Effects of Nearly Zero Energy Building Renovation on the Thermal Comfort in a Swedish Multi-apartment Building

Abstract

A considerable share of the existing building stock in Europe is expected to last for at least the next 30 years and has low energy performance. These buildings have high space heating demand and give low thermal comfort for the occupants. This study investigates the effects of nearly zero energy building (NZEB) renovation on the thermal comfort levels in a typical Swedish multi-apartment building in Växjö, Sweden. Dynamic simulation is performed to assess the thermal comfort levels in the building before and after implementing the energy efficiency measures (EEMs). The percentage of discomfort hours for three representative apartments before and after renovation are modelled with the building’s existing heating, ventilation, and air conditioning (HVAC) system, without active cooling device. The building before the notional renovation had final energy use of 133 kWh/m² year for space heating, domestic hot water (DHW) and facility electricity. The results show a significant reduction in the hours of discomfort after the NZEB renovation during winter period, demonstrating the effectiveness of the thermal envelope improvements in enhancing the building’s thermal comfort during the heating season. On the contrary, during the summer period, the situation dramatically changes after the NZEB renovation, with the operative temperatures exceeding the 26°C threshold in 60%, 97% and 99% of the occupancy hours for the months of June, July and August, respectively. Notwithstanding summer overheating, the total percentage of discomfort hours for the whole year decreased by 61% when the EEMs were modelled for the studied building. This study suggests the need to integrate thermal comfort improvement strategies such as, installation of external shading devices and cooling devices, when renovating buildings to the NZEB standard.