1. device that, on proper variable sensing, initiates control signals or actions to conserve energy. Note: The economizer decision should be made at a fixed outside air temperature, or by comparing return and outside air tempera-tures, or by comparing the return and outside air total heat (enthalpy).

2. control system that reduces the mechanical heating and cooling requirement. Usually refers to use of outside air, but with logic to maintain a fixed minimum of outside air and to take only the minimum amount of outside air when the total heat of the return air exceeds the total heat of the outside air.