Numerical assessment of the thermal performance of a heated and cooled floor containing upgraded phase change materials

Abstract
A two-dimensional numerical model of a radiant floor heating system integrating phase change material (PCM) microcapsules microencapsulated in polyethylene spheres was elaborated to estimate its thermal performance. The outcomes point that ideal incorporation of the microcapsules directly above the heating pipes, with a 15% concentration in the cement mortar layer, meaningfully increases heat transfer to the upper floor surface. The parametric study highlights that increasing the pipe space extends the PCM melting time, stabilizes the surface temperature during the heating and cooling phases, and allows for a decrease in the number of pipes, thus improving the system's economic performance. A heating start-up temperature of 35°C is within the limits of thermal comfort, while higher temperatures generate discomfort, primarily during the heating phase. Evaluation between organic and inorganic PCMs shows that inorganic PCMs, particularly S27 hydrated salts, exhibit the best thermal performance, with a 4°C increase in temperature range and a 5,5-hour phase shift assessed to a floor without PCMs. The addition of conductive nanoparticles to form enhanced phase-change materials (NePCMs) achieves a total phase shift of 6.5 hours, ensuing significant cost savings. Finally, in cooling mode with water circulating at 19°C, a 4.5°C reduction in internal surface temperature is achieved.

Keywords: latent heat storage, microcapsules, NePCM, phase shift, thermal comfort.