Famco Danfoss Maneurop MT, Руководство пользователя

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19
SYSTEM DESIGN RECOMMENDATIONS
Crankcase heater
Liquid line solenoid valve &
pump-down
Suction accumulator
Tests must be conducted to ensure
that the appropriate oil temperature
is maintained under all ambient
conditions.
According our standard recom-
mendation oil temperature has to be
maintained 10K above the saturated
LP temperature of the refrigerant.
Under extreme conditions such as
very low ambient temperature a belt
type crankcase heater could be used.
The belts crankcase heater must be
positioned on the compressor shell
as close as possible to the oil sump to
ensure good heat transfer to the oil.
Belt crankcase heaters are not self-
regulating. Control must be applied
to energise the belt heater once
the compressor has been stopped
and then to de-energise it while the
compressor is running. The belt heater
must be energised 12 hours before
restarting the compressor following
an extended shutdown period.
If the crankcase heater is not able to
maintain the oil temperature at 10 K
above the saturated LP temperature
of the refrigerant during off cycles
or if repetitive fl oodback is present,
a Liquid Line Solenoid Valve (LLSV)
+ pump-down cycle is required,
possibly in conjunction with a suction
accumulator.
The use of the trickle circuit wiring
is allowed on single phase MPZ
compressors. This specifi c wiring
allows heating of the compressor
during off period, feeding the auxiliary
winding through the “trickle” capacitor
with a small current.
In refrigeration applications, the Liquid
Line Solenoid Valve (LLSV) is highly
recommended. During the off -cycle,
the LLSV isolates the liquid charge in
the condenser side, thus preventing
refrigerant transfer or excessive
migration of refrigerant into the
compressor. Furthermore, when using a LLSV in conjunction with a pump-
down cycle, the quantity of refrigerant
in the low-pressure side of the system
will be reduced.
A pump-down cycle design is required
when evaporators are fi tted with
electric defrost heaters.
A suction accumulator off ers
considerable protection against
refrigerant fl
oodback at start-up,
during operation and in hot gas
defrost systems.
The suction accumulator must
be selected in accordance with
the accumulator manufacturer
recommendations. As a general rule,
Danfoss recommends to size the
accumulator for at least 50% of the
total system charge. Tests however
must be conducted to determine the
optimal size.
Liquid fl oodback at change
over cycles in reversible
heat pumps
I n heat pumps, change over from
cooling to heating cycles, defrost and
low load short cycles may lead to liquid
refrigerant fl
oodback or saturated
refrigerant return conditions.
The negative eff ects are:
• oil dilution
• in extreme situations with high
system refrigerant charge and large
amounts of fl oodback, liquid slugging
could appear.
Frequency Models
Standard wiring Trickle wiring
Permanent capacitor
(μf)
Trickle capacitor
(μf)
Additional capacitor
(μf)
230V
50 Hz
MPZ038-048-054 40 30 10
MPZ061-068 45 35 10
208-230V
60 Hz
MPZ038-048-054 40 25 15
MPZ061-068 45 25 20