Systems and methods for defrosting an outdoor heat exchanger of a heat pump

Abstract

An embodiment of a heat pump for conditioning an interior space includes an outdoor unit including an outdoor heat exchanger to exchange heat between a refrigerant and an outdoor environment and an outdoor expansion device. In addition, the heat pump includes an indoor unit including an indoor heat exchanger to exchange heat between the refrigerant and the interior space and an indoor expansion device to expand the refrigerant flowing into the indoor heat exchanger. Further, the heat pump includes a thermal storage device and a reversing valve that is actuatable between: a first position during the heating mode to direct refrigerant through the indoor heat exchanger, the thermal storage device, the outdoor expansion device, and then the outdoor heat exchanger; and a second position during the defrost mode to direct refrigerant through the outdoor heat exchanger and then the thermal storage device.

What is claimed is: 
     
         1 . A heat pump for conditioning an interior space, the heat pump comprising:
 an outdoor unit comprising:
 an outdoor heat exchanger that is configured to exchange heat between a refrigerant and an outdoor environment; 
 an outdoor expansion device that is configured to expand the refrigerant flowing into the outdoor heat exchanger when the heat pump is operating in a heating mode; 
   an indoor unit comprising:
 an indoor heat exchanger that is configured to exchange heat between the refrigerant and the interior space; and 
 an indoor expansion device that is configured to expand the refrigerant flowing into the indoor heat exchanger when the heat pump is operating in a defrost mode; 
   a thermal storage device in fluid communication between the outdoor expansion device and the indoor expansion device; and   a reversing valve that is actuatable between:
 a first position during the heating mode to direct refrigerant through the indoor heat exchanger, the thermal storage device, the outdoor expansion device, and then the outdoor heat exchanger to heat the interior space and to transfer heat from the refrigerant to the thermal storage device; and 
 a second position during the defrost mode to direct refrigerant through the outdoor heat exchanger and then the thermal storage device to transfer thermal energy to the outdoor heat exchanger from the thermal storage device. 
   
     
     
         2 . The heat pump of  claim 1 , wherein the thermal storage device comprises a phase change material that is configured to at least partially change phase to transfer heat to and from the refrigerant. 
     
     
         3 . The heat pump of  claim 2 , further comprising a bypass line that is configured to bypass refrigerant emitted from the thermal storage device around the indoor expansion device and the indoor heat exchanger to the reversing valve when the reversing valve is in the second position. 
     
     
         4 . The heat pump of  claim 3 , further comprising a defrost expansion device positioned in the outdoor unit, downstream of the outdoor expansion device, wherein the defrost expansion device is configured to expand the refrigerant flowing into the thermal storage device when the reversing valve is in the second position. 
     
     
         5 . The heat pump of  claim 1 ,
 wherein the indoor unit includes a blower that is configured to generate an airflow that is directed through the indoor heat exchanger and then to the interior space, and   wherein the heat pump further comprises a controller that is communicatively coupled to the blower and that is configured to terminate operation of the blower during the defrost mode.   
     
     
         6 . The heat pump of  claim 5 , further comprising a compressor that is configured to compress the refrigerant, wherein the controller is also communicatively coupled to the compressor and is configured to reduce an operating speed of the compressor during the defrost mode relative to the heating mode. 
     
     
         7 . The heat pump of  claim 1 , wherein the thermal storage device is positioned in the outdoor unit. 
     
     
         8 . The heat pump of  claim 1 , further comprising a second bypass line that bypasses the thermal storage device between the outdoor expansion device and the indoor expansion device. 
     
     
         9 . A method of operating a heat pump to condition an interior space, the heat pump including an outdoor heat exchanger to exchange heat between a refrigerant and an outdoor environment, an outdoor expansion device, an indoor heat exchanger to exchange heat between the refrigerant and the interior space, and an indoor expansion device, wherein the method comprises:
 (a) routing the refrigerant through the indoor heat exchanger, a thermal storage device, the outdoor expansion device, and then an outdoor heat exchanger to heat the interior space via the indoor heat exchanger and to transfer heat from the refrigerant to the thermal storage device, the thermal storage device being in fluid communication between the indoor expansion device and the outdoor expansion device; and   (b) routing the refrigerant through the outdoor heat exchanger and then the thermal storage device to transfer thermal energy to the outdoor heat exchanger from the thermal storage device.   
     
     
         10 . The method of  claim 9 , further comprising:
 (c) at least partially transitioning a phase change material in the thermal storage device from solid state to liquid state during (a); and   (d) at least partially converting the phase change material in the thermal storage device from liquid phase to solid phase during (b).   
     
     
         11 . The method of  claim 10 , further comprising:
 (e) bypassing the indoor heat exchanger after (b) to return the refrigerant to a compressor of the heat pump.   
     
     
         12 . The method of  claim 11 , further comprising:
 (f) expanding the refrigerant between the outdoor heat exchanger and the thermal storage device during (b).   
     
     
         13 . The method of  claim 9 , further comprising:
 (g) operating a blower during (a) to induce an airflow through the indoor heat exchanger; and   (h) terminating operation of the blower during (b).   
     
     
         14 . The method of  claim 13 , further comprising:
 (i) compressing the refrigerant with a compressor during (a) and (b);   (j) operating the compressor at a first operating speed during (a); and   (k) operating the compressor at a second operating speed that is less than the first operating speed during (b).   
     
     
         15 . A heat pump for conditioning an interior space, the heat pump comprising:
 an outdoor unit comprising:
 an outdoor heat exchanger that is configured to exchange heat between a refrigerant and an outdoor environment; 
   an indoor unit comprising:
 an indoor heat exchanger that is configured to exchange heat between the refrigerant and the interior space; 
 an indoor expansion device that is configured to expand the refrigerant; and 
 a thermal storage device that is configured to exchange heat between the refrigerant and a thermal storage medium; and 
   valving that is actuatable to operate the heat pump in:
 a heating mode in which refrigerant is flowed through the indoor heat exchanger and the thermal storage device in parallel and then is flowed to the outdoor unit to heat the interior space via the indoor heat exchanger and to transfer heat from the refrigerant to the thermal storage medium of the thermal storage device; and 
 a defrost mode in which refrigerant is flowed through the outdoor heat exchanger and then is flowed through the thermal storage device in bypass of the indoor heat exchanger to transfer heat from the thermal storage medium of the thermal storage device to the outdoor heat exchanger. 
   
     
     
         16 . The heat pump of  claim 15 , wherein the thermal storage medium is configured to at least partially change state from solid to liquid during the heating mode and is configured to at least partially change state from liquid to solid during the defrost mode. 
     
     
         17 . The heat pump of  claim 16 , wherein the valving is actuatable to flow the refrigerant through an indoor expansion device before flowing the refrigerant through the thermal storage device in the defrost mode. 
     
     
         18 . The heat pump of  claim 17 , wherein the valving is actuatable to return the refrigerant to a compressor after flowing through the thermal storage device in the defrost mode. 
     
     
         19 . The heat pump of  claim 18 ,
 wherein the indoor unit includes a blower that is configured to generate an airflow that is directed through the indoor heat exchanger and then to the interior space, and   wherein the heat pump further comprises a controller that is communicatively coupled to the blower and that is configured to terminate operation of the blower during the defrost mode.   
     
     
         20 . The heat pump of  claim 19 , wherein the controller is also communicatively coupled to the compressor and is configured to reduce an operating speed of the compressor in the defrost mode relative to the heating mode.