Planar Multilayer Thin Film Coatings for Passive Winter Thermal Management

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Asad, Muhammad
Nanophotonics , Passive heating , Zero energy building
Buildings are responsible for 40% of global energy consumption. 76% of that energy is spent on comfort control including heating, cooling and ventilation. This large energy consumption results in significant greenhouse gas emission, which adversely affects the global climate. The high cost of fossil fuel also causes widespread energy poverty. Adoption of passive heating schemes which utilize solar energy for indoor heating can greatly reduce the energy requirement of buildings in the cold climate. Currently available passive heating schemes often require significant investment and they cannot be easily retrofitted to existing buildings. Windows are a major source of heat loss in a typical building in the cold climate. Development of transparent solar energy harvesting coatings for windows can play a major role in reducing energy consumption and fuel costs. In recent years, there has been a great research effort towards designing transparent solar absorber coatings using nanophotonic structures for passive heating of windows. These coatings are highly efficient and can be retrofitted to existing windows. However, the nanophotonic designs proposed so far either require expensive materials for their implementation or require expensive fabrication processes, which are difficult to scale up. The objective of this thesis is to explore designs of transparent solar absorber coatings for windows which will overcome the limitations of previously reported nanophotonic designs. We investigate the applicability of planar multilayer thin films consisting of low cost materials for this purpose. Our study led to the proposals of two designs that predict temperature rise of 21 K and 25 K, while maintaining mean visible transmittance over 60%. We experimentally observed 6.9 K rise in temperature under sunlight for our design, which compares favorably against previously reported designs which are significantly more expensive and difficult to implement. The performance of our designs is expected to improve significantly if the fabrication process is optimized. These results illustrate the great promise that nanophotonics holds for the reduction of energy consumption of buildings, which will be a significant step towards helping the environment and improving the quality of life of people in many countries around the world.
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