APPLICATION GUIDELINES
FRCC.PC.007.B5.02
35
SPECIFIC APPLICATION RECOMMENDATIONS
Discharge line
and reversing valve
The Performer® SH scroll compressor is a high vol-
umetric machine and, as such, can rapidly build
up pressure in the discharge line if gas in the line
becomes obstructed even for a very short period
of time which situation may occur with slow-act-
ing, reversing valves in heat pumps. Discharge
pressures exceeding the operating envelope may
result in nuisance high-pressure switch cutouts
and place excess strain on both the bearings and
motor.
To prevent such occurrences, it is important that
a 1-meter minimum discharge line length be al-
lowed between the compressor discharge port
and the reversing valve or any other restriction.
This gives suffi cient free volume for the discharge
gas to collect and to reduce the pressure peak dur-
ing the time it takes for the valve to change posi-
tion. At the same time, it is important that the se-
lection and sizing of the reversing or 4-way valve
ensure that the valve switches quickly enough to
prevent against too high discharge pressure and
nuisance high-pressure cutouts.
Check with the valve manufacturer for optimal
sizing and recommended mounting positions.
The use of a suction line accumulator is strongly
recommended in reversible-cycle applications.
This because of the possibility of a substantial
quantity of liquid refrigerant remaining in the
evaporator, which acts as a condenser during the
heating cycle.
This liquid refrigerant can then return to the com-
pressor, either fl ooding the sump with refriger-
ant or as a dynamic liquid slug when the cycle
switches back to a defrost cycle or to normal cool-
ing operations.
Sustained and repeated liquid slugging and fl ood
back can seriously impair the oil’s ability to lubri-
cate the compressor bearings. This situation can
be observed in wet climates where it is necessary
to frequently defrost the outdoor coil in an air
source heat pump. In such cases a suction accu-
mulator becomes mandatory.
Suction line accumulator
Defrost and reverse cycle The Performer® SH scroll compressor has the abil-
ity to withstand a certain amount of liquid refrig-
erant dynamic slug. However we advise that the
system is unloaded to the minimum capacity step
for defrost or when the cycle is reversed.
Heat pumps frequently utilize high condensing
temperatures in order to achieve a suffi cient tem-
perature rise in the medium being heated. At the
same time, they often require low evaporating
pressures to obtain suffi cient temperature diff er-
entials between the evaporator and the outside
temperature. This situation may result in high
discharge temperature; as such, it is mandatory
that a discharge gas thermostat be installed on
the discharge line to protect the compressor from
excessive temperatures. Operating the compres-
sor at too high discharge temperatures can result
in mechanical damage to the compressor as well
as thermal degradation of the compressor lubri-
cating oil and a lack of suffi cient lubrication. The
discharge gas thermostat should be set to shut
down the compressor in the event discharge gas
rises above 135°C.
Discharge temperature
thermostat
Sump heaters Sump heaters are mandatory on reversible cy-
cle applications given the high probability of
liquid migration back to the compressor sump
during off -cycles due to the outdoor location of
most units and operations during low ambient
conditions.
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