86
JOHNSON CONTROLS
5276178-JIM-C-0118
Installation
GAS HEATING
On VAV units with gas fired furnace,
all individual room damper boxes must
be controlled full open during heating
operation to ensure proper airflow over
the furnace. A control contact powered
by the “VAV OPEN” terminals on the
control is provided for the damper box
interlock. This contact is normally
open, and is closed during heating
operation.
Gas Piping
Proper sizing of gas piping depends on the cubic feet
per hour of gas flow required, specific gravity of the gas
and the length of run. National Fuel Gas Code Z223.1-
Latest Edition should be followed in all cases unless
superseded by local codes or gas company requirements.
Refer to Table 31.
The heating value of the gas may differ with locality. The
value should be checked with the local gas utility.
TABLE 40 - PIPE SIZES
LENGTH
INFEET
NOMINAL IRON PIPE, SIZE
1-1/4 IN.
1
1-1/2 IN.
1
2 IN.
1
10
1,050
1,600
3,050
20
730
1,100
2,100
30
590
890
1,650
40
-
760
1,450
50
-
-
1,270
60
-
-
1,150
70
-
-
1,050
80
-
-
990
1. Maximum capacity of pipe in cubic feet of gas per hour
(based upon a pressure drop of 0.3 inch water column and 0.6
specific gravity gas).
There may be a local gas utility require
-
ment specifying a minimum diameter
for gas piping. All units require a 1-1/4
inch pipe connection at the entrance
fitting. Line should not be sized smaller
than the entrance fitting size.
Gas Connection
The gas supply line should be routed within the space
and penetrate the roof at the gas inlet connection of the
unit.
Refer to Figures 6through 9 to locate the access
opening. Typical supply piping arrangements are shown
in Figure 28.
Gas piping recommendations:
1. A drip leg and a ground joint union must be in-
stalled in the gas piping.
2. When required by local codes, a manual shut-off
valve will have to be installed outside of the unit.
3. Use wrought iron or steel pipe for all gas lines. Pipe
dope should be applied sparingly to male threads
only.
Natural gas may contain some pro
-
pane. Propane, is an excellent solvent
and will quickly dissolve white lead or
most standard commercial pipe sealing
compounds. Therefore, special shellac
base pipe dope compounds such as
Gaskolac or Stalastic, and compounds
such as Rectorseal #5, Clyde’s or John
Crane must be applied for wrought
iron or steel pipe.
4. All piping should be cleaned of dirt and scale by
hammering on the outside of the pipe and blow-
ing out the loose particles. Before initial start-up,
be sure that all of the gas lines external to the unit
have been purged of air.
FIGURE 28 – TYPICAL GAS PIPING CONNECTION
LD14187
Содержание 40 25 TON
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