A variable thermal transmittance adaptive wall: comparison between CFD simulations and experimental tests

• A wall with variable thermophysical properties is proposed; • The wall thermal transmittance may be reduced up to ten times in a few minutes; • CFD simulations assess the thermal behaviour in different conditions; • Hot box experimental tests validated the performance of the innovative wall. Building energy consumption plays a major role in global greenhouse gas emissions. Traditional building envelopes struggle to adapt to fluctuating environmental conditions. This study investigates an innovative solution: the variable thermal transmittance wall: an adaptive building envelope capable of dynamically modifying its insulation level to optimize energy performance. The system incorporates embedded fluid-filled coils on both inner and outer wall surfaces. By controlling the fluid circulation, the wall can switch between insulating and conductive states, enhancing thermal comfort and reducing reliance on HVAC systems. A comprehensive approach combining Computational Fluid Dynamics (CFD) simulations and experimental testing was used to evaluate the wall performance. CFD analyses provided detailed insights into temperature distributions and thermal transmittance, while experimental tests using a hot box apparatus validated the numerical results. Materials used in the wall were also tested with a guarded hot plate to ensure accurate input data. Results show that the thermal transmittance can be adjusted by over a factor of ten (from 0.32 W/m 2 K up to 3.22 W/m 2 K), allowing the wall to function adaptively across different seasonal and diurnal conditions. The close agreement between CFD and experimental data, with differences moving from 3 % to 13 %, confirms the potential of this technology to significantly reduce energy consumption and improve building sustainability.