Surfactant effects on air pressure transients in building drainage, waste and ventilation (DWV) systems

Building drainage, waste and ventilation (DWV) systems isolate the habitable space from the waste material with water trap seals at various points in the network. Current design guides aim to produce systems which protect these trap seals from unwanted air pressures, but are based on steady state experiments utilising cold clean water as a test media, and include a large ‘safety factor’ with no formal basis. However, most ‘gray’ and ‘black’ water sources are dosed with detergent, and are often warm, which significantly alters the behaviour when compared to clean water. This paper describes the current status of the investigation of paramaters affected in systems operating with detergent-dosed waste water over typical temperature ranges, then uses an existing EPSRC-funded mathematical model (AIRNET) based on these findings to assess the impact of the effect of detergents on existing building codes. The results quantify the effects of detergency with temperature and indicate a general shortfall in current code-based predictions, and suggest that building codes may need revision.