Novel indicators to quantify the effectiveness of phase change materials in buildings

The actual effectiveness of phase change materials (PCMs) in achieving building energy savings strongly depends on the number of entire phase change cycles they undergo within a year. While advanced building performance simulation tools are available, evaluating and enhancing the annual effectiveness of PCMs can be challenging. This research aims to address this issue by introducing novel effectiveness indicators that provide a better understanding of the physical behavior of passive PCMs in buildings, thereby enhancing their thermal performance. The proposed indicators quantify the effectiveness of PCMs by comparing the PCM-driven annual energy savings with the PCM heat latent storage capacity installed in the building. A sensitivity analysis is conducted using the Morris method to assess the influence of design variables related to both the building and the PCMs on the new PCM effectiveness indicators. For this, a case study building in Zone 4A (Mixed), according to the ASHRAE 169-2021 climate classification, is employed, and building energy simulations are performed using the EnergyPlus software to evaluate the performance of the different designs. The results reveal that building design variables, such as the window-to-wall ratio, have a significantly higher impact on the effectiveness of PCMs than typically employed PCM design variables, such as melting temperatures. These unprecedented findings indicate that designers could significantly improve the performance of passive PCMs in buildings by simultaneously designing the PCMs along with other building design variables, preferably at the initial stages. Moreover, the results show that a contradiction can exist between the building’s energy performance and the effectiveness of PCMs. This means that buildings with low energy performance achieve the best effectiveness for PCMs