Page 205 - Water Loss Control

Contr olling Appar ent Losses—Customer Meter Inaccuracy 179

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 moti-
vate 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 ben-
eficial to more accurately register the total flow. Figure 12.6 presents graphically cus-
5
tomer meter test data gathered under a wide range of flows. 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 consump-
tion 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 consump-
tion in industrialized nations to occur from outdoor irrigational use. Yet the high out-
door 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

10
Water Water meter is too small
meter is
0 too large

–10
Error (%) –20

–30

–40

–50

–60
Qmin Flow rate Qmax

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