2020-388 Spectrally Selective Thermal Radiators for Cooling of Vertical or Horizontal Surfaces with Limited View of the Sky

SUMMARY

UCLA researchers in the Department of Materials Science and Engineering have developed a passive radiative cooling design for building surfaces that have a limited view of the sky by using spectrally selective thermal radiating materials.

BACKGROUND

Passive radiative cooling (PRC), a process where objects on Earth radiate heat into outer space, is a promising method for cooling buildings and surfaces exposed to the sky. As a potential alternative to air-conditioners, the effectiveness of PRC has been severely limited due to available view (exposure) of these surfaces to the sky. In addition, PRC heat loss occurs only at wavelengths in the thermal window of the atmosphere, but heat gain occurs across all thermal wavelengths. The resulting heat gain radiated from nearby objects is typically greater than the heat loss through PRC, resulting in buildings heating up, even when not exposed to direct sunlight. For PRC to be a viable cooling method, innovations are needed for its use with surfaces with a limited view of the sky and exposure to thermal radiation.

INNOVATION

UCLA researchers have developed a method for achieving passive radiative cooling in vertical (e.g. walls of buildings) and horizontal (e.g. roofs) surfaces with limited view of the sky. The method uses selective emitters made of polymer coatings on metal, which are highly scalable, cheaply manufactured and easily applied onto surfaces. The emitter absorbs and emits in specific portions of the infrared wavelengths, allowing for lower steady-state temperatures and, in most situations, a net cooling effect even with limited view of the sky. The polymer composition can be modified for application. By restricting heat loss and gain only to specific wavelengths, a large amount of radiative heat from terrestrial sources is reflected, enabling a higher degree of cooling.

POTENTIAL APPLICATIONS