Two-phase single circuit reheat cycle and method of operation

Abstract

A refrigerant system has a refrigerant circuit comprising a compressor for compressing a refrigerant and delivering it downstream to a condenser. A bypass line is provided around the condenser for selectively allowing at least a portion of refrigerant to bypass the condenser. Valves are provided on a line leading to the condenser and on the bypass line to individually control the flow of refrigerant. An expansion device is located downstream of the condenser, and an evaporator is located downstream of the expansion device. A reheat cycle is incorporated into the system. The reheat cycle includes a valve for selectively delivering at least a portion of refrigerant through a reheat heat exchanger, which is positioned in the path of air downstream of the evaporator. A control is provided for the system to achieve a desired level of dehumidification and temperature control to air being delivered into the environment to be conditioned.

1 . A refrigerant system comprising:
 at least one refrigerant circuit comprising at least one compressor for compressing a refrigerant and delivering it downstream to a heat rejection heat exchanger;   a bypass line provided around said heat rejection heat exchanger for selectively allowing at least a portion of refrigerant to bypass said heat rejection heat exchanger;   a first valve controlling flow to said heat rejection heat exchanger and a second valve on said bypass line to individually control the flow of refrigerant through said heat rejection heat exchanger and around said heat rejection heat exchanger;   an expansion device positioned downstream of said heat rejection heat exchanger, and an evaporator positioned downstream of said expansion device, refrigerant from said evaporator passing back to said at least one compressor;   a reheat cycle incorporated into said refrigerant system, including a third valve for selectively delivering at least a portion of refrigerant through a reheat heat exchanger, said reheat heat exchanger being positioned in the path of air downstream of said evaporator; and   a control for said system being operable in a dehumidification mode to achieve a desired level of dehumidification and temperature control to air being delivered over said evaporator and said reheat heat exchanger and into an environment to be conditioned, said control initially opening said first valve on said bypass line to a relatively open position to achieve additional reheat control, and said control then beginning to close said second valve on said line leading to said heat rejection heat exchanger to achieve additional reheat control.   
     
     
         2 . The refrigerant system as set forth in  claim 1 , wherein said reheat cycle incorporates an inlet positioned between said heat rejection heat exchanger and said expansion device, and a return line downstream of said inlet, but upstream of said expansion device. 
     
     
         3 . The refrigerant system as set forth in  claim 1 , wherein said first valve on said bypass line is initially substantially fully open, and said second valve leading to said heat rejection heat exchanger then begins to be closed. 
     
     
         4 . The refrigerant system as set forth in  claim 1 , wherein said control changes a level of capacity provided by said compressor to achieve evaporator discharge air temperature control, in combination with changing the position of said first and second valves to achieve a desired level of reheat control. 
     
     
         5 . The refrigerant system as set forth in  claim 1 , wherein there are at least a pair of refrigerant circuits within said refrigerant system, with a first of said refrigerant circuits incorporating said reheat heat exchanger, and said bypass around said heat rejection heat exchanger, and a second of said refrigerant circuits including airflow downstream of an evaporator passing over said reheat heat exchanger in said first of said refrigerant circuits. 
     
     
         6 . The refrigerant system as set forth in  claim 1 , wherein said control provides head pressure control when said position of said at least one of first and second valves is such that head pressure control is deemed desirable. 
     
     
         7 . The refrigerant system as set forth in  claim 1 , wherein at start-up, said control moves said second and third valves to at least a partially open position. 
     
     
         8 . The refrigerant system as set forth in  claim 1 , wherein said control operates in oil return mode when at least one of said first and second valves is in a position to indicate a need for oil return. 
     
     
         9 . The refrigerant system as set forth in  claim 8 , wherein said control enters said oil return mode if said first valve is closed below a minimum position, and said control opens said first valve when in said oil return mode. 
     
     
         10 . The refrigerant system as set forth in  claim 1 , wherein at a transition to a cooling mode, said control cycling said third valve on and then off periodically. 
     
     
         11 . The refrigerant system as set forth in  claim 1 , wherein a check valve is provided on said bypass line, and adjacent to a location where said bypass line re-enters a main flow line. 
     
     
         12 . The refrigerant system as set forth in  claim 1 , wherein said second valve is positioned upstream of said heat rejection heat exchanger. 
     
     
         13 . A method of operating a refrigerant system including the steps of:
 operating a refrigerant circuit and incorporating a reheat cycle into said system; and   providing a desired level of dehumidification and temperature control to air being delivered over an evaporator and a reheat heat exchanger in a dehumidification mode by initially opening a first valve to bypass refrigerant around a heat rejection heat exchanger, and allowing the bypassed refrigerant to enter a reheat heat exchanger, and to move said valve to a relatively open position to achieve additional reheat control, and then beginning to close a second valve on a line leading to the heat rejection heat exchanger to achieve additional reheat control.   
     
     
         14 . The method as set forth in  claim 11 , including the step of changing a level of capacity provided by a compressor to achieve evaporator discharge air temperature control, in combination with changing the position of said valves to achieve a desired level of reheat control. 
     
     
         15 . The method as set forth in  claim 11 , wherein head pressure control is provided when the bypass valve is passing the majority of refrigerant around the heat rejection heat exchanger. 
     
     
         16 . The method as set forth in  claim 11 , wherein said valve on said bypass line is moved to at least a partially open position at start-up. 
     
     
         17 . The method as set forth in  claim 11 , wherein when at least one of said first and second valves is in a position to indicate a need for oil return, an oil return mode is provided. 
     
     
         18 . The method as set forth in  claim 17 , wherein said oil return mode includes opening said first valve. 
     
     
         19 . The method as set forth in  claim 17 , further including the steps of entering the oil return mode when the system is in a cooling mode, but not a dehumidification mode, after a period of time, and includes the steps of opening said first valve on said bypass line. 
     
     
         20 . The method as set forth in  claim 11 , wherein during a transition to a cooling mode, cycling a reheat valve is cycled on and then off periodically to allow and then block flow of refrigerant to the reheat heat exchanger.