Feasibility of ventilation heat recovery in retrofitting multi family buildings.

The work concentrated on estimating the effects of building leakages and terrain parameters on the air infiltration. The analysis was performed mainly using a multi zone airflow model Movecomp with which the building and its ventilation system could be described in detail. The computations were performed for a flat in a 418-storey building. The highest infiltration occurred in an untight two-facade flat in open terrain. The calculations gave valuable information on the effect of the location of the leakage. The vertical distribution of the leakage had the most significant effect on infiltration. On the other hand, the tightness of the floorlceiling and the apartment door did not have significant effect on the whole building infiltration, nor did the number of storeys. The knowledge gained from these simulations will be used in designing sealing techniques for existing multi-family buildings. The results revealed a significant reduction in the economic feasibility of heat recovery ventilation when the air-tightness of the envelope decreased. It was estimated that, in Finnish climate and energy prices, the air-tightness of the envelope should be in the range of 2-3 air changes at 50 Pa, or better, in order to air to air heat recovery to be economically feasible in existing buildings. This means that the renovation of the ventilation system to include air to air heat recovery should almost always be connected with sealing of the building envelope.