Specific Application Recommendations; Low Ambient Compressor Operations; Low Ambient Operation And Minimum Pressure Differential; Low Ambient Start-Up - Danfoss Performer SM Series Selection & Application Manuallines

speciFic application RecoMMendations

low ambient compressor
operations
low ambient operations
and minimum pressure
differential

low ambient start-up

Head pressure control under
low ambient conditions

crankcase heaters

24
The Performer® scroll compressor
requires a minimum pressure dif-
ferential of 43 to 58 psi between the
suction and discharge pressures to
force the orbiting scroll-down against
the oil film on the thrust bearing.
Anything less than this differential
and the orbiting scroll can lift up,
causing a metal-to-metal contact.
It is therefore necessary to maintain
sufficient discharge pressure in order
Under low ambient temperature
conditions (< 32°F), start-up pressure
in the condenser and receiver (if
present) may be so low that there is not
sufficient pressure differential across
the expansion device to properly feed
the evaporator. A deep vacuum may
result, which can lead to compressor
failure due to internal arcing and
instability of the scroll members.
Under no circumstances should the
compressor be allowed to operate
under vacuum. The low-pressure
Several possible solutions are available
to prevent the compressor from
developing vacuum at start-up under
low ambient conditions. For air-cooled
units, cycling the fans with a head
pressure controller will ensure that
the fans remain off until condensing
pressure reaches a satisfactory level.
For water-cooled units, the same can
be performed using a water regulator
valve operated by condensing
pressure, thereby ensuring that the
water valve does not open until
condensing pressure reaches
satisfactory level.
Crankcase heaters are
recommended on all systems where
the compressor is exposed to cold
ambient temperatures,
in split and remote
to ensure this pressure differential.
Care should be taken during low
ambient operations
removal from air-cooled condensers
is greatest and head pressure control
may be required for low ambient
temperature applications. Operation
under low pressure differential may
be observed by a significant increase
in the sound power level generated by
the compressor.
control must be set in accordance
with the table on page 22 in order to
prevent vacuum operation.
Low pressure
also cause the expansion device
"hunting," which can cause surging
in the evaporator with liquid spillover
into the compressor. This effect is
most pronounced during low load
conditions that frequently occur
during low ambient temperature
conditions.
Note: The minimum condensing
pressure must be set at the minimum
saturated condensing temperature
shown in the application envelopes.
Under very low ambient conditions,
in which testing has revealed that the
above procedures might not ensure
satisfactory condensing and suction
pressures, the use of a liquid receiver
with condenser and receiver pressure
regulators would be possible.
For further information, please contact
Danfoss Technical Support.
a
strongly installations. The crankcase heater will
minimize refrigerant migration caused
by the large temperature gradient
especially between the compressor and the
condenser remainder of the system.
when heat
differentials can