Numerical study on latent heat storage and energy saving potential of PCM walls

The goal of this study is to numerically investigate the effects of different phase change material (PCM) types, thicknesses, and placement positions within the external wall structure on latent heat storage and, consequently, on heating and cooling energy savings in residential buildings. Three different PCM types were analyzed and compared with a phase stabilized material (PSM), which possesses identical thermal properties but does not undergo phase transition, to isolate and quantify the specific contribution of latent heat. In addition, comparisons with a conventional wall without PCM were carried out, enabling the evaluation of both latent heat contribution and the overall effect on thermal inertia. The analyses were conducted under the climatic condition of Istanbul, Turkey, which is classified as a Csa (hot-summer Mediterranean) climate according to the Koppen-Geiger classification. This study addresses not only annual and monthly analyses but also daily and hourly assessments, enabling a deeper understanding of the transient thermal behavior and thermal inertia of PCMs. The findings underline the importance of optimizing PCM type, thickness, and placement in building envelope design to maximize energy efficiency. The results reveal that placing PCM closer to the inner surface provides the most effective latent heat utilization and the highest energy savings, with 30mm RT18 reducing annual heating and cooling energy demand by up to 4% compared to the base case. While increasing PCM thickness from 1 mm to 30 mm generally reduced total annual energy demand (by 2.5% on average), the cooling load response was not consistent. For instance, when RT18 was placed near the outer surface, a 1 mm layer has same cooling demand as base case while an 18 mm layer increased it by 1% due to delayed heat release during peak cooling periods. For some cases, such as when RT21 and RT25 PCMs were positioned near the outer surface, the latent heat effect was negligible, resulting in nearly the same total annual load as the reference case. Moreover, when PCMs were placed closer to the inner surface, the latent heat contribution remained consistently positive across all thicknesses.