Three decades ago, long before cool roof systems had become a commonplace concept in energy efficiency research, a small elementary school on Florida's Space Coast provided one of the earliest field demonstrations that painting could reduce the power costs of a structure. This school was Our Savior's Elementary School in Cocoa Beach and its study, which spanned two years, is commonly considered to be among the earliest field demonstrations of reflective roofs.
The school's roof was unremarkable at the start: an unexceptional 10,000-square-foot roof of gray modified bitumen over a plywood substrate, with a solar reflectance of only 23%, according to the Florida Solar Energy Center's baseline monitoring. Researchers on the 'Demonstration of Cooling Savings of Light Colored Roof Surfacing in Florida Commercial Buildings' project monitored the school's thermal performance for a full year before and after the roof was coated, tracking roof and ceiling temperatures, weather conditions, and the electricity use of the chiller and air handlers. The initial year was crucial for the research. Without that year of data, there wouldn't be a way to distinguish between the effect produced by the roof coating and any particular mild summer season.
What changed once the roof turned white
The roof coating using an acrylic white elastomeric finish was done in May 1995. In just three coats, reflectance increased to 68%, while after a year, in spite of weathering and dirt accumulation, it remained at 63%. This appeared to have an immediate effect on the chiller's performance. When comparing the same summer weekday hours across the two years, the chiller's electrical demand during the 3-4 p.m. EST peak window fell by 35%, dropping from 16.2 kW to 10.6 kW, according to the Florida Solar Energy Center's report on the monitoring project. On an annual basis, the chiller's energy usage has been reduced on average by 10%, which equals 13,000 kWh in annual savings. The 10% reduction in chiller energy usage is notable on its own, and the 35% reduction in peak-hour demand is also significant for utilities because peak demand can drive infrastructure costs and higher rates.
Why the findings extend well beyond one school
While results from a single building, regardless of the quality of the data, do not imply results in the real world at scale, a different body of work by Ronnen Levinson and Hashem Akbari at Lawrence Berkeley National Laboratory’s Heat Island Group is highly informative in this respect. Their 2010 paper, ‘Potential Benefits of Cool Roofs on Commercial Buildings: Conserving Energy, Saving Money, and Reducing Emission of Greenhouse Gases and Air Pollutants’, published in the journal Energy Efficiency, simulated the effect of converting 80% of U.S. commercial roof area to white, high‑reflectance roofs.
