Development of innovative mortars incorporating phase change materials and by-products for high performance radiant floor systems

Radiant floors’ performance is highly dependent on the thermal properties of the heat transfer medium embedding the hydronic piping system for heating and cooling, which for wet construction is often a mortar. The objective of this paper is to study the effect that latent heat storage capacity and improved thermal conductivity have on the thermal performance of Radiant Floor Systems (RFS). To that end, two innovative mortars were developed: one incorporating Phase Change Materials (PCM); and another incorporating a dense by-product of the steel industry. The first mortar aims to provide the RFS with thermal energy storage capacity and the later has the goal of improving the mortar’s thermal conductivity by incorporating this high-density aggregate into its composition. The methodologic approach comprises the characterization of the thermophysical properties of the mortars developed, as well as the subsequent application of the selected compositions into an experimental RFS apparatus to evaluate the thermal performance under continuous and intermittent heating. The selected mortar incorporating microencapsulated PCM (mPCM) exhibited a mechanical strength loss of 68.1% (compressive strength) and 47.5% (flexural strength) in relation to the reference mortar, thermal conductivity of 0.33 W·m−1·K−1 and specific heat capacity of 1222 J·Kg−1·°C−1. The selected mortar incorporating high-density aggregates revealed a reduction of 16.1% for compressive strength and an increase of 10.0% of flexural strength, in relation to the same reference. Its thermal conductivity resulted of 0.87 W·m−1·K−1 and specific heat capacity of 379 J·Kg−1·°C−1. The thermal behaviour of the RFS specimens revealed the potential of incorporating mPCM into RFS, when intermittent heating relying on night-time operation is adopted, considering the maximum temperature fluctuation of 4.02 °C (PCM-RFS). Mortars with high conductive matrixes portray suitable solutions for quicker thermal responses, exhibiting heating rates of up to 9.6 °C·h−1, if followed by a continuous heating strategy with lower supply water temperatures.