Study shows how to cool one of the world’s hottest cities by 4.5°C

It is possible to significantly reduce the temperatures of a large city in a hot desert climate while reducing energy costs, a new study from UNSW Sydney shows.

The results, published in Nature Citiesdetail a multi-faceted strategy to cool Saudi Arabia’s capital by up to 4.5°C, combining highly reflective “super cool” building materials developed by the High Performance Architecture Lab with irrigated greenery and energy renovation measures.

The study, conducted in collaboration with the Riyadh Royal Commission, is the first to investigate the large-scale energy benefits of modern heat mitigation technologies when implemented in a city.

“The project demonstrates the enormous impact that advanced heat mitigation technologies and techniques can have to reduce urban overheating, decrease cooling needs and improve lives,” says Mattheos (Mat) Santamouris, professor at the UNSW Scientia, Anita Lawrence Chair in High Performance Architecture and lead author. of the study.

Professor Santamouris specializes in developing heat mitigation technologies and strategies to reduce urban temperatures in cities. Extreme urban heat affects more than 450 cities worldwide, increasing energy consumption needs and negatively impacting health, including heat-related illness and death.

Riyadh, the capital of Saudi Arabia, is one such city. Located in the center of a desert, it is one of the hottest cities in the world, with temperatures reaching over 50°C in summer. Additionally, climate change and rapid urbanization are increasing the magnitude of overheating.

“Limited greenery and large artificial surfaces made of conventional building materials like asphalt and concrete trap heat, meaning the city continues to get warmer,” says Professor Santamouris. “Additional heat from automobile pollution and industrial activities also increases the city’s temperature.”

Simulation of city-scale heat mitigation scenarios

For the study, the team led by UNSW researchers carried out large-scale climate and cooling energy simulations of Riyadh’s Al Masiaf district, including the energy performance of 3,323 urban buildings, under eight different scenarios heat mitigation to evaluate optimal strategies for lowering temperature. of the city and reducing cooling needs.

The modeling, which took into account different combinations of supercool materials, vegetation types and energy renovation levels, revealed that it was possible to reduce the city’s outdoor temperature by almost 4.5°C by summer. The strategy would also improve cooling energy savings for the city by up to 16%.

The recommended heat mitigation (or cooling) scenario for Riyadh includes the use of super-cold materials implemented on the roof of buildings and more than doubling the number of irrigated trees to improve transpiration cooling.

On the contrary, indiscriminate implementation of district cooling techniques not based on detailed and advanced scientific optimization, such as the use of non-irrigated greenery, can lead to a substantial increase in city temperature.

“By implementing the right combination of technologies and advanced heat mitigation techniques, it is possible to lower the ambient temperature at the enclosure scale,” explains Professor Santamouris. “For a sweltering city the size of Riyadh, significantly reducing cooling requirements is also great for sustainability.”

Professor Santamouris says that lowering the city’s temperature helps increase the thermal comfort of residents, reduce health problems linked to intense heat, reduce the concentration of pollutants and improve human productivity. Although not part of this study, previous research has found that implementing similar cooling strategies in other cities can help reduce heat-related deaths.

Reducing energy demand on an urban scale

The research also simulated the energy impact of renovation measures for all 3,323 buildings, as well as heat mitigation technologies implemented on an urban scale. Combining optimal cooling technologies with energy retrofit options, i.e. improving the building envelope through better windows, better insulation, solar and cold roofs, could reduce cooling demand by up to 35%.

“This represents a substantial reduction in Riyadh’s energy needs, which would help further reduce the costs associated with cooling the city while improving the quality of life of the local population,” says Professor Santamouris.

The researchers now hope to work with the Riyadh Royal Commission to begin implementing the city’s tailor-made heat mitigation plan, which would be the largest of its kind in the world.

“Once implemented citywide, these advanced heat mitigation technologies will produce important health, sustainability and economic outcomes for the city for years to come,” says Professor Santamouris.