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Figure 12.4 Graph produced from customer consumption meter data-logging showing minimum/ average/maximum flow rates. (Source: F. S. Brainard & Co.)

customer consumption profile graphs derived from data-logging are given in Figs. 12.4 and 12.5.

If large meters have been in service for many years, current customer flows may not match the water demand variation occurring just after the meter was installed. Low flows may not be registered by some large, old meters and data-logging may prove the need to downsize the existing meter to an appropriate size. In regions with changing demographics and economies, customer consumption patterns can change significantly and this can affect water meter accuracy. For example, a 6-in turbine meter that reliably

Waterford MUA (Colgate Drive)

Waterford MUA (Colgate Drive)

431,744 377,776 323,808 269,840 215,872 S 161,904 107,936 53,968 0

0-10 10-40 40-100 100-200 200-300 300-400 400+ Flow rate (gpm)

Figure 12.5 Graph produced from customer consumption meter data-logging showing minimum/ average/maximum flow rates. (Source: F. S. Brainard & Co.)

0-10 10-40 40-100 100-200 200-300 300-400 400+ Flow rate (gpm)

431,744 377,776 323,808 269,840 215,872 S 161,904 107,936 53,968 0

Figure 12.5 Graph produced from customer consumption meter data-logging showing minimum/ average/maximum flow rates. (Source: F. S. Brainard & Co.)

measured consumption in a small factory using a steady volume of water becomes much less accurate when the factory building is converted to office space with much lower water consumption. The consumption profile in the office setting will likely motivate a switch to a smaller meter—perhaps several sizes smaller—in order to ensure that flows throughout the high and low ranges of the consumption profile are measured accurately. In order to determine whether or not meters are properly sized for existing customers, consumption profiles for a representative sample of large meter accounts should be obtained via data-logging or fixed network AMR. Data-logging devices can be attached to the customer meter and record individual meter pulses in order to develop a detailed customer consumption profile showing consumption variation at short time intervals. Meters with consumption consistently occurring in the low range of the meter suggest that the existing meter is oversized and downsizing would be beneficial to more accurately register the total flow. Figure 12.6 presents graphically customer meter test data gathered under a wide range of flows.5 As shown, meter error increases rapidly at very low flow rates. At very high flow rates the meter can under-perform due to excessive wear. The shaded area on the graphic represents flow rates that should be avoided in selecting the proper size of the meter.

When obtaining customer consumption data to develop a usage profile, recognize that it is very important not to base the decision only on 24 hours of data. A customer's consumption can vary greatly on a daily, weekly, or seasonal basis. Care should be taken to locate seasonal use information and also to understand the type of consumption for each specific case. Data should be gathered for at least several consecutive days, preferably 1 week. Separate weekly data collection periods may need to be scheduled in order to obtain consumption data from high- , medium- , and low-demand seasons.

Residential properties in warm climates often incur a significant seasonal increase in water consumption that reflects the hot weather and irrigation needs of residential landscapes. It is not unusual for more than 50% of warm climate residential consumption in industrialized nations to occur from outdoor irrigational use. Yet the high outdoor irrigation demand may only occur for 4 to 6 months out of the year. Similar swings in consumption might also occur in vacation properties that are unoccupied in the off

Figure 12.6 Range of appropriate sizing of a customer consumption meter to ensure necessary accuracy. (Source: Ref. 5)

season and heavily utilized during the peak season. Care needs to be taken when gathering consumption data so that consumption profile(s) are obtained to reflect the variations in demand that the customer property will incur. In many communities water consumption is notably higher during the warm or hot months of the year. Much of this increased water consumption goes to outdoor irrigation, but additional showers and bathing also occur during this time of year. Peak period consumption patterns can have a big impact on any potential meter sizing decision. When looking at consumption profiles in vacation or resort areas, obvious care has to be taken with the season. When considering the consumption profile of a large apartment block during winter and summer, the occupancy rate could change from 10 to 100%. Again the volume used will change dramatically, however most of the use will be at peak times, as people prepare for the day or evening ahead.

Large meters (1-in diameter and larger) are typically installed in multiunit residential buildings as well as commercial, industrial, or agricultural settings. Water demand profiles can vary widely among the different types of building uses and/or manufacturing processes that occur in some of these properties. Normally the largest variations are seen in commercial or industrial properties between weekday use and weekend use with minimal weekend consumption since business is closed during this period. Seasonal consumption variations depend upon the type of manufacturing or business process. Certain manufacturing processes may incur steady water consumption throughout the day, and maintain this pattern continuously. Other processes may utilize large quantities of water in batches, with high volume flows alternating with periods of minimal use. Some factories shut down processes during nights and weekends or may close for several weeks during holiday periods. The water utility manager should inquire about the water usage patterns of a particular facility before determining which periods of time to analyze using customer water consumption profiles.

The economics of meter right-sizing must also be taken into account. The water rate or tariff structure of most North American water utilities includes several component charges. A water charge is typically based upon consumption, with variations for class of customer as well as for volumes of consumption; typically increasing block charges, declining block charges or other billing structures. A separate waste water charge, or even storm water charge, may be included for water utilities that provide these additional services. Most water utilities also assess a fixed service charge to cover the administration expenses of metering, billing, and other overhead functions. Many water utilities base the service charge on the size of the customer meter, with the charge increasing dramatically with meter size. In downsizing from a larger meter of poor accuracy to a smaller meter of high accuracy, the water utility can more reliably capture the volume of water consumption and increase revenue from the usage charge. However, in reducing the size of the meter, the water utility could lose some revenue due to a smaller service charge. The net change in revenue to the utility, therefore, depends upon the amount of recovered revenue due to improved accuracy, offset by reduced service charges. Each customer account being considered for downsizing should, therefore, be carefully reviewed to determine the exact economic impact to the water utility. The Greater Cincinnati Water Works reported on the success of a structured large meter downsizing effort, but noted the dilemma of downsizing certain large meters when anticipating a net loss of revenue due to a significantly lower service charge.6

^Seasonal use variations of customer properties should be carefully checked when sizing meters.

Meter downsizing decisions should be approached with sensitivity when it appears that a reduced service charge makes the downsizing decision uneconomic for the water utility. Keeping a customer account with an oversized meter means that the recorded flow remains understated and the apparent loss is not reduced. Also, it becomes evident that the customer is paying a higher service charge than necessary since they could function (more accurately) with a smaller water meter. Water utilities that specifically avoid downsizing in this manner risk customer dissatisfaction should this information reach the customer. If many customers perceive that they are being overcharged by the water utility, a public relations backlash could result in negative media attention or fines if such actions violate any regulations. If the water utility manager maintains a "big picture" perspective of the value of meter accuracy and apparent loss reduction, he or she can tolerate the uneconomic downsizings of some large meters in order to provide equity to its customers and strive to optimize its apparent loss reduction from meter sizing improvements.

Meter right-sizing initiatives typically address large meters in settings where customer consumption patterns have changed due to building occupancy changes, or where an inappropriately selected or sized meter was originally installed. However, accurate and reliable small meters also incur low flow limitations in which a portion of flow is not registered. No meter is 100% accurate. While most meters have limitations only at very low flow rates, such unregistered flows can occur in hundreds or thousands of customer meters in a water utility, therefore the cumulative volume of unmeasured water can be significant. A common occurrence in North America is of flows below detectable limits (BDL) occuring from toilet leaks. Slight leaks in toilet flapper valves allow a continuous trickle of water to pass into the toilet and drain to waste. It is very common that these flows are so slight as not to be registered by many reliable brands of water meters. A similar low-flow condition has been documented in Europe in communities where it is common for individual buildings to have small roof tanks. The slow closing of ball valves included in the roof tanks results in flows that are lower than the starting flow of the customer water meter. One device that has been created to address metering low flow limitations is the unmeasured-flow reducer (UFR) which changes the flow regime passing through the water meter to batches that the water meter can measure.7 In this way, only flow rates that are sufficient to be registered by the meter are passed through the meter.8 Innovations in meter technology, data-logging, AMR, and devices such as the UFR continue to offer water utilities the means to measure water consumption with ever-improving accuracy. It is incumbent on the water utility manager, however, to assess the overall accuracy and reliability of their customer meter population and seek to improve where needed.

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