Demand defrost control method and apparatus

Claim 3

The method of Claim 1 wherein the second enabling step is initiated only while the outdoor heat exchanger is at or below the predetermined level.

Claim 6

A compressor-condenser-evaporator type heat pump system including a defrost controlling means for governing defrosting of the outdoor refrigerant heat exchanger by initiating a defrost cycle, said defrost controlling means comprising: a) an outdoor atmospheric air temperature monitoring sensor; b) an outdoor heat exchanger temperature monitoring sensor; c) a time defrost system for accumulating the aggregate running time of the compressor when the sensed outdoor air temperature is below a predetermined level and enabling initiation of an outdoor heat exchanger defrost cycle after a predetermined compressor running time has been accumulated, said time defrost system constructed to enable defrosting at accumulated com­pressor run times which are relatively short at atmo­spheric temperatures approaching said predetermined temperature and lengthen as atmospheric temperatures are reduced; d) a frosting condition responsive system for detecting the differential between the outdoor air temperature and the outdoor heat exchanger temperature and comparing said differential to a value which varies according to sensed outdoor air temperature, said frosting condition responsive system enabling initiation of a defrosting cycle when the differential and the value bear a predetermined relationship, said frost condition sensing system tending to enable initiation of defrosting cycles at relatively small sensed differential tempera­tures when atmospheric air temperatures are substantially below said predetermined value with the sensed temperature differential required to initiate defrost increasing as atmospheric air temperatures increase toward said pre­determined level; e) controller means for initiating a defrost cycle in response to said time defrost system and said frost condition sensing system both enabling a defrost cycle; and f) said time defrost system and said frost condition responsive system coacting so that when outdoor air temperatures approach said predetermined temperature defrosting of said heat pump is initiated primarily in response to sensed temperature differential and when outdoor air temperatures are substantially below said predetermined temperature the heat pump is defrosted primarily in response to elapsed compressor run time.

Claim 7

A compressor-condenser-evaporator type heat pump system including a defrost controlling means for governing defrosting of the outdoor refrigerant heat exchanger by initiating a defrost cycle, said defrost controlling means comprising: a) an outdoor atmospheric air temperature monitoring sensor; b) an outdoor heat exchanger temperature monitoring sensor; c) a time defrost system for accumulating the aggregate running time of the compressor when the sensed outdoor air temperature is below a predetermined level and enabling initiation of an outdoor heat exchanger defrost cycle after a predetermined compressor running time has been accumulated, said time defrost system constructed to enable defrosting at accumulated com­pressor run times which are relatively short at atmo­spheric temperatures approaching said predetermined temperature and lengthen as atmospheric temperatures are reduced; d) a frosting condition responsive system for detecting the differential between the outdoor air temperature and the outdoor heat exchanger temperature and comparing said differential to a value which varies according to sensed outdoor air temperature, said frosting condition responsive system enabling initiation of a defrosting cycle when the differential and the value bear a predetermined relationship, said frost condition sensing system tending to enable initiation of defrosting cycles at relatively small sensed differential tempera­tures when atmospheric air temperatures are substantially below said predetermined value with the sensed temperature differential required to initiate defrost increasing as atmospheric air temperatures increase toward said pre­determined level; e) controller means for initiating a defrost cycle in response to said time defrost system and said frost condition sensing system both enabling a defrost cycle; and f) said time defrost system and said frost condition responsive system coacting so that when outdoor air temperatures approach said predetermined temperature defrosting of said heat pump is initiated primarily in response to sensed temperature differential and when outdoor air temperatures are substantially below said predetermined temperature the heat pump is defrosted primarily in response to elapsed compressor run time.

Claim 10

The method of Claim 5 wherein a defrost pro­cedure is terminated after a predetermined time or once the coil temperature is greater than a defrost termination temperature.

Claim 11

The method of Claim 5 wherein the accumulated compressor period is maintained and updated as the coil temperature fluctuates above and below the enable tem­perature.

Claim 12

The method of Claim 5 additionally comprising a step of monitoring an ambient temperature sensor failure and in the event of such a failure defrosting the expansion coil at timed periods of compressor run time if the expansion coil is below the enable temperature for said timed periods.

Claim 13

The method of Claim 5 wherein the expansion coil temperature used in the comparing steps is determined by averaging a number of successive sensed expansion coil temperatures.

Claim 14

The method of Claim 5 wherein the predetermined compressor lockout period is increased at low temperature.

Claim 15

Heat pump control apparatus for use with a heat pump system having an indoor heat exchanger, outdoor heat exchanger, compressor, and flow control means to direct a flow of refrigerant through said indoor and outdoor heat exchangers, said heat pump control apparatus comprising: first temperature sensor means for monitoring ambient temperature in proximity to an outdoor heat exchanger coil and second temperature sensor means for monitoring outdoor heat exchanger coil temperature; storage means for storing an adjustable enable temperature to adjust defrosting of said system; processor means to compare the temperature of the heat exchange coil with the adjustable enable tempera­ture and to set a status indicator if the heat exchanger coil temperature is less than the enable temperature; and defrost control means to defrost the heat exchange coil; said processor means having timing means to monitor the status indicator and activate the defrost control means after the status indicator has been set for a predetermined compressor run period related to ambient temperature.

Claim 16

Heat pump control apparatus for use with a heat pump system having an indoor heat exchanger, outdoor heat exchanger, compressor, and flow control means to direct a flow of refrigerant through said indoor and outdoor heat exchangers, said heat pump control apparatus comprising: first temperature sensor means for monitoring ambient temperature in proximity to an outdoor heat exchanger coil and second temperature sensor means for monitoring outdoor heat exchanger coil temperature; storage means for storing an adjustable enable temperature to adjust defrosting of said system; processor means to compare the temperature of the heat exchange coil with the adjustable enable tempera­ture and to set a status indicator if the heat exchanger coil temperature is less than the enable temperature; and defrost control means to defrost the heat exchange coil; said processor means having timing means to monitor the status indicator and activate the defrost control means after the status indicator has been set for a predetermined compressor run period related to ambient temperature.

Claim 17

The control apparatus of Claim 11 where the storage means includes means to store one or more para­meters that define a coil frosting function related to ambient temperature and the processor means includes means to compare a difference between ambient temperature and heat exchanger coil temperature with the coil frosting function and to activate the defrost control means sub­sequent to the predetermined compressor run period if said difference exceeds the coil frosting function.

Claim 18

The control apparatus of Claim 11 additionally comprising means to signal said processor means when the heat pump compressor is running to cause said proces­sor means to begin comparing the heat exhange coil tem­perature with the enable temperature.

Claim 19

The control apparatus of Claim 11 wherein the processor means includes averaging means to average a number of successive coil temperature readings and provide an average coil temperature for comparing with the enable temperature.

Claim 20

The control apparatus of Claim 11 wherein said processor means comprises means for sensing a failure in said first temperature sensor means and means for adjusting the predetermined compressor run period to a constant independent of ambient temperature.

Claim 21

The control apparatus of Claim 15 wherein the processor means includes means for sensing a failure in said second temperature sensor and suspending controlled defrosting in the event of such a failure.

Claim 24

The method of Claim 17 wherein the monitoring of compressor run time and temperature difference between the heat exchanger coil and ambient temperature is con­ducted only when the heat exchanger coil temperature drops below an enable temperature.