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 typically +/- 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 unfavourable
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
temperature 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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