Patent Publication Number: US-2021180807-A1

Title: Heat pump with dehumidification

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/213,338, filed Dec. 7, 2018, which claims the benefit of U.S. Provisional Patent Application No. 62,597,719, filed Dec. 12, 2017, all of which are incorporated by reference herein in their entirety. 
    
    
     BACKGROUND 
     The instant disclosure relates generally to heating, ventilation, and air conditioning systems and methods and, more particularly but without limitation, to heat pump systems. 
     SUMMARY 
     Disclosed are various embodiments of heat pump systems and methods of operating the heat pump systems for conditioning air in a space. 
     In one embodiment, a heat pump system for conditioning air in a space includes a heat pump loop comprising a refrigerant circuit that fluidly interconnects: (1) a compressor having a discharge outlet port and an inlet suction port; (2) a source heat exchanger operable as either a condenser or an evaporator; (3) a source heat exchanger bypass circuit comprising a bypass valve to modulate refrigerant flow through the source heat exchanger; (4) a space heat exchanger operable as either an evaporator or a condenser for cooling or heating the air in the space; (5) a reversing valve positioned on the discharge side of the compressor and configured to alternately direct refrigerant flow from the discharge outlet port of 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 suction inlet port of the compressor; (6) a reheat circuit comprising a reheat heat exchanger to reheat the air when the system is in a dehumidification mode, and operable to act as an auxiliary condenser when the system is in a heating mode, where the space heat exchanger and the reheat heat exchanger are positioned in an air flow path for conditioning the air in the space; (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, the first and second bypass circuits comprising first and second check valves, respectively, to control a direction of refrigerant flow in the first and second bypass circuits; 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. 
     The compressor may be a variable capacity compressor. The heat pump system may include a liquid pump associated with the source heat exchanger and the pump may be a variable capacity pump. The heat pump system may include a fan associated with the space heat exchanger and the fan may be a variable airflow fan. The bypass valve may be bi-directional. The first and second expansion devices may be fixed orifice devices, mechanical valves, or electronic valves. The first expansion device may be positioned between the source heat exchanger and the 3-way valve. The second expansion device may be positioned between the reheat circuit and the space heat exchanger. The reheat circuit may include a reheat bypass valve to modulate refrigerant flow through the reheat heat exchanger. 
     The heat pump system may include 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 bypass valve, the 3-way valve, and the first and second expansion devices, the compressor, the liquid pump for circulating water or brine solution through the source heat exchanger, and the fan for flowing air over the space heat exchanger and the reheat heat exchanger. 
     To operate the system in a cooling mode, the controller may be configured to: (a) close the bypass valve to cause refrigerant flow through the source heat exchanger; (b) close the first expansion device to cause refrigerant flow through the first expansion device bypass circuit and the first check valve; (c) control the 3-way valve to inactivate the reheat circuit and to cause refrigerant flow to the second expansion device; (d) control an opening of the second expansion device to cause refrigerant flow through the second expansion device, and thereafter, the space heat exchanger, wherein an orientation of the second check valve prohibits flow of refrigerant through the second expansion device bypass circuit; and (e) control the reversing valve to cause refrigerant flow from the discharge outlet port of the compressor to the source heat exchanger and to return flow from the space heat exchanger to the suction inlet port of the compressor. 
     To operate the system in the dehumidification mode, the controller may be configured to: (a) control an opening of the bypass valve to modulate refrigerant flow through the source heat exchanger and through the source heat exchanger bypass circuit; (b) close the first expansion device to cause refrigerant flow through the first expansion device bypass circuit and the first check valve; (c) control the 3-way valve to cause refrigerant flow from the first expansion device bypass circuit to the reheat circuit, and thereafter, to the second expansion device; (d) control an opening of the second expansion device to cause refrigerant flow through the second expansion device, and thereafter, the space heat exchanger, wherein an orientation of the second check valve prohibits flow of refrigerant through the second expansion device bypass circuit; and (e) control the reversing valve to cause refrigerant flow from the discharge outlet port of the compressor to the source heat exchanger and to return flow from the space heat exchanger to the suction inlet port of the compressor. The controller may be configured to control an opening of a reheat bypass valve positioned along the reheat circuit to modulate refrigerant flow through the reheat heat exchanger. 
     To operate the system in the heating mode, the controller may be configured to: (a) control the reversing valve to cause refrigerant flow from the discharge outlet port of the compressor to the space heat exchanger and to return flow from the source heat exchanger to the suction inlet port of the compressor; (b) close the second expansion device to cause refrigerant flow through the second expansion device bypass circuit and the second check valve, and thereafter, the reheat heat exchanger; (c) control the 3-way valve to cause refrigerant flow in the reheat circuit, and thereafter, to the first expansion device; (d) control an opening of the first expansion device to cause refrigerant flow through the first expansion device, wherein an orientation of the first check valve prohibits flow of refrigerant through the first expansion device bypass circuit; and (e) close the bypass valve to cause refrigerant flow through the source heat exchanger. The controller may be configured to control an opening of a reheat bypass valve positioned along the reheat circuit to modulate refrigerant flow through the reheat heat exchanger. 
     In one embodiment, a method of conditioning air in a space is disclosed, comprising the steps of: (1) providing a heat pump loop comprising a refrigerant circuit that fluidly interconnects (a) a compressor having a discharge outlet port and an inlet suction port; (b) a source heat exchanger operable as either a condenser or an evaporator; (c) a source heat exchanger bypass circuit comprising a bypass valve to modulate refrigerant flow through the source heat exchanger; (d) a space heat exchanger operable as either an evaporator or a condenser for cooling or heating the air in the space; (e) a reversing valve positioned on the discharge side of the compressor and configured to alternately direct refrigerant flow from the discharge outlet port of 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 suction inlet port of the compressor; (f) a reheat circuit comprising a reheat heat exchanger to reheat the air when the system is in a dehumidification mode, and operable to act 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; (g) first and second expansion devices; (h) first and second expansion device bypass circuits configured to allow refrigerant to bypass the first and second expansion devices, respectively, the first and second bypass circuits comprising first and second check valves, respectively, to control a direction of refrigerant flow in the first and second bypass circuits; (i) a 3-way valve configured to selectively direct refrigerant flow to the first expansion device, the reheat circuit, and the second expansion device; and (2) operating a control system configured to operate the heat pump loop in a plurality of modes in response to air conditioning demands in the space, wherein the plurality of modes includes a cooling mode, the heating mode, and the dehumidification mode. 
     In connection with the foregoing method, the compressor may be a variable capacity compressor; the bypass valve may be bi-directional; the heat pump system may include a liquid pump associated with the source heat exchanger and the pump may be a variable capacity pump; the heat pump system may include a fan associated with the space heat exchanger and the fan may be a variable airflow fan; the first and second expansion devices may be fixed orifice devices, mechanical valves, or electronic valves; the first expansion device may be positioned between the source heat exchanger and the 3-way valve; the second expansion device may be positioned between the reheat circuit and the space heat exchanger; the reheat circuit may include a reheat bypass valve to modulate refrigerant flow through the reheat heat exchanger; and the reheat circuit may include a reheat bypass valve to modulate refrigerant flow through the reheat heat exchanger. 
     The control system may include 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 bypass valve, the 3-way valve, and the first and second expansion devices, the compressor, the liquid pump for circulating water or brine solution through the source heat exchanger, and the fan for flowing air over the space heat exchanger and the reheat heat exchanger. 
     Operating the controller in the cooling mode may include the steps of: (i) closing the bypass valve to cause refrigerant flow through the source heat exchanger; (ii) closing the first expansion device to cause refrigerant flow through the first expansion device bypass circuit and the first check valve; (iii) controlling respective openings in the 3-way valve to inactivate the reheat circuit and to cause refrigerant flow to the second expansion device; (iv) controlling an opening of the second expansion device to cause refrigerant flow through the second expansion device, and thereafter, the space heat exchanger, wherein an orientation of the second check valve prohibits flow of refrigerant through the second expansion device bypass circuit; and (v) controlling the reversing valve to cause refrigerant flow from the discharge outlet port of the compressor to the source heat exchanger and to return flow from the space heat exchanger to the suction inlet port of the compressor. 
     Operating the controller in the dehumidification mode may include the steps of: (i) controlling an opening of the bypass valve to modulate refrigerant flow through the source heat exchanger and through the source heat exchanger bypass circuit; (ii) closing the first expansion device to cause refrigerant flow through the first expansion device bypass circuit and the first check valve; (iii) controlling respective openings in the 3-way valve to cause refrigerant flow from the second expansion device bypass circuit to the reheat circuit, and thereafter, to the second expansion device; (iv) controlling an opening of the second expansion device to cause refrigerant flow through the second expansion device, and thereafter, the space heat exchanger, wherein an orientation of the second check valve prohibits flow of refrigerant through the second expansion device bypass circuit; and (v) controlling the reversing valve to cause refrigerant flow from the discharge outlet port of the compressor to the source heat exchanger and to return flow from the space heat exchanger to the suction inlet port of the compressor. The method may include the step of controlling an opening of a reheat bypass valve positioned along the reheat circuit to modulate refrigerant flow through the reheat heat exchanger. 
     Operating the controller in the heating mode may include the steps of: (i) controlling the reversing valve to cause refrigerant flow from the discharge outlet port of the compressor to the space heat exchanger and to return flow from the source heat exchanger to the suction inlet port of the compressor; (ii) closing the second expansion device to cause refrigerant flow through the second expansion device bypass circuit and the second check valve, and thereafter, the reheat heat exchanger; (iii) controlling respective openings in the 3-way valve to cause refrigerant flow in the reheat circuit, and thereafter, to the first expansion device; (iv) controlling an opening of the first expansion device to cause refrigerant flow through the first expansion device, wherein an orientation of the first check valve prohibits flow of refrigerant through the first expansion device bypass circuit; and (v) closing the bypass valve to cause refrigerant flow through the source heat exchanger. The method may include the step of controlling an opening of a reheat bypass valve positioned along the reheat circuit to modulate refrigerant flow through the reheat heat exchanger. 
     In another embodiment, a heat pump system for conditioning air in a space is disclosed, comprising a heat pump loop comprising a refrigerant circuit that fluidly interconnects: (1) a compressor having a discharge outlet port and an inlet suction port; (2) a source heat exchanger operable as either a condenser or an evaporator; (3) a space heat exchanger operable as either an evaporator or a condenser for cooling or heating the air in the space; (4) an expansion device positioned between the source heat exchanger and the space heat exchanger; (5) a reheat circuit comprising a reheat heat exchanger to reheat the air when the system is in a dehumidification mode, and operable to act 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; (6) a reversing valve to alternately direct refrigerant flow 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 suction inlet port of the compressor; and (7) a 3-way valve positioned downstream of the compressor and configured to selectively direct refrigerant flow to the reversing valve and the reheat heat exchanger. 
     The compressor may be a variable capacity compressor. The heat pump system may include a liquid pump associated with the source heat exchanger and the pump may be a variable capacity pump. The heat pump system may include a fan associated with the space heat exchanger and the fan may be a variable airflow fan. The expansion device may be a fixed orifice device, a mechanical valve, or an electronic valve. The reheat circuit may include a reheat bypass valve to modulate refrigerant flow through the reheat heat exchanger. The reheat bypass valve may be bi-directional. The reheat circuit may include a shutoff valve positioned downstream of the reheat heat exchanger and upstream of the reversing valve. 
     The heat pump system may include a controller comprising a processor and memory on which one or more software programs are stored. The controller may be configured to control operation of the reversing valve, the 3-way valve, the shutoff valve, the expansion device, the compressor, the liquid pump for circulating water or brine solution through the source heat exchanger, and the fan for flowing air over the space heat exchanger and the reheat heat exchanger. 
     To operate the system in a cooling mode, the controller may be configured to: (a) control the 3-way valve and the shutoff valve to inactivate the reheat circuit and to cause refrigerant flow from the discharge port of the compressor to the 3-way valve, thereafter the reversing valve, and thereafter the source heat exchanger; (b) control an opening of the expansion device to cause refrigerant flow from the source heat exchanger to the expansion device, and thereafter the space heat exchanger; and (c) 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 suction inlet port of the compressor. 
     To operate the system in the dehumidification mode, the controller may be configured to: (a) control the 3-way valve and the shutoff valve to activate the reheat circuit and to cause refrigerant flow from the discharge port of the compressor to the 3-way valve, thereafter the reheat heat exchanger, thereafter the shutoff valve, thereafter, the reversing valve, and thereafter, the source heat exchanger; (b) control an opening of the expansion device to cause refrigerant flow from the source heat exchanger to the expansion device, and thereafter the space heat exchanger; and (c) 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 suction inlet port of the compressor. The controller may be configured to control an opening of a reheat bypass valve positioned along the reheat circuit to modulate refrigerant flow through the reheat heat exchanger 
     To operate the system in the heating mode, the controller may be configured to: (a) control the 3-way valve and the shutoff valve to activate the reheat circuit and to cause refrigerant flow from the discharge port of the compressor to the 3-way valve, thereafter the reheat heat exchanger, thereafter the shutoff valve, thereafter, the reversing valve, and thereafter, the space heat exchanger; (b) control an opening of the expansion device to cause refrigerant flow from the space heat exchanger to the expansion device, and thereafter the source heat exchanger; and (c) 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 suction inlet port of the compressor. The controller may be configured to control an opening of a reheat bypass valve positioned along the reheat circuit to modulate refrigerant flow through the reheat heat exchanger. 
     In another embodiment, a heat pump system for conditioning air in a space is disclosed comprising a heat pump loop comprising a refrigerant circuit that fluidly interconnects: (1) a compressor having a discharge outlet port and an inlet suction port; (2) a source heat exchanger operable as either a condenser or an evaporator; (3) a source heat exchanger bypass circuit comprising a source heat exchanger bypass valve to modulate refrigerant flow through the source heat exchanger; (4) a space heat exchanger operable as either an evaporator or a condenser for cooling or heating the air in the space; (5) a reversing valve positioned on the discharge side of the compressor and configured to alternately direct refrigerant flow from the discharge outlet port of 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 suction inlet port of the compressor; (6) a reheat heat exchanger to reheat the air when the system is in a dehumidification mode, and operable to act as an auxiliary condenser when the system is in a heating mode and as an auxiliary evaporator when the system is in a cooling 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; (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, the first and second expansion device bypass circuits comprising first and second expansion device bypass valves, respectively, where the first expansion device is positioned between the source heat exchanger and the reheat heat exchanger and the second expansion device is positioned between the reheat heat exchanger and the space heat exchanger. 
     The compressor may be a variable capacity compressor. The heat pump system may include a liquid pump associated with the source heat exchanger and the pump is a variable capacity pump. The heat pump system may include a fan associated with the space heat exchanger and the fan may be a variable airflow fan. The second expansion device bypass valve may be bi-directional. The second expansion device bypass circuit may be positioned between the reheat heat exchanger and the space heat exchanger. The first and second expansion devices may be fixed orifice devices, mechanical valves, or electronic valves. 
     The heat pump system may include a controller comprising a processor and memory on which one or more software programs are stored. The controller may be configured to control operation of the reversing valve, the source heat exchanger bypass valve, the first and second expansion devices, the first and second expansion device bypass valves, the compressor, the liquid pump for circulating water or brine solution through the source heat exchanger, and the fan for flowing air over the space heat exchanger and the reheat heat exchanger. 
     To operate the system in a cooling mode, the controller may be configured to: (a) close the source heat exchanger bypass valve to cause refrigerant flow through the source heat exchanger; (b) close the first expansion device bypass valve to cause refrigerant flow through the first expansion device and then through the reheat heat exchanger; (c) close the second expansion device to cause refrigerant flow through the second expansion device bypass circuit and then through the space heat exchanger; and (d) control the reversing valve to cause refrigerant flow from the discharge outlet port of the compressor to the source heat exchanger and to return flow from the space heat exchanger to the suction inlet port of the compressor. 
     To operate the system in the dehumidification mode, the controller may be configured to: (a) control an opening of the source heat exchanger bypass valve to modulate refrigerant flow through the source heat exchanger and through the source heat exchanger bypass circuit; (b) close the first expansion device to cause refrigerant flow through the first expansion device bypass circuit and then through the reheat heat exchanger; (c) close the second expansion device bypass valve to cause refrigerant flow through the second expansion device; (d) control an opening of the second expansion device to modulate refrigerant flow from the reheat heat exchanger through the second expansion device, and thereafter, the space heat exchanger; and (e) control the reversing valve to cause refrigerant flow from the discharge outlet port of the compressor to the source heat exchanger and to return flow from the space heat exchanger to the suction inlet port of the compressor. 
     To operate the system in the heating mode, the controller may be configured to: (a) close the source heat exchanger bypass valve to cause refrigerant flow through the source heat exchanger; (b) close the first expansion device bypass valve to cause refrigerant flow through the first expansion device and then through the source heat exchanger; (c) close the second expansion device to cause refrigerant flow through the second expansion device bypass circuit and then through the reheat heat exchanger; and (d) control the reversing valve to cause refrigerant flow from the discharge outlet port of the compressor to the space heat exchanger and to return flow from the source heat exchanger to the suction inlet port of the compressor. The controller may be also configured to control an opening of the second expansion device bypass valve to modulate flow through the space heat exchanger and the reheat heat exchanger. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic showing an embodiment of a heat pump system of the instant disclosure in a cooling mode. 
         FIG. 2  is a schematic showing the embodiment of  FIG. 1  in a dehumidification mode. 
         FIG. 3  is a schematic showing the embodiment of  FIG. 1  in a heating mode. 
         FIG. 4  is a schematic showing another embodiment of a heat pump system of the instant disclosure in a cooling mode. 
         FIG. 5  is a schematic showing the embodiment of  FIG. 4  in a dehumidification mode. 
         FIG. 6  is a schematic showing the embodiment of  FIG. 4  in a heating mode. 
         FIG. 7  is a schematic showing another embodiment of a heat pump system of the instant disclosure in a cooling mode. 
         FIG. 8  is a schematic showing the embodiment of  FIG. 7  in a dehumidification mode. 
         FIG. 9  is a schematic showing the embodiment of  FIG. 7  in a heating mode. 
         FIG. 10  is a schematic showing a controller and exemplary heat pump components that may be controlled by the controller. 
     
    
    
     DETAILED DESCRIPTION 
     Although the figures and the instant disclosure describe one or more embodiments of a heat pump system, one of ordinary skill in the art would appreciate that the teachings of the instant disclosure would not be limited to these embodiments. It should be appreciated that any of the features of an embodiment discussed with reference to the figures herein may be combined with or substituted for features discussed in connection with other embodiments in this disclosure. 
     The instant disclosure provides improved and flexible heat pump operation when dehumidification of a conditioned space is required. In one embodiment of a vapor compression circuit, a reheat heat exchanger is positioned upstream of a 3-way valve with respect to the refrigerant flow. In another embodiment, a reheat heat exchanger is positioned downstream of the 3-way valve but upstream of a source heat exchanger with respect to the refrigerant flow. In yet another embodiment, a reheat heat exchanger is positioned downstream of a source heat exchanger with respect to the refrigerant flow. 
     All three of the foregoing embodiments provide operational flexibility via a modulating, pulse width modulating (PWM) or rapid cycle solenoid valve diverting at least a portion of the refrigerant around the reheat heat exchanger in the dehumidification mode of operation. Alternatively or additionally, an ON-OFF 3-way valve and a bypass valve may be replaced by the modulating, PWM or rapid cycle solenoid 3-way valve. A controller comprising a processor coupled to memory on which one or more software algorithms are stored may process and issue commands to open, partially open, or close any of the valves disclosed herein. Open or closed feedback loops may be employed to determine current and desired valve positions. 
     All three of the embodiments may employ variable speed or multi-speed refrigerant and/or source fluid pumps, fan and/or blower motor, and compressor to control dehumidification capability and head pressure. The controller may be configured to operate any or all of these devices to provide the desired system performance. In the heating mode, the reheat heat exchanger may act as an auxiliary condenser or evaporator to enhance system performance and avoid the “cold blow” effect. Any of the expansion valves disclosed herein may be any type of expansion device, including a thermostatic expansion valve, and can be electronic, mechanical, electromechanical, or fixed orifice type. The charge migration or condensation of refrigerant in the reheat heat exchanger can be controlled by a charge compensator or a shutoff valve. The potential oil accumulation in the reheat heat exchanger when the reheat refrigeration circuit is inactive can be controlled by periodically activating the reheat circuit for a short period of time. In at least one of the embodiments described herein, a portion of the existing space heat exchanger may act as a reheat heat exchanger during the dehumidification mode of operation. All of the embodiments described herein provide improved comfort level, system performance, and system reliability. 
     Turning now to the drawings and to  FIGS. 1-9  in particular, there are shown various embodiments of a heat pump system configured to provide dehumidification of a conditioned space when required. For example,  FIGS. 1-3  show heat pump system  10  configured in a cooling mode, a dehumidification mode, and a heating mode, respectively.  FIGS. 4-6  show heat pump system  60  configured in a cooling mode, a dehumidification mode, and a heating mode, respectively.  FIGS. 7-9  show heat pump system  110  configured in a cooling mode, a dehumidification mode, and a heating mode, respectively. Systems  10 , 60 , 110  are designed for conditioning the air in a predetermined space. As used herein, “air conditioning” and related terms related to heating, cooling, or dehumidifying the air, and to any combination of these. 
     In the embodiment of  FIGS. 1-3 , heat pump system  10  includes a heat pump loop  16  comprising a reheat circuit  18 . Heat pump system  10  includes compressor  20 ; reversing valve  22 ; source heat exchanger  24 ; source heat exchanger bypass circuit  26  comprising bypass valve  28 ; expansion valve  30 ; expansion valve bypass circuit  32  comprising check valve  34 ; three-way valve  36 ; reheat circuit  18  comprising reheat bypass valve  38  and reheat heat exchanger  40 ; expansion valve  42 ; expansion valve bypass circuit  44  comprising check valve  46 ; and space heat exchanger  48 . Compressor  20  includes a suction inlet port  50  and a discharge outlet port  52 . The heat pump system  10  may include a fan  12  associated with the space heat exchanger  48  and the fan  12  may be a variable airflow fan. 
     Referring to  FIG. 1 , heat pump system  10  is shown in a cooling mode with reheat circuit  18  inactive. Compressed gaseous refrigerant exiting the compressor  20  at discharge outlet port  52  is conveyed to the reversing valve  22  where the refrigerant is then conveyed to the source heat exchanger  24  acting as a condenser. In cooling mode, bypass valve  28  is closed, which causes source heat exchanger bypass circuit  26  to be inactive. The capacity (e.g. speed) of the liquid pump  14  circulating the fluid through heat exchanger  24  may be adjusted to control heat rejected by the heat exchanger  24  and system discharge pressure. Likewise, with expansion valve  30  being closed, and with the orientation of check valve  34  permitting flow therethrough, the expansion valve bypass circuit  32  is configured to be active. Thus, all of the refrigerant from the compressor discharge conduit passes through the source heat exchanger  24  and the expansion valve bypass circuit  32 , after which the refrigerant is conveyed to three-way valve  36 . 
     Three-way valve  36  is configured to direct the refrigerant to expansion valve  42  rather than entering the reheat circuit  18 . With expansion valve bypass circuit  44  inactive due to the opposite flow orientation of check valve  46 , the refrigerant is directed to the expansion valve  42  where the refrigerant is metered, expanded and cooled before entering the space heat exchanger  48 . Refrigerant conveyed in the coil of the space heat exchanger  48 , which acts as an evaporator when system  10  is in cooling mode, absorbs heat from air flowing over the coil of the space heat exchanger  48  thereby cooling the air for conditioning a space. Refrigerant exiting the space heat exchanger  48  is then conveyed to the reversing valve  22 , which directs the refrigerant back to the compressor  20  to start the cycle over again. It should be noted that the coil in the reheat heat exchanger  40  may be filled with subcooled liquid refrigerant. 
     Referring to  FIG. 2 , system  10  is shown configured in a dehumidification mode. In this mode, the flow of refrigerant through heat pump loop  16  is the same as shown in  FIG. 1  except the source heat exchanger bypass circuit  26  may be active (i.e., bypass valve  28  may be fully opened, partially opened, or fully closed to obtain optimum refrigerant conditions at the inlet of the reheat heat exchanger  40 ), the expansion valve bypass circuit  32  is active (i.e., expansion valve  30  is closed), and the expansion valve bypass circuit  44  is inactive (due to the opposite flow orientation of check valve  46 ). In addition, rather than three-way valve  36  directing refrigerant to expansion valve  42 , three-way valve  36  instead directs the refrigerant to reheat heat exchanger  40 , which is positioned downstream of the space heat exchanger  48  relative to air flowing over the respective coils. Thus, air flowing over the coil of the space heat exchanger  48  is cooled and dehumidified by the space heat exchanger  48  and then the air is directed to flow over the reheat heat exchanger  40  to add heat to the air to avoid overcooling the air. Bypass valve  28  may be automatically controlled to be fully opened, partially opened, or fully closed as needed to control the refrigerant inlet condition(s) to reheat heat exchanger  40 . Bypass valve  28  may be automatically cycled open and closed and/or controlled on and off with a PWM signal to modulate the amount of refrigerant flowing through the source heat exchanger  24 . The capacity (e.g. speed) of the liquid pump  14  circulating the fluid through heat exchanger  24  may be adjusted to control heat rejected by the heat exchanger  24  and system discharge pressure. 
     If the three-way valve  36  is configured to be adjustable, the three-way valve  36  may control the refrigerant mass flow rate flowing through reheat circuit  18  to provide adjustable outlet air temperature exiting from the coils of the space heat exchanger  48  and reheat heat exchanger  40  for distribution to the air-conditioned space. If the three-way valve  36  is not adjustable, reheat bypass valve  38  may be configured to cause some of the refrigerant flow to bypass the reheat heat exchanger  40  to reduce the mass flow rate entering the reheat heat exchanger  40 . The reheat bypass valve  38  may be automatically cycled opened and closed and/or controlled on and off with a PWM signal to modulate the amount of refrigerant flowing through the reheat heat exchanger  40 . 
     Referring to  FIG. 3 , system  10  is shown configured in a heating mode with added capacity for heating the conditioned air using the reheat heat exchanger  40 . In this mode, hot gaseous refrigerant exiting the compressor  20  at discharge outlet port  52  is directed to reversing valve  22 , which directs the refrigerant to the space heat exchanger  48 . Space heat exchanger  48  acts as a condenser when system  10  is in heating mode. With a closed expansion valve  42 , refrigerant exiting the space heat exchanger  48  is directed to the active expansion valve bypass circuit  44  and through check valve  46 . The refrigerant is then conveyed to the reheat heat exchanger  40 . To heat a space, air flowing over space heat exchanger  48  picks up heat from the space heat exchanger  48  before the air is directed to flow over the reheat heat exchanger  40  to pick up additional heat. Reheat heat exchanger  40  therefore acts as an auxiliary condenser in this heating mode. 
     Refrigerant exiting the reheat heat exchanger is then directed to three-way valve  36 , which directs the flow to expansion valve  30  while expansion valve bypass circuit  32  is inactive. The expansion valve  30  expands the refrigerant thereby cooling the refrigerant before entering the source heat exchanger  24  while source heat exchanger bypass circuit  26  is inactive (i.e., bypass valve  28  is closed). The source heat exchanger  24  acts as an evaporator to fully evaporate the refrigerant before the refrigerant is directed to the reversing valve  22 , which directs the refrigerant to the suction inlet port  50  of the compressor  20  to continue the cycle. With the reheat heat exchanger  40  acting as an auxiliary condenser, system  10  may improve the subcooling and consequently the capacity and efficiency of system  10  while in this heating mode, as well as increase supply air temperature preventing the “cold blow” effect. In cold climates, reheat heat exchanger  40  provides additional heating capacity to avoid auxiliary (e.g. electric) heaters. 
     Referring to  FIGS. 4-6 , there is shown another embodiment of a heat pump system configured in a cooling mode, a dehumidification mode, and a heating mode, respectively. Heat pump system  60  includes heat pump loop  66  comprising reheat circuit  68 . Heat pump loop  66  includes compressor  70 , reversing valve  72 , source heat exchanger  74 , expansion valve  92 , space heat exchanger  98 , and three-way valve  86 . Reheat circuit  68  of heat pump loop  66  includes reheat heat exchanger  90 , reheat bypass valve  88 , and shutoff valve  96 . Compressor  70  includes suction inlet port  100  and discharge outlet port  102 . Three-way valve  86  is positioned downstream of the compressor discharge outlet port  102  of compressor  70  and upstream of reversing valve  72 . The heat pump system  60  may include a fan  62  associated with the space heat exchanger  98  and the fan  62  may be a variable airflow fan. 
     Unlike heat pump system  10 , heat pump system  60  does not require expansion valve bypass circuits. And although the reheat heat exchanger is positioned downstream of the space heat exchanger in terms of the direction of air flowing over the coils of these two heat exchangers, the refrigerant connection conduits for the reheat circuit  68  connect with the heat pump loop  66  downstream of the compressor  70  and upstream of the reversing valve  72 . Similarly to the previous embodiment, the bypass around source heat exchanger  74  may be applied, but not shown for simplicity. 
     Referring  FIG. 4 , heat pump system  60  is shown configured in a cooling mode with the reheat circuit  68  inactive. Hot gaseous refrigerant exiting the discharge outlet port  102  of compressor  70  is directed by a conduit to the three-way valve  86 , which directs the gas to reversing valve  72 , which in turn directs the gas to source heat exchanger  74 . Refrigerant exiting source heat exchanger  74  acting as a condenser is directed to expansion valve  92 . Refrigerant exiting the expansion valve  92  is directed to space heat exchanger  98 . Refrigerant exiting space heat exchanger  98  acting as an evaporator is directed to the reversing valve  72 , which in turn directs the gas back to the suction inlet port  100  of compressor  70 . Shutoff valve  96  in combination with proper control of three-way valve  86  insures that hot gas from the compressor  70  does not enter reheat circuit  68  when heat pump system  10  is operating in cooling mode. Refrigerant conveyed in the coil of the space heat exchanger  98  absorbs heat from air flowing over the space heat exchanger  98  thereby cooling the air for conditioning a space. 
     Referring to  FIG. 5 , heat pump system  60  is shown configured in a dehumidification mode. In this mode, reheat circuit  68  is active. Hot gaseous refrigerant exiting compressor  70  at discharge outlet port  102  is directed to three-way valve  86 , which in turn directs the refrigerant to reheat heat exchanger  90  positioned downstream of space heat exchanger  98  such that air cooled after flowing across the space heat exchanger  98  is then caused to flow over the reheat heat exchanger  90  to pick up an heat, thereby preventing overcooling the air distributed to the air-conditioned space. 
     Refrigerant exiting reheat heat exchanger  90  is directed to open shutoff valve  96 . The refrigerant is then directed to reversing valve  72 , which directs the refrigerant to source heat exchanger  74  to exchange heat with the source fluid. The refrigerant is then conveyed to the expansion valve  92 , which expands and therefore causes the pressure and temperature reduction of the refrigerant, before refrigerant enters space heat exchanger  98 . Refrigerant exiting the space heat exchanger  98  acting as an evaporator is then directed to the reversing valve  72 , which in turn directs the refrigerant back to the suction inlet port  100  of compressor  70 . Thus, air flowing over the space heat exchanger  98  is cooled by the space heat exchanger  98  and then the air is directed to flow over the reheat heat exchanger  98  to add heat to the air to prevent overcooling the air. 
     The three-way valve  86  may be adjustable as described above to adjust the refrigerant mass flow rate provided to the reheat circuit  68  for optimum supply air temperature that is distributed to the air-conditioned space. Alternatively, as described above, the three-way valve may not be adjustable. In that case, reheat bypass valve  88  may be configured as a simple on-off valve. As described above, reheat bypass valve  88 , may be controlled via a PWM algorithm that controls the mass flow rate of refrigerant entering reheat heat exchanger  90  by cycling reheat bypass valve  88  open and closed according to the algorithm. The capacity (e.g. speed) of the liquid pump  64  circulating the fluid through heat exchanger  74  may be adjusted to control heat rejected by the heat exchanger  74  and system discharge pressure. 
     Referring to  FIG. 6 , heat pump system  60  is shown configured in a heating mode. In this mode, reheat circuit  68  is active (i.e., reheat bypass valve  88  is closed) and the reheat heat exchanger  90  acts as an additional condenser to supplement the air heating capacity of space heat exchanger  98  to heat air flowing across the space heat exchanger  98  and reheat heat exchanger  90 . 
     In this mode, hot gaseous refrigerant exiting the discharge outlet port  102  of compressor  70  is directed to three-way valve  86 , which in turn directs the refrigerant to reheat heat exchanger  90 . The refrigerant is then directed to open shutoff valve  96 , after which the refrigerant is directed to reversing valve  72 . The refrigerant is then conveyed to space heat exchanger  98 , after which the refrigerant is conveyed to the expansion valve  92 . The expanded refrigerant of reduced pressure and temperature after passing through the expansion valve  92  is then conveyed to the source heat exchanger  74 , which acts as an evaporator. The refrigerant discharged from the source heat exchanger  74  is conveyed to the reversing valve  72 , which directs the refrigerant back to the suction inlet port  100  of compressor  70 . 
     To heat a space, air flowing over the space heat exchanger  98  picks up heat from the space heat exchanger  98  before the air is directed to flow over the reheat heat exchanger  90  to pick up additional heat. Reheat heat exchanger  90  therefore acts as an auxiliary condenser in this heating mode. The extra condenser provided by reheat heat exchanger  90  helps to increase the heat transfer to the air, increase the subcooling of the refrigerant, and increase the capacity and efficiency of heat pump system  60 , as well as increase temperature of the air supplied to a conditioned space therefore avoiding a “cold blow” effect. The capacity (e.g. speed) of the liquid pump  64  circulating the fluid through heat exchanger  74  may be adjusted to control heat rejected by the heat exchanger  74  and system discharge pressure. 
       FIG. 7-9  shows another embodiment of a heat pump system. As shown in the figures, heat pump system  110  includes compressor  120  comprising suction inlet port  150  and discharge outlet port  152 , reversing valve  122 , source heat exchanger  124 , source heat exchanger bypass circuit  126  comprising bypass valve  128 , expansion valve  130 , expansion valve bypass circuit  132  comprising bypass valve  134 , reheat heat exchanger  140 , expansion valve  142 , expansion valve bypass circuit  144  comprising bypass valve  146 , and space heat exchanger  148 . The heat pump system  110  may include a fan  112  associated with the space heat exchanger  148  and the fan  112  may be a variable airflow fan. 
     Heat pump system  110  is schematically similar to heat pump system  10 , but instead of employing two different air coils, a larger space coil is employed. In this embodiment, expansion valve bypass circuit  144  and expansion valve  142  of heat pump system  110  are positioned between reheat heat exchanger  140  and space heat exchanger  148  and therefore divide the larger space coil into two parts. One part may be used as a reheat coil and the other part may be used as a main space heating/cooling coil. 
     Referring to  FIG. 7 , heat pump system  110  is shown in a cooling mode. Hot gaseous refrigerant exiting the discharge outlet port  152  of compressor  120  is directed by a conduit to the reversing valve  122 , which in turn directs the refrigerant gas to source heat exchanger  124 . Refrigerant exiting source heat exchanger  124  acting as a condenser is directed to expansion valve  130 , which is configured to meter, expand and cool the refrigerant before the refrigerant enters reheat heat exchanger  140 , which is the first stage of the two-stage space heat exchanger  149 . Upon exiting the reheat heat exchanger  140  acting as an evaporator, the refrigerant bypasses a closed expansion valve  142 . The refrigerant instead is conveyed through expansion valve bypass circuit  144  and bypass valve  146  to then flow through the space heat exchanger  148 , which is the second stage of the two-stage space heat exchanger  149 . In cooling mode, space heat exchanger  148  acts as an extension of the evaporator provided by reheat heat exchanger  140  to increase the size of the evaporator. Thus, refrigerant conveyed in the space heat exchanger  148  and the reheat heat exchanger  140  absorbs heat from air flowing over these coils to cool the air for conditioning a space. 
     For control purposes, bypass valve  146  may be automatically cycled open and closed and/or controlled on and off with a PWM signal. Refrigerant exiting the space heat exchanger  148  is conveyed to reversing valve  122 , which directs the refrigerant to suction inlet port  150  of compressor  120 . 
     Referring to  FIG. 8 , heat pump system  110  is shown in a dehumidification mode. In this mode, hot gaseous refrigerant exiting the discharge outlet port  152  of compressor  120  is directed to the reversing valve  122 , which in turn directs the refrigerant to source heat exchanger  124  acting as a condenser. As shown in the figure, source heat exchanger bypass circuit  126  is active via bypass valve  128 , and the expansion valve bypass circuit  132  is active via bypass valve  134 . Consequently, some, none, or all of the heated refrigerant may be permitted to flow through the source heat exchanger  124 , and some, none, or all of the refrigerant may be permitted to flow through the source heat exchanger bypass circuit  126  to obtain optimum refrigerant conditions at the inlet of reheat heat exchanger  140 . Bypass valve  128  controls the amount of refrigerant mass flow that traverses through the source heat exchanger bypass circuit  126 , which affects the amount of refrigerant mass flow traversing through the source heat exchanger  124 . Bypass valve  128  may be automatically cycled open and closed and/or controlled on and off with a PWM signal to modulate the amount of refrigerant flowing through the source heat exchanger bypass circuit  126 . The capacity (e.g. speed) of the liquid pump  114  circulating the fluid through heat exchanger  124  may be adjusted to control heat rejected by the heat exchanger  124  and system discharge pressure. 
     Refrigerant exiting the source heat exchanger  124  acting as a condenser and source heat exchanger bypass circuit  126  are combined and then directed to expansion valve bypass circuit  132 . In dehumidification mode, none of the refrigerant enters the expansion valve  130 . 
     Refrigerant exiting the expansion bypass circuit  132  is directed to reheat heat exchanger  140 . Upon exiting reheat heat exchanger  140  and with bypass valve  146  being closed, subcooled refrigerant is directed to expansion valve  142 , which meters, expands and cools the refrigerant before the refrigerant enters space heat exchanger  148  acting as an evaporator. Upon leaving space heat exchanger  148 , the refrigerant is directed to the reversing valve  122 , which then directs the flow back to the suction inlet port  150  of compressor  120 . Thus, air flowing over the space heat exchanger  148  is cooled by the space heat exchanger  148  and then the air is directed to flow over the reheat heat exchanger  140  to add heat to prevent overcooling the air. 
     Referring to  FIG. 9 , heat pump system  110  is configured in a heating mode. For example, hot gaseous refrigerant leaving the discharge outlet port  152  of compressor  120  is directed to reversing valve  122 , which directs the refrigerant to space heat exchanger  148  acting as a condenser. Refrigerant exiting space heat exchanger  148  is directed to bypass valve  146 , which in turn directs the refrigerant to reheat heat exchanger  140 . The expansion valve  142  is not needed for heating mode. To heat a space, air flowing over the coil of space heat exchanger  148  picks up heat from the space heat exchanger  148  before the air is directed to flow over the reheat heat exchanger  140  to pick up additional heat. Reheat heat exchanger  140  therefore acts as an auxiliary condenser in this heating mode. 
     Refrigerant leaving reheat heat exchanger  140  is directed to expansion valve  130 . Expansion valve bypass circuit  132  and source heat exchanger bypass circuit  126  are not active (i.e., bypass valves  128 , 134  are closed) when heat pump system  110  is configured in the heating mode. Refrigerant leaving the expansion valve  130  is directed to source heat exchanger  124  acting as an evaporator to exchange heat with the source fluid. Refrigerant leaving source heat exchanger  124  is then directed the reversing valve  122 , which directs the refrigerant back to the suction inlet port  150  of compressor  120 . The extra condenser provided by reheat heat exchanger  140  helps to increase the heat transfer to the air, increase the subcooling of the refrigerant, and increase the capacity and efficiency of heat pump system  110 , as well as increase temperature of the air supplied to a conditioned space therefore avoiding a “cold blow” effect. The capacity (e.g. speed) of the liquid pump  114  circulating the fluid through heat exchanger  124  may be adjusted to control heat rejected by the heat exchanger  124  and system discharge pressure. 
     Heat pump loops  16 , 66 , 116  include a conduit through which refrigerant flows and which fluidly connects the components of heat pump systems  10 , 60 , 110  to one another. Compressors  20 , 70 , 120  may each be a variable capacity compressor, such as a variable speed compressor, a compressor with an integral pulse-width modulation option, or a compressor incorporating various unloading options. These types of compressors allow for better control of the operating conditions and management of the thermal load on the heat pump loops  16 , 66 , 116 . 
     Reversing valves  22 , 72 , 122  are positioned along the conduit on the discharge side of compressors  20 , 70 , 120  and are configured to selectively operate the heat pump loops  16 , 66 , 116  in a cooling mode, a dehumidification mode, and a heating mode by controlling the direction of refrigerant flowing in the heat pump loops  16 , 66 , 116 . 
     Source heat exchangers  24 , 74 , 124  may each be a refrigerant-to-water, refrigerant-to-brine, or refrigerant-to-air heat exchanger and is not limited to any particular heat exchanger type or configuration. Source heat exchangers  24 , 74 , 124  are fluidly connected to a source  15 , 65 , 115 , and the fluid, usually but not necessarily water, is circulated by pumps  14 , 64 , 114 . Pumps  14 , 64 , 114  may be a variable capacity pump (e.g. a variable speed pump, a pump controlled by PWM signal, a cycling ON/OFF pump, a pump with a bypass circuit or other means of unloading) for a more efficient operation and better system control. Similarly, space heat exchangers  48 , 98 , 148  are not limited to any particular heat exchanger type or configuration. 
     Expansion valves  30 , 42 , 92 , 130 , 142  may each be an electronic expansion valve, a mechanical expansion valve, a fixed-orifice/capillary tube/accurator, or any combination of the these. These valves may have bi-directional functionality or may be replaced by a pair of uni-directional expansion devices coupled with the associated bypass check valves to provide refrigerant rerouting when the flow changes direction throughout the refrigerant cycle between cooling and heating modes of operation. 
     Valves  28 , 38 , 88 , 96 , 128 , 146  may each be electronically controllable, mechanically and/or electromechanically actuated valves, and may have bi-directional flow functionality. 
     Referring to  FIG. 10 , heat pump systems  10 , 60 , 110  may include controller  78  comprising processor  80  and memory  82  on which one or more software programs are stored. The controller  78  may be configured to control operation of the check valves  34 , 46 , the shut off valve  96 , the reversing valves  22 , 72 , 122 , the bypass valves  28 , 38 , 88 , 128 , 134 , 146 , the 3-way valves  36 , 86 , the first and second expansion devices  30 , 42 , 92 , 130 , 142 , the compressors  20 , 70 , 120 , the liquid pumps  14 , 64 , 114  for circulating water or brine solution through the source heat exchangers  24 , 74 , 124 , the fans  12 , 62 , 112  for flowing air over the space heat exchangers  48 , 98 , 148 , and the reheat heat exchangers  40 , 90 , 140 . 
     While specific embodiments have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the disclosure herein is meant to be illustrative only and not limiting as to its scope and should be given the full breadth of the appended claims and any equivalents thereof.