Evaporation and air movement:
The energy source for the solar sludge drying process is basically the solar radiation. This radiation is transmitted through the building shell and absorbed by the sewage sludge and is warming up this sludge. This causes an increase of the vapor pressure in the sludge and is therefore driving out water molecules into the air above.
Without air movement, this evaporation is causing a saturated layer of air right above the sludge surface.
This humid layer of air leads to a decreased evaporation rates, this need to be avoided. Thus, the halls need to be ventilated proper.
The fresh air is let in through openings at the bottom of the side walls, the exhaust air is discharged through the roof flaps – wet, warm air is lighter than dry air.
The internal ventilators are destroying the saturated layer of air, this assists the drying process.