Sydney scientists claim ‘cool roof’ breakthrough could keep cities cooler, greener

As India emerges from what is shaping up to be the world’s fifth deadliest heatwave, scientists from Sydney’s University of Technology (UTS) claim to have made a technological breakthrough that achieves the “elusive target” of keeping a roof cooler than the air around it – even in hot Australian summers.

The development of the “coated polymer stack” cool roof material is the result of a study by Dr Angus Gentle and Emeritus Professor Geoff Smith, published in the latest edition of the journal Advanced Science.

And it is believed to have major implications for reducing both the heat island effect in urban areas, as well as peak power demand from air-conditioning – and greenhouse gas emissions.

In tests conducted by the UTS team on the roof of the university’s science building, the newly developed surface – a combination of specially chosen polyesters on a silver layer – stayed 11 degrees or more colder than an existing state-of-the-art white roof nearby, absorbing only 3 per cent of incident sunlight while simultaneously strongly radiating heat at infrared wavelengths that are not absorbed by the atmosphere.

“We demonstrate for the first time how to make a roof colder than the air temperature around it, even under the most intense summer conditions,” UTS Professor Smith said.

“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.

Smith says the plastic materials used for the demonstration are available commercially and potentially suited to use on basic roofing.

“Cool roofing reduces the severity of the urban heat island problem in towns and cities and helps eliminate peak power demand problems from the operation of many air conditioners,” he said.

“The added feedback benefits from cool roofs are not yet widely appreciated, but recent reports have shown they are substantial. Examples include ventilation with cooler air and higher performance of rooftop air-conditioning installations.”

Professor Smith also notes that the surface maintained its high performance in all 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.

“Much of the world’s population lives in warm climates. Keeping a roof cool saves energy and makes building interiors comfortable in summer. If enough roofs in a precinct are kept cool then the local climate can also be beneficially influenced,” he said.