1. An enthalpy computing system for use in controlling an environmental condition of a room, comprising: a temperature sensor having an output RT indicative of temperature; a humidity sensor having an output CS indicative of humidity; an electronic circuit having the output RT as a first input and the output CS as a second input, wherein the electronic circuit provides an output h of the form: EQU h=K1+K2*F1(RT)+K3*F2(CS)+K4*F1(RT)*F2(CS); a source of energy controlled air; a source of external air; a damper, connected to the source external air and further connected to the source of energy controlled air, wherein a position of the damper determines how much of the external air and the energy controlled air is provided to the room, and wherein the position of the damper is based on the output h.