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

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 suc-
tion piping. Suction connections are on the air entering side
when the coil is properly installed. Matching distributor con-
nections for each coil split are on the air leaving side. See
unit label or certified drawing to assure connection to match-
ing suction and liquid connections.
NOTE: Distributor nozzles are factory selected and installed
for adequate performance in many unit applications. For best
performance, use Carrier's AHUBuilder
nozzle sizes for each unit and replace the factory-installed
nozzles as required. See the Distributor Nozzle Change-Out
section on page 84 for further details.
CAUTION
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.
CAUTION
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. 68 for face split coil or Fig. 69 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-diame-
ter-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
remaining 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 compres-
sor damage during prolonged light load operation, an accu-
mulator can be used in the suction line of first-on, last-off cir-
cuit.
The first-on, last-off circuits shown in Fig. 68 and 69 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 par-
tial load.
® program to select
83
COIL
CASING
TXV
UPPER
SENSING
SPLIT
BULB
AIRFLOW
15 DIAMS
MIN
10
DIAMS
LOWER
SPLIT
TXV
SENSING
BULB
AIRFLOW
15
DIAMS
MIN 10
DIAMS
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LEGEND
TXV — Thermostatic Expansion Valve
Fig. 68 — Face-Split Coil Suction-Line Piping
TXV SENSING
BULBS
AIRFLOW
10 DIAMS
15
DIAMS
MIN 15
DIAMS
MIN
DIAMS
10 DIAMS
EVAPORATOR COIL
FIRST-ON, LAST-OFF
LEGEND
TXV — Thermostatic Expansion Valve
Fig. 69 — Row-Split Coil Suction-Line Piping
UNIT
CASING
SOLENOID
SIGHT
VALVE
GLASS
FILTER
DRIER
8
DIAMS
SOLENOID
MIN
VALVE
SIGHT
GLASS
FILTER
DRIER
TXV
INSIDE
CASING
(TYP)
DISTRIBUTOR
(TYP)
8 DIAMS
MIN
EVAPORATOR
COIL
FIRST-ON, LAST-OFF
COIL
UNIT
CASING CASING
SOLENOID
VALVE
SIGHT
GLASS
FILTER
DRIER
SOLENOID
VALVE
SIGHT
GLASS
FILTER
DRIER
8
MIN
TXV
8
INSIDE
DIAMS
CASING
MIN
(TYP)
DISTRIBUTOR
(TYP)
a39-2367