Refrigerant Piping, Direct-Expansion Coils; Suction Piping - Carrier Aero 39MN Series Installation, Start-Up And Service Instructions Manual

are expanded into plate fins. The completed assembly includes the
supply and condensate header and side casings which are built to
slant the fin/tube bundle back toward the condensate header. The
slanting of the assembly ensures that condensate will flow toward
the drains. This condensate must be removed through the return
piping to prevent premature failure of the coil. The fin/tube bundle
is slanted vertically for horizontal airflow coils, and horizontally
for vertical airflow coils.
IDT Steam Coil Piping — The following piping guidelines will
contribute to efficient coil operation and long coil life:
1. Use full size coil outlets and return piping to the steam
trap. Do not bush return outlet to the coil. Run full size to
the trap, reduce at the trap.
2. Use float and thermostatic (F & T) traps only for conden-
sate removal. Trap size selection should be based on the
difference in pressure between the steam supply main and
the condensate return main. It is good practice to select a
trap with 3 times the condensate rating of the coil to
which it is connected.
3. Use thermostatic traps for venting only.
4. Use only / -in., 15-degree swing check valves installed
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horizontally, piped open to atmosphere, and located at
least 12 in. above the condensate outlet. Do not use 45-
degree, vertical lift and ring check valves.
5. The supply valve must be sized for the maximum antici-
pated steam load.
6. Do not drip steam mains into coil sections. Drip them on
the pressure side of the control valve and trap them into
the return main beyond the trap for the coil.
7. Do not use a single trap for two or more coils installed in
series. Where two or more coils are installed in a single
bank, in parallel, the use of a single trap is permissible,
but only if the load on each coil is equal. Where loads in
the same coil bank vary, best practice is to use a separate
trap for each coil.
Variation in load on different coils in the same bank may
be caused by several factors. Two of the most common
are uneven airflow distribution across the coil and stratifi-
cation of inlet air across the coil.
8. Do not try to lift condensate above the coil return into an
overhead main, or drain into a main under pressure with a
modulating or on/off steam control valves. A pump and
receiver should be installed between the coil condensate
traps and overhead mains and return mains under
pressure.
9. Use a strainer ( / -in. mesh) on the steam supply side,
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as shown in the piping diagrams, to avoid collection of
scale or other foreign matter in the inner tube distributing
orifices.
Note: The IDT coils must be installed with the tubes draining
toward the header end of the coil. Carrier's IDT steam coils are
pitched toward the header end as installed in the unit.
10. Ensure the AHU is installed level to maintain the inherent
slope. Also ensure the unit is installed high enough to al-
low the piping to be installed correctly, especially the
traps which require long drip legs.
11. Do not fail to provide all coils with the proper air vents to
eliminate noncondensable gasses.
12. Do not support steam piping from the coil units. Both
mains and coil sections should be supported separately.
IDT Steam Coil Installation — Refer to drawings to position the
coils properly with regard to the location of the supply and return
connections. Ensure that the IDT coil is pitched with the tubes
draining toward the header. Carrier's AHUs provide proper coil
pitch when the AHU is installed level.
Refer to schematic piping diagrams and piping connection notes
for the recommended piping methods.

Refrigerant Piping, Direct-Expansion Coils

Direct-expansion (DX) coils are divided into 2 or 4 splits depend-
ing upon the unit size and coil circuiting. Each split requires its
own distributor nozzle, expansion valve, and suction piping. Suc-
tion connections are on the air entering side when the coil is prop-
erly installed. Matching distributor connections for each coil split
are on the air leaving side. See unit label or certified drawing to as-
sure connection to matching suction and liquid connections.
NOTE: Distributor nozzles are factory selected and installed for
adequate performance in many unit applications. For best perfor-
mance, use Carrier's AHUBuilder
for each unit and replace the factory-installed nozzles as required.
See the Distributor Nozzle Change-Out section on page 131 for
further details.
To prevent damage to the coil or coil headers: Do not use the
headers to lift the coil. Support the piping and coil connections
independently. Do not use the coil connections to support pip-
ing. When tightening coil connections, use a backup wrench
on the stub outs.
Direct-expansion coils are shipped pressurized with dry air.
Release pressure from each coil split through valves in protec-
tive caps before removing caps.
Do not leave piping open to the atmosphere unnecessarily.
Water and water vapor are detrimental to the refrigerant sys-
tem. Until the piping is complete, recap the system and charge
with nitrogen at the end of each workday. Clean all piping
connections before soldering joints.

SUCTION PIPING

Connect suction piping as shown in Fig. 103 for face split coil or
Fig. 104 for row split coil.
NOTE: The lower split of face split coils should be first-on, last-
off. Row split coils utilize special intertwined circuits; either split
of these row split coils can be first-on, last-off.
Suction line from coil connection to end of the 15-diameter-long
riser should be same tube size as coil connection to ensure proper
refrigerant velocity.
Refer to Carrier System Design Manual, Part 3, and size remain-
ing suction line to compressor for a pressure drop equivalent to
2.0°F. This will provide a total suction line header pressure drop
equivalent to approximately 2.7°F.
To minimize the possibility of flooded starts and compressor dam-
age during prolonged light load operation, an accumulator can be
used in the suction line of first-on, last-off circuit.
The first-on, last-off circuits shown in Fig. 103 and 104 assume a
single condensing unit. Note that in both figures the last-on, first-
off circuit is looped above the common return line to prevent oil
entrapment in the non-operating coil at partial load.
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program to select nozzle sizes
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