Indirect evaporative cooling by sub-roof forced ventilation to counter extreme heat events

In a pitched ventilated roof, an air stream enters a cavity below the roof surface through openings at the level of the gutters, then it flows up along the roof and is finally discharged through openings along the ridge. The heat brought by the absorbed solar radiation is removed thanks to the flow established by natural ventilation, but only in part because the flow is relatively weak and unstable. As shown in previous work, a stronger and more regular air flow can be ensured by forced ventilation, extracting the air by means of a fan after it has been collected along the ridge by a properly designed manifold. This setup can be further enhanced by humidifying and saturating the air as it enters the cavity, thus significantly lowering the downstream air temperature. An indirect evaporative cooling system is thus obtained, by which an inhabited space under the roof can be cooled through the ceiling while remaining sealed and unaffected by the evaporative process. In this work, the setup is analyzed by a mathematical model and the concept tested by means of a small scale test bed, showing that it can be used to counter extremely hot ambient conditions with a relatively low consumption of liquid water and almost negligible energy need.