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Operating Checks
Air Flow Rate Determination for Fans
with Overhung Impeller
After the system has been installed and activated, it is
possible to regulate the air flow through the unit equipped
with a fan with overhung impeller using the simple method
of measuring in the diffuser. This method eliminates to
some extent errors in results determined by speed mea-
surements in a wind tunnel, which are caused mainly by
turbulent and non-linear air flow. For the diagram of the
measurement determination of the difference in the static
pressures in front of the inlet fan diffuser and in the fan
diffuser, refer to figure 24. The air flow rate is related to
the difference in static pressures in front of and in the fan
with overhung impeller; refer to the measurement diagram.
Figure 24
The air flow rate (of the fan) can be determined by the
calculation using the following formula:
. . . . .
V = k √Δ
If the fan is operated at a temperature different from
20 °C, the air flow rate will then be calculated using
the following formula:
V
&
=
Table 1
ρ
op
Impeller
k-factor
RH 22 C
RH 25 C
RH 28 C
RH 31 C
RH 35 C
121
RH 40 C
154
RH 45 C
197
RH 50 C
262
RH 56 C
308
RH 63 C
381
RH 71 C
490
RH 80 C
620
RH 90 C
789
RH 10 C
999
RH 11 C
1233
Table of K factor values for RH-C (Ziehl-Abegg) fan with
overhung impeller.
√Δ
√Δ
√Δ
√Δ p
.
w
ρ
k
p
20
⋅
⋅
Δ
.
w
20
ρ
op
qv = air flow rate
k –factor of the fan
47
(provided by the fan
ρ
60
&
=
V
20
⋅
k
manufacturer)
ρ
75
Δpw – static pressu-
op
95
re difference (mea-
sured value)
ρ
– air density at
op
the given tempera-
ture
Air Handling Units
Unit Operation Screening Checks
The operating staff's checking activities must be focused
on the following:
The air-handling unit operation and functioning, leak
tightness of connections, inspection doors and service
panels, temperature of energy media and transported air.
The condition and operation of systems associated with
the air-handling unit, whose proper functioning is needed
for proper operation of the air-handling unit as well as for
operation of the entire air-handling system.
Wiring
M & C system
Water heater system – circuit, pump operation
and water filters (also in SUMX)
Cooling system
Sanitary installation – condensate drainage
Gas heater system
Regular Inspections
The user will determine the intervals for regular inspections
of the air-handling unit according to the operating condi-
tions, however, at least once every three months. Within
the framework of the inspection, check the following:
Overall Check
Clean all parts of the air-handling unit
Fan Inspection
Check the fan operation (strange noises and excessive
vibrations of the unit) and, if needed, balance the fan, refer
to the section Unit First Start Inspection.
Check the impeller for cleanliness.
Check the tightening of the hub threaded pins.
Check the impeller for integrity and free rotation.
Check the assembly screw connections
for tightening.
Check the silent blocks for condition (damage).
Check the fan assembly elastic sleeves.
Check the motor and fan bearings in the fan case.
Check the fan belts for wear (if necessary, all fan
belts must be replaced).
⋅
Δ
p
Check the tension of the fan belts (if used)
.
20
w
Turn the tensioning screw to set the proper belt tension.
Excessive belt tension can cause overheating of the bea-
tings and damage or overloading of the fan motor.
Figure 25 – belt tensioning
tensioning screw
15
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