Ekonomi i Passivhus : En studie av två verkliga byggnader
The aim of this report was to investigate the economy of passive houses. The work was focused on economy in total and on the economy of different components such as windows, insulation, heat exchanger and the air tightness of the climate shell. No attention was paid on the comfort factor or to the impacts on the environment.
Two houses, aspiring to be passive were chosen; A big one and a small one. Hence, comparisons considering the size of the building have been possible to do as well.
The comparisons were made by calculating “break even” between two concepts; passive and BBR- concept. These were made for each component and for the building as a whole. The calculations were made using the method of net present value of the life cycle costs. Two parameters were chosen as uncertain, and for that reason as variables. Those parameters were the interest rate of calculation and the future price of energy. Break even could thereby be represented as a graph in the plane with the parameters on the axes.
Conclusions were made based on the assumptions that the interest rate should be 4%, the future price on electricity was 3 SEK/kWh and that the future price on electricity will be double the price of the district heating.
The investigation also exhibited the known fact that the smaller building is the more effective for the climate shell in optimum. This property gave more reliability to the whole investigation. The reason for this fact is that the balance temperature is higher for smaller buildings. This means that heat loss through the climate shell results in a higher energy use for more of the year. The energy loss, in fact a power, is proportional to the difference in temperature between indoor and outdoor climate. The bigger building gets rid of the energy loss between the balance temperatures of the buildings when comparing a big and a small house.
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