Future Overheating Risks in Buildings complying with current Codes

In many countries, thermal performance simulations during the design stage of buildings for code compliance rely on using a typical reference year (TRY). A TRY is an artificial dataset for a specific location, constructed from weather data spanning 15-30 years, representing the mean weather of the past. Therefore, new buildings are currently designed to meet criteria, such as overheating, for an average year of the past.

This practice is problematic as recent simulation-based studies indicate that likely climate change scenarios will significantly increase the risk of overheating in buildings designed for past climates. Studies also suggest that overheating problems can vary significantly across a country and between urban, suburban, and rural areas. However, there is a lack of studies challenging the appropriateness of local building design traditions. These traditions are influenced by architectural trends and building legislation that dictates the use of historical mean weather data for documenting energy performance and maximum overheating criteria.

This paper presents a simulation-based analysis of how the risk of overheating in buildings designed according to current Danish traditions would be affected by different climate change scenarios. The research question is: To what extent are dwellings designed using the Danish Design Reference Year resilient to overheating due to future local effects of climate change?

A total of 11,086 building zone models were generated, of which 4,115 were not overheated according to current Danish legislation using a historical mean reference year. A subset of 321 of these zones was selected for climate change resilience assessment. The overheating in all 321 buildings was assessed using TRY weather data files for the climate change scenarios RCP 2.6, RCP 4.5, and RCP 8.5 for the five most populated cities in Denmark. These files were generated in .epw format for the periods 2030-2059, 2050-2079, and 2070-2099.

The results indicate significant differences in thermal performance between the five cities during the same TRY periods; thus, one typical year file for Denmark might leave some dwellings less resilient in the future. The results also show that the fraction of the 321 zones that are overheated increases significantly with more severe climate change scenarios and periods. This implies that current Danish design practices may not be resilient against climate change. Further insights about thermal capacity and solar heat gain can also be derived from the data to propose guidelines for a more thermally resilient building stock.