Abstract: The residential structure ventilating apparatus disclosed herein employs a variable speed exhaust fan. The speed is responsive to a sensor which detects air temperature at the exhaust port. The fan is energized when the sensed air temperature rises above a first preselectable temperature and the external environmental air is cooler that the air at the exhaust port. The fan speed is increased progressively from about one-half full speed at the preselected turn on temperature to full speed at a predetermined higher temperature. The fan is turned off when the exhaust port temperature falls below a second preselected temperature, lower than the first preselected temperature or when the external environmental temperature rises above the inside temperature, the fan speed being essentially constant between the first and second preselected temperatures.

Abstract: The fan speed controller disclosed herein is particularly useful in the cooling of electronic equipment and provides a feedback control characteristic from an exhaust air temperature sensor such that the change in outlet temperature over the range of air flow rates is substantially equal to the change in temperature rise of typical heat generating devices in electronic equipment over that same range. Accordingly, device temperature is maintained substantially constant over a range of varying input air temperatures. Preferably, the controlled fan includes a d.c. motor which is energized in a pulsed d.c. mode to prevent stalling or instability at low flow rates.

Abstract: The fan speed controller disclosed herein mounts directly on a fan whose speed is to be controlled and provides electronic speed control circuitry mounted in a disk-like enclosure aligned with the fan hub. The enclosure is compartmented and apertured to provide a representative air flow past a temperature sensitive element employed by the circuitry. Fan speed is controlled as a function of air temperature above a sharply defined minimum to provide effective cooling with minimal noise generation.