A MEMS flow sensor applied in a variable-air-volume unit in a building air-conditioning system

A MEMS flow sensor was applied in a variable-air-volume (VAV) unit, composed of a butterfly damper and a flow sensor, to precisely control the supply of air in a large-scale air-conditioning network system used in a building. The MEMS flow sensor is composed of a hot-wire anemometer with an underside cavity to shorten the response time, and it was fabricated on a 25-μm-thick polyimide film by photolithography and film deposition. The total thickness of the sensor structure is only 525 μm. Four sensors were attached at 90° to each other on the inner surface of an 8-in. duct, and the outputs obtained by the sensors were averaged. The results of an experimental evaluation of the sensor are as follows. First, the averaged sensor output depends on damper angle and the distance of the sensor from the damper. Second, it is higher than that obtained by a similar sensor in a straight duct. Third, a conversion curve was derived and used to calculate flow rate from the obtained outputs of the four sensors fitted in the VAV unit.