Thermal environment in eight low-energy and twelve conventional Finnish houses

• Perceived IEQ was as slightly better in the low-energy than conventional houses.
• The occupants want lower room temperatures than ISO 7730 optimal temperature.
• The occupants adjust room air temperatures to their liking in single house.
• Significant difference between the mean temperature and humidity was not found.

We assessed the thermal environment of eight recently built low-energy houses and twelve conventional Finnish houses. We monitored living room, bedroom and outdoor air temperatures and room air relative humidity from June 2012 to September 2013. Perceived thermal environment was evaluated using a questionnaire survey during the heating, cooling and interim seasons. We compared the measured and perceived thermal environments of the low-energy and conventional houses. The mean air temperature was 22.8 °C (21.9–23.8 °C) in the low-energy houses, and 23.3 °C (21.4–26.5 °C) in the conventional houses during the summer (1. June 2013–31. August 2013). In the winter (1. December 2012–28. February 2013), the mean air temperature was 21.3 °C (19.8–22.5 °C) in the low-energy houses, and 21.6 °C (18.1–26.4 °C) in the conventional houses. The variation of the air temperature was less in the low-energy houses than that in the conventional houses. In addition, the occupants were on average slightly more satisfied with the indoor environment in the low-energy houses. However, there was no statistically significant difference between the mean air temperature and relative humidity of the low-energy and conventional houses. Our measurements and surveys showed that a good thermal environment can be achieved in both types of houses.