Significance and Use
Airtightness—Building airtightness is one factor that affects building air change rates under normal conditions of weather and building operation. These air change rates account for a significant portion of the space-conditioning load and affect occupant comfort, indoor air quality, and building durability. These test methods produce results that characterize the airtightness of the building envelope. These results can be used to compare the relative airtightness of similar buildings, determine airtightness improvements from retrofit measures applied to an existing building, and predict air leakage. Use of this standard in conjunction Practice E1186 permits the identification of leakage sources and rates of leakage from different components of the same building envelope. These test methods evolved from Test Method E779 to apply to orifice blower doors.
Applicability to Natural Conditions—Pressures across building envelopes under normal conditions of weather and building operation vary substantially among various locations on the envelope and are generally much lower than the pressures during the test. Therefore, airtightness measurements using these test methods cannot be interpreted as direct measurements of natural infiltration or air change rates that would occur under natural conditions. However, airtightness measurements can be used to provide air leakage parameters for models of natural infiltration. Such models can estimate average annual ventilation rates and the associated energy costs. Test Methods E741 measure natural air exchange rates using tracer gas dilution techniques.
Relation to Test Method E779—These test methods are specific adaptations of Test Method E779 to orifice blower doors. For nonorifice blower doors or for buildings too large to use blower doors, use Test Method E779.
Single-Point Method—Use this method to provide air leakage estimates for assessing improvements in airtightness.
Two-Point Method—Use this method to provide air leakage parameters for use as inputs to natural ventilation models. The two-point method uses more complex data analysis techniques and requires more accurate measurements (Tables X1.1 and X1.2) than the single-point method. It can be used to estimate the building leakage characteristics at building pressure differences as low as 4 Pa (0.016 in. H2O). A variety of reference pressures for building envelope leaks has been used or suggested for characterizing building airtightness. These pressures include 4 Pa (0.016 in. H2O), 10 Pa (0.04 in. H2O), 30 Pa (0.12 in. H2O), and 50 Pa (0.2 in. H2O). The ASHRAE Handbook of Fundamentals uses 4 Pa.
Depressurization versus Pressurization—Depending on the goals of the test method, the user may choose depressurization or pressurization or both. This standard permits both depressurization and pressurization measurements to compensate for asymmetric flow in the two directions. Depressurization is appropriate for testing the building envelope tightness to include the tightness of such items as backdraft dampers that inhibit infiltration but open during a pressurization test. Combining the results of depressurization and pressurization measurements can minimize wind and stack-pressure effects on calculating airtightness but may overestimate air leakage due to backdraft dampers that open only under pressurization.
Effects of Wind and Temperature Differences—Calm winds and moderate temperatures during the test improve precision and bias. Pressure gradients over the envelope caused by inside-outside temperature differences and wind cause bias in the measurement by changing the building pressure differences over the test envelope from what would occur in the absence of these factors. Wind also causes pressure fluctuations that affect measurement precision and cause the data to be autocorrelated.
Scope
1.1 These test methods describe two techniques for measuring air leakage rates through a building envelope in buildings that may be configured to a single zone. Both techniques use an orifice blower door to induce pressure differences across the building envelope and to measure those pressure differences and the resulting airflows. The measurements of pressure differences and airflows are used to determine airtightness and other leakage characteristics of the envelope.
1.2 These test methods allow testing under depressurization and pressurization.
1.3 These test methods are applicable to small indoor-outdoor temperature differentials and low wind pressure conditions; the uncertainty in the measured results increases with increasing wind speeds and temperature differentials.
1.4 These test methods do not measure air change rate under normal conditions of weather and building operation. To measure air change rate directly, use Test Methods E741.
1.5 The text of these test methods reference notes and footnotes that provide explanatory material. These notes and footnotes, excluding those in tables and figures, shall not be considered as requirements of the standard.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific hazard statements see Section 7.
