A novel approach based on equivalent sky radiative temperature for quick computation of radiative cooling in building energy simulation

Passive radiative cooling materials (RCM) can cool surfaces by radiating heat to outer space via long-wave radiation. In simulation application, co-simulation of the thermal process between RCMs and building structures is generally required; however, the high computing time cost and low integration level have hindered the integrated whole-building simulation in architectural design. Traditional building energy simulations utilize the effective sky temperature to numerically approximate the effect of sky radiation. However, given the limitations of effective sky temperature concept, it is more suitable to evaluate diffusive gray surfaces while not fully capturing the characteristics of radiative heat transfer for spectrum-selective surfaces. In this study, an innovative equivalent-sky-radiative temperature was introduced as a new equivalent parameter to accurately simulate the thermal performance of RCMs in buildings. Embedding this new parameter into whole-building energy simulation tools such as EnergyPlus and DeST is expected to significantly improve the calculation accuracy and reduce the computational cost. Case studies in this work have shown an average error of 5.47 W/m2. The generation of the new parameter for 50 cities worldwide also demonstrated the technical feasibility of applying the equivalent-sky-radiative temperatures to evaluate the thermal performance and energy savings of real-world RCMs in buildings.