IM 178 / Page 21
1. 5 psi (34.5 kPa) steam must be supplied to coils at all
times.
2. Modulating valves are not recommended. Control should
be by means of face and bypass dampers.
3. As additional protection against freeze-up, the tap should
be installed sufficiently far below the coil to provide an
adequate hydrostatic head to ensure removal of conden-
sate during an interruption on the steam pressure. Esti-
mate 3 ft. (914 mm) for each 1 psi (7 kPa) of trap differential
required.
4. If the unit is to be operated in environments with possible
freezing temperatures, an optional freezestat is recom-
mended. Refer to “Freeze Protection” in the “Unit Op-
tions” section of this manual.
Coil piping vestibule
When a unit coil is installed in a heating only or cooling only
section (including the draw-through cooling/supply air fan
section on the RDS 800C), all piping may be done internal to
the unit without requiring a piping vestibule.
For all contractor coils and all unit coils installed in a
combination coil section, the coil connections project to the
inside surface of the door panel. Holes may be cut in the door
panels for the piping to be connected to the coils, or an
accessory piping vestibule may be added to the unit to
provide piping space. Refer to the section on vestibule
assembly instructions. The piping may then be routed back
within the unit.
To avoid piping penetrations through the roof external to
the curb, holes may be cut through the floor of the unit at the
locations specified on the certified drawings. Caution: All
holes in the unit floor must be sealed to prevent water
leakage into the building.
2. Do not reduce pipe size at the coil return connection.
Carry return connection size through the dirt pocket,
making the reduction at the branch leading to the trap.
3. It is recommended that vacuum breakers be installed on
all applications to prevent retaining condensate in the
coil. Generally, the vacuum breaker is to be connected
between the coil inlet and the return main. However, if the
system has a flooded return main, the vacuum breaker
should be open to the atmosphere and the trap design
should allow venting of the large quantities of air.
4. Do not drain steam mains or takeoffs through coils. Drain
mains ahead of coils through a steam trap to the return line.
5. Do not attempt to lift condensate.
6. Pitch all supply and return steam piping down a minimum
of 1" (25 mm) per 10 feet (3 m) of direction of flow.
Steam trap recommendations
1. Size traps in accordance with manufacturers’ recommen-
dations. Be certain that the required pressure differential
will always be available. Do not undersize.
2. Float and thermostatic or bucket traps are recommended
for low pressure steam. Use bucket traps on systems with
on-off control only.
3. Locate traps at least 12" (305 mm) below the coil return
connection.
4. Always install strainers as close as possible to the inlet
side of the trap.
5. A single tap may generally be used for coils piped in
parallel, but an individual trap for each coil is preferred.
Steam coil freeze conditions
If the air entering the steam coil is below 35
°
F (2
°
C), note the
following recommendations:
Vestibule Assembly Instructions
An accessory vestibule is available to provide additional
piping space for coils installed in a 40" (1016 mm) section. A
vestibule is required to maintain door access on a combina-
tion heating and cooling section. The vestibule should be
assembled to the unit part by part as shown in Figures 16a
through 16d. Note: The door, hinge, and latch assemblies
from the unit are used on the vestibule.
Step 1
Remove door from section where vestibule is to be located
by removing screws holding hinges to upright support (leave
hinges on door). Set door aside and save for Step 4.
Remove door latch assembly or a wrench to remove
screws holding latch assembly in place. Save door latch
assembly, screws and bushings for Step 4.
Figure 16a.
Door Latch Assembly
Door
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