SAVING WATER: It might sound counterintuitive but in South Australia, government officials are no longer telling people to let their lawns die over summer.
Why? Because the cooling effect of green gardens takes pressure off airconditioners – leading to lower energy use and a more stable grid in a state where that’s a top priority.
The idea struck SA Water’s business development manager, environmental opportunities, Greg Ingleton, as he was flying over the Adelaide airport and looked down at the vast expanse of dry grass surrounding the runway.
This led to a pilot project of using recycled water to irrigate a small patch of lucerne at the airfield. The crop managed to cool the surrounding air by three degrees, which created a ripple of excitement in the airline industry because planes use more fuel to take off in warmer air.
Ingleton also put the theory to the test at his 130-year-old home. Wondering how its former owners kept the house cool before airconditioning, Ingleton set about using small amounts of water – no more than two- or three minutes-worth in the shower – to irrigate the garden surrounding the house.
He says he managed to bring the air temperature down by as much as 10 degrees – enough that the family could stay outside rather than cower inside with airconditioner on. The cool external air also helped keep the house cool when the windows were kept open.
As a result, the household managed to shave around $200 off the annual electricity bill. The water bill went up a fraction, he says, but there was certainly a net saving on bills overall.
He took this a step further the following year with ultra water efficient water misters and digital thermometers across the homes of around 100 SA Water employees. Practically every participating house reported reduced air temperatures by as much as 10 degrees and huge savings in electricity.
“It really showed that this was a viable and sustainable alternative to sitting inside with aircon on.”
If adopted across an entire neighbourhood, there’s an accumulative cooling effect. This creates a more liveable suburb, and potentially higher property values.
Ingleton says using non-potable recycled water to cool neighbourhoods is unfortunately not a feasible option at this stage as misting systems could spray out unsafe particles and pose a health risk. Large particles in recycled water can also clog up misters.
A combination of natives and non-natives is key
Ingleton mentioned that native plants don’t have the same cooling affect as non-native species. “They are low water use so don’t transpire, they don’t breathe out the cool air.”
A mix of both native and non-native provides both biodiversity outcomes and cooling benefits.
Better on the climate – but water at the right time of day and only around your home
On a macro level, airconditioning is a huge energy guzzler and contributor to climate change unless its running on 100 per cent renewable energy sources. Using strategic irrigation as a cooling tactic, by contrast, leads to sequestered carbon by growing plants.
The environmental downside is the huge amounts of energy it takes to pump water around. Ingleton says this impact can be mitigated by keeping water use down, such as using water efficient misters, watering before the heat of the day and only irrigating directly around the home or building.
By following these techniques, Ingleton is confident people can create the desired cooling effect using the equivalent water of a few minutes in the shower each day.
“Our message is be conscious about when and where you use that water, for example, don’t do your deep soaking in the peak of the heat wave.”
Better on the grid
Another flow on benefit of the cooling technique, if adopted at scale, is that it can take pressure off the grid in the peak demand afternoon period.
In summer, demand for energy typically spikes in the early afternoon and evening as people return home and turn on their airconditioners. Unfortunately, this tends to coincide with a drop in solar generation as the sun starts to go down. Much of the afternoon peak demand pressure could be alleviated if most homes swapped out airconditioning for this alternative cooling method, Ingleton says.
The government is also looking into the use of misting cooling as an alternative for low socio-economic households who can’t afford to run an airconditioner. The results so far have been promising.
Liveability is usually the first to go in a drought, but it doesn’t have to be
During a drought, Ingleton says that liveability tends to be the first thing to suffer as parks are left to go brown and dead, rather than the cool oases that they could be.
“Green parks are really beneficial and people want to be able to get outside when its summer.”
Local governments in the state are starting to weigh up the economic costs, including intangible social costs, of letting these public assets dry out against the costs of using a little bit of water to keep them green.
After a successful trial, many councils are now using an irrigation software package that leverages Bureau of Meteorology weather data to help councils decide when and where to irrigate that week for best water efficiency.
This means water for irrigation is spread more evenly and efficiently across a municipality’s parks. A number of schools are also now using the software package.
Ingleton says it helps that the state is already fairly advanced on water sensitivity, with water recycling and stormwater schemes now common. He believes South Australia is ahead of some other states and territories on water conservation because it didn’t forget what it learnt during the Millennium Drought.