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Control and Protection Functions
Control and Protection Functions
Note: This chapter describes only the basic control functions – the
detailed design, respectively compatibility, of the entire device
is ensured by the configuration performed using the AeroCAD
design software. For more detailed information, contact the
manufacture, REMAK a.s.
Main Control Features
The VCS control unit enables automatic control of the following
basic functions for air temperature adjustment:
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Heating
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Cooling
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Mixing
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Recuperation (Heat Recovery)
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Dehumidification
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Humidification
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PID controllers with pre-set control constants are assigned for
all the above-mentioned functions. Basic settings of parameters
are performed in the factory. The parameters can be changed
using the HMI controller in the List of Data Points menu, part
Settings – Control Constants.
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A check, respectively optimization, of the unit settings must
always be performed when commissioning the unit.
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Control ensures energy-saving operation. Cascade tem-
perature control – room temperature control or supply air
temperature control.
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The required temperature for the air-conditioned room can
be set by selecting one of two temperature modes – comfort
or economy. Each mode has two pre-set temperature values
to maintain the required temperature (an upper limit for heating
and a lower limit for cooling). These values can be changed using
the HMI controller in the List of Data Points, section Settings –
Temperature Modes.
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First, the control algorithm will start to control the func-
tions which don't require energy, i.e. heat-recovery and mixing
(depending on the user option). If this is not enough to maintain
the required parameters or these features are not included in the
air-handling unit, heating and cooling functions will be applied.
If the heating or cooling control is not effective enough, an air
output control will be added (heating/cooling-dependent fan
speed compensation or cooling control – user option).
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If the unit is also configured for humidity control, the setpoints
for dehumidification (upper humidity limit in the room) and/or
humidification (lower humidity limit) are available for setting in
the HMI menu under Settings - Humidity Modes.
Temperature Correction and Limitation
The control unit enables adjustment and settings of the restricting
limits for maximum and minimum supply air temperatures. In
addition, it is possible to set the supply air and room temperature
limits, respectively other correction or comfort options (e.g. set-
point value compensation or heating/cooling-dependent fan
speed compensation).
Main Control Feature and
Protection Description
Using the appropriate sensors, the VCS control unit can provide
comprehensive protection of the air-handling unit, such as ac-
Control units VCS
tive antifreeze protection, fan state monitoring, filter fouling or
over-temperature detection of the required temperature. Any
deviations from the defined states or parameters are monitored
and signalled and simultaneously, safety features are activated.
Depending on the failure consequence, the following happens:
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The failure is only signalled and safety features are automati-
cally activated. Once the failure has ceased, the unit will return
to the standard mode without interference from the operator.
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If a serious failure occurs, the unit will be switched to
the STOP mode, and it can only be restarted after the
failure has been removed and the operator's interference.
The VCS control unit system enables the air-handling
unit behaviour (fan action) to be set when fire is detected
(external failure, inlet or outlet air high temperature).
The settings can be as follows: the inlet or outlet fan is activated,
both fans are activated or both fans are stopped (air-handling
unit shutdown). The control unit is switched to the fire mode.
The settings can be performed using the HMI controller in the
List of Data Points, section Checks, System and Network Set-
tings – Fire Alarm.
Heating Control
Control is based on the required temperature, i.e. the selected
temperature mode and data from the supply air temperature
sensors, outdoor temperature and the water heat exchanger
return water temperature. Control can be affected by correction
values, maximum and minimum limits or antifreeze protection.
Water heating
It is controlled by the SUMX mixing set actuator using a 0–10V
continuous control signal (working range of 2–10V).
Heating Mixing Set Pump Control
The mixing set pump is controlled depending on the outdoor
temperature value and valve position (required heater output).
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If the air-handling unit is in the STOP and Run mode, the pump
is switched on when the outdoor temperature drops below 5°C
and switched off when the outdoor temperature rises above
6°C. In this case, the pump is stopped without any run-down.
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If the air-handling unit is in the Run mode, the pump is controlled
by the valve actuator control algorithm. The pump is switched
on when the request for the valve opening is higher than 5%.
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If the pump has not been used for 168 hours, it will be switched
on and turned for 60 seconds.
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Failures (electrical) of the pump are sensed by the pump circuit
breaker's auxiliary contact even in the STOP mode.
Water Heater Antifreeze Protection Operation
The VCS control unit uses so-called active antifreeze protection.
It uses a three-stage concept. Antifreeze Protection Features:
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Switching of the unit to the STOP mode
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Switching off of the fans
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Closing of the dampers
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Freezing danger signalling
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Mixing set control
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Pump starting
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If the air-handling unit is in the Run mode, then antifreeze
protection is activated when the outdoor temperature drops
below 10 °C (factory settings) and the water heat exchanger
return water temperature drops below 15 °C (factory set-
tings).
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