A research by Australian scientists has suggested that a heat pump based on nanoparticles could one day cool buildings without the need for energy-intensive air conditioning.
According to a report by ABC News, the research was carried out by Applied physicist professor Geoff Smith and Dr Angus Gentle of the University of Technology, Sydney.
Air conditioning is especially a problem in cities, which have a lot of heat-retaining surfaces, contributing to what is called the "urban heat island effect".
Smith and Gentle have created a coating that can be used as an efficient heat pump and reduce the need for energy-guzzling air conditioning.
It relies on a phenomenon known as "night sky cooling", in which energy absorbed by surfaces during the day is emitted back into the atmosphere.
Smith and Gentle's invention takes advantage of the fact that certain wavelengths of radiation emitted from the Earth are less likely to be reabsorbed by the atmosphere.
These wavelengths - between 7.9 and 13 mm - are more likely to escape all the way back into space than others.
Smith and Gentle have found that a mixture of silicon carbide and silicon dioxide (CO2) nanoparticles emit heat radiation at wavelengths that best take advantage of this atmospheric 'window'.
They have found a surface coated with the 50-nanometre sized particles can get down to 15 degrees cooler than ambient temperature in Sydney.
According to Smith, the nanoparticle coating could be used to make a kind of reverse solar collector.
Air, or water, would flow in channels beneath a plate coated with the nanoparticle mixture.
Rather than absorbing the radiation for heating purposes, the set up would emit radiation, cooling air or water that could then be pumped through buildings to cool them.
As well as cooling buildings, the technology could also be used as a coating on refrigerators, especially in remote areas.
"The technology would mainly work at night, but could sometimes work on the shady side of buildings," Smith said.