Lennox FLEXY II Series Installation, Operating And Maintenance page 39

VENTILATION : AIRFLOW BALANCING
EX AMPLE
The unit used f or this example is a FGM170ND with standard supply and return airf low conf iguration. It is also f itted with an
economiser and an electric heater type H.
It is fitted with 2 ADH450 L fans which curv e is shown on page 36 and 2x 5.5 kW motors..
-
Motor rpm: 1447 rpm
- cos = 0.83
- Voltage = 400V
- Current = 9.00A (per f an)
The unit is also f itted with 2 transmission kits 3.
- Fixed Fan pulley: 200mm
- Motor adjustable pulley ty pe "8550" opened 4 turns from fully closed or measured distance between pulley end plates is
29.1mm: from table_1 it can be determined that each motor pulley has a diameter of 114.2mm
630Pa
IOM – FLEXY II – 1007 – E
= V x I x 3 x cos x 
P
mec h fan
= 400 x 9.00 x 3 x 0.83 x 0.86 x 0.9 = 4.00kW
rpm = rpm
FAN MOTOR
x 
mec h motor
x D / D = 1447 x 114.2 / 200 = 826 rpm
M F
Using the fan curv e, the operating point can
be located.
In order to facilitate the calculation, you
won't make any mistake by considering
that the external static pressure available
is the one calculated
providing the half of the nominal flow
(here 15000m3/h).
It can be determined that the fan is providing
approximately 15000 m3/h with a total
pressure P
826rpm
The pressure losses in the unit are the sum
of all pressure drops across the different
parts of a unit:
Pa f or electric heater H

The dy namic pressure at 15000m
at the bottom of the f an curve.
The external static pressure av ailable is
theref ore
ESP = P
369 Pa
Trans mission
= 630 Pa
TOT
- Coil and f ilter (measured) = 89 Pa
- Inlet into the unit = 50 Pa
- Options = 16 Pa f or economiser and 15
P = 89 + 16 + 15 +50 = 170 Pa
Pd = 81 Pa

- Pd - P =630 - 91 - 170 =
TOT INT
with one fan
3
/h is given
Page 37