There are other circumstances that require the control of air flow for example, to control smoke and fire spread through air spaces and building voids and shafts, but these are situations that deal with extreme events, not typical service. Convective circulation and wind washing both reduce the effectiveness of thermal insulation and thus increase energy transfer across the envelope.Ĭomfort and health – cold drafts and the excessively dry wintertime air that results from excessive air leakage directly affect human comfort, wind-cooled portions of the interior of the enclosure promote condensation which supports biological growth which in turn affects indoor air quality, airborne sound transmission control requires good airflow control, and odors and gases from outside and adjoining buildings often annoy or cause health problems. Approximately 30% to 50% of space conditioning energy consumption in many well-insulated buildings is due to air leakage through the building enclosure. Moisture control – water vapor in the air can be deposited within the envelope by condensation and cause serious health, durability, and performance problems.Įnergy savings –air leaking out of a building must be replaced with outdoor air which requires energy to condition it. Therefore, there are three primary classes of reasons why the control of air flow is important to building performance: the south-eastern States) and in some cases in cool climates, especially when air conditioning or cooling (e.g. Warm weather infiltration condensation is often a problem in warm and humid climates (e.g. Wintertime exfiltration condensation is, however, acknowledged as a common building performance problem in cold climates. Water vapor diffusion, while amenable to simple analysis, is often (but definitely not always) an insignificant source of moisture in modern building envelopes. comfort, health, energy, durability, etc.) problems. Uncontrolled air leakage through the enclosure is therefore often a major cause of performance (e.g. Air flow through the enclosure can also carry, exhaust gases, odours, and sounds through enclosures as well as mold spores and off gassing generated within the enclosure. Wintertime condensation of water vapor in exfiltrating air (or summertime condensation of infiltrating air) within assemblies is one of the two major sources of moisture in the above-grade enclosure (driving rain being the other). A large fraction of a modern, well-insulated building's space conditioning energy load is due to uncontrolled air leakage. That this statement is true for all climates has been a more recently developed awareness. It has long been recognised that the control of air flow is a crucial and intrinsic part of heat and moisture control in modern building enclosures.
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