air tightness evaluation

There are several methods for measuring air tightness that may result in different values and sometimes quite different uncertainties. The two main approaches trade off bias and precision errors and thus result indifferent outcomes for accuracy and repeatability.  To interpret results from the two approaches, various questions need to be addressed, such as the need to measure the flow exponent, the need to make both pressurization and depressurization measurements and the role of wind in determining the accuracy and precision of the results.

Air tightness is an important property of building envelopes.  It is a key factor in determining infiltration and related wall-performance properties such as indoor air quality, maintainability and moisture balance.  Air leakage in U.S. houses consumes roughly 1/3 of the HVAC energy but provides most of the ventilation used to control IAQ.  There are several methods for measuring air tightness that may result in different values and sometimes quite different uncertainties.