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

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 fail-
ure of the coil. The fin/tube bundle is slanted vertically for hor-
izontal 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 con-
densate 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 prac-
tice 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 in-
1
2
stalled horizontally, piped open to atmosphere, and lo-
cated 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 an-
ticipated 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 per-
missible, 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 stratification 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 ( 3 / -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 distribut-
ing 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 in-
herent slope. Also ensure the unit is installed high
enough to allow the piping to be installed correctly, es-
pecially 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 separate-
ly.
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
depending upon the unit size and coil circuiting. Each split
requires its own distributor nozzle, expansion valve, and
suction piping. Suction connections are on the air entering
side when the coil is properly installed. Matching distribu-
tor connections for each coil split are on the air leaving
side. See unit label or certified drawing to assure connec-
tion to matching suction and liquid connections.
NOTE: Distributor nozzles are factory selected and
installed for adequate performance in many unit applica-
tions. For best performance, use Carrier's AHUBuilder
program to select nozzle sizes for each unit and replace the
factory-installed nozzles as required. See the Distributor
Nozzle Change-Out section on page 127 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 connec-
tions independently. Do not use the coil connections to sup-
port piping. 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 pro-
tective 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. 95 for face split coil or Fig. 96 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 re-
maining suction line to compressor for a pressure drop equiva-
lent to 2.0°F. This will provide a total suction line header pres-
sure drop equivalent to approximately 2.7°F.
To minimize the possibility of flooded starts and compres-
sor damage during prolonged light load operation, an accumu-
lator can be used in the suction line of first-on, last-off circuit.
The first-on, last-off circuits shown in Fig. 95 and 96 as-
sume 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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CAUTION
CAUTION
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