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Helios
Design of ventilation systems Fan laws and performance curves
Fan performance units
Air flow volume V [m3/h, m3/s] Total pressure
Aptotal = Apstat. + pdyn. [Pa]
Static pressure
Apstat. = Aptotal - pdyn. [Pa]
Dynamic pressure pdyn = p/2-c2 [Pa] Shaft power Pw [W, kW]
Nominal motor power P [W, kW] Sound power/pressure level
LwA,LpA,[dB(A)]
All figures were measured on a test chamber stand to DIN 24163 Pt. 2. The noise figures were measured in an acoustic room simulating spherical sound level propagation conforming to DIN 45635 Pt. 1, 2.
Performance curves
The characteristic of a fan is shown in form of a performance curve. In a performance curve the air flow volu­me is given in relation to a static pressure (Apstat) or a total pressure (Aptot). The working point WP is the meeting point between the fan's performance curve and the syste­m's resistance curve (Apstat.). The air flow volume can be determined by drawing a vertical line down­wards.
System resistance curve
The pressure of a system changes as a square of the changing air flow volume.
System's resistance
Ap = k • V2
Calculation of the required shaft power of a fan
VAR.. 400/2
n = 2900 1/min
Fig.
Frequency
Hz
Total
125
250
500
1k
2k
4k
8k
16
Lwa Air noise
dB(A)
98
69
80
91
94
94
90
81
LpA4m Air noise
dB(A)
78
49
60
71
74
74
70
71
Pw1 = V ' A pto 1 ' [kW] 1000 ' n
Apstat
Pa 100
80
60
40
20
p = 1,20 kg/m3
Aptot= Total pressure increase [Pa] r| = Efficiency of the fan V = Air flow volume in [m3/s]
When using a pole-switching motor
c
m/s
Pole
Air flow
Pressure
Power
figure
volume
AP2
Pw2
n1/n2
Ap1
Pw1
4/2
8/4
2
4
8
12/6
6/4
1.5
2.25
3.38
8/6
1.33
1.78
2.37
0
0
200
400
600
800
1000
1200
V m3//
KD 355/4/70/40
Frequency
Hz
Total
125
250
500
1k
2k
4k
8k
Lwa
Case breakout
dB(A)
73
65
67
65
68
63
63
59
Lwa
Inlet
dB(A)
84
78
70
70
75
74
71
68
Lwa
Extract
dB(A)
86
76
75
79
81
79
77
72
Fig. 17
Fan laws
The performances of geometrically similar fan ranges can be calculated using the relations between fan speed, diameter and density. Change in speed (R.P.M.):
Apstat
Pa
800 4=-
p= 1,20 kg/m3
600
\2
n2
V2 = V1 ' — ; Ap2 = Ap1
7 A3
400
Pw2 = P
w1
200
If you half the speed, you half the air flow and quarter the pressure.
1000 2000 3000 4000 5000 6000
V m3//
Change in diameter:
AVD 800/6
n = 945 1/min
Frequency
Hz
Total
125
250
500
1k
2k
4k
8k
Lwa
15°
dB(A)
80
65
66
72
76
76
72
65
Lwa
25°
dB(A)
82
67
68
74
78
78
74
67
Lwa
35°
dB(A)
84
69
70
76
80
80
76
69
7 A 3
D ; AP2 = Ap
7 A 2 D2 .
Fig. 18
V2= V-
To be considered when selecting a fan:
5
/
i
p = 1,20 kg/
m3
Stal are
ing \ a
s.
/
Y
\
1
0°
15°
20°
35°
r
V
V
/
\
\
\
\N
Apstat
Pa 120
: APtot. - Pd [Pa]
Apsl
P = P
' w2 1 w
The static pressure Apstat. is the pressure drop of the system (duc­ting, bends, filters and other compo­nents).
Figure 16
In the performance curve of a mixed flow VAR... fanthe total pressure @, the static pressure © and the dynamic pressure © are shown. Line @ shows the air flow velocity through the fan at a certain air flow volume. The working point (WP) is, where the fan curve and the system resistance curve cross.
Figure 17
The performance curve of a speed controllable rectangular centrifugal fan shows the performance curves for the various speed steps (trans­former voltages).
Figure 18
For HELIOS AVD... models (above 0 > 710 mm), the fan's per­formance can be adjusted to the required duty by changing the pitch angle (at standstill).
If you double the diameter, the air flow grows by power 3 and the pressure in square.
c
m/s
80
40
Change in temperature / density:
V1 =
V'2 =
const.
AP2
Ap
p1 72
AP2
= Ap1
p1
Pw2
= Pw1
J3^ =
p1
5000 10000 15000 20000 25000
V m3//
Table 19 Atmopheric pressure in relation to altitude
Altitude above sea level in m 0 500
1000
2000
3000
Atmospheric pressure in mbar 1013 955
899
795
701
Ap
1-^ Pal
72
T: Ambient temperature (T = 273+t) [°C] t: Air flow temperature [°C]
Index 1: Original condition Index 2: Modified condition
Use of a fan in different altitudes Calculation of density:
pa [hPa] ' 100 Ri ■ 7
[kg/m3]
P
PaiAir pressure [/Pa, mbar] figure 19 R¡: Gas constant (air: 287 J/(kgK))
15
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