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This paper examines the sensitivity of the predicted air infiltration rate to measured building airtightness data and the wind exposure index determined from site inspection. Results of airtightness tests in New Zealand houses are presented to indicate the range of leakage resistance for components (windows, doors, and chimneys, etc.), for solid materials (such as wall and ceiling lining materials), and for cracks separating major components such as the floor and walls. The distribution of leakage opening is discussed in relation to the driving forces of wind- and stack-induced airflows and also in relation to New Zealand styles of house building.
The building site exposure class must be determined in order that standard wind engineering formula can be used to calculate site wind speeds from meteorological weather data recorded some distance away. In the New Zealand situation, with high wind speeds and modest indoor-outdoor temperature differences, predicted natural air infiltration rates are particularly sensitive to site exposure details. Examples of measured and predicted air change rates are given for a number of houses together with comment on the sensitivity to experimental error.
air infiltration, airtightness, air leakage in buildings
Scientist, Building Research Association of New Zealand, Private Bag, Porirua, New Zealand