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5.8 - Demand limit
Generally, demand limit is used by an energy management
system in order to restrict the unit electricity consumption.
The PRO-DIALOG Plus control system for 30GX & 30HX
provides two methods of demand limit:
• By reference to a limiting signal from a user-controlled
volt-free contact: the capacity of the unit cannot exceed
the demand limit setpoint (which can be modified in the
Setpoints menu) when the limit contact is closed.
• By reference to an external 0-10 V d.c. signal: the
capacity of the unit cannot exceed the demand limit
imposed by this external signal. It is a linear function and
its para-meters are configurable in the User1 menu
(voltages at 0% limitation and 100% of limitation). This
function is not available if Reset by reference to an
external 0-10 V d.c. signal has already been selected.
Whatever the method used, demand limit is active in all
operating types: Local, Remote or CCN. However, in
Local operating type, demand limit can be disabled with
keypad commands (see section 4.3.3) and in CCN
operating type, demand limit can be controlled directly
with the aid of CCN commands.
NOTE: A limitation value of 100% means that the unit may
call upon the full array of its capacity stages.
Here is an example of demand limit by an external 0-10 V d.c.
signal. This example assumes that the limitation parameters are
such that at 0 volt the authorised capacity shall be maximum
capacity, and at 10 volts the authorised capacity shall be zero
(this is the default configuration).
Demand limit by 0-10 V d.c. signal
0-10 V dc demand limit
No demand limit
Total demand limit
Maximum permitted
capacity
5.9 - Capacity control
This function activates the compressors and capacity unloaders
to keep the entering or leaving 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 tempera-
ture 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.
NOTE: If the same compressor undergoes too many starts
(per hour) this automatically brings about reduction of
compressor starts, which makes leaving water temperature
control less precise.
5.10 - Determining the lead circuit
This function commands the start/stop sequence of the two
refrigerant circuits called A and B. The circuit authorised to
start first is the lead circuit. Three methods can be configured
by the user in the Configuration menu:
• Auto mode: the control system determines the lead circuit
so as to equalise the number of starts on each circuit
(value weighted by the operating times of each circuit).
Thus, the circuit with the least number of starts is always
given precedence to start. The lead circuit is stopped last.
This function is only available in two-circuit units.
NOTE: If one circuit has more unloaders than the other, this
circuit is always the lead circuit, independent of the
configuration and the operating hours of the two circuits.
• Circuit A as leader: Circuit A is always the lead circuit.
It is the first to start and the last to stop.
• Circuit B as leader: Circuit B is always the lead circuit.
It is the first to start and the last to stop. This choice is
only available in two-circuit units.
5.11 - Circuit loading sequence
Two circuit loading sequences are available. The choice of
sequence can be configured by the user in the Configuration
menu (see section 4.5.7.3). This function is only available in
two-circuit units.
• Balanced circuit loading: If this sequence is selected, the
control system tries to keep the capacity of circuits A and
B equal as the total load on the unit increases or decreases.
• Loading with priority given to one circuit: If this
sequence is selected, the control system loads the lead
circuit completely before the second circuit starts up. When
there is a demand limit, the second circuit is unloaded first.
NOTE: If the unit is air-cooled and if the saturated
condensing temperature of one of the two circuits is lower
than 0°C at the start-up of one circuit, the priority capacity
loading sequence of the circuits is used by the control,
independent of the configuration.