Probabilistic analysis of air infiltration in a single family house.

A Probabilistic model of air change rate in a single family house based on full-scale measurements has been developed. The probability of air change rate exceeding certain prescribed limits (risk of improper ventilation or excessive heat flow) is evaluated by utilising the distribution function based on calculated air flow rate. In this way the results are expressed in terms of the R-S model generally used in the safety analysis of structures. In particular, the probability of excessive andlor insufficient air infiltration can be expressed in terms of safety index P to describe the reliability of the building with respect to natural ventilation. The probability density functions for the air change rate have been established for different wind directions Two methods of reducing the risk of unhygienic conditions have been studied. The first one is based on introducing extra small openings uniformly distributed over the building envelope and providing a fully naturally ventilated system. The second method consists in introducing mechanical exhaust ventilation system coupled with natural ventilation. Probability distributions of air change rates have been analysed for these two cases.