Experimental study of the hydrodynamic and thermal performances of ventilated wall structures

The presence of a ventilated air gap behind the external cladding in a building envelope is known to have a tangible contribution to the overall performance of the wall assembly. In the present study, the hydrodynamic and thermal performances of ventilated wall structures in a full-scale test facility are experimentally investigated using data collected during a full-year measuring campaign. In particular, the impact of varying outdoor conditions, façade orientation, and thermal inertia of the walls on the airspeed in the cavity, temperature distribution on the surfaces, heat flux through the interior space, and heat flow in the air gap are evaluated. Additionally, the discussion on transient responses of the wall structure, driving forces applied to the airflow, the overall heat gain/loss through the interior surface of the wall, and heat recovery potential from the cavity are provided. Moreover, variation of the thermal resistance caused by the ventilated air-space is analyzed. The results reveal the importance of monitoring the outdoor microclimate conditions adjacent to the wall of interest to examine the performance of the wall structure properly. It is observed that the airflow characteristics in the cavity are better correlated with outdoor temperature than other weather parameters. It is shown that the thermal resistance of the ventilated cavity dynamically varies and is generally higher in the summertime compared to the wintertime. The results highlight the potential of harvested heat flow from the ventilated cavity reaching 158 kWh/month, which could be used as an additional energy source for buildings. The optimized air change rate in the air-space obtained in this research to simultaneously provide high cavity thermal resistance and high heat recovery from the air gap shows the necessity for considering a fan system to supply specific airflow in the cavity.