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Control and Protection Functions
Air Quality-Dependent Damper Position
Compensation
Functionality is similar and the settings are common with the
air quality-dependent fan speed compensation. The fan output
or mixing damper position can be affected by the difference
between the measured and pre-set required CO
centration in the room. The volume of fresh air will be increased if
the measured value is higher than the required value. The volume
of circulated air will be decreased. The compensation extent is
affected by the settings of the PID controller constants.
Humidity-dependent Damper Position Compensation
If dehumidification using cooling is not sufficient (or not available),
humidity-dependent mixing damper position compensation is the
next step. This is adjusted depending on the required humidity
and measured humidity in the room. If the measured humidity is
higher than the required humidity in the room, the compensation
will be activated.
Humidity-dependent Fan Speed Compensation
The fan output is controlled depending on the required humidity
and measured humidity in the room. If the measured humidity is
higher than the required humidity in the room, the compensation
will be activated. The compensation function can either be set to
increase or reduce the fan output.
The compensation functions can be enabled using the HMI
controller, refer to the chapter Additional Operating Mode and
Function Setting Options.
Fan Speed Control
The VCS control unit enables either software or manual air output
control, i.e. the speed of the following fans:
n
Single-speed fans (ON/OFF control)
n
Two-speed fans (two-stage control)
n
Single-speed fans' backup (ON/OFF control)
n
Five-stage TRN voltage controllers
n
Fan frequency inverters using the Modbus bus – five-stage
control
A standard control can be completed with a 3rd auxiliary fan
which is controlled from the outlet or inlet fan depending on the
control unit configuration.
Two-Speed Fans
The two-speed fans are always started using the first stage at
the air-handling unit start-up. The transition time from the first to
second stage can be adjusted. The transition time can also be ad-
justed for the reverse transition from the second to the first stage.
TRN Voltage Controllers
The control unit enables the voltage controllers to be connected
and controlled in five output stages. Depending on the request,
inlet and outlet control can be common or independent. The
required output stage is always set in common. If the fans are
controlled independently, it is possible to set the outlet control-
ler correction against the inlet controller (see the Data Point
Settings – TRN Correction). However, the control unit must
be specially manufactured for this function (depending on the
customer request). Either the same correction can be set for
all the speed stages or for each speed stage independently. For
the correction settings, refer to the chapter Optional Function
and Mode Settings.
Single-Speed Fan Backups (ON/OFF Control)
The backup motor is started if the main motor fails. The backup
is used either for the inlet or outlet fan, respectively for both. The
motors are equipped with thermal protection (thermo-contact)
and current protection. If the backup motor has been started, it
is not possible to restart the main motor without resetting the
(VOC, CO) con-
failure. The main and backup motor current protection has a delay
2
pre-set. Switching from the main to backup motor is immediate
without delay if the main motor fails.
Backup fan control via Modbus communication bus
Using the Modbus communication bus, the five-stage fan control
enables a backup fan or a pair of backup fans to start up if the
main fan fails. If the backup fan or pair of backup fans fails, the air-
handling unit will be shut down. Information about air-flow failures
and motor overheating is sent via the Modbus communication
bus and signalled accordingly.
The fan speed control parameters are available through the HMI
controller in the List of Data Points in the section Settings – Fans
(inlet fan backup, outlet fan backup, TRN correction).
Constant Air Flow/Pressure Control
When designing constant flow, pressure, overpressure and
underpressure control, it is advisable to consider the overall
design of the air-handling unit, respectively application of the
mixing damper, and how the control behaviour can affect the
measured pressure value.
Constant Air Flow Control
Fan speed is controlled depending on the desired air flow rate
(m
/h). The air flow rate (air pressure in the diffuser recalcu-
3
lated to the air flow rate using the "k-factor") is measured by a
sensor; the control system evaluates this value and compares
it with the required value. The resulting fan speed is controlled
so that the required air flow rate will be reached at the point
of measurement (fan diffuser).
It is necessary to set the following pressure sensor pa-
rameters (see the Sensor Operating Manual):
n
Mode (for CPG = Mode 5.00)
n
Measuring range: As needed
The correct range can be determined
using a formula:
(where k = "k-factor", Vmax = designed air flow rate of the
device). The correct sensor range is then set according to the
calculated pmax value.
n
K-factor of the respective fan
It is necessary to set the following parameters of the VCS
control Unit (see List of HMI Data Points):
n
Air flow sensor measuring range – (maximum value from
the CPG air flow sensor in m
n
This can be calculated using the formula or read from the
CPG sensor menu (see the Sensor Operating Manual).
n
The maximum measured air flow rate can be calculated
according to the following formula:
= k × DP
V
max
Control units VCS
Dp
/h)
3
max
V
2
max
=
k
2
max
17
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