Method and apparatus of optimizing performance of fume hoods

An apparatus comprising

• a sensor configured to sense simultaneously total pressure within an inner chamber of a housing, and differential pressure between the inner chamber of the housing and outside of the housing;
• a computer processor which is configured to receive a signal from the sensor based on the total pressure and the differential pressure;
• a flapper connected to the housing adjacent to an exhaust opening of the housing, at least partially residing in a bell mouth of the housing leading to the exhaust opening wherein the flapper has a blade having a plurality of openings, and teeth having a plurality of openings;
• a shaft;
• wherein the blade of the flapper extends from the shaft into the bell mouth of the housing;
• a damper connected to housing at the exhaust opening of the housing, closer to the exhaust opening than the flapper, and outside of the bell mouth of the housing, wherein the damper regulates the amount of air escaping from the inner chamber of the housing through the exhaust opening;
• and wherein the computer processor is programmed by computer software stored in computer memory to control a rate at which the blade of the flapper oscillates, in response to rotation of the shaft, wherein a first end of the blade is fixed to the shaft while a second end of the blade, opposite the first end, moves freely, based on the total pressure signal from the sensor, to thereby control the direction of the flow of air from the inner chamber of the housing through the plurality of openings of the blade, through the plurality of openings of the teeth, and the computer processor also controls a rate at which the damper regulates the amount of air flow based on differential pressure signal from the sensor, to thereby maintain constant face velocity at the window opening, and out the exhaust opening of the housing.