VENTILATION : AIRFLOW BALANCING
FLEXYII_WSHP-IOM-0909-E Page 51
2
nd
method when adjusting the pulley :
-Close the pulley fully and count the number of turns
from fully closed position. Using table_1 determine the
motor pulley actual diameter.
-Record the fix fan pulley diameter.(DF)
-Determine the fan speed using the following formulae:
FMMOTORFAN
/DDrpmrpm ×=
Where: rpm
MOTOR
:from the motor plate or table_2
D
M
: from table_1
D
F
: from machine
Once the pulleys are adjusted and the belt checked and
tensioned, start the fan motor and record the Amps and
Voltage between the phases:
Using the measured data and table_2
-Theoretical mechanical power at the fan shaft:
P
meca fan
= P
meca Motor
x η
Transmission
P
meca fan
= P
elec
x η
meca motor
x η
Transmission
P
meca fan
= V x I x √3 x cosϕ x η
meca motor
x η
Transmission
This formula can be approximated in this way
P
meca fan
= V x I x 1.73 x 0.85 x 0.76 x 0.9
With the fan “rpm” and the mechanical power at the fan
shaft an operating point and the supplied airflow can be
estimated using the fan curves.
CHECKING AIRFLOW AND ESP
Using the fan curves on page 36 to 40, the airflow, the total
pressure available (P
TOT
) and the corresponding dynamic
pressure (Pd) can now be estimated, for a specific
operating point;
The next step consists in estimating the pressure losses
across the unit.
This can be achieved using the “dirty filter pressure sensor”
and the accessories pressure drop table: table_3
Also the pressure drop due to the duct inlet into the roof-top
unit can be taken as 20 to 30 Pa.
∆P
INT
= ∆P
filter + coil
+ ∆P
Inlet
+ ∆P
Options
Using the results from above, the external static pressure
(ESP) can then be estimated:
ESP = P
TOT
- Pd - ∆P
INT
Table_ 2 Motor information
Motor Size Nom. Speed
Cos ϕ η
meca motor
0.75 kW 1400 rpm 0.77 0.70
1.1kW 1429 rpm 0.84 0.77
1.5kW 1428 rpm 0.82 0.79
2.2kW 1436 rpm 0.81 0.81
3.0kW 1437 rpm 0.81 0.83
4kW 1438 rpm 0.83 0.84
5.5kW 1447 rpm 0.85 0.86
7.5kW 1451 rpm 0.82 0.87
9.0kW 1455 rpm 0.82 0.88
11.0kW 1451 rpm 0.85 0.88
Table_3 Accessories pressure drops
Economiser
G4
Filters
F7
Filters
UV
LIGH
T
Hot
Water
coil S
Hot
Water
coil H
Electric
Heater
S
Electric
Heater
M
Electric
Heater
H
Heating
Gaz
fired H
Adjustable
roofcurb
Multidire
ctional
Roofcurb
Heat
Recovery
Modul
Fresh Air
12000 12 1 75 18 9 15 3 5 6 14 17 22 164
15000 19 7 105 30 13 22 6 7 7 23 27 33 204
85
23000 45 28 199 63 26 44 7 9 11 53 63 73 313
14000 17 5 94 26 11 19 6 7 8 20 23 30 191
18500 29 15 143 44 18 31 8 10 11 34 41 51 252
100
23000 45 28 199 63 26 44 11 14 16 53 63 78 313
15000 19 7 105 30 13 22 7 8 9 23 27 35 204
20500 36 21 167 52 21 37 10 12 13 42 50 62 279
120
23000 45 28 199 63 26 44 12 15 17 53 63 78 313
18000 6 1 75 15 6 10 4 5 7 16 30 35 170
150
26000 12 12 130 33 12 19 9 10 13 33 62 72 245
35000 22 29 204 54 19 33 15 18 23 59 112 131 329
21000 8 5 94 21 8 14 8 9 10 21 40 49 198
30000 16 19 161 42 15 25 10 13 15 44 82 95 282
170
35000 22 29 204 54 19 33 17 19 21 59 112 131 329
24000 12 3 88 18 7 11 16 15 14 21 53 67 173
35000 26 18 154 39 13 22 22 21 20 44 112 133 252
200
43000 39 31 211 54 19 31 24 26 29 66 169 195 310
27000 15 7 105 24 8 14 18 18 17 26 67 84 195
39000 32 24 182 46 16 26 24 24 25 55 139 163 281
230
43000 39 31 211 54 19 31 24 26 29 66 169 195 310
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