Pressure Alarms From Probe; High Pressure Prevention; Prevent Low Suction Pressure; Low Suction Pressure From Probe - Carel PRK300L3FK User Manual

8.3.2

Pressure alarms from probe

The parameters corresponding to these alarms can be set in branch
C.a.e/C.b.e of the main menu for the suction pressure and D.a.e/D.b.e for
the condensing pressure.
For these types of alarms, reset is automatic and the activation threshold
and diff erential can be set, as well as the type of threshold, which may be
absolute or relative to the control set point. The fi gure shows an example
of setting the threshold to relative.
HP
Relative threshold
Setpoint
Fig. 8.b
Note: for temperature control, the alarms from probe are managed
based on temperature even when pressure probes are fi tted.
The eff ects of the diff erent pressure alarms from probe are described
below.

Low suction pressure from probe

The low suction pressure alarm from probe has the eff ect of stopping all
the compressors, ignoring the times.
High suction pressure from probe
The high suction pressure alarm from probe has the eff ect of forcing
all the compressors on, ignoring the control times, but observing the
compressor protection times.
Low condensing pressure from probe
The low condensing pressure alarm from probe has the eff ect of stopping
all the fans, ignoring the times.
High condensing pressure from probe
The high condensing pressure alarm from probe has the eff ect of forcing
all the fans on and stopping all the compressors, ignoring the times.
8.3.3

High pressure prevention

pRack pR300 can manage 3 types of high condensing pressure prevention
actions, involving:
•
overriding the compressors and fans
•
activating heat recovery
•
activating ChillBooster
Prevent by overriding the compressors and fans
The parameters relating to this function can be set in branch G.b.a/G.b.b
of the main menu.
The eff ect of this type of prevent action is to force all the fans on at
maximum and switch all the compressors off , except for the minimum
capacity stage, ignoring the control times but observing the compressor
protection times. The minimum capacity stage means one compressor in
the case of compressors without capacity control and modulation devices,
or the minimum capacity stage for capacity-controlled compressors (e.g.
25%), or alternatively the minimum output of the modulation device in
the case of inverters, Digital Scroll
with continuous modulation.
As well as the activation threshold, which is always absolute, and the
activation diff erential, a compressor deactivation time can be set,
corresponding to the time needed to switch off all the compressors,
except for the minimum capacity stage.
In addition, both the monitoring time and the number of activations in
the specifi ed period can be set. If the number of activations is higher,
reset becomes manual.
Pressure
Differential
Alarm
TM compressors or screw compressors
Prevent by activating heat recovery
The parameters corresponding to this function can be set in branch
G.b.a/G.b.b of the main menu, if the heat recovery function is present.
As well as enabling the function, an off set from the activation threshold
for the prevent by overriding devices function must be set. The activation
diff erential for this function is the same as set for the prevent by overriding
devices function.
When reaching the threshold, pRack pR300 activates the heat recovery
function, if the conditions allow; see paragraph 6.6.3 for details.
Prevent by activating ChillBooster
The parameters relating to this function can be set in branch G.b.a/G.b.b
of the main menu, if the ChillBooster function is present.
As well as enabling the function, an off set from the activation threshold
for the prevent by overriding devices function must be set. The activation
diff erential for this function is the same as set for the prevent by overriding
devices function.
When reaching the threshold, pRack pR300 force activates the
ChillBooster, if the conditions allow; see paragraph 6.6.5 for details.
The following fi gure illustrates the activation thresholds for the prevent
function and the safety devices:
Pressure
8.3.4

Prevent low suction pressure

pR300 off ers the possibility to reduce compressor capacity in the event of
low suction pressure. The parameters relating to this function can be set
in branch G.b.a/G.b.b of the main menu.
The eff ect of this function is to operate the compressors at a set
percentage of capacity as soon as pressure falls below the prevent set
point and related diff erential (screen Gab06)
In addition to the activation threshold, which is always absolute, and
the activation diff erential, a compressor deactivation time can be set,
corresponding to the time needed to switch off all the compressors
except for the minimum capacity step.
The evaluation time and number of activations allowed in a certain time
period can also be set. If the number of activations exceeds the setting,
manual reset is required (screen Gab07)
When the prevent function is activated, an alarm icon is shown on the
main screen, and a warning screen appears in the alarms.
Prevent low suction pressure with auxiliary control
Advanced confi gurations are available when using auxiliary control, so as
to ensure a better response when activated.
If the suction pressure falls below the set threshold (screen Gba08),
compressor capacity is reduced proportionally to the limit set point.
Normally, when the prevent function ends, the current capacity is
instantly brought to the level needed to meet the control request.
If the parameter "Align request after prevent" is enabled (screen Gba09),
the current request is aligned with the limit value.
77
HP by pressostat
HP by probe
Prevent
Offset
Heat reclaim
or ChillBooster
time
Fig. 8.c
pRack +0300025EN rel. 1.3 - 17.12.2015
ENG