Researchers at the
University of Technology Sydney have developed a new material that stays cooler than the ambient air temperature even under the heat of the Australian summer sun.
As temperature rise globally and more and more people move to cities the Urban Heat Island effect is becoming an increasing issue. Dark coloured surfaces such as roofs absorb heat and stay hot for prolonged periods. Even white roofs absorb some sunlight.
Dr Angus Gentle and Professor Emeritus Geoff Smith layered polyesters on a silver layer to create a ‘coated polymer stack’.
"Roofs heat up by absorbing sunlight, so darker roofs can get very hot. Even white roofs still absorb enough sunlight to warm up by 9 degrees Celsius to 12 degrees Celsius” said Smith
"This new surface, however, stayed 11 degrees or more colder than an existing state-of-the-art white roof nearby because it absorbs only 3 per cent of incident sunlight while simultaneously strongly radiating heat at infrared wavelengths that are not absorbed by the atmosphere.
"Furthermore the plastic materials used for the demonstration were available commercially and potentially suited to use on basic roofing."
The researchers believe the technology has knock-on implications, including increasing the effectiveness of air conditioning units as the ambient air temperature is lowered.
The material was tested in typically harsh urban conditions. "Extensive dew formation is inevitable for a super cool roof and dew drops precipitate dirt. This roof site being 25 metres above a busy city transit road was a stern test. Results show that excellent thermal performance can be maintained.”
The research, funded by the Australian Research Council, was published in the journal Advanced Science.
Image Dr Angus Gentle holding a piece of the special material over an existing cool roof used in testing. Courtesy University of Technology Sydney
