Heat meter
35
Notes on accuracy
The accuracy of all measured energies and energy flows depends on many factors and is to be
subject to closer consideration here.
• PT1000
class B
temperature sensors have an accuracy of +/- 0.55 K (at 50 °C).
• Errors in temperature capture by the X2 device are typ/- 0.4 K per channel.
For an assumed spread of 10 K, these two measuring errors result in a
maximum
measuring error
between the flow and return of +/- 1.90 K =
+/- 19.0 %
for class B and +/- 13.0 % for class A.
• At a lower spread, the percentage measuring error
increases
• The accuracy of the FTS 4-50DL flow sensor is approx.
+/- 1.5 %
In the
worst case
scenario, the maximum overall measuring error for heat metering therefore
equals:
1.19 x 1.015 = 1.208
This means heat metering accuracy of
+/- 20.8 %
in the
worst case scenario
(at 10 K spread,
without calibrating
the temperature sensors), although all measuring errors would then skew the
results to the
same
extent.
Experience has shown that a worst case scenario
never
actually occurs and in an unfavorable
scenario, half of this value can be expected. However, even 10.4 % is not justifiable.
After
calibrating
the temperature sensors (see above), the measuring error of the overall tempera
-
ture measurement reduces to a maximum 0.3 K. Relative to the spread of 10 K as assumed above,
this equals a measuring error of 3 %.
The maximum overall measuring error for the performance factor therefore equals:
1.03 x 1.015 = 1.045
At a
10 K spread
and
with calibrated
temperature sensors, heat metering accuracy therefore
improves for the
worst case scenario
to
+/- 4.5 %.
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