Bipolar Ionisation

It disperses positively and negatively charged ions into the air, which react with VOCs, bacteria, viruses and particulate matter — breaking down or clustering them so they're easier to filter out or fall out of the breathing zone entirely. It's a long-established technology, with the underlying ionisation process studied for over a century.

These various indoor air quality improvements can also lead to a reduction in energy costs, when utilised correctly. Due to the reduced need for HVAC cleaning and filter changes, ventilation systems can go longer without servicing.

The cost of worker ill-health due to workplace air quality also cannot be understated; BPI reduces the likelihood of absenteeism due to work-related health complications.

Bipolar ionisation HVAC integration position depends on your HVAC system design.

AHU-mounted: treats incoming air before it reaches occupied spaces, clustering ultrafine particles that have passed through filters and breaking down VOCs as air moves through the ductwork.

Branch duct-mounted: lets you match the level of ionisation to the pollutant load in specific zones, useful where different parts of a building have different air quality demands.

FCU-mounted: ions are generated and distributed into the room almost immediately, giving the highest concentrations and strongest effect at the point of need. Maintenance can be carried out alongside routine FCU filter servicing.

 

Properly designed, UL2998-certified, bipolar ionisation systems don't produce any measurable levels of ozone.

Some older or uncertified ionisation devices can produce ozone as a by-product, which is exactly why certification matters when choosing equipment (but simply turning down the power level can sometimes ease this concern). 

We exclusively specify and install Plasma Air systems that are UL2998 certified for zero ozone emissions, so you get the air-cleaning benefit without the risk.

Ionisers broadly fall into two categories. Dielectric barrier discharge (DBD), which applies more energy and can produce fragmentary, reactive ions, and a small amount of ozone. Needlepoint bipolar ionisation (NPBPI) is currently the most widely used ionisation product — considered safer as it doesn't form as much ozone. It's the technology behind the systems we specify, chosen for its strong evidence base and consistent safety profile.

The two work differently and often complement each other.

Bipolar ionisation disperses charged ions into the airstream and out into occupied spaces, reacting with VOCs, particulates and pathogens wherever air travels.

UVC (or UVGI) uses ultraviolet light, usually installed inside the AHU, to sterilise coils and break down organic matter such as bacteria, viruses, and mould as air passes directly through the light's path — its effect is largely confined to the unit rather than the room beyond it.

Many of our installations use both together: ionisation for room-level air cleaning, UVC to keep AHU components hygienic and cut maintenance. We go into more detail in our UVGI vs bipolar ionisation comparison article.

Dielectric Barrier Discharge systems require replacement tubes approximately every 24 months.

There are no consumables to replace for needlepoint systems (NPBPI).

All BPI units need periodic inspection, electrode cleaning, and ion output verification to keep performance consistent. For ionisers fitted into FCUs, this is usually carried out alongside routine filter servicing; for AHU and duct-mounted units, we can build inspection into your existing ventilation maintenance schedule.

BPI is an enhancement, not a substitute.

Ions still rely on air movement to reach contaminants, so effectiveness depends on having good air distribution alongside a correctly sized, correctly placed device. We check both as part of our assessment.

Outside of the UK, ASHRAE 62.1 you can reduce outdoor air requirements if using air cleaning technologies. Our CEO, Adam Taylor, presented at the CIBSE ASHRAE 2020 Technical Symposium; you can read the abstract below.

Although the positives definitely outweigh the negatives, bipolar ionisation is not perfect. There are no magic bullets for improving air quality. For example, it can't break down nitrogen dioxide or carbon dioxide. Read more about the pros and cons in our blog.

A comprehensive review published in the Journal of Negative Results in Biomedicine, titled A Comprehensive Review of Air and Respiratory Function Outcomes, analysed more than 60 years of peer-reviewed research into the effects of air ions on human health. The authors concluded that, collectively, the available evidence does not provide reliable proof that either negative or positive air ions have any measurable effect on pulmonary, respiratory, or metabolic function.


In addition, independent laboratory testing and real-world installations have consistently demonstrated that needlepoint bipolar ionisation technology does not increase ozone, carbon dioxide, volatile organic compounds (VOCs), nitrogen dioxide, or fine particulate matter. Instead, it has been shown to significantly reduce concentrations of airborne pollutants, often to levels well below those typically found in outdoor air.

The majority of solutions for improving indoor air quality have a significant cost in terms of consumables and/or energy consumption.

Bipolar ionisation is an inexpensive addition to an HVAC system that costs very little to run.

Using just a small amount of electricity to run continuously, ionising units only cost a few pounds per month to keep running.