Engineers have developed a high-performance external PDRC (passive daytime radiation cooling) polymer coating with air gaps ranging from nanometres to miniscels that can be used as a spontaneous air cooler for rooftops, buildings, water tanks, vehicles and even spacecraft — anything that can be painted.They used a solution-based phase conversion technique to give the polymer a porous foam-like structure.When exposed to the sky, the porous polymer PDRC coating reflects sunlight and heats up to achieve temperatures lower than typical building materials or even ambient air.
With rising temperatures and heat waves disrupting lives around the world, cooling solutions are becoming increasingly important.This is a key issue, especially in developing countries, where summer heat can be extreme and is expected to intensify.But common cooling methods, such as air conditioning, are expensive, use a lot of energy, require ready access to electricity, and often require ozone-depleting or greenhouse-warming coolants.
The alternative to these energy-intensive cooling methods is PDRC, a phenomenon in which surfaces cool spontaneously by reflecting sunlight and radiating heat to the cooler atmosphere.If the surface has the solar reflectance (R) can minimize the increase of the sun’s heat, and with a high rate of thermal radiation (Ɛ) can maximize the sky of the radiant heat loss, the PDRC is most effective.If R and Ɛ is high enough, even if the net heat loss will occur in the sun.
Developing practical PDRC designs is challenging: many recent design solutions are complex or expensive, and cannot be widely implemented or applied on roofs and buildings with different shapes and textures.So far, cheap and easy to apply white paint has been the benchmark for PDRC.However, white coatings usually have pigments that absorb ultraviolet light and do not reflect the longer wavelengths of sunlight well, so their performance is only moderate.
Columbia Engineering researchers have invented a high-performance external PDRC polymer coating with nanometer-to micron-scale air gaps that can be used as a spontaneous air cooler and can be dyed and painted on roofs, buildings, water tanks, vehicles, and even spaceships — anything that can be painted.They used a solution-based phase conversion technique to give the polymer a porous foam-like structure.Because of the difference in refractive index between the air voids and the surrounding polymer, the air voids in the porous polymer scatter and reflect sunlight.The polymer whitens and thus avoids solar heating, while its inherent emissivity allows it to efficiently radiate heat into the sky
Post time: Mar-18-2021