Application guidelines
49
FRCC.PC.021.A5.22
Installation
Filter driers
Refrigerant charging
Refrigerant charge limit
A properly sized & type of drier is required.
Important selection criteria include the driers
water content capacity, the system refrigeration
capacity and the system refrigerant charge.
The drier must be able to reach and maintain
a moisture level of 50 ppm end point dryness
(EPD).
For new installations with PSH compressors with
polyolester oil, Danfoss recommends using the
Danfoss DML (100% molecular sieve) solid core
filter drier. Molecular sieve filter 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)
filter driers containing activated alumina are
recommended.
The drier is to be oversized rather than under
sized. When selecting a drier, always take into
account its capacity (water content capacity),
the system refrigeration capacity and the system
refrigerant charge.
After burn out, remove & replace the liquid line
filter drier and install a Danfoss type DAS burnout
drier of the appropriate capacity. Refer to the DAS
drier instructions and technical information for
correct use of the burnout drier on the liquid line.
For the initial charge the compressor must not
run and eventual service valves must be closed.
Charge refrigerant as close as possible to the
nominal system charge before starting the
compressor.
This initial charging operation must be done in
liquid phase. The best location is on the liquid
line between the condenser outlet and the
filter drier. Then during commissioning, when
needed, a complement of charge can be done
in liquid phase: slowly throttling liquid in on
the low pressure side as far away as possible
from the compressor suction connection while
compressor is running. The refrigerant charge
quantity must be suitable for both summer and
winter operations.
Vacuum or charge from one side can seal the
scrolls and result in a non-starting compressor.
When servicing, always ensure that LP/HP
pressures are balanced before starting the
compressor.
Be sure to follow all government regulations
regarding refrigerant reclamation and storage.
For more detailed information see
“Recommended refrigerant system charging
practice” news bulletin FRCC.EN.050.
Danfoss PSH compressors can tolerate liquid
refrigerant up to a certain extend without major
problems. However, excessive liquid refrigerant in
the compressor is always unfavourable for service
life. Besides, the installation cooling capacity may
be reduced because of the evaporation taking
place in the compressor and/or the suction line
instead of the evaporator. System design must be
such that the amount of liquid refrigerant in the
compressor is limited.
In this respect, follow the guidelines given
in the section:”Essential piping design
recommendations” in priority.
Use the tables below to quickly evaluate the
required compressor protection in relation with
the system charge and the application.
Model
Refrigerant charge limit
in the compressor (lb)
Com
pr
es
sor PSH051-064
29.8
PSH077
32
Tandem
PSH104
38.6
PSH115
38.6
PSH130
38.6
PSH128
38.6
PSH141
38.6
PSH154
38.6
Tr
io
PSH153
50.7
PSH192
50.7
PSH231
54
