Australasian Science: Australia's authority on science since 1938

Cool Paint Blows Air Con Costs Away

A study of houses, schools, offices and retail spaces in Brisbane and Townsville has found that roofs painted in a special reflective paint resulted in a 2°C reduction in the internal temperature of non-air conditioned rooms.

The white paint used in the study reflects 88% of the sun’s energy. In comparison, a standard light-coloured roof reflects less than 65% and a dark roof reflects less than 25%.

“We saw average energy savings of between 5% and 30% across the range of buildings, with most buildings showing savings above 15%,” said Prof Bell of Queensland University of Technology.

“For an air conditioned block of two classrooms in Springfield to the west of Brisbane, for example, we reduced electricity use by 1144 kWh/year, which is roughly 1 tonne of CO2 per annum reduction for these two classrooms alone. Both electricity consumption and peak demand were significantly reduced, resulting in lower electricity bills for the school.”

Bell said that a cool roof could be a viable alternative to air conditioning classrooms. “At Nundah we had a reduction of roof temperature of around 15° during the hottest part of the day,” he said. “This resulted in a reduction of between one and three degrees in the internal temperature. That meant it rarely got above 27°, which is arguably cool enough to eliminate the need for air conditioning, especially if ceiling fans are used.

“Unlike air conditioners, this is a passive cooling solution that does not require ongoing investment in the electricity network or in housing. Because of this, it would be a worthy candidate for inclusion in the building regulations, much as they have done in the California energy code since 2005.”

Dr Wendy Miller said a combination of colour and chemistry made the roof coating effective. “The trials indicate the economic benefits of cool roof coatings would be greatest for single-storey buildings, buildings with aged, dark or medium-coloured roofs, buildings with no or low levels of roof insulation, and buildings with high air conditioning use,” she said.