Constant flow ventilation systems, how do they work?

The mechanical ventilation usually varies the air flows that are extracted or introduced into a room to improve the comfort and health of those who inhabit it. Still, what we really want to ensure in our homes and in private environments is not the flow of air introduced or extracted, but the necessary flow rate. Because depending on the circumstances of the fans or other external causes, in order to maintain a flow rate, a greater airflow will be necessary. This is the reason why there are constant flow ventilation systems.

What these systems aim to ensure is that the same flow rate is always given, even if the situation of the device changes where it has been installed. If, for example, the air filters or the fan blades become dirty, there will be a loss of load, the flow rate will be incorrect, and the necessary efficiency will be lost, which affects comfort and can even become annoying. Constant flow ventilation systems, on the other hand, will overcome this problem by increasing the fan speed to ensure the same flow rate.

This is why solutions with constant flow are used in places where excellent conditions are required, such as public venues and even operating rooms in hospitals, but also in our homes, where we undoubtedly spend a lot of time.

Constant flow ventilation systems are common in single-flow solutions, and they are usually referred to as CAV, which stands for Constant Air Ventilation. However, this does not mean that constant flow options are exclusive to single-flow systems.

 

Constant flow ventilation systems in double flow

  The double flow mechanical ventilation has two fans, one that supplies outside air and another that extracts stale air from inside. It is the most complete system as it is not limited only to extraction. However, in order for the system to operate at its best conditions, the ventilation must be balanced.

In double flow systems, there can be no losses of load or energy, and issues of depression or overpressure must be overcome. If this occurred, the same thermal performance and necessary comfort could not be guaranteed. Therefore, the flow rate must be constant. And in the sector, it is common to be aware of the necessity that it is not enough to have a system with a constant flow.

The patented double flow ventilation system by Siber Zone uses reactive direct current fans (with blades tilted backward) and with constant flow. In this way, we can ensure the necessary conditions to maintain the same efficiency. All this also translates into the following benefits:

• A reduction in electric consumption.
• Better acoustic comfort without noise.
• Easier maintenance of the fans.

Constant flow ventilation systems became popular in single-flow solutions to be able to adapt to the specific flow needs specified in the Technical Building Code.

In the same CTE, the possibility of using double flow systems is also mentioned to guarantee current ventilation needs. Using a constant flow solution in double flow equipment makes everything more efficient and prevents losses in efficiency. This system, thanks to the heat recovery unit, is capable of cooling or heating the air that is introduced into the room.

 

Standard constant flow or with direct current

  In the most common constant flow ventilation systems, the turbines of the centrifugal fans have curved blades facing forward - tilted in the same direction as the rotation of the wheel - which makes it relatively simple to calculate the flow of the fan based on the torque and the rotational speed. The torque of this type of fan increases proportionally to the square of the rotational speed, and the result is a power curve to which we can assign, for each point, a pressure. This then allows us to determine the airflow.

The new Siber systems vary as they operate with direct current reactive flow, with the blades in the fans inclined backward, in the opposite direction of rotation. Unlike fans with forward-tilted blades, the torque of these fans does not increase proportionally to the square of the rotational speed.

This is why it is not possible to determine the pressure nor the airflow associated. The alternative solution consists of a differential pressure measurement. The pressures are collected at two different points, one at the internal diameter and the other at the external diameter of the fan. Their differential allows calculating the airflow ensured by the motors of the fans. Thanks to these constant flow ventilation systems in double flow, noises are lower and energy efficiency is greater, thus saving energy and gaining comfort.

Constant flow ventilation systems adapt to actual ventilation needs and avoid losses of load or efficiency.