GENER
AL INFORMA
TION
PR
ODUC
T INFORMA
TION
INTEGR
ATION INT
O SY
STEM
ORDERING INFORMA
TION
SY
STEM DESIGN
Manage off cycle migration
R
Requirement
System evaluation
Off -cycle refrigerant migration happens:
• when the compressor is located at the coldest
part of the installation, refrigerant vapor
condenses in the compressor.
• or directly in liquid-phase by gravity or pressure
difference. When the compressor restarts,
the refrigerant diluted in the oil, or stored
in evaporator, generates poor lubrication
conditions, and may reduce bearings life time. In
extreme situations, this leads to liquid slugging
that can damage the compressor scroll set.
• Compressor can tolerate occasional flooded
start, but it should remain exceptional situation
and unit design must prevent that this situation
happen at each start.
• Right after start, liquid refrigerant must not flow
massively to compressor
• The charge limit is a threshold beyond some
protective measures must be taken to limit risk
of liquid slugging and extreme dilution at start.
Use the table below in relation with the system
charge and the application to quickly define
necessary safeties to implement.
Application
BELOW charge limit
ABOVE charge limit
All
Ensure tightness between condenser & evaporator when system is OFF
• Thermostatic expansion Valve (TXV) , Liquid Line Solenoid Valve LLSV** strongly
recommended
• Electronic expansion valve (EXV) must close when system stop including in power shut
down situation
Non split
No test or additional safeties required
• Surface Sump Heater *
• External Non-Return Valve ****
Split
Since each installation is unique, refrigerant charge may vary
• Surface Sump Heater *
• Liquid Line Solenoid Valve**+ pump-down cycle***
• External Non-Return Valve
*Surface Sump heater
The surface sump heater are designed to protect
the compressor against off-cycle migration of
refrigerant.
For DSH090-105-120-140-161-184, the surface
sump heater is located on the compressor shell.
For better standby energy consumption, Danfoss
provides 48W and 80W two optional surface
sump heater. The selection of surface sump
heater could refer to below principle:
For DSH240-295-381-485, the 56W surface sump
seater is located below the sump, associated with
a thermal insulation.
Compressor Surrounding
Ambient
Surface Sump Heater
Unit has enclosure, no wind
48W SSH
Unit has no enclosure, with
wind
80W SSH
Unit has no enclosure,
wind >5m/s (ft/s)& ambient
temperature <-5°C
80W SSH + additional
SSH/thermal insulation
The heater must be turned on whenever all the
compressors are off.
Surface sump heater accessories are available
from Danfoss (see section “Accessories”).
**Liquid line solenoid valve (LLSV)
A LLSV is used to isolate the liquid charge
on the condenser side, thereby preventing
against charge transfer to the compressor
during off -cycles. The quantity of refrigerant
on the low-pressure side of the system can be
further reduced by using a pump-down cycle in
association with the LLSV.
DSH240
to
DSH485
DSH090 to 184
41
FRCC.PC.045.A7.02
Summary of Contents for DSH Series
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