Thermal effects of air leakages on the thermal performance of building structures.

Simulation of the thermal performance of a building to take account of uncontrolled infiltration shows that infiltrating air on a leakage path is efficiently warmed up, especially if infiltration flow rates are low. For allowable infiltration flow rates with respect to thermal comfort, (0.5 -0.7 dm3/sm), the heating is 25 - 60 per cent of the temperature difference between the outside and inside air. For the longest leakage path, the incoming air is even near to the room air temperature. The warming up of infiltrating air depends on the infiltration flow rate and the length of the leakage path, as well as the thermal properties of the structure around the crack. The calculation method presented can be used to study the principle of the warming up of infiltrating air, and of leakage from inside to outside.