The new European standard EN 13779 focuses on achieving a comfortable and healthy indoor environment in all seasons with acceptable installation and running costs. It is now a national standard in all countries. It specifies the required filter performance in a system to achieve a good Indoor Air Quality (IAQ) taking into consideration the outdoor air. The outdoor air is categorised in 5 levels, from ODA 1 where the air is pure except for temporary pollution such as pollen, up to ODA 5 with high concentrations of both gases and particles. The particulate matter refers to the total amount of solid or liquid particles in the air. Most outdoor air guidelines still refer to PM10 (particle diameter up to 10 µm). But for the purpose of health protection, there is a growing acceptance that emphasis should be placed on particles much smaller than 10 µm. The gaseous pollutants refer to the concentrations of CO2, CO, NO2, SO2 and VOC’s.
The table below indicates typical concentration levels in outdoor air, together with a suggestion for how to categorize the quality.
Notice, that in most cities what is termed a “normal concentration level” for particulates actuallly falls in the upper range (poor quality) for outdoor i.e. ODA 4 or ODA 5. For particulate matter the World Health Organization has established targets to reach an annual mean of PM10 below 40 µg/m3. That target is not yet reached. In other words, most people in Europe spend most of their time in areas where the outdoor air must be categorized as ODA 4 or ODA 5. It can be readily concluded that the application of appropriate filtration is critical for health concerns.
The new standard classifies the indoor air quality from IDA 4 (low IAQ) up to IDA 1 (high IAQ). One traditional but limited method to determine the IAQ is to study the CO2 levels. CO2 is the product of human respiration. It is a good indicator of effective ventilation but not absolute air quality. Another established method for spaces with human occupancy is to specify the rate of external air added for each person.These type of values are often used to size the ventilation system. The table below lists typical ranges for CO2 levels and recommended rates for added external air to achieve different categories of indoor air quality. Note, neither method takes account of the particulate and gaseous pollutants brought into the building with the external air.
