national multiple family submetering and allocation billing program ...

- Plumbing systems are space constrained and meters are being installed in existing
systems; conditions of this existing plumbing dictate that these meters will end up in
an infinite number of configurations.
- A requirement for measurement at very low flows exists because of leakage in many
plumbing systems.
- If the accuracy tolerances required in laboratory tests are different from those
required in field applications, there should be a technical justification.
- Once installed, maintenance tolerances are the same as “acceptances tolerances” in
California. “Acceptance tolerances” are applied on new equipment or equipment that
has been adjusted and is being returned to service. “Maintenance tolerances” are
applied everywhere else.
- Conditions of temperature, water pressure, and orientation should be included in the
test regime; each test condition, however, would be in isolation from the other
conditions.
- If the device is designed for only one orientation, then the manufacturer should mark
the device as such.
- Repeatability is critical, both in the laboratory and in the field.
- A meter cannot be accurate to within ±1.5 percent if it is tested or used in both hot
and cold applications, because water expands by more than 1.5 percent from 60 to
140 degrees F. However, there are some non-POU meters where accuracy is not
affected by orientation and the meter can be calibrated to be accurate at any water
temperature. But these meters cannot avoid the accuracy compromise when the
temperature changes from one measurement to another, or during a single flow event.
However, the expansion of the water has no bearing on the measurement of the
volume unless there is a requirement to adjust back to some standard temperature,
which there is not.
- No correction is applied to account for expansion of water at the meter. The only
corrections made are to account for temperature change, if there is any during testing.
They are:
- Temperature change after the water is seen by the meter and when the prover is being
read, and
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