US3280579A

US3280579A - Heat pump defrost control unit

Info

Publication number: US3280579A
Application number: US395452A
Authority: US
Inventors: Daryl F Kayl
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-09-10
Filing date: 1964-09-10
Publication date: 1966-10-25
Anticipated expiration: 1983-10-25

Description

Oct. 25, 1966 o. F. KAYL 3,280,579

HEAT PUMP DEFROST CONTROL UNIT CONTROL umT I ELEMENT 1 E ELEMENT 2 ELEMENT 3 i 1/ OUTSIDE COlL 4-WAY REVERSING COMPRESSOR VALVE mswE COIL

REVERSING VALVE CONTROL INVENTOR W' 1 DARYL F. KAYL ATTORNEY Oct. 25, 1966 D. F. KAYL HEAT PUMP DEFROST CONTROL UNIT 2 Sheets$heet 2 Filed Sept. 10, 1964 INVENTOR DARYL F. KAYL ATTORNEY United States Patent 3,286,579 HEAT FUMP DEFRGST CONTROL UNIT Daryl F. Ka-yi, 2751 6th Ave., Merced, Calif. 95340 Fiied Sept. 10, 1964, Ser. No. 395,452 1 Claim. (Cl. 62--156) This invention relates to coil frost control for an air-toair heat pump apparatus and more specifically to a defrost system utilizing two separate cycle controls.

It is well known that in heat pumps of the air-to-air type, heat is extracted from one source of air and rejected to another. When a heat pump is employed to supply heated air to a space, heat extracted from a source of air flowing over an outdoor heat transfer coil is rejected to a stream of air flowing over a heat transfer coil located in an inside space being treated. Under circumstances where the ambient temperature is substantially reduced, the amount of heat in the outdoor air is likewise relatively reduced.

Basically, in a heat pump, a charge of refrigerant is sealed in a closed circuit. This refrigerant is changeable between its liquid and vapor states at the normal heat pump temperatures and at the commercially operable pressures. A compressor is utilized to compress the vaporous refrigerant after which the refrigerant is directed to a condenser coil. The heat transfer between the condenser coil and the ambient fluid withdraws heat from the refrigerant thereby condensing the refrigerant to a liquid at high pressure. This liquid refrigerant is then throttled into an evaporator coil so that the pressure of the liquid refrigerant is less than the vapor pressure of the refrigerant ambient in the evaporator coil. Due to the heat transfer between the evaporator coil and the fluid adjacent thereto, the low pressure liquid refrigerant is caused to boil and become a vapor. This vapor is then returned by appropriate conduits to the compressor for recycling.

It is well known that the surface of the evaporator coils tends to accumulate frost thereon. This is due to the fact that when the surface temperature of the coil drops below 32 degrees Fahrenheit, any moisture condensed out of the air flowing over the coil will freeze on the surface of the evaporator coil. Any build up of frost or ice on the evaporator coil acts as an insulator, decreasing the rate of heat transfer through the coil and substantially minimizing the efficiency of the refrigeration cycle and may eventually render it ineffective. It is therefore apparent that it is not only desirable, but mandatory, to provide some means for preventing excessive frost accumulation.

The defrosting of an evaporator coil may be accomplished in a variety of ways which are Well known. Included in these methods are the stopping of the refrigeration cycle, followed by either blowing warm air over the evaporator coil, or discharging the relatively warm condenser gas into the evaporator coil. It is apparent that this is neither an eflicient nor desirable method of solving the problem of frost accumulation.

Simple thermostats or pressure switches have also been used. These devices either cut out or initiate the defrost cycle when a drop in the predetermined evaporator suction temperature is detected and cut back in when the defrost cycle is completed as the result of reaching a suction temperature in excess of 32 degrees. Another defrosting method includes a device which responds to the static pressure drop in the air stream passing over the coils. Another responds to the velocity of the air passing through the coil. The latter two types are difficult to keep in adjustment since they are constantly exposed to cold temperatures and the temperature or pressure responsive devices are not adequate because of the wide range of evaporator coil temperatures normally encountered even in the absence of frosting.

Temperature sensing bulbs have previously been disposed in spaced locations, but systems of this type often result in false and/or early defrost cycle termination, to the end that either a short cycling of the equipment or an excessive accumulation of frost results. Moreover, apparatus of this type has been hampered by the lack of adjustable, separate initiation and termination controls.

It is therefore an object of this invention to provide a separate, fully adjustable initiation and termination control.

It is a further object of this invention to provide control means which will terminate defrost only when the outlet line temperature indicates a condition reflecting a complete defrost of outside coil.

It is a still further object of this invention to provide two separate cycle controls in one case.

An additional object of this invention is to provide a device which precludes false and/ or early termination of the defrost cycle.

The foregoing objects and advantages are provided by this invention which utilizes three power elements connected to temperature sensing devices which operate one set of contacts in an electrical switching means. Specifically, two of the three power elements are on a hinged lever operatively connected so that only the differential between the two is active. When this differential, brought about by the frosting of the coil, is great enough, as measured across the coil-heat exchanger, the resultant force opens one pair of contacts and closes a second set. This action accomplishes two things, first, air flow across the blocked coils is stopped and second, the position of a four-way reversing valve which circulates hot gas through the coil to be defrosted is reversed.

The third power element is then actuated which in turn actuates an auxiliary heating system which may continue the flow of warm air through heating ducts if the system is being used in that mode. This third power element also operates to reverse the process by resetting the original contacts when defrost is completed, for example, when the temperature of the outside coil has reached a preset value. in the inventive device, both differential and termination elements are adjustable.

Other objects and advantages of the invention will be apparent from the following detailed description of the invention when taken in reference to the accompanying drawings wherein:

FIGURE 1 is a block diagram of an air-to-air heat pump system utilizing the invention;

FIGURE 2 is a more detailed schematic view of FIG- URE 1.

As shown in FIGURE 1, the system basically comprises a pair of coiled heat exchangers interconnected by piping, a four-way reversing valve and a compressor. The operation of the system is controlled by a control reversing valve 17 the refrigerant flows to the unit which initiates the reversing valve control. Three capillary reference elements are disposed so that the control unit contains two separate cycle controls in a single case.

FIGURE 2 depicts a more detailed schematic view of the invention in which an inside heat exchanger or coil 11 is interconnected with an outside heat exchanger or coil 13 by a compressor 15, a four-way reversing valve 17, and associated auxiliary piping 19 and 19'. In equipment of this type the inside coil 11 is located within the area to be served by the heat pump, while the outside coil 13 is usually located in the ambient area.

During the normal cooling cycle the compressor 15 discharges a relatively hot gaseous refrigerant through the four-way reversing valve 17 through a portion ofthe system including the auxiliary piping 19 in order to obtain the desired cooling effects. The reversing valve 17 is controlled by electrical switching means 18. From the outside coil 13 where condensation of the hot gaseous refrigerant occurs as ambient air is blown over the surface thereof by fan 21 driven by motor 23.

Liquid refrigerant formed in the coil flows through a suitable expansion device 24 to an indoor coil 11 serving as an evaporator. In this indoor coil the liquid refrigerant is converted to a vaporous refrigerant as it extracts heat from a stream of air diverted over the coil by fan 25 driven by motor 27. The vaporous refrigerant which is formed thereby then flows again through the reversing valve 17 into the compressor 15 thereby completing the refrigerant cycle.

As has been brought out previously, when the temperature of the ambient air and the moisture contained therein are such that frost is formed on the coil of an outside heat exchanger, in order to preserve the efficiency of the system, it is necessary to defrost the unit. This invention functions as a defrost control for an air-to-air heat pump of the type hereinabove described and the control will operate and defrost the outside coil only when defrosting is needed. This control will defrost the coil under all normal operating conditions and will defrost completely before the control will terminate the defrost cycle. In addition, there is provided an auxiliary heating element 61 which may be placed in service to maintain the duct heat during the defrost period when the system is being used as a heater.

In accomplishing this function a'first capillary reference element 31 is installed in the outside air stream before the air enters the outside coil. A second capillary reference element 33 is located adjacent to the auxiliary piping 19 and interposed between the outside coil 13 and the four-way reversing valve 17. Capillary reference bulb element 31 is connected to bellows power element 35 while capillary reference bulb 33 is connected to bellows power element 37. These reference capillary and power elements are so chargedand located above the initiation lever assembly 39 to initiate defrost when the differential temperature increases to ten degrees to thirty degrees between the outside ambient air temperature which is represented by capillary reference element 31 and the defrost initiation capillary reference element 33. This ten-degree to thirty-degree differential will be less than if the evaporator is free of frost.

Adjustment of the temperature difference may be made by moving the

power elements

35 and 37 on the case 38 relative to the pivot point of the hinge pin initiation lever assembly 39.

In the event that frostor icing causes blockage of the air flow over the outside coil, the coil temperature sensed by defrost initiation capillary reference element 33 will lower rapidly and cause an increase in temperature differential between that point and the reference temperature sensed by capillary reference element 31. This will cause the power element 35 to exert more pressure on the initiation lever assembly 39 than is caused by power element point is adjustable to varying frost conditions. In addi-' 37. This difference in the force results in the initiation lever assembly rotating about its hinge pin and in so doing causes toggle switch 41 to change its position and cut off outside motor 23 and thereby stopping fan 21. In addition the closing of the electrical contacts in toggle switch 41 initiates interconnecting electrical switching means 18 whereby the four-way reversing valve will change position and allow hot gas to enter the outside coil. This hot gas will initiate coil defrosting. The coil will defrostprogressively from inlet side 43.0f coil 13 to outlet 45 of coil 13. Outlet side 45 being the last part of the outside coil 13 to defrost thereby assuring that a complete defrost will be accomplished each cycle before the unit can terminate defrost and reverse to a normal heating cycle.

When outlet side 45 has reached a temperature of 4547 degrees, the defrost capillary reference element 47 will actuate defrost power unit 49 which will develop sufficient power due to its long arm through termination lever assembly 51 to overdrive initiation lever assembly 39 and operate switch 41v which will then be positioned to cause the reversing valve to return to its normal cooling position and start motor 23 and fan 21.

The auxiliary heat relay will be dropped out unless the structure heating thermostat 53 calls for auxiliary heat.

Initiation temperature adjustment means 55 is located proximate the end of initiation lever assembly 39-opposite the hinge pin. Initiation temperature adjustment means 55 comprises a thumb screw adjustment which is connected by biasing means to the end of said initiation lever assembly 39.

A similar termination temperature adjustment means 57 is located on the termination lever assembly 51 proximate the end opposite its pivot point. Said adjustment means being adjustable between 40 and degrees.

From the foregoing it will be clear that applicant has provided a novel automatic defrosting means wherein cut-off points or defrost initiation points operate only when they are needed and only when the outside coil is fully refrigerated .and/ or closed with frost. This cut-off tion this control allows the separate and independent adjustment of the termination temperature of the defrost cycle. Further this defrost termination occurs only when the outlet 45 is completely freeof frost or ice and then and only then will termination lever assembly 51 be actuated to return the system to the structure heating cycle.

There is provided a case heater 59 and automatic thermostat means 53 for the maintenance of an even operation ambient within and surrounding the power elements. This will counteract the problems of the temperature control case being located in colder ambients and the termination power element bellows thereby causing a paralyzed condition of the power element bellows and rendering this side of the cycle non-operated.

It may be desirable in some applications to obtain the same result by enlarging the reference capillary elements so that liquid is always present in the bulb thereof, thereby preventing paralysis of thebellows. By so doing, the necessity for heating the case is obviated.

While only one embodiment of the invention has been shown by way of illustration, there are many changes which may be obvious to one skilled in the art, and the scope of the invention is limited only by the appended claim.

I claim:

A control unit for controlling the defrost cycle of an ai-r-to-air heat pump comprising,

a case,

a first lever, pivotally mounted in said case,

first and second power elements adjustably mounted on said case for differential cooperation with said first lever,

a second lever pivotally mounted in said case,

a third power element adjustably mounted on said case for cooperation with said second lever,

References Cited by the Examiner UNITED STATES PATENTS Lathrop 62210 X Jones 62160 X Fifield 62160 X Felter 6216O Krueger 62-209 X thermostatic means for controlling said heating means. 10 LLOYD L. KING, Primary Examiner.