Thermal performance profiling of phase change materials integrated building envelopes through simulation-data envelopment analysis approach

Phase change materials (PCM) regulate the heat flow between the ambient and the indoor spaces by their latent capacitance. Performance assessment of PCM integrated wall systems are often based on the gross energy demand reduction or reduction in heat gain over the year. However, the efficacy of PCM integrated wall systems is also driven by the effective utilization of the maximum latent thermal energy storage capacity. This paper presents a framework for thermal performance profiling of PCM-integrated envelopes using a relative performance metric termed thermal calibre. Data Envelopment Analysis technique is used for determining the thermal calibre, where minimizing the heat gains & inside surface temperature of the envelope and maximizing the utilization of the latent heat capacity of PCM are the objective functions. The approach is demonstrated by considering 190 PCM-integrated building envelopes applied to a residential building in a hot-dry climatic region. The thermal calibre of the envelopes vary from 0.62 to 1. Thermal calibre effectively captures the impact of thermo-physical property, location of PCM in the envelope, variations in thermal boundary conditions, seasonal and diurnal variations. The thermal calibre of envelopes increases with an increase in thickness of internal PCM layers. In contrast, the thickness of external PCM layers does not significantly affect their thermal calibre. This approach reveals the efficacy of the wall system over time of the year and presents an opportunity to solicit season-optimal performance. This method can be used as a post-hoc assessment to building simulations and pareto optimization facilitating informed decision making in the material selection process.