Urban overheating directly influences the level of energy consumption of urban environments. Higher temperatures result in additional energy for cooling purposes while the energy for heating usually decreases.
Presenting the keynote speech at the recent 2017 Sustainability Live industry panel, Mattios Santamouris, professor of High Performance Architecture at UNSW pointed out that cooling a home in the western suburbs of Sydney - home to half the city’s population, costs much more than it does for those living closer to the coast.
In terms of actual numbers, says Santamouris, “the cooling load ranges from 17kWh/m2 in Canterbury to 28kWh/m2 in Penrith.”
“This means the same residential building will consume 64 percent more energy for cooling if it is located in Penrith rather than in Canterbury,” he says.
Given that the average monthly power bill for Sydney is around $250, that means residents in areas such as Penrith are paying on average up to $100 per month more than those living closer to the coast.
Santamouris found that “urban heat island and global warming increase ambient temperature and modify the energy budget of buildings.”
In Australia, we are adding to the problem thanks to our over-reliance on coal-generated electricity, with the latest Australian Energy Statistics showing that 63 percent of all our electricity comes from the burning of thermal coal.
“The increase to the cooling demand is due to the considerable increase of the ambient temperature in the north-western part of Sydney,” says Santamouris.
“High ambient temperatures are due to the synoptic weather conditions that transfer warm air from the desert and the blockage of the sea breeze by the CBD area.”
However, for Santamouris, this is hardly a revelation. Writing in the Energy and Building journal in 2014, he found that “urban warming has a very significant impact on human life – including increasing the energy consumption, deteriorating the comfort levels, increasing the pollution concentration, threatening the human health and affecting the urban economy.
Therefore, to reduce the cooling demand, Santamouris says that a range of mitigation technologies need to be used to decrease the ambient temperature in the considered urban zones.
These mitigation technologies involve the use of cool reflective materials, evaporation techniques, and additional greenery.
“Building design should provide solar and thermal protection to people,” he says.
This can be achieved using adequate insulation level at the building envelope, high quality double glazed windows, proper solar control, day and night time ventilation, a reflective roof and measures to reduce internal heat gains.
"Such measures can reduce the cooling needs of buildings up to 60-70 percent,” says Santamouris.
"A further reduction of the cooling needs can be achieved by increasing the thermal mass of the building and link it to a low temperature heat sink like the ground"
"Improving the microclimate around the building is of extreme importance,” he says.
“A mature tree located out of a house contribute as three small size air conditioners,” notes Santamouris.
“When such mitigation technologies are used, the peak ambient temperature may decrease up to 2.5 degrees Celsius, which corresponds to a reduction of the cooling demand up to 40 percent,” he says.
A further reduction of the cooling demand can be achieved using solar and thermal protection systems, heat amortisation techniques and heat dissipation technologies.
This is translated, he says “into proper envelope technologies for the individual buildings, use of adequate insulation levels, double glazing, proper solar control, reduced internal heat gains, night ventilation, use of ceiling fans, etc.”
“When passive cooling techniques are used, the energy consumption for cooling purposes may decrease by up to 85 percent,” he says.