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Control and Protection Functions
Inverter Unit and Single-Stage Condensing Unit
Combination
When cooling is required, the inverter will be switched on
first and then the output will be raised to the maximum.
Consequently, the single-stage condensing unit is switched
on while the inverter output is lowered to 30 % of the control
signal. If the request for cooling is still rising, the inverter
output will be increased from 30 % up to the maximum level
of the control signal.
If the request for cooling is decreasing, the inverter output will
start to decrease and will be switched off at 0% of the control
signal. The single-stage condensing unit is still in operation.
In this phase of control, time blocking of the inverter is ap-
plied and simultaneously the single-stage condensing unit is
prevented from being switched off. If the request for cooling
is still decreasing once this time has elapsed, the inverter
will be switched on with a maximum control signal and the
single-stage condensing unit will be switched off. When the
single-stage condensing unit is switched off, the inverter
output will be at the maximum. Then the inverter output is
reduced in accordance with the request. Thus step-less control
is ensured in the entire cooling capacity range.
Direct Evaporator Protection
This protection is ensured using the CAP 2M capillary thermo-
stat, which disconnects the control signal in the event of ice
build-up on the evaporator. If two evaporators are used, each
of them will have its own thermostat.
Heat Recovery Control
Heat Recovery control of the rotary heat regenerator is en-
sured by step-less control using the heat exchanger frequency
inverter through the Modbus communication bus. The plate
heat exchanger, respectively plate heat exchanger bypass, is
controlled using a 0–10 V (2–10 V) continuous signal. 100%
of the step-less control signal equals 100 % heat recovery,
i.e. maximum speed of the rotary heat regenerator or closed
bypass of the plate heat exchanger. A digital output for two-
point control (ON/OFF) is another option – thus, for example,
the glycol circuit pump can be switched.
Heat Exchanger Antifreeze Protection
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Rotary heat regenerator protection is ensured using the
NS 120 temperature sensor situated in the outlet air duct
behind the heat exchanger. If the temperature drops below
the pre-set ice build-up threshold, the speed of the rotary
heat regenerator will be reduced. If the speed reduction is not
enough to de-freeze the heat exchanger, the heat exchanger
will be stopped. The heat exchanger speed reduction depends
on the PID controller's constant setting.
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Similarly as the rotary heat regenerator, control of the plate
heat exchanger is ensured using the NS 120 temperature
sensor and bypass actuator control. If the temperature behind
the plate heat exchanger drops below the pre-set ice build-up
threshold, the bypass damper actuator will be activated and
the damper will stay open until the ice build-up melts from the
heat exchanger. A pressure loss sensor or a CAP 3M capillary
probe can also be used in some cases.
Protection of the plate heat exchangers without bypass can
be ensured by a fan speed reduction.
Control units VCS
Plate heat exchanger
– air-handling unit run-out
In some cases, the run-out will be performed when the
air-handling unit is stopped. This will ensure drying of the
heat-exchanger and prevent the creation of conditions for
the growth of microorganism. Temperature and humidity
sequences are active during this run-out. This feature is
conditioned by previous operation of the heat recovery and the
outside air temperature. As default, this feature is switched off.
For the change in all values, refer to List of Data Points – Fans.
Mixing Damper Control
It is ensured by step-less control of the mixing damper actua-
tors using a 0–10V (2–10V) continuous signal. The signal is
directly proportional to the air circulation, i.e. 100 % of the
signal corresponds to 100 % of the required air circulation
(0 % of fresh air).
The maximum level of air recirculation (when the fans are
running) is limited by the minimum (hygienic) request for
fresh air. If the device is in the STOP mode, the inlet and outlet
duct dampers are closed and the circulation damper is open.
Heat Recovery and Mixing Economy Control
If the temperature in the room (in the outlet duct) is lower
than the outdoor temperature and a request for cooling
simultaneously exists, the heat recovery and air recirculation
functions will be automatically switched on at the maximum
level to minimize the energy demand for cooling. This hap-
pens if the temperature difference reaches 3 °C (the room
temperature is lower than the outdoor temperature) while the
temperature in the room (in the outlet duct) is higher than the
required temperature and the difference between these two
temperatures is at least 2 °C.
Heat recovery and mixing functions will be switched off when
the outdoor temperature is lower or equal to the room (outlet
air) temperature, or the room (outlet air) temperature is higher
or equal to the required room temperature. Heat Exchanger
control function activation settings are described in the chap-
ter Additional Operating Mode and Function Setting Options.
Heat Recovery and Mixing Control
at Air-Handling Unit Start-Up
The starting outdoor temperature and time are set for heat
recovery and mixing (see Data Points). If the outdoor tem-
perature is lower than the pre-set value at the air-handling
unit start-up, the heat recovery and mixing functions will be
switched on at the maximum level.
Mixing Sequence Selection
The mixing sequence for heating control is optional – the pre-
set sequence for heating is as follows: first, the mixing function
is applied and if the request for heating still increases, then the
heating function will be applied (pre-set). This sequence can be
changed according to user needs, see the chapter Additional
Operating Mode and Function Setting Options.
Humidity Control
The control unit evaluates the control signal for humidification
or dehumidification depending on the room and inlet humidity
sensors and the required humidity selected by the user.
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