Carrier AERO 39MN Installation, Start-Up And Service Instructions Manual page 81

This is not always the case, especially if the coil hand has
been changed in the field. Coils must be piped for counter-
flow; otherwise, a capacity reduction of 5% for each coil row
will result. To ensure counterflow, chilled water coils are
piped so that the coldest water meets the coldest air. Hot
water coils are piped so that the warmest water meets the
warmest air.
VENT
RETURN
SUPPLY
DRAIN
INTEGRAL FACE AND BYPASS COIL SHOWN
1/2 IN. WATER COIL SHOWN
Fig. 62 — Coil Connections and Lifting Points
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 return header connection for condensate drainage. See
Fig. 63-67.
Figure 63 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 dis-
pense with the / -in. petcock for continuous venting located
1
4
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 intended to
relieve any vacuum forming in the condensate outlet of a con-
densing 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
AIRFLOW valve would be piped into the condensate line between the
trap and the gate valve instead of open to the atmosphere.
Figure 64 illustrates the typical piping at the end of every
steam supply main. Omitting this causes many field problems
and failed coils.
Figure 65 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 66 shows a multiple coil arrangement applied to a
gravity return, including the open air relief to the atmosphere,
which DOES NOT replace the vacuum breakers.
Figure 67 illustrates the basic condensate lift piping.
Following the piping diagrams in Fig. 63-67, make all
connections 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 con-
trol 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 down-
stream trap.
• To lift condensate above the coil return line into overhead
steam mains, or pressurized mains, install a pump and
receiver between the condensate trap and the pressurized
main. Do not try to lift condensate with modulating 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
a39-4341
supply main and the return main.
• Load variations can be caused by uneven inlet air distribu-
tion or temperature stratification.
• Drain condensate out of coils completely at the end of the
heating season to prevent the formation of acid.
80
3 / -in. mesh strainer in the
32