Powerhouse Kjørbo
Making old buildings energy-positive

Located just outside Oslo in Sandvika, Norway the very first Powerhouse, Powerhouse Kjørbo is situated. The two joint-together office blocks from the 1980s are upgraded to energy-positive and modern offices, which means that over its lifetime the building will generate more energy than consumed. This implies that the building produces and exports more energy than is used for construction, renovation, operation, and end-of-life.

In addition to the ambitious objectives, the project has been rewarded with the highest classification in the BREEAM-NOR environmental certification system ‘outstanding’ for the design phase. Powerhouse Kjørbo is as far as we know the first rehabilitation office project in the world to have received this certification. Several factors working together make this building unique: The energy needed is covered by a heat pump and a photovoltaic system and geothermal wells in the park outside the buildings provide heating for radiators, water and ventilation air, and cooling in the summer. An efficient and unorthodox ventilation concept has been developed that reduces the overall energy demand for operation with exposed concrete decks for thermal storage, the speed of the ventilation air halved and the staircases used as an open ventilation channel. Zoning of the plans together with sensors that control the need for light, ventilation, and heat/cooling further ensures efficient use of energy. Other important design parameters are daylight utilization, disciplined and consequent use of low VOC emitting products.

The high heat losses for windows, ventilation, infiltration, and thermal bridges before renovation are reduced by 90%. Walls, ceilings, and windows are well insulated with a detailing that ensures an extremely airtight climate shell. A comfortable and attractive indoor environment was an important factor in the success of the project. Exterior see-through sun shading screens controls heat in summer and glare when the sun is seasonal low without obstructing the view. As the building is very well insulated and the windows only count for 40 % of the façade, there is almost no need for heating or down draft protection. A few radiators in the core are only there to cover extremely cold winter days. The heat pump pre-heats the supply of air and provides domestic hot water. In summer cooling is provided by circulating the brine from the boreholes through a heat exchanger in the ventilation system. Heat loads are further kept low through the chosen lighting system. The tenants of the building report better indoor climate, acoustic conditions, and lighting, and a more comfortable temperature than prior to the renovation. There is even no draft or sound from the displacement ventilation system as the air is let in at a low speed.

To reduce the embodied energy of the materials and components, all existing reinforcing steel and concrete constructions were maintained and reused in the refurbished building. The existing glass facade panels were reused as interior office fronts in the refurbished buildings. For the façade cladding, charred wood was chosen for several reasons – one; to minimize the energy for production, two; the technique retains the dark color of the former building, tree; the layer of char on the outside makes the cladding more fire-resistant and resistant to rot and bugs. Finally, the technique gives an environmentally friendly and maintenance-free surface that is beneficial in terms of embodied energy and has a relatively long service life with low maintenance frequencies. The mindset is representative of all materials brought into the project, they meet the highest environmental standards, at the same time as they are low in embodied energy.