Ventilation systems commonly used in buildings, especially in spaces such as bedrooms and bathrooms, often include a ventilation duct to one end of which a fan is coupled. A ventilation device is arranged at the other end. Often, also one or more additional ventilation devices is/are connected to mouths of the ventilation ducts at different positions along the ventilation ducts. Said ventilation duct often extends over several different spaces in the property, for ventilation of those spaces. The ventilation device has an adjustable opening, here referred to as airflow opening, with which the airflow through the ventilation device between the ventilation duct and outside space can be adjusted. When the ventilation device is connected to a mouth of the ventilation duct, the airflow into or out of the ventilation duct can be adjusted by adjusting the size of the airflow opening.
The airflow through a ventilation device depends on factors such as the fan's effect, the dimensions of the ventilation duct, and the size of the airflow opening of the ventilation device. Here, the dimension of the ventilation duct refers to its diameter. When the ventilation system comprises a plurality of ventilation devices, such devices are generally set such that the various ventilation devices have different sizes of the airflow opening in order to thereby adjust the pressure distribution in the ventilation system. By adjusting the airflow opening of the various ventilation devices, unnecessarily high pressures can be throttled down. In this way, a predetermined airflow is obtainable through the respective ventilation devices, i.e. a desired degree of ventilation is obtainable in all spaces in which one or more ventilation devices is/are arranged. Too low airflow causes inadequate ventilation, while too high airflow causes increased energy costs.
The airflow, i.e. amount of feed air or exhaust air, is generally set according to current practice, in accordance with the dimensions of the ventilation duct.
To achieve that airflow calls for a certain pressure distribution in the ventilation system.
It is a problem with these systems that they generate sound which may be perceived as disturbing. For these ventilation systems there are therefore threshold values for maximum recommended sound effect level. Especially, sound is generated in the ventilation device at airflow through its opening towards the surroundings, i.e. the airflow opening. The threshold values for permissible sound effect level generated by the respective ventilation devices set limits to how large a pressure drop can be accomplished over the ventilation device, i.e. which opening degree the respective ventilation devices can have. This also sets limits to which airflow can be obtained through the ventilation device.
As mentioned above, a ventilation system usually comprises a plurality of ventilation devices at different distances from the fan. As the pressure generated by the fan is lowest at the ventilation device located furthest from the fan, said ventilation device is set with maximal opening, i.e. said ventilation device has maximal airflow opening size. The pressure required over said ventilation device to achieve a specified airflow determines the fan's operating conditions. To minimize energy consumption, a pressure drop should be as low as possible.
At the same time, a specified airflow must be obtained also through other ventilation devices being positioned closer to the fan and thus experiencing a higher pressure from the fan. Therefore, a certain degree of throttling of the pressure over the respective ventilation devices, a certain degree of pressure drop, is called for so that the specified airflow is neither exceeded nor underpassed. However, the recommended maximum sound effect level sets limits as to how much the pressure over a ventilation device can be throttled, because of the sounds occurring at airflow through the ventilation device. As will be described in more detail below, factors, such as the size of the airflow opening of the ventilation device, the dimensions of the ventilation device, and the size of an airflow there through, affect the sound effect level generated in the ventilation device at airflow there through. Therefore, the maximal degree of throttling of the pressure in a ventilation device obtainable over a ventilation device, without the recommended maximum sound effect level being exceeded, should be as high as possible to obtain effective ventilation throughout the entire ventilation system. Overall, these factors thus set limits as to the ventilation system.
A ventilation system for feed air ventilation has been described above. The same applies also to exhaust air ventilation.