Ystem Design Recommendations; General; Essential Piping Design Considerations - Danfoss MLM Series Application Manuallines

A G
PPLICATION UIDELINES

General

Essential piping design
considerations
fig.1
0.5 % slope,
4 m/s or more
max. 4 m
U-trap, as short as possible
8 to 12 m/s
max. 4 m
0.5 % slope,
4 m/s or more
U-trap, as short as possible
S

YSTEM DESIGN RECOMMENDATIONS

Successful application of scroll compressors is
dependent on careful selection of the compres-
sor for the application. If the compressor is not
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.
If the evaporator lies above the compressor the
addition of a pump-down cycle is strongly recom-
mended. If a pump-down cycle were to be omit-
ted, the suction line must have a loop at the evap-
orator outlet to prevent refrigerant from draining
into the compressor during off -cycles.
If the evaporator were situated below the com-
pressor, the suction riser must be trapped to en-
sure the oil return to the compressor (see fi g.1).
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-
To condenser
U-trap
Evaporator
FRCC.PC.015.A4.02
correct for the system, it will operate beyond the
limits given in this manual. Poor performance, re-
duced reliability, or both may result.
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 (see fi g. 2). The
maximum elevation diff erence between the in-
door and outdoor section cannot exceed 8 m.
System manufacturers should specify precau-
tions for any applications that exceed these limits
to ensure compressor reliability.
Piping should be designed with adequate three-
dimensional fl exibility (fi gure 2). It should not be
in contact with the surrounding structure, un-
less 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 dam-
age, excess vibration may be transmitted to the
surrounding structure and generate an unaccept-
able sound level within that structure as well (for
more information on sound and vibration, see the
section on: "Sound and vibration management").
fig. 2
Upper loop
HP
U-trap
LP
3D flexibility
Condenser
27