Evaluation of overheating risks and passive cooling measures in low energy Swedish dwellings

Abstract: Overheating in buildings is becoming a major concern and cause for various health issues. Existing research and previous studies on the issue were examined to acquire relevant information about the definition of overheating, its possible causes, and the heath impacts it could have on human health. The review included data on the current status of thermal comfort and overheating regulations in Sweden and neighbouring countries and information on the history of heatwaves and future climatic trends. Further research was conducted to gain more knowledge on passive cooling methods that could be implemented into buildings and new constructions to mitigate overheating to safer thresholds. This study is divided into two major parts, the first part includes an analysis of overheating risks during the months of July and August of the year 2018, using data measurements for temperature and relative humidity recorded in 150 low energy detached houses located in various cities across Sweden. The measurements were analysed according to three Swedish and international standards which define overheating differently. It was concluded that overheating was occurring in most dwellings for prolonged hours particularly those located in urban areas. The results were evaluated according to CIBSE’s overheating threshold which considered the annual occupancy schedule and showed higher overheating occurrences when compared to FEBY’s threshold which considered overheating between April and September. Boverket’s suggested threshold was associated with the highest overheating occurrences due to setting a single temperature threshold of 26° C, regardless of occupancy or the specification of a period of time. Novel parameters were also proposed to evaluate the duration of exposure to overheating. In the second part, using building performance simulation program IDA-ICE, a simulated model of a study case based in Sundsvall, Sweden was used to investigate the possibility of incorporating passive cooling measures and determining their efficiency in mitigating indoor overheating. The final results revealed that opening windows for prolonged periods of time at night-time, as well as employing cross-ventilation can significantly reduce overheating to minimum thresholds. Lowering the g-value of the glazing and applying external shading yielded results within FEBY’s threshold for some cases, whereas only relying on solar control through internal shading did not generate desirable outcomes.