Discharge demand analysis on a drainage stack for residential buildings

Abstract

PurposeTo determine the probable drainage load for sizing a stack serving a number of domestic washrooms in high‐rise buildings, with various occupant loads served by an appliance and simultaneous use of appliances in a domestic washroom taken into account.Design/methodology/approachWith the reported probable demand patterns of domestic appliances from laboratory testing results, on‐site measurements and survey studies, the probable maximum discharge flow rates from a number of domestic washrooms in a stack are estimated with Monte‐Carlo simulations.FindingsThe results demonstrated that the occupant loads and the usage patterns of an appliance had significant effects on the sizing of a drainage stack. It was reported that a reduction of 16 per cent in the design discharge flow rate for a washroom, at an occupant load of 4.2 persons per apartment, could be achieved with no more than one appliance discharging at a time. Influence of the occupant load served by an appliance on the probable maximum drainage demand at the stack was addressed. The results also showed a reduction of the predicted discharge flow rate at the stack serving a number of typical domestic washrooms from −26 to +21 per cent as compared with those predicted by the nominal occupant load in current practice.Research limitations/implicationsThe model parameters were determined from surveys for some high‐rise residential buildings in Hong Kong and from some laboratory testing results for typical domestic sanitary appliances. The model therefore may require adaptation for use in other countries.Practical implicationsA useful source of information in determining the stack size serving a number of domestic washrooms for those involved in building design and management related to drainage systems of residential buildings.Originality/valueThis paper proposes mathematical expressions in sizing a drainage stack serving a number of domestic washrooms in high‐rise buildings, where drainage demands are dependent on the building occupant loads at certain discharge patterns of appliances in a domestic washroom.