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6 - STANDARD CONTROL OPERATIONS AND OPTIONS
6.6.2 - Reset
Reset means the active setpoint is modified so that less machine
capacity is required. In the cooling mode the setpoint is increased,
whereas in the heating mode it is decreased. This modification is
in general a reaction to a drop in the load.
The reset can be based on the following parameters:
■ Return water temperature (ΔT provides the average building load)
■ Dedicated 4-20 mA input
■ Space temperature (EMM option)
The source of the reset can be configured in the Reset
Configuration menu (RESETCFG). In response to a change in the
delta T, or 4-20 mA reset signal reading, or space temperature,
the control point is reset to optimise unit performance.
In response to a drop in the reset source, the cooling setpoint is
normally reset upwards in order to optimise unit performance.
The amount of reset is determined by linear interpolation
based on the following parameters:
■ A reference at which reset is zero (no reset value).
■ A reference at which reset is maximum (full reset value).
■ The maximum reset value.
Reset example in Cooling mode
10
Reset based on space temperature
3
Reset based on delta T
4
Reset based on analog input
no_reset
Legend
A:
Maximum reset value
B:
Space temp. / ΔT / 4-20 mA for no reset
C:
Space temp. / ΔT / 4-20 mA for full reset
D:
Building load
To select the type of reset
1. Navigate to the Configuration menu.
2. Select Reset Configuration (RESETCFG).
3. Set Cooling Reset Select [cr_sel]
OR Heating Reset Select [hr_sel].
Cooling Reset Select [cr_sel]
Heating Reset Select [hr_sel]
0
None
2
Delta T
3
4-20 mA control
4
Space Temp
38
Selection
full_reset
6.7 - Capacity limitation
The SmartVu
TM
the unit capacity by setting its maximum allowable capacity.
The main control system enables to limit the unit capacity
using one of the external orders:
■ By means of user-controlled volt-free contacts. Units without
the energy management module have one contact. Units with
the energy management module permit three capacity limitation
levels (see also section 3.8.3). The unit capacity can never
exceed the limit setpoint activated by these contacts. The limit
setpoints can be modified in the SETPOINT menu.
■ By lag limit set by the master unit (master/slave assembly).
■ By night mode limitation control. The demand limit value in the
night mode is selectable if the value is below the selected limit.
A limit value of 100% means that the unit can use all capacity
stages.
To set Switch Limit Setpoint
1. Navigate to the Main menu.
2. Select Setpoint Table (SETPOINT).
3. Set Switch Limit Setpoint (1,2,3) [lim_sp1/lim_sp2/lim_sp3].
Switch Limit Setpoint ... [...]
0 to 100
To set Night Capacity limitation
1. Navigate to the Configuration menu.
2. Select General Configuration (GENCONF).
3. Set Night Capacity Limit [nh_limit].
Night Capacity Limit [nh_limit]
0 to 100
In certain conditions, the unit power consumption can exceed
the capacity limitation threshold to protect the compressors.
6.8 - Current limitation
20
Current limitation is used via the demand limit function. If the
5
current limitation is active (Current Limit Select in the GENCONF
menu), the control calculates the sum of compressors current to
20
obtain the total compressor current. If this value exceeds the pre-
defined limit, the control commands a reduction of the compressor
load, until it is below the limit again. Before loading a capacity
stage, the control estimates the future total compressor current
and ensures that it does not exceed the limit.
The current limit is based on two parameters:
■ The current limit that corresponds to 100% capacity
(CurrentLimit at 100%, GENCONF – General Configuration)
■ The active demand limit determined either by the demand limit
contact (see also section 3.8.3) or by the network (Active
Demand Limit Val, GENUNIT – General Parameters)
Chiller current limit is displayed in the GENUNIT menu.
Current limitation is disabled if the unit operates in the master/
slave mode, the unit is controlled by a System Manager or the
night mode is active.
control system allows for the constant control of
%
%
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