Colours key to climate control for home and planet
A CQUniversity building and architectural engineering expert has found a colourful solution to keeping houses warm in the winter and cool in the summer.
A study across the hot-desert climate of Alice Springs and the humid subtropical climate of Sydney during winter has proved that the approach can handle Australia's diverse weather conditions.
Dr Hassan Khan, a Built Environment lecturer at CQUniversity, led the research to test the impact of coloured fluorescent films on passive daytime radiative cooling (PDRC) technologies.
Dr Khan explained that PDRCs, also known as 'super cool' materials, which are highly reflective and emissive of white and silver surfaces, may provide sub-ambient temperature, but are limited to commercial development due to glare and aesthetic issues in the urban environment.
"This approach hasn't always been cost-effective for residential homes, and because traditional PDRC materials are white or silver, their high reflectivity can create glare," he explained.
"Also, highly reflective PDRC materials induce heating penalties during winter, as solar radiations are reflected to the atmosphere, and residents are more likely to use heaters."
In the research, Dr Khan and a UNSW team developed passive coloured radiative cooling (PCRC) materials in orange, green and red colours, using quantum dots and fluorescent dyes, which can be applied to roofing and other urban surfaces without having glare and aesthetic issues. More colours of PCRCs are being fabricated and tested.
"Overall, the best cooling performance was observed for the orange-fluorescent prototype PCRC – in dry-hot conditions in Alice Springs, this prototype achieved the same surface temperature as highly reflective corresponding PDRCs, and 2.7 °C higher cooling than the conventional white cooling roofing during the daytime," he explained.
"During the night, all three coloured PCRCs were 7 to 8 °C below the ambient temperature."
The orange roofing also performed best under the humid-cold Sydney's winter conditions, insulating to 4.5 °C compared to the conventional white.
Dr Khan said the findings had implications for thermal comfort and energy-saving in residential and commercial buildings and provided a solution to counteract the urban overheating issues and global climate change.
"How our urban surfaces absorb and reflect light and solar radiation from the sun also affects ambient temperatures in our suburbs, and also global warming."
The study results were published in the peer-reviewed journal Solar Energy Materials and Solar Cells.
Dr Khan said researchers could now develop other forms of the "coloured super-cool" material.
"We hope to bring coloured super-coolers into a paint form, and those paints can be applied on any surface," he said.
Using fluorescent dyes was also more affordable than bright white alternatives, Dr Khan said.
The researchers are now working on improving durability and extending the life of the fluorescent materials from about five years to upwards of 15.
The Australian Research Council has funded this fluorescent cooling project, which was supported by UNSW facilities and equipment.
