Sep 24, 2009, 14:55 GMT
Berlin - The vision of a house which makes such efficient use of energy that those living in it never have to pay for their own heating has been a reality ever since the 1980s, a decade which spawned the first low-energy homes.
Experiments have also been carried out with houses which functioned without fossil fuels. Until recently however there was no going beyond the baseline of net zero-energy consumption and net zero carbon dioxide emissions annually.
Today it is possible to build homes which actually produce more energy than they consume, while at the same time earning money for the owner.
The basis for such a dwelling is what the Germans call a passive house, which is defined by Sabine Stillfried of the Passive House Institute in Darmstadt as a house in which a comfortable living temperature is maintained without the use of any heating or air-conditioning systems.
In Germany a state-run bank awards grants to people who opt to build a dwelling along such futuristic, eco-friendly lines. In order to qualify for the name passive house, the building has to adhere to rigourous energy efficiency standards which can result for example in a net heating oil consumption of less than 1.5 litres of oil a year per square metre of living area.
Yet much more can be achieved: 'More than 10 years ago a zero-energy house was developed in conjunction with the Fraunhof Institute for Building Physics,' said Klaus-Dieter Schwendemann who works the firm of Weber Haus in Baden-Wuerttemberg state. Key features of the concept were good insulation, a southern aspect to catch the sun and warmth and the optimal use of regenerative energy. Unfortunately, the extra equipment needed made such houses expensive.
'Since solar panels were used for the heating there was a need for a long-term storage device so that owners could weather the winter months,' said Schwendemann. This meant installing a 20,000-litre storage tank which could easily occupy half of the basement floor area of the house and in many cases the extra cost of the tank and heavy-duty insulation it needed were not necessarily recouped through energy savings.
One of the first energy-plus houses in Europe was built by architect Rolf Disch near his home in the south-west city of Freiburg as a test-bed for solar systems. Dubbed Heliotrop, the house rotates so that the photovoltaic panels on the roof catch the sun.
The start-up costs for such a house are more than for a conventional dwelling. 'The cost of an energy plus house works out at about 15,000 euros (22,000 dollars) more than for a comparable standard building,' said Tobias Bube who works for the Disch architectural office. At the same time, the photovoltaics on the roof and outside walls generate more electricity than is needed to power the house.
Under German energy laws, the owner of a house like this is paid at a standard rate for the power which the house feeds into the national grid and buys back the electricity needed by the building at a cheaper rate. This results in a considerable profit for the home owner of around 3,000 euros annually. At the same time, the cost of heating and warming water for an energy-plus house are reasonable too - around 150 euros a year for a living area of between 130 and 140 square metres.
'One further advantage of an energy-plus home is that it can be built in phases, with modules added as you go along,' said Schwendemann. This makes the project easier to finance. For those on a tight budget it is possible to start off with a passive house which can be gradually upgraded to an energy-plus building.
Internet: http://en.wikipedia.org/wiki/Zero-energy_building
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