System design recommendations
To obtain optimum efficiency of the complete
refrigerant system, optimised R410A heat
exchangers must be used. R410A refrigerant has
good heat transfer properties: it is worthwhile
designing specific heat exchangers to gain in size
and efficiency.
An evaporator with optimised R410A distributor
and circuit will give correct superheat at outlet
and optimal use of the exchange surface. This is
critical for plate evaporators that have generally a
shorter circuit and a lower volume than shell and
tubes and air cooled coils.
For all evaporator types a special care is required
for superheat control leaving the evaporator and
oil return.
A sub-cooler circuit in the condenser that creates
high sub cooling will increase efficiency at high
condensing pressure. In R410A systems the
positive effect of sub cooling on system efficiency
will be significantly larger than in R22/R407C
systems.
Furthermore, for good operation of the
expansion device and to maintain good
efficiency in the evaporator it is important
to have an appropriate sub cooling. Without
adequate sub cooling, flash gas will be formed at
the expansion device resulting in a high degree
of vapour at the expansion device inlet leading to
low efficiency.
Heat exchangers
Refrigerant charge limit
Danfoss CH compressors can tolerate liquid
refrigerant up to a certain extend without major
problems. However, excessive liquid refrigerant in
the compressor is always unfavorable 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
(kg)
CH290
13.5
CH485
17
More detailed information can be found in the paragraphs hereafter.
Please contact Danfoss Technical Support for any deviation from these guidelines.
Recommended
Required
No test or additional safeties required
Note: for special conditions such as low ambient temperature, low refrigerant load or brazed plate heat exchangers please refer to
corresponding sections.
REQ
REC
BELOW charge limit
ABOVE charge limit
Cooling only systems,
Packaged units
No test or additional safeties required
Refrigerant migration and flood back test
Sump heater
Cooling only systems
with remote condenser
and split system units
Refrigerant migration and flood back test
Sump heater
Refrigerant migration and flood back test
Sump heater
Liquid receiver (in association with LLSV and
pump down)
Reversible heat pump system
Specific tests for repetitive flood back
Sump heater
Defrost test
For more details, refer to section ”Reversible heat pump system“
REC
REC
REQ
REQ
REQ
REQ
REQ
REQ
REQ
REC
23
FRCC.PC.026.A4.02
Application Guidelines