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Over the past ten years, the measurement of the airtightness of single-family building envelopes has made the transition from laboratory research tool to practitioner's (home energy auditor's) tool. Along with this transition have come ASTM and CGSB standards for fan pressurization measurements, and an ASHRAE standard for single-family building airtightness levels. Two major sources of uncertainty identified for fan pressurization measurements of effective leakage area (the air leakage parameter specified in the ASTM and ASHRAE standards) were the statistical uncertainty associated with extrapolating fan pressurization measurements down to 4 Pa and the individual flow and pressure uncertainties induced by the wind and by instrumentation inaccuracies. This report analyzes the effects of wind on fan pressurization measurements and describes a series of experiments performed to examine a methodology that combines two techniques for reducing these effects. The methodology for reducing the effects of wind on fan pressurization measurements, which employs four-surface pressure averaging and time averaging of pressure and flow data, is examined using multiple fan pressurization measurements at a single site. The results of these experiments are compared with a similar experimental examination of the standard ASTM procedure under calm conditions. It is shown that the combined surface-averaging/time-averaging technique has significantly lower scatter at calm conditions (3 versus 6.5%), and that the scatter remains below 11% up to a windspeed of 5 m/s. Another significant result is that surface pressure averaging always causes a negative bias in the leakage area measured at high windspeeds. Despite this bias, it is concluded that surface-pressure averaging generally should provide better leakage area measurements compared to using single-pressure-tap measurements.
air leakage, field measurement, measurement uncertainty, pressure measurement, residential buildings, wind
Lawrence Berkeley Laboratory, Berkeley, CA
University of Alberta, Edmonton,