Climatic design conditions for buildings and impacts of climate change in Finland

With the aim of supporting the design of healthy, safe, and energy-efficient buildings in the changing climate of Finland, tailored hourly weather data files have been constructed and used to assess indoor conditions, energy efficiency and moisture safety of buildings. First, 30-year hourly weather datasets were compiled using observations at four measurement sites in 1989-2018. These datasets were then transformed to represent alternative future climates by modifying the observational values in accordance with CMIP5 climate model projections. The data files for the recent past and projected future initially contained the following variables: temperature, relative humidity, wind speed and direction, three solar radiation variables and precipitation. Later, the data files were supplemented with atmospheric downward longwave radiation (LW_dn).

For building physics, LW_dn is relevant because it is one of the factors that affect the energy balance of buildings. In the lack of sufficiently long time series of direct measurements, its past values were taken from the ERA5 reanalysis. To produce future time series of LW_dn that are consistent with the future values of the other variables in the weather data sets, machine learning was utilized.

Based on the 30-year multivariable data files for the recent past and future climates, shorter periods of weather information were selected for specific purposes. These included Test Reference Years (TRY) for assessing the average annual energy use for heating and cooling; Moisture Design Years (MDY) for simulations of, e.g., mould growth in building envelope structures; Design Days for Cooling (DDC) at various risks levels; and a Heat Wave Summer (HWS) for space overheating risk, representing a year with severe heatwaves in summer.

The presentation provides examples of climate change impacts on different building types. While average temperature and wind-driven rain are projected to increase, technical aspects in the buildings strongly affect how noticeable impact this has e.g., on mould growth. Future changes in corrosion of reinforced concrete structures and freeze-thaw damage depend on the location of the buildings and the orientation of their facades as well as on durability properties of concrete. More frequent and severe heatwaves in the future increase the risks of overheating, thermal discomfort and adverse health effects, particularly among the elderly, in dwellings without efficient cooling. 

The work is linked to the Healthy Premises 2028 programme, set by the Prime Minister’s Office of Finland, and to the Climate Change and Health (CLIHE) programme of the Academy of Finland.