Energy modeling and climate change
As modeling tools and practitioners become increasingly skillful, energy models are nevertheless still limited by input assumptions. One of the major assumptions is weather data. For decades modelers have used such weather files as the Typical Meteorological Year-type, now existing in multiple versions (TMY, TMY2, and TMY3). The TMY and other weather file types such as EnergyPlus Weather (EPW) and International Weather for Energy Calculation (IWEC) generally use the same commonly available data, and although there are some differences between types, a constant commonality is that all are derived from historical data over the past 30 to 50 years. With changing weather patterns and climatological data indicating that a climatic shift is underway, it is important to consider how this impacts energy model results and, perhaps more importantly, how to account for the shift.
Weather data is used not only to drive the hour-by-hour response of the building to the climate, but in many cases also to size the systems in model, thus affecting capacities, performance curves, and possibly the types of systems to use. All the effects have an impact on the predicted energy use in the model. If practitioners use the older climate data solely, they may very well be underestimating the peak conditions, and likely the increased frequency of warmer conditions that will exist in 20, 40, or 60 years.
No single climate model will be accurate. The benefit to the building design community is that it is now possible to quickly evaluate a range of climate change scenarios over different timeframes. The intent is not to predict what will happen but to provide a risk assessment. As practitioners, it is possible to provide insights about the likelihood of energy and water use increases. Fuel escalation rates, which are effectively climate escalation rates, can be considered in tandem with climate projections. Because many building and campus utility infrastructure investments are made on a 50-year time horizon, it is important to understand and mitigate risks to the extent possible.
Using research conducted by the Hadley Centre for Climate Change Prediction and Research at the U.K. Meteorological Office, any energy model can be simulated using predicted changes in the local climate of any location in the world. Timeframes for these future weather predictions include the 2020s, 2050s, and 2080s, to see multiple distinct future scenarios that facilities might encounter. The modern standard for weather and future climate change prediction is the Hadley Centre’s HadCM3 model, one of the major models used by the Intergovernmental Panel on Climate Change (IPCC) to develop its predictions for possible future weather conditions.
By using predicted future weather data in an energy model, it is possible to predict increases in future energy consumption due to climate change, as well as increases in future design conditions for sizing equipment. In this way, we can provide our clients with systems capable of facing an uncertain climate future. Knowing the long-term impact of climate change on a building can also inform lifecycle cost analysis efforts—a technology that isn’t attractive given current climate patterns might become more viable if the future is warmer/colder and wetter/drier than our current conditions.
These new techniques being employed are straightforward to implement and provide for a future—and even a present—where energy modeling efforts will benefit from sensitivity analyses with regard to climate change.
Paul Erickson is sustainable practice leader at Affiliated Engineers Inc., where he champions integrated design on an array of project types using performance modeling tools to help guide exploration and decision making. Bill Talbert is sustainable department facilitator at Affiliated Engineers Inc. He leads the firm’s building performance modeling team and is a member of the ASHRAE Standard 90.1 SSPC Energy Cost Budget Subcommittee.