Click on the image to view photos of the house's exterior.
So how do you power a self-governing house?
In total, the Home for Life ought to use about 60 percent of the energy of a traditional single-family house in Denmark: 15 kWh per square meter per year for lighting, household appliances, and running the active components of the house and 32 kWh/m² per year for hot water and heating. It's the latter where the Home for Life really stands out: Its heating consumption is just half that of an ordinary Danish home. Once all the systems are fine-tuned, we estimate that the house will generate a surplus of about 9 kWh/m² per year.
The shape of the house made a big difference. Its overall surface area was kept to a minimum because that is a major factor in heat loss. In addition, the tip of the roof is tilted to the north, which increases its surface facing south. That side of the roof is covered with solar panels, solar thermal collectors, and skylights, each of which plays an important part in determining the house's overall energy budget.
First, let's look at the electricity. The 50 m² of polycrystalline solar panels generate about 5500 kWh a year. That's 20 percent more electricity than the house needs, although in winter it does draw some power from the electricity grid. These solar cells, with 13 percent efficiency, aren't the best on the market, but they're a good compromise for the price.
Then there's the heating, which comes in through the windows or the solar thermal collectors. The 6.7 m² of collectors catch the sun's rays on copper plates installed on the lowest part of the roof. Underneath the plates, copper pipes circulate a fluid that absorbs the heat of the plates, converting 95 percent of the sun's energy into heat. The collectors can catch indirect sunlight, too, so the house still has heat on cloudy days.
Should more interior heating be needed, we use an air-source heat pump. In one common configuration of this type of pump, air passes through a heat exchanger placed outside the house to transfer the air's warmth to a liquid. The liquid travels to an electrically powered compressor inside the house, which applies pressure to raise the fluid's temperature further. In general, a heat pump is far more energy efficient than conventional oil or electric heating, and it has lower CO2 emissions, too. But the pump's performance depends heavily on the amount of heat contained in the air; when it's cold outside, these heat pumps aren't efficient.
To avoid that problem, we used a heat pump designed by another VKR subsidiary, Sonnenkraft, which uses the solar collectors to preheat the cold winter air before it reaches the heat pump. The pump can now easily produce 20 °C water even when the outside air is below freezing. After the liquid is compressed, the heat travels through pipes in the floors and to radiators. In all, our solar collectors and pump can produce about 8000 kWh's worth of heat a year.
Generating power and heat was only part of our design goal, though. Equally important to us was the wish to pay off the energy invested in the materials. To meet that challenge, we chose materials that require less energy to produce. We used wood for most of the construction, with a few steel beams added for load-bearing parts of the structure. We made the facades and roof out of natural slate rather than brick, which has a larger energy footprint.
Click on the image for a larger view.
Our careful innovations and calculations didn't always line up with the family's preferences, however. As the weather grew colder, the Simonsens complained that they weren't warm enough. We ended up raising the temperature of the heating under the floors by 2 degrees, and we stopped lowering the room temperatures at night.
The net result was, of course, an increased energy load. Fortunately, we'd overestimated how much electricity the Simonsens would use for lighting and appliances, so we reduced our estimates for those activities from 3.5 watts per square meter to 2 W/m². Then again, they sometimes kept the blinds drawn during the day—for privacy and to reduce glare—which lowered the amount of radiation available to heat the house.
In time, though, we think the Simonsens would have kept the blinds open more as they grew to understand how the windows affected their energy consumption. We know the family recognized the house's energy performance and is proud of it. On one particularly bright day, Sverre examined the computer display in the hallway that charts the house's energy performance, and the power of the sun truly hit home. "It was obvious here on Sunday when the sun came out," he wrote in the family's diary. "I just had to go and check: Was it really affecting energy output? Yes it was! That was a real ’ta-da!' moment."
We plan to share all these observations and data with the world in a new set of metrics we're now drafting, which encompass not only theoretical energy consumption but also the environmental impact and the inhabitants' well-being. We've also begun the next three Active House experiments: Green Lighthouse, a round building on the University of Copenhagen campus, as well as two single-family homes in Austria and Germany.
The Simonsens will be moving out of the house in one month, and the Home for Life will go on the market. If the family's satisfaction is any indication, we're well on our way to proving that environmentally friendly, carbon-neutral homes make for happy, satisfied inhabitants.
This article originally appeared in print as "Home, Smart Home."
About the Author
Ellen Kathrine Hansen led the design team for a futuristic green house in Århus, Denmark, named Home for Life. She drew inspiration from her childhood, which she spent in an even greener place—Lolland, a Danish island known for its sugar beet fields. She left Lolland to attend architecture school at the Royal Danish Academy of Fine Arts, in Copenhagen, where she now lives. Hansen says that when she took her 5-year-old daughter to see the Home for Life, she asked, "Mom, why don't we just live here?"