Control processes

A review of the various control processes is described below.

Control via CO2 sensor

Control via CO2 sensor

A CO2 sensor measures the CO2 level in the room, and sends the reading to the control system. The control system then adjusts the rate of air replacement in the room according to the CO2 level, reducing the unit's energy consumption to the minimum.

Air volume control (figure 1)
The unit can be set to run with a reduced standard air volume (min.) for basic ventilation. If the CO2 level in the room exceeds the programmed lower limit (A), the CO2 sensor will cut in and increase air volume. If CO2 levels continue to rise, the air volume will be increased linearly up to the maximum volume (max.) at the upper CO2 limit (B) and above.

Start, stop air volume control (figure 2)
If the unit is completely controlled by the CO2 sensor, it will start with a little more than the standard air volume (min. +x) when the CO2 level exceeds the programmed lower limit plus 10% (A + 10%). If CO2 levels continue to rise, the air volume will be increased linearly up to the maximum volume (max.) at the upper CO2 limit (B) and above. If the CO2 level falls below the programmed lower limit (A), the unit will stop again.

Figure 1

Figure 2

 

Control via motion sensor (PIR)

Control via motion sensor (PIR)

The air handling unit is set to start/stop via a signal from a PIR sensor. The unit will start upon a signal from the PIR sensor, e.g. triggered by movement in the sensor zone. The unit will start in normal operation with the programmed air volume and inlet temperature. When the signal ceases, the unit will stop after the preprogrammed run-on time. PIR control is often used to activate full operation on units which provide basic ventilation when there is no-one present.

Control via humidostat

Control via humidostat

Wall-mounted humidostat
A wall-mounted humidostat registers relative air humidity, and sends either a start or stop signal to the air handling unit. The humidostat is used to set the level of relative air humidity at which the signal is given. The humidostat contains hygroscopic carbon fibres, the length of which depend on relative air humidity. When the relative air humidity goes over or under the level set, the humidostat sends a start/stop signal to the air handling unit. This is often used to activate full operation on units which otherwise provide basic ventilation, when the relative air humidity setting is exceeded.

Dealing with condensate

Dealing with condensate

When heat recovery is running up to 95%, the exhaust air is cooled considerably in the counterflow heat exchanger. The humidity in exhaust air can then condense in the heat exchanger, and is collected in a condensate tray. A float registers a high level of condensate in the tray automatically. To prevent stoppages, a drain can be fitted to the condensate tray to remove water from the unit. Alternatively, the ventilation unit can be fitted with a condensate pump to pump condensate away when it forms.

Frost protection

Frost protection

When the outdoor temperature approaches freezing point, the exhaust temperature behind the counterflow heat exchanger drops. This can result in condensate freezing in the heat exchanger. The Airlinq control system prevents the formation of ice by increasing exhaust air and reducing inlet, causing the exhaust temperature to rise again. If this process is insufficient to prevent ice forming in the heat exchanger, Airlinq will protect the unit by shutting down operation.

"Preheating" with electric preheater
If the ventilation unit is fitted with an electric preheater, it will heat the outdoor air before it meets the counterflow heat exchanger, preventing the formation of ice. To maintain balance ventilation, the Airlinq control system controls the temperature in the unit. It does so by the heater being connected when needed and keeping energy consumption to a minimum.

"Virtual preheat" with electric heating surface
Alternatively, ice formation can be prevented using a high capacity electric heating surface with "virtual preheat" function. A bypass damper diverts some of the outdoor air past the counterflow heat exchanger. The electric heating surface heats the outdoor air to the inlet temperature required. The exhaust air is cooled down less in the heat exchanger, preventing ice formation. This process can also be taken over by a water heating surface.

Controlled inlet temperature

Controlled inlet temperature

To achieve the highest level of heat recovery, Airmaster ventilation units are fitted with highly-efficient counterflow heat exchangers. A comfort heater (which can be fitted to all Airmaster units) is therefore only used to align minimal heat loss with ventilation. Balanced ventilation is maintained as long as the inlet temperature remains within acceptable limits as standard.

Without comfort heater: If the inlet temperature cannot be maintained, Airlinq will reduce inlet and increase exhaust air to compensate for a low outdoor temperature. The function is also active if comfort heater capacity is utilised 100%. The balance between supply and exhaust air, plus a draught-free zone, is maintained via a comfort heater. The same applies in the event of extremely low outdoor temperatures.

Electric comfort heater
An electric comfort heater heats the inlet after the counterflow heat exchanger to the inlet temperature set if needed. The Airlinq control system controls the temperature in the unit, and automatically activates the comfort heater if it is needed.

Water heating surface
Most ventilation heaters can have a water heating surface fitted as an alternative to an electric comfort heater. This will also ensure the desired inlet temperature. The large surface area of the heater ensures efficient transfer of heat energy to the inlet. The Airlinq control system starts and stops the heater using a motor-driven valve. The heater is supplied built-in to the ventilation 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 ventilation unit is switched off. All nominal values for the water heating surface are preprogrammed into the Airlinq control system to ensure it is protected against frost, and always functional.

Energy meter

Energy meter

All Airmaster ventilation units can be fitted with an energy meter, to provide a precise overview of the unit's electricity consumption. The figures can be read directly on the meter's display. Consumption on units with the P control system can also be read on PC using Airlinq Service Tool.

Automatic bypass

Automatic bypass

If the inlet temperature exceeds the level set, the Airlinq control system will gradually open the bypass. Cooler outdoor air will be allowed to bypass the counterflow heat exchanger, ensuring that the inlet temperature set is maintained.

Airlinq will adjust the inlet temperature to achieve a higher cooling effect. If the room temperature exceeds the level set, e.g. as a result of strong sunshine, the bypass will open automatically.

If a cooling module is fitted to the ventilation unit, Airlinq will activate it automatically if cooling using outdoor air is insufficient. When the cooling module is working, the bypass is still used to regulate the inlet temperature.

Night time cooling

Night time cooling

If the room temperature exceeds the maximum level set during the day, all Airmaster ventilation units can automatically cool down the room using colder night air. We call this function "night time cooling". It will be registered by the Airlinq control system, and started automatically. If necessary, the function will use the bypass damper and cooling module to achieve the cooling effect required. The building and its contents will be cooled, and room temperature will reach a lower level than otherwise obtainable.

Cooling using the cooling module

Cooling using the cooling module

The automatic bypass function and night time cooling ensure that the inlet and room temperature are kept down. If this is insufficient, effective temperature reduction can be achieved using a cooling module. Airlinq automatically activates the cooling module, which reduces the outdoor air's temperature by up to 15°C. Outdoor air is then supplied to the ventilation unit, enabling the inlet temperature to be maintained using the automatic bypass function at the level set.

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