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Application guidelines
36
FRCC.PC.014.A4.22
The working pressure in systems with R410A is
about 60% higher than in systems with R22 or
R407C. Consequently, all system components and
piping must be designed for this higher pressure
level.
Proper piping practices should be employed to
ensure adequate oil return, even under minimum
load conditions with special consideration given
to the size and slope of the tubing coming from
the evaporator. Tubing returns from the evapora-
tor should be designed so as not to trap oil and
to prevent oil and refrigerant migration back to
the compressor during off-cycles.
In systems with R410A, the refrigerant mass flow
will be lower compared to R22/R407C systems.
To maintain acceptable pressure drops and ac-
ceptable minimum gas velocities, the refrigerant
piping must be reduced in size compared to R22
/ R407C systems. Take care not to create too high
pressure drops neither since in R410A systems
the negative impact of high pressure drops on
the system efficiency is stronger than in R22/
R407C systems.
When the condenser is mounted at a higher po-
sition than the compressor, a suitably sized «U»-
shaped trap close to the compressor is necessary
to prevent oil leaving the compressor from drain-
ing back to the discharge side of the compressor
during off cycle. The upper loop also helps avoid
condensed liquid refrigerant from draining back
to the compressor when stopped.
Piping should be designed with adequate
three-dimensional flexibility. It should not be in
contact with the surrounding structure, unless
a proper tubing mount has been installed. This
protection proves necessary to avoid excess
vibration, which can ultimately result in connec-
tion or tube failure due to fatigue or wear from
abrasion. Aside from tubing and connection
damage, excess vibration may be transmitted to
the surrounding structure and generate an unac-
ceptable noise level within that structure as well.
For more information on noise and vibration, see
«Sound and Vibration Management» section.
CDS302 frequency converter integrates a special
feature in the compressor functions in order to
improve and secure the oil recovery from the sys-
tem. Refer to “Oil Return Management” section.
If the evaporator lies above the compressor, as
is often the case in split or remote condenser
systems, the addition of 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 refrig-
erant from draining into the compressor during
off-cycles.
If the evaporator were situated below the com-
pressor, 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.
Essential piping design
considerations
Suction lines
Discharge lines
HP
13 ft/s or more
0.5% slope
To condenser
max. 13 ft
max. 13 ft
0.5% slope
U-trap, as short as possible
U-trap
13 ft/s or more
U trap, as short as possible
Evaporator
LP
26 to 40 ft/s
HP
LP
Condenser
3D flexibility
U Trap
Upper loop
System design recommendations