Installation and service
Installation checks
Oil charge and oil level
After a few running hours the main system
parameters shall be verified to ensure that the
system is working correctly or eventually to
adjust the settings.
• The evaporating temperature and condensing
temperature shall be compared with the
design conditions.
• The superheat at the evaporator outlet must
be adjusted to optimise the evaporator
performance. Generally a value of 10K is
recommended.
• The compressor suction temperature gives
information about the suction gas superheat
at the compressor. NTZ compressors can
be operated at a maximum suction gas
temperature of 20°C. Note that extremely
low superheat values can increase the risk of
unwanted liquid floodback to the compressor.
When a too high superheat is noted while the
expansion valve setting is correct, the suction
line insulation between evaporator and
compressor should be checked and eventually
replaced by a higher quality insulation.
• A too high discharge gas temperature can
indicate a malfunctioning condenser, too
high suction gas superheat. Measurements
through a probe sensor pushed against the
discharge tube are not accurate. From 115°C,
we recommend to use a thermocouple, brazed
and insulated on the discharge tube, 10 cm
far from the compressor body. The maximum
allowed discharge temperature is 135°C.
• Power and current consumption shall be
compared with the table values at measured
evaporating and condensing temperature.
• When after commisioning the liquid sight
glass indicates moisture, the filter drier must
immediately be replaced.
The oil charge must be checked before
commissioning (1/4 to 3/4 of the oil sight
glass). Watch the oil level at start and for the
first 15 minutes after start. Check the oil level
again after a minimum of 2 hours operation at
nominal conditions. In most installations the
initial compressor oil charge will be sufficient.
In installations with line runs exceeding 20 m or
with many oil traps or an oil separator, additional
oil may be required. Normally the quantity of oil
added should be no more than 2% of the total
refrigerant charge. This percentage does not
take into account oil contained in accessories
such as oil separators or oil traps. If this amount
has already been added and the oil level in the
compressor keeps decreasing, the oil return in
the installation is insufficient. Refer to section
"Piping design". In installations where slow oil
return is likely such as in multiple evaporator or
multiple condenser installations an oil separator
is recommended. Use Danfoss 175PZ lubrificant
for systems with NTZ compressors.
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AB245486497018en-000601
Application Guidelines
