Stack Effect

The stack effect can be described as follows: warm air is lighter than cool air and it rises being replaced by cooler air. In UDDTs for instance, the solar radiation heat the vent pipe, which is constructed outside (exposed to the sun) and painted in black. When the air in the pipe heats up, it rises upwards out of the vent; a downward draught of cooler air of higher density then flows in through the squat plate hole, replacing the vacuum space created after warm air rising. The rate of ventilation is directly proportional to the size of openings ant the height difference between inlet and outlet. Aeration of the toilet cabin can increase the airflow and allow wind to pass through the cabine.