![background image](http://html1.mh-extra.com/html/danfoss/maneurop-ntz-series/maneurop-ntz-series_selection-and-application-manuallines_3394249016.webp)
Maneurop® NTZ compressors have
been designed and qualifi ed for sta-
tionary equipment using standard al-
ternating power supply. Danfoss does
not warrant the compressors for use
on mobile applications such as trucks,
railways, subways, ships etc.
These selection and application guide-
lines concern single compressors
only. For guidelines on manifolding
Maneurop® NTZ compressors, please
refer to literature called "Parallel Appli-
cation Guidelines".
16
SYSTEM DESIGN RECOMMENDATIONS
Piping design
Oil in a refrigeration circuit is required
to lubricate moving parts in the com-
pressor. During normal system opera-
tion small oil quantities will continu-
ously leave the compressor, with the
discharge gas. Therefore, the system
piping shall be designed in a way
which allows a good oil circulation,
avoiding oil being trapped in the
system and ensuring a constant oil
return to the compressor. As long as
the amount of oil circulating through
the system is small it will contribute to
good system operation and improved
heat transfer effi
ciency.
Lubricant getting trapped in the
evaporator or suction lines will aff ect
system performance and will ulti-
mately lead to compressor lubrication
failures. Where a poor oil return situ-
ation exists, adding lubricant will not
help safeguard the compressor. Only
a correct piping design can ensure
adequate oil circulation maintaining
safe oil level in the compressor.
Suction line
Horizontal suction line sections shall
have a slope of 0.5% in the direction
of refrigerant fl ow (5 mm per meter).
The cross-section of horizontal suction
lines shall be such that the resulting
gas velocity is at least 4 m/s. In vertical
risers, a gas velocity of 8 to 12 m/s is
required to ensure proper oil return.
A U-trap is required at the foot of each
vertical riser. If the riser is higher than
4 m, additional U-traps are required for
each additional 4 meters.The length of
each U-trap must be as short as pos-
sible to avoid the accumulation of
excessive quantities of oil (see fi gure
below).