Distribution and variation of indoor temperatures in apartment blocks with individual metering and billing of space heating costs—on building, apartment, and room level

Abstract

A good indoor thermal climate is important. To reduce energy demands for space heating, individual metering and billing (IMB) for space heating costs is common, though not yet in Sweden. To obtain a better picture of the thermal climate conditions, the distribution of the measured indoor temperatures was investigated in each apartment in 14 apartment blocks with a total of 419 apartments. All blocks had an IMB system for space heating with a traditional feed-forward control. In the studied buildings, temperatures were measured in each living room and each bedroom, and were registered at 2.1 m over floor level, every 15 min over a period of 12 months. Seasonal mean temperatures, standard deviations, skewness, and kurtosis are presented for apartment blocks. For one, with 75 apartments, these values are monthly, and for January and April, the temperature range for each apartment is presented in boxplots. It can be concluded that there are variations in temperature between different apartments: both variations in temperature levels and in temperature ranges. The overall conclusions are that differences in indoor temperature are achievable for different apartments in an apartment block with a certain set point temperature and that the temperatures are not dependent on an apartment’s location in the building. Both the building owner’s goal to keep a certain average temperature for energy saving reasons, and the tenants’ goals, possibility to vary the indoor temperature at individual apartment level, seems to be possible to reach. The measured temperatures are close to being normally distributed, though they have a mild negative skewness and a mild kurtosis during heating periods. The results support that indoor temperatures can be modeled as normally distributed in energy simulations of buildings. Further, it can be seen that temperature variations follow the seasons. The temperatures on individual apartment level show that there is a tendency for warm apartments to be warm all the year round and vice versa. There are also daily variations, with a magnitude of 0.3–0.4 °C and with 0.1–0.3 °C difference between weekdays and weekends. Every single indoor temperature measurement for a whole year covering all seasons as a function of outdoor temperature is presented in iso-plots. Temperature levels are mainly within the limits of standards for thermal comfort, thus showing that a thermal satisfying indoor climate is met in these apartment blocks with IMB. It also seems that it was possible to achieve the desired temperatures irrespective of the apartment’s location.