Demand Limit; Night Mode; Capacity Control; Head Pressure Control - Carrier AQUASNAP 30RB Manual De Controles Y Soluciones De Defectos

5.6.2 - RESET
Reset means that the active setpoint is modifi ed so that
less machine capacity is required (in cooling mode, the
setpoint is increased, in heating mode it is decreased).
This modifi cation is in general a reaction to a drop in the
load. For the Pro-Dialog control system, the source of the
reset can be confi gured in the User 1 confi guration: it can
be provided either by the outdoor temperature (that gives
a measure of the load trends for the building) or by the
return water temperature (delta T that gives an average
building load) either for the reset setpoint based on a 4-20
mA input (with energy management option) or based on
the room temperature, using a room temperature sensor
(when the energy management option is used). In response
to a drop in the outdoor temperature or to a drop in delta
T, the cooling setpoint is normally reset upwards in order
to optimise unit performance:
In the three cases the reset parameters, i.e. slope, source
and maximum value, are confi gurable in the Setpoints
menu (see section 4.3.8). 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.
Reset example in cooling mode based on the outside
temperature

5.7 - DEMAND LIMIT

The demand limit is used to restrict the unit power
consumption. The Pro-Dialog 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
demand limit level (only one contact: control contact 3).
The units equipped with energy management option
permit three demand limit levels (2 contacts). The unit
capacity can never exceed the limit setpoint activated
by these contacts. The limit setpoints can be modifi ed
in the setpoint menu.
• By means of a 4-20 mA input type on the energy
management board. The limit is now based on a
linear interpolation from 0 to 100%, based on the input
signal. The demand limit in night mode is selectable (if
the value is below the one controlled by the external
signal).

5.8 - NIGHT MODE

The night period is defi ned (see User confi guration) by a
start time and an end time that are the same for each day
of the week. During the night period, the number of fans
operating can be reduced, and the unit capacity may be
limited (but a minimum capacity value can be confi gured).

5.9 - 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 fl ow 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).

5.10 - HEAD PRESSURE CONTROL

The head pressure is controlled by a maximum of six fans in
each circuit, and one of these may have variable speed. The
head pressure is independently controlled for each circuit,
based on the saturated condensing temperature value.
Fan start-up:
ATTENTION: The fans can be started periodically (for
cleaning), even if the unit is switched off.
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