motor, and means in said other circuit effecting periodic energization of said motor to cause said motor to operate at a speed less than the speed achieved by the motor when energized through said first circuit.
References Cited by the Examiner UNITED STATES PATENTS 2,110,693 3/38 Bailey 17 2,195,924 4/40 Hoesel.
2,297,970 10/ 42 Men.
2,401,560 6/46 Graham et a1. 165l7 2,780,442 2/ 57 Breeding 16517 2,793,834 5/57 Henney et al 165--12 CHARLES SUKALO, Primary Examiner.
HERBERT L. MARTIN, FREDERICK L.
MATTESON, JR., Examiners.