Zero Energy Buildings : A concept review and case study of terraced houses in Sweden

Abstract: The building sector consumes about 40 % of the total global primary energy, 60 % of the total electricity and accounts for about 30 % of all greenhouse gas emissions (UNEP, 2015). The zero energy building (ZEB) concept is considered as a step towards reducing the environmental impact of the building sector (European Parliment, Council of the European Union, 2010). This work has reviewed the concept of ZEBs by looking at three different definitions available in Sweden: nearly ZEB by Boverket (the Swedish Board of Housing, Building and Planning), ZEB by Sveriges Centrum för Nollenergihus (SCNH), Swedish center for ZEBs, and net primary ZEB by Skanska. The proposal by Boverket may form a basis for the statutory requirements for all new buildings in Sweden after 2020. The work also comprised a performance analysis, as well as a review of the development process, of terraced houses in Sweden built by Skanska according to their net primary ZEB definition.The overall objective was to facilitate the implementation of future ZEB projects. This was done by highlighting differences among the three definitions and how the implementation of Boverket’s proposal will impact other definitions. The performance analysis and process review pinpointed problem areas, acknowledging both technical, social, and economic aspects linked to the ZEB concept, which can be improved in order to successfully implement ZEBs in the future.To compare the definitions, a framework developed by Sartori et al. was used (Sartori, et al., 2012). A deductive approach was then used where a numerical analysis of one the terraced houses energy system was compared to simulations. The focus for the definition and performance analysis was the energy use of the building. In order to take other perspectives into account, the occupant experience as well as the building development process were investigated. This was done using an inductive approach by conducting semi-structured qualitative interviews with occupants and employees of the construction company.The definition comparison showed that there are important differences among the three definitions. The main differences were the system boundaries, the net balance and the energy efficiency requirements. It also showed that Skanska’s definition is directly affected by Boverket’s proposal, while SCNH’s definition may be indirectly affected.The performance analysis together with the interviews with occupants showed that uncomfortable indoor temperatures were the main problem in the buildings of study. The conclusion was that the specifications of a ZEB has to be acknowledged when choosing technical installations in a building. Furtherly, information to the occupants is seen as an important aspect in order to help them maintain a comfortable indoor environment in their homes.Interviews with employees showed that some problems may have occurred due to a lack of understanding of and commitment to the ZEB concept. Furtherly, all involved in a ZEB project needs to be informed of the concept and energy targets and encouraged to successfully reach goals and to avoid miscommunication.For “pilot projects” like the one studied in this report, it is suggested to include detailed design earlier in the project, in order to include cost for specific solutions needed for a ZEB. Interviews with occupants indicated that some may be willing to pay more for a ZEB building, therefore it is recommended to investigate the value of marketing this.