Energy efficiency strategies for residential buildings in a subarctic climate- impact on building energy use and indoor thermal climate

Sammanfattning: A large share of the building stock in Europe is old and its poor energy performance contributes to substantial energy use and greenhouse gas emissions. The old building stock is in need of renovation that can not only improve the building energy performance but can also improve the indoor thermal climate. As there exists potential for minimizing energy use in the existing buildings, obtaining energy efficiency strategies can bring significant energy savings. Buildings situated in cold climate region use considerable amount of energy for space heating to maintain an optimum temperature indoor. Subarctic climate is characterized by cold and dark winter accompanied by heavy snow and mild short summer. In addition to that, around 15% of the annual sunshine hours occur during the coldest months from October to February so, passive solar gains contribute negligibly to space heating during this period. Therefore, there exists scope for improving energy efficiency of buildings located in the subarctic. However, there is a lack of documented studies that analyze energy efficiency of buildings in the subarctic. Scarcity of information in report and existing literature can act as a motivation for performing this research as new contribution can be made through exploration. Therefore, the aim of this study is to contribute to an increased knowledge of strategies for improving energy efficiency and indoor thermal climate of residential buildings in the subarctic climate. The research is based on evaluations of the energy performance of three case study buildings in the subarctic climate of northern Sweden.  Literature studies and workshops arranged by the partners of the research project and stakeholders helped to determine the aims and objectives of the research. Building energy simulations were performed to evaluate the energy performance and indoor thermal climate of the three case study buildings, which included: a passive house  in Kiruna (Sjunde Huset), a multifamily building from the 1980s in Piteå (Mörtgatan) and a low energy glazed highrise building in Piteå (Stadstornet). Indoor temperature was evaluated in Sjunde huset and Stadstornet using sensors and simulations.  Construction drawings and static metered energy data was collected and used as basis for performing the building energy simulations through IDA ICE. The life cycle energy analysis accounted for operational energy use (heating energy use) and embodied energy use (energy required to produce different insulation materials, windows and ventilation system).  For Sjunde huset, the results show that simulated heating energy use was comparatively higher  than the measured energy use because the building remained unoccupied during the measured year. It means that no electric appliances and occupant heat contributed in heating and neither there was heat gain from domestic hot water supply. Therefore, the heating system was using more energy to maintain an optimum temperature indoor. It was found that both the measured and simulated heating energy use fulfils the Swedish passive house criteria although it seemed from the results that it is difficult to fulfill the international passive house standard. It clarifies the strict requirement regarding the heating energy use which seems hard to achieve in the subarctic climate. For Mörtgatan, it was found that optimal solutions that can provide significant life cycle energy savings are a combination of retrofit solutions. Such solutions are replacement of existing windows to a more energy efficient type, changing the traditional extract ventilation to a heat recovery ventilation system and added insulation in external wall and roof. These combined measures can lead to achievement of the new-built Swedish energy standard. For Stadstornet, the energy performance was found considerably good for a building in the subarctic climate. Parametric simulations showed lower heating energy use in more southerly locations such as Lund, Malmö compared to more northerly location such as Stockholm and Luleå. The reason is the solar irradiation during late autumn and early spring which resulted in heat gains and eventually led to lower heating energy use in southerly locations. On the contrary, the overheating hours obtained through simulation were higher in more southerly location compared to the base location Piteå. The results provide guidance towards establishing set of energy-efficient strategies useful for building owners to adopt and implement for buildings in subarctic climate. For further research, life cycle cost analysis can add value to the existing research, as it can help building owners to make choices for adopting energy efficiency. Such analysis can also be beneficial for researchers who wants to explore  scenarios and associated cost for buildings located in such climate. 

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