Minimum air volume control device

Claim 1

In an air distribution system for delivering conditioned airflow at a preselected substantially constant temperature to a plurality of zones wherein the temperature at each of said zones is controlled by varying the volume of airflow to said zone; an air throttling means for varying the volume of conditioned air delivered to said zone; an electric motor operator coupled to said air throttling means to drive the latter in opposite directions to increase and decrease the volume of airflow; a thermally responsive thermostat control switch disposed to sense temperature in said zone and connected with said motor operator for actuating the latter to vary airflow to maintain substantially constant temperature in said zone; a first override control switch connected to said motor operator, said first override control switch effective when actuated to override said thermostat control switch and actuate said motor operator to stop further decrease in the volume of airflow to thereby establish a minimum volume of conditioned airflow delivered to said zone, said first override switch including means for sensing the volume of airflow to said zone and for actuating said first override switch whenever said volume of airflow drops to a predetermined minimum level; an electrically controlled heat source in said zone; and a second override control switch connected with said heat source and operable to activate said heat source upon being actuated by said airflow sensing means whenever said volume of airflow drops to a preselected level, said preselected level of airflow being greater than said predetermined minimum level.