Northline Express EXHAUSTO RS 12, Руководство по применению

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Analysing a fireplace venting system.
This is an example on how to analyze and estimate
fireplace system:
One-sided fireplace, opening = 24"x36"
Ambient temperature = 60°F
Mean chimney temperature = 300°F
Flue material = Single wall steel pipe
Flue size = 8"
Chimney height from top of firebox = 25'
Off sets = One 30° off-set (= 2 x 30° elbows)
d
m
= 0.075 lb/ft3 @ 60°F
= 0.047 lb/ft3 @ 300°F
1. Determine flow:
Q
t
= q x A
inlet
x V
inlet
/ 144
= 1.6 x 24 x 36 x 48 CFM
= 460 CFM
2. Determine k-values:
Pipe:
k
L
= F x L /D
i
= .32 x 25/8
= 1.0
Components:
2 x 30° elbows = 2 x .15 .30
Inlet from firebox 2.00
Total k-value 2.30
Σ Σ
Σ Σ Σ
k = 1.0 + 2.3 = 3.3
3. Determine flow resistance:
P
s
= .015 x d
m
x (Q
t
/A
pipe
)² x
Σ
k
= .015 x .047 x (460/50)² x 3.3
= .015 x .047 x 84.64 x 3.3
= .197"WC
4. Determine natural draft:
D
t
= .2554 x B x H x (1/T
o
- 1/T
m
)
= .2554 x 29.92 x (1/530 - 1/710)
= 191.04 x (.002 - .0014) = .115"WC
5. Determine available draft:
-Da = -Dt + Ps
= - .115 + 0.197
= + .082"WC
The available draft is positive. In other words, the
system should be back-drafting. One way of solving this
problem could be to increase the flue size from 8" to 10".
Going through the same calculations, a 10" flue would
give these results:
Q
t
= 460 CFM (no change)
k
L
= .8
Σ
k = 3.1
P
s
= .015 x .047 x (460/78.5)² x 3.1
= .015 x .047 x 34.34 x 3.1
= .075"WC
D
t
= .115"WC (no change)
D
a
= -.115 + .075
= -.04"WC
Now there is draft in the system, so a 10" vent is the
appropriate size for venting a 24"x36" fireplace.
Analyzing other factors
If the fireplace and the flue seem to be sized
correctly, but there is a smoke problem other informa-
tion may be needed.
F.inst. a depressurized building will negatively affect
the draft situation. If the negative pressure is found to
be, let's say .1"WC the available draft in above example
would be:
D
a
= -.04"WC + .1"WC
= +.06"WC
In other words, the negative building pressure easily
overcomes the draft and makes the system back-draft.
24
EXHAUSTO
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