Multiscale characterization of phase change materials for building thermal energy storage applications

Abstract

Phase change materials (PCMs) store and release large amounts of thermal energy because of their high latent energy storage capacity. However, long-term cyclic stability and subcooling issues are two of the major challenges for their use in building thermal energy storage (TES) applications. In this study, we conducted a comprehensive multiscale characterization of two commercially available organic PCMs, Puretemp 18 and Puretemp 23. At the microscale, differential scanning calorimetry (DSC) was utilized to characterize phase change temperature, specific heat, and latent heat. At the mesoscale, a heat flow meter apparatus (HFMA), following ASTM C1784 standard, was employed to measure the phase change temperature, specific heat and latent heat properties. A comparative analysis of latent heat as a function of temperature was conducted by integrating the DSC and HFMA results. At the macroscale, the thermal performance and cyclic stability of the TES system were evaluated using Puretemp 23. The TES system consisted of a finned tube heat exchanger with a storage volume of 0.0189 m3 (5 gallon), which represents a compact, real-world TES solution suitable for building energy storage. The results showed consistent thermal stability of the PCM over 200 cycles and the subcooling temperature remained within 0.2°C, which was not detected in smaller scale characterization methods. This underscores the importance of conducting the bulk-size PCM (macroscale) characterization. The proposed multiscale PCM characterization method provides a holistic comparison of important thermal storage properties while investigating the bulk-size behaviors. This approach can be extended to other PCM classes to guide the development of next generation TES applications.