Use of cooling technologies in buildings along with irrigated vegetation could reduce daytime summer outdoor temperatures across one of the world’s hottest cities by almost five degrees, new research shows.

And the measures could slash the volume of energy which is needed to condition the city’s buildings.

In its latest research, the University of New South Wales Sydney (UNSW Sydney) collaborated with the Royal Commission of Riyadh to quantify the effect which advanced heat mitigation technologies and techniques can have in terms of outdoor temperature and building energy consumption across the Saudi Arabian capital city of Riyadh.

It found that by using combinations of super cool building materials, irrigated vegetation types and energy retrofitting measures for existing buildings, it was possible to reduce average outdoor summertime temperatures across the city by as much as 4.5 degrees Celsius.

The measures would also reduce the volume of energy that is needed to cool buildings by up to 35 percent.

The latest research comes amid increasing concern about the impact which climate change may have upon major cities in coming decades.

Already, as many as 450 cities around the world are impacted by extreme urban heat.

This can not only lead to higher cooling requirements but can also have significant impacts upon quality of life and human health – with higher urban temperatures being associated with more heat related illness and death.

The effect is likely to increase further in the future on account of global warming and rapid urbanisation.

Riyadh, the capital of Saudi Arabia, is centred in the middle of this.

Situated in the centre of a desert, the city is one of the hottest in the world.

During summer, temperatures can exceed 50 degrees Celsius.

For the study, the research team ran large-scale cooling climatic and energy simulations of the Al Masiaf precinct of Riyadh.

The aim was to determine the overall impact of various combinations of cooling measures on the city’s overall outside temperature.

The team also modelled the energy performance of 3,323 urban buildings across the city to determine the effect of the measures in terms of energy requirements for the cooling of buildings.

During the research, the team applied eight different heat mitigation scenarios to evaluate optimal strategies for lowering the temperature of the city and reducing cooling needs.

These scenarios consisted of:

• Vegetation, including that which is irrigated through provision of ample watering and that which is non-irrigated (drought-resistant vegetation) through limited or no watering.
• Use of cooling building materials. These include reflective materials that reflect solar heat along with ‘super-cool‘ materials such as radiative cooling coatings.
• Retrofitting options, including better windows, insulation, solar and cool roofs.

Overall, it found that the best possible strategy involved using super cool materials which are incorporated into the roof of the buildings as well as more than doubling the number of irrigated trees to improve transition cooling.

Using this strategy would decrease the average outdoor temperature during summertime across the city by almost 4.5 percent.

The measures would also reduce the volume of energy which is needed to cool buildings across the city by up to 16 percent.

Further, when these optimal strategies are combined with optimal retrofitting options for existing buildings, the reduction in energy cooling consumption can be increased from the 16 percent referred to above to as much as 35 percent.

However, the report warned against a ‘blind’ implementation of measures that are not based on a careful analysis of detailed scientific optimisation.

For example, the research found that use of low-level, non-irrigated greenery may actually deliver an increase in daytime temperature.

The researchers now hope to work with the Royal Commission of Riyadh to begin implementing the tailored heat mitigation plan across the city.

This will represent the largest rollout of such a plan anywhere in the world.

Professor Mattheous Santamouris, Anita Lawrence Chair in High-Performance Architecture at USW Sydney and senior author of the study, said the importance of the research should not be underestimated.

As things stand, Santamouris says that significant use of conventional building materials is exacerbating the city’s heat problems.

He says implementation of the recommended cooling strategies could deliver substantial benefits.

“Limited greenery and large artificial surfaces made of conventional building materials like asphalt and concrete trap heat, meaning the city continues to heat up,” Santamouris said.

“Additional heat from car pollution and industrial activities also increases the city’s temperature.

“By implementing the right combination of advanced heat mitigation technologies and techniques, it is possible to decrease the ambient temperature at the precinct scale.

“For a sweltering city the size of Riyadh, significantly reducing cooling needs is also tremendous for sustainability.

“Once implemented at the city scale, these advanced heat mitigation technologies will deliver important health, sustainability and economic outcomes for the city for years to come.”

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