Recommendations and tips
EN 13779: the standard for a comfortable indoor climate
The European EN 13779 standard is a guideline for the performance requirements for indoor air. The object of the standard is clear: To create a comfortable and healthy indoor climate, while maintaining acceptable installation & operating costs. EN 13779 defines the filter performance standards that systems should meet in order to achieve suitable indoor air quality (IDA). The standard also takes account of the outdoor air quality (ODA) in which area three levels are distinguished, ODA1 = pure air only polluted temporarily (pollen) to ODA3. which contains the very high concentrations of gaseous pollutants and particulate matter often found in industrial cities.
Recommendations and tips
EN 13779 defines particulate matter as the total amount of solid or liquid particles in the outdoor air. In terms of gaseous pollutants, it refers to concentrations of CO2. CO, NO2. SO2 and volatile organic substances (VOS). Table 1 indicates the limits of the ODA categories. Filtration is aimed at achieving a certain level of indoor air quality (IDA). There are four IDA levels, IDA1 being that of the purest category, and IDA 4 is the most heavily polluted. As shown in Table 2 below, IDA classification is based on a combination of the CO2. in comparison to that of the outdoor air, and the volume of outdoor air per person, per hour that the system has to introduce. Table 3 shows which filter classes (F5 to F9 inclusive) the EN 779:2002 standard maintains are required to achieve the desired IDA, on the basis of the ODA. GF stands for gas filter, or activated carbon filter.
Filter efficiency versus penetration
Which filter do you need to achieve the efficiency you require? The answer to this question can be found in Table 4. The filtration efficiency of air filters is largely dependent on the quantity of particulate matter trapped. The term (submicron) particulate matter applies to particles in the range of 0.3 to 1 micron in diameter. The extent to which such particles become embedded in the filter is known as the penetration factor. The penetration factor is based on the penetration of the F9 class (penetration factor 1). An F7 filter has a penetration of 46%, while an F5 filter has 93%. The penetration factor is indicated in Figure 1. You can see what types of particles are trapped by which type of filter.
Recommendations for the replacement of air filters
Whenever one considers replacing air filters, the economic aspect always plays a major role. There are various parameters which determine whether you should replace your filters. For instance, the terminal pressure (energy consumption), hygiene (bacteria and mould growth) and the number of operating hours of the system need to be taken into consideration. In table 5. we have plotted the initial resistance against the terminal resistance for filter classes F5 to F9 inclusive, starting from the same airflow volume and airspeed. Table 6 shows the frequency at which the first and second stage filters and the re-circulated air filter – return or exhaust air – need to be replaced. The replacement frequency is expressed in operating hours and years. A filter of at least class F5 is required for return and extraction air, with a view to adequately protecting extraction and exhaust systems. It is advisable to fit the same filter class as that used for the intake air.
