Climate-Responsive Optimization of Phase Change Materials for Energy-Efficient Building Envelopes in Diverse Climatic Regions of Ethiopia

Passive thermal energy storage systems, notably phase change materials (PCMs), offer promising solutions for improving energy efficiency amid rising global temperatures and increasing cooling demands. To address the need for climate-specific design strategies, this study investigates the thermal performance of PCM-integrated building envelopes across the diverse climatic zones of Ethiopia, a country marked by significant topographical and altitudinal variability. 22 representative locations were selected using the Köppen climate classification system. Five PCMs with distinct phase change temperature (PCT) (21 °C, 23 °C, 25 °C, 27 °C, and 29 °C) were analyzed under three installation scenarios: exterior (Case 1), interior (Case 2), and both sides (Case 3) of the insulation layer. Energy simulations, based on an ASHRAE Standard 90.1-2022 mid-rise apartment prototype, were conducted to assess annual cooling energy demand. Results reveal that the effectiveness of PCM is strongly influenced by both the installation position and the selected PCT. Case 2 generally yielded the most favorable outcomes. For instance, in the cooler highland regions of Robe (Cfb), a PCM with a PCT of 25 °C reduced cooling energy use by over 25 %, whereas in hotter desert areas such as Gode (BWh), PCMs with a PCT of 29 °C were more suitable. These findings highlight the critical role of climate-responsive PCM selection and placement in maximizing energy savings. The proposed optimization approach provides a valuable framework for passive thermal design in regions with similar climatic diversity, pending further empirical validation.