Annual performance assessment of phase change material–enhanced radiative cooling roofs through coupled thermal-dew modelling

• A coupled thermal-dew model for radiative cooling roofs simulation is developed. • The thermal-dew model accounts for both condensation and evaporation. • The model predicted up to 10% higher annual heat loss than conventional models. • Incorporating phase change material reduced annual heat transfer by up to 20%. • The model is applicable to building energy simulation and radiative dew collection. Passive daytime radiative coolers (PDRCs) are an effective solution for mitigating urban overheating and minimising building cooling energy consumption. Phase change material-enhanced radiative cooling (PCM-RC) roofs can further enhance summer passive cooling and mitigate winter overcooling. Most prior studies on PCM-RC roofs rely on short-term, summer-focused, material-level experiments for proof-of-concept demonstrations, leaving their year-round performance inadequately evaluated. Therefore, a reliable roof model is critically needed for long-term performance assessment. However, existing simulation models commonly neglect surface condensation and evaporation, even though these phenomena influence latent heat transfer and thermal performance. Here, a coupled thermal-dew model for year-round PCM-RC roof simulations was developed and validated against outdoor measurements. The discrepancies during evaporation and condensation accounted for a maximum 4.9% and 8.1% of the daily heat transfer and were further analysed to clarify the model limitations. The model was used to perform annual simulations of four representative roof types in Sydney’s climate, incorporating PDRC, PCM-RC, and reference coatings. Compared with the conventional model (without surface condensation/evaporation), the thermal-dew model predicted up to a 10% increase in the annual through-roof heat loss for PDRC roofs and a 4% increase for PCM-RC roofs. PCM-RC roofs exhibited up to 20% and 49% lower annual through-roof heat transfer than PDRC and reference black roofs, respectively, while maintaining comparable urban overheating mitigation performance. This work presents an experimentally validated thermal-dew model for year-round evaluation of PDRC and PCM-RC roofs, applicable to building performance simulation and dew collection analysis of radiative coolers.