"The new aluminium windows have been customized for Powerhouse Kjørbo," Thomas Aasen says about the windows currently being installed at Kjørbo, in the town of Sandvika near Oslo.

Aasen works in Building Systems, and has helped to develop the energy-efficient solutions at Kjørbo. He says that the new windows will be significantly larger than the original windows from 1980.

"To reduce the energy used for artificial lighting, we need to let in plenty of daylight. So the new windows are bigger," says Aasen.

He says Powerhouse Kjørbo will have an annual energy consumption as low as 20 kWh per square meter. This in stark contrast to around 200 kWh in a typical office building. With the help of solar panels on the roof, the building will produce more energy than it uses.

Tight windows

Powerhouse has already tested the air leakage, also called air tightness, of the fully installed windows in one of the rooms in the office building. The results are reassuring. The room with the new windows had a leakage rate of only 0.3 air changes per hour. For comparison, the requirement for a "passive" or low-energy building is 0.6.

"Most air – and therefore energy – is normally lost where the window meets the façade. In fact, the test was carried out in a corner office where the windows form a continuous element around the corner. This makes these results even more positive," Aasen says.

The original windows at Kjørbo had dark tinted glass that allowed less sun into the offices. The remodeled energy-positive building uses clear glass instead in order to maximize daylight. On very sunny days, the office workers can use external sun shades.

The new windows have two sections and the lower one can be opened for comfort ventilation.

"We are committed to creating user-friendly solutions. This means of course being able to open the windows to get fresh air, even if permanently closed windows insulate better," Aasen says.

The ability to open windows increases comfort, and fulfills a specific requirement for BREEAM certification, a widely recognized measure of a building's environmental performance.

Aasen adds that Powerhouse is committed to finding the solutions that are best for the building as a whole, not just solutions that are good individually.

Reuse and Recycle

Reuse of materials is a key principle for Powerhouse. Most of the original construction will therefore be left standing. Some materials are also used in new ways. For example, dado glass from under the windows in the original façade will be reused for interior partitions in the new super building.

The aluminium frames of the new windows will also be recycled in the future when the new modern building at Kjørbo is outdated and ready for demolition.

"Aluminium can be recycled over and over again using only five percent of the energy needed when the metal was produced for the first time. So it is good that 95 percent of all aluminium in the building will be recycled," said Aasen.

Complete in February 2014

The energy-positive office building at Kjørbo will be completed in time for Asplan Viak to move in at the beginning of February 2014.