The mandatory regulations governing air quality, from the point of view of the design and operation of air conditioning systems, is the Regulation of Thermal Installations in Buildings (RITE). Currently in force under RD 1027/2007 but with the latest modification in 2021 with the appearance of RD 178/20211 .
This regulation addresses the need for filtering, and the type of filters to be used, in the IT 1.1.4.2.4. about “Minimum ventilation outdoor air filtration”.
In addition to the RITE, since it is referenced in it, the applicable standard is UNE-EN ISO 16890:1:2017 on air filters used in general ventilation - Part 1: Technical specifications, requirements and efficiency classification based on particulate matter. (ISO 16890-1:2016)
HOW IS THE FILTRATION REQUIREMENT MADE?
In the technical instruction itself (IT 1.1.4.2.4. Minimum filtration of outside ventilation air) it is required that the outside ventilation air must be introduced duly filtered into the buildings. In addition, it establishes the minimum filtration classes to be used, depending on the quality of the outside air (called ODA) and the quality of the inside air required (called IDA). Specifically, the requirements are regulated in table 1.4.2.5 of the regulation. It is reproduced below.
Air quality (Table 1.4.2.5 of RD 178/2021)
EXTERIOR CAI | INTERIOR CAI |
| IDA 1 | IDA 2 | IDA 3 | IDA 4 |
ODA 1 | F9 | F8 | F7 | F5 |
ODA 2 | F7 + F9 | F6 + F8 | F5 + F7 | F5 + F6 |
ODA 3 | F7 + GF* + F9 | F7 + GF + F9 | F5 + F7 | F5 + F6 |
* GF= Gas (carbon) filter and/or chemical or physical-chemical filter will be necessary in case ODA 3 is reached due to excess gases.
HOW TO INTERPRET THE REQUIREMENT? DETERMINING FILTER EFFICIENCY
As can be seen in the table above, the requirement for the “quality” of the filtration is categorized with an alphanumeric code. Although the current standard is UNE EN ISO 16890:12 These references are based on EN 779:2013.
This standard set an average filtration capacity measured in three levels: For the so-called "coarse dust" corresponding to particles larger than 10 μm (equivalent to 0.01 mm), class G was established. Classified from G1 to G4, according to a certain average arrestance (Am). Arrestance is the capacity of a filter to retain particles in the air, but it refers to the capacity to retain larger particles and is measured as a percentage.
For the so-called “fine dust” the F filters were used. For particles larger than 2.5 μm (equivalent to 0.0025 mm and designated ePM2.5, where “e” is the efficiency) the M5, M6, F7, F8 and F9 groups were used.
To have a certain efficiency in retaining fine particles suspended in the air smaller than 1 micron (equivalent to 0.001 mm) and designated ePM1 from the F7 filtration class.
Filter classification under EN779 standard
Group | Class | Pressure Drop final (test) in pascals | Arrestance average (Am) synthetic dust 10 μm % | Average efficiency (Em) with particles of 0.4 μm % | Min. effectiveness with particles of 0.4 μm |
Big Particles | G1 | 250 | 50≤Am<65 | - | - |
G2 | 250 | 65≤Am<80 | - | - |
G3 | 250 | 80≤Am<90 | - | - |
G4 | 250 | 90≤Am | - | - |
Medium Particles | M5 | 450 | 450 | 40≤Em<60 | - |
M6 | 450 | 450 | 60≤Em<80 | - |
Thin Particles | F7 | 450 | 450 | 80≤Em<90 | 35 |
F8 | 450 | 450 | 90≤Em<95 | 55 |
F9 | 450 | 450 | 95≤Em | 70 |
Summary table extracted from EN779 standard
But now, filter manufacturers and air conditioning equipment manufacturers are obliged to inform and comply based on the UNE-EN ISO 16890:1:2017 standard referenced in the RITE as explained above.
WHAT IS THE RELATIONSHIP BETWEEN UNE-EN ISO 16890:2017 AND UNE 779:2013 IN TERMS OF REGULATORY COMPLIANCE?
The UNE-EN ISO 16890:2017 standard defines the testing requirements for air filters used in general ventilation. It came into force in 2017 and replaces the aforementioned UNE EN779 in both Europe and the United States.
The standard allows for a more precise selection of air filters for HVAC systems and a better understanding of the size of air particles actually retained by the filter of the sizes discussed.
Depending on the size of the particles, the UNE EN ISO 16890 standard groups air filters into four categories, which are those already mentioned, namely, ePM1, ePM2.5, ePM10 and coarse dust.
As explained above, the effectiveness of a filter is measured by the percentage of particles of the target particle size that it retains, which must be greater than 50%. That is, a particle filter that retains more than 50% of ePM10 will be classified as an “ISO ePM10” filter, and so on.
Based on the above we have the following equivalences: with what is requested in the RITE:
Equivalences with RITE UNE EN 779:2013 vs. UNE EN 16890
UNE EN 779:2013 | UNE EN 16890:2017 Average efficiency | |
filter class | ePM1 | ePM2,5 | ePM10 | Coarse |
G1 | - | - | - | - |
G2 | - | - | - | 30%-50% |
G3 | - | - | - | 45%-65% |
G4 | - | - | - | 60%-85% |
M5 | 5%-35% | 10%-45% | 40%-70% | 80%-95% |
M6 | 10%-40% | 20%-50% | 60%-80% | >90% |
F7 | 40%-65% | 65%-75% | 80%-90% | >95% |
F8 | 65%-90% | 75%-95% | 90%-100% | >95% |
F9 | 80%-90% | 85%-95% | 90%-100% | >95% |
Comparative table between UNE EN 779:2013 and UNE EN 16890