150
CONTROL PANEL
INSTALLATION
RESET
Reset means that the active setpoint is modified so that a lower
capacity of the machine is requested. In cooling mode the set-
point is increased while in heating mode it is decreased.
The reset is set according to:
−
outdoor air temperature (OAT) that provides the building load
trend value
−
return water temperature (ΔT provides the building average load)
−
4-20 mA dedicated input.
To check the reset source and the reset parameters:
− Move to the Configuration Menu.
− Select Configuration Reset
.
− Check the reset source values and the reset parameters.
In response to a reset source change (e.g. OAT), the setpoint is
usually reset to optimize unit performance.
The reset is determined by the linear interpolation based on
the following parameters:
− one reference where reset is zero (no reset value)
− one reference where reset is maximum (complete reset
value)
− Maximum reset value.
Reset example in Cooling mode:
%Building load
Reset v
alue
20
Reset according to OAT
25
0
Reset according to delta T
3
4 Reset according to analogue input 20
no_reset
Selection
full_reset
Legend:
A: Maximum reset value
B: Reference for reset to zero
C: Reference for maximum reset
D: Building load
3.7.8
Free cooling option
NXC
chillers and
NXH
heat pumps can be equipped with dry
cooler that allows reducing the energy consumption, that in
turn translates in energy and cost savings.
The installation of a dry cooler allows the "free cooling", i.e. a
method that exploits the low temperature of the outdoor air
to refrigerate the water that will later be used in the air-con-
ditioning system. Maximum system efficiency is reached when
the outdoor air temperature is lower than 0°C (32°F).
FREE COOLING START-UP
Free cooling mode is ENABLED when free cooling OAT [fc_oat] is
lower than the hydraulic circuit temperature and start thresh-
old:
fc_oat < fc_wloop – fc_start
fc_oat:
Free Cooling OAT
fc_wloop: Free Cooling Water Circuit Temperature
fc_start: Free Cooling Start Threshold.
9
The [fc_wloop] and [fc_oat] temperatures measured
through the control are read-only values that can be
checked in the
Cooling Status
.
To check the hydraulic circuit temperature of the Dry Cooler
[fc_wloop]:
− Move to the Main Menu.
− Select Cooling Status
.
− Check the Cooling Water Circuit Temperature.
To check the Free Cooling OAT [fc_oat]:
− Move to the main menu.
− Select Cooling Status
.
− Check Free Cooling OAT.
FREE COOLING STOP.
Should the cooling power of the dry cooler not be sufficient
to reach the cooling setpoint, the mechanical cooling will be
started.
Usually, Free Cooling stops when free cooling OAT [fc_oat] is
higher than the hydraulic circuit temperature and start/stop
threshold:
fc_oat > fc_wloop - fc fc_stop
fc_oat:
Free Cooling OAT
fc_wloop: Free Cooling Water Circuit Temperature
fc_start: Free Cooling Start Threshold
fc_stop:
Free Cooling Stop Threshold.
Mechanical cooling can be started when Free Cooling is at full
capacity.
9
Start and Stop parameters of Free Cooling can be config-
ured by
R
Technical Support Service only.
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