Abstract:
A humidity control method is provided for a multi-stage cooling system having two or more refrigerant circuits that balances humidity control and cooling demand. Each refrigerant circuit includes a compressor, a condenser and an evaporator. A hot gas reheat circuit having a hot gas reheat coil is connected to one of the refrigerant circuits and is placed in fluid communication with the output airflow from the evaporator of that refrigerant circuit to provide additional dehumidification to the air when humidity control is requested. The hot gas reheat circuit bypasses the condenser of the refrigerant circuit during humidity control. Humidity control is only performed during cooling operations and ventilation operations. During a first stage cooling operation using only one refrigerant circuit and having a low cooling demand, the request for humidity control activates the hot gas reheat circuit for dehumidification and activates a second refrigerant circuit to provide cooling capacity. During a second stage cooling operation using two or more refrigerant circuit and having a high cooling demand, the request for humidity control is suspended and is initiated only upon the completion of the second stage cooling demand.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to U.S. Provisional Application No. 60/425,172 filed Nov. 8, 2002. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to a humidity control application for a cooling system. More specifically, the present invention relates to a method for performing humidity control using hot gas reheat in a two-stage cooling unit.  
       BACKGROUND OF THE INVENTION  
       [0003]     Air delivery systems, such as used in commercial applications, typically are systems that can be used to cool or to accomplish dehumidification when ambient conditions are such that there is no demand for cooling. This demand for dehumidification can often occur on days when the temperature is cool and there is a high humidity level, such as damp, rainy spring and fall days. Under such conditions, it may be necessary to switch the operation of the air delivery system from cooling mode to dehumidification mode.  
         [0004]     When switching an air delivery system, such as are used in commercial applications, from the cooling mode to the dehumidification mode in a reheat system that includes a reheat coil and a condenser coil configured in a parallel arrangement, some refrigerant will become trapped in the condenser coil. As the outdoor temperature falls, the amount of refrigerant that becomes trapped in the condenser coil will increase, resulting in a drop in the quantity of refrigeration available in the remainder of the refrigerant system to accomplish dehumidification. Without adequate refrigerant in the dehumidification circuit, operational problems will occur with the air delivery system. Some refrigerant can become trapped in a system that includes a reheat circuit even on warm days when dehumidification is required, but cooling is not required. The refrigerant can become trapped in the condenser coil, and if switching is required to the cooling mode, additional refrigerant can be trapped in the reheat circuit.  
         [0005]     One of the problems is decreased system capacity as the refrigerant normally available in a properly operating system is trapped in the condenser coil and not available to the compressor. Associated with this problem is inadequate suction pressure at the compressor, since the gas refrigerant that normally is available to the compressor from the evaporator is trapped as a liquid in the condenser.  
         [0006]     What is needed is an air delivery system that can remove refrigerant trapped as a liquid in the condenser, which is exacerbated in cooler, damp weather, and make the refrigerant readily available to the compressor, thereby restoring the capacity, efficiency and stability of the system and allow for the system to operate in the dehumidification mode regardless of the outdoor ambient temperature.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention utilizes a hot gas reheat circuit in a standard cooling system to control temperature and humidity of an interior space in a building. The hot gas reheat circuit is connected to the high-pressure side of the compressor. In the dehumidification mode, when additional cooling is not required, the hot gas reheat circuit is activated to provide hot refrigerant gas to heat cooled air to the required temperature after the air has been dehumidified.  
         [0008]     In order to prevent refrigerant from being trapped in the condenser thereby depleting the available refrigerant for compressor operation as refrigerant is trapped in the condenser coils when the reheat circuit is activated and the condenser is isolated from the compressor, when the hot gas reheat circuit is activated, which readily occurs on cool days, and to prevent additional refrigerant from being trapped in the reheat coils when the reheat circuit is inactivated and isolated from the compressor, the present invention incorporates a reheat by-pass circuit and a cooling by-pass circuit into the system.  
         [0009]     The cooling refrigerant recovery circuit, when activated, is in fluid communication with the hot gas reheat circuit. It is activated when the hot gas reheat circuit is inactivated and the cooling mode is restored, in order to remove refrigerant from the reheat coil to the low-pressure side of the compressor.  
         [0010]     The reheat by-pass circuit, when activated, is in fluid communication with the condenser. It is activated when the hot gas reheat circuit is activated and the cooling mode is inactivated, so as to remove refrigerant from the condenser to the low-pressure side of the compressor.  
         [0011]     An advantage of the present invention is that refrigerant is not trapped in an inactive coil when switching between cooling cycles and reheat (dehumidification) cycles, thereby assuring that adequate refrigerant is available to the compressor.  
         [0012]     Another advantage of the present invention is that comfort cooling in the interior space of a building is not compromised when there is a demand for humidity control.  
         [0013]     Yet another advantage is that refrigerant can be quickly removed from a condenser, regardless of ambient conditions, to a location within the system where the refrigerant is available on demand to the compressor when the system is not in a cooling mode.  
         [0014]     Still another advantage of the arrangement of the present invention is that the reheat by-pass circuit utilizes heat that otherwise would be transferred to the outdoor condenser, which is an energy savings, and the removal of trapped refrigerant from the inactive condenser or the inactive reheat coil allows the system to operate more efficiently.  
         [0015]     Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  illustrates schematically an embodiment of the present invention in a single compressor ventilation and air conditioning system.  
         [0017]      FIG. 2  illustrates schematically an embodiment of a heating, ventilation and air conditioning system for use with the present invention.  
         [0018]      FIG. 3  illustrates a flow chart detailing the humidity control method of the present invention. 
     
    
       [0019]     Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0020]      FIG. 1  illustrates one embodiment of a ventilation and air conditioning (HVAC) system  1  for an interior space of a building. The HVAC system  1  provides both air conditioning control and humidity control to an interior space of a building. The HVAC system  1  typically is a single stage cooling system using compressor  2  to provide cooling capacity and humidity control in an interior space of a building which requires cooling and/or humidity control. Compressor  2  may be a any type of a compressor, such as screw compressor, a scroll compressor, a centrifugal compressor, a rotary compressor or a reciprocating compressor. In most moderate climates where cooling and humidity control is required, such as in the refrigeration section of a commercial establishment, for example a supermarket, heating is not required throughout the year. In those climates where extreme cold temperatures exist, such as for example, in the northern portions of the continental United States, Alaska and Canada, additional heating circuits can be added as will be discussed.  
         [0021]     In operation, the system  1  includes the usual components of a cooling system, a compressor  2 , connected by conduit to a condenser  6  which is connected by conduit to an evaporator  12 , which is connected by conduit to compressor  2 . In the cooling mode, refrigerant sealed in system  1  is compressed into a hot, high-pressure gas in compressor  2  and flows through conduit to condenser  6 . The condenser  6 , a heat exchanger, includes a fan  10  which blows air across the condenser coils. In the condenser, at least some of the hot, high-pressure gas refrigerant undergoes a phase change and is converted into a fluid of high-pressure refrigerant liquid or a fluid mixture of high-pressure refrigerant liquid and refrigerant vapor. In undergoing the phase change, the refrigerant transfers heat through the coils of the condenser to the air passing over the coils with the assistance of fan  10 . Additional heat, heat of condensation, is given off by the refrigerant as it condenses from a gas to liquid. The high-pressure fluid passes through a conduit to an expansion device  16 . As the fluid passes through expansion device  16 , it expands, flashing some of the liquid to gas and ideally converting any remaining refrigerant gas to low-pressure liquid, while reducing the fluid pressure. The low-pressure fluid then passes to the evaporator  12 . In evaporator  12 , the refrigerant passes through the evaporator coils where the liquid refrigerant undergoes a second phase change, where the liquid refrigerant is converted to a vapor. This conversion requires energy, provided in the form of heat, which is drawn from air passing over the evaporator coils. This airflow is assisted by a fan which forces air over the coils. As shown in  FIG. 1 , the air is drawn over the coils by indoor blower  18 . After passing over the evaporator coils, the air which is now cooler, as heat has been transferred to assist in the refrigerant phase change, can be supplied to the space that requires refrigeration. Of course, the ability of the cooled air supplied to the space to hold moisture in the form of humidity is reduced below its capacity when it passed over the evaporator coils, so the air passing into the space is also dehumidified. The excess moisture is removed from the air as condensate as it passes over the coils and is directed to a drain. The refrigerant gas, now at low-pressure and low temperature is returned to compressor  2 . As shown in  FIG. 1 , there is an accumulator  13  which can store any excess liquid refrigerant and lubricant until a system demand calls for it. A suction line circuit  44  includes a bleed line  46 . The line  46  runs from suction line  42  to valve  29  to activate or inactivate valve  29  in response to a signal from a controller (not shown).  
         [0022]     Prior art units include a reheat circuit that runs from the high-pressure side of the compressor, across reheat coils proximate to coils of evaporator  12  similar to reheat circuit  26  shown in  FIG. 1 . These prior art circuits run from the high pressure side of the compressor to direct the flow of hot refrigerant through a reheat coil proximate the evaporator coils and back to the system in the high pressure side between the condenser  6  and the thermal expansion valve  16 . The purpose of the reheat circuit is to provide dehumidification of the area to be serviced on days when no additional cooling is required. The reheat circuit utilizes hot refrigerant gas from the compressor discharge port to heat the cool, dehumidified air that has passed over the evaporator coils. This will prevent an undesirable high humidity condition in the area, as the air sent to the building space is dehumidified but, prevents further cooling as the air temperature is modulated by the reheat circuit. This is advantageous, for example, in the cold food sections of supermarkets to prevent condensation on the surfaces of coolers, which surfaces may include glass doors wherein condensation limits visibility. The high temperature, high-pressure fluid from the compressor travels through the reheat circuit into the reheat coils where heat is transferred to the cold dehumidified air that has passed over the evaporator to raise the air temperature. Any suitable logic controls and properly located sensors can be used to control the operation of the compressor and/or the flow of air and refrigerant fluid through the reheat circuit to provide the appropriate heat balance to maintain the temperature within predetermined limits during dehumidification. Proper sizing of the reheat coil so that the available surface area for air passing over the reheat coil can be matched with the available surface area of the evaporator coil. A wide range of varying sizes for both the reheat coil and the coils of the evaporator  12  that otherwise would not be effective together can be matched provided that logic controls can precisely control refrigerant flow, compressor operation and air flow, either individually or in combination.  
         [0023]     The prior art reheat circuit presents a problem on humid days in which no additional cooling of the area is required but in which the reheat circuit must be activated so that proper dehumidification can be provided. When the reheat circuit is activated on such days, refrigerant is trapped in the condenser coil. On colder days, as the outdoor temperature falls, increasing amounts of refrigerant are trapped in the condenser coil, which is typically an outdoor unit located on a roof, although the outdoor unit can be located at any other convenient location. The increased refrigerant in the condenser coil results in decreased amounts of refrigerant and lubricant available in the remainder of the system, in particular, in the reheat or dehumidification circuit, which can lead to operational problems. The worst-case scenario is compressor damage due to inadequate lubrication and/or system failure due to icing of the evaporator. Less serious problems include: decreased system capacity due in part to the inability to properly dehumidify the building space and system instability due to inadequate suction pressure at the compressor as the amount of refrigerant at the compressor inlet is reduced. These problems may also occur when a cooling demand is required. In this instance, the liquid can become entrapped in the reheat coil as the reheat circuit is inactivated.  
         [0024]     The system of the present invention, which is diagrammatically depicted in  FIG. 1  includes a hot gas reheat circuit  26  that further includes a main loop  27 , a reheat refrigerant recovery circuit  60  and a cooling refrigerant recovery circuit  50 . Reheat refrigerant recovery circuit  60  comprises conduit that runs from the low-pressure side of compressor  2 , preferably connected to the system or conduit between the evaporator  12  and a refrigerant accumulator  13 , to the line between valve  29  and condenser  6 , and a solenoid valve  62  to control the flow of fluid through the circuit.  
         [0025]     Cooling refrigerant recovery circuit  50  comprises a conduit that connects the main loop  27  between hot gas reheat coil  32  and valve  29  to the low pressure side of compressor  2 , preferably connected to the system or conduit running between the evaporator  12  and accumulator  13 , and a solenoid valve  52  to control the flow of fluid through the circuit. Circuits  60  and  50  prevent substantial amounts of refrigerant from being trapped in the condenser  6  and hot gas reheat coil  32  respectively, as will be explained.  
         [0026]     When the system is in the cooling mode and switches to the reheat mode, as will happen under excessively humid conditions, a controller (not shown) will send a signal to open the three-way hot gas reheat solenoid valve  29  causing gas to flow through main loop  27 . In addition, the controller will send a signal to close valve  52  and open valve  62 . The closing of valve  52  and opening of valve  29 , which may be a two way valve, cycles hot refrigerant gas through main loop  27  to hot gas coil  32  through check valve  31  and to thermal expansion valve  16 . Check valve  34  prevents hot refrigerant from flowing to condenser  6 . The opening of valve  62  connects the low pressure side of the system to condenser  6 , which is at a higher pressure as the system has just been switched from cooling mode to reheat mode. The pressure differential between condenser  6  and conduit on the low-pressure side of compressor  2 , as well as the suction of the compressor  2  as it operates, draws high-pressure refrigerant from the condenser  6  to the low-pressure side of the compressor  2  and to the accumulator  13 , as depicted by the arrow in  FIG. 1 , showing the flow of refrigerant from the condenser to circuit  60 , where it can be utilized to ensure proper operation of the system. Valve  62  can remain open or can cycle closed after a preselected period of time, the time selected based on drawing out all or a large portion of the refrigerant. Thus, more refrigerant is available to the system to provide it with the necessary capacity.  
         [0027]     When the system is in the reheat mode and switches to the cooling mode, as will happen on moderately cool days as the ambient temperature rises, a controller (not shown) will send a signal to close the three-way hot gas reheat solenoid valve  29 , shutting off the flow of gas through main loop  27  and directing the flow of gas to condenser  6 . The controller also sends a signal to accomplish the closing of valve  62 , if it is not already closed, to prevent high pressure refrigerant gas from the compressor from flowing through circuit  60 . The controller also sends a signal to open valve  52  in cooling by-pass circuit. The high-pressure, high temperature refrigerant gas from the compressor flows through the condenser and through check valve  34  to thermal expansion valve  16 . Check valve  31  prevents the flow of refrigerant through hot gas reheat circuit  26 . The opening of valve  52  connects hot gas reheat coil  32  to the low-pressure side of the system, as shown. Reheat coil  32  is still at a higher pressure than the low-pressure side to which it has just been connected, as the system has just been switched to cooling mode from dehumidification mode. The pressure differential between reheat coil  32  and conduit on the low-pressure side of compressor  2  to which it is connected via conduit as well as the suction of the compressor as it operates, draws refrigerant from the reheat coil  32  to the low-pressure side of the compressor  2  and to accumulator  13 , where it can be used by the system as needed. Valve  52  can remain open or can cycle closed after a preselected period of time. The time selected is based on drawing out all or a large portion of the refrigerant from the reheat coil  32 . Thus, more refrigerant is available to compressor  2  to allow it to function as required and provide the necessary cooling capacity.  
         [0028]      FIG. 2  illustrates one embodiment of a heating, ventilation and air conditioning (HVAC) system  100  for an interior space of a building. The HVAC system  100  can also provide humidity control to the interior space of a building. The HVAC system  100  is preferably a two stage cooling system using two compressors  102 ,  104  to provide two (or more) levels of cooling capacity in the interior space. Each of compressors  102 ,  104  can be a screw compressor, a reciprocating compressor, a rotary compressor, a scroll compressor or a centrifugal compressor. Compressors  102 ,  104  may have the same capacity or may be of different capacities. The two levels of cooling capacity can be obtained by operating either one of the compressors  102 ,  104  or both of the compressors  102 ,  104  depending on the cooling demand. The first level of cooling capacity is obtained by operating just one of the compressors  102 ,  104  during period of lower cooling demand. One of the compressor  102 ,  104  used to provide the first level of cooling capacity can be referred to as the primary compressor or the stage one compressor. To simplify the explanation of the present invention and to correspond to the system  100  as shown in  FIG. 1 , compressor  102  will be referred to as the stage one or primary compressor. It is to be understood that in another embodiment of the present invention, compressor  104  can be used as the stage one or primary compressor instead of compressor  102 .  
         [0029]     The stage one compressor  102  is preferably operated during times when the cooling demand in the interior space of the building is low. As the cooling demand in the interior space increases in response to a variety of factors such as the increasing exterior (ambient) temperature, compressor  104  is energized and will be referred to as the stage two or secondary compressor. The operation of the two compressors  102  and  104  provides the maximum amount of cooling capacity from the HVAC system  100 . A control program or algorithm executed by a microprocessor or control panel in response to sensor readings is used to determine when the stage two compressor  104  is to be started in response to the higher cooling demand. The control program can receive a variety of possible inputs, such as temperature, pressure and/or flow measurements, to be used in making the determination of when to start the stage two compressor  104 . It is to be understood that the particular control program and control criteria for engaging and disengaging the stage two or secondary compressor  104  can be selected and based on the particular performance requirements of the HVAC system  100  desired by a user of the HVAC system  100 .  
         [0030]     Compressors  102 ,  104  are each used with a separate refrigeration circuit. The compressors  102 ,  104  each compress a refrigerant vapor and deliver the compressed refrigerant vapor to a corresponding condenser  106 ,  108  by separate discharge lines. The condensers  106 ,  108  are separate and distinct from one another and can only receive refrigerant vapor from its corresponding compressor  102 ,  104 . The condensers  106 ,  108  can be located in the same housing, and can be positioned immediately adjacent to one another, as shown in  FIG. 2 , or alternatively, the condensers  106 ,  108  can be spaced a distance apart from one another. The positioning of the condensers  106 ,  108  can be varied so long as the separate refrigeration circuits are maintained. The refrigerant vapor delivered to the condensers  106 ,  108  enters into a heat exchange relationship with a fluid, preferably air, flowing through a heat-exchanger coil in the condenser  106 ,  108 . To assist in the passage of the fluid through the heat exchanger coils of condensers  106 ,  108 , fans  110  can be used to draw air over the coils of the condensers  106 ,  108 . The refrigerant vapor in the condensers  106 ,  108  undergoes a phase change to a refrigerant liquid as a result of the heat exchange relationship with the air flowing over the heat-exchanger coils, the air removing heat from the refrigerant. The condensed liquid refrigerant from condensers  106 ,  108  flows to a corresponding evaporator  112 ,  114  after passing through corresponding expansion valves  116 . Similar to the condensers  106 ,  108 , the evaporators  112 ,  114  are separate and distinct from one another and can only receive refrigerant from its corresponding condenser  106 ,  108 . The evaporators  112 ,  114  can be located in the same housing, can be positioned immediately adjacent to one another or alternatively, the evaporators  112 ,  114  can be spaced a distance apart from one another. The positioning of the evaporators  112 ,  114  can be varied as desired, so long as the separate refrigeration circuits are maintained.  
         [0031]     The evaporators  112 ,  114  can each include a heat-exchanger coil having a plurality of tube bundles within the evaporator  112 ,  114 . A fluid, preferably air, travels or passes through and around the heat-exchanger coil of the evaporators  112 ,  114 . Once the air passes through the evaporators  112 ,  114  it is discharged by blower  118  to the interior space via supply duct  120 . The liquid refrigerant in the evaporators  112 ,  114  enters into a heat exchange relationship with the air passing through and over the evaporators  112 ,  114  to chill or lower the temperature of the air before it is provided to the interior space by the blower  118  and the supply duct  120 . The refrigerant liquid in the evaporators  112 ,  114  undergoes a phase change to a refrigerant vapor as a result of the heat exchange relationship with the air passing through the evaporators  112 ,  114 , the refrigerant absorbing heat from the air. In addition to cooling the air, the evaporators  112 ,  114  also operate to remove moisture from the air passing through the evaporators. Moisture in the air condenses on the coils of the evaporators  112 ,  114  as a result of the heat exchange relationship entered into with the refrigerant in the heat-exchanger coil. The vapor refrigerant in the evaporators  112 ,  114  then returns to the corresponding compressor  102 ,  104  by separate suction lines to complete the cycle.  
         [0032]     In addition, system  100  can include one or more sensors  122  for detecting and measuring operating parameters of system  100 . The signals from the sensors  122  can be provided to a microprocessor or control panel (not shown) that controls the operation of system  100 . Sensors  122  can include pressure sensors, temperature sensors, flow sensors, or any other suitable type of sensor for evaluating the performance of system  100 .  
         [0033]     System  100  shown in  FIG. 2  also has a heating mode and a ventilation mode. When system  100  is required to provide heating or ventilation to the interior space, the compressors  102 ,  104  are shut down and the air passes over the coils of evaporators  112 ,  114  to the blower  118  without any substantial change in temperature. The blower  118  then blows the air over a heater  124  located in the supply duct  120 , with heater  124  switched off, or immediately adjacent to the supply duct  120  to heat the air to be provided to the interior space for the heating mode, or alternatively the air is provided to the interior space through the supply duct  120  for the ventilation mode. The heater  124  can be an electrical heater providing resistance heat, a combustion heater or furnace burning an appropriate fuel for heat or any other suitable type of heater or heating system.  
         [0034]     As mentioned above, system  100  of  FIG. 2  can provide humidity control to the interior space. In a preferred embodiment, the humidity control can be obtained through the use of a hot gas reheat circuit  126  that is connected to the refrigeration circuit of the first stage compressor  102 . The reheat circuit operates in the same manner as the circuit set forth in  FIG. 1  described above. The reheat circuit  126  includes a main loop  127  as well as a cooling refrigerant recovery circuit  150  and a reheat refrigerant recovery circuit  160 , The reheat circuit  126  includes a first valve  129 , which preferably is a three-way valve, positioned between the compressor  102  and the condenser  106 . A second solenoid valve not shown in  FIG. 2 , which also may be a two-way valve positioned between the condenser  106  and the expansion valve  116 . Alternatively, a pair of check valves  131 ,  134  may be substituted for the second solenoid valve and positioned as shown in  FIG. 2 , between the expansion valve  116 , reheat coil  132  and condenser  106  as shown. A reheat coil  132  is in fluid communication with the first valve  129 . The reheat coil is also in fluid communication with the air exiting evaporator  112  (and possibly the air exiting evaporator  114 ) and the air entering the blower  118 , the air passing over the evaporator coils as refrigerant flows through the evaporator coils.  
         [0035]     When system  100  is in a cooling mode, valve  129  is configured or positioned so that refrigerant flows from the compressor  102  to the condenser  106 . A check valve  131  prevents flow of refrigerant from condenser  106  into reheat coil  132  in the cooling mode. In contrast, when the HVAC system  100  is in a humidity control mode, three-way hot gas reheat valve  129  is configured or positioned to permit refrigerant to flow from the compressor  102  to the reheat coil  132  and check valve  134  prevents refrigerant from flowing to condenser  106 . Check valves  131  and  134  are the most economical way of controlling the flow. However, they may be replaced by a switchable two-position valve that regulates the flow of refrigerant through the appropriate circuit in response to a signal from a controller. The reheat circuit  126  is used to bypass the condenser  106 , when the HVAC system  100  is in the humidity control mode. The reheat coil  132  then performs the functions of the condenser  106  when the HVAC system  100  is in humidity control mode. Reheat circuit includes a main loop  127 , a cooling refrigerant recovery circuit  150  and a reheat refrigerant recovery circuit  160 . Cooling refrigerant recovery circuit  150  includes a solenoid valve  152  and has the same arrangement and operation in the system as described above for cooling refrigerant recovery circuit  50  of  FIG. 1 . Reheat refrigerant recovery circuit  160  includes a solenoid valve  162  and has the same arrangement and operation in the system as described above for reheat refrigerant recovery circuit  60 . The second compressor  104  and heater  124 , however, provide system  100  with more flexibility as will become obvious.  
         [0036]     The operation of system  100  in the humidity control mode is controlled by controller, which may be a microprocessor or control panel. The control panel receives input signals from sensor(s), such as may be found in a thermostat or humidistat, and determines whether there is a demand for cooling, heating, ventilation and/or humidity control. More specifically, the control panel can receive input signals from sensors and determine whether there is a demand for stage one cooling, stage two cooling, humidity control, heating, and ventilation. In another embodiment of the present invention, the control panel can receive input signals from sensors and determine whether a demand exists for stage one cooling and/or stage  2  cooling instead of a general signal indicating a cooling demand. The control panel then processes these input signals using the control method of the present invention and generates the appropriate control signals to the components of the HVAC system  100  to obtain the desired response to the input signals received from the sensor(s).  
         [0037]      FIG. 3  illustrates a flow chart detailing the humidity control method of the present invention for a HVAC system  100  as shown in  FIG. 2 . The process begins with a determination of whether a humidity control signal has been received in step  202 . The humidity control signal is generated by a controller in response to a signal from a sensor and determines that humidity control is required in the interior space of the building. If a humidity control signal is not received in step  202 , the hot gas reheat circuit  126  is disabled, i.e. the valve  129  is positioned to prevent flow of refrigerant to the hot gas reheat coil  132 , in step  204  and the process is ended. Otherwise, the process continues to step  206  to determine if the HVAC system  100  is currently in the heating mode in view of the receipt of a humidity control signal.  
         [0038]     If the HVAC system  100  is in the heating mode in step  206 , then primary and secondary compressors  102 ,  104  are disabled and/or shut down in step  208  and the hot gas reheat circuit  126  is disabled as described above in step  204 . The process then returns to the beginning to determine if a humidity control signal is present in step  202 . When the HVAC system  100  is in the heating mode, the compressors  102 ,  104  and the hot gas reheat circuit  126  are disabled because the heating of the air by the heater  124  provides adequate dehumidification of the air provided to the interior space of the building.  
         [0039]     If the HVAC system is not in the heating mode in step  206 , the process advances to step  210  to determine if the HVAC system  100  is in a cooling mode. If the HVAC system  100  is in a cooling mode in step  210 , control advances to step  212  to determine if the HVAC system  100  is in a stage one cooling mode. As discussed above, in the stage one cooling mode there is a low cooling demand and only primary compressor  102  is operating. If the HVAC system  100  is in the stage one cooling mode, the secondary compressor  104  is enabled and/or started in step  214  and then the hot gas reheat circuit  126  is enabled in step  216  to provide humidity control to the air provided to the interior space. The hot gas reheat circuit  126  is enabled by positioning valve  129  to prevent the flow of refrigerant to condenser  106  and to permit the flow of refrigerant through the reheat coil  132  to further dehumidify the air from the evaporator  112 . Reheat refrigerant recovery circuit  150  prevents refrigerant from being trapped in the condenser as described above. The starting of the secondary compressor  104  in step  214  enables evaporator  114  to provide additional cooling to the air to satisfy the cooling demand. In this mode, the HVAC system  100  can provide both cooling and dehumidification to the air to satisfy both cooling demands and humidity control demands.  
         [0040]     If the HVAC system  100  is in a cooling mode, as determined in step  210 , but not in a stage one cooling mode in step  212 , then the HVAC system  100  necessarily must be in a stage two cooling mode and both primary and secondary compressors  102 ,  104  are in operation to provide cooling to the interior space. The hot gas reheat circuit  126  is disabled in step  204  after the determination in step  212  is negative and then proceeds to the beginning to start the process again and refrigerant is withdrawn from reheat coil  132  in circuit  150  of the present invention as described above. Humidity control using the hot gas reheat circuit  126  is not provided when the HVAC system is providing two-stage cooling. The operation of evaporators  112 ,  114  to cool the air provides dehumidification of the air to the interior space of the building. Once the demand for cooling is lowered or reduced, the hot gas reheat circuit  126  is enabled to provide dehumidification as discussed in greater detail above with regard to steps  212 - 216 .  
         [0041]     Referring back to step  210 , if the HVAC system  100  is not in a cooling mode, a determination is made in step  218  to determine if the HVAC system  100  is in a ventilation mode. If the HVAC system is not in a ventilation mode in step  218 , blower  118  is enabled and/or started in step  220 , the primary compressor is enabled and/or started in step  222  and the hot gas reheat circuit  126  is enabled in step  216  to provide humidity control to the air for the interior space. If the HVAC system  100  is in the ventilation mode, then the primary compressor  102  is enabled and/or started in step  222  without activating blower  118  and the hot gas reheat circuit  126  is enabled in step  216  to provide humidity control to the air for the interior space.  
         [0042]     As can be seen in the control process of  FIG. 3 , humidity control using the hot gas reheat circuit  126  and reheat coil  132  can be provided when the HVAC system  100  is in a stage one cooling mode or a ventilation mode. By engaging the hot gas reheat circuit  126  for humidity control in the above mentioned modes, the humidity control method of the present invention can balance the need for cooling with the need for humidity control.  
         [0043]     In another embodiment of the present invention, the user of HVAC system  100  can view a control panel to determine the particular humidity control mode. For example, if an LED on the control panel is flashing two times in a predetermined time interval, then the HVAC system  100  is in humidity control mode without any demand for cooling. However, if the LED on the control panel is flashing three times in a predetermined time interval, then the HVAC system  100  is in a humidity control mode while there is a demand for comfort cooling. It is to be understood that the display method for the humidity control mode on the control panel can be modified as desired for the particular requirements or needs of the user to indicate the mode that the system is in. Thus, for example, an assortment of LED&#39;s can be mounted on the control panel to further indicate stage one cooling, stage two cooling, heating, ventilation etc. as desired, and the panel can be configured to user requirements or preferences.  
         [0044]     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.