Roof-based rainwater cooling could reduce AC demand

UK: Roof-based rainwater cooling could reduce energy demand, lower urban temperatures and help cities adapt to intense heatwaves, according to new research from The University of Manchester.

In the study, published in Earth’s Future, researchers used process-based numerical simulations and Artificial Intelligence (AI) to test a system that stores rainwater collected from rooftops and automatically sprays it onto buildings during hot weather.

Using AI-assisted simulations and based on Tokyo, the research found that cooling rooftops reduced the amount of energy needed for air conditioning. The cooler roofs transferred less heat into buildings, while lower air conditioning use meant less waste heat was released into the city.

Roof watering has previously emerged as a cooling strategy to mitigate the excess heat in urban areas. The roof sprinkling is expected to reduce AC energy consumption as it increases the roof evaporation, thereby cooling the roof surface and decreasing the heat transferred into buildings. It is estimated that such a system can cool the roof surface by 5.5°C–19.5°C. 

However, the effectiveness of sprinkling is inherently constrained by the availability and allocation of water resources. Drawing on the concept of rainwater harvesting, coupling roof sprinkler cooling with a rainwater collection system is seen as a viable strategy to mitigate water expenses and strengthen the sustainability of such interventions. 

Lead author Dr Zhonghua Zheng, co-lead for environmental data science and AI at Manchester Environmental Research Institute (MERI) and senior lecturer (associate professor) in data science and environmental analytics at The University of Manchester, said: “Cities around the world are facing growing challenges from extreme heat. Air conditioning can help keep people safe and comfortable, but it also consumes large amounts of energy and releases additional heat into the urban environment.

“Our study shows that harvesting rainwater from roofs and using it strategically for cooling could provide a practical way to reduce both energy demand and urban temperatures.

“What is particularly encouraging is that the benefits become even greater during hotter years, suggesting this approach could become increasingly important as the climate continues to warm.”