One of the benefits of designing buildings for greater resilience is the ability to withstand and recover quickly from extreme events. A big complication in trying to achieve that goal is that buildings are designed for long lifespans — 50 years or more — and we are experiencing climate change that is already affecting the conditions under which a building must operate. Predicting the loads a building might experience today is difficult enough, but estimating what conditions might be like many years down the road is even more challenging.
Despite the enormous undertaking to provide robust predictions of future climactic conditions, many organizations are attempting to include the effects of climate change in their standards, guidelines, and codes. ASHRAE Standard 169, which provides climate information for use in the design of building systems, is referenced in multiple standards, including 90.1 for energy use in buildings and 189.1 for high-performance building design. Standard 169 is regularly updated, and climate change is affecting the heating and cooling loads required for buildings. For example, in the 2013 edition of 169, approximately 10% of communities in the U.S. changed climate zones. However, the data used in 169 is historical and does not presently include predictions of future changes.
A recent report from the Global Resiliency Dialogue looks at how often code-writing bodies update their requirements to include changes in weather data. In the U.S., the values range from every three years for the International Energy Conservation Code (IECC) to five years for American Society of Civil Engineers (ASCE) 7 (wind and snow loads). Internationally, the Australian energy provision climate data is also updated every three years; however, most countries and standards have longer update cycles, such as the National Building Code of Canada (five years), New Zealand wind maps (10 years), Australia climate data (15 years), or New Zealand rain maps (30 years).
Moreover, as stated in the report, “Currently, none of the building codes in use in the surveyed countries address future climate risk — all are focused on addressing risk based on past weather experiences and extreme events.”
Part of the reason for this is inertia — the codes have always used historical data — and part of the reason is the uncertainty in the future predictions and the resulting debate over which models to use for the updates. This may not be a huge issue for HVAC systems, since they are likely to be replaced over the life of the building, but even for HVAC systems, there are components, such as ducts, plumbing, etc., that are unlikely to change, and, if sized incorrectly, could make future modifications expensive. However, some items, such as the structural system or envelope, are essentially fixed during initial construction, and large-scale modifications can be difficult and expensive if the loading regime changes.
The potential impact on building performance, and, hence, design, is clear. The 10 hottest years globally have all occurred since 2005, and these extremes are becoming more unpredictable. In terms of affecting design practice, ASHRAE is currently looking at having two climate zone maps and their related information, one based on historical data as is currently done, and one providing predictions of future conditions. Although the biggest problem with using predictions might be political in nature, the uncertainty in the model results, with differences in excess of 4°C in the mean global temperature predictions for 2100, is certainly a contributing factor. Finding ways to overcome that variability is crucial in the effort to produce designs that account for future conditions but do not severely over- or under-predict the load requirements.
Of course, like any other advanced design concept, you can account for the effects of climate change in your buildings today. However, without guidance from the building code and standards, you will need to convince both the building owner and the local code authority that not only is considering climate change necessary, but that the way you are attempting to account for it is both technically correct and provides long-term economic and building occupant comfort benefits. Designing for the expected loads over the life of the building will certainly lead to greater resilience with all its benefits for both the building owner and the surrounding community.