Control processes

To follow is a look at the different advanced control processes.

Dealing with condensate

With the high level of heat recovery of up to 95%, extract air in the counterflow heat exchanger undergoes intense cooling. This may, under certain conditions, cause moisture in the extract air to condense in the exchanger. If this occurs, the condensation will then be collected in a condensation tray, where a swimmer automatically records how much water there is. The unit is fitted with an automatic condensation management process, which means that in rooms with normal humidity, such as offices, meeting rooms and classrooms, it is not typically necessary to connect a condensation drain.

When ventilating rooms with high humidity, the condensation can be directed away from the unit to a drain to prevent outages, for example by fitting the unit with a fully automatic condensation pump.

Automatic condensation management process

If the condensation water reaches a certain level it activates the swimmer and the controlling automatically starts the condensation management process. The process shuts down the supply fan and raise the extraction fan to 100 % airflow trying to eliminate the condensation water. The process runs 20 minutes and will retry 4 times. If the condensation management process is effective and eliminate the condensation water, it will clear the condensation alarm. If it does not have an effect, the air handling unit will stop. The condensation alarm will still appear, and the water has to be removed manually before the air handling unit can start again.


Built-in float sensor detects
build-up of condensate.

Operation of Airmaster ventilation untis in cold climate

Airmaster’s decentralised ventilation units are also designed to function optimally in cold regions such as in northern Scandinavia and Greenland, where a large number of units are already in operation.

The ventilation units have built-in intelligent control processes which automatically regulate components and can adjust the operation of the unit, if necessary, to frost-proof the unit, or to maintain the desired supply temperature during periods of low outdoor temperatures.

Frost protection

The high efficiency of the heat exchangers ensures low energy consumption for heating the supply air, which is both environmentally and economically beneficial. However, this high efficiency may cause the exhaust air to condense in the heat exchanger during cold periods. If the outside air is cold enough, there is a risk of the condensation freezing and thereby blocking the exhaust air in the heat exchanger.

It goes without saying that this problem has been addressed in Airmaster’s ventilation units. The Airlinq® control efficiently prevents the formation of ice by gradually reducing the volume of the supply air and possibly increasing the volume of the exhaust air to the level required. As a result, the exhaust temperature rises again. If this process is not enough to prevent the formation of ice in the heat exchanger, the Airlinq® control will protect the unit by shutting it down and activating an alarm signal.

Controlled inlet temperature

To achieve the highest level of heat recovery, Airmaster air handling units are fitted with highly-efficient counterflow heat exchangers. A comfort current is therefore used only to equalise the minimal heat loss from ventilation. A heating element is therefore only used to offset the minimal heat loss during ventilation, ensuring that full operation can be maintained, even in cold geographical regions. Balanced ventilation is maintained as long as the inlet temperature remains within acceptable limits as standard.

If the inlet temperature cannot be maintained at low fresh temperatures, Airlinq will reduce inlet air and increase extract air to compensate for the low temperature.

The function is also active if comfort heating surface capacity is utilised 100%. This function means that in certain climates the comfort heating surface is not required.

Electric comfort heating surface with adaptive control

The electrical comfort heating surface is controlled automatically by the Airlinq controls system, which checks the temperature conditions in the air handling unit and switches on/off the comfort heating surface as required. Adaptive control means that the electrical comfort heating surface warms the inlet air after the counterflow heat exchanger with only the energy required to maintain the desired inlet air temperature. In other words, adaptive control ensures that the supply air has an even temperature. 

The balance between the supply air and extract air can be maintained via an electrical comfort heating surface, even at very low outdoor air temperatures.

The location of the comfort heating surface is illustrated in Figure 1.

Varmeveksler Eftervarmeflade GB

Figure 1: Simplified principle sketch of ventilation unit with heat exchanger and heating element.

Elektrisk eftervarmeflade

Electric comfort heater

Water heating surface

Most air handling units can have a water heating surface fitted as an alternative to an electric comfort heating surface. A water heating surface also ensures the required inlet temperature. The large surface area of the heating surface ensures efficient transfer of heat energy to the inlet air.

The Airlinq control system starts and stops the heating surface using a motor-driven valve. The heating surface is supplied built-in to the air handling unit, or as part of the duct system. Connection to the local heating system is therefore quick and simple.

Frost protection of water heating surface

The water heating surface is fitted with a separate, self-controlling heat retention valve, which ensures a minimum temperature even when the air handling unit is switched off. All nominal values for the water heating surface are preprogrammed into the Airlinq control system. The heating surface is therefore protected against frost and is directly functional.


Water heating surface


Airmaster ventilation units can be fitted with an electric pre-heating element or a “virtual pre-heating element”.

If the air handling unit is fitted with an electric preheating surface, it will heat the fresh air before it meets the counterflow heat exchanger, preventing the formation of ice. To maintain balanced ventilation, the Airlinq control system controls the temperature in the unit. This is achieved by the preheating surfaces only cutting in if the requirement exists. Energy consumption can thus be kept at a minimum.

The location of the pre-heating element is illustrated in Figure 2.

Varmeveksler Forvarmeflade GB

Figure 2: Simplified principle sketch of ventilation unit with heat exchanger and pre-heating element.

elektrisk forvarmeflade

Electric pre-heating surface

Virtual pre-heating

Alternatively, on some units, frost protection can be provided by means of a heating element and the “virtual pre-heating” (VPH) function.

During periods when there is a risk of ice forming, a small volume of supply air can be made to bypass the heat exchanger via the bypass damper (see Figure 3). This prevents the exhaust air from cooling as much in the heat exchanger, thereby preventing the formation of ice. The supply air which bypasses the heat exchanger is remixed with the supply air which has passed through the heat exchanger before the heating element heats the air to the desired supply temperature.

Varmeveksler Forvarmeflade Eftervarmeflade GB

Figure 3: Simplified principle sketch of ventilation unit with heat exchanger and heating element for virtual pre-heating function (VPH).

If the ventilation unit is fitted with a pre-heating element, or a heating element combined with the “virtual pre-heating” function, the control will only cause an imbalance in the airflow to the extent necessary once the capacity of the heating element is utilised 100%.

Flow control 

Most air handling units can control the airflow using flow control. Flow control means that the airflow is stated in m3/h and ensures balanced operation, at varying pressure difference on the supply and extract air. To convert airflow to m3/h, a measuring nozzle is fitted inside the air handling unit between the fan and the main box, which measures the differential pressure.

The differential pressure is measured for the supply air and extract air respectively, and then converted to an airflow in m3/h.

Ventilation unit with the option of separate pre-heating and heating elements.

AM 300 AM 500 AM 800 AM 900 AM 1000 AM 1200

Ventilation unit with the option of heating element with virtual pre-heating function.

AM 150 DV 1000

Ready for a breath of fresh air

At Airmaster, we are “decentral” through and through. We are unrivalled when it comes to creating the best indoor climate and optimal well-being because we take each room and its occupants into account – and because we constantly strive to improve on what we do.