Monitoring the change of indoor environmental conditions of refurbished buildings in Milan

The energy performance gap, i.e. the difference between measured and predicted behaviour of buildings, is one of the main challenges for the building simulation community and it is highly relevant due to the increasing number of building renovations fostered by recent European Directives. In fact, occupants have a high influence on the building energy use for space heating and cooling, especially in refurbished buildings. The user behaviour may be indirectly investigated by monitoring the indoor environmental conditions before and after the refurbishment. However, in the literature there is a lack of monitoring studies that study the impact of user habits on the predicted energy savings for retrofitted buildings. This study contributes to filling this gap by analysing the air temperature and relative humidity monitored in twenty apartments in the city of Milan (Italy) during two consecutive years. Among them, eight were refurbished during the spring/summer period between the two monitored heating seasons. The analysis of the measured data shows that there is a slight increase in the average indoor air temperature of refurbished apartments. Moreover, the application of a simple hygrometric balance show that users are likely to increase air change rate in naturally ventilated buildings after their refurbishment. Finally, Energy Plus simulations of two monitored apartments showed that such changes in the indoor environmental conditions lead to significant variation in the energy needs for space heating.