Energy savings potential of building envelope refurbishment in Swedish single-family houses

Abstract: Sweden has ca. 2 million single family houses (SFH) housing 52% of the population and representing 44.6% of the overall heated floor area. SFHs account for 39.5% of the total heating demand in Sweden. Energy consumption in older SFHs is much higher than in new ones. SFHs built in the 1960s consume ca. 170% of the annual heating energy demand of SFH built in the 2010s. This study aims to explore the energy savings potential in existing SFHs built between 1960 and 1975 in Sweden through refurbishment of elements of the building envelope and analyze their energy and costefficiency of these measures. Furthermore, it aims to study the effects of variations in climate in Sweden on the energy and cost efficiency of these measures. A hypothetical un-refurbished SFH was modeled and defined using energy simulation tool IDA-ICE based on statistical data and relevant literature reviews. Variations in climate between regions of Sweden were analyzed and 4 suitable locations were suggested to place the hypothetical model in. Suitable building envelope refurbishmentmeasures were selected for the elements of the building envelope. These measures were (a) adding extra insulation to the outer side of external wall (b) replacing and insulating the slab on ground (c) insulating the cold attic on top the existing horizontal slab, and (d) replacing the exiting external doors and windows. Suggested U-values for renovated SFHs from Boverket were used as a goal for the suggested refurbishment measures to reach. Energy performance simulations were performed to estimate savings potential in energy used for heating purposes for the un-refurbished building and each of the suggested measures. Life cycle cost (LCC) study using UPV' method was performed over a lifespan of 30 years. The results of the energy performance simulation showed energy savings potential in all the suggested measures, ranging from ca. 6% to ca. 20% with the measure of replacing the external doors and windows had the most savings potential. The study highlighted rate of improvement in U-values, surface area within which heat losses are occurring, status of thermal bridges, and differences in temperature between air and soil as factors effecting the energy savings potential. The results showed no significant effects of changing locations on the savings potential. LCC analysis showed that the measure of adding extra insulation in the cold attic is the most cost-efficient. It also showed that higher heating demands in colder climate led to more significant role for the energy savings potential in determining the cost efficiency, while the initial costs played a bigger role in warmer climate. The study also showed that choosing materials and products with longer lifespan in addition to having a good energy savings potential may lead to a change in results on the cost-efficiency analysis. The study concludes with highlighting the energy savings potential in building envelope refurbishment and the importance of including both and energy and cost efficiency perspectives when choosing refurbishment measures for existing SFH.