By Fabian Papa and Bradley Jenks
In recognition of the intrinsic connection between water supply and energy consumption, and more particularly the needless use of energy to pump water which is lost through leaks in municipal water distribution systems, a multi-year project has recently been initiated with the support of Ontario’s Independent Electricity Services Operator (IESO) Grid Innovation Fund.
This cross-sectoral collaboration which realizes broader energy efficiency gains by transcending typical municipal jurisdictional boundaries is being led by HydraTek & Associates, in collaboration with the Ontario Clean Water Agency, the Ontario Water Works Association, the University of Toronto, and the Regions of Durham and York, and the City of Ottawa.
The goal of the project is to provide municipalities with a cost-efficient method to measure minimum night flows (MNFs), being an indicator of leakage. It will also test whether the application of permanent pressure management systems to reduce leakage and, hence, pumping as well as other energy inputs, will yield sufficient benefits to warrant their implementation. Finally, it will provide valuable system performance information and drive awareness on leakage reduction practices and value.
The project will involve conducting field tests across 20 temporary district metered areas (DMAs) in various municipalities throughout Ontario. DMAs are segmented portions of a water distribution system isolated from other parts, so inflows and outflows can be accurately measured. In addition to receiving direct, accurate and reliable performance measurements of selected parts of their networks, participating municipalities will be able to compare how these performances compare amongst their peers and industry benchmarks.
Minimum night flow
The concept behind MNF analysis is that the degree of leakage may be accurately determined when customer consumption is at a minimum. (See Figure 1) The flow into a DMA that is in excess of this legitimate consumption is leakage. Of course, to estimate the leakage with reasonable accuracy, one must know the degree of consumption. This can be estimated based on minimum night factors as demand characteristics of residential customers are often quite consistent.
Another method to understand minimum night consumption is to have customer-level metering data at a suitable interval (e.g., one hour, preferably less) which is becoming increasingly available as municipalities migrate towards smart meters and automatic meter reading (AMR) and/or advanced metering infrastructure (AMI).
This project focuses primarily on residential areas so as to derive data and statistics that are directly comparable and can be used for benchmarking purposes. As well, testing will be restricted to non-irrigation months (generally November to April) given that the impact of irrigation systems (which are often automated) on demand patterns can be significant and in some cases can dwarf what would be a typical diurnal demand pattern.
The objective is to achieve the highest quality of data that can be used as a basis for meaningful comparison with other testing conducted in similar circumstances.
British engineer and water loss expert, Dewi Rogers, has worked in over 30 countries around the world. In the absence of direct customer meter readings (e.g., AMR or AMI) to compare DMA inflows to consumption for purposes of leakage estimation, he applies typical demand profiles derived from the monitoring of a large sample of customer meters. More particularly, he uses a minimum night factor which is defined as the lowest fraction of average consumption in a typical diurnal pattern. His assessment of thousands of residential properties across multiple countries shows that the results are surprisingly consistent.
Data collected from various Canadian utilities suggest a lower threshold in MNF relative to DMA size, representing well-performing DMAs. (See Figure 2)
Results from this project will provide additional data to strengthen such benchmarking methods for use in the Canadian context, as well as the reliability in interpreting any individual results, including identifying poorly performing DMAs relative to their peers.
Apart from the MNF measurements under normal operating conditions, the project also involves testing the effectiveness of applying reduced pressures to the DMAs in respect of leakage reduction. That is, given that leakage is pressure-dependent, a reduction in pressure will result in a reduction in leakage. This project aims to seek the degree to which this can be achieved through direct and affordable measurements, such that reliable business cases for intervention can be developed.
If appropriate, permanent installations of DMAs with pressure management, commonly referred to as pressure managed areas (PMAs), may be warranted.
Mobile testing unit
While it is desirable to be able to measure flows into a DMA on a permanent basis, the investment to do so is not trivial.
Mobile testing allows for a rather affordable means to obtain meaningful measurements. These can be used to help make informed decisions about where investment may be most cost-effectively directed. It also allows for a consistent means of measurement, which can be used to determine the degree of performance improvement realized by any system interventions to reduce leakage. It is important to note that IESO is expected to offer further incentive funding for those municipalities that demonstrate performance improvement.
The mobile unit consists of a flow meter, appropriately selected to be able to accurately and reliably measure MNF rates from rather small DMAs (or subsets thereof), an adjustable pressure reducing valve (PRV), and piping, ports, pressure gauges and related fittings.
In terms of its application, it is highly important that the hydraulic integrity of the DMA be established to ensure that no flow passes at any of the isolation valves which separate the DMA from the remainder of the network. This is accomplished by performing zero-pressure tests between the isolation valve and an adjacent valve. Although brief in duration, this requires careful planning and communication with affected customers. Flow into the mobile testing unit occurs through bypassing a closed isolation valve.
In earlier work, conducted by Ottawa over a decade ago, taps were installed within chambers on either side of isolation valves. This procedure is expected to be applicable to most of the testing sites in this program.
The mobile unit is specifically designed for accurate and reliable MNF measurement. Depending on the size of the DMA and its demand characteristics, it may not be suitable for use due to the hydraulic losses that would accompany higher velocities, particularly during the diurnal peak periods. For each temporary DMA, testing is planned to be conducted over a series of three to four night periods, from 12 a.m. to 6 a.m.
Participating municipalities wanted
There is funding available to support up to 20 testing locations. Participation involves in-kind contributions in the form of operator support in preparation for, and during, testing, as well as a modest financial contribution. Included with participation are two workshops. One will be held prior to testing for general training to raise awareness and elevate understanding of water loss management. The second will be held after testing is done to re-review the concepts from the first workshop as well as to review and interpret results of the testing.
Anyone interested in participating in the study, should contact the authors.
This article appears in ES&E Magazine’s April 2019 issue.