Increasing global industrialisation over the past decades has led to a rise in air pollution. Although some sources are natural, the main contributors stem from human activity. Numerous chemical substances are released into the atmosphere — this, whether we choose it or not, is now part of our daily lives.
Our increasingly sedentary lifestyles mean we spend on average 70 to 90% of our time indoors — at home, in the office, in transport, shops, schools, etc. We are therefore increasingly exposed to gaseous and particulate pollution originating from outdoor air. In situations where fresh air renewal is very low, several studies have shown that the air we breathe can be up to 10 times more polluted indoors than outdoors. Enclosed spaces, where we spend most of our time, can therefore cause serious harm to human health (allergies, asthma, etc.).
Through breathing, particles enter the body and respiratory system. The same applies to gaseous pollutants, which pass from the lungs into the bloodstream and then infiltrate the entire body. Even though these pollutants are normally invisible, we can “see” them: vehicle exhaust fumes and dust clouds, factory chimneys, cigarette smoke, etc.
European Standard EN 13779 for ventilation
The standard applies to the design and implementation of ventilation and air conditioning systems in non-residential buildings occupied by people, excluding industrial process applications. It defines the key and essential parameters for such installations. However, it does not apply to naturally ventilated buildings.
Currently under revision, EN 13779 focuses on achieving a comfortable and healthy indoor environment using ventilation systems with acceptable operating costs. It specifies the required filtration system performance for ventilation systems to ensure good indoor air quality (IAQ), based on external air quality.
External air is classified into three levels:
- ODA 1: clean air, except for temporary pollution (e.g. pollen)
- ODA 2: moderately polluted
- ODA 3: highly concentrated levels of gases and particles
Based on the “side effects” of these substances, the World Health Organization (WHO) recommends not exceeding the following exposure limits for indoor pollutants:
| Air pollutant | Exposure time | Maximum concentration in air | |
|---|---|---|---|
| µg/m³ | ppm | ||
| CO | 8 hours | 10 000 | 9 |
| PM10 | 1 year | 40 | – |
| PM2,5 | 1 year | 15 | – |
| Total PM | 1 year | 100 | – |
| O3 | 8 hours | 120 | 0.06 |
| COV | 1 hour | 500 | – |
In this standard, regarding external pollution, reference is also made to PM10 (particles up to 10 microns in diameter). However, to protect health, it is widely recognised that much smaller particles should be considered. The standard refers to concentrations of CO₂, CO, NO₂, SO₂ and VOCs for gaseous pollutants.
As a guideline, the following table links the level of external air quality to the annual concentration of these pollutants according to geographic area:
| Category | Geographic area | Average concentration in outdoor air | |||||
|---|---|---|---|---|---|---|---|
| CO (mg/m³) | CO₂ (ppm) | SO₂ (µg/m³) | NO₂ (µg/m³) | Tot. PM (mg/m³) | PM10 (µg/m³) | ||
| ODA1 | Rural area | < 1 | 350 | < 5 | 5 ÷ 35 | < 0.1 | < 20 |
| ODA2 | Suburban area | 1 ÷ 3 | 375 | 5 ÷ 15 | 15 ÷ 40 | 0.1 ÷ 0.3 | 10 ÷ 30 |
| ODA3 | Polluted city centre | 2 ÷ 6 | 400 | 10 ÷ 50 | 30 ÷ 80 | 0.2 ÷ 1.0 | 20 ÷ 50 |
As for the classification of indoor air (IDA) in buildings, it is divided into four categories, from IDA1, indicating the highest quality level, to IDA4, representing low indoor air quality.
A precise definition of these categories is not possible, as it depends on the nature of pollution sources and individual perception or health effects. One practical method of classification relies on CO₂ concentration, which is a good indicator of human bio-effluent emissions, though not of the absolute amount of air. To determine airflow requirements for adequate air quality, another useful indicator is the outdoor air flow rate per occupant.
The table below summarises indoor air quality classification, based on the practical methods described above:
| Category | CO₂ level above ODA | Airflow per person [m³/h] no smoking area | ||
|---|---|---|---|---|
| Typical range [ppm] | Default value [ppm] | Typical range [ppm] | Default value [ppm] | |
| IDA 1 | ≤ 400 | 350 | 54 | 72 |
| IDA 2 | 400 ÷ 600 | 500 | 36 ÷ 54 | 45 |
| IDA 3 | 600 ÷ 1000 | 800 | 22 ÷ 36 | 29 |
| IDA 4 | > 1000 | 1200 | < 22 | 18 |
Recommended air filters according to EN 13779
La norme EN 13779 spécifie clairement la classe du filtre à air à utiliser pour atteindre la qualité d’air souhaitée.
The EN 13779 standard clearly specifies the air filter class required to achieve the desired air quality.
As many users are not yet familiar with the new ISO 16890 standard, we have chosen to refer to air filter classes in accordance with EN 779:2012.
According to EN 13779, for example, if a building is located in a city centre and the target is medium (IDA2) or high (IDA1) indoor air quality, a particulate air filter alone is insufficient — a filter capable of retaining gaseous pollutants is also required.
| Outdoor air | IAQ (indoor air quality) | |||
|---|---|---|---|---|
| IDA1 | IDA2 | IDA3 | IDA4 | |
| ODA1 | F9 | F8 | F7 | F5 |
| ODA2 | F7/F9 | F6/F8 | F5/F7 | F5/F6 |
| ODA3 | F7/GS/F9 | F7/GS/F9 | F5/F7 | F5/F6 |
The EN 13779 standard also provides guidance on air filter replacement intervals:
“Air filters must be replaced when the specified final pressure drop is reached, or when the specified hygiene conditions are no longer met — whichever occurs first. If system operating hours can be estimated, this criterion may be used for filter replacement as follows:
– The pre-filter should be replaced after 2,000 operating hours, or at most once per year.
– The second filtration stage, as well as filters used in exhaust air or recirculation systems, should be replaced after 4,000 operating hours, or at most once every 2 years.
– For hygiene reasons, the filter should be replaced in autumn, after the pollen and spore season.
– If requirements are particularly strict, air filters may be replaced in spring, after the heating season, to eliminate odorous combustion byproducts.”
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