Extraction requirements in ventilation systems

According to the CTE DB HS 3, Indoor air quality, "buildings shall have means for their rooms to be ventilated properly, eliminating contaminants that are produced regularly during their normal use, such that a sufficient flow of outside air is provided and the extraction and expulsion of stale air containing contaminants is ensured".

Thus, a ventilation system will be available, which can be hybrid or mechanical. We talk about hybrid ventilation when the inflow of fresh air from outside occurs naturally, through openings or grids made in the envelope or in the carpentry, and extraction occurs by mechanical means. We talk about mechanical ventilation when both inflow and extraction occur through mechanical processes. To provide a sweeping effect that generates the air currents necessary for a proper airflow for ventilation and, consequently, an adequate renewal of the air in the rooms, admission openings will be provided in dry rooms and extraction openings in humid rooms. If we talk about mechanical ventilation, we talk about balanced ventilation, as the aim is to achieve a balance between the ventilation flow and pressure.

The extraction in the overall system

According to the UNE-CEN/TR 14788 IN, Building ventilation. Design and sizing of ventilation systems in dwellings, the ventilation system must allow for minimal pressure loss, so that the energy consumption of the fans is minimal. As the standard reminds us, and also the CTE, extraction ducts must have a surface that prevents them from becoming dirty, as the accumulation of dust inside also causes pressure losses and can impair the pressure balance of the system. Likewise, ducts must be accessible for necessary cleaning and maintenance actions, both at the top as well as at their origin.

According to the UNE standard, in ventilation systems with mechanical extraction, the central fan, connected to the humid areas, can be located on the roof or in some habitable area of the dwelling, such as the laundry room, storage room, or garage. Another option is to locate extraction fans in each dwelling and have them discharge directly to the outside.

If the mechanical ventilation system has a heat exchanger capable of recovering up to 90% of the energy, it is not necessary for it to share the same unit with the fans, which facilitates the design of the entire system.

In central ventilation systems, that is, when serving more than one dwelling, air flow from one dwelling to another through the duct network should be avoided.

Ventilation and energy efficiency

As the standard reminds us, the main objective of ventilation systems is to provide optimum indoor air quality in rooms and to prevent the building structure from deteriorating due to a high relative humidity rate. However, to comply with environmental regulatory demands, it must be ensured that this air renewal process does not come with a high energy and environmental cost. Therefore, the installation of adjustable systems that allow control over operation (duration) and flow is highly recommended.

It is also highly convenient to employ automatic controls that enable the system to act where and when it is needed. Thus, the system can provide high airflow in rooms at night when they are occupied, but not during the day when no one is there. The same would happen in living rooms, but during daylight hours.

Given their high relative humidity rates, this system should not be used in kitchens or bathrooms. In these humid areas, an efficient ventilation system should consider humidity production rather than occupancy.