an environmental control unit for regulating humidity and temperature and removing certain constituents from air in a generally confined volumetric region comprises an enclosure having an actuable heating element associated with a blower driven dry air flow path extending through a plurality of parallel high thermal conductivity tubes to an outlet opening to the confined volume . water may be sprayed by an actuable pump from a reservoir onto a high - surface area evaporative covering on the tubes . a blower driven evaporation path in heat exchange and non - fluid exchange relationships to the dry air flow path extends generally transverse to the tubes about the evaporative covering and through controllable vents to humidify by expelling evaporation path air into the confined volume , and to dehumidify or cool by condensing room air moisture within the chilled tubes . a temperature and humidity responsive control unit is integrally coupled to selectively actuate the controllable vents , the blowers , the pump and the heating element . heat loss energy from the dry flow path blower motor drives a refrigeration loop including chill tubes coupled to reduce reservoir water temperature to enable cool air exiting the unit to drop below the wet - bulb temperature of the covered tubes . this arrangement is compact , requires low power , and is economical , but can purify and dehumidify , humidify , cool or heat air in a room with substantial efficiency .