Uncertainties in Fan Pressurization Measurements Available to Purchase

The ASTM Method for Determining Air Leakage Rates by Fan Pressurization Test (E 799-87) measures the airtightness of building envelopes using fan pressurization. Uncertainty is introduced in the process from the uncertainty of the airflow and pressure measurements as well as from nonlinearities in the system to be measured. This paper analyzes the precision and bias associated with making a measurement using E 779 in typical field situations. Model specification (or modelization) errors may also contribute significantly to the overall uncertainty in the estimates of the 4 Pa leakage; the sources and sizes of these modelization errors interact with the instrumentation errors in making a fan pressurization test. Insufficient field data exist to fully include the effects of modelization and other low-pressure phenomena, but the current standard can nevertheless by improved by tightening the instrumentations and procedural specifications and by judicious choice of pressure measurement stations.