750-211 (revised 2009)
Promethean Boilers, Model 4WI Manual
6-15
6.16 — Gas Pressure and Flow Information
6.16.2 — Gas Flow
The volume of gas flow is measured in terms of cubic feet and is determined by a meter reading. The gas flow rate
required for maximum boiler output depends on the heating value (Btu/cu. ft.) of the gas supplied and boiler effi-
ciency. The supplying utility can provide the information.
INPUT = OUTPUT x 100%
EFFICIENCY
GAS FLOW = INPUT
GAS BTUs/FT
3
= OUTPUT x 100
EFFICIENCY x GAS BTUs/FT
3
6.16.3 — Pressure Correction
The flow rate outlined in Section 6.17 is based on a “base” pressure, which is usually atmospheric or 14.7 psia.
Meters generally measure gas in cubic feet at “line” or supply pressure. The pressure at which each cubic foot is
measured and the correction factor for the pressure must be known in order to convert the quantity indicated by
the meter into the quantity which would be measured at “base” pressure.
TABLE 6-3. 4-Pass Wetback Boilers with Integral Burner (4WI) Firing Rates
Natural Gas, 1000 Btu/hr No. 2 Oil, GPM
Boiler HP Low-Fire High-Fire Low-Fire High-Fire
100 1021 4082 7.3 29.2
125 1276 5103 9.1 36.4
150 1531 6124 10.9 43.7
200 2041 8165 14.6 58.3
250 1021 10206 9.1 72.9
300 1225 12247 10.9 87.5
350 1428 14280 12.8 102.1
400 1633 16329 14.6 116.6
500 2042 20415 18.2 145.8
600 2449 24494 21.9 175.0
700 2858 28576 25.5 204.1
750 3062 30617 27.3 218.7
800 3266 32659 29.2 233.3
NOTE: Fuel input rates are based on nominal 82% efficiency.
No. 2 Oil = 140,000 Btu/gal.
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