System design recommendations
5.1 Piping design
Connection sizes! Unsuitable refrigerant flow
rate!
NOTICE
Do not assume that the liquid/
suction connection sizes on the unit are in fact
the correct sizes to run your interconnecting
refrigeration pipes!
The pipes should be sized to ensure optimum
performance and good oil return. The sizing must
also take into account the full capacity range
through which this particular unit will need to
operate.
Pipe runs should be kept as short as possible,
using the minimum number of directional
changes. Use large radius bends and avoid
trapping of oil and refrigerant. This is particularly
important for the suction line.
All pipes should be adequately supported to
prevent sagging which can create oil traps. The
recommended pipe clamp support distance is
shown in Table below:
The suction line should:
• secure gentle slope towards the unit
(recommended slope minimum 0,5/100).
• have P traps, double risers and reduced pipe
diameters where long vertical risers cannot be
avoided.
The suction gas velocity must be sufficient to
ensure a good oil return, within 8 to 12 m/s in
vertical risers. In horizontal pipes this velocity
can decrease down to 4 m/s. The use of U-trap
and double suction risers is often required. These
suction risers must always be fitted with a U-trap
at the bottom and a P-trap at the top and never be
higher than 4 m unless a second U-trap system is
fitted.
If the evaporator lies above the CU, a pump-down
cycle is strongly recommended. If a pump-down
cycle were to be omitted, the suction line must
have a loop at the evaporator outlet to prevent
refrigerant from draining into the compressor
during off-cycles. If the evaporator are situated
below the CU, the suction riser must be trapped
so as to prevent liquid refrigerant from collecting
at the outlet of the evaporator while the system is
idle, which would mislead the expansion valve’s
sensor (thermal bulb) at start-up.
Maximum safety length of pipes between CU and
last evaporator is 20 m.
If pipes length is more than 20 m special
adjustment of complete system is needed (oil
and refrigerant charge adjustments).
Tube size
Distance between 2 clamp supports
12 mm (1/2")
1 m
16 mm (5/8")
1,5 m
19 mm (3/4")
1,8 m
22 mm (7/8")
2 m
8 to 12 m/s at minimum speed
8 to 12 m/s at minimum speed
26
FRCC.PC.044.A6.02
Application Guidelines
