RVR Energy Technology MICROMAT EC 45, Инструкция по использованию, установке и пусконаладке, Страница: 18 / 56

E n e r g y T e c h n o l o g y
Ltd.
18
14.0 calculating flue resistance
flue pressure loss
example I
A MICROMAT EC 62 boiler is installed with a concentric flue system
which takes an all horizontal route to a wall terminal. Length of flue = 3m
including one 90
°
bend.
Resistance =
3 x 1m length 70/125 concentric tube @ 16.6 Pa = 49.8
1 x 90
°
70/125 concentric bend @ 16.6 Pa =16.6
I x 70/125 concentric wall terminal @ 21.4 Pa = 21.4
Total Resistance = 87.6Pa
conclusion: Total resistance is less than 100 Pa. therefore, no alternative
design required and no effect on boiler output, or positioning required
example 2
A MICROMAT EC 45 boiler is installed with a concentric flue system
which takes a part horizontal, part vertical route to a roof terminal with
rain cap.
Length of horizontal section = 1m, vertical section = 6m, system includes
1 x 90
°
bend.
Resistance =
7 x 1m lengths 70/125 concentric tube @ 10.7 Pa = 74.9
1 x 90
°
70/125 concentric bend @ 10.7 Pa= 10.7
1 x 70/125 roof terminal @ 21.9 Pa = 21.9
Total Resistance = 107.5 Pa
Take into account that 6m of vertical (assume uninsulated, as air for
combustion direct from outside air surrounds the flue gas tube) flue creates
10 Pa of up-draught,
then final resistance = 107.5 - 10 = 97.5 Pa.
conclusion: Final operating resistance is less than 100 Pa, therefore,
no alternative design required and no effect on boiler output.
example 3
A MICROMAT 1-75 boiler is installed (non room sealed) with a proposed
flue using DN 70 PPS single skin flue components which takes a part
horizontal, part vertical route to a vertical open termination with bird mesh.
Length of horizontal section = 4m, length of vertical (uninsulated) section
= 11m with 4 x 90
°
bends, and 2 x 45
°
bends.
Resistance =
15 x 1m lengths DN 70 PPS tube @ 21.4 Pa = 321
4 x 90o DN 70 PPS bends @ 21.4 Pa = 85.6
2 x 45o DN 70 bends @ 10.7 Pa = 21.4
1 x DN 80 open termination @ 15.6 Pa = 15.6
Total Resistance: 443.6 Pa
Take into account that 11m of vertical uninsulated flue creates 18 Pa of
up-draught, then final resistance would be 443.6-18 = 425.6 Pa. Reference
to the graph of resistance effect on boiler output shows the output would
be reduced to approximately 59kW. If this is unacceptable, then the flue
resistance must be re-calculated using a larger size flue tube as shown
below or consideration given to moving the boiler position.
Re-calculating proposed flue installation using DN 100.
15 x 1m lengths DN 100 PPS tube @ 3.0 Pa = 45
4 x 90o DN 100 bends @ 3.0 Pa = 12
2 x 45o DN 100 bends @ 1.5 Pa = 3.0
1 x DN 100 open termination @ 4.0 Pa = 4.0
Total Resistance: 64 Pa
Take into account thermal up-draught created (as before) 18 Pa. Therefore
operating resistance = 64 – 18 = 46 Pa, with no effect on boiler output.
Vertical Flue Lengths - metres
Draught - Pa
thermal updraught when flue gas
temp 80
°
C and outside temp -5
°
C
A = Insulated or within the building
B = Uninsulated and exterior to the building
A
B
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
MICROMAT EC76
MICROMAT EC 62
MICROMAT EC 45
29
31
33
35
37
39
41
45
47
49
51
53
55
57
59
61
63
65
67
69
71
73
43
0 50 150 200 250 300 350 400 450 500 100
effect of flue system resistance on boiler output
Boiler output kW at: flow 80
°
C Return 60
°
C
Flue System resistance - Pa