Discharge demand analysis on a drainage stack for residential buildings

Purpose - To 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/approach - With 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. Findings - The 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/implications - The 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 implications - A 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/value - This 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.