E. J. M. Blokker

Simulating Nonresidential Water Demand with a Stochastic End-Use Model

A water demand end-use model was developed to predict water demand patterns with a small time scale (1 s) and small spatial scale (residence level). The end-use model is based on statistical information of users and end-uses: census data such as the number of people per household and their ages; the frequency of use; duration and flow per water-use event; occurrence over the day for different end-uses such as flushing the toilet, doing the laundry, washing hands, etc. With this approach, water demand patterns can be simulated. The simulation results were compared to measured water demand patterns on attributes such as peak flow and daily total water use, as well as on the shape of the pattern and the frequency distribution of flows and accelerations in flow. The simulation results show a good correspondence to measured water demands. Because the end-use model is based on statistical information rather than flow measurements, the model is transferable to diverse residential areas in different countries. Th...

Radial transport processes as a precursor to particle deposition in drinking water distribution systems

Various particle transport mechanisms play a role in the build-up of discoloration potential in drinking water distribution networks. In order to enhance our understanding of and ability to predict this build-up, it is essential to recognize and understand their role. Gravitational settling with drag has primarily been considered in this context. However, since flow in water distribution pipes is nearly always in the turbulent regime, turbulent processes should be considered also. In addition to these, single particle effects and forces may affect radial particle transport. In this work, we present an application of a previously published turbulent particle deposition theory to conditions relevant for drinking water distribution systems. We predict quantitatively under which conditions turbophoresis, including the virtual mass effect, the Saffman lift force, and the Magnus force may contribute significantly to sediment transport in radial direction and compare these results to experimental observations. The contribution of turbophoresis is mostly limited to large particles (>50 μm) in transport mains, and not expected to play a major role in distribution mains. The Saffman lift force may enhance this process to some degree. The Magnus force is not expected to play any significant role in drinking water distribution systems.

COMBINING THE PROBABILISTIC DEMAND MODEL SIMDEUM WITH A NETWORK MODEL

Modeling of water quality in water distribution systems can be improved significantly when using stochastic demands. The stochastic demand pattern generator SIMDEUM is based on stochastic information on end users as retrieved from surveys. Stochastic demand patterns from SIMDEUM were applied in a small network model of 550 demand nodes in a residential area in the Netherlands. An EPANET based network solver was used to assess velocities and travel times. The actual measurements agree well with the simulations.

THE SELF-CLEANING VELOCITY IN PRACTICE

The Dutch drinking water companies are constructing velocity based self-cleaning residential drinking water distribution systems (DWDS). Field studies with particle counters have shown that these DWDS indeed do not foul. Laboratory studies have shown the settlement and re-suspension of particles in water mains under constant flow conditions. However, the relation between mains fouling and hydraulic conditions under realistic (variable) flows has not been determined. In the presented study, the effect of variable flow velocities on particles in a real residential DWDS was studied through a detailed analysis of turbidity measurements during flushing in combination with a detailed EPANET network model. Firstly, each pipe stretch was flushed with 1.5 m/s for three turnovers and most of the pipes appeared to be clean after the first turnover. This means that it was possible to link the measured turbidity to the location in the pipe from where it was re-suspended. Secondly, an all-pipes EPANET network model was filled with realistic demand patterns from the end-use model SIMDEUM; a small hydraulic time step (0.01 h) was used. This allowed for determining the maximum daily velocity occurring in each pipe stretch. The combination of the first and second step led to a graph of resuspended turbidity against maximum daily velocity. The study showed that in this residential DWDS there is a threshold value for the maximum velocity of 0.2 to 0.25 m/s above which the pipes remain clean. Thus, the existence of the self-cleaning velocity was demonstrated. This study helps in understanding particle behavior in DWDS.

COMPARISON OF WATER DEMAND MODELS: PRP AND SIMDEUM APPLIED TO MILFORD, OHIO, DATA

There is growing interest in modeling water demands on short time scales (as brief as one second) and small spatial scales (typically single homes). Buchberger et al. (1996, 2003) have developed the Poisson Rectangular Pulse (PRP) model for this purpose. Blokker et al. (in prep.) have developed an end-use model SIMDEUM (which stands for SIMulation of Demand, and End-Use Model) which is based on statistical information from end-uses and does not require any flow measurements. SIMDEUM was developed and validated for Dutch water use. In this paper the PRP model and SIMDEUM are compared with each other and with measured indoor water demands from 21 homes in Milford, Ohio. Both models compare well to the measurements; the PRP model works better in simulating the cumulative flows of a sum of 20, SIMDEUM works better in simulating the flows of a single home.

Self-Cleaning Networks Put to the Test

The Dutch drinking water companies design their water distribution systems according to the so-called New Design Rules, which allow for smaller and more branched distribution systems. Due to higher velocities these design rules hypothetically lead to resuspension and removal of particles and thus to self-cleaning networks. Three distribution networks were selected to test the validity of the new design rules. The first is a conventional (looped) network from 1986. The second network was built in 2002 and is branched but with relatively large diameters (110 and 63 mm). The third one was built in 2004 according to the new design rules: a branched PLUS network (with, at the ends, pipe diameters as small as 40 mm). By means of particle counting, flow measurements and flushing experiments it was proven that the branched PLUS network is self-cleaning, the branched network is partly self-cleaning and in the looped network sediment is building up leading to an increased discoloration risk.

SUBSTANDARD SUPPLY MINUTES IN THE NETHERLANDS

The new performance indicator Substandard Supply Minutes (SSM) is an extension of the performance indicator Customer Minutes Lost (CML). CML measures the average interruption time due to failures. SSM measures the average time that no drinking water is supplied. Substandard water supply is defined as supplying water that does not meet the quality standards or water that is supplied in too little quantity (too little pressure or an interruption of the water supply); the standards for water quality and pressure are defined in the Dutch Drinking Water Act. SSM includes interruptions due to failures of the distribution system as well as due to planned repairs and replacements. From September 2004 to March 2005 SSM was measured in a pilot project. Of the 13 Dutch water companies 7 joined this project. In 2006, SSM has become part of the benchmark of the Dutch water companies and most water companies use SSM in their asset management processes.

EXTERNAL EFFECTS OF PIPE BURSTS

Pipe bursts typically result in a deficient supply in terms of quantity and pressure or the introduction of pollutants. In January 2004 an incident took place in the Netherlands where a dike of a main transportation canal was leaking and almost collapsed. Leakage stopped after closing valves in a water main. This incident raised the awareness of the risks of pipe bursts to third parties (or so-called external effects). The Dutch drinking water branch initiated an inventory of water mains at risky locations and prepared to take corrective measures if deemed necessary. This article discusses how mains at risky locations are assessed based on the likelihood of a pipe burst and the possible consequences. It also includes a list of measures to limit the risk of pipe bursts.

MODELLING CHARACTERISTIC VALUES FOR NON-RESIDENTIAL WATER DEMAND

Little is known about the water demand of non-residential users. This complicates the design of outdoor and indoor water distributions systems. In general, it results in overdimensioned designs that potentially lead to water quality problems. Also in non-residential buildings, insufficient knowledge is available on hot water demand, complicating the choice of the proper type and capacity of the heater. For proper design of the drinking water distribution system outside as well as inside buildings, knowledge of the peak demand value is essential. Existing guidelines do generally overestimate peak demand and do not provide insight into hot water demand. Therefore, new design rules are desired that predict peak demand more accurately in order to obtain an economic, hygienic and microbiological reliable water system. In this paper, a procedure is developed to derive design rules to calculate peak demand values of both cold and hot water for different types of non-residential buildings of different sizes. The models are based on water demand patterns simulated by SIMDEUM, an end-use model to simulate residential and non-residential water demand patterns. The outcomes of the developed rules are compared with measured peak demand values and with existing design guidelines. The SIMDEUM based rules give a better prediction of the measured peak values for cold water flow than the existing guidelines and for several types of buildings. Therefore, they will lead to improved design of distribution network, of indoor plumbing and water heater capacity, resulting in more hygienic and economical installations. Due to the modular structure of SIMDEUM, it can be employed to construct all type of buildings, such as schools, sport complexes, restaurants, for which similar rules can be developed applying the presented procedure.