Thermal coupling of leakage air flows and heating load in building components and buildings.

Simulation models basing on 2-dimensional finite-difference approach were developed for the steady-state and dynamic analyses of the thermal coupling of leakage airflows and building components. The considered types of leakage flows were crack flow and filtration through porous materials. At building level analyses a static flow network approach was applied in order to calculate airflow balance of a building, while for the thermal coupling of convective heat flows of air leakages and transmission heat flows of leaky structures a 2-dimensional modified transfer-function approach was applied. It is suggested in the paper that the value of transmission heat losses should be corrected by a factor, modified Nusselt number, in order to take into account the heat recovery effect of leakage airflows. Depending on leakage airflow rate, thermal properties and dimensions of the structure as well as the leakage route, the correction factor of transmission heat losses can be as low as 0.60. The correction factor of total heat losses can be 0.86, respectively. According to measurements the correction factor of transmission heat losses was 0.35-0.85, while it for total heat losses was 0.86- 0.96. The heat recovery effect is approximately the same for both infiltration and exfiltration. At the building level, the correlation between airtightness, leakage distribution, air change rates and thermal performance of a single family house was analyzed. The house was supplied with mechanical exhaust ventilation system and the supply air was taken in as leakages through building envelope. The calculated annual heating energy consumption of the building was 6-9 % less compared with the calculation results where the heat recovery effect was not taken into account. If the heat recovery effect was taken into account in calculation of transmission heat losses, the average correction factor was 0.85- 0.90. Actual values depend on airtightness and leakage distribution of building envelope.