27
7.6.2 - 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:
•
OAT that gives the measure of the load trends for the
building
•
Return water temperature
(
Δ
T provides the average building load)
•
Space temperature (EMM option)
•
Dedicated 4-20 mA input
The.reset.source.and.the.reset.parameters.can.be.configured.in.
the Main menu (RESETCFG – Reset Configuration). In
response to a drop in the reset source, the cooling setpoint is
normally reset upwards 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
20
Reset based on OAT
25
0
Reset based on delta T
3
4
Reset based on analog input
20
no_reset
selection
full_reset
Legend:
A: Maximum reset value
B: Reference for zero reset
C: Reference for maximum reset
D: Building load
7.7 - Capacity limitation
The Touch Pilot control system allows for the constant control
of 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 3.9.4). 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.
In certain conditions, the unit power consumption can exceed
the capacity limitation threshold to protect the compressors.
7.8 - Current limitation
Current limitation is used via the demand limit function. If
the current limitation is active (
Current Limit Select
in the
GEN_CONF menu), the control calculates the sum of
compressors current to 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%
, GEN_CONF – General
Configuration)
•
The active demand limit determined either by the
demand limit contact (see also section 3.9.4) 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.
7.9 - Capacity control
This function adjusts the capacity using the compressor slide
valve to keep the water exchanger temperature at its setpoint.
The control system continuously takes account of the
temperature error with respect to the setpoint, the rate of
change in this error and the difference between entering and
leaving water temperatures in order to determine the optimal
moment at which to add or withdraw capacity.
Compressors are started and stopped in a sequence designed
to equalise the number of start-ups (value weighted by their
operating time). For more information about compressors
sequence, see
Balanced loading sequence
and
Staged loading
sequence
in section 7.13.
7.10 - Night mode
Night.mode.allows.users.to.configure.the.unit.to.operate.with.
specific.parameters.in.a.specific.time.period..During.the.night.
period, the unit capacity is limited and the number of
operating fans is reduced.
The.night.period.is.defined.by.a.start.time.and.an.end.time.
that are the same for each day of the week. The Night mode
settings.or.the.maximum.capacity.value.can.be.configured..
via the Configuration menu (GEN_CONF – General
Configuration)..
Only logged-in users can modify Night Mode settings (see
also section 4.3.3).
