Crii Modulation In Neutral Zone; Times; Extra Cooling Fan - Carel PRK300L3FK User Manual

150
100
50
0
50
-50
Fig. 6.aq

CRII modulation in neutral zone

The type of control can be selected between proportional-integral
and neutral zone. If choosing neutral zone control, CRII compressor
modulation can be enabled inside the zone. CRII modulation requires
the defi nition of a new band, comprising the set point and a diff erential
called "Diff CRII", this band defi ned must fall inside the neutral zone.
CASE 1: suction pressure is inside the neutral zone and is increasing.
Starting from current capacity, at the moment when "min mod" is
exceeded, the compressor will activate the capacity steps until reaching
"max mod" at 100%.
CASE 2: suction pressure is inside the neutral zone and is decreasing.
Starting from current capacity, at the moment when "min mod" is
exceeded, the compressor will deactivate the capacity steps until
reaching "max mod" at 0%.
min mod.
diff
CRII
diff NZ
Set point
Fig. 6.ar
Legenda:
MIN mod. = actual capacity CRII
MAX mod. = 100% capacity
MAX mod. = actual capacity CRII
MIN mod. = 0% of CRII
Total capacity doesn't change
In both cases, in the grey area between the neutral zone thresholds and
the CRII diff erentials, total capacity does not change.
Note: when the suction pressure falls outside of the neutral zone,
the compressors are switched off in sequence, varying CRII capacity to
achieve correct modulation. The CRII compressor will go to 0% capacity
before another compressor is shut down, and can remain in this condition
for a set time, as long as there are other active compressors. If it is the last
compressor active at that moment, after reaching 0% capacity it will
immediately shut down.
Rising (%)
Falling (%)
100 150
max mod.
diff
CRII
Psuct
diff NZ
Confi guration
A system with CRII compressors can be configured directly from the
wizard. The following procedure shows the selection of a CRII compressor
with two capacity steps, 50%-100%:

Times

Min Ton, minimum ON time:
•
120 s up to 5.5kW
•
180 s up to 15kW
•
300 s above 15kW
Min Toff , minimum OFF time:
•
range [5 s ... 999 s]
Min start same compressor, minimum time between two consecutive
starts of the same compresso:
•
range [ 5 s ... 999 s]
Max time with compressor on with load bypassed is the maximum time
in which the CRII compressor can remain active at 0% capacity after
which capacity control will be activated.
•
up to 120 s
CRII unloader delay is the delay on activation of capacity control.
•
range [5 s ... 999 s]

Extra cooling fan

To prevent malfunctions of the CRII compressor due to high operating
temperature, pR300 can activate a fan installed on the compressor to
provide extra cooling. pR300 does not manage the CRII compressor
envelope. The extra cooling fan is activated based on two variables:
•
Current CRII capacity
•
Condensing pressure
with specifi c cases for the medium temperature and low temperature line.
41
ENG
pRack +0300025EN rel. 1.3 - 17.12.2015