Novel methods of inducing air flows within buildings.

Water use is distributed throughout building structures. Energy used to pump the water to higher levels in the building is not currently recovered, and is dissipated by performing work on air in the ventilation system which is vented to the atmosphere, when the water is discharged into the drainage stack. This energy can be utilised productively, however, by strategically placing the air inlet for the drainage stack inside the building, thereby utilising the potential energy stored in the water to draw air through the building. Airflow induction by falling water films is a well known problem in the drainage industry, and airflow rates of 10-20 times the water flow rate are common. Basic analysis of the ventilation requirements for typical large buildings suggest that this may contribute between 1 and 7.5% of the total ventilation requirement. Air admittance valves would be effective at isolating the habitable space from the waste water.