Highly efficient electrostatic precipitators purify circulating air from air conditioning systems while killing viruses

Highly efficient electrostatic precipitators purify circulating air from air conditioning systems while killing viruses

To cool the air in production halls, supermarkets and other premises, air conditioning systems are often used in air recirculation mode – but without the addition of a filter. The air is drawn from the room, cooled by the air conditioner and fed back into the room. The circulating air is considered to facilitate the spreading of viruses, as the circulating air keeps the aerosols in motion. Integrating a highly efficient filter into the circuit prevents viruses from being distributed via this system.

Aerosols transfer viruses

The coronavirus COVID-19 (SARS-CoV-2) is mainly transmitted via aerosols in the air and only to a small extent via droplet and smear infection. Aerosols are mixtures of gas (usually air) and solid or liquid components. In infected people, the lungs increase the production of aerosol particles which are then released via respiration. These miniscule airborne particles are mainly released during breathing and speaking. While larger droplets sink to the ground after only about 1.5 meters due to their weight, however aerosol particles float through the air for up to several hours due to their small size (about 0.1-0.4 µm). Air recirculation systems intensify this aerosol movement and distribute them thorugh the entire room.

Electrostatic precipitators filter viruses from the circulating air, killing them in the process

To extract viruses from the exhaust air, many filtration systems are based on HEPA filters. However, scientific articles show that these fabric filters are only suitable to a limited extent. First of all, HEPA filters extract the viruses from the  exhaust air but they do not simultaneously inactivate them. Thus, aerosols and viruses are agglomerated in the filter and are hence prevented from re-entering the circulating air. However, this way dense filter fabrics form a breeding ground for bacteria and viruses. Therefore, replacing the filter regularly by safety-trained personnel is highly necessary. Furthermore, retrofitting HEPA filters into existing air recirculation systems leads to a significant increase in pressure loss: First, the exhaust air has to pass through a pre-filter before entering the HEPA filter, otherwise the HEPA filter would clogg quickly. All in all, high pressure losses occur, which result in increased fan performance and thus lead to a higher energy consumption and increased noise.

This is not the case with electrostatic precipitators. KMA electrostatic precipitator cells have been developed for the high-grade separation of a large particle spectrum (from smallest particles below 1 µm up to dust and aerosols of more than 10 µm) and, due to the filter design, and present practically no pressure loss. The ionization electrode of the electrostatic precipitator generates a strong electric field on low energy input. The resulting charge difference forces impurities in the incoming exhaust air, including viruses, to settle on the collector plates. The high voltage of 12 – 12.5 kilovolt ensures that viruses are killed. For particularly high safety standards (e.g. for SARS-CoV-2 viruses), KMA offers an additional UV light level. it uses moisture-resistant high-performance UV tubes with vacuum UV radiation to eliminate the virus. Scientific tests have shown that intensive irradiation with UV light at an appropriate radiation dose ensures a separation of over 99.998% even at extremely high virus concentrations.

The filter’s durability and consistently high performance is based on its robust design. The entire filter construction, as well as electrodes and support rods are made of stainless steel, the collectors of aluminum and the insulators of durable ceramic. Unlike HEPA or other mechanical filters, no contaminated filter media needs to be replaced. In contrast, the KMA electrostatic precipitators are cleaned automatically by the integrated filter cleaning system, which contributes to their proven longevity. The filter elements are additionally sterilized, through cleaning with 95°C hot washing water or alternatively with steam. The electrostatic precipitator is therefore characterized by its high energy efficiency and high-grade separation efficiency.

Specializing in large exhaust air volumes

KMA exhaust filtration systems are available in different sizes. The module sizes are staggered and are determined according to the occurring exhaust air volume. The largest modular unit has a capacity of 30,000 m³/h. To filter even higher exhaust air volumes, two or more filter modules can be connected in parallel. KMA has installed more than 3,000 filter plants in various industries worldwide.

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Highly efficient electrostatic precipitators purify circulating air from air conditioning systems while killing viruses

Ansgar Dobers

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KMA realises efficient air filtration in production plants of Nemak in Slovakia.