Article Source: Temasek
Article Link: https://www.temasek.com.sg/en/our-community/temasek-gives/community/how-to-keep-cool-without-air-con.html
How to Keep Cool Without Air Con
Why not take the humidity out of the Singapore weather instead? This alternative will not only keep electricity bills low, but it is also friendlier to the environment – all these while improving the comfort of residents.
When Assistant Professor Tan Swee Ching stepped foot on home soil after living in the United States and Britain for seven years, he was given an unceremonious slap in the face by an old foe: Singapore’s humidity.
This was quickly followed by heat, sweat and the familiar stickiness that spread across his body.
While temperatures often soared above 30 deg C during summertime overseas, it never felt as hot as it is in Singapore, and he puts it down to the relative humidity of the air.
Relative humidity affects how we perceive temperature, the National University of Singapore (NUS) Assistant Professor explained. “When the air is humid, the water on your body is not able to evaporate, and instead traps heat on your skin.”
At a relative humidity of 80 per cent – a usual level in Singapore – 32 deg C would feel like a scorching 45 deg C.
“Hence, if we can reduce the amount of water vapour in the air, we will also be able to lower the temperature we perceive,” he added.
So he went on a mission to create a material that can do just that three years ago. He has come up with a potential gem – a hydrogel that is able to absorb up to four times its weight in water.
An electricity-free way to keep cool
The creation of the ideal hydrogel has been arduous. Prof Tan has lost count of the number of versions of hydrogel he went through before coming up with the final product.
Earlier versions could only absorb 20 per cent of its weight, about as efficient as commercial dehumidifiers. This left him discouraged and led him to drop the project for about a year.
He revived it in late 2016 when a sudden brainwave prompted him to experiment with zinc oxide – a compound commonly found in skincare products like sunscreen.
“What we have now is a solution that does not require a single watt of electricity, which is cheaper and more environmentally-friendly than using air conditioning,” he explained.
Air conditioning accounts for more than 40 per cent of the energy used in most buildings. They also contain harmful chemical refrigerants such as chlorofluorocarbons and halogenated chlorofluorocarbons, which are common greenhouse gases that trap heat and lead to depletion of the ozone layer.
Tests showed that the hydrogel he developed is able to reduce the relative humidity of an enclosed space by 20 per cent in just seven minutes. This reduces the perceived temperature by seven to nine deg C.
“While it will not be able to cool a room as well as an air con, it will make you feel far less sticky, which will greatly improve the comfort level,” he said.
A typical HDB bedroom, with its windows open, will need a sheet of hydrogel large enough to cover at least one wall to have that effect.
To ensure that the hydrogel will not have to be replaced, Prof Tan has developed another material with the ability to digest water.
“By coating this water-digesting material behind the hydrogel, the hydrogel will technically be able to keep absorbing water vapour from the air indefinitely,” he said.
Trials to start next year
The hydrogel coating, which was developed over 18 months, will be piloted at an indoor location in the first half of next year, with the support of Temasek Foundation Ecosperity.
The pilot will last four to five months, and the location will likely be a dormitory room, an office, or a public space.
Following that, Prof Tan, who is from NUS’ Department of material science and engineering, plans to trial the hydrogel coating at a shaded outdoor location, such as a bus stop or sheltered walkway.
“As our population increases, so will demand for air conditioning. We need to find a less energy-intensive and greener way to keep ourselves cool, he said.
“We might just have found it.”