Passive houses

The energy in a "passive house" comes from heat sources such as fridges, cookers and computers, and by utilising solar radiation.

The idea behind a ”passive house” is that it does not require a traditional heating system run, for example, on oil, wood or electricity. Instead, the energy should come from other heat sources, such as fridges, cookers and computers, and by utilising solar radiation. These heat sources may be supplemented by other measures which minimise the heat loss from the building.

A passive house is extremely well insulated and there is very little heat loss through walls, doors, windows and roofs. To prevent the house being ventilated through, for example, cracks in the walls, a plastic layer is added between the inner wall and the insulation (climate screen). Ventilation losses can be further reduced by mechanical intake and exhaust air systems using heat exchangers. Since the householder does not have to invest in a traditional heating system, he can make the most of the reduced costs by adding further insulation to walls and windows. A solar collector on the roof can add the energy required for heating water.

But in the Swedish climate, it is difficult to cope completely without some form of heating. For this reason, passive houses are also fitted with a very small heating system: an electric heater connected to the intake air system, with the output no greater than that of a hairdryer or a vacuum cleaner. It is also possible to use a heat pump which takes warmth from the outside air and heats the hot water and the intake air in the house. The latter solution is common in Germany, where it is also used in schools and offices.

In Sweden, passive houses have been built in a number of locations, including Lindås outside Gothenburg and Glumslöv in the province of Skåne. The 20 terraced houses in Lindås have an average annual energy consumption for heating, hot water and household electricity of approximately 70 kWh per square metre. In Glumslöv, plans have been drawn up for an annual energy consumption of 60 kWh/square metre, compared with the National Swedish Board of Building, Planning and Housing’s requirement for an annual consumption of 110 kWh/square metre in new houses.

Skanska builds energy-efficient apartment blocks

The construction company, Skanska, is involved in several projects involving passive houses, including the self-heated terraced houses in Glumslöv, which are regarded as one of the pioneering projects for the technique in Sweden. Skanska also builds large passive buildings. In partnership with Karlstad bostadsaktiebolag (KBAB), the company has created Sweden’s largest energy-efficient apartment complex – the twelve-storey Seglet block. In Alingsås, Skanska carried out energy- efficient refurbishments on 300 rented apartments built in the 1970s, as well as some new construction. This is one step towards Alingsåshem’s target of ensuring that its property portfolio has an energy system which is sustainable in the long term.

House without electricity bills

The construction company NCC has developed a concept house which it calls ”the house without energy bills”. It consists of two parts: firstly a well-insulated, energy-saving passive house, secondly an energy-generating roof, known as an energy spoiler, added to the outside. The spoiler is made up of solar cell panels with a sufficient surface area fitted at the optimum angle towards the sun. The spoiler also protects against the cooling effects of the wind and creates protective courtyards in its lee between the house and the spoiler. NCC is currently involved in the construction of Sweden’s largest passive house, the Hamnhuset building in Gothenburg, on behalf of Älvstrandens Utvecklings AB. NCC has made the decision to produce its own passive houses in all regions in Sweden. The Group has also expanded the energy declaration concept into a more comprehensive climate declaration.

This article was first published in Advantage Environment printed in February 2008

Facts about Skanska

  • Skanska is one of the world’s leading construction companies. The Group currently has 56,000 staff in selected domestic markets in Europe, the USA and Latin America.
  • Sales in 2006 amounted to SEK 126 billion.

Facts about NCC

  • NCC is one of the leading construction and property development companies in the Nordic region.
  • Sales in 2006 amounted to SEK 56 billion, and the company had around 22,000 employees.

The energy consumption of all new houses must be calculated

As of 1 July 2007, energy consumption calculations must be carried out for newly-built houses, which must meet the National Swedish Board of Building, Planning and Housing’s requirement of a maximum of 110 kWh/sq.m. per year. Before this date, an estimated average U-value was sufficient. The U-value is a measure of the heat flow through a building, which shows how well a house retains heat. Better insulation generates a lower value. To obtain a U-value, calculations are carried out for walls, roofs, foundations, windows, doors and the areas of these.

In calculating the energy consumption of a house and examining heating, household electricity and hot water figures, thermal bridges, the number of people in the house, the location of a house, points of the compass and other factors are also taken into account.

More information on passive houses

A number of basic requirements must be met before the passive house concept can be applied to a building. The aim of this is to ensure that the meaning of the word will be quality-assured in the marketing and communication of the construction and management process.

In Sweden, the Forum for Energy-efficient Buildings has developed a voluntary specification for passive houses2. The specification is based on the German equivalent, but has been adapted to Swedish conditions, partly because we have a colder climate. The specification lays down that the heating requirement, expressed as added output, is minimised in a passive house. The building should achieve a sufficiently high thermal comfort level by utilising the incoming ventilation air. The term thermal comfort does not only refer to the temperature in a room, but also to how that temperature is distributed. Downdraught, for example, is not an example of good thermal comfort. The specification also limits the total consumption of household electricity, hot water and heating, but the home must, at the same time, meet high standards for a comfortable indoor environment.

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