Drivers of winter indoor temperatures in Swedish dwellings: Investigating the tails of the distribution

Residential indoor climate is a key factor for occupant comfort, health and wellbeing, while also affecting the buildings' energy demand. A strong focus has been traditionally placed on low winter indoor temperatures in dwellings due to their considerable health impacts. However, there is a trend towards high and stable indoor temperatures, which also have significant implications. This paper investigates the drivers of winter indoor temperatures by analysing the following three metrics of measured temperatures in a sample of 1039 Swedish dwellings: a) level, through the sample dwellings' standardised indoor temperatures at 5 degrees C outdoor temperature, b) daily variation, through the standard deviation of the indoor temperature and c) shape, using daily indoor temperature profiles derived from cluster analysis. The study explores the association of these metrics to building-, dwelling- and occupant-related parameters. The analysis shows that 80% of the standardised indoor temperatures were above 21 degrees C, with one third of the latter being above 23 degrees C, while 82% of dwellings had constant temperatures throughout the day. High winter indoor temperatures were more evident in middle-placed apartments in multi-family buildings connected to district heating and in better insulated single-family houses. High temperatures were also associated with experiencing draft from windows, too warm conditions in winter and difficulty to control the indoor temperature, but not with the overall thermal comfort assessment which was very positive in both the high and low temperature tails. Long-term adaptation effects, established norms and comfort expectations are discussed as important confounding factors in the development of residential indoor temperatures.

Automated summary

Residential indoor climate significantly impacts occupant comfort, health, and energy demand. This study in Sweden found that a majority of indoor temperatures were above 21 degrees C, with one third exceeding 23 degrees C, and most dwellings maintained constant temperatures throughout the day. High winter indoor temperatures were more common in middle-placed apartments in multi-family buildings and well-insulated single-family houses, and were associated with draft from windows, overheating, and difficulty in temperature control. However, overall thermal comfort assessment was positive regardless of high or low temperatures.