Energy Saving; Set Point Compensation; Floating Suction Pressure Set Point; Floating Condensing Pressure Set Point - Carel PRK300L3FK User Manual

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6.5 Energy saving

pRack pR300 can activate energy saving functions by adjusting the
suction and condensing pressure set points.
The suction and condensing pressure set points can be applied with two
diff erent off sets, one for the closing period and one for the winter period,
activated by:
•
Digital input
•
Time band
•
Supervisor
In addition, the suction pressure set point can be modifi ed from analogue
input, applying a linearly variable off set based on the value read by a
probe.
As well as set point compensation from digital input, scheduler, supervisor
or analogue input, two further energy saving functions are available,
fl oating suction and condensing pressure set point.
The functions can be enabled and the related parameters set in main
menu branch C.a.d/C.b.d and D.a.d/D.b.d.
6.5.1

Set point compensation

Compensation from digital input, scheduler or supervisor is similar for the
suction and condensing pressure set points, consequently the following
description applies to both.
Two diff erent off sets can be defi ned, which apply to:
•
Closing periods, defi ned by the scheduler, activation of a digital input
or supervisor
•
Winter period, defi ned by the scheduler
The two off sets add to the set point defi ned by the user when the
corresponding condition is active.
Example 1: closing off set 0.3 barg, winter off set 0.2 barg, suction
pressure compensation from scheduler and from digital input
activated. When the digital input is activated, for example with a day/
night function, 0.3 barg is added to the operating set point, and when the
winter period is in progress a further 0.2 barg is added. The operation can
be schematised in the following fi gure:
Digital Input
ex.: day/night
Summer/Winter
Setpoint
Note: the same digital input is used for set point compensation on
each line, so if suction and condensing pressure set point
compensation is activated by digital input, both compensation functions
are active at the same time.
Compensation from analogue input only applies to the suction pressure
set point and can be enabled separately. If compensation from analogue
input is enabled, a off set that is linearly variable to the value read by a
dedicated probe can be applied to the suction pressure set point, as
shown in the fi gure.
Offset
Offset max
Offset min
Lower value
pRack +0300025EN rel. 1.3 - 17.12.2015
User setpoint +0,5 barg
time
Fig. 6.w
Probe value
Upper value
Fig. 6.x
6.5.2

Floating suction pressure set point

For the suction line, the fl oating set point is managed by the supervisor.
The suction pressure set point set by the user is changed by the supervisor
in range between a settable minimum and maximum. The operation is
illustrated in the following fi gure:
Floating setpoint
Max
Real variation
Max variation
Min
The set point is calculated by the supervisor and acquired by the pRack
pR300 controller at set intervals, the maximum variation allowed for the
set point in each sampling period can also be set; if the value acquired
diff ers from the previous value by more than the maximum variation
allowed, the variation is limited to the maximum value. If the supervisor
is disconnected, after 10 minutes (fi xed) the pRack pR300 controller starts
decreasing the set point with variations equal to the maximum variation
allowed each sampling period, until reaching the minimum set point
allowed with fl oating suction pressure.
Note: if set point compensation from scheduler, digital input or
supervisor is also active, the off set is added to the minimum and
maximum limits for the fl oating set point.
6.5.3

Floating condensing pressure set point

For the condenser line, the fl oating set point is based on the outside
temperature. The fl oating condensing pressure set point is achieved by
adding a constant programmable value to the outside temperature and
limiting the resulting value between a settable minimum and maximum,
as shown in the fi gure:
Floating setpoint
Max
Min
external temperature
Note: if set point compensation from scheduler, digital input or
supervisor is also active, the off set is added to the minimum and
maximum limits for the fl oating set point.

6.6 Accessory functions

pRack pR300 can manage several accessory functions. Of these, the
economizer and liquid injection have already been described in paragraph
6.3 on compressor operation, while the others are described below.
6.6.1 Oil management
pRack pR300 features oil management for the individual compressors, as
well as common management for each line:
•
Individual compressor: oil alarm, high oil temperature, and, for screw
compressors only, oil warning, oil cooling and oil level
•
Line: common oil alarm, high oil temperature warning, oil cooling
44
time
Sampling time
Fig. 6.y
offset
time
Fig. 6.z