CC-000202
HP
LP
1
2
1
2
Condenser
Upper loop
Figure 22: Avoid condensed liquid refrigerant from draining back
Sump heater
When the unit idles, refrigerant migrates to the coldest point of the system. Sump heater are designed to avoid
compressor becoming the coldest point of system and accumulate refrigerant in sump.
See Test and components required per application to know when to use heater Surface sump heater accessories are
available from Danfoss (see section Accessories and Spare parts).
100W belt sump heater should be mounted on compressor shell to guarantee safe cold start-up even at the worst
condition.
Basing on customer unit design and application situation, customer can select lower power belt sump on condition
that safe cold start-up can be guaranteed.
Sump heater control logic
The heater is typically controlled by a unit controller and shall be ON whenever all compressors within the circuit
are OFF.
For units that may be totally power shut down on a regular basis, such as exhibition hall, it is strongly recommended
to the heater to a secured power supply in order to maintain migration protection.
Sump crankcase heater installation is mandatory. When compressor is put on hold, crankcase heater should be
powered on.
At commissioning, the surface sump heater must be energized at least 6 hours in advance to remove refrigerant
from sump.
To optimize energy
efficiency
of heater, oil sump temperature can be permanently monitored by the unit controller,
and the heater can be turned
off
when oil superheat (oil temperature – evaporating temperature) is above 12K
(21.6°F).
To further protect against
flooded
starts, a logic can be programmed in the unit controller. After each unit power up,
the compressor can start only if the oil super heat is above 12K (21.6°F). More details regarding the oil sump
temperature measurement can be found in section "Application- Manage Superheat "
Non return valve
Non-return valve
at discharge prevents from liquid or gas migration. Selection of non-return valve is a
trade-off
between pressure dropping at high speed, and the state of the valve stability while at low speed. Non-return valve is
mandatory.
© Danfoss | Climate Solutions | 2023.08
AB392939083370en-000202 | 43
Scroll compressors, VCH115 | Application
