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Isolating The Building Thermal Envelope

The evaluation of the thermal integrity of building envelopes by infrared scanning tech-niques is often hampered in mild weather because temperature differentials across the envelope are small. Combining the infrared scanning with positive or negative building pressures, induced by a "blower door" or the building ventilation system, considerably extends the periods during which meaningful diagnostics can be conducted. Although missing or poorly installed insulation may lead to a substantial energy penalty, it is the search for air leakage sites that often has the largest potential for energy savings. Infrared inspection of the attic floor with air forced from the occupied space through ceiling by-passes, and inspecting the interior of the building when outside air is being sucked through the envelope reveals unexpected leakage sites. Portability of the diagnostic equipment is essential in these surveys which may include access into some tight spaces. A catalog of bypass heat losses that have been detected in residential housing using the combined infrared pressure differential technique is included to point out the wide variety of leakage sites which may compromise the benefits of thermal insulation and allow excessive air infiltration. Detection and suppression of such leaks should be key items in any building energy audit program. Where a calibrated blower door is used to pressurize or evacuate the house, the leakage rate can be quantified and an excessively tight house recognized. Houses that are too tight may be improved with a minimal energy penalty by forced ventilation,preferably with a heat recuperator and/or by providing combustion air directly to the furnace.