Roadmap towards Cleaner Fossil Fuels in South Africa Phase 2

This is a brief explanation of Cool Surfaces technology, particularly in the context of roofing and its relevance in energy efficiency of the built environment. This serves as the basis for further research, study and discussion with the aim being the formal inclusion of cool surface technology in the relevant South African National Standards regulations and codes.

Cool surfaces are those building materials that remain cooler in relation to other surfaces exposed to the same environmental conditions with specific reference to solar radiation.

Solar radiation refers to the full spectrum of electromagnetic radiation emitted by the sun, starting from extremely high frequency and short wavelength gamma radiation through x-ray radiation, ultra-violet radiation, visible light, near-infrared radiation, infrared radiation, microwave radiation, radio-waves to long wavelength radio waves. The highest level of energy is carried by the shorter, higher frequency radiation (such as gamma radiation) and the lowest energy by the longer, lower frequency radiation (such as radio waves).

Earth’s atmosphere reflects, scatters (a form of reflection) and absorbs much of the sun’s radiation. It only allows some wavelengths to be transmitted through the atmosphere to the surface of the planet – what we then experience as sunlight. Fortunately for us the high energy gamma, x-ray and most of the ultraviolet radiation does not reach us. For example, ozone in the atmosphere absorbs ultraviolet radiation. Much of the infrared band is also absorbed or reflected by the atmosphere. The wavelengths beyond the infrared band do not carry much energy and therefor do not have much impact on heating surfaces on the planet. For example, radio waves are continually passing through our bodies but do not raise our body temperature.

We are concerned with the wavelengths of solar radiation that do cause significant heat gain when absorbed by materials on the planet’s surface. This heat gain manifests from the absorption of a small portion of ultra-violet radiation (5% contribution to heat gain) the entire spectrum of visible light (roughly 51% contribution to heat gain) and mainly the near -infrared wavelengths of the infrared radiation spectrum (mainly the remaining 44% contribution to heat gain)