Weather impacts on simulated indoor conditions

According to the current National Building Code of Finland, the room temperature in new residential buildings should not exceed the threshold of 27 °C by more than 150 degree hours per year. The code also demands that new buildings pass the nearly zero-energy requirements for energy performance and conformity. The fulfilment of these requirements in the design phase of the new buildings needs to be verified by dynamic building performance simulation tools that use specific meteorological reference year weather data sets as hourly input. In addition to commercial purposes, such simulation software’s, like the IDA Indoor Climate and Energy (ICE) tool, may be used for education and research.

Here we describe several sets of hourly weather data that have been recently used in Finland as input to IDA-ICE simulations. TRY2020 data sets describe typical present-day weather conditions during twelve months that originate from different years of the period 1989-2018. They were selected based on a standard methodology (ISO 15927-4) with a few modifications. The same 30-year period was used to choose new cooling design days (1% risk) for Finland on the basis of another standard method (ISO 15927-2). HWS2018 data set, in turn, consists of weather observations of heatwave summer 2018.

All the data sets include the following variables: air temperature, relative humidity, global, diffuse and normal direct solar radiation as well as wind speed and direction. While the data sets describing the recent past climate are based on observations, their counterparts corresponding to future climates are based on CMIP5 climate model projections and delta-change methods.

The IDA-ICE tool was used, among others, to simulate the risk of too warm indoor conditions. According to the results, already nowadays during a prolonged heat wave the annual degree hours above 27 °C in apartment buildings without mechanical cooling may be several times the limit of 150. In the future, hotter summers are expected to become more common and the risk of overheating of dwellings will continue to increase. This would cause an increase in the heat-related health and mortality risks. Although solar protection windows and openable windows were found to be effective in reducing indoor temperatures, the results show that active cooling systems will be needed to eliminate the overheating risk.

Ref: Velashjerdi Farahani et al. 2020, https://doi.org/10.3390/app11093972