Carrier Aero 39MN Series Installation, Start-Up And Service Instructions Manual page 124

STEAM COILS — Position the steam supply connection at
the top of the coil, and the return (condensate) connection at the
bottom. The coil tubes must incline downwards toward the re-
turn header connection for condensate drainage. See Fig. 90-
94.
Figure 90 illustrates the normal piping components and
the suggested locations for high, medium, or low-pressure
steam coils. The low-pressure application (zero to 15 psig)
can dispense with the / -in. petcock for continuous venting
1
4
located above the vacuum breaker (check valve).
Note the horizontal location of the 15-degree check
valve, and the orientation of the gate/pivot. This valve is in-
tended to relieve any vacuum forming in the condensate
outlet of a condensing steam coil, and to seal this port when
steam pressure is again supplied to the coil. It must not be
installed in any other position, and should not be used in the
supply line.
For coils used in tempering service, or to preheat outside
air, install an immersion thermostat in the condensate line
ahead of the trap. This will shut down the supply fan and
close the outdoor damper whenever the condensate falls to a
predetermined point, perhaps 120°F.
NOTE: Do NOT use an immersion thermostat to override a
duct thermostat and open the steam supply valve.
For vacuum return systems, the vacuum breaking check
valve would be piped into the condensate line between the
trap and the gate valve instead of open to the atmosphere.
Figure 91 illustrates the typical piping at the end of every
steam supply main. Omitting this causes many field prob-
lems and failed coils.
Figure 92 shows the typical field piping of multiple coils.
Use this only if the coils are the same size and have the
same pressure drop. If this is not the case, an individual trap
must be provided for each coil.
Figure 93 shows a multiple coil arrangement applied to a
gravity return, including the open air relief to the atmo-
sphere, which DOES NOT replace the vacuum breakers.
Figure 94 illustrates the basic condensate lift piping.
Following the piping diagrams in Fig. 90-94, make all con-
nections while observing the following precautions:
• Install a drip line and trap on the pressure side of the inlet
control valve. Connect the drip line to the return line
downstream of the return line trap.
• To prevent scale or foreign matter from entering the con-
trol valve and coil, install a
steam supply line upstream from the control valve.
• Provide air vents for the coils to eliminate noncondens-
able gases.
• Select a control valve according to the steam load, not
the coils supply connection size. Do not use an oversized
control valve.
• Do not use bushings that reduce the size of the header
return connection. The return connection should be the
same size as the return line and reduced only at the
downstream trap.
• To lift condensate above the coil return line into over-
head steam mains, or pressurized mains, install a pump
and receiver between the condensate trap and the pres-
surized main. Do not try to lift condensate with modulat-
ing or on-and-off steam control valves. Use only 15-
degree check valves, as they open with a lower water
head. Do not use 45-degree or vertical-lift check valves.
• Use float and thermostatic traps. Select the trap size
according to the pressure difference between the steam
supply main and the return main.
• Load variations can be caused by uneven inlet air distri-
bution or temperature stratification.
3 / -in. mesh strainer in the
32
• Drain condensate out of coils completely at the end of
the heating season to prevent the formation of acid.
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* When end of supply main, see Fig. 91.
NOTES:
1. Flange or union is located to facilitate coil removal.
2. Flash trap may be used if pressure differential between steam and con-
densate return exceeds 5 psi.
3. When a bypass with control is required.
4. Dirt leg may be replaced with a strainer. If so, tee on drop can be
replaced by a reducing ell.
5. The petcock is not necessary with a bucket trap or any trap which has
provision for passing air. The great majority of high or medium pressure
returns end in hot wells or deaerators which vent the air.
Fig. 90 — Low, Medium or High Pressure
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NOTES:
1. A bypass is necessary around trap and valves when continuous opera-
tion is necessary.
2. Bypass to be the same size as trap orifice but never less than
Fig. 91 — Dripping Steam Supply to
Condensate Return
124
Coil Piping
1
/ inch.
2