A case study of air pressure fluctuations in drainage stacks of high-rise residential buildings

Pressure variation in drainage stack is one of the key design parameters for a healthy drainage system in high-rise residential buildings as it might deplete the water seals of any connected appliances that prevent the ingress of foul gases into a habitable space. In this study, diurnal pressure variations in a drainage stack of a typical in-use high-rise residential building in Hong Kong were investigated. With the survey data of occupant load variations and diurnal WC flushing patterns collected from a number of similar local buildings, a significant association between the expected hourly WC flushes in the building and the air pressure variations in the stack was reported. Mathematical expressions were proposed to correlate the occurrence of maximum air pressure at certain locations in a stack with the expected hourly WC flushes in high-rise residential buildings. The results would be a useful source of reference to the development of control strategies against probable appliance seal loss in high-rise residential buildings.