US 4,467,613 AGranted

Apparatus for and method of automatically adjusting the superheat setting of a thermostatic expansion valve

AssigneeEmerson Electric Co.

InventorsJoseph L. Behr, David P. Hargraves

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Abstract

Apparatus for and a method of automatically adjusting the superheat setting of a thermostatic expansion valve of a refrigeration system is disclosed in which the superheat of the refrigeration system is maintained at a low superheat level so as to maximize the operating efficiency of the refrigeration system, and yet which prevents the return of excessive amounts of liquid refrigerant to the compressor which would be likely to cause damage to the compressor. This apparatus includes an electric heater for biasing the thermostatic sensing bulb of the thermostatic expansion valve and a control for the heater which is responsive to a refrigeration system parameter, such as the temperature of the lubricant in the compressor sump, so as to effect an increase in the temperature of the thermostatic bulb above the refrigerant temperature upon an indicated change in the parameter being monitored thereby to, in effect, reduce the superheat setting of the thermostatic expansion valve and to increase the flow of refrigerant through the refrigeration system. Upon sensing another indicated change in the parameter, the heater is de-energized (or at least the heater power is reduced) thereby to effect an increase in the superheat setting of the thermostatic expansion valve and to reduce the flow of refrigerant.

Claims9

Dependent claims

In a heat pump system comprising a compressor having an inlet and an outlet, a first coil located out of doors, a second coil located indoors, said indoor and outdoor coils being in communication with one another, a shiftable valve connected to the outlet and the inlet of the compressor and to the outdoor and indoor coils, said valve being selectively shiftable between a first position in which refrigerant is delivered from the outlet of the compressor to the outdoor coil such that the heat pump system is operated in a cooling mode and a second position in which refrigerant is delivered from the outlet of said compressor to said indoor coil such that said heat pump system is operated in a heating mode, and a thermostatic expansion valve between said indoor and said outdoor coils, said thermostatic expansion valve having a thermostatic sensor in heat transfer relation with the refrigerant discharged from one of said coils for automatically varying the flow of refrigerant through said thermostatic expansion valve so as to maintain the refrigerant entering said compressor at a predetermined superheat level, said thermostatic expansion valve being pre-set at a predetermined superheat setting, wherein the improvement comprises:

an electric heater in heat transfer relation with said thermostatic sensor, and control means responsive to an operating parameter of said heat pump system operating parameter for varying the heat output of said heater thereby to vary said superheat setting of said thermostatic expansion valve, said control means including means responsive to said heat pump system operating parameter when the heat pump system is in its heating mode for operating said heater along a first heater power output versus said operating parameter value function and being further responsive to said heat pump refrigeration system operating parameter when the heat pump system is in its cooling mode for operating said heater along a second heater power output function versus said operating parameter value function.

A method of automatically controlling the superheat setting of a thermostatic expansion valve in a heat pump system, said heat pump system comprising a compressor having an inlet and an outlet, a first coil located out of doors, a second coil located indoors, said indoor and outdoor coils being in communication with one another, a shiftable valve connected to the outlet and the inlet of the compressor and to the outdoor and indoor coils, said valve being selectively shiftable between a first position in which refrigerant is delivered from the outlet of the compressor to the outdoor coil such that the heat pump system is operated in a cooling mode and a second position in which refrigerant is delivered from the outlet of said compressor to said indoor coil such that said heat pump system is operated in a heating mode, and a thermostatic expansion valve between said indoor and said outdoor coils, said thermostatic expansion valve regulating the flow of refrigerant into one of said coils and having a thermostatic sensor in heat transfer relation with the refrigerant discharged from said one coil and returning to said compressor, said thermostatic sensor effecting a change in said thermostatic expansion valve so as to vary the flow of refrigerant therethrough whereby the temperature of said refrigerant entering said compressor is at a temperature above the evaporation temperature of the refrigerant, this last-mentioned temperature being referred to as superheat, said thermostatic expansion valve being preset at a predetermined superheat setting, said method comprising the steps of:

monitoring a parameter of said heat pump system responsive to the superheat of the refrigerant being returned to said compressor;
and
heating said thermostatic sensor in response to variations of said heat pump system parameter being monitored along a first relationship of heater output versus parameter value when said heat pump system is in its heating mode and along a second relationship of heater output versus parameter value when said heat pump system is in its cooling mode thereby to vary the effective superheat setting of said thermostatic expansion valve and to permit said heat pump system to be operated at a predetermined relatively low superheat level thus maximizing the operating efficiency of said heat pump system and yet insuring that no damage results to the refrigeration system due to liquid refrigerant being returned to said compressor regardless of whether the heat pump system is operated in its heating or cooling mode.

Dependencies are inferred from the claim text.