Abstract: A system and method for introducing external air into an enclosure having an exhaust fan for removing internal air at an outflow rate. A sensor measures a quantifiable characteristic which is indicative of the outflow rate. Based on the measured quantifiable characteristic, a controller determines a speed of a makeup air fan that results in the inflow rate matching the outflow rate, and opens a damper and runs the makeup air fan at the determined speed. For example, the sensor may measure an amount of electrical current flowing to the exhaust fan, and low and high speed exhaust fan values are stored in a memory, and corresponding low and high makeup air fan speeds are set. The controller then controls operation of the makeup air fan based on the amount of current flowing to the exhaust fan and the corresponding makeup air fan speed to match the inflow and outflow rates.

Abstract: A system and method for introducing external air into an enclosure having an exhaust fan for removing internal air at an outflow rate. A sensor measures a quantifiable characteristic which is indicative of the outflow rate. Based on the measured quantifiable characteristic, a controller determines a speed of a makeup air fan that results in the inflow rate matching the outflow rate, and opens a damper and runs the makeup air fan at the determined speed. For example, the sensor may measure an amount of electrical current flowing to the exhaust fan, and low and high speed exhaust fan values are stored in a memory, and corresponding low and high makeup air fan speeds are set. The controller then controls operation of the makeup air fan based on the amount of current flowing to the exhaust fan and the corresponding makeup air fan speed to match the inflow and outflow rates.