Environmental Engineering Reference
In-Depth Information
Figure 11.6
Air leakage sites on a single-family house with basement substructure.
story house on a basement. Major structure-related leakage areas include the
sole plate where the building frame is fastened to the substructure, and
cracks around windows, doors, exterior electrical boxes, light fixtures,
plumbing vents, and various joints. Leakage also occurs through exhaust
fans, supply/return ducts, and combustion appliance flues. Leakage is par-
ticularly pronounced when combustion appliances such as furnaces, hot
water heaters, and fireplaces are in operation. Leakage can also occur
through duct systems which provide heating and cooling when duct runs
are in crawlspaces, attics, and garages.
The size of leakage areas and their distribution in a building determine
the magnitude of infiltration and exfiltration air exchange when measured
under similar environmental conditions. They also determine the nature of
air flow patterns into and out of buildings.
Building leakage potentials are commonly assessed using fan-pressur-
ization or blower-door techniques. By pressurizing buildings with a fan
installed into a test door, the overall leakage potential of residential buildings
can be determined to identify leakage areas that need to be caulked or sealed.
Such leakage characterization is commonly conducted in weatherization
programs which target low-income housing.
II. Measuring building air exchange rates
Building air exchange rates (ACH) associated with wind and thermally
induced pressure flows, as well as those associated with mechanical venti-
