Cool Roofs: Coatings, Glazings and Structures for Enhanced Thermal Performance

摘要

The roof of a building typically receives the highest solar energy intensities of any surface and can radiantly pump away a lot of heat to the atmosphere. If partly transparent and diffusive as in some skylights it is able to uniformly illuminate large internal areas. Care is needed with both opaque and transmitting systems to limit solar based heating of interiors. Enhancing or limiting heat loss also needs consideration. Various coating and doping strategies available for this purpose will be compared in terms of overall thermal performance via solar reflectance and thermal emittance, plus potential for local and global environmental impact when used at scale. The optimum coating and surface optical properties depend also on (a) overall roof structure; including sub-roof insulation, orientation, tilt and surface profile (b) local average climate conditions. Multiple benefits of optimized designs arise and extend beyond those experienced by the occupants. Summer peak load reductions can be very large if enough roofs have optimized properties. Simple roof modifications which enable collection and storage of substantial "cold" down to 6°C to 8°C below the coldest night-time ambient will be briefly outlined.