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AB243586442172en-001401
Specific application recommendations
Discharge line, reversing
valve, solenoid valves
The Danfoss SH scroll compressor is a high
volumetric 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-acting 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
allowed between the compressor discharge port
and the reversing valve or any other restriction.
This gives sufficient free volume for the discharge
gas to collect and to reduce the pressure peak
during the time it takes for the valve to change
position. At the same time, it is important that
the selection 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.
In applications with heat recovery or condenser
partialisation, servo piloted solenoid valve has
to be properly sized or associated with a second
small valve in parallel, in order to avoid quick
discharge pressure drops when opening. This
phenomenon could lead to hammering effects
and create constraints on the non return valve
integrated in discharge fitting (SH180 to 485).
Defrost and reverse cycle
The Danfoss SH scroll compressor has the
ability to withstand a certain amount of liquid
refrigerant dynamic slug.
When compressors are installed in parallel,
in order to limit liquid amount handled per
compressor when beginning and ending defrost,
it is recommended to avoid running part load
(keep all compressors running or keep them
stopped when moving 4-way valves).
For further details, please refer to Parallel
application guidelines FRCC.PC.008.
EXV can also be opened when compressors are
stopped and before 4 way valve is moving in
order to decrease pressure difference. Opening
degree and time have to be set in order to keep
a minimum pressure difference for 4 way valve
moving. Each application design however should
be thoroughly tested to ensure acceptable
operating characteristics.
To ensure compressor reliability, the 4-way
valve must not reverse when the compressor is
stopped due to heating or cooling demand (stop
on thermostat).
Heat pumps frequently utilize high condensing
temperatures in order to achieve a sufficient
temperature rise in the medium being heated.
At the same time, they often require low
evaporating pressures to obtain sufficient
temperature differentials 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 compressor at too high discharge
temperatures can result in mechanical damage
to the compressor as well as thermal degradation
of the compressor lubricating oil and a lack
of sufficient 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
cycle 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.
R
Application Guidelines
Summary of Contents for SH485
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