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Building airtightness (also called envelope airtightness) can be defined as the resistance to inward or outward air leakage through unintentional leakage points or areas in the building envelope. This air leakage is driven by differential pressures across the building envelope due to the combined effects of stack, external wind and mechanical ventilation systems.〔G. Guyot, F. R. Carrié and P. Schild, “Project ASIEPI – Stimulation of good building and ductwork airtightness through EPBD,” 2010〕 Airtightness is the fundamental building property that impacts infiltration (the uncontrolled inward leakage of outdoor air through cracks, interstices or other unintentional openings of a building, caused by pressure effects of the wind and/or stack effect).〔M. Limb, "Technical note AIVC 36- Air Infiltration and Ventilation Glossary," International Energy Agency energy conservation in buildings and community systems programme, 1992〕 An airtight building has several positive impacts〔Building Energy Codes, “Building Technologies Program: Air Leakage Guide”, U.S Department of Energy, September 2011〕 when combined with an appropriate ventilation system (whether natural, mechanical, or hybrid): * Lower heating bills due to less heat loss, with potentially smaller requirements for heating and cooling equipment capacities * Better performing ventilation system * Reduced chance of mold and rot because moisture is less likely to enter and become trapped in cavities * Fewer drafts and thus increased thermal comfort A number of studies have shown substantial energy savings by tightening building envelopes.〔〔〔 The ASIEPI project technical report on building and ductwork airtightness estimates the energy impact of envelope airtightness in the order of 10 kWh per m2 of floor area per year, for the heating needs in a moderately cold region (2500 degree-days).〔 Experimental data showing the energy savings of good airtightness were also published by the Building Research Establishment in the UK〔D. Butler and A. Perry, "Co-heating Tests on BRE Test Houses Before and After Remedial Air Sealing," Building Research Establishment〕 as well as REHVA journals' special issue on airtightness.〔R. Coxon, “Research into the effect of improving airtightness in a typical UK dwelling,” The REHVA European HVAC Journal-Special issue on airtightness, vol. 50, no. 1, pp. 24-27, 2013.〕 They conclude 15% of the space conditioning energy use can be saved in the UK context going from 11.5 m3/(m2·h) @50 Pa (average current value) down to 5 m3/(m2·h) @50 Pa (achievable). Given its impacts on heat losses, good building airtightness may allow installation of smaller heating and cooling capacities. Conversely, poor airtightness may prevent achieving the desired indoor temperature conditions if the equipment has not been sized with proper estimates of infiltration heat losses. From an energy point of view, it is almost always desirable to increase air tightness, but if infiltration is providing useful dilution of indoor contaminants, indoor air quality may suffer.〔M.H. Sherman and R. Chan, "Building Airtightness: Research and Practice", Lawrence Berkeley National Laboratory report NO. LBNL-53356, 2004〕 However, it is often unclear how useful this dilution is because building leaks cause uncontrolled airflows and potentially poorly ventilated rooms although the total building air exchange rate may be sufficient.〔L. Mouradian and X. Boulanger, "QUAD-BBC, Indoor Air Quality and ventilation systems in low energy buildings," AIVC Newsletter No2, June 2012〕 This adverse effect has been confirmed by numerical simulations in the French context which has shown that typical mechanical ventilation systems yielded better indoor air quality with tighter envelopes.〔 Air leaking out of the envelope may cause condensation damage as its temperature drops below dew point.〔TightVent Europe: Building and Ductwork Airitightness Platform, http://tightvent.eu/〕〔J.Langmans "Feasibility of exterior air barriers in timber frame construction", 2013〕 ==Air leakage pathways== Leakage typically occurs at the following locations on the building envelope:〔F.R. Carrié, R. Jobert, V. Leprince: “Contributed report 14. Methods and techniques for airtight buildings”, Air Infiltration and Ventilation Centre, 2012〕 * Junctions between walls and other walls or floors * Junctions between window frames and walls * Electrical equipment * Access doors and other wall penetrations Common leakage sites are listed in the Figure and explained below: # Junction lower floor / vertical wall # Junction window sill / vertical wall # Junction window lintel / vertical wall # Junction window reveal / vertical wall (horizontal view) # Vertical wall (Cross section) # Perforation vertical wall # Junction top floor / vertical wall # Penetration of top floor # Junction French window / vertical wall # Junction inclined roof / vertical wall # Penetration inclined roof # Junction inclined roof / roof ridge # Junction inclined roof / window # Junction rolling blind / vertical wall # Junction intermediate floor / vertical wall # Junction exterior door lintel / vertical wall # Junction exterior door sill / sill # Penetration lower floor / crawlspace or basement # Junction service shaft / access door # Junction internal wall / intermediate floor 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Building airtightness」の詳細全文を読む スポンサード リンク
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