Patent ID: 7963749

Claim:
A fan unit for an air delivery system for delivering conditioned air to a space, the fan unit comprising: a centrifugal fan wheel supported in the air delivery system for rotation about an axis of rotation; a fan inlet to direct air from the air delivery system upstream of the fan wheel into the fan wheel; a fan motor for driving rotation of the fan wheel; a variable speed control operatively associated with the motor for controlling the speed of the fan wheel in response to the condition of the air in the space; an unloading disk supported inside the fan wheel to vary the available wheel width that is exposed to air flow through the fan, the disk being axially movable relative to the axis of rotation of the fan wheel bidirectionally between an open position and a closed position in response to air pressure, wherein in the open position the air flow through the fan wheel is substantially unobstructed and wherein in the closed position air flow through the fan wheel is substantially obstructed, and wherein the disk is configured to vary the wheel width that is exposed to air flow through the fan as the disk is moved between the open and closed position; and an actuator operatively engaged with the unloading disk, the actuator comprising a biasing member tensioned to hold the disk in an intermediate position between the open and the closed position and to yield in response to air pressure on the disk so that, as air flow through the fan wheel increases, the disk is pressed toward the open position from the intermediate position.