Variable-air-volume diffuser, actuator assembly and method

Abstract

An adaptive control device ( ) and method ( ) for control of the operation of an actuator ( ), and particularly thermally-powered actuator ( ) of the type used in a variable-air-volume diffuser ( ). The preferred adaptive control device is an expert system circuit which controls a heater ( ) provided on a thermally-powered actuator ( ) to implement an adaptive process ( ) in which a sensed variable, such as room air temperature, is driven toward a target temperature control range (±0.25° F.). Most preferably, the process steps ( ) include driving the room air temperature toward a gross (broader) temperature control range (±1.0° F.) by moving a diffuser damper assembly ( ) to a substantially fully open or substantially fully closed position. Thereafter, and while inside the gross temperature control range, the process steps ( ) include adjustments to the position of the damper assembly ( ) are made only when a sensed parameter, preferably the supply air flow rate, is in a stable condition. Most preferably, the damper ( ) is temporarily “kicked” farther open or farther closed than necessary, to minimize hysteresis effects, and then adjusted to a posiiton which tends to drive the room air temperature into the narrower, targeted temperature control range.