One change that could cool your home by 12 degrees

A green wall in the Adelaide CBD. Research shows green walls help maintain better inside temperatures. SCIENCE AND TECHNOLOGY
A green wall in the Adelaide CBD. Research shows green walls help maintain better inside temperatures.

With South Australia now the most expensive city in the world for electricity, consumers are desperate to find ways to make savings in the midst of a long, hot summer.

UniSA PhD student Rosmina Bustami may have found a solution.

A vertical garden / green wall.A vertical garden / green wall.

The civil engineering PhD candidate is investigating the energy savings that can be achieved by installing vertical gardens on household external walls.

Green walls – often referred to as living walls – consist of multiple pot plants housed within a frame, mounted to the wall and watered with a drip system.

The walls not only soften a harsh façade, providing an attractive feature, but can reduce the transfer of heat into the home with temperatures differing by as much as 12 degrees, Rosmina has found.

Her experiment involved installing a vertical garden on a west-facing wall, containing six different species of native plants – 144 pots in total.

Temperatures of the wall directly behind the vertical garden were taken, and compared with a control wall without plants, both western-facing.

The experiment was carried out between December 2015 and August 2016, encompassing the hottest and coolest months of the year.

The biggest temperature difference – 12 degrees – in the study was recorded in January 2016 while the smallest was in June 2016 (2.5 degrees).

However, outside the official experiment period, Rosmina recorded an even more remarkable difference. On Adelaide’s hottest day of 2017, 8 February, when the temperature outside peaked at 42.4 degrees, Rosmina recorded a difference in temperature reading of 26.6 degrees Celsius between the green wall and its corresponding control wall.

“I observed a positive difference during the day and a negative difference at night and early morning when the green wall acted as an additional layer of insulation for the house on cold nights,” she says.

Rosmina says the South Australian climate, with hot and dry summers, is ideally suited to green walls.

Singapore, renowned for its green credentials where the government has set a target of 50 per cent tree cover, holds the world record for the largest vertical garden.

Attached to a 24-storey apartment building, the green wall measures more than 2229 square metres and results in energy savings of between 15-30 per cent, according to the Singapore Government.

While the green facades are also popular in Europe, they are yet to take off in Australia, partly due to cost, with planter boxes averaging from $500 to $700 a square metre.

While the upfront costs are expensive, the energy savings are considerable and over a period of time would more than offset the initial outlay, Rosmina says.

“The big savings are in cooling costs. If the walls are very warm the air conditioner has to work that much harder to cool the house down. Similarly, in winter, the living wall insulates the wall against the cold, reducing the temperature difference between the inside and outside of the house.”