Uncertainties in energy calculations and their effect upon the results of theoretical specific energy usage

In Sweden forty percent of the total energy usage is connected to the building sector. Decreasing the energy usage in this sector is therefore essential with regards to the greenhouse emissions. A number of rules have been formulated by the Swedish National Board of Housing, Building and Planning (Boverket) to govern the amount of energy that is used for heating, cooling and running buildings. The rules set limitations for the amount of energy used for running buildings, and require that in situ measurements are done within two years after the building has been taken in use to verify that the limits are not exceeded. These regulations raise higher demands for accurate predictions of the energy usage in buildings. A poor prediction would result in large deviation in comparison to the measured value and therefore demand a higher safety margin in the theoretical analysis. The purpose of this master’s thesis has been to examine the calculation procedure used in energy analysis in order to estimate the size of the uncertainties concerning specific energy usage. Moreover, the parameters that mostly affect the analysis can be identified and thus clarified where in the calculation process the emphasis must be to provide a more precise result. This was done by going through the calculation procedure step by step and in each part looking at the options available and then analysing the differences between them. The ongoing analysis was continuously compared to a residential building, which was provided by NCC Teknik. A literature review has been conducted to clarify the structure of the parameters. The calculation software used were IDA Indoor Climate and Energy 4.0 and VIP-Energy 1.0. The results show that the deviations in calculated specific energy usage can, depending on the software used in the analysis, reach the magnitude of 30 %. This size of deviation is possible but unlikely to achieve and can be lowered by changing the procedure used, with the means to decrease the likeliness for assumptions made by the single designing engineer. According to our findings, the parameters with the potential to cause the largest deviations are the climate files used, the setting of the indoor temperature and the choice of horizon angle which affects the shading of a building.