Influence of phase change materials on thermal comfort, greenhouse gas emissions, and potential indoor air quality issues across different climatic regions: A critical review

There has been growing interest in applying phase change materials (PCMs) in buildings owing to their energy conservation/latent heat storage properties and potential to improve thermal comfort. Various reviews have extensively discussed the thermophysical properties of PCMs and their energy-saving potential in buildings. However, comprehensive reviews on the indoor thermal/ personal comfort behavior of PCMs under different climates remain limited. Therefore, this study aims to present a comprehensive state-of-the-art review of the impact of PCMs on indoor thermal comfort levels in buildings located in cities within different subclimate zones and their personal cooling effect when integrated with clothing (vest). In addition, greenhouse gas (GHG) mitigation potentials and indoor air pollutant emission properties of PCM-enhanced buildings were also reviewed. Hundreds of published articles of PCMs in PubMed and Scopus databases, including a manual search approach, were utilized. The results from this state-of-the-art study have shown that incorporating PCMs in buildings satisfactorily reduced the indoor air temperature of most buildings located in hot climate (BSh, BWh) zones, but very limited studies have been performed in the cold (Dfc, BSk) environments. In general, there was an improvement in the thermal comfort levels of the PCM-enhanced buildings. However, these were mostly assessed using indices such as predicted mean vote, predicted percentage of dissatisfied, comfort index, and total discomfort change, without any comprehensive survey studies (eg, based on sensation votes) using human subjects. The majority of personal cooling studies of PCM-integrated vests/garments showed good improvement in thermal comfort, especially in terms of skin temperature and thermal sensation. However, very few studies have shown a considerable reduction in the GHG emissions of PCM-enhanced buildings, and the knowledge of the long-term carbon dioxide (CO2) reduction capabilities of PCMs is limited. The profiling of PCMs revealed the presence of volatile organic compounds. However, studies on indoor air pollutant emissions and the potential health effects of PCMintegrated buildings are still lacking. The study is crucial to motivating green building engineers, indoor environmental quality (IEQ) researchers, and epidemiologists to embark on potential future research. Innovative technologies such as machine learning, artificial intelligence, Internet of Things, uncertainty analysis, and optimization can be utilized to predict thermal comfort, IEQ, and GHG emissions in PCM-incorporated buildings.