Advancing cooling load assessment in solar-intensive climates: A ΔT-based solar-air temperature approach for enhanced free cooling modeling

This study introduces a novel solar-air temperature (T_sa)-driven framework to enhance the conventional Cooling Degree Hour (CDH) method for accurately assessing cooling demand and free cooling potential in high solar irradiance regions. Unlike standard CDH models that rely solely on ambient temperature and thus underestimate cooling loads, the proposed model incorporates T_sa, a composite parameter that integrates solar radiation, sky temperature, surface emissivity, and absorptivity, capturing both convective and radiative effects. A ΔT-based sky classification algorithm was developed using 31 years of hourly meteorological data for Muğla, Turkey, to dynamically estimate sky temperatures under varying cloud conditions. The study systematically investigates three indoor setpoint temperatures (18 °C, 22 °C, 26 °C) and multiple emissivity scenarios to quantify mechanical and free cooling demands. The results reveal that using T_sa instead of ambient temperature can increase the calculated CDH by up to 12 °C during peak summer midday, exposing the limitations of traditional models. At a setpoint of 26 °C and emissivity ε = 0.9, mechanical cooling demand drops by over 30 %, and annual free cooling hours exceed 61,000 °C·h. Even at lower setpoints (18 °C, 22 °C), considerable nighttime and shoulder-season free cooling potential was observed. This hybrid approach bridges empirical simplicity and physical realism, offering a scalable, low-data solution for early design decisions and policy applications. By addressing a key research gap, the exclusion of radiative gains in simplified cooling models, this study provides a climate-responsive methodology to advance sustainable building cooling strategies, especially in Mediterranean and solar-intensive climates.