Filters & air cleaning units Filter with a killer instinct
‘Air cleaning units’ - certainly a more appropriate term for the practice of achieving air hygiene within HVAC systems, than ‘filters’. The reality is that many air filters do not ‘clean’ air says Craig Chapman
micro-climate creat- ed by most mechanical ventilation systems, the air filters act as the hygiene tool and yet they collect a very wide range of bacteria, fungi, algae and yeast, which then incu- bates in dark, warm, moist sur- rounds and under constant air pressure for 6-12 months at a time. Some larger gram-positive bacteria and fungi spores will be held with- in most filters, however many smaller, acidic, rod-shaped, gram- negative pathogenic cells can easi- ly penetrate filters under constant air pressure, often where filter capacity is exceeded by air volume or where filters are made from media quite rightly downgraded in EN779:2012. Even the yellow F8 microfine bag filter has a minimum penetration allowance of 10 per cent under lab conditions. The existing EN779:2012 air filter test standards managed by Eurovent are carried out in nominated labora- tories and utilise specific test dust, therefore there is no opportunity to observe or report the bacteria cell activity typically caught from out- door or re-circulated indoor air, and neither is the volume of air entering a building ‘after’ the filters specified, which greatly affects the cost of heating or cooling a building. The test is a useful guideline and absolutely filter-specific, yet many filters supplied within the UK market are not submitted for testing – ask for your supplier’s EN779:2012 test certificate.
Where building occupants are healthy with strong immune sys- tems, problems caused by the above described conditions will of course be fewer, however reports of ventilation-associated illness and infections are coming through from schools, leisure centres and of course hospitals, where the occupants mostly have impaired immunity through illness or chemo and warfarin-type medication. The well-publicised drive against hos- pital acquired infections has not dented the previous one in 10 rate, which has led planning teams to closer investigate how HVAC can assist infection control. GVS offers a solution which in most cases, more than pays for itself in energy saving and carbon reduction-associated benefits. The
30 | July 2014 | HVR
Above:
The Bacticell Filter from GVS Below: An example of dirty ductwork
award-winning Bacticell filter is impregnated with anti-microbial agent Bacti-G. This is NHS and MOD tested to kill-on-contact a very wide range of gram positive and negative micro-organisms, long term, without evaporating in a warm airstream. Bacti-G is impregnated throughout the filter media prior to pleating for 100 per cent coverage.
The Bacticell can be retro-fitted into most air handling units without a pre filter and whilst significantly improving the hygiene of the tem- pered air, it will in most cases, reduce HVAC system kWh too. Its aero-dynamic construction is proven as GVS utilises the same mini-pleating techniques in the vac- uum filters we design and supply to the biggest names in that industry. Proving its worth as both ‘Air Conditioning and Sustainable Product of the Year’ in the trade press, the Bacticell will lower fan motor kWh in variable speed (VAV) systems long term and through maintaining unrivalled air volumes with very little compara- tive drop-off over 8,000 AHU hours, will often prevent back-up heating or cooling apparatus from coming on line, to compensate for lost air change per hour rates which distribute this expensively created tempered air.
It will be very interesting for most buildings to calculate their 18 month filter budget versus the sav- ings from their back-up chiller sys-
tem staying offline throughout the coming summer months. Filter waste reductions of up to 80 per cent can also be achieved, along with many saved man-hours from changing filters every six months. Back to the hygiene aspect again, condensation within an HVAC system is usually caused by air being slowed down and over- cooled, often due to high filter resistance preventing optimum air volumes. Some of this can be drained away through specific floor traps, however the filters also adsorb airborne moisture which acts as a catalyst for the micro- organisms caught within. By main- taining air volumes and therefore reducing the need for such high level cooling within the AHU, the Bacticell acts as a preventive and a reactive tool, especially in high humidity leisure centre and chilled food production environments. GVS has also noted other knock-on benefits from fitting the Bacticell filter. Internal comms room air coolers, fan coil units and the likes of hospital theatre canopies all benefit from tem- pered air being better distributed from source, thereby reducing the kWh of the entire mechanical ven- tilation system and not just the AHU fan motor.
There is talk of trialling UV-C systems to reduce indoor airborne pathogenic bacteria levels, (e.g.) between hospital patients, staff and visitors. UV-C does not actual-
ly kill bacteria and requires strictly controlled air movement. In this role, GVS recommends the Aircare air cleaner which in a previous life was the ‘Daddy of Pub Smoke Cleaners’. It filters to F8 level, kills bacteria, absorbs airborne odours and is used increasingly more in healthcare, rest homes, police sta- tions, offices etc. The World Health Organisation will soon be introducing ODA/IDA comparisons (outdoor air/indoor air) for all non-residential build- ings, which will root out under- performing filters. GVS now offers this service and has recorded improvements by a factor of 8+ for office blocks alongside the busy M6 motorway in the Midlands, through using Bacticell filters in AHUs. The sub 2.5 micron particle penetrates lungs and enters the blood stream, affecting immune system capabilities. GVS now offers two ‘Physics & Biology of Air Filtration’ training seminars, one focused on health- care HVAC and the other more commercially based. The health- care presentation has been recom- mended for CPD recognition. // The author is an air hygiene specialist with GVS Filter Technology //
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