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Compressor with variable capacity
Digital scroll compressor
The capacity is divided into period times as "PWM per". 100% ca-
pacity is delivered when cooling takes place for the whole period.
An off time is required by the by-pass valve within the period and
an on time is also permitted. There is "no cooling" when the valve
is on.
The controller itself calculates the capacity needed and will then
vary it according to the cut-in time of the by-pass valve.
A limit is introduced if low capacity is needed so that the cooling
does not go below 10%. This is because the compressor can cool
itself. This value can be increased if necessary.
Refrigeration
No refrigeration
Period time
Min. capacity
Copeland Stream compressor
The PWM signal can also be used to control one stream compres-
sor with one unloader valve (Stream 4) or one with two unloaders
(Stream 6).
Stream 4: The compressor capacity is distributed by up to 50% for
one relay and the remaining 50-100% for the unloader.
Stream 6: The compressor capacity is distributed by up to 33% for
one relay and the remaining 33-100% for the unloader.
Bitzer CRII Ecoline
CRII 4: The pulse signal can also be used to control one CRII with
two unloaders (4-cylinder version).
The compressor capacity can be controlled from 10 to
100%, depending on the pulsation of the unloaders. The
compressor start signal is connected to a relay output, and
the unloaders are connected to fx DO1 and DO2.
Unloader 2 follows unloader 1,
but it remains displaced by a
half period.
CRII 6: The pulse signal can also be used to control one CRII with
three unloaders (6-cylinder version).
The compressor signal is connected to one relay output.
The two unloaders are connected to fx DO1 and DO2. The
third is connected to a relay output.
The compressor capacity can be controlled from 10 to 67%,
depending on the pulse of the unloaders.
The relay is then connected to the third unloader. When
this relay is on, the capacity will be controlled between 33
and 100%.
96
Unloader 1
Unloader 2
Capacity controller RS8HF102 © Danfoss 2017-07
Individual Sd monitoring
When regulating with Sd monitoring, one of the three compressor
types will increase capacity if the temperature nears the Sd limit.
This will result in better cooling of the unloaded compressor.
Extra refrigeration capacity ("extra compressor")
This function improves the system's refrigeration capacity by
increasing the pressure in the gas cooler. The function will start
when the compressor capacity has been at 100% for 5 minutes.
The cooling performance increases to Q0+dh0.
The function also increases the load on the compressor motor as
pressure increases. Power consumption increases to Qm+dQm.
AK-PC 772A
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