A
PPLICATION
GUIDELINES
S
PECIFIC
APPLICATION
RECOMMENDATIONS
Low load operations
The compressor should be run for a minimum
period to ensure that the oil has sufficient time to
properly return to the compressor sump and that
the motor receives enough cooling under condi-
tions of lowest refrigerant mass flow.
Brazed plate
heat exchangers
A brazed plate heat exchanger needs very little in-
ternal volume to satisfy the heat transfer require-
ments. Consequently, the heat exchanger offers
very little internal volume for the compressor to
draw vapour from the suction side. The compres-
sor can then quickly enter into a vacuum condi-
tion. It is therefore important that the expansion
device be sized correctly and that a sufficient pres-
sure differential across the expansion device be
available to ensure adequate refrigerant feed into
the evaporator. This aspect is of special concern
when operating the unit under low ambient and
load conditions. For further information on these
conditions, please refer to the previous sections.
Due to the small volume of the brazed plate heat
exchanger, no pump-down cycle is normally re-
quired. The suction line running from the heat
exchanger to the compressor must be trapped to
avoid refrigerant migration to the compressor.
When using a brazed plate condenser heat ex-
changer, a sufficient free volume for the discharge
gas to accumulate is required in order to avoid ex-
cess pressure build-up. At least 3 ft of discharge
line is necessary to generate this volume. To help
reduce the discharge gas volume immediately
after start-up, the supply of cooling water to the
heat exchanger may be opened before the com-
pressor starts, to remove superheat and condense
the incoming discharge gas more quickly.
Water utilising systems
Apart from residual moisture in the system after
commissioning, water could also enter the re-
frigeration circuit during operation. Water in the
system shall always be avoided. Not only because
it can shortly lead to electrical failure, sludge in
sump and corrosion but in particular because it
can cause serious safety risks.
Common causes for water leaks are corrosion and
freezing.
Corrosion: Materials in the system shall be compli-
ant with water and protected against corrosion.
Freezing: When water freezes into ice its volume
expands which can damage heat exchanger walls
and cause leaks. During off periods water inside
heat exchangers could start freezing when ambi-
ent temperature is lower than 30°F. During on pe-
riods ice banking could occur when the circuit is
running continuously at too low load. Both situa-
tions should be avoided by connecting a pressure
and thermostat switch in the safety line.
30
FRCC.PC.016.A1.22
