Phase change materials in thermally activated building systems: A comprehensive review

Abstract

Heating and cooling requirements in modern buildings are considerably high, where the building sector contributes 40% to the current end-use energy consumption, and its related CO2 emissions have increased by 1% in the past decade only. Different novel solutions have been proposed in the literature to reduce energy consumption and peak loads while maintaining the same thermal comfort levels within the building envelope. The use of phase change materials (PCMs) as thermal energy storage media is a promising concept for storing energy as latent heat and then releasing it when the temperature is lower than the melting point. This has the potential of shifting and dampening peak loads and stabilizing space air temperatures. PCMs can be integrated into the well-established low-temperature radiant heating technologies and/or the emerging high-temperature radiant cooling ones for additional benefits of enhanced thermal comfort, system size reduction, and annual energy savings. Multiple review articles on radiant systems or the application of PCMs in modern buildings are available in the literature, but there are no review articles focused on the interaction between the two technologies. This review article provides a brief background and a gentle introduction to radiant heating and cooling systems (RHCSs), as well as the use of PCMs in modern building applications. Then, the article comprehensively reviews the relatively limited state-of-the-art research on the use of PCMs in RHCSs to better understand the research progress and identify research gaps and questions to be tackled in future research. The literature shows a generally favorable impact of PCMs on radiant systems, with heating and cooling energy savings up to 54% and 50%, respectively, extended comfortable occupied hours by more than two folds, system cost reductions up to 5%, and payback periods of as low as 3.32 years. Some discrepancies exist among reported studies, especially regarding the performance of PCMs in dual mode (heating and cooling) systems, which is mainly due to the lack of clear integration schemes. It is concluded that the merits of using PCMs in RHCSs are outstanding, but the existing studies are not nearly sufficient to address such complex and dynamic systems. Hence, different future directions have been highlighted to accelerate the progress of this research field, including the need for optimizing the relative position of PCM layers, studying the economic aspects of using PCMs, detailed experimental case studies of full-scale buildings, user-friendly numerical models, and advanced control strategies to handle the slow thermal response of the PCM in RHCSs. Highlights Studies on the use of phase change materials in radiant systems are reviewed. Different integration schemes are analyzed for radiant heating and cooling. PCMs reduce heating and cooling energy consumption by up to 50%. PCMs extend the comfortable occupied hours by more than two folds. A clear lack of advanced control strategies is noticed in the literature.