Hygrothermal Simulations of Buildings Concerning Uncertainties of the Future Climate

Doctoral thesis, 2012

Global warming and its effects on climate are of great concern. Climate change can affect buildings in different ways, i.e. it can change the energy demand or the moisture durability of buildings in the future. In Sweden, most of the last 20 years have been mild and wet compared to the 1961-1990 climate reference period. Future needs and risks of the building sector depend on the future climate which can be simulated by climate models. It is possible to assess the future conditions of buildings using simulated climate data. Since climate models are not certain there exist different scenarios for the future climate. Impact assessment of the climate change on buildings in Sweden has been performed in this study. The hygrothermal conditions of attics and the energy performance of buildings in Sweden were simulated. The study was mainly based on comparative analysis of different scenarios, buildings and periods. Four attic constructions, and the building stocks of four cities, were studied considering 12 climate scenarios for the period of 1961-2100 and one reference scenario for the period of 1961-2005. Future climate data sets were generated by the global climate models (GCMs) which were downscaled using regional climate models (RCMs) at the Rossby Centre at the Swedish Meteorological Hydrological Institute (SMHI). Climate scenarios were selected in a way to assess climate data uncertainties caused by different GCMs, RCMs, emissions scenarios, initial conditions and spatial resolutions. With the help of different statistical methods, uncertainties of the climate data and their effects on the hygrothermal simulations were analysed in different time scales. According to the results of this work, a reliable impact analysis of the climate change cannot be based on a few number of climate scenarios. Uncertainties of the climate data can affect the building simulation results considerably. Depending on the case, some uncertainty factors of the climate data might be neglected, however it depends on the building construction, the phenomenon and the season that are considered. Among the climate uncertainties which were studied in this work, the uncertainty caused by GCMs affected the hygrothermal simulations the most. The Swedish building sector can gain or recede from changes in climate; the heating demand of buildings will decrease by having warmer climate but the moisture problems will increase by having more humid climate. Results point to an increment of the moisture problems in attics. The absolute safe case for preventing mould growth is using controlled mechanical ventilation in attics which consumes energy. The energy simulations of the building stocks showed that the heating demand and its variations will decrease in the future. Comparing the indoor temperature in buildings with and without mechanical cooling system showed that there is no substantial need for increased mechanical cooling in the future.