Calculating The Total Ducting Length - Miele PDR 908 EL Marine Operating And Installation Instructions

Calculating the total ducting
length
The entire ducting system (including
bends and components) generates air
resistance that pushes against the ex-
haust air. The relative pipe lengths and
total ducting length have to be calcu-
lated for this reason:
– The  relative pipe length (table I)
indicates how much greater the air
resistance of a bend is, for example,
when compared to 1 metre of a
straight plastic waste water pipe.
– Adding all of these relative pipe
lengths together gives the  total
ducting length. This is not the actual
length but a calculated figure. The
total ducting length (table II) ex-
presses the air resistance of the en-
tire exhaust air system.
Because a larger  pipe diameter (ta-
ble II) reduces the air resistance, a
longer total duct length requires a
greater pipe diameter.
Procedure
 Measure the length needed for the
straight sections of ducting. Multiply
the length by the corresponding rel-
ative pipe length from table I.
 Calculate the number of bends and
elbows needed. Use table I to help
you add together their relative pipe
lengths.
 Calculate the total duct length: add
together all of the relative pipe
lengths calculated under  and .
 Refer to table II for the pipe diameter
needed for the total duct length.
Installation of the ducting
Table I
Components
Exhaust air hose (highly flexible)*
1 m, laid straight
45° bend (radius of bend = 0.25 m)
90° bend (radius of bend = 0.25 m)
Exhaust air hose (flexible or flex-
ible aluminium)*/plastic waste
water pipe
1 m, laid straight/straight pipe
45° bend (radius of bend = 0.25 m)
90° bend (radius of bend = 0.25 m)
Wall pipe* or window connection*
With inserted grille
With non-return flap (swinging flap)
Non-return flap* for integration
into the ducting
(see "Shared exhaust air duct")
Flat ducting (for stacked installa-
tion)*
* Optional accessories
Table II
 Total duct length
Maximum of 20 m
Maximum of 40 m
Maximum of 80 m
 Relat-
ive
pipe
length
1.8 m
1.5 m
2.5 m
1.0 m
0.6 m
0.8 m
3.8 m
1.5 m
14.3 m
11.0 m
 Pipe diameter
100 mm
125 mm
150 mm
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