Modeling system demands for domestic flushing in residential buildings

Domestic flushing water demands are transient and influenced by occupant load variations as well as appliance usage patterns. For proper planning of flushing water supply and treatment plant facilities in Hong Kong, this study proposes a mathematical model to describe the flushing water demands for high-rise residential buildings. The model parameters were identified from a recent survey on the WC usage patterns of occupants in 14 high-rise residential buildings of Hong Kong. The occupant load factor, diurnal variation of flushing, discharge and refilling durations and volume of WC cisterns recorded from 597 households were used to determine the uncertainties of the system demands and the risks of overloading the flushing water plant. The model predictions were compared with field measurements from typical residential buildings in Hong Kong. Uncertainties due to appliance usage patterns, occupant load variations and discharges to the drainage system were also demonstrated, it was found that the user demand contributed significantly to the uncertainties. The output of this study provides a template in developing a demand model for the flushing water system design of highrise residential buildings. Together with the consideration of the associated risks of plant overloading, the model would be useful for calculating the capacity of a flushing water plant.Department of Building Services EngineeringRefereed conference pape