Danfoss SH090 Application Guidelines

26
FRCC.PC.007.B8.02
Application guidelines
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 e
 ciency and may dra w 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 tabl
e. 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
Operating conditions
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 c
ompressor running
time of 2 minutes so as to provide for su cient
motor cooling after start-up along with proper oil
return. Note that the oil return may vary since it
depends upon system design.
There m
ust 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 t
hat these two di erent low pressure
switches also require di erent settings. The low
pressure pump down switch setting must always
be within the operating envelope, for example
2.3 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 di erential betw
een the discharge
and suction pressures surpasses 31 to 38 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
T
H
KA
A1
A2 A3A1
180 s
A2
KA
~
~
Pressure settings R410A
Working pressure range high side bar (g) 13.5 - 44.5
Working pressure range low side bar (g) 2.3 - 11.6
Maximum high pressure safety switch setting bar (g) 45
Minimum low pressure safety s
witch setting * bar (g) 1.5
Minimum low pressure pump-down switch setting ** bar (g) 2.3
* 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 2.3 bar(g)
HP
LP
Relief valve

Danfoss SH090 Specifications

General

Brand	Danfoss
Model	SH090
Category	Air Compressor
Language	English