26
INSTALLATION AND SERVICE
Refrigerant charging For the initial charge, the compressor
must not run and service valves must
be closed. Charge refrigerant as close
as possible to the nominal system
charge before starting the compres-
sor. Then slowly add refrigerant on
the low pressure side as far away as
possible from the compressor suction
connection. The refrigerant charge
quantity must be suitable for both
winter and summer operation. R404A
is a near-azeotropic mixture and must
be charged in the liquid phase. R507A
is an azeotropic mixture and can be
charged either in liquid or gas phase.
Warning:
When a liquid line solenoid valve is
used, the vacuum in the low pressure
side must be broken before applying
power to the system.
Installation checks After a few running hours the main
system parameters shall be veri ed to
ensure that the system is working cor-
rectly or eventually to adjust the set-
tings.
z
The evaporating temperature and
condensing temperature shall be com-
pared with the design conditions.
z
The superheat at the evaporator out-
let must be adjusted to optimise the
evaporator performance. Generally a
value of 5 to 6 K is recommended.
z
The compressor suction tempera-
ture gives information about the suc-
tion gas superheat at the compressor.
NTZ compressors can be operated at
a maximum suction gas temperature
of 20°C. However it is recommended
to keep the suction gas superheat at a
lower value to increase the compres-
sor performance and service life. On
the other hand, note that extremely
low superheat values can increase the
risk of unwanted liquid oodback to
the compressor. When a too high su-
perheat 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 qual-
ity insulation.
z
A too high discharge gas tempera-
ture can indicate a malfunctioning
condenser, presence of non-conden-
sable gasses, too high suction gas
superheat, refrigerant overcharging,
etc... The maximum allowable dis-
charge line temperature as measured
with a temperature probe directly af-
ter the compressor discharge connec-
tion is 115°C.
z
Power and current consumption
shall be compared with the table val-
ues at measured evaporating and con-
densing temperature.
z
When after commisioning the liquid
sight glass indicates moisture, the lter
drier must immediately be replaced.
Oil charge and oil level The oil charge must be checked be-
fore commissioning (1/4 to 3/4 of the
oil sight glass). Watch the oil level at
start and for the rst 15 minutes after
start. Check the oil level again after
a minimum of 2 hours operation at
nominal conditions. In most installa-
tions the initial compressor oil charge
will be su cient. In installations with
line runs exceeding 20 m or with
many oil traps or an oil separator, ad-
ditional 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 accesso-
ries 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 insu cient. Refer to sec-
tion "Piping design". In installations
where slow oil return is likely such as
in multiple evaporator or multiple con-
denser installations an oil separator is
recommended. Always use Danfoss
160Z lubricant for systems with NTZ
compressors and R404A or R507A.
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