PTAC dehumidification without reheat and without a humidistat

A method of operating a refrigerant system to control an air temperature associated with a comfort zone, wherein the refrigerant system is selectively operable in a cooling mode and a dehumidifying mode to provide the comfort zone with air that may include some outside air, wherein the refrigerant system includes a compressor;

• a fan selectively operable at a faster speed and a slower speed to move the air at different flow rates;
• and a fresh air damper selectively movable to an open position for introducing the outside air into the comfort zone and a substantially closed position for substantially inhibiting the outside air from entering the comfort zone, the method comprising:
• establishing a setpoint temperature, an upper temperature limit, a lower temperature limit, and a sub-cooling temperature limit, wherein the setpoint temperature is between the upper temperature limit and the lower temperature limit, and the sub-cooling temperature limit is less than the lower temperature limit;
• in the cooling mode, controlling the compressor and the fan to regulate the air temperature between the upper temperature limit and the lower temperature limit;
• in the dehumidifying mode, controlling the compressor, the fan, and the fresh air damper to regulate the air temperature between the upper temperature limit and the sub-cooling temperature limit and doing so regardless of any change in the humidity of the air;
• in the dehumidifying mode, running the fan at the faster speed when the air temperature is above the setpoint temperature and is decreasing;
• in the dehumidifying mode, running the fan at the slower speed when the air temperature is below the setpoint temperature and is decreasing;
• and
• in the dehumidifying mode, closing the fresh air damper as the air temperature is decreasing toward the sub-cooling temperature limit.

A refrigerant system charged with a refrigerant and being operable to provide a comfort zone with air that includes at least one of a recirculated air and an outside air, the refrigerant system comprising:

• a compressor for compressing the refrigerant;
• an evaporator through which the compressor forces the refrigerant to flow in order to cool the air;
• an electric heater for heating the air;
• a fresh air damper being selectively movable to an open position for introducing the outside air into the comfort zone, and a substantially closed position for substantially inhibiting the outside air from entering the comfort zone;
• a fan for forcing the air across the evaporator and across the electric heater;
• a temperature sensor providing a temperature feedback signal that varies in response to an air temperature of the comfort zone;
• an input for providing a plurality of commands including a cooling setpoint temperature, a heating setpoint temperature, a heating command, a cooling command and a dehumidify command;
• and
• a controller operatively coupled to receive the temperature feedback signal from the temperature sensor, operatively coupled to the input to receive the plurality of commands, and operatively coupled to control the compressor, the fan, the electric heater and the fresh air damper such that:
• a) in response to the heating command, the controller controls the electric heater and the fan to regulate the air temperature of the comfort zone at about the heating setpoint temperature;
• b) in response to the cooling demand, the controller controls the compressor, the fan and the fresh air damper to regulate the air temperature of the comfort zone at about the cooling setpoint temperature;
• and
• c) in response to the dehumidify command, the controller controls the compressor, the fan, and the fresh air damper to help maintain the air temperature between an upper temperature limit and a lower temperature limit, wherein the following is true:
• (i) the cooling setpoint temperature is closer to the upper temperature limit than to the lower temperature limit;
• (ii) the fan runs at a faster speed and the fresh air damper can be open when the air temperature is between the cooling setpoint temperature and the upper limit while the air temperature is decreasing;
• and
• (iii) the fan runs at a slower speed, the electric heater is deactivated, and the fresh air damper is at the substantially closed position when the air temperature is between the cooling setpoint temperature and the lower temperature limit while the air temperature is decreasing.