Browsing by Author "Meyer, Daniel (Niel)"

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    The effect of controlled pressure adjustment on consumer water demand in an urban water distribution system
    (Stellenbosch : Stellenbosch University, 2018-03) Meyer, Daniel (Niel); Jacobs, H. E.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: Pressure management is commonly employed as part of water conservation and water demand management strategies in water distribution systems (WDS). Most of the earlier work on this subject focussed on the reduction of water leakage and of burst pipes as a result of pressure reduction, and few studies have been undertaken to investigate the pressure-demand relationship. In this regard, a series of pressure adjustments in three operational district metered areas (DMAs) were successfully planned and conducted to assess the impact of pressure change on the total water demand in each DMA as well as on the water demand of 76 consumers. All three research sites reported a positive relationship between pressure change and consumer demand, where reduced pressure resulted in reduced demand. The impact of pressure on demand varied from one research site to the next. Two significant factors were identified which could influence elasticity of demand to pressure, namely: the presence of on-site leakage and the presence of household plumbing pressure reducing valves (PRVs). For the sites investigated, on-site leakage was one of the main factors behind the pressure-demand relationship and where on-site leakage was excluded the impact of pressure changes on demand was generally found to decrease. The power regression model suggested an elasticity of demand to pressure in the range of ≈0.15 to ≈0.30 where on-site leakage was included, and in the range of ≈0.05 to ≈0.25 where on-site leakage was excluded. The impact of pressure changes on consumer demand may be perceived to be relatively low, but could be partially explained by the presence of household plumbing PRVs. If the pressure to a building is regulated by a household plumbing PRV (often installed on the supply to a hot water geyser) then changes in the WDS pressure are not expected to influence supply pressure at individual end-uses downstream of such a plumbing PRV, unless the WDS pressure is reduced below the setting of the plumbing PRV. The elasticity of demand to pressure (excluding on-site leakage) was in the range of ≈0.05 for DMAs with a high likelihood of household plumbing PRVs and in the range of ≈0.25 for the DMA where fewer properties were expected to have such PRVs. The finding has significant implications for pressure management programmes, suggesting that consumer demand in suburban areas (excluding on-site leakage) may in some cases not reduce notably with relatively large changes in pressure, probably due to the presence of household plumbing PRVs which would have controlled pressure to some end-use points in the home in the first place. The field exercise confirmed that individual consumer demand would not necessarily decrease with reduced pressure, and that the impact of non-technical aspects could surpass pressure-induced change for an individual consumer. A basic but useful approach was proposed to estimate the demand component in the DMA from the flow recording data. The study also highlighted the practical lower limit of pressure reduction in the DMAs investigated, which may be of use for water utilities when planning pressure reduction programmes.