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AB243586442172en-001401
Operating conditions
Cycle rate limit
A low-pressure (LP) safety switch must be used.
Deep vacuum operations of a scroll compressor
can cause internal electrical arcing and scroll
instability. Danfoss SH scroll 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.
Low pressure
Danfoss recommends a restart delay timer to
limit compressor cycling. The timer prevents
reverse compressor rotation, which may occur
during brief power interruptions.
The system must be designed in a way that
guarantees a minimum compressor running
time of 2 minutes so as to provide for sufficient
motor cooling after start-up along with proper oil
return. Note that the oil return may vary since it
depends upon system design.
There must be no more than 12 starts per hour, a
number higher than 12 reduces the service life of
the motor-compressor unit. A three-minute (180-
sec) time out is recommended.
Note that these two different low pressure
switches also require different settings. The low
pressure pump down switch setting must always
be within the operating envelope, for example
1.7 bar for R410A. The compressor can be
operated full time under such condition.
The minimum low pressure safety switch setting
may be outside the normal operating envelope
and should only be reached in exceptional
(emergency) situations, for example 1.5 bar for
R410A.
The SH380 and SH485 incorporate an internal
relief valve set to open between the internal high
and low pressure sides of the compressor when
the pressure differential between the discharge
and suction pressures surpasses 42.4 bar.
This safety feature prevents the compressor from
developing dangerously high pressures should
the high pressure cut-out, for whatever reason,
fail to shut down the compressor.
Internal pressure relief valve
T
T
TH
TH
KA
A1
A2
A3
A1
180 s
A2
KA
~
~
Pressure settings
R410A
Working pressure range high side
bar (g)
13.5 - 44.7
Working pressure range low side
bar (g)
1.7 - 11.6
Maximum high pressure safety switch setting
bar (g)
46.1
Minimum low pressure safety switch setting *
bar (g)
1.5
Minimum low pressure pump-down switch setting **
bar (g)
1.7
* LP safety switch shall never be bypassed and shall have no time delay.
** Recommended pump-down switch settings: 1.5 bar below nominal evap. pressure with minimum of 1.7 bar(g)
HP
LP
Relief valve
Application Guidelines
Содержание SH485
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