Adaptive makeup air system and method for tight enclosures

A makeup air system for introducing external air into a building enclosure to minimize underpressurization of the building enclosure, the building enclosure having an exhaust fan for removing internal air from the building enclosure at an outflow rate, the makeup air system comprising:

• an intake extending through an exterior wall of the building enclosure and connected to an air passage operable to direct the external air to enter the building enclosure;
• a damper configured to open and close the air passage;
• a heater positioned downstream of the damper and configured to temper the external air flowing through the air passage;
• a filter unit configured to remove undesirable matter from the external air flowing through the air passage;
• a makeup air fan positioned in the air passage and configured to move the external air into the enclosure at an inflow rate;
• a sensor configured to measure an amount of electrical current flowing to the exhaust fan and to communicate a signal representative of the amount of electrical current, wherein the amount of electrical current is indicative of the outflow rate;
• and a controller configured to receive the signal from the sensor, open the damper, start the heater, run the makeup air fan at a speed such that the inflow rate of external air into the enclosure approximately matches the outflow rate of internal air out of the enclosure, and thereby minimize underpressurization of the building enclosure.

A method of introducing external air into a building enclosure to minimize underpressurization of the building enclosure, the building enclosure having an exhaust fan for removing internal air from the building enclosure at an outflow rate, the method comprising:

• receiving a signal from a sensor configured to measure an amount of electrical current flowing to the exhaust fan, wherein the signal is representative of the amount of electrical current, and the amount of electrical current is indicative of the outflow rate;
• storing in an electronic memory a low speed value received from the sensor when the exhaust fan is operating at a low speed;
• setting a low speed value for a makeup air fan at which the inflow rate approximately matches the outflow rate for the low speed value of the exhaust fan;
• storing in the electronic memory a high speed value received from the sensor when the exhaust fan is operating at a high speed;
• setting a high speed value for the makeup air fan at which the inflow rate approximately matches the outflow rate for the high speed value of the exhaust fan;
• and controlling with an electronic controller operation of a damper configured to open and dose an air passage operable to direct the external aft to enter the building enclosure, and operation of the makeup aft fan positioned in the air passage and configured to move the external air into the building enclosure at the inflow rate, thereby minimizing underpressurization of the building enclosure, wherein when the low speed value for the exhaust fan is received from the sensor the controller causes the makeup aft fan to operate at the low speed value for the makeup aft fan, when the high speed value for the exhaust fan is received from the sensor the controller causes the makeup air fan to operate at the high speed value for the makeup air fan, and when an intermediate value for the exhaust fan is received from the sensor the controller causes the makeup air fan to operate at a proportionally intermediate speed value for the makeup air fan.