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5.5.1 - Active setpoint
Two setpoints can be selected for the heating mode. Usually,
the second setpoint is used for unoccupied periods.
Depending on the current operating type, the active setpoint
can be selected:
•
by choosing the item in the GENUNIT menu,
•
via the user’s volt-free contacts,
•
via network commands
•
via the setpoint timer program (schedule 2).
The following tables summarise the possible selections
depending on the control types (local, remote or network)
and the following parameters:
•
Setpoint select in local control: item LSP_SEL in the
GENUNIT menu permits selection of the active set-
point, if the unit is in local operating type.
•
Operating mode.
•
Setpoint selection contacts: setpoint selection contact
status.
•
Schedule 2 status: schedule for setpoint selection.
5.6 - Capacity limitation
Capacity limitation is used to restrict the unit power
consumption. The Pro-Dialog control system allows
limitation of the unit capacity, using user-controlled volt-
free contacts.
Capacity limitation can result in a demand limit, a capacity
loss or a limit demand in the night mode.
The unit capacity can never exceed the limitation setpoint
activated by these contacts. The limitation setpoints can be
modified in the SETPOINT menu.
5.7 - Capacity control
This function adjusts the number of active compressors to
keep the heat exchanger water temperature at its setpoint.
The precision with which this is achieved depends on the
capacity of the water loop, the flow rate, the load, and the
number of stages available on the unit. 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 a capacity stage.
If the same compressor undergoes too many starts (per
hour) or runs below one minute each time it is started this
automatically brings about reduction of compressor starts,
which makes leaving water temperature control less precise.
In addition, the high pressure, low pressure or defrost
unloading functions can also affect the temperature control
accuracy. Compressors are started and stopped in a sequence
designed to equalise the number of start-ups (value weighted
by their operating time).
5.8 - Defrost function
Defrost is activated to reduce frost build-up on the air heat
exchanger. During the defrost cycle the fans of that circuit
are stopped, and the four-way refrigerant valve is reversed,
forcing the circuit to cooling mode. The fan can temporarily
be restarted during the defrost cycle. The defrost cycle is
fully automatic and does not require any setting.
LOCAL OPERATING MODE
PARAMETER STATUS
Operating mode
Local setpoint
selection
Time schedule 2
status
Active setpoint
Heating
sp1
-
Heating setpoint 1
Heating
sp 2
-
Heating setpoint 2
Heating
auto
occupied
Heating setpoint 1
Heating
auto
unoccupied
Heating setpoint 2
REMOTE OPERATING MODE
PARAMETER STATUS
Operating mode
Setpoint selection
contact
Active setpoint
Heating
sp 1 (open)
Heating setpoint 1
Heating
sp 2 (closed)
Heating setpoint 2
5.5.2 - Reset
Reset means that the active setpoint is modified so that less
machine capacity is required. The setpoint is decreased.
This modification is in general a reaction to a drop in the
load. For the Pro-Dialog control system, the source of the
reset can be configured in the HCCONFIG table.
This reset can be based on:
•
either the outside temperature:
-
this gives a measure of the load trends for the
building
-
if the outside temperature decreases, the setpoint
will again increase.
•
or the return water temperature:
-
this is the heat exchanger delta T and gives an
average building load
-
if the temperature difference is reduced, the
setpoint will decrease.
In both cases the reset parameters, i.e. slope, source and
maximum value, are configurable in the RESETCFG menu.
Reset is a linear function based on three parameters.
•
A reference at which reset is zero (outdoor temperature
or delta T - no reset value).
•
A reference at which reset is maximum (outdoor
temperature or delta T - full reset value).
•
The maximum reset value.
