From lab to building: Real-world integration of phase change materials for comfort, energy, and flexibility

Phase change materials (PCMs) are widely promoted for improving thermal comfort and reducing energy demand in buildings. Yet, most studies remain laboratory- or simulation-based, offering limited insight into real-world performance. This paper bridges that gap by synthesizing evidence from eight full-scale, monitored buildings at Technology Readiness Levels (TRL) 6-9, complemented by insights from an expert focus group. Results show that PCM effectiveness is governed primarily by design integration, not material formulation, with placement depth, control strategy, and climate alignment proving decisive. Across cases, measured performance indicates consistent but conditional benefits: peak indoor temperature reductions of 1-3 degrees Celsius, heating or cooling load savings of 10-25 %, and emerging though under-reported contributions to demand-side flexibility. A typology of PCM integration strategies is proposed, mapping observed outcomes by building type, climate, placement, and control logic. KPI synthesis reveals a previously undocumented trend: a moderate negative correlation between areal storage capacity and comfort-hour improvement, suggesting that greater storage does not necessarily yield better results. The study also identifies structural barriers to deployment, including the regulatory invisibility of latent storage and the absence of standards for building-level PCM testing and certification. By reframing PCMs as integrated building-system components rather than niche materials, this work offers design guidance, performance benchmarks, and a roadmap to advance PCM adoption toward more flexible, resilient buildings.