How window ventilation behaviour affects the heat resilience in multi-residential buildings

Abstract

To what extent is the overheating risk in dwellings affected by the individual window ventilation behaviour of residents? To answer this question six window ventilation profiles, obtained from surveys, are implemented in building performance simulation models of a large panel construction and a “Gründerzeit” multi-residential building located in Germany. The impacts of these different ventilation types are analysed for the top floor dwellings, including wind and temperature gradient-driven infiltration in the simulation. The results demonstrate the tremendous impact of the chosen window ventilation profile on overheating intensity. Low overheating is obtained if windows and room doors are fully opened, even if this is only done in the early morning and evening hours. Tilted windows are not adequate to ensure sufficient air exchange and lead to high overheating and critical room temperatures up to 35 °C. Regarding the building type, the above described effects are more pronounced in the “Gründerzeit” building whereas the large panel construction building exhibits a much higher heat resilience. However, overheated neighbouring dwellings shows a pronounced influence on overheating for the large panel construction building. Both findings can be attributed to building physics. In addition, the impact of meteorological conditions like tropical nights are found to significantly reduce the efficacy of passive cooling by nocturnal window ventilation. The overall findings clearly that a more accurate representation of natural ventilation is essential to draw correct conclusions from overheating assessments when using building performance simulation. In contrast, applying simplified natural ventilation boundary conditions in current overheating standards entails the risk of misinterpretations.