38
Fig. 36 — Multiple Coil Low Pressure
Piping Gravity Return
Fig. 37 — Condensate Lift to Overhead Return
Refrigerant Piping, Direct-Expansion (DX) Coils
Direct-expansion coils are divided into 2 or 4 splits depending
upon the unit size and coil circuiting. See Tables and for coil cir-
cuiting data. Each split requires its own distributor nozzle, expan-
sion valve, and suction piping. Suction connections are on the air
entering side when the coil is properly installed. Matching distrib-
utor connections for each coil split are on the air leaving side. See
unit label or certified drawing to assure connection to matching
suction and liquid connections. See Table 14 for distributor part
numbers.
Fig. 38 — Typical Direct-Expansion
Row Split Coil
SUCTION PIPING
Connect suction piping as shown in Fig. 39 for face split coil or
Fig. 40 for row split coil.
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 2.5°F. Refer to Fig. 41 for piping ris-
ers to the compressor.
To minimize the possibility of flooded starts and compressor dam-
age during prolonged light load operation, install an accumulator
in the suction line or a solenoid in the liquid line of
last-on, first off
split in row-split applications.
Unit
Unit
Note 1
Control Valve
(Notes 2 and 3)
Strainer
Gate Valve
Steam Supply
*
15° Check Valve
for Breaking
Vacuum
Thermostatic Trap (1/2 in.)
Dirt Leg (6 in.)
15° Check Valve
Float or Bucket
Trap (Note 4)
Note 1
Gate Valve
Condensate
Return
12" Min.
Open Air Relief to Atmosphere
* When end of supply main, see Fig. 34.
NOTES:
1. Flange or union is located to facilitate coil removal.
2. When control valve is omitted on multiple coils in parallel air flow.
3. When a bypass with control is required.
4. Coils with different pressure drops require individual traps. This
is often caused by varying air velocities across the coil bank.
NOTES:
1. Flange or union is located to facilitate coil removal.
2. To prevent water hammer, drain coil before admitting steam.
3. Do not exceed one foot of lift between trap discharge and return
main for each pound of pressure differential.
4. Do not use this arrangement for units handling outside air.
Note 1
Gate Valve
Unit
Steam Supply
Main
Overhead
Condensate
Return Main
Gate Valve
Check Valve
Bucket Trap
(located below
coil outlet)
Note 1
12"
Min.
Drain Valve
(Gate, Note 2)
CAUTION
Direct-expansion coils are shipped pressurized with dry air.
Release pressure from each coil split through valves in
protective caps before removing caps.
Do not leave piping open to the atmosphere unnecessarily. Wa-
ter and water vapor are detrimental to the refrigerant system.
Until the piping is complete, recap the system and charge with
nitrogen at the end of each workday. Clean all piping connec-
tions before soldering joints.
The lower split of face split coils should be
first on, last off.
Row split coils utilize special intertwined circuits (as shown in
Fig. 38); either split of these row split coils can be
first on, last
off.
Suction
Connection
Circuit 1
Air Flow
Suction
Connection
Circuit 2
Distributer
Circuit 1
Distributer
Circuit 2