Sauter flexotron®800
ventilation
Functional description
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When the controller switches from "Normal speed" to "Reduced speed", there is a
settable retardation time from disengagement to activation. See the section Retardation
time.
The extract air fan and the supply air fan have individual start and stop delays which
are normally set so that the extract air fan is started before the supply air fan. If there
are not enough digital outputs for individual control, both fans will have to be started
using the signal for the supply air fan, and the delay be created using an external time
relay.
5.4.1
Pressure control
Frequency control pressure
When running pressure control, two analogue output signals are used for supply and
extract air respectively. The signals control the fan speeds via frequency converters,
thereby maintaining constant pressure. A digital activation signal is normally used for
each fan ("Start SAF frequency converter" and "Start EAF frequency converter"), for
sending a start signal to the frequency converters. The start signal is activated as long
as the fan is expected to be running.
For the supply and extract air fans, there are two individually settable setpoint values,
one corresponding to normal speed and one corresponding to reduced speed.
Changing between the two setpoint values is done using the timer channels for normal
and reduced speed or using digital input signals ("Extended Operation, Normal" and
"Extended Operation, Reduced").
Outdoor compensation
When running pressure control, it is also possible to outdoor compensate the pressure
setpoint value.
The outdoor compensation is linear and is set using two parameter pairs which give the
value of the compensation at two different outdoor temperatures. The compensation
can be positive or negative.
The outdoor compensation is set in the menu Actual/Setpoint.
Using CASE flexotron®, you can also choose to only outdoor compensate the pressure
value of the supply air fan. In that case, the extract air fan is controlled with constant
flow, independent of the outdoor temperature.
Extra compensation curve
As a complement to the above outdoor compensation, there is a function called
’’Extra
compensation curve
’’ which can be used to set a compensation based on the room,
extract air or supply air temperature. The curve has three parameter pairs which
correspond to the value of the compensation at three different temperatures.
Frequency control flow
Instead of giving a pressure setpoint value, it is possible to use an airflow volume value
in m
3
/h. The value from the pressure transmitter is recalculated to a volume flow using
the formula below and the fans will be controlled to give a constant flow.
Flow = K *
P
X
Where K and
X
are settable constants dependent on the fan size and
P is the
differential pressure, measured in Pa, over the fan. Each fan has its own set of
parameters.
X
is normally 0.5 indicating that the flow is proportional to the square root of the
differential pressure.
Outdoor compensation
Also when running flow control, it is possible to outdoor compensate the setpoint value.
