Electrostatic Filters – Improving Air Quality & Reducing Energy
The need for improving air quality inside buildings is being brought back into attention
Retrofitting Electrostatic Filters into central air handling systems is a solution for gaining E11 EPA Filtration Class, without compromising air handling unit airflow and capacity.
Contaminated central air handling systems can become breeding grounds for biological contaminants, which will then distribute the contaminates inside a building. In the last twenty years, air quality in confined indoor atmospheres has been given particular attention with regard to the protection of public health. This attention has increased further with the on-going COVID-19 pandemic crisis, which lends itself for building owners to review the risk of microbiological contamination in air handling systems and look to improve air quality.
Retrofitting and replacing traditional bag filters with Electrostatic filters are a perfect way to increase the filter efficiency of Air Handling Units (AHU) and other HVAC equipment.
Usually, the higher the filtration efficiency in a system, the higher the pressure drop through the equipment.
However, Electrostatic Filters do not use physical filter media, so they considerably reduce the pressure drop through the AHU, compared to traditional bag filters. This gives a huge advantage of increasing airflow performance and cooling capacity.
The Technology
Qey’s Electrostatic Filter Retrofit solution uses Sabiana’s Crystall 150 filter product, which has the same filtration efficiency of an E11 EPA Filter at certain flowrates.
Normal bag filters rely on filter media to ‘catch’ particles larger than the gap between the media as they pass through material. Instead of filtration media, Electrostatic Filters use an Ionizing effect to attract positively charged particles to a negatively charged Anode plate.
When the particle makes its way through the AHU, it eventually reaches the first stage of the electrostatic filter, which is a positive Ionizing field. Whilst positively charged, the particle continues to move through to the second stage to a negatively charged anode plate. This is where the particle becomes attracted to the plate and ‘sticks’ to collector, eventually dropping into the collector tray.
This process gives the air handling unit the ability to filter extremely small particle sizes, greatly improving the filter efficiency compared to bag filters and most importantly, improving the overall air quality. This is all achieved with a 150 mm deep filter assembly, that simply replaces bag filters.
Sabiana Crystall 150 Technology
Sabiana’s Electrostatic Filter product; the Crystall 150, uses a patented technology for how the particle collector tray is utilized and is patented for manufacture by Sabiana.
This new solution features two separate and distinct sections, using different construction technology, each with its own functional purposes. The first section (Stage 1), defined as an active section or polarisation, is an integral part of the supporting structure and consists of thread-like tungsten emission electrodes, whose design ensures reliability and safety without using special, delicate and expensive materials (isolators).
The second section (Stage 2), called a passive section with an induced or collection anode, consists of laminated aluminium profiles that are placed opposite to each other and suitably spaced out. They create an electric field without applying an additional power source, thus ensuring they can be removed for maintenance purposes (cleaning).
Normally, the filter cell and collector are manufactured in one piece, meaning the whole filter cell and collector needs to be removed together for maintenance.
However, with Sabiana’s Crystall 150 range of filters, when maintenance is required, the collector tray is simply removed, whilst the filter cell stays in position. The tray is then simply washed out with water and put back into position. This makes the filter substantially easier to maintain over other brands.
Thanks to this patented technology, each area of the collector is autonomous, thus avoiding any accidental short-circuits on one section that may affect the operation of the entire filter. This is important for ensuring filtration can still occur during a fault.
The standard sizes match those used in the field of mechanical filters, and have a limited depth of just 150 mm. This means it can be easily installed, not only on new air handling units, but also on retrofitted to existing units of any brand or manufacturer.
How the retrofit is done
Retrofitting and replacing traditional bag filters with Electrostatic filters are a perfect way to increase the filter efficiency of Air Handling Units (AHU) and other HVAC equipment
For a typical AHU, the existing bag filters, including the bag filter frame, is completely removed from the AHU. A new frame is installed into the AHU in the same position. This frame holds the new electrostatic filter cells in place. The filters are then simply positioned into the new frame ready for the electrical connection.
The electrostatic cells are the same standard sizes of bag filter cells, to suit retrofit applications perfectly.
A small DC power supply is then connected to a provided connection box for powering the filter assembly.
The AHU pre-filter is left in position and continues to filter the larger particles, with, the Electrostatic filter taking care of tiny particles down to 0.1 Microns in size.
The electrostatic cells are the same standard sizes of bag filter cells, to suit retrofit applications perfectly
Energy Savings
Retrofitting Electrostatic Filters also brings the ability to decrease the energy consumption of the fan of the air handling unit due to less air pressure drop through the filter. As long as demand ventilation control is utilized on the fan in the AHU, in addition to the higher filtration class that can be gained, the retrofit allows a Return on Investment figure to be calculated.
With a decrease in pressure drop, the AHU airflow increases. This then allows the fan speed to be reduced for the same airflow as before the retrofit was conducted
This ability also enables Qey’s Electrostatic Filter solution to be perfectly combined with our EC Plug Fan retrofit for Air Handling Units.
The Coronavirus question
A big question surrounding Electrostatic Filters is ‘Can it filter COVID-19 particles?’.
The answer is complex because still a lot is being learned about the COVID-19 pandemic, but the simple answer is, to some effect and it can reduce the risk of further contamination.
As we know, the Sabiana Crystal 150 filters have the same filter class as E11 EPA filters and can filter particles down to 0.1 Microns.
According to scientists, the largest known COVID-19 particles are 0.1 Microns. The smallest particles are 0.06 Microns. It is important to know that this is still not proof that the filters will filter 100% of COVID-19 particles but it moves closer to reducing the risk of contaminations that are being seen in central air handling plants in buildings. This also includes the eradication of bacterial growth that can be seen with a build-up of filtered particles on fabric filtration media.
A test was also conducted by Marche Polytechnic University, Ancona in Italy, in conjunction with Sabiana. The study is attached to the bottom of this article.
It proved that 88% of E. coli (which has a particle size of approximately 0.5 Microns in diameter), were filtered through the Electrostatic Filter. Benchmarking this against the larger COVID-19 particle size of 0.10 Microns, we can conservatively calculate that 25% of the larger COVID-19 particles would be filtered.
