Basic Documentation

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Siemens Universal controllers RMU710B, RMU720B, RMU730B CE1P3150en
Building Technologies Aggregates 03.10.2011
Unit:
This operating line contains the unit in text form. It is displayed for volumetric flow
display values. The numbers are matched to the standard unit m³/s. If another unit
is requested (e.g. m³/h), the K-factor must account for this.
Speed 1, Speed 2:
A two-speed fan allows for controlling to the volumetric flow values for speed 1 and
speed 2.
For 1-speed operation, the setpoints for Speed 1 and Speed 2 are the same.
K-factor:
If measurement of the dynamic pressure (internal volumetric flow calculation) is
configured (Case 1), the plant-specific K-factor must be calculated and indicated in
this operating line.
Use the following formula to calculate the K-factor:
K-factor
1000
_



dynp
flowvolumetric
Dynamic pressure and volumetric flow at a particular operating point are given.
The measured dynamic pressure of 500 [Pa] corresponds to a volumetric flow of
3.0 [m³/s] (10 800 [m³/h]) in the operating point.
This results in a K-factor
1000
][500
]/[3
3

Pa
sm
= 134
Air duct cross-sectional area, volumetric flow and atmospheric density are given.
The air duct has the following dimensions (width x height) 750 x 400 mm, resulting
in a cross section of A = 0.3 m². The volumetric flow is 1.4 [m³/s] (5'000 [m³/h]).
This results in an air velocity of:
v = volumetric flow / area = 1.4 [m³/s] / 0.3[m²] = 4.67 [m/s].
The dynamic pressure is calculated from the air velocity and the atmospheric
density by applying the following formula:
Dynamic pressure ∆p dyn
2
1

ρ *
2
v = 12.2 [Pa]
with ρ = atmospheric density, ca. 1.12 [kg / m³]
This results in a K-factor
1000
][2.12
]/[4.1
3

Pa
sm
= 401
If a volumetric flow measuring box provides the volumetric flow as 0…10 V signal
(Case 2), the value can be used as is.
The K-factor does not need to be calculated.
Note
Case 1
K-factor: Example 1
K-factor: Example 2
Case 2