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Freudenberg Filtration Technologies

Key Energy Performance Number

The new energy rating concept used in Eurovent 4/21

Dr. Thomas Caesar, Director Global Filter Engineering at Freudenberg Filtration Technologies

Rising energy cost and the imperative of reducing carbon dioxide emissions are increasingly focusing attention on the energy consumption of air handling systems. In an average industrial plant, approximately 10 % of the total energy is consumed by fans in HVAC systems, in office buildings around 40% and in cleanrooms even 80%. Depending on the size and the design of the HVAC units, approximately 10 - 50% of this portion is related to the pressure drop of filters. A reduction of the pressure drop of air filter systems, equipped and operated with variable speed drives, is accordingly a significant contribution towards saving energy and reducing carbon dioxide emissions. At the same time, there is an increasing demand for higher air quality all kinds of air filter applications including the need for better indoor air quality in building ventilation, resulting in the use of more efficient air filters with typically a higher flow resistance. This leads to a concomitant increase in energy consumption and runs counter to the above-mentioned needs to reduce the energy consumption.

To make it easier for users to choose the most energy-efficient air filters, based on EN 779 test data an European energy efficiency classification system for air filters was developed by EUROVENT, Europe’s Industry Association for Indoor Climate (HVAC), Process Cooling, and Food Cold Chain Technologies. The methodology of this energy efficiency classification is described in the EUROVENT Guideline 4/21 and the classification system is defined by EUROVENT Certita Certification as part of the certification program for fine air filters.

The new standard ISO 16890 for filter testing and assessment was just recently published and will replace EN 779 with a transition period of 18 months. This new method for the evaluation of air filter elements represents a paradigm shift. In future, filter efficiencies will be determined with regard to the particulate classes PM1, PM2,5 and PM10, which are also used as evaluation parameters by the WHO (World Health Organization) and environmental authorities. Based on these benchmarks, users will in future be able to more precisely select filters according to their individual requirements.

The introduction of this new standard made it also necessary to revise the EUROVENT energy rating system and consequently, a second edition of the EUROVENT guideline 4/21 was published.

The concept of Key Energy Performance (kep) numbers was already introduced by the experts of Freudenberg Filtration Technologies in the year 2008 on the 10th World Filtration Congress and was now adopted by EUROVENT in the revised guideline 4/21. The pressure drop and the particle collection efficiency of a filter can be related to each other by defining kep numbers as given in the Equation below.


ePMx is the efficiency value to particulate matter as reported in the new ISO classes (e.g. with ISO ePM10 50% the value ePM10 = 50%). This concept is already well-known for long time in the filter media development as so-called Alpha or 100 Gamma value, which can be directly derived from the physics of filtration. The average pressure drop is measured at a given flow rate of 3400 m³/h using AC Fine (ISO A2) test dust according to the loading procedure described in ISO 16890-3. The filter is loaded with a fixed amount of dust given in the table below for the different PM groups.

The amount of dust given in EUROVENT 4/21 e.g. for filters of the ISO ePM10 group, can be derived from an ambient PM10 concentration of 35 µg/m³, a flow rate of 3400 m³/h per filter and an operating time per year of 6000 h. This would calculate to a yearly dust feed of 714 g. Also the values of the filter element constant C are give in the table above.

The kep numbers introduced by EUROVENT guideline 4/21 are a direct measure for the energy efficiency of an air filter, and hence, will be used as the parameter for the energy efficiency classification table which will be defined by EUROVENT Certita Certification during 2017. By this, the energy classes A+, A, B, ... will be redefined and linked to the kep numbers.

The yearly energy consumption W in kWh/a of a fine air filter also can be calculated by using the Equation below defined by EUROVENT guideline 4/21.

In this Equation, an air flow rate of 3400 m³/h, a fan efficiency of 50% and 6000 operating hours per year are assumed.

During 2017, the EUROVENT Certita Certification program for fine air filters will prepare itself for the implementation of the new ISO 16890 classification system as well as the new energy efficiency rating system, both becoming effective on January 1st, 2018.


Eurovent 4/21 - 2016: Energy Efficiency Evaluation of Air Filters for General Ventilation Purposes, second edition, EUROVENT Association, November 2016.

RS 4/C/001 - 2016: Rating Standard for the Certification of Air Filters, EUROVENT Certita Certification, January 2016.

Mayer, M.; Caesar, T.; Klaus, J.: Energy efficiency classification of air filters, Proc. 10th World Filt. Cong., Vol. 3, p. 313 — 317, April, 14 — 18, 2008, Leipzig, Germany.