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The building sector is one of the sectors that consume the most energy in Sweden. In order to deal with this problem Swedish government aims to reduce the energy consumption in the building sector 50% by 2050. Another ambitious goal set by the Swedish government is zero greenhouse gas emissions by 2040.

Most of the buildings in Sweden were built during 1950-1990 before the first energy regulations were voted in Europe. A high percentage of these buildings date to 1950 and the majority of them are multi family buildings. Apartments built during this period are now requiring major renovation and retrofitting measures in order to comply with the energy and indoor environment regulations.

Despite the urgent need for retrofitting expressed above, the retrofitting ratio in Sweden was 0.88% in 2013, so the number of buildings that haven’t gone through any energy retrofitting is still high making it clear that the biggest opportunity for energy savings lies within the existing building stock and that the retrofitting ratio has to enhance in order to achieve the governments energy and emission goals for 2050.

In this study a new patented innovative energy retrofitting method is studied within IDAICE simulation program in order to find the heat load and the energy savings after applying this method. The simulated building is a three story multi family building with building characteristics from 1950 and the simulation takes place in two different climate zones (Stockholm and Umeå). Three different insulation thicknesses were tested creating three different variant cases in order to investigate the difference in energy savings an increase of the insulation thickness will bring. This retrofitting method except installation of extra facade insulation includes roof insulation, replacement of the air handling unit with heat recovery ventilation whose pipe system runs through the insulation behind the radiators of each zone and replacement of the old windows with triple glazed low U-value windows.

The results show a high reduction in heat supplied after the retrofit, 66.4% room unit heat reduction in Stockholm and 59.6% in Umeå and even higher energy reduction 68.3% in Stockholm and 68.9% in Umeå. The CO2 emission reduction was 58.4% in Stockholm and 60.9% in Umeå. The difference in room unit heat, energy consumption and CO2 emissions among the Variant cases varies between 1-2%. The explanation for such a small difference lies in the fact that the only difference among these cases is the insulation thickness of the facade. The thermal comfort was also investigated and has shown an increase in hours of dissatisfaction after the retrofitting and as the insulation increased due to overheating. However it must be stated here that the reason behind the increase in dissatisfaction is that no window shading or window opening schedules were taken into account in the simulation maximizing the solar heat gains of the building.

The study concludes that the studied retrofitting method is very efficient and the studied building achieves higher energy reduction than the goal that the Swedish government has set for 2050. The results of this study bring this retrofitting method ahead of the 2050 energy reduction goals set by the Swedish government with significant reductions in CO2 emissions and heat load.