Bryan Boilers Forced Draft Steam Boilers User Manual

Page 17

Table 1.8.15B ALTITUDE CORRECTION FACTOR, F

(Multiple factor times sea level input, MBH)

Altitude (ft)

Factor, F

Altitude

(ft) Factor,

0 to 1999

2000
2500
3000
3500
4000
4500
5000
5500

1.00

1.075
1.096
1.116
1.136
1.157
1.180
1.202

1.25

6000
6500
7000
7500
8000
8500
9000

10000

1.247
1.272
1.296
1.322
1.346
1.373
1.399
1.453

STEP 3: SELECT TRIAL DIAMETER
Determine the NET STACK HEIGHT for the vent.
(The net stack height is the vertical distance from
the top of the atmospheric boiler draft control to
the top of the stack. On forced draft boilers it is
the distance from the boiler flue connection to the
top of the stack.)

Find the vent of TRIAL STACK DIAMETER. Enter
Table 1.8.15C at the Net Stack Height column
equal to the system net stack height. Then
proceed down the column to the input which is
just larger than the equivalent to an input which is
just larger than the Equivalent Input of the
system. Read the Trial Stack Diameter in the left
hand column.

NOTE: This is only a trial diameter. Proceed to
Step 4 to calculate the system k-factor to
determine the actual stack diameter required.

STEP 4: CALCULATE SYSTEM K-FACTOR
The system "k-factor" accounts for the pressure
drop through fittings and vent piping. It is
calculated by adding up the individual k-factors
for each of the fittings plus the k-factor for the
vent pipe(s).

From Table 1.8.15D find the k-factors for each of
the elbows, tee fittings, draft regulators, etc. in the
system. Then calculate the vent piping k-factor
from the formula:

piping

= 0.4 x L/D eq.

15C

L = total length of piping in feet

D = diameter of piping in inches

Add all the k-factors together to determine the
total system k-factor:

total

= k

piping

+ k

fittings

eq.

15D

NOTE: On multiple appliance systems, multiply
the k-factor times 1.5. This is required only on
atmospheric boiler vent systems, not on forced
draft systems.

Table 1.8.15D: Vent Fitting k-Factors

Vertical Draft Hood

Barometric Draft Control

1.50
0.50

Low Resistance Cap

Round Elbow, 90 deg F
Round Elbow, 45 deg F

0.75
0.30

Converging Exit

Cone

(D1/D2)

- 1

(D1 is larger than D2)

Tee or 90 degF Breeching

Y Breeching

1.25
0.75

Tapered Reducer

1 - (D2/D1)

(D1 is larger than D2)