Chalmers: Round housing is smarter

By April of next year, "Halo" will be complete. The house will then be taken apart and sent by boat to China to compete with 22 other energy-saving buildings from around the world.

The plan is for the concept to be used for permanent student housing in Gothenburg, say Agnes Hammer and Astrid Humerfelt, two of the 26 students at Chalmers now working full-time on the project. The competition is called Solar Decathlon. The goal is to promote the development of solar energy housing made of material that is available on the market. The championship was started ten years ago by the U.S. Department of Energy. Since then, it has been held both in the U.S. and in Europe. Next year marks its first time in Asia.

Chalmers is the first Swedish university to compete in Solar Decathlon, and the only Nordic team in China. Last year, Chalmers won a partial competition with "Halo", an 80-square metre house  now been taken over by new students.

"It's an exciting challenge," says Agnes. "Our task is to make these ideas a reality. We have a materials budget of 1.7 million SEK which cannot be exceeded. Meanwhile, solar cells are developing further every day. We have to take into account how far these will have progressed when we build the house next year.”

The course devoted to energy-smart housing is called "sustainable building". In it are 26 students; half are aspiring architects and half are future engineers. (Agnes and Astrid are studying for a "Masters in Sustainable Development" at Chalmers School of Architecture). The original idea is a round house, inspired by the portable huts of the Sami. The shape is key. Cold wind passes more easily by a circular building. The perimeter is smaller, and thermal bridges in the corners can be avoided.

The windows present a problem. Everyone wants a bright home, but the more windows you have, the more energy escapes. A few large ones are better than many small ones. The reason is that window frames are more permeable than the windows.

"But not all windows need to be openable. You can let the glass reach further into the wall and thus avoid a cold bridge. The building is clothed with a vaulted ceiling covered with Grätzelceller that mimic the process of photosynthesis. The cells are manufactured in Sweden, which is also important from an energy standpoint. “

“According to our calculations, the house will be able to run on solar energy and the heat generated by its residents. In the summer, excess energy can be transferred to the grid. When it gets cold, you can recover the excess. The domed shape allows for a maximum number of cells to face the sun during the day. But the construction is expensive. We are now looking at a simpler solution with straighter shapes, which makes the design more economical.”

The basic material in the house is wood. Dried hemp was chosen as insulation for the walls. It has about the same U-value as glass wool and other traditional insulation materials. Hemp is cheap, and it grows in Sweden. Energy efficient living is also about lifestyle. The students based the project on collective housing, which has long tradition in Sweden. "We chose to build student accommodation with small bedrooms and large common areas. This house is intended for four.” But the idea is that there will be room in the house for all 26 participants at the housewarming party, which will also be held in April of next year. The result of the competition is to be decided in August.

The students have chosen to insulate the house with hemp. Hemp has a long history of use, including for ropemaking. At the beginning of the 1970s, however, all hemp cultivation was banned in Sweden, based on the argument that hemp is a narcotic. However, there is difference a between marijuana and industrial hemp. The latter contains very little narcotic substance, but that which is there keeps pests away. The ban on hemp cultivation, which came to include practically the entire OECD area, is based on strong industrial interests in the United States, where hemp is seen as a serious competitor to both oil and wood. Hemp has gradually come back into favour in a number of countries. But Sweden was not among them until 2003, when the ECJ exerted pressure to end the ban. Hemp insulation is made up of mats with compressed fibres from the plant stem. It has natural fungus- and bacteria-inhibiting properties and does not require impregnation. Hemp can store moisture and has excellent sound insulating properties.