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5.7.2 - Reset
Reset means the active setpoint is modified so that less
machine capacity is required (in cooling mode the setpoint
is increased, in heating mode it is decreased). This modification
is in general a reaction to a drop in the load. For the Touch
Pilot control system, the reset source can be configured in
the menu Status => RESETCFG: it can be based on the
outdoor temperature (gives a measure of the load trends for
the building) or used with the energy management option at
the reset setpoint. In response to a drop in the space
temperature or to a drop in
∆
T, the cooling setpoint is
normally reset upwards to optimise unit performance.
In the three cases the reset parameters, i.e. slope, source and
maximum value, are configurable in the Setpoint menu. Reset
is a linear function based on three parameters:
•
A reference at which reset is zero (space temperature or
∆
T - no reset value).
•
A reference at which reset is maximum (space tempera-
ture or
∆
T - full reset value).
•
The maximum reset value.
Reset example in cooling mode for the space
temperature
Legend
A
Maximum reset value
B
Space temperature for zero reset
C
Space temperature for maximum reset
D
Building load
Space temperature (SPACETEMP)
R
eset v
alue
% Building load
5.9 - Night mode
The night period is defined (see menu Config => GEN_
CONF) by a start time and an end time that are the same for
each day of the week. During the night period unit capacity
is limited
(a maximum capacity value can be configured - see
configuration menu GEN_CONF).
5.10 - Capacity control
This function adjusts the compressor capacity to keep the
heat exchanger water temperature at its setpoint. The control
system continuously takes account of the temperature error
with respect to the setpoint, as well as the rate of change in
this error and the difference between entering and leaving
water temperatures, in order to determine the optimum
moment at which to add or withdraw capacity.
In addition, the high pressure or low pressure unloading
functions can also affect the temperature control accuracy.
Compressors are started in a sequence designed to equalise the
number of start-ups (value weighted by their operating time).
5.11 - Compressor short cycling protection
The Touch Pilot control constantly monitors the control point
which determines the operation of compressor(s). Compressors
are turned on and off in order to maintain the required
control point and satisfy the current cooling/heating demand.
To avoid the risk of compressor short cycling, the Touch Pilot
control provides a protection that prevents the premature
starting of compressors. The service-configured temperature
threshold (acting upon the control point) is used for
compressor(s) control.
This compressor short cycling protection can be enabled via
the touch screen by setting the “short cycle management”
parameter in the General Configuration menu (GEN_
CONF) to “yes”.
5.12 - Option 152 - saturated condensing temperature
control
Saturated condensing temperature control is assured if the
three-way valve option is selected. The saturated condensing
temperature is controlled based on a fixed setpoint that can
be configured by the user via the SETPOINT table. The
three-way valve control can be configured by the service
department via the SERVICE table.
5.8 - Capacity limitation
The Touch Pilot control system allows limitation of the unit
capacity, using one of two methods:
•
by means of user-controlled volt-free contacts. The units
without energy management option only have one
contact (control contact 3). The units equipped with
energy management option permit three capacity
limitation levels (2 contacts). The unit capacity can never
exceed the limit setpoint activated by these contacts. The
limit setpoints can be modified in the Setpoint table.
•
by means of a capacity limitation setpoint output on the
energy management board. The capacity limitation
value in 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.
ATTENTION: In certain conditions, the unit power con-
sumption can exceed the capacity limitation threshold to
protect the compressors.
