Inventors:
Robert B. Smith - Madison WI
International Classification:
F24F 1304
Abstract:
A variable air volume ventilation system (10) is disclosed in which the output air flow from a supply fan (13), delivered through a supply duct (11) to various places within a building, is returned by a return duct (15) through a return fan (17) and then through a connecting duct (18) back to the inlet (20) of the supply fan (13). The static pressure in the supply duct (11) is sensed by a static pressure sensor (40), and the output signal indicative of pressure is used by a variable frequency power supply (44) to provide power to drive the fan motors (36, 37) at a frequency inversely proportional to the difference between the sensed static pressure and a desired static pressure, thereby adjusting the flow through the ventilation system to match demand. Outside make-up air is provided through an outside air duct (50) and is fed into the return duct (15) at a position (52) near the inlet (16) of the return fan (17). The air flow through the outside air duct is controlled to a constant flow rate which matches the expected rate of exhaust air from the building so that the flow of air into and out of the building is balanced despite changes in the rate of flow through the ventilating system in response to demand.