Phase change materials in passive solutions for maintaining thermal comfort in buildings

Accelerating climate change and the growing demand for energy-efficient solutions are driving research into innovative passive technologies for buildings. This study investigates the integration of Phase Change Materials (PCM) with an underfloor heating system in ground contact floors to enhance thermal performance and thermal comfort. Numerical simulations carried out in the ANSYS Transient Thermal module were used to develop and verify 3D models incorporating Rubitherm RT21 PCM (latent heat 165 kJ/kg, melting range 19 °C – 24 °C). An analysis of 27 different heating schedules was performed over 96-hour simulation periods. The results show that PCM integration reduces indoor air temperature amplitude by approximately 2 °C – 3 °C compared to the reference model without PCM. The PCM layer effectively absorbs heat during peak heating periods and releases it during cooling phases, thereby creating more stable indoor temperatures. The findings indicate that strategic scheduling of underfloor heating, combined with an appropriately designed PCM layer, is crucial for improving thermal stability without increasing energy consumption and provide practical guidance for the design of future hybrid passive-active systems in buildings, particularly in heating-dominated climates.