Whole-building ventilation
Whole building ventilation should dilute interior pollutants by creating an air exchange within the home. This can be achieved by one or more of three basic methods:
- Exhaust-only: Exhaust fans remove air from the building. As a result of exhausting air, outside air is sucked into the home to replace the air that was just exhausted. Replacement air typically enters through the holes in the building nearest the location of the fan, which may result in poorly distributed ventilation air. This method is also not recommended for moist climates, where pulling moisture through building assemblies is not desired.
- Supply-only: This method brings in outside air though mechanical means, generally connecting with the heating and cooling system’s ductwork. This method creates a positive pressure in the home, which is ideal for moist climates, as it will not pull in moist air through the building envelope. The disadvantage is that the incoming air is not conditioned when the HVAC system is not running and thus may cause minor comfort problems.
- Balanced: This method generally utilizes a heat-recovery ventilator or energy-recovery ventilator. Both of these devices move air out of the home and into the home, creating an air exchange that is pressure-neutral. These devices also pre-condition the air by transferring heat (HRV) or heat and moisture (ERV) from one airflow pathway to the other. This can reduce loads on the building and reduce energy consumption during extreme weather.
To determine the amount of whole-building ventilation, ASHRAE 62.2 has provided a simple equation (as well as a complex one) to determine the cubic feet per minute required.