Abstract
The current study demonstrates the possibilities of reducing energy use and construction costs and provides evidence that wooden nearly-zero-energy buildings (nZEB) are technically possible at affordable construction costs by using novel design processes and procurement models that enable scalable and modular production. The energy efficiency solutions were derived by increasing/decreasing the insulation value of the building envelope in successive steps. Financial calculations were based on the investment needed to achieve the nearly-zero-energy levels. Overall, many opportunities exist to decrease the cost and energy use compared to the current (pre-nZEB) practice because the net present value can change up to 150 €/m² on the same energy performance indicator (EPI) level. The EPI in the cost-even range was reached by combining a ground-source heat pump (between 115 and 128 kWh/(m2·a)) and efficient district heating (between 106 and 124 kWh/(m2·a)). As energy efficiency decreases, improving energy efficiency becomes more expensive by insulation measures. Throughout the EPI range the most cost efficient was investment in the improvement of the thermal transmittance of windows (3−13 €/(kWh/(m2·a))) while investments in other building envelope parts were less effective (4−80 €/(kWh/(m2·a))). If these were possible to install, photovoltaic (PV) panels installed to the roof would be the cheapest solution to improve the energy performance. Integrated project delivery procurement (design and construction together) and the use of prefabricated wooden structures reduced the constructing cost by half (from ~2700 €/net m2 to 1390 €/net m2) and helped to keep the budget within limits.