17
Discharge line
When the condenser is mounted above
the compressor, a loop above the con-
denser and a U-trap close to the com-
pressor are required to prevent liquid
draining from the condenser into the
discharge line during standstill.
SYSTEM DESIGN RECOMMENDATIONS
Gas velocities higher than 12 m/s will
not contribute to signifi cantly better
oil return. However they will cause
higher noise levels and result in higher
suction line pressure drops which will
have a negative eff ect on the system
capacity. Note that the suction ro-
tolock valves, which can be ordered
from Danfoss as accessories, are de-
signed for average pipe sizes, selected
for systems running at nominal condi-
tions. The pipe sizes selected for spe-
cifi c systems may diff er from these av-
erage sizes.
The suction line must always be insu-
lated to limit suction gas superheat.
Oil charge and oil separator
In most installations the initial com-
pressor oil charge will be suffi
cient.
In installations with line runs exceed-
ing 20 m, or with many oil traps or an
oil separator, additional oil may be
required. In installations with the risk
of slow oil return such as in multiple
evaporator or multiple condenser in-
stallations, an oil separator is recom-
mended. Also refer to the section "Oil
charge and oil level".
Filter driers
For new installations with NTZ com-
pressors Danfoss recommends using
the Danfoss DML 100% molecular
sieve, solid core fi lter drier. Molecular
sieve fi lter driers with loose beads from
third party suppliers shall be avoided.
For servicing of existing installations
where acid formation is present the
Danfoss DCL solid core fi lter driers
containing activated alumina are
recommended.
The drier is to be oversized rather than
undersized. When selecting a drier,
always take into account its capacity
(water content capacity), the system
refrigerating capacity and the system
refrigerant charge.
Suction line heat exchanger
A suction line heat exchanger is
recommended for low temperature
applications, better performance and
effi
ciency are expected. However
in hot location this may cause high
suction gas superheat which can result
in too high discharge temperature.
Suction pressure control
An MOP-type expansion valve or suc-
tion pressure regulator (i.e. Danfoss
KVL) must be used to limit suction
pressure at a maximum of 4 bar rela-
tive (-5°C). Do not apply both of these
devices in combination with one an-
other.
When compressors are mounted onto
a rack for a multi-evaporator system
(i.e. supermarket) or when evapora-
tors operate at diff erent temperatures,
use pressure regulators (Danfoss KVP)
without an MOP expansion valve.
