The effect of airflow rate control on the performance of a fan-assisted solar air heating façade

Solar Air Heating Façades (SAHF) can exploit solar radiation to partially fulfil the building heating and ventilation demand. This study was developed starting from an experimental campaign on a full scale fan-assisted SAHF applied to an outdoor test cell (TWINS) located in Torino (Italy). The data gathered from the monitoring activity were used to validate a white box model, developed in EnergyPlus. An axial fan drives the airflow through the façade; therefore, the supplied air temperature can be controlled by changing the fan speed. For this purpose, a PID (Proportional Integrative Derivative) controller was developed. This study demonstrates that the application of different control strategies significantly affects the façade overall performance and behaviour. Results highlight that the system can reach an average seasonal solar efficiency of up to 30%. Furthermore, by operating the system in heating-mode only and controlling the supply air temperature at 25°C, the system operates for 30% of the heating season, while at 40°C the system can provide fresh pre-heated air with an higher exergy level for the 10% of the winter period. Fan-assisted SAHF represent a valuable retrofit strategy solution in all buildings that present space limitations for the installation of centralised ventilation systems, helping to address the nZEB target requirements. (paper)