Lennox ROOFTOP FLEXY FXK 100, Installation, Operating And Maintenance

Page: 39 / 110

IOM – FLEXY II – 1007 – E Page 37
EXAMPLE
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)
P
mec h fan
= V x I x

3 x cos

x

mec h motor
x

Trans mission
= 400 x 9.00 x

3 x 0.83 x 0.86 x 0.9 = 4.00kW
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 114.2 mm
rpm
FAN
= rpm
MOTOR
x D
M
/ D
F
= 1447 x 114.2 / 200 = 826 rpm
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 with one fan
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
TOT
= 630 Pa
The pressure losses in the unit are the sum
of all pressure drops across the different
parts of a unit:
- Coil and f ilter (measured) = 89 Pa
- Inlet into the unit = 50 Pa
- Options = 16 Pa f or economiser and 15
Pa f or electric heater H

P = 89 + 16 + 15 +50 = 170 Pa
The dy namic pressure at 15000m
3
/h is given
at the bottom of the f an curve.
Pd = 81 Pa
The external static pressure av ailable is
theref ore
ESP = P
TOT
- Pd -

P
INT
=630 - 91 - 170 =
369 Pa
VENTILATION : AIRFLOW BALANCING
826rpm
630Pa