Heat pump with dehumidification

Abstract

Various embodiments of a heat pump system are disclosed to provide improved and flexible heat pump operation when dehumidification of the conditioned space is required. In one embodiment, a heat pump system includes a heat pump loop comprising a refrigerant circuit that fluidly interconnects (1) a compressor; (2) a source heat exchanger; (3) a source heat exchanger bypass circuit comprising a bypass valve; (4) a space heat exchanger; (5) a reversing valve positioned on the discharge side of the compressor; (6) a reheat circuit comprising a reheat heat exchanger; (7) first and second expansion devices; and (8) first and second expansion device bypass circuits configured to allow refrigerant to bypass the first and second expansion devices, respectively, where the first and second bypass circuits include first and second check valves, respectively; and (9) a 3-way valve configured to selectively direct refrigerant flow to the first expansion device, the reheat circuit, and the second expansion device.

1 . A heat pump system for conditioning air in a space, comprising:
 a heat pump loop comprising a refrigerant circuit that fluidly interconnects:
 a compressor; 
 a source heat exchanger for exchanging heat with a source liquid; 
 a space heat exchanger for cooling or heating the air in the space; 
 a reversing valve configured to alternately direct refrigerant flow from the compressor to one of the source heat exchanger and the space heat exchanger and to alternately return flow from the other of the source heat exchanger and the space heat exchanger to the compressor; 
 a reheat circuit comprising a reheat heat exchanger, an upstream leg, a downstream leg, and a reheat bypass valve joining the upstream leg and the downstream leg, wherein the reheat heat exchanger is configured to reheat the air when the system is in a dehumidification mode and operate as an auxiliary condenser when the system is in a heating mode, wherein the space heat exchanger and the reheat heat exchanger are positioned in an air flow path for conditioning the air in the space; 
 an expansion device positioned downstream of the source heat exchanger and upstream of the space heat exchanger; 
 a 3-way valve positioned between the compressor, the reversing valve, and the reheat heat exchanger and configured to direct refrigerant flow from the compressor and selectively to the reversing valve and to the reheat heat exchanger, wherein the reheat bypass valve is positioned between the 3-way valve and the reversing valve to modulate refrigerant flow through the reheat heat exchanger. 
   
     
     
         2 . The heat pump system of  claim 1 , wherein the compressor is a variable speed compressor. 
     
     
         3 . The heat pump system of  claim 1 , wherein the source heat exchanger is a refrigerant-to-liquid source heat exchanger. 
     
     
         4 . The heat pump system of  claim 1 , wherein the space heat exchanger is a refrigerant-to-air space heat exchanger. 
     
     
         5 . The heat pump system of  claim 1 , wherein the source heat exchanger is operable as either a condenser or an evaporator. 
     
     
         6 . The heat pump system of  claim 5 , wherein the space heat exchanger is operable as either a condenser or an evaporator. 
     
     
         7 . The heat pump system of  claim 1 , wherein the expansion device is a bi-directional expansion device. 
     
     
         8 . The heat pump system of  claim 7 , wherein the bi-directional expansion device is an electronic bi-directional expansion device. 
     
     
         9 . The heat pump system of  claim 1 , wherein the reheat bypass valve is bi-directional. 
     
     
         10 . The heat pump system of  claim 1 , including a variable-capacity liquid pump configured to circulate the source liquid to or from the source heat exchanger. 
     
     
         11 . The heat pump system of  claim 1 , including a variable airflow fan associated with the space heat exchanger. 
     
     
         12 . The heat pump system of  claim 1 , wherein to operate the system in a cooling mode:
 the 3-way valve is configured to inactivate the reheat circuit and direct refrigerant flow from the compressor and to the reversing valve; and   the reversing valve is configured to direct refrigerant flow from the 3-way valve to the source heat exchanger and to return flow from the space heat exchanger to the compressor.   
     
     
         13 . The heat pump system of  claim 12 , wherein the reheat circuit further includes a shutoff leg along the downstream leg to prevent hot gas discharged from the compressor from entering the reheat circuit when the system is operating in the cooling mode. 
     
     
         14 . The heat pump system of  claim 1 , wherein to operate the system in the dehumidification mode:
 the 3-way valve is configured to direct refrigerant flow from the compressor to the reheat circuit and subsequently to the reversing valve; and   the reversing valve is configured to direct refrigerant flow from the reheat circuit to the source heat exchanger and to return flow from the space heat exchanger to the compressor.   
     
     
         15 . The heat pump system of  claim 1 , wherein to operate the system in the heating mode:
 the 3-way valve is configured to direct refrigerant flow from the compressor to the reheat circuit and subsequently to the reversing valve; and   the reversing valve is configured to direct refrigerant flow from the reheat circuit to the space heat exchanger and to return flow from the source heat exchanger to the compressor.   
     
     
         16 . The heat pump system of  claim 1 , further including a controller comprising a processor and memory on which one or more software programs are stored, the controller configured to control operation of the reversing valve, the reheat bypass valve, the 3-way valve, the expansion device, and the compressor. 
     
     
         17 . The heat pump system of  claim 16 , wherein to operate the system in a cooling mode, the controller is configured to:
 control the 3-way valve to inactivate the reheat circuit and to cause refrigerant flow from the compressor and to the reversing valve; and   control the reversing valve to cause refrigerant flow from the 3-way valve to the source heat exchanger and to return flow from the space heat exchanger to the compressor.   
     
     
         18 . The heat pump system of  claim 16 , wherein to operate the system in the dehumidification mode, the controller is configured to:
 control the 3-way valve to cause refrigerant flow from the compressor to the reheat circuit and subsequently to the reversing valve; and   control the reversing valve to cause refrigerant flow from the reheat circuit to the source heat exchanger and to return flow from the space heat exchanger to the compressor.   
     
     
         19 . The heat pump system of  claim 16 , wherein to operate the system in the heating mode, the controller is configured to:
 control the 3-way valve to cause refrigerant flow from the compressor to the reheat circuit and subsequently to the reversing valve; and   control the reversing valve to cause refrigerant flow from the reheat circuit to the space heat exchanger and to return flow from the source heat exchanger to the compressor.   
     
     
         20 . The heat pump system of  claim 16 , wherein the controller is configured to control an opening of the reheat bypass valve to modulate refrigerant flow through the reheat heat exchanger.