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The Active House


This article was published in the Guardian on May 21, 2009.

Lystrup is the last place you’d expect to find the solar-powered home of the future. The suburbs of Denmark’s second city, Aarhus, are grey from street to sky. The spring sun, hidden behind a bank of clouds which didn’t break once on my week long visit, barely seems strong enough to run a pocket calculator, let alone meet the energy needs of a family of four. But it is here that a dream of zero carbon living is being realised.

The world’s first Active House stands at the crest of an estate. Its south-facing roof is covered in solar panels and solar cells, which between them harness more than enough power to keep the occupants warm and the appliances running. In around thirty years, if designers have got their sums right, the excess electricity flowing from the house to Denmark’s grid will have cancelled out the energy costs of building it, leaving a non-existent footprint on the earth’s resources.

It was conceived as a response to the Passive House, which has set the standard for sustainable living in the last decade. These homes, which are popular in Austria, Germany and Scandinavia, rely on incredibly effective insulation, plus a heat exchanger that warms fresh air on the way in during winter. A true Passive House has no conventional heating system, because in theory, it doesn’t need one. In practice, owners tend to install back-up, because it’s no fun being cold, no matter how virtuous you feel.

Rikke Lildholdt, project manager for the Active House, shows me round. “Many people have the idea that if it’s ecological, it must be difficult, you have to grow your own vegetables or whatever,” she says. “This is about living a comfortable life in a house that produces more energy than it uses.”

Unlike Passive Houses, which are typically only open to the south, there are huge windows on all sides. The cynic in me notes that VELFAC, best known in Britain for its skylight brand, Velux, had good reason to commission a design that uses so much glass – at 40% of the floor surface area, the house has roughly double the average window space. Even on this grim, drizzly day, the rooms are remarkably bright. The triple-glazing cannot match well insulated walls, but there’s less need to turn the lights on.interior-house

The solar panels provide hot water for under floor radiators, but when the sun doesn’t shine, an electric pump kicks in. Eight months a year, the solar cells produce excess energy to sell to the grid. In the winter months, the house buys back electricity – from renewable sources, of course. When a mass market battery car finally reaches the market, there will be a charger for it in the garage and energy to spare.

The interior climate is controlled by a computer, linked to a thermostat, which opens and closes windows according to the temperature, season and time of day. Chief engineer Amdi Worm assures me that there is a manual override. “If they open a window, then in an hour or so the window will close automatically a little,” he says. “If they really insist, they can choose to do it again, but I’m sure that the house will tell them that the way they are handling it is not energy efficient.”

Sverre Simonsen, his wife Sophie and their two children, aged eight and six, will be the first family to live in this nanny home. “We have never been especially conscious about environmental issues,” Simonsen says, “but my wife often asks ‘why don’t they invent something new?’ And this is definitely something new.” They move in for a year on July 1 and have promised to keep a diary of their experiences.

The house has two flat screen televisions and a washing machine, but no tumble dryer, in order to meet an energy consumption target of 4,000 KWh per year – a little less than the Danish average. Giving that up is “one of the few sacrifices we have to make, because with kids there’s a lot of washing,” Simonsen says. The dryer in their current home broke down a month ago, so they’re getting used to hanging clothes on a line.

Lildholdt is coy about how expensive the house was to build, describing it as “the Rolls-Royce version” and insisting that as a commercial product, it would cost no more than a regular three-bedroom detached. When pressed, she tells me the bill came to around £500,000.

At the moment, it is just a concept. “Hopefully we’ll set a standard for what houses will look like in the future. But this is an experiment,” she says. “We’re not building houses, we’re building an idea.” Seven more Active Houses are under construction around Europe. If it can work under the leaden skies of Aarhus, it can work in Britain.