air exchange

The work presented is the continuation of the research on the probabilistic modelling of air infiltration carried out by the author over many years. The approach has consisted in considering uncertainties coupled to the climatic/environmental input data to the physical models, or to the threshold criteria for a good performance. The concept of risk/reliability evaluation of building/environment system performance was proposed and exemplified for the air exchange model.  

Old buildings that represent and maintain historic values often have poor indoor conditions and energy efficiency. The aim of this work was to evaluate the influence of building structures on airtightness and energy performance of certain historic building types. In this study on-site measurements, dynamic simulation and questionnaires were used. Significant differences between the levels of the airtightness of the historic houses exist in the studied region. No statistically significant correlation was found between the structure types and the envelope tightness.

The airtightness of the building envelope was studied in field measurements in recently constructed experimental small test buildings. Two types of research studies were carried out: the effect of special air tight sealing and the experimental determination of air exchange rate (h-1) under real operating conditions. In very small buildings with many joints between materials and construction the role of the air tight sealing is very important; the experiments show changes in measured air tightness.

Indoor environment quality in buildings strongly depends on the proper ventilation. Still a large amount of single- and multifamily buildings are equipped with the natural ventilation system.
When the air exchange in the building is estimated, the main uncertainty concerns the air tightness of the given object. This parameter is used as the input data when the ventilation air flows in building are simulated, and therefore a reliable determination of the air tightness is essential.

The energy consumption of a building is evaluated by neglecting the heat loss which can occur when the air passes through the envelope. However, recent studies showed that air leakage plays asignificant role by affecting the thermal performances of walls and the energy consumption. Moststudies have focused on the quantification of air leakage flows through the building shell, withoutaddressing the problem of the heat exchange between this airflow and the construction materials asthe air passes through the envelope.

Research and test results presenting measurements of air infiltration rates in residences are reviewed. In particular, comparison of electric and combustion heating shows (on average) infiltration rates to be 0.1 to 0.25 higher for residences with combustion heating.