The new EU directive EPBD2, Energy Performance of Buildings Directive (recast), adopted 2010, specifies that all new buildings must be so-called nearly-zero-energy-buildings by year 2021. A nearly-zero-energy-building is a building with very high energy performance, which is provided with renewable energy to a large extent. How this should be interpreted and where the requirement is to be placed on energy usage is up to each country to decide. There is currently a debate about this going on in Sweden, and the Swedish Energy Agency has been asked to design a strategy to meet the goals for nearly-zero-energy-buildings. The environmental goal for reducing the carbon footprint by 2020 and 2050 is also closely linked to this question. In order to set a reasonable level of requirement for energy use, both economic-, technical- and environmental aspects must be taken into account. This report studies a new building area in Västra Sörhaga, Alingsås, to find out how to build it in order to achieve the standard for nearly-zero-energy-buildings. A wider study is also made to find out where it is reasonable to set the level of requirements for energy use for nearly-zero-energybuildings throughout the country. The energy calculation software VIP-energy is used for simulating four buildings, off different sizes, and studying their energy consumption.
Where the system boundary is placed has a big impact on the outcome of the measurement of a building's energy use. EPBD2 determines that the building's energy performance should be a priority, before the supply of renewable energy sources. In order to attain a building with a high energy performance, an optimized construction performance is first required, with an airtight and highly insulated building envelope and a ventilation system with heat recovery, and then an efficient energy system and an efficient energy supply should be ensured. When this is reached, the focus can then be put on making sure that the energy supplied is renewable to as large extent as possible. It is therefore important to optimize the building performance first and then take the energy supply system and energy sources into account, whereby the building also has a low primary energy use and is supplied with as much renewable and environmentally friendly energy as possible.
The Swedish Energy Agency’s proposes an energy requirement of half the current energy requirements as a goal for nearly-zero-energy-buildings. One example of energy reducing measures that would result in achieving this standard for a cottage in Kiruna is: elimination of thermal bridges, heat exchange of the ventilation air with 90 % efficiency, windows with a heat transfer coefficient of 0.7 W/m2K and doors with 0.6 W/m2K, airtightness of 0.2 l/s,m2 and a window proportion of 10 %. This is a stretch of what is possible to achieve with today’s technology. Heat exchangers with an efficiency of 90 % exist today, but since they require defrosting in cold climate, which decreases the real efficiency, it could be difficult to achieve in Kiruna. However, with future technological developments and experiences of building low energy buildings, this would be a reasonable standard for nearly-zero-energy-buildings throughout the country. It would also be advantageous to divide the country into more climate zones, or at least divide them more equally. The variation in energy use for a building is today much larger in the most northern climate zone than in the southernmost.
thermal bridges, heat exchange of the ventilation air with 90 % efficiency, windows with a heat transfer coefficient of 0.7 W/m2K and doors with 0.6 W/m2K, airtightness of 0.2 l/s,m2 and a window proportion of 10 %. This is a stretch of what is possible to achieve with today’s technology. Heat exchangers with an efficiency of 90 % exist today, but since they require defrosting in cold climate, which decreases the real efficiency, it could be difficult to achieve in Kiruna. However, with future technological developments and experiences of building low energy buildings, this would be a reasonable standard for nearly-zero-energy-buildings throughout the country. It would also be advantageous to divide the country into more climate zones, or at least divide them more equally. The variation in energy use for a building is today much larger in the most northern climate zone than in the southernmost.
It would be possible to use the passive house standard requirements for nearly-zero-energybuildings in the southern parts of Sweden, but it is not recommended in the north. Especially small buildings are very difficult to build in the passive house standard in cold climates today. To reach passive house standard for a small building in the northern most part of Sweden could require an indoor temperature no higher than 20°C and an airtightness of 0.1 l/s,m2. This is not reasonable, mostly because it is common to have a higher indoor temperature in Sweden and because this very high air tightness cannot be guaranteed today. The area in Västra Sörhaga, Alingsås, is realistic to build with requirements of passive house standard because it is in climate zone III, and that would almost certainly also satisfy the standard for nearly-zero-energy-buildings. If the area was built in the passive house standard it would result in a total specific energy consumption of around 50 kWh/m2 per year, which is 45 % of the energy use for the same area built to meet today’s energy requirements.
The national board of housing’s proposed energy requirements for the revision of the construction rules for 2011 are deemed not to be ambitious enough and makes it very difficult to achieve environmental objectives by 2020. Further studies need to be made on the economic viability of buildings with low energy use, and in order to assess the amount of energy in a uniform manner, primary energy factors need to be developed. These should include both efficiency in manufacturing, energy form and energy sources. Energy sources, in turn, should be judged by the degree of renewability, access and storage capacity. Construction of low-energy buildings requires a large change in the existing construction market and energy structure. We have to start now to achieve this by 2021!