Radiative properties of buildings for passive cooling

The need for air-conditioning in residential areas is increasing, not only because of global warming, but also because of a combination of phenomena linked to building design and occupants: urban heat islands (UHIs), the growing accessibility of air-conditioning systems for the majority of people, the increasing frequency of heatwaves and the growing needs of vulnerable populations.

With an average residential air-conditioning growth scenario of 750% by 2050, the radiative treatment of building envelopes represents an important part of the solutions for passive cooling or for mitigating the energy requirements of active systems.

This radiative treatment of envelope elements aims to control summer solar gain on façades or roofs directly exposed to the sun. We describe here the use of materials with so-called "cold-selective" surface properties. These materials, which include traditional products used since antiquity, are now characterized by standardized protocols for assessing their performance (e.g. for "cool roof" products) and standards that are more or less well integrated into thermal or environmental regulations.

This article explains the mechanisms and standards involved in these cold selective product techniques. Numerous documented reference cases have highlighted the potential benefits for building design, but also for limiting global warming and local heat islands.

Recent developments in new surface treatment techniques have opened up numerous avenues for significantly increasing the passive cooling potential of buildings and the urban environment. These innovative techniques hold great promise for adapting to climate change, thanks to their potential for use on facades and roofs in dense urban environments. Cool colored products, retroreflectives, electrochromes, thermochromes, fluorescents and many other alternatives and combinations are discussed here.