AAON RQ SERIES, Установка, эксплуатация и обслуживание, Страница: 41 / 100

41
Table 8 - Propane (kBtu/hr)
- Specific Gravity = 1.52, Supply Pressure = 11” w.c., Pressure Drop, 0.5” w.c.
Pipe Size
Length of Pipe
20 ft 50 ft. 100 ft. 150 ft. 200 ft.
1/2”
189 114 78 63 55
3/4”
393 237 162 132 112
1”
732 448 307 252 213
1-1/4” 1496 913 630 511 440
1-1/2” 2299 1417 976 787 675
2”
4331 2646 1811 1496 1260
Do not use gas piping smaller than unit gas
connections. Natural gas pipe runs longer
than 20 feet and propane gas pipe runs
longer than 50 feet may require a larger
supply pipe than the unit connection size.
Some utility companies may also require
pipe sizes larger than the minimum sizes
listed.
Piping Sizing Examples
A 100 ft pipe run is needed for a 1080 MBH
natural gas heater. The natural gas has a
rating of 1000 Btu/ft
3
and a specific gravity
of 0.6 (Obtain these values from the local
gas supplier.)
 
Btu
ft
MBH
1000
1080
3
1080 ft
3
/hr
From the natural gas maximum capacities
table, at 100 ft and 1080 ft
3
/hr the required
minimum pipe size is 2”.
A 100 ft pipe run is needed for a 270 MBH
propane gas heater.
270
MBH = 270 kBtu/hr
From the propane gas maximum capacities
table, at 100 ft and 270 kBtu/hr the required
minimum pipe size is 1”.
Inlet and Manifold Pressures
For natural gas units, the minimum inlet gas
pressure to the unit is 6” w.c. and maximum
inlet gas pressure to the unit is 10.5” w.c.
For propane units, the minimum inlet gas
pressure to the unit is 11” w.c. and the
maximum inlet gas pressure to the unit is
13” w.c. A field provided 1/8” NPT pressure
tap is required to be installed in the piping
just upstream of the shutoff valve for test
gage connection to allow checking of the
gas supply pressure at the unit.
A factory installed pressure tap on the outlet
end of the gas valve can be used to verify a
manifold pressure of 3.5” w.c. for natural
gas, or 10.5” w.c. for propane.
For two stage gas valves, the low stage
setting should be set at 1.1” w.c. for natural
gas, 5.0” w.c. for propane. For modulating
heaters, the safety shut-off valve would be
set following the instructions above, then
from a provided pressure tap in the gas train
immediately preceding the burner manifold
the modulating valve is set to maintain a
maximum of 3.5” w.c. and a minimum of
0.4” w.c.
Heater should be disconnected from
the gas supply piping during pressure
testing of the supply piping system
with pressures in excess of ½ psi. Gas
valves can be damaged if subjected to
more than ½ psi.
CAUTION