national multiple family submetering and allocation billing program ...

- Expansion of the steel or aluminum prover to the heated water.
- If the design handles both cold and hot water accurately, it is not likely any test would
be performed to vary the water temperature during a single volumetric test.
- Distortions in meter readings as a result of pipe bends near the meter must be
considered in testing for accuracy as with such installations..
- Pipe bends should be included in the test protocol by incorporating an elbow within
an inch or so of the inlet to the meter if this is consistent with the meter application.
- Must also consider the slug of air that precedes the water to a showerhead or tub
spout. This is unavoidable in POU applications, and would compromise the
performance of any meter design.
- For lower flow ranges, wider tolerances are required; tolerance should be 10 percent;
the ASME standard specifies the minimum sensed flow at 0.1-gpm
- NIST is not too concerned with the tolerance at the lower flow ranges; standard
should specify some reasonable number.
- Handbook 44 tightens the tolerance of error for one meter in repeated tests to 1/5 the
range allowed by the ASME and AWWA standards. This requirement in Handbook
44 is new, and not strictly enforced, in part because testing errors often exceed the
tolerance allowed. If this requirement were to be strictly enforced, many meters in
common use today would be forced off the market, and most testing labs would have
to be upgraded.
- Plumbing systems are limited by code to 80 psi. POU manufacturers design meters
for that system and do not want meters tested under conditions that are not legal, and
potentially dangerous. Recent code changes are also being added to limit hot water
temperature to 130 degrees Fahrenheit.
- No water meter standard specifies accuracy at very low flows. POU meters may not
even rotate at 0.1 gpm under certain conditions. So how can they possible be within
10% accuracy? The AWWA standards specify no accuracy requirement between the
minimum sensed flow and the minimum measurable flow. ASME requires the
minimum measurable flow to be 0.25 gpm, and AWWA sets this level at 0.5 gpm.
- Issues to be considered in testing:
(1) Drying out and slug of air (tub and shower)
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