Ellen Phiddian
Cosmos science journalist
Researchers have made a cooling device that they say can chill environments with 50% of the energy used by conventional air conditioning.
They are using the physics of radiative cooling.
The personalised device works by making an extremely cold surface, rather than blowing air about.
The Chinese team has published its results in Cell Reports Physical Science.
Refrigerative air conditioners work by blowing warm air over cooling coils and into a room. (The coils are cooled by a liquid refrigerant which is re-cooled by being pumped through a series of chambers outside.)
According to a 2021 report by the Department of Agriculture, Water, and the Environment, air conditioning equipment used 25% of the electricity produced in Australia in 2020, accounting for 12% of annual national greenhouse gas emissions.
Because they rely on blowing air, and work best in sealed environments, air conditioning systems in large buildings can also make it easier for viruses to spread, and cause noise.
Scientists have proposed that radiative cooling devices – instruments that cool a room or a person directly, without blowing air – could be more energy efficient and less disruptive.
But it’s difficult to make them powerful enough, and hard to stop water in the atmosphere condensing on the surface of these cooling devices (like it does on a glass of cold water), lowering their performance further.
This research team, based at the Hong Kong University of Science and Technology and an air conditioning manufacturing company in Guangdong (Guangdong Midea Refrigeration Equipment Co.), developed a prototype radiant cooling device that could overcome these problems.
Their device uses a thermoelectric cooling module, which they describe as “in essence, a heat pump”, connected to 4 pipes and a fan on one side, and an aluminium panel on the other.
While the pipes and fan act as a heat sink, the aluminium panel is used to make a radiant surface extremely cold.
The researchers tested their device on a human skin simulator, and found it was able to cool the simulator by 7.3°C.
It could also save up to 50.4% of the energy typically used to cool an environment, depending on different conditions the researchers tested it in.
“It should be noted that our device can achieve both pure radiant cooling and heating simply by changing the direction of the current,” point out the researchers in their paper.
“However, in this study, we only demonstrated the cooling function because cooling is often considered the most difficult process in radiant air-conditioning systems due to air condensation and so on.”
The researchers say that the device would ideally be combined with a dehumidifier in humid environments, as it can’t remove moisture from the air.
The team believes that better thermoelectric devices could reduce the energy cost further, and other materials like aerogel might serve as better cooling surfaces.
“We believe that our work can stimulate more research efforts in pure radiant cooling,” they write.
“We also expect that our work can revolutionise the design of air-conditioning systems and personalised thermal management systems.”
