Abstract
Instantaneous flow rate estimation is essential for sizing pipes and other components of water systems in buildings. Although various demand models have been developed in line with design and technology trends, most water supply system designs are routinely and substantially over-sized to keep failure risks to a minimum. Three major types of demand models from the literature are reviewed in this paper: (1) deterministic approach; (2) probabilistic approach; and (3) demand time-series approach. As findings show some widely used model estimates are much larger than the field measurements, this paper proposes a Bayesian approach to bridge the gap between model-based and field-measured values for the probable maximum simultaneous water demand. The proposed approach is flexible to adopt estimates as its prior values from a wide range of existing water demand models for determining the Bayesian coefficients for reference models, codes, and design standards with relevant measurement data. The approach provides a useful method not only for evaluating the corresponding demand values from various design references, but also for responding to the call for sustainable building design.
Highlights
Estimation of instantaneous flow rates is essential for sizing pipes and other components in a building water system [1]
Konen and Goncalves [7] reviewed a number of design flow determination standards and guidelines and concluded that deterministic equations and/or graphs developed for pipe sizing were mainly based on Rydberg’s model, Hunter’s model [2], or expressions that relate the sum of unitary flow rates to the design flow rate
A formula of design flow rate qs used for dimensioning of supply pipes in Scandinavian countries is given by the following equation, where pi is the probability of average water flow from each fixture qi, μ, qi is the nominal flow rate of fixture I, and k is the constant for a selected failure factor, q qs = qi,max + pi ∑ qi − qi,max + k qi,μ pi ∑ qi − qi,max
Summary
Estimation of instantaneous flow rates is essential for sizing pipes and other components in a building water system [1]. Design criteria have been judgmentally established to ensure the immediate provision of water services at an allowable failure rate [2]. Mazumdar et al [5] suggested reducing the confidence levels in Hunter’s binomial probability function [2] for better descriptions of water-saving appliances. Suitable confidence levels for various applications have not yet been derived based on field measurement data and that increases the need for re-evaluating the theoretical basis, as well as design practices for practical pipe sizing [6]. Measurements that rely on an opportunistic time series of flows make data validation complex and difficult [7]
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