Methods and apparatuses for operating heat pumps in hot water systems

Abstract

A method for operating a heat pump ( 100 ) in low ambient air temperatures comprises periodically or temporarily halting flow of refrigerant through an evaporator ( 170 ) of the heat pump ( 100 ) and providing forced airflow across the evaporator ( 170 ) while the refrigerant flow is halted. The method enables operation of the heat pump ( 100 ) at low ambient temperatures and provides a means for de-icing the evaporator ( 170 ) when operating at low ambient temperatures. The method is particularly applicable to heat pumps having an evaporator located outdoors, such as domestic and industrial water heating systems.

1 . A method for operating a heat pump in low ambient air temperatures, said method comprising the steps of:
 periodically halting flow of refrigerant through an evaporator of said heat pump; and   providing forced airflow across said evaporator while said refrigerant flow is halted.   
     
     
         2 . The method of  claim 1 , wherein said step of periodically halting flow of refrigerant through an evaporator comprises the step of repeatedly turning a compressor of said heat pump off for a first predetermined time period and on for a second predetermined time period, said second predetermined time period greater than said first predetermined time period. 
     
     
         3 . The method of  claim 1 , wherein said method is performed when the ambient air temperature falls below a predetermined temperature value. 
     
     
         4 . The method of  claim 1 , wherein said heat pump in used to heat water in a hot water system and a condenser of said heat pump is positioned in a heat exchanging relationship with a body of water in said hot water system. 
     
     
         5 . An apparatus comprising:
 a heat pump circuit comprising a compressor, a condenser, a pressure-lowering device, and an evaporator, said heat pump circuit adapted to hold a charge of refrigerant;   a fan adapted to generate airflow across said evaporator;   a temperature sensor adapted to measure ambient air temperature; and   an electronic controller coupled to said compressor, said fan and said temperature sensor, said electronic controller adapted to:   obtain ambient air temperature values from said temperature sensor;   repeatedly turn said compressor on and off while said ambient air temperature values are lower than a first predetermined temperature value; and   operate said fan to provide forced airflow across said evaporator while said compressor is turned off.   
     
     
         6 . The apparatus of  claim 5 , wherein said electronic controller is adapted to cyclically operate said compressor by repeatedly turning said compressor off for a first predetermined time duration and on for a second predetermined time duration, said second predetermined time duration greater than said first predetermined time duration. 
     
     
         7 . The apparatus of  claim 5 , wherein said electronic controller is further adapted to turn said compressor off an said fan off when said ambient air temperature values are less than a second predetermined temperature value. 
     
     
         8 . The apparatus of  claim 5 , wherein said electronic controller is further adapted to operate said fan and said compressor continuously while said ambient air temperature values are greater than or equal to said first predetermined temperature value. 
     
     
         9 . The apparatus of  claim 5 , wherein said pressure-lowering device comprises a thermostatic expansion valve (TX valve). 
     
     
         10 . A hot water system, comprising:
 a water tank for storing water;   a heat pump circuit comprising a compressor, a pressure-lowering device, an evaporator, and a condenser in a heat exchanging relationship with said water in said water tank;   a fan adapted to generate airflow across said evaporator;   a first temperature sensor adapted to determine ambient air temperature; and   an electronic controller coupled to said compressor, said fan and said first temperature sensor, said electronic controller adapted to:   obtain ambient air temperature values from said temperature sensor;   repeatedly turn said compressor on and off while said ambient air temperature values are lower than a first predetermined temperature value; and   operate said fan to provide forced airflow across said evaporator while said compressor is turned off.   
     
     
         11 . The hot water system of  claim 10 , further comprising a second temperature sensor coupled to said electronic controller and adapted to determine temperature of water in said water tank, and wherein said electronic controller is further adapted to:
 obtain water temperature values from said second temperature sensor; and   turn off said compressor and said fan when said water temperature exceeds a third predetermined temperature.   
     
     
         12 . The hot water system of  claim 10 , wherein said electronic controller is adapted to cyclically operate aid compressor by repeatedly turning said compressor off for a first predetermined time duration and on for a second predetermined time duration, said second predetermined time duration greater than said first predetermined time duration. 
     
     
         13 . The hot water system of  claim 10 , wherein aid electronic controller is further adapted to turn said compressor off and said fan off when said ambient air temperature values are less than a second predetermined temperature value. 
     
     
         14 . The hot water system of  claim 10 , wherein said electronic controller is further adapted to operate said fan and said compressor continuously while said ambient air temperature values are greater than or equal to said first predetermined temperature value. 
     
     
         15 . The hot water system of  claim 10 , wherein said pressure-lowering device comprises a thermostatic expansion valve (TX valve). 
     
     
         16 . A method for operating a heat pump in low ambient air temperatures, said method comprising the steps of:
 temporarily halting flow of refrigerant through an evaporator of said heat pump; and providing forced airflow across said evaporator while said refrigerant flow is halted.   
     
     
         17 . The method of  claim 1 , wherein the step of providing forced airflow comprises forcing airflow onto a side of said evaporator that is less susceptible to icing. 
     
     
         18 . The apparatus of  claim 5 , wherein said electronic controller is adapted to control said fan to blow air onto a side of said evaporator that is less susceptible to icing. 
     
     
         19 . The hot water system of  claim 10 , wherein said electronic controller is adapted to control said fan to blow air onto a side of said evaporator that is less susceptible to icing. 
     
     
         20 . A method for operating a heat pump in a hot water system, said method comprising the steps of:
 providing forced airflow across an evaporator of said heat pump while said heat pump is operational to heat water in a tank of said hot water system; and   temporarily halting flow of refrigerant through said evaporator and reversing the direction of said forced airflow across said evaporator while ambient air temperature is lower than a predetermined temperature value.   
     
     
         21 . The method of  claim 20 , wherein said step of temporarily halting flow of refrigerant through aid evaporator and reversing the direction of said forced airflow across said evaporator is performed periodically while said heat pump is operational to heat water in said tank of said hot water system and ambient air temperature is lower than a predetermined temperature value. 
     
     
         22 . The method of  claim 21 , wherein said flow of refrigerant through said evaporator is halted and the direction of said fan is reversed for a period of approximately 30 minutes every 2 hours. 
     
     
         23 . The method of  claim 20 , wherein the direction of said fan is reversed to provide forced airflow onto a side of said evaporator that is less susceptible to icing. 
     
     
         24 . A hot water system, comprising:
 a water tank for storing water;   a heat pump circuit comprising a compressor, a pressure-lowering device, and evaporator, and a condenser in a heat exchanging relationship with said water in aid water tank;   a fan adapted to provide forced airflow across said evaporator;   a temperature sensor adapted to determine ambient air temperature; and   an electronic controller coupled to said compressor, aid fan and said temperature sensor, said electronic controller adapted to:   obtain ambient air temperature values from said temperature sensor;   operate said fan to provide forced airflow across said evaporator while said heat pump is operational to hot water in said water tank; and   temporarily halt flow of refrigerant through said evaporator and reverse the direction of said forced airflow across said evaporator while ambient air temperature is lower than a predetermined temperature value.   
     
     
         25 . The hot water system of  claim 24 , wherein said electronic controller adapted to periodically halt flow of refrigerant through said evaporator and reverse the direction of said forced airflow across said evaporator while said heat pump is operational to heat water in said water tank and ambient air temperature is lower than a predetermined temperature value. 
     
     
         26 . The hot water system of  claim 25 , wherein said flow of refrigerant through said evaporator is halted and the direction of said fan is reversed for a period of approximately 30 minutes every 2 hours. 
     
     
         27 . The hot water system of  claim 24 , wherein the direction of said fan is reversed to provide forced airflow onto a side of said evaporator that is less susceptible to icing.