B023 Slope drain demands

Influence of a horizontal drainage pipe on stack demands for domestic washrooms

Brief:

A ‘fixture unit’ approach has been used to determine the drainage loads at a stack, with the assumptions of simultaneous operation of all connected appliances and no attenuation effect of flow rate along the drainage pipe. In this study, empirical expressions are proposed to determine the probable drainage loads for a stack serving a number of domestic washrooms of high-rise buildings in Hong Kong, taking into account the factors of the attenuation effects of an assigned gradient in a horizontal drainage pipe, as well as the discharge patterns and simultaneous use of appliances in a typical domestic washroom. With reported probable demand patterns of domestic appliances from laboratory testing results, on-site measurements and survey studies, the probable discharge flow patterns in the stack are estimated with Monte-Carlo simulations for the probable maximum discharge flow rates from a number of domestic washrooms at a limiting failure rate. The results showed that, as compared with the estimation method in current practice, a reduction of predicted discharge flow rate at the stack serving a number of typical domestic washrooms would be up to 12% by taking account of the above two factors.

Further information:

Wong LT, Mui KW, 2005. Influence of a horizontal drainage pipe on stack demands for domestic washrooms, Hubei-Hong Kong Joint symposium 2005 on Building Services Design, System Control and Value Evaluation, Wuhan, 1-2 July 2005, China. pp. 54-60.