Method for Probabilistic Energy Calculations—Passive House Case Study

Abstract

Swedish building regulations require proof that a building fulfills a specific energy use during the design stage. This is done by doing an energy calculation. The result of this calculation is always reported to the nearest integer, for example an energy calculation of a building might predict that it should use 89 kWh/m² year when the building regulation limits the actual energy use to maximum 90 kWh/m² year. This can lead to conflicts if the measured energy use is greater than the calculated energy use. With the currently available energy calculation tools, if you want to see which risks are associated to the design and material properties, you need to do a parametric study. These types of studies are usually time consuming. Investigations of different buildings show that energy measurements can vary significantly in identical houses. To take into account these differences and avoid costly parametric studies, it is common to add an uncertainty factor to the calculated results. In the project, “Calculation method for probabilistic energy use in buildings” two commercial energy calculation programs developed in Sweden were modified to use Monte Carlo simulations. This method was then tested using a passive house design which was used in the Vallda Heberg passive house development. The calculation results were then compared with the actual measured energy. The results show that a variation of 15 input parameters could explain most of the difference between measured energy use and calculated energy use. The results from the probabilistic energy calculation even showed that the original energy calculation was on the high-end of the calculated energy distribution. It showed that the probability that the measured energy use would fulfil the Swedish building code was over 95%.