B082 Fixture units

Fixture units at choices of reference design flow rates for simultaneous demand problems of larger water supply systems of Hong Kong

Brief:

Fixture unit approach used for estimating the probable maximum simultaneous demands in building water supply systems is based on a fact that a given simultaneous reference design flow rate may be produced by different numbers of identical appliances characterized by the appliances’ discharging flow rates and discharge probabilities. Each appliance is represented by a fixture unit value, which indicates the appliance associated with the same simultaneous demand of a number of base case appliances characterized by the base case discharging flow rate and discharge probability. The validity of the selected reference design flow rate and its sensitivity to the probable maximum simultaneous demand for water systems in high-rise residential buildings are examined in this paper. In particular, fixture units and the estimated probable maximum simultaneous demands due to appliances attributed by discharge probabilities and discharging flow rates ranged from 1/8 to 8 times the based case attributes are considered. Estimated demands from the fixture unit approach are compared with computational results for an example water supply installation by Monte-Carlo simulations. The results showed that the existing choice of a reference flow rate at 10 Ls^-1 for the fixture unit approach would be sufficient in determining the probable maximum simultaneous demands not to exceed a probable failure rate of 1% for 900 pairs of WC-and-washbasin installations in residential buildings. An increased reference design flow rate would be required for the applications of the fixture unit approach in demand analysis of larger water installations in similar densely built environment.

Further Information:

Wong LT, Mui KW, 2009. Fixture units at choices of reference design flow rates for simultaneous demand problems of larger water supply systems of Hong Kong, The 35th CIBW062 International Symposium of Water Supply and Drainage for Buildings, 7-9 September, Düsseldorf, Germany, pp. 26-38.