Subcooling; Individual Compressor Oil Management; Heat Recovery; Line Oil Management - Carel PRK300L3FK User Manual

The function can be enabled and the related parameters set in main
menu branch E.a.a/E.a.b or C.a.e/C.b.e (for the individual compressor
alarms).

Individual compressor oil management

For the description of the oil alarm and warning corresponding to the
individual compressor see Chapter 8. For screw compressors, an oil cooler
can be managed for each compressor, made up of a heat exchanger, a
fan and 1 or 2 pumps. The operation of the cooler varies according to the
setting of the output, which may be:
•
Analogue: one pump only
•
Digital: 1 or 2 pumps
The control probe is the compressor oil temperature probe, and the
following need to be set: set point, diff erential and, for 2 pumps only, an
activation delay for the second pump. The operation of the cooler when
using an analogue output is shown in the fi gure:
Oil cooler 0...10 V
Differential
Setpoint
Fig. 6.aa
If a digital output and just one pump is used, the fan and the pump are
activated/deactivated at the same time:
Oil cooler
0...10 V
Fan/Pump
Differential Differential
Setpoint
Fig. 6.ab
If a digital output and two pumps are used, the operation of the fan and
the fi rst pump is Similar to the previous case, while the second pump
is activated when the oil temperature is greater than the set point +
diff erential for a time at least equal to the delay, and is deactivated when
the oil temperature falls back below the set point minus the diff erential.
The oil level can be managed for the fi rst 6 compressors on each suction
line. If a compressor alarm is confi gured as an oil alarm, this alarm can
be associated with oil level management, enabling the function and
setting the compressor alarm number to be used: when the digital input
associated with the alarm is activated (this thus Signals the low oil level),
a valve is activated with intermittent operation to restore the level, with
opening and closing times that can be set. If after a set time, the digital
input is still active, that is, the minimum level has not been reached,
pRack pR300 Signals an alarm and stops the compressor.

Line oil management

pRack pR300 features an alarm digital input for each line; this is with
Signal only, that is, has no eff ect on the operation of the devices.
For details on this alarm see chapter 8.
For all types of compressors, a common oil cooler can be managed for
each line; the operation of this is Similar to the cooler for each individual
compressor described previously.
Note: for screw compressors, if common cooling is selected,
cooling for each compressor cannot be activated.
Fan
Pump
Oil temperature
Differential
Oil temperature
6.6.2

Subcooling

pRack pR300 can control subcooling in two diff erent ways:
•
with the condensing temperature and the liquid temperature
•
with the liquid temperature only
In the fi rst case, subcooling is calculated as the diff erence between
the condensing temperature (obtained by converting the condensing
pressure) and the liquid temperature measured after the exchanger.
The corresponding output is activated below a set threshold, with fi xed
diff erential.
Digital output
In the second case, the output is active for liquid temperature values
greater than a threshold, with fi xed diff erential.
Digital output
1°C/°F
Threshold
The subcooling function can be enabled and the related parameters set
in main menu branch E.b.a/E.b.b.
Note: the subcooling function is active when at least one
compressor is on.
6.6.3

Heat recovery

pRack pR300 can manage heat recovery for types of system with heat
recovery in series with the main condenser.
Heat recovery can be activated by:
•
Probe
•
Time bands
•
Supervisor
The heat recovery function can be enabled and the related parameters
set in main menu branch E.e.a/E.e.b.
A digital input is managed that acts as a trigger for activating the function.
When the digital input is not active, heat recovery is not operating, while
when the digital input is active heat recovery is operating when at least
one of the other conditions is true, as shown in the fi gure:
Digital Input
Probe
Scheduler
Supervisor
Heat reclaim
If the digital input is not confi gured, only the other conditions are taken
into consideration.
When the heat recovery function is active, a digital output is activated
to trigger the pump and a digital or analogue output for an On/Off or
modulating 3-way valve.
45
ENG
1°C/°F
Fig. 6.ac
Tliq.
Fig. 6.ad
Fig. 6.ae
pRack +0300025EN rel. 1.3 - 17.12.2015