Danfoss VZH 088 Application Manuallines Download

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Application guidelines

FRCC.PC.023.A7.22

Single compressors

Operating conditions

Low pressure

Crankcase heating function

Electronic expansion valve

Pressure settings

A low-pressure (LP) safety switch must be
used. Deep vacuum operations of a scroll
compressor can cause internal electrical arcing
and scroll instability. VZH compressors exhibit
high volumetric efficiency and may draw very
low vacuum levels, which could induce such
a problem. The minimum low-pressure safety
switch (loss-of-charge safety switch) setting is
given in the following table. For systems without

pump-down, the LP safety switch must either be
a manual lockout device or an automatic switch
wired into an electrical lockout circuit. The LP
switch tolerance must not allow for vacuum
operations of the compressor. LP switch settings
for pump-down cycles with automatic reset are
also listed in the table below. Lock-out circuit or
LP switch or series with other safety devices must
be connected to CDS303 input 27.

A DC-hold current through the motor windings
can be used as an alternative to an external
crankcase heater to keep the compressor warm
when stopped.

For VZH088 and VZH117 this function is factory
preset to "disabled". Go to parameter 28.3x in the
frequency converter for settings (factory presets
are done).

For VZH170, this function must not be used and is
factory preset to “disabled”. An external crankcase
heater is required, and surface sump heater type
should be preferred. Refer to accessory list for
code numbers.

With variable capacity systems, an electronic
expansion valve (EXV) is the mandatory solution
to handle refrigerant mass flow variations.
Danfoss recommend to use ETS products.
Ramp-up and ramp-down settings, of both EXV
and compressor, must be done with great care.
Customer could also use thermostatic expansion
valve(TXV) if they have qualified their systems
and get Danfoss approval.

Ramp-up of the EXV must be shorter than
the ramp-up of the compressor, to avoid any
low pressure operation on suction side of the
compressor. The EXV can also be opened, up
to a certain degree, before the start up of the
compressor.

Ramp-down of the EXV must be longer than the
ramp-down of the compressor, also to avoid low
pressure operation (except with pump-down).

EXV should be closed, and remained closed,
when the compressor is off, to avoid any liquid
refrigerant entering the compressor.

It is recommended to use expansion valve with
MOP (Maximum Operating Pressure) function.
MOP is a feature added to EXV’s (also to TXV’s)
that limit the maximum suction pressure of the
unit. The customer would need to set this at the
15°C limit we have on our VS operating envelope.
Regardless of EXV or TXV, customer needs to
qualify the expansion device. Testing needs to be
done at both max and min operating conditions
to guarantee the valve closes enough on the min
and opens far enough on the max.

Pressure settings

R410A

Working pressure range high side

psi(g)

195.8 - 645.42

Working pressure range low side

psi(g)

33.36 - 168.24

Maximum high pressure safety switch setting

psi(g)

652.67

Minimum low pressure safety switch setting *