Background/Objectives

Cooling and heating systems make up a significant portion of a building’s total energy usage, carbon footprint and operations cost. The cost of conditioning the interior of a building can be heavily dependent on the temperature characteristics of the environment within which the building sits. This is especially true in buildings whose envelopes are dominated by windows, and in buildings that require large amounts of fresh outdoor air for ventilation. In the case of new designs, climate conditions published by groups such as the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) are typically used to estimate energy usage – but these conditions are no longer the norm, as climate model projections indicate that the trend of warmer temperatures is expected to accelerate. Cooling seasons will lengthen, heating seasons will shorten, and both will become warmer. Whether the cost of increased cooling demand is counteracted by a corresponding decrease in heating depends heavily on a building’s location and energy sources. A recent case study serves to enhance the understanding of this relationship in by modeling the operations cost implications for the publicly owned buildings in the diverse locations of Los Angeles County and the State of Wisconsin.

Approach/Activities

Cooling and heating system energy usage was calculated for over 5,000 municipal-, county- and state-owned buildings using a relationship between degree days and energy usage. Cooling and heating degree days are temperature-based metrics that are commonly used to quantify cooling and heating demand over a given period. Degree day results were calculated for 2040, 2060 and a historic baseline period using the latest suite of Coupled Model Intercomparison Project 6 (CMIP6) climate models downscaled to 1/16^th degree across the United States¹. The US Department of Energy Commercial Reference Building energy models were used to quantify a degree day to energy usage relationship for a variety of building types in all US climate zones². The relationship was then applied to each building in the inventory to determine energy usage implications for each building on a cooling, heating, and net (cooling plus heating) basis.

Results/Lessons Learned

Present-day Los Angeles is already a cooling-dominated climate where building owners expect cooling costs to eclipse heating costs. This is compounded by the premium that is currently paid for electric cooling versus natural gas heating. Study results for the historic baseline mirror this concept, with cooling making up 94% of the average municipality’s net annual cost. The opposite is true in Wisconsin, where cooling only makes up 33% of the annual cost.

Warming temperatures serve to increase net costs in both locations. By 2060, the average municipality is projected to see cooling costs rise 25 to 48% in Los Angeles and 67 to 153% in Wisconsin. Meanwhile, heating costs decrease by 3 to 4% is Los Angeles and 18 to 19% in Wisconsin. While this does not counteract the rise in cooling costs in either case, the balance is closer in Wisconsin, where average net energy costs are projected to rise from 1 to 13%. Pronounced imbalance exists in Los Angeles where net energy cost rise is 23 to 44%.

The described methodology can inform adaptation strategies for municipalities and utilities nationwide as they navigate the uncertainties of future climate change and its impacts on operational budgets.