6.3 Volume flow rate measurement
For testing the volume flow rate or differential pressure
transducer, the differential pressure
∆
p
w
(effective pres-
sure) can be measured directly at the differential pres-
sure sensor of the air terminal unit by means of a pres-
sure gauge (not on type TVE).
Attention:
During the measurement, the actuator of the
control component must be switched off, e.g. by
switching off the supply voltage.
The connection for the pressure gauge must be
selected depending on the transmitter type (dynamic or
static) of the fitted control component:
Dynamic - Pressure measurement only directly at the
differential pressure sensor of the terminal
unit (parallel measurement can falsify the
result).
Static
- Parallel measurement to the transducer of
the control component with its hose connec-
tions attached; the measurement is per-
formed at T-pieces inserted in the meas-
uring hoses at the factory.
Alternative measurement point
Differential pressure measurement directly in the
ducting as an alternative to the differential pressure
sensor of the terminal unit requires a high degree of
expertise and experience.
For sufficiently reliable differential pressure measure-
ment results, a complex network measurement (gravity
line method) and a final error propagation calculation in
accordance with EN 12599 must be adhered to.
6.3.1 Volume flow rate calculation
The volume flow rate is calculated according to the fol-
lowing formula:
Fig. 30: Calculation of the volume flow rate
Volume flow rate
∆
p
w
Measured effective pressure in Pascal [Pa]
C
Unit constant for air density
ρ
= 1.2 kg/m³,
Chapter 9 ‘K values’ on page 29
It should be noted that the volume flow rate determined
depends on the current flow conditions in the ducting
and that the measurement only corresponds to an
instantaneous value without any averaging.
Note:
It is not possible to calculate the volume flow rate
according to this formula for the LCV and TVE types, as
the unit constant C depends on the current blade angle.
Commissioning and operation
Volume flow rate measurement > Volume flow rate calculation
VAV terminal units VARYCONTROL
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