High latent refrigerant control circuit for air conditioning system

Air conditioning apparatus with controlled latent cooling comprising a compressor having a suction side to which a working fluid is supplied as a vapor at low temperature and a discharge side from which the working fluid is discharged as a vapor at a high pressure and elevated temperature;

• a condenser heat exchanger supplied with said vapor at high pressure for exhausting heat from the working fluid and discharging the working fluid as a liquid at high pressure;
• an indoor evaporator coil supplied by a liquid line from said condenser heat exchanger with said working fluid at high pressure, including expansion valve means for reducing the pressure of said working fluid to liquid at said low pressure and heat exchanger means in which heat from a stream of indoor air is absorbed by said low pressure liquid such that said working fluid is converted to a low pressure vapor and said low pressure vapor is passed to the suction side of said compressor;
• and means for reducing the relative humidity of the indoor air leaving said indoor coil, including a sub-cooler heat exchanger having an inlet coupled to said condenser heat exchanger to receive said high pressure liquid and an outlet coupled to the expanding valve means of said indoor evaporator, said sub-cooler heat exchanger being positioned in the indoor air stream leaving said indoor evaporator heat exchanger means for subcooling said working fluid and raising the temperature of said leaving indoor air stream, and control means operative, when cooling and dehumidification are called for, to route the high pressure liquid working fluid first through said sub-cooler heat exchanger and then to said indoor evaporator coil, and when cooling-only is called for, to bypass the sub-cooler heat exchanger and route the high pressure liquid working fluid from said condenser heat exchanger directly to said evaporator coil;
• wherein said liquid line has a first branch coupled to the expansion valve means of said evaporator coil and a second branch coupled to the inlet of said sub-cooler heat exchanger, and a second liquid line couples the outlet of said sub-cooler heat exchanger to the expander valve means of said evaporator coil, said second liquid line including a flow restrictor device, and said control means including a liquid line solenoid valve interposed in said first branch and control circuit means coupled to said solenoid valve for opening said solenoid valve when cooling only is called for and closing said solenoid valve when cooling and dehumidification are called for;
• and wherein said control circuit includes a thermostat having a cooling lead that supplies a signal to actuate said compressor when a cooling setpoint temperature is reached;
• and a humidity control line coupled to said cooling lead including a humidistat in series with control lead means for actuating said liquid line solenoid valve.