Experimental and numerical evaluation of a thermally activated precast concrete sandwich wall

Abstract

This study investigates the thermal performance of a thermally activated precast concrete sandwich wall (TA-PCSW) for low-temperature radiative heating and cooling in commercial buildings. A full-scale TA-PCSW panel was fabricated and tested using a rotatable guarded hot box to quantify effective thermal resistance (R-value) and thermal energy storage behavior under controlled boundary conditions. A 3D finite element model in COMSOL Multiphysics was then developed to assess how glass fiber–reinforced polymer (GFRP) shear connectors influence heat transfer, and the results guided development of a multilayer resistance-capacitance network comprising 13 thermal resistances and 12 capacitive elements (13R12C). To represent transient heat exchange between embedded hydronic loop and surrounding materials, the RC model was coupled with a number of transfer units (NTU) based formulation (13R12C-NTU) and calibrated using measured surface and outlet water temperatures. Results show GFRP shear connectors reduce the R-value by less than 1%, confirming minimal steady-state impact. Sensitivity study indicates charging time is highly dependent on inlet conditions: in cooling mode, 𝑡90 (time to reach 90% of steady-state) decreases from ~4.5 h at 1.9 L/min (0.5 gpm) and 14°C to ~2 h at 5.7 L/min (1.5 gpm), with each +1°C rise extending charging by ~12 min. Heating exhibits similar trends but requires 0.5–1 h longer, with ~1.7 h saved per 3.8 L/min (1 gpm). Overall, flow rate provides the primary driver at low rates, while temperature offers finer control at high rates.