Controlled inlet airflow in ventilated facades: a numerical analysis

A research study was conducted to investigate the summer thermal performance of different ventilated façades, by means of experimentally validated numerical simulation. Three ventilated configurations were tested: L, with a lightweight external layer, IM and EM with a massive cladding respectively in the inner and outer side of the air cavity. TRNSYS was used to simulate the thermal behaviour of the façades. Five increasing air speeds were imposed at the inlet (from 0.2m/s to 2m/s). Air temperature and heat flux trends, at different wall positions, were surveyed. The experimentation was carried out on a lightweight and hyper-insulated mock-up in Central Italy. The airflow rate at the inlet was controlled by means of pulse width modulation (PWM) controlled axial fans installed on top of the air gaps. Temperature, air velocity, and thermal flux measurements were collected to validate the model. Simulation results were later post-processed by means of linear regression analysis. As expected, as the airflow speed increased, the air temperature within the cavity gradually and asymptotically decreased. With air speeds above 1.6 m/s, the cavity temperatures in the massive configurations EM and IM settled at around the same value. Further investigation regarded the comparison of the heat flux profiles. The EM prototype was found to outperform the others since it more effectively prevented the heat from entering the test room and allowed a significant heat share to be released, too.