US3157227A

US3157227A - Heat pump

Info

Publication number: US3157227A
Application number: US155952A
Authority: US
Inventors: Jewell S Palmer
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1961-11-30
Filing date: 1961-11-30
Publication date: 1964-11-17
Anticipated expiration: 1981-11-17

Description

J. S. PALMER Nov. 17, 1964 HEAT PUMP Filed Nov. 30,

BUILDING WALL AIR TO BUILDING REGISTERS ill FIG.

FIG- 2.

I INVENTOR. JEWELL S. PALMER ATTORNEY.

United States Patent 3,157,227 HEAT PUB/[P lewell S. Palmer, Eaytown, Tex, assignor, by mesne assignments, to Essa Research and Engineering 6on1 pany, Elizabeth, Null, a corporation of Delaware Filed Nov. 30, 1951,Ser.No. 155,952 1 (Ilairn. (El. 165-29} The present invention relates to a method and apparatus for improving the performance of heat pumps during cold-Weather operation. More particularly, the present invention relates to improvement of efficiency of heat pumps which comprise a compressor, an evaporative coil, and a condensing coil by providing a source of heat for said evaporative coil during use of said heat pump at low temperatures.

The heat pump has obtained broad recognition as a year-around source of air conditioning, providing cooling in the summer and heating in the winter. These heat pumps operate on a closed cycle, compression based refrigeration system which includes a compressor, an evaporative coil, a condensing coil, and a refrigerant. in the operation of these heat pumps, the refrigerant is compressed, liquefied by heat exchange with an air current which is thereby heated, and the liquefied refrigerant is allowed to vaporize through a choke valve into an evaporative coil which is contacted by a second stream of air which is thereby cooled. The evaporated refrigerant is recycled through the compressor for liquefaction and a repetition of the above-described process. The heating capacity of a heat pump is sensitive to ambient temperature conditions, falling off rapidly with lower ambient temperatures. This is due to the decrease in temperature diilerential between the air passing across the evaporative coil and the temperature of the liquid vaporizing therewithin. In the prior art, for operation at extremely low temperatures, it has been necessary to supplement the heat pump with an electric resistance heater placed in the stream of air circulated inside the building being heated,

or to utilize gas heaters placed within the building and normally vented to the atmosphere because of building code requirements. Either alternative is an expensive expedient in that electrical energy is an expensive source of heat in most areas, and the requirement of venting for gas heaters placed within inhabited buildings involves a great loss of heat in .flue gas which is exhausted to the atmosphere.

The present invention obviates the use of these supplementheating means Within the building being heated by providing heating means for the evaporative coil of the heat pump. This source of heat may be a gas or oil burner, the exhaust gases from a gasoline-driven engine used to operate the compressor of the heat pump, circulating water from the jacket of such gasoline engine, exhaust steam from a steam engine used to drive the compressor, including turbine-driven compressors which are themselves driven by steam, or any other source of heat which may be available for use.

By the practice of the present invention, all combustible fuels may be kept out of the space being heated,

thereby complying with building code requirements and providing safe operation while avoiding losses or" heat due to venting of line gases. Further, during the operation of a heat pump at low temperatures, it has frequently been necessary to make provision for defrosting the evaporative coil periodically in order to remove condensed and frozen moisture which collects upon these coils during the heating cycle. By the practice of the present invention, such provisions for defrosting are no longer necessary and the entire defrosting concept can be eliminated. 1

In the use of the present invention, wherein substanti-- "ice ally total recycle of the heated gases within the evaporator housing is utilized, heat losses are minimized and approach those of gas fired space heaters utilized without venting. Thus, although nonvented space heaters are forbidden by ordinance in most cities, the eliiciency associated with nonvented space heaters may still be obtained by using a heat pump modified in accordance with the present invention. Thus, it is apparent that the heat pump, by incorporating the present invention, is made practical for use in even the most extreme of cold climates rather than being limited to mild climates as is presently the case.

As an indication of the diminution of heating capacity in a commercial heat pump as the ambient temperature declines, the following information set forth in Table I relates the heating capacity and compressor watts to the ambient temperature at which the heat pump is operating:

T able I Outdoor Temperature, degrees Heating Compressor Capacity Watts In order to illustrate more fully the concept of the present invention, reference is directed to the drawings wherein:

FIG. 1 is a representation of a split-unit heat pump wherein the compressor and one coil are located outside the building being heated during the winter and cooled during the summer; and

FIG. 2 is a schematic representation of an automatic control system for operating the valves to insure full recycle of the air within the coil housing in response to the temperature of the ambient air.

Referring now to FIG. 1, there is schematically set forth a heat pump utilizing the present invention. In PEG. 1 the heat pump is made up of a compressor ltltl communicating by way of line 1&1, four-way valve 102,

and line 193 with a condensing coil 1% wherein heat is transferred to the air flowing Within a building duct 146 by means represented schematically by fan 1 95. Coolant is passed from the condensing coil 104 by Way of line 1% into an evaporating coil 1% and from thence by Way of line 107 and four-way valve 1% into line 1&8

for return .into the compressor 1%. The compressor 1% is shown as being driven by an internal combustion engine 111 although it might suitably be driven by an electric motor, a steam engine, a steam turbine, or other motive means. The evaporating coil 1% is shown as being placed Within a housing 111, comprising an air inlet 112 controlledby valve 113, the air being passed through the housing and over the evaporative coil 1% by means of fan 114. The air is passed from the housing by Way of outlet 115. Recycle duct means 116 are provided whereby during very low temperature operation, the valve 113 may be substantially closed and valve ll! which serves both outlet 115 and recycle duct 116 is substantially closed, leaving only so much clearance as isrequired for the circulation through the housing 111 of sufficient oxygen to support combustion when a gas or fuel oil fired flame is used as a source of heat. During cold temperature operations, the cooling Water from the internal combustion engine 110 is circulated by Way of

lines

120 and 121, pump 122 and line 123 to a heat transfer radiator 124 within the housing and in the path of circulating air before it contacts the evaporative coil 1%.

The cooling water is returned by way of line 125 into the jacket of the engine 110. During summer operations when the additional heat is not desired, or in winter but when the heat load on the heat pump is less than its capacity at ambient temperatures, all or a portion of the water may be circulated through external radiator 127 for providing sutlicient cooling for the internal combustion engine. The amount of water circulated through the radiator 124 may be controlled by a heat responsive element 129 which actuates a valve 130 within the circulating water line in order to control the amount of heat delivered to the inside of housing 111. Supplementary to the circulating water from the internal combustion engine, where the amount of heat abstracted from the circulating water is insufficient, a burner 132 is supplied with gas by way of line 133 controlled by valve 134. The valve 134 is controlled by a temperature responsive element 129 similar to the manner in which valve 130 is controlled. The amount of heat supplied by the gas burner 132 may supplement the heat available from the engine 110 or may be in lieu of the circulating water source above described.

During cold weather operation, assuming that the gas burner is necessary to provide at least a portion of the heat required, the

valves

113 and 117 are moved to the dotted line position shown in FIG. 1, under which condition the air circulated through the housing 111 will be sufiicient only to supply the oxygen needed for combustion of the gas burned, and a partial recycle stream of air is provided. It should be noted that when the heat supplied by the circulating water from the motor 110 is sufiicient to supply the heat load for the heat pump, the

valves

113 and 117 may be completely closed, resulting in a full recycle of air within the housing 111.

Under these conditions, the heat pump operates merely as a means for transferring heat from the gas burner or internal combustion motor into the building to be heated. Since the housing 111 normally will be supplied with insulation, the amount of the heat lost into the atmosphere is negligible and is comparable in degree to the minor heat losses which are experienced with the use of space heaters not vented to the atmosphere. Thus, the advantages of a nonvented space heater are obtained without the danger of suffocation or asphyxiation of persons within the building being heated, and in full compliance with city ordinances. Further, defrosting of the evaporative coil is no longer required.

It should be recognized that when a steam-driven prime mover is used instead of the internal combustion engine 110, exhaust steam may be circulated through the radiator 124 for supplying heat to the heat pump. Likewise, where an electrical prime mover is used instead of engine 110, the gas burner 132 will provide all of the heat for the heat pump. and the

valves

117 and 113 will be only partially closed in providing recycle operation.

The recycle operation above described is particularly useful at extremely low ambient temperatures, wherein the temperature difference between ambient temperature and the temperature downstream of the evaporative coil becomes quite low. For example, at temperatures below about 30 F., the air circulating across the evaporative coil 106 in once-through operation may be insuflicient to provide more than a nominal amount of heat, considered apart from that heat added by the gas burner. Assuming, for example, that the heat pump is being operated at a heat load of about 35,700 Btu. per hour, with the temperature upstream of the evaporative coil 106 being maintained at 40 F. by the addition of extraneous heat from radiator 124, the temperature downstream of the coil being 28.5 F., and assuming that the ambient temperature is 285, no heat will be abstracted from the ambient air circulating through the housing. This is so because under the conditions stated, the temperature downstream of the evaporative coil is equal to ambient temperature, and no net loss in heat content or enthalpy will be experienced by the air in its passage through the housing. Since the downstream temperature will remain at 28.5 if the upstream temperature is maintained at 40 F., as the ambient temperature drops below 28.5 a net loss of heat to the ambient atmosphere will be experienced by reason of the difference between the 285 F. discharge temperature and the ambient temperature. Assuming an ambient temperature of 18.5", it will be seen that a 10 F. ditference in temperature between the exhausted air and ambient atmosphere will be suffered and that the heat in the discharged air representing the 10 difference will be a net loss to the system. Under these conditions, a substantially total recycle of the air within the housing will limit the heat loss to the atmosphere to that amount of air which necessarily must be circulated in order to provide oxygen for combustion of the heating fuel.

Therefore, it is preferred to operate the heat pump of the present invention under substantially total recycle of air within the housing 111 when ambient temperature is equal to or below that down-stream of the evaporative coil under full load.

Referring now to FIG. 2, there is schematically shown a system whereby automatic control of the recycle feature may be controlled by ambient temperature. In the schematic diagram shown in FIG. 2, the housing 211, similar to housing 111, is provided with

valves

213 and 217, similar to the

valves

113 and 117. The

valves

213 and 217 are movable between fully open positions and a substantially closed position as shown by the dotted lines in the diagram by moving means indicated by the

boxes

218 and 220. These means 218 and 220 may comprise two position solenoid type movers or other type two position motors supplied with suitable linkages in order to move the

valves

213 and 217 in the desired manner. These linkages may include bell cranks and push rods, ratchets and ratchet gears, etc., all is is well known in the art. The particular linkages form no part of the present invention. The ambient atmosphere is sensed by a temperature responsive means 222, and upon the ambient temperatures becoming lower than the set point, the

means

218 and 220 are actuated in order to move the

valves

213 and 217 to the positions shown in the solid lines. As ambient temperature rises above the set point, the

movers

213 and 220 would move the

valves

213 and 217 in the positions shown by the dotted lines. The temperature set point would be related to the temperature downstream of the evaporative coil 206, under full-load conditions. It could be this temperature exactly, or 1 or so above that temperature in order to avoid loss of added heat to the atmosphere. The heater 232 is controlled by temperature sensitive means 234 which controls the valve 236. It should be understood that a pilot light will be provided in order to maintain a means for lighting the valve 232 should the gas flow be shut off completely by valve 236. The override means 224 positioned in the circulating air duct 205 may be provided to reset the temperature responsive means 234 to a higher temperature, providing a larger temperature difference between the circulating air within housing 211 and the liquid within the evaporative coil 206 and thereby increasing the flow of heat into the condensing coil 206 for transmission into the flowing air within duct 205. Thus, a dual control system is provided which will maintain temperatures within the comfort range within the building being heated while maintaining a recycle air stream within the duct 211 at ambient temperatures which require this recycle stream for optimum efficiency.

It should be noted that the system set forth above is applicable not only to the split unit type of heat pump as is shown in FIG. 1, but also to the combined unit which is contained in a single housing, which would merely mean an adaptation of the heating means to provide heat adjacent the evaporative coil. It might also be noted that during summertime operation, the heating system of the present invention is inactivated, the valve 102 would be rotated in order to change the direction of coolant flow, in which case the coil 106 would become the condensing coil and coil 104 would become the evaporative coil. This would provide for cooling within the building duct 146.

By means of the invention as above set forth, a process for increasing the efficiency of heat pumps at low ambient temperatures has been provided, which comprises supplying additional heat to the air stream upstream of the evaporative coil whereby the apparent ambient temperature is raised above that actually obtaining. It has been. shown that by the practice of this process, the capacity of a heat pump may be maintained near an optimum, and heat losses to the ambient atmosphere are minimized. Accordingly, therefore, the process of increasing the efficiency of a heat pump and the apparatus therefor, as set forth above, should be limited not by the specific examples given, but rather by the scope of the appended claim.

I claim:

In a heat pump system comprising a first duct containing a condensing coil and means passing air thereover, a compressor, an evaporating coil, and means fluidly connecting said compressor, said condensing coil, and said evaporating coil for circulation of a refrigerant in a closed system, I

the improvement which comprises a housing having an air inlet and an air outlet,

wall means interiorly dividing said housing into a main duct and a recycle duct, said wall means terminating proximate to said outlet,

said evaporating coil being located in said main duct,

means for circulating air through said main duct and said recycle duct,

heating means in said housing,

first valve means associated with said air inlet and movable to an open position and a closed position,

second valve means associated with said air outlet and movable to an open position whereby said recycle duct is closed and said'outlet is open, and to a closed position whereby said recycle duct is open and said outlet is closed,

first temperature sensing means located eXteriorly of said housing,

means responsive to said temperature sensing means to move said first and second valve means to said closed positions over said air inlet and air outlet thereby opening said recycle duct means at a predetermined lower ambient temperature, and to said open positions over said air inlet and air outlet thereby closing said recycle duct means at a predetermined higher ambient temperature,

second temperature sensing means in said first duct,

third temperature sensing means in said housing upstream of said evaporating coil,

and means responsive to both of said second and third sensing means for controlling said heating means;

References Cited in the file of this patent UNITED STATES PATENTS 1,737,040 Bulkeley et al Nov. 26, 1929 2,124,268 Williams July 19, 1938 2,209,787 Miller July 30, 1940 2,263,476 Sunday Nov. 18, 1941 2,468,626 Graham Apr. 26, 1949 2,799,482 Rawdon July 16, 1959