Comprehensive evaluation of thermal and energy performance of radiative roof cooling in buildings

This paper newly established a radiative roof cooling performance model to conduct thorough parametric studies on pivotal factors governing achievable equilibrium temperature and net cooling power in building roofs. A detailed building model integrated with radiative roof cooling considering typical climate regions in China was correspondingly developed to evaluate building thermal response and energy efficiency. The results indicate that compared with broadband and transmittance based adaptive emitters as roof surfaces, atmospheric window based selective emitter can achieve the minimum sub-ambient equilibrium temperature. Net cooling powers are reduced by 13-33.6 W/m2 and sub-ambient equilibrium temperatures are weakened by 7.1-13.5 degrees C with atmospheric precipitable water vapor increasing from 2.3 to 10 mm. The cooler degree of roof top temperature can reach over 30 degrees C under radiative roof surface which is conducive to avoiding thermal shock. The roof bottom temperature reduction noticeably reaches up to 13.8 degrees C for non-air-conditioned buildings, guaranteeing a more thermally comfortable built environment. The annual energy savings turn out to be positive for five typical cities, where cooling load dominant regions exhibit the most saving potentials with the saving rates of 7.1% for Hong Kong and 9.3% for Kunming respectively. With the application of a radiative roof cooling surface, the heat resistance layer can be removed from the thermal perspective for cost savings. The study sheds light on the promising benefits of radiative roof cooling for achieving energy efficient buildings in China.