Abstract:
A refrigerant system is provided with a reheat circuit. A pulse width modulation control is provided to achieve variable reheat capacity and thus to satisfy a wide spectrum of temperature and humidity levels in an environment conditioned by a refrigerant system. The pulse width modulation signal provided for the reheat flow control device achieves incremental amounts of reheat while avoiding temperature and humidity variations in the conditioned space.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates to a pulse width modulation control that allows for continuous or precise stepwise reheat capacity to be provided by a refrigerant system. 
         [0002]    Refrigerant systems are utilized in many applications such as to condition an environment. Air conditioners and heat pumps are used to cool and/or heat the air entering an environment. The cooling or heating load on the environment may change with ambient conditions, and as the temperature and/or humidity levels demanded by an occupant of the environment vary. Obviously, the refrigerant system operation and control have to adequately reflect these changes to maintain stable temperature and humidity conditions within the environment. 
         [0003]    In some cases, while the system is operating in a cooling mode, the temperature level of the indoor air stream to provide a comfortable environment in a conditioned space may need to be higher than the temperature that would provide the ideal humidity level. On the other hand, by lowering the temperature of the air stream, more moisture can be removed from the air. These contradicting trends presented challenges to refrigerant system designers. One way to address such challenges is to utilize various schematics incorporating reheat coils. In many cases, a reheat coil, placed in the indoor air path downstream of the evaporator, is employed for the purposes of reheating the air supplied to the conditioned space, after it has been cooled in the evaporator, and where the moisture has been removed. 
         [0004]    In the prior art, controls can be programmed to optionally actuate the reheat function. However, the capacity provided by the reheat circuit is increased or decreased in steps. It would be desirable to provide the ability to vary the reheat capacity and overall system performance between these discrete steps. 
         [0005]    While pulse width modulation controls have been provided for various purposes in refrigerant systems, they have not been utilized to provide varying steps in a reheat capacity. 
       SUMMARY OF THE INVENTION 
       [0006]    In a disclosed embodiment of this invention, a pulse width modulation control is provided for selectively varying capacity provided by a reheat circuit and thus overall system performance. The “on/off” cycle time interval is selected such that the overall effect on the system in terms of external operational characteristics, due to system thermal inertia, is negligible. That is, an occupant of an environment being conditioned would not recognize that the flow of refrigerant to the reheat circuit is being periodically turned on and off. 
         [0007]    In various embodiments, the control is operable to vary the width of the pulse to achieve a desired time interval for a flow control device such as a valve being opened to direct refrigerant to the reheat heat exchanger. In this manner, a broad range of reheat capacities can be covered and variable reheat control can be provided. 
         [0008]    In specific schematics, the present invention may also be provided in combination with a circuit that allows for bypass of refrigerant around a condenser to allow for additional operational flexibility in the reheat functionality and control. 
         [0009]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows a first schematic. 
           [0011]      FIG. 2  shows a second schematic. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0012]    A refrigerant system  20  is illustrated in  FIG. 1  including a compressor  22  compressing refrigerant and delivering it to a downstream condenser  24 . A fan  25  blows air over the condenser  24 . Refrigerant passes from the condenser  24  to a downstream expansion device  26 , then to an evaporator  28 , and finally returns to compressor  22 . A three-way valve  30  is placed on a discharge refrigerant line, and as illustrated, between the compressor  22  and the condenser  24 . The three-way valve  30  is controlled by a control  38  for a purpose that will be described below. When the three-way valve is in an open position, it will deliver refrigerant through a reheat heat exchanger  34  and a check valve  35 , and then return the refrigerant back to a position  31  still upstream of the condenser  24 . As is known, a fan  36  blows air over the evaporator  28 , and the reheat heat exchanger  34  is placed such that it is in the path of that air stream behind the evaporator  28 . 
         [0013]    The purpose of the reheat heat exchanger  34  is to allow the evaporator  28  to cool the air passing over it to a level that is lower than may be desired by an occupant of an environment and requested through a thermostat  32  in order to remove sufficient amount of moisture from the air and maintain desired humidity level in the environment. Lower temperatures of air passing over the evaporator  28  result in more moisture been removed from the air. The air then passes over the reheat heat exchanger  34 , and is reheated back towards the desired temperature. In this manner, utilization of a reheat circuit provides both desired temperature and humidity levels in the conditioned environment. 
         [0014]    The control  38  sends a pulse width modulation signal to the valve  30 . The valve  30  is of a three-way type that is typically in a normally open position (during a cooling mode of operation) communicates refrigerant from the compressor  22  directly to the condenser  24 , and may be driven to an alternate position (during a reheat mode of operation) at which it allows refrigerant to flow from the compressor  22  through the reheat heat exchanger  34  to the condenser  24 . When a pulse width modulation signal is provided by the control  38  to the valve  30 , it moves the valve to this alternate position. Since the control  38  is determining the required reheat capacity, the control can then determine the width of the pulse and the time interval between the pulses sent to the valve  30 , such that the valve  30  can be in the open position precisely for an amount of time to provide this required reheat capacity. In this manner, just the right reheat capacity is provided, and temperature and humidity in a conditioned environment are precisely controlled. The present invention thus offers a relatively inexpensive and efficient method of providing a variable reheat function with essentially an infinite number of reheat stages. 
         [0015]      FIG. 2  shows another embodiment  37 , which is similar to the  FIG. 1  embodiment, however, rather than having a three-way valve, conventional on/off solenoid valves  38  and  40  are controlled by the pulse width modulation signal. When a reheat branch is active, the valve  40  is opened and the refrigerant is tapped from a point  100  and is returned to point  102  of the main circuit. The pulse width modulation is controlled in a manner similar to that described with the  FIG. 1  embodiment. 
         [0016]    Valve  40  may be opened and closed to achieve a variable reheat capacity similar to the three-way valve  30  in  FIG. 1 . Valve  38  may also be operated by the pulse width nodulation signal and allows control over the refrigerant flow in a main refrigerant circuit in conjunction with the valve  40 . 
         [0017]    The  FIG. 2  schematic also provides the option of including a condenser bypass line  42  passing through a bypass valve  44  to allow rerouting of at least a portion of refrigerant around the condenser  24 . The bypass valve  44  is activated when dehumidification is desired with little or no cooling of the air. The operation and control of the bypass valve  44  is as known in the art, however the provision of the condenser bypass function that can also be operated by the pulse width modulation signal along with the variable pulse modulation control for the reheat circuit itself provides increased flexibility in operation to precisely achieve desired parameters (in terms of temperature and humidity) in an environment conditioned by the refrigerant system  37 . 
         [0018]    Obviously both embodiments shown in  FIGS. 1 and 2  may be configured either with a three-way valve or a pair of solenoid valves. Further, although only two reheat concepts are disclosed, any known reheat schematic can benefit from the invention. 
         [0019]    Pulse width modulation controls are known, and valves operated by the pulse width modulation signal are known. The present invention utilizes this known technology in a unique manner to achieve goals and benefits as set forth above. 
         [0020]    Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.