Evaluation of urban thermal loads
Introduction
Reflective surfaces are those surfaces that offer high solar reflectance (the ability to reflect the visible, infrared and ultraviolet wavelengths of the sun, reducing heat transfer to the surface) and high thermal emission (the ability to radiate absorbed or unreflected solar energy).[1] Reflective surfaces are a form of geoengineering.
cold roofs
The most well-known type of reflective surface is the "cold roof." While cool roofs are primarily associated with white roofs, they come in a variety of colors and materials and are available for both commercial and residential buildings. Today's cool roof pigments allow metal roofing products to be EnergyStar rated in dark colors, even black.
The efficiency of roof color varies depending on the type of climate. In subtropical climates, such as in Australia or Argentina, roofs with zinc-plated or aluminized steel sheets (generally corrugated or trapezoidal) reflect solar radiation better than white, as long as they do not age and become opaque. In the European construction market, darker colored roofs predominate to follow trends imposed by market fashions.
Uses
The use of cold roofs would improve durability and reduce both cooling thermal loads and the urban heat island effect.
Cooling roofs is an effective alternative to improve thermal insulation in humid tropical and subtropical climates. Thicker mass thermal insulation can be partially replaced by roofing systems that reflect solar and high-emission radiation to the night sky. This dual function is crucial, and is based on the performance of the roof materials in the visible spectrum (which must be reflected) and the far infrared spectrum that must be emitted. The problem of the system lies in how to maintain a clean and polished surface and its adoption must be meticulously studied.
The cold roof can also be used as a technique to reduce global warming based on the principle of solar radiation management, provided that the materials used not only reflect solar energy but also emit infrared radiation. This technique can give between 0.01-0.19 W/m² average emissions reduction, depending on whether all cities or settlements are treated with this system. This is generally small compared to the 3.7 W/m² positive forcing a doubling of CO. However, in many cases, it can be achieved at little or no cost, simply by selecting different materials. Additionally, it can reduce the need for air conditioning, which causes CO emissions to decrease.