What is an Electrostatic Precipitator and how does it work?

Electrostatic Precipitator

Filter classification according to the new standard

The general purpose of ventilation is to remove the used “contaminated” indoor air and supply fresh and clean outside air in the right amount into the space.  The key parameter is cleanliness, i.e. the air stream is free of pollution and dust. To achieve this, we can equip our ventilation device or ductwork with an appropriate filter. An accepted standard on the market are class G4 filters (according to the withdrawn EN 779 standard) or their equivalent Coarse filters with efficiency 60-70% (according to the new, current ISO 16890 standard). The new applicable standard defines Coarse (coarse filter), ePM1, eMP2.5, ePM10 air filter classes. The numbers 1, 2.5 or 10 mean the size of particulate matter (PM), i.e. 1, 2.5 or 10 microns (µm), while the percentage is the filtration efficiency. Therefore the ePM2.5 70% filter, for example, filters 2.5-micron particles with 70% efficiency.

The lists of additional equipment for ventilation devices for residential buildings often include F7 filters or eMP1 50-65%. It should also be noted that the old EN 779 standard had 5 classes of pre-filters and fine filters, while the ISO 16890 classification differentiates over 30 classes. The mentioned above aspect and different test methods of the particles size tested means that there is no direct possibility to compare old and new classes. However, the new methodology allows for better and more accurate filter selection in relation to the outside air quality and the expected indoor air quality.

Aif filter for PremAIR heat recovery unit

An example of a fabric air filter for heat recovery units

What does EUROVENT recommend?

Eurovent, which is the biggest European organisation dealing with ventilation systems, recommends using a filtration level according to the quality of indoor air (ODA) and the expected quality of supplied air (SUP). The recommended air quality in residential buildings is SUP2 category and the table below helps you to select the minimum filter for permanent residence (e.g. heavily industrial areas require ODA 3, as average annual PM concentration exceeds the WHO guidelines by a factor > 1.5).

Tabela minimalna skuteczność filtrów

Table of recommended minimal filtration efficiencies acc. to Eurovent Guide 4/23 2018..

ODA (Outdoor Air) and SUP (Supply Air) are the abbreviations for outdoor-air and supply-air quality
* Minimum filtration requirements ISO PM1 50% refer to a final filter stage
** Minimum filtration requirements ISO PM2,5 50% refer to a final filter stage

It should be noted that the ePM1, eMP2.5, and ePM10 suspended particulate matter is the main component of smog, and in highly polluted areas 90% of the dirty air gets into buildings if no air filtration is used. Thus, the initial barrier to polluted air will be an air filter installed in your heat recovery unit. It will be a non-woven, fabric filter. Such filters are quite cheap but require frequent changing. Naturally, they also generate resistance (pressure drops), which increase with the dirt level. The use of such air filters with increased filtration efficiency is too challenging for the standard fans installed in household air handling units.

Anti-smog air filter MOCarz series

Anti-smog air filter series MOCarz: standard version - MOCarz, version with an activated carbon MOCarz-CA and newest one - electrostatic filter e-MOCarz.


How does an electrostatic precipitator work?

The use of electrical discharges is an interesting and completely different filtration method. Thanks to corona discharge, it is possible to purify air from dust using electrostatic precipitators. In design terms, the filter consists of two main parts – the ionization and the collector section. Polluted air flows through a strong electric field (produced by a conductor, e.g. wires), where the air particles get ionized receiving, for example, a positive charge. Ionization consists in releasing cations (+) or anions (-) from atoms or particles. The charged particles migrate towards the oppositely charged electrodes, which act as a dirt collector. Thanks to this technology, requiring no filtration fabric, flow resistance is extremely low, just a few Pascals.

This means that you can easily expand your system with such a filter, not worrying whether the fan or recuperator will handle the extra load. This translates into very low running costs resulting from low energy consumption (less than 10 W) and no need to replace filtration inserts. The electrostatic filters can be washed many times and, if undamaged, they can last for years. The investment cost is higher, but it can be repaid in 2 to 5 years in a typical home installation (up to 450 m3/h), when compared to using a standard filter with regularly replaced inserts.

Electrostatic Precipitator

Electrostatic Precipitator eMOCarz

The e-MOCarz electrostatic filter features all of the advantages mentioned above. The maximum filtration efficiency of the ePM1 filtration is as high as 95%. Even with airflow over 700 m3/h, it will still filter with eMP2.5 80% efficiency.
The efficiency of the filter, depending on airflow and airspeed (as per ISO 16890):

Filtration efficiency table for e-MOCarz

Filtration efficiency table for e-MOCarz filters.

The e-MOCarz filter has a maximum power consumption of 9 W. It can be fitted with suitable duct connectors with a diameter of 160, 200 or 250 mm. Optionally, an ionizer for filtered air is also available (negatively ionized air has a positive effect on your mood and health), or a module with active carbon granules, which will effectively trap any unpleasant smells.

echnical sheet for electrostatic filter eMOCarz
Electrostatic precipitator e-MOCarz - the highest level of air filtration
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Alnor Ventilation Systems
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05-552 Wola Mrokowska

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