Airtightness and natural ventilation : a case study for dwellings in Poland

Recently, in the Polish building sector, there has been a conflict between ventilation techniques and a strong tendency toward increasing building airtightness. Despite this increasing airtightness, the ventilation process in the majority of these buildings still depends on the uncontrolled supply of air through gaps in windows combined with natural exhaust air ducts. To improve energy efficiency in the building sector, more airtight envelopes constructed of modern materials of low air leakage coefficient are being constructed. These coefficients are lower (tighter) than commonly used standard values. While some contractors argue that houses need to breathe and thus do not construct airtight shells, others adopt a high airtightness strategy in which case controlled ventilation is necessary. The main objective of this paper is to present an analysis of airtightness and ventilation rates in typical Polish dwellings. A case study involving a ground floor and top floor apartment in a three storey apartment building is described. This includes an analysis of airtightness, metabolic carbon dioxide concentration and simulations of natural air flow. The results show that, as construction becomes more airtight, continued reliance on natural leakage openings for ventilation is not sufficient. In this case study building, for example, ventilation was inadequate and carbon dioxide concentrations in excess of 3000 ppm could occur. To provide adequate natural ventilation, additional window vents are needed. Ideally these should be coupled to CO2 and/or humidity sensors to control the rate of airflow according to demand.