Building drainage demands are assumed random and intermittent. The existing Hunter-based models have been developed to aid in the sizing of pipes for instantaneous demands but not to predict the occurrence and duration of such demands. This paper proposes a time series model to determine the occurrence and duration of drainage demand, which are greater than some predefined flow rates due to a number of appliances that discharge randomly and intermittently with variable flow rates. While the duration is resolved using the time series data for simultaneous demands, the occurrence together with the time-dependent flow rate is quantified via Monte Carlo simulation based on occupant usage patterns and appliance discharge profiles derived from appliance flushes at the base of the main vertical stack. The applicability of this model is demonstrated with example discharges from a number of water closet (WC) cisterns with reduced flush volume.

Practical application

This study will help designers determine the duration and occurrence of drainage demand due to a number of appliances that discharge randomly and intermittently with variable flow rates.