PLUMBING PIPE SIZING IN THE INDIAN CONTEXT

Abstract

The estimation of design water flow is the main determining factor in pipe sizing for water distribution within the building. The NBC of India. UIPC and IPC recommend the Hunter's Method (1940) for estimating water demand that solves complex problem based on the probabilistic approach. The number of fixtures employed to supply water, the probability of certain number of fixtures being simultaneously busy and the flow rate q of each type of fixtures are the three key parameters which affect design flow or demand in a building. But recently, serious questions have arisen about the accuracy of Hunter's method. With changes in personal habits, fixture design and building use, the feasibility of this 70 years old method is put into question. Hunter's thorough and classic method is not flexible to incorporate the current changes in water use patterns and high efficiency fixtures. In some instances, using the curve proposed in the method to estimate the water-demand load has given highly extended results. Incorrect pipe sizing results in higher material and labor costs. Household plumbing fixture changes need to be identified since the probabilistic method uses the mathematical parameters of a fixture's flow rate, the duration of the flow, and how often the fixture is in use. These fixture parameters have significantly changed since the original Hunter method. Hunter's curve was based on 1940 high-flow fixtures with a very high confidence level of 99th percentile in consumer satisfaction. Many researchers have proposed modifications to Hunter's curve by incorporating low flow rates of modern fixtures, the reduced probability of a modern fixture being on at any moment, and reduced level of services. Water use pattern in four multistoried residential buildings in lIT Roorkee campus has been studied in this work. A water demand table was developed using MS-Excel. The table utilizes the binomial distribution in hourly probability and maximum frequency of use. The result of these probabilities has used to generate a cumulative distribution function of demand flows, and the design 991h and 95th percentile water demand has been calculated. A comparison with probable peak water demand methods showed that Hunter's curve overestimates the water demand. The methodology can be extended to pipe sizing for other uses of drinking water - institutional, commercial, public etc. in future studies.