A shot in the dark: The current state of PCM hysteresis modelling in building energy simulation software

Phase change materials (PCM) are receiving ever-growing attention as a promising construction material for improving building energy performance through thermal storage and peak load shifting. The analysis of PCM performance and decision-making related to PCM implementation in building envelopes often relies on building energy simulation software such as EnergyPlus – a de facto standard in the academic world and the industry. For a precise modelling of the dynamic PCM behaviour, it is essential to correctly account for PCM hysteresis. This work introduces two new implementations of PCM hysteresis models in EnergyPlus. Further, it provides an in-depth analysis of four publicly available EnergyPlus-based hysteresis models, including the two newly introduced ones, and identifies the existing limitations for each of them. Finally, it explores the effects of PCM model selection on decision-making using the example of novel PCM-embedded material development. The results of this study show that the current built-in hysteresis model in EnergyPlus is not implemented correctly, and none of the other analysed models is completely free of limitations. Moreover, this work draws attention to the existing contradictions between different PCM modelling approaches, highlighting the critical impact the selection of a PCM model has on PCM-related decision-making. We conclude that while the existing hysteresis models in EnergyPlus are operable – albeit with great caution – they are not yet at the stage where they could be used as a reliable decision-making support tool. Practical real-world integration of PCM in building envelopes is hardly possible without having dependable modelling tools to back it up, and the development of such tools requires far more attention than it is given at the moment.