Suction Riser; Step 6 - Complete Refrigerant Piping; Connections - Carrier Gemini 38AU Series Installation, Start-Up And Service Instructions Manual

Suction Riser

A suction riser condition exists when the outdoor unit is located
above the indoor (evaporator) unit and suction vapor must flow
vertically up to return to the compressor. Oil return is a concern
when the suction tube size is too large to produce the minimum re-
frigerant velocity to ensure oil return at minimum load conditions.
38AUZ (ALL) AND 38AUD (A,B) WITHOUT HGBP
Check Table 11 for maximum suction tube size for 38AU units at
minimum load conditions. Consider suction speed riser (reduced
tube size for vertical segment only) or double suction riser ar-
rangement if the planned suction tube size does not provide neces-
sary minimum flow-rates for this riser.
Table 11 — 38AU Maximum Suction Pipe Size
MODEL UNIT SIZE
38AUZA, B
38AUZD, E
38AUDA, B
38AUDC
38AUDC12 WITH OPTIONAL HOT GAS BYPASS
Special consideration for suction riser requirements must be con-
sidered when applying this factory-installed hot gas bypass. It is
extremely important to consider the lowest possible refrigerant
tons of refrigerant flow when hot gas bypass is functioning to as-
sure proper oil return up suction risers.
Table 10 provides recommended tube sizes for model 38AUDC12
unit which includes the factory-installed hot gas bypass system on
Circuit 1. The selections in this table are based on evaluations of
system minimum load operating conditions for comfort cooling
applications, with compressor saturated suction pressure to 28°F
(–2.2°C) minimum.
Table 10 includes liquid line size selections based on use of RTPF
coil option only.
Table 10 includes three different suction line size selections for
Circuit 1 based on the elevation difference conditions between
the 38AUD unit and the evaporator coil location.
Outdoor Unit ABOVE Evaporator Coil
This installation will have at least one suction riser segment. If the
vertical elevation difference is less than 20-ft (6.1 m) linear feet
and requires only one or two segments, consider a speed riser se-
lection for Circuit 1; use the line marked VAPOR RISER RE-
QUIRED; NOT GREATER THAN 20 FT (6.1 M). See Fig. 5.
Tube S is the horizontal line size; tube A is the reduced diameter
riser size.
A
LEGEND
S
A - Suction Riser With Trap
S - Suction Line to Condensing Unit
Fig. 5 — Suction Line Piping - Speed Riser
MAXIMUM TUBE SIZE
07 1 3 /
8
08 1 /
5
8
12 1 /
5
8
14 2 1 /
8
07 1 1 /
8
08 1 1 /
8
12 1 /
3
8
14 1 /
5
8
12 See Table 10
CONDENSING
UNIT
20-FT (6.1 M)
MAX
If the vertical elevation difference is greater than 20-ft (6.1-m) lin-
ear feet or requires more than two short lift segments, select the
Circuit 1 suction line size from Double Suction Riser lines data
under VAPOR RISER GREATER THAN 20 FT (6.1 M). See
Fig. 6. Tube S is the horizontal line size. Tube A is the reduced di-
ameter riser size without bottom trap; Tube B is the parallel riser
size with bottom oil trap.
S
FROM
EVAPORATOR
A - Suction Riser Without Trap
B - Suction Riser With Trap
S - Suction Line to Condensing Unit
Fig. 6 — Suction Line Piping - Double Riser
Outdoor Unit BELOW Evaporator Coil and No Vertical Riser
Segments
Select Circuit 1 suction line size from NO VAPOR RISER line.
Circuit 2 Suction Line
Because there is no hot gas bypass system in Circuit 2, no special
riser selections are necessary. Select Circuit 2 suction line from
bottom line for all 38AUDC installations.
Vertical Separation (outdoor unit above indoor unit)
Vertical elevation difference of 200 ft (60 m) is permitted when
the outdoor unit (38AUZ or 38AUD) is located above the indoor
unit.
Step 6 — Complete Refrigerant Piping

Connections

IMPORTANT: DO NOT BURY REFRIGERANT LINES.
IMPORTANT: A refrigerant receiver is not provided with the
unit. Do not install a receiver.
PROVIDE SAFETY RELIEF
If local codes dictate an additional safety relief device, purchase
locally and install locally. Installation will require the recovery
of the factory shipping charge before the factory tubing can be
cut and the supplemental relief device is installed.
Model 38AUD has two separate refrigeration systems. If required,
each circuit will require a field-supplied/installed supplemental re-
lief device.
CHECK 38AU MODEL WITH EVAPORATOR COIL
CONNECTIONS
Confirm before installation of unit that the evaporator coil con-
nections are consistent with this 38AU model. See Table 3 on
page 3.
INSULATE SUCTION LINES
Apply closed-cell tubular insulation to all suction lines between
evaporator coil connection and 38AU unit's suction service valve.
10
A
B
LEGEND
S