Constant airflow ventilation systems: operation and advantages

Mechanical ventilation usually varies the air flows that are extracted or introduced into a room to improve the comfort and health of its inhabitants. However, what we really want to ensure in our homes and in private environments is not the introduced or extracted airflow, but the necessary flow rate. Because depending on the circumstances of the fans or other external causes, maintaining a flow rate will require a greater airflow to be provided. And for that, there are constant airflow ventilation systems.

A double flow mechanical ventilation system is equipped with two fan motors, one that provides fresh air and the other for extracting stale air from inside. If the air flows of these two fans are not identical (balanced ventilation), energy losses due to overpressure or depressurization of the premises will be immediate, and the thermal performance will not be achieved, neither of the accommodation nor of the double flow mechanical ventilation.

That is why, for years, at Siber Zone we are fully convinced that the effectiveness of balanced ventilation, with double flow systems, does not only depend on using fan motors with identical and truly constant air flows. Compared to our competitors using constant flow fans, we have developed an exclusive patented technology of fans with continuous current, reactive (with backward inclined blades) and constant airflow ventilation systems.

Constant airflow double flow ventilation systems

The double flow mechanical ventilation has two fans, one that provides air from outside and another that extracts stale air from the inside. It is the most complete system as it is not limited solely to extraction. But for the system to operate under optimal conditions, the ventilation must be balanced.

These fans must ensure a constant airflow. This type of fan is not regulated according to its rotation speed (rpm - revolutions per minute) like standard constant speed centrifugal fans, but operates according to a certain airflow, determined by the dimensions of the installation.

If the air resistance increases (increase in load loss which generally, with a standard fan, should reduce the airflow), the fan motor will automatically spin faster to always achieve the same predefined amount of air, regardless of the increase in load loss.

Obviously, the motor of the constant airflow ventilation systems will operate conversely in case of reduced air resistance (the motor will spin more slowly). Constant flow fans therefore automatically modify their rotation speed, in order to ensure in all circumstances that the airflow remains identical and that the indoor air quality remains optimal.

In contrast, standard fans use a constant rotation speed: airflow modulation is performed only through the setup of the device at the time of startup or through a regulator. They provide a weaker airflow in the case of increased air resistance. The airflow is not automatically adjusted.

Why are constant flow fans preferable?

In a location using balanced double flow ventilation, two fans ensure ventilation (fresh air supply fan / stale air extraction fan). In a context where these fans do not have the same air flows, we could detect the following problems:

• If the flow rate of supplied fresh air is greater than the flow rate of exhausted stale air, this would result in overpressure in the premises (positive pressure), causing the inside heat to escape to the outside through air leaks in the building structure.
• If the flow rate of extracted stale air is greater than the flow rate of supplied fresh air, the result would be depressurization (negative pressure), allowing cold outside air to enter through air leaks in the building structure.

This would cause an immediate loss of thermal efficiency of the premises. The loss of efficiency would be even more significant if the two air flows were not identical within the heat exchanger, in which case the optimal performance of the heat exchanger would not be possible.

For example, if the two air flows are 80 and 100 m3/h, the performance of the exchanger will be only one eighth or one tenth of the normal efficiency of the heat exchanger, that is, a performance of 72% for a heat exchanger that should have a nominal efficiency of 90%.

Siber Zone Automatic Balanced Constant Flow System

Thanks to the automatic balancing system we have patented at Siber Zone, it is guaranteed that the flow rate of supplied fresh air to the home is exactly the same as the extraction flow rate.

The imbalance between the supply network regarding the extraction causes negative thermal effects;

• Depressurization (negative pressure): When extraction is greater than supply, cold air is sucked in from the outside through infiltrations in the envelope.
• Overpressure (positive pressure): When supply is greater than extraction, hot air is expelled from the inside to the outside through infiltrations in the envelope.

This solution with constant airflow ventilation systems continuously balances the flows, preventing the need for manual balancing work for the fans of the supply and forced extraction network so that the VMC DF system operates correctly upon installation startup.

With the automatic balanced Siber system, we avoid the need for periodic adjustments of the fans' balance with measurements taken in the home, which is mandatory for equipment that does not have this technology.

Thanks to the constant airflow ventilation systems from Siber Zone, with balanced and double flow ventilation, the user does not have to worry about almost anything. They do not have to adjust the fan motors at startup since everything is automatic. The end customer will obtain a constant airflow, permanently maintaining air quality and the thermal performance of the premises.