Guidance on Using Future Climate Data for Building Performance Simulation

Why do we need to design for the future climate?

The shifting climate in Canada has the potential to transform weather patterns and temperature regimes in ways that could render buildings designed to the contemporary climate as inefficient, uncomfortable, or even unsafe. As Canada’s climate continues to change, buildings and their occupants face a host of challenges. These include considerable changes in energy needs for heating and cooling purposes. In addition, more frequent extreme daytime high temperatures due to climate change increase the risk of overheating in buildings during the summer months, particularly where cooling systems like air conditioning have not been required historically.

The building industry now faces an important challenge: to design buildings that are energy efficient and comfortable for all occupants in the current climate, yet are climate-resilient and continue to provide protection under future climatic conditions until the end of their design service lives.

What are ‘Weather Files’?

A ‘weather file’ is used to describe the climatic conditions of a specific location and is critical input for building performance simulation. Commonly used weather files are based on a Typical Meteorological Year (TMY) method derived from historical climate observations. A TMY file represents a typical year of weather that is created by statistical selection and compilation of historical climate data from a multi-year period (typically spanning 15, 20 or 30 years). Refer to the next Learning Zone article for more information on TMY method.

While weather files have ‘weather’ in the name, actually, they are intended to capture long-term climate conditions. As many building simulations involve hourly calculations, the weather file consists of 8760 lines of data, one line for each hour in a non-leap year, for multiple variables. In Canada, historical weather files known as Canadian Weather Year for Energy Calculation (CWEC) – created using the TMY method – are the primary climate data used by building professionals in simulation and design. However, because these files are based on historical climate data, they are no longer sufficient to design future climate-ready buildings, and thus, there is a pressing need for building professionals to also use future weather files, which is becoming an increasingly expected standard of care.

Figure 1 shows the energy simulation results for a medium office building, comparing energy loads under current and future climates. The results indicate that cooling demand is expected to increase, while heating demand is expected to decrease, in both Toronto and Victoria. Additional simulation has shown this to be the case for other cities in Canada as well. These findings demonstrate the importance of designing buildings for future climate.

By making use of future climate data, we can ensure that buildings are designed to be energy-efficient, comfortable, and safe to use in the face of changing climate conditions. This means taking into account the potential impacts of climate change on the building’s performance and occupants, as well as designing strategies to address these impacts.

What future weather files are available?

Future weather files for various locations across Canada are now available from:

• The Pacific Climate Impacts Consortium (PCIC)
• The National Research Council of Canada (NRC)

These future weather files are specifically intended for use in building simulation, like the current CWEC historical files.

What is the difference between the two future weather file datasets?

PCIC and NRC’s future weather files differ in terms of technical approaches, outlined in the next Learning Zone article. Files from the two methods offer somewhat different data availability and may be suited for different building performance simulation purposes.

PCIC’s dataset includes climate change-adjusted dry bulb temperature, dew point temperature, relative humidity, and surface pressure for a high emissions scenario, for three time periods: 2020s (2011 to 2040), 2050s (2041 to 2070), 2080s (2071 to 2100). Here, historical CWEC weather files are adjusted or “morphed” using the results from climate model projections. The PCIC dataset makes use of results from multi-model ensembles to address climate uncertainty.

On the other hand, NRC used a regional climate model (CanRCM4 LE) output to create eight weather files that include a baseline file (1991 to 2021) – produced from the modelled historical data, and seven future files representing different levels of global warming, from +0.5°C to +3.5°C. NRC’s dataset also provides the corresponding time-periods for each global warming levels: 2003–2033, 2014–2044, 2024–2054, 2034–2064, 2042–2072, 2051–2081, and 2064–2094. NRC applied the same TMY method used to create the CWEC files to produce future weather files. In addition to the TMY files, Moisture Reference Year, as well as Extreme Cold and Warm Year are provided for hygrothermal – heat and moisture – simulation and designing for extreme conditions.

Guidance on the use of these two future weather file datasets

Table 1 summarizes the data from the two different datasets, providing a comparison of key metrics. The table includes information on variables that were climate change-adjusted, time period of the future weather files, as well as the types of weather data made available for use in building performance simulation. The following bullet points offer direction to aid users in determining the most suitable dataset for their needs:

• If one or more of dry bulb temperature, dew point temperature, relative humidity, or pressure are most important in your building design, you may want to consider using PCIC’s future weather files.
• In the case of temperature, a statistical downscaling method (known as BCCAQv2) was used by PCIC to ensure that projected changes reflect local climate effects. They also used an ensemble of projections from the Canadian Downscaled Climate Scenarios (CanDCS), ensuring that the future climate change applied is not specific to a particular climate model.
• If you are simulating a naturally ventilated building or are interested in solar radiation, you may want to consider using the NRC files that also have future hourly projections for solar radiation, wind speed/direction, and cloud cover.
• NRC’s future weather file includes projections for variables such as solar radiation, cloud cover, as well as wind speed and direction that are not available for PCIC’s future weather files.
• If you are concerned about peak energy loads or overheating, consider using both the TMY and “extreme” future weather files (Cold and Warm Year) produced by NRC.
• To assess hygrothermal behaviour of the building assembly using simulation tools, you may want to consider using “Conditioning and Extreme Moisture Reference Year” files produced by NRC, as they include projected rainfall values.
• In the case where weather files for your location are not available, you can always contact the Canadian Centre for Climate Services Support Desk for guidance.

Given the rapid evolution of climate science and services, it is expected that there will be future advancements in producing future weather files. As a result, building designers may want to periodically check for updates. We also recommend checking for updated versions of CWEC files as they become available too.

If you are interested in background information on weather files, how they are developed, and learn more about the methods used to produce each set of future weather files, refer to the ‘An In-Depth Look at Weather Files’ article.

Table 1. Summary of the two sets of future weather files developed by PCIC and NRC.

References

1. BC Housing. 2022. Extreme Heat and Buildings: An Analysis of the 2021 Heat Dome Related Deaths in Community Housing in British Columbia. Retrieved from: Extreme Heat Report 2022 (bchousing.org)