New air cleaning systems and improved filter technology and testing methods look set to improve air quality and lower HVAC energy consumption for various cleanroom applications. Susan Birks reports.
HVAC is a major quality provider but a large energy consumer for cleanroom users; however, new technologies are entering the market that could improve on the performance of current systems. This second report from the IMechE conference held in London in June looks at the topic of new air cleaning systems plus new filter requirements and innovations. Greg Kiernan, from engineering and technology specialist SciTech, highlighted several developments in non-mechanical air cleaning techniques for cleanrooms. These included systems based on ozone, ultraviolet (UV) light, electrostatics and charged field non-thermal plasma technologies.
Kiernan was well equipped to provide this overview as SciTech has recently investigated several such systems in order to specify an air system for the control of biological contamination in a client’s large germ-free animal facility. The facility had an airflow of 50m3/s through eight different zones and needed to be kept sterile for 18 months while animals were grown in isolators.
The client wanted an alternative sterilising mechanism to HEPA filters to improve sterility and performance. It also required a target of a 5 log kill for bacteria and spores and a 10 log kill for viruses. The system also had to be robust enough to cope with long-term industrial use without downtime.
Furthermore, the client requested independent test data to demonstrate the effectiveness of the technology proposed across a range of robust microbes, including gram positive/negative bacteria, endospores, and capsid viruses around the 20nm range.
The first technology considered by SciTech was ozone. This is both well established and familiar in the VOC and odour pollution sectors, said Kiernan, but despite being an excellent sterilant, it is restricted in pharma sectors to pure water systems due to a tendency to degrade elastomers and other cleanroom construction materials.
In trials, the proposed system injected 4ppmV O3 into the air handling unit with ‘in flight’ contact onto a pair of conventional H14 high efficiency particulate air (HEPA) filters and an O3 destruct catalyst or UV. This system proved promising, said Kiernan, because the air stream, which was relatively wet and thus presented a risk of mould growth, was continuously sanitised by the O3. PlasmaClean, of Stockport in the UK, is one company that can supply such systems that were able to meet the effectiveness targets required, said Kiernan.
UV germicidal inactivation is another technology used widely in the pure water industry, but this project required something more robust. According to Kiernan, post 9/11 and the anthrax attacks, the US government sought out technologies that could protect workers from biological attack. Developments from that work are now finding wider application. For example, Novatron, of California, US, produces the BioProtector line of UV devices for pharma use.
Kiernan described the BioProtector as having a reflective cavity that bounces UV light back and forth achieving a high intensity, uniform fluence of <150 mJ/cm2. This system achieved a 6–7 log kill for spores, and although the energy consumption was relatively high, it gave a greater neutralisation of airborne biological contaminants with smaller size, lower power and less cost compared with other such systems, he said.
Electrostatic systems can also help clean air by getting the particles close enough to the filter fibre for them to stick to the filter. A relatively recent version of Electrically Enhanced Filtration is the Bioplus line of in duct filters developed by US company Technovation Systems. This technology maintains the filter under an ionising field as opposed to a simple electrostatic field and keeps it high across the filter media so that air coming in gets charged, bacteria then start to stick and get caught on filter media.
The technique also improves filter penetration so that a 95% effective filter can be made to perform like a HEPA and with a lower pressure drop. “Air goes through easier, so if you put a HEPA in place, it works like an ultra low particulate air (ULPA) filter,” said Kiernan.
Non-thermal plasma systems are mostly directed towards pollution abatement but some recent systems are being used for pharma and medical air handling – the Ozone generator (PlasmaClean) and the Airmanager (Quest International) are two examples.
The latter system uses Close Couple Field (CCF) technology to generate an electron avalanche that has a disruptive effect at the atomic level on biohazards, VOCs and chemicals, explained Kiernan.
Quest is currently working with the aircraft industry on a system that removes VOCs from oil seals and cleans the recirculation air from the aircraft cabins (see Fig. 1). It also produces CCF systems for other HVAC applications. SciTech found that it could achieve more than a 5 log kill in one pass-through, and more than a 100-fold reduction of VOCs with such a system.
However, kill performance is not the only criterion to be considered. Energy efficiency is also a factor. When considering energy effectiveness, the CCF air plasma device was most effective, said Kiernan. All these systems will no doubt see modification and improvement with wider use and all deserve consideration for varying applications.
Filter effectiveness
Tim Triggs, business development director, DOP Solutions, looked at filter use in various cleanroom environments and its impact on energy use. HEPA filters are found in many applications and range from simple installations in cleanrooms to the more difficult-to-access installations, such as in ‘bag in bag out’ systems or safe change filter housing (used in nuclear, radiological, pharmaceutical and biological sectors), microbiological safety cabinets and RABS.
The key points that Triggs highlighted were that HEPA filters are not easy to test but new equipment – sparge pipes, aerosol challenge hoods and scanning probe kits, etc. – are making it easier.
The key standard for filter testing is BSEN ISO 14644, said Triggs, and the Published Document (PD) 6609, introduced in 2007, gives some practical guidance on how to apply ISO 14644. However, the current guidance covers only filters that can be face scanned and not filters that are inaccessible or within complex installations. “The irony for the cleanroom sector is that we don’t know how to test the filters for some of the more hazardous applications safely and properly,” said Triggs.
Some new guidance is on its way, however. According to Triggs, a new draft PD is currently in progress (based on Annex C), which will include advice on the testing of difficult configurations.
Data reporting
Data collection arising from the testing of these filters has also traditionally been a manual process as, until recently, there was no system or instrument available that could take data from these systems. Now there is software available to do this, said Triggs. It can provide trends and even make predictions of a likely future failure. As a result, manual data collection for HEPA filter testing will no longer be accepted as meeting standards, he said.
Triggs then looked at how energy savings can also be influenced by filter choice. For example, some filter suppliers are starting to offer filters made with new synthetic materials that offer performance and cost benefits. In addition, companies are turning down the air changes when facilities are not being used. The air changes are then ramped back up again prior to use. This action requires careful proof that the changes do not affect safety or quality, but they could be applied easily in many ancillary facilities.
New technologies, such as filter pre-ionisation systems that improve filter performance are also being developed. Triggs’ work in this area has so far been only with a pre-filter, but this has shown an initial starting pressure drop of 55 pascals and had an initial F8 grade filtration specification that traditionally would have a pressure drop of double this.
Smart buildings
Triggs also looked at technologies being developed as part of the move towards ‘smart buildings’ – buildings that adapt to changes in the external environment.
For example, what if, in regions with frequent events of high pollution, there was a filtration system that could link in to the environment monitoring and adapt to external changes? It is possible to build devices that link to a particle monitoring system of the air inlet so that the filtration modifies itself to save energy and cut costs. These systems are already being produced, he said, but in the conservative world of pharma manufacturing, adopting new technology requires much validation work.
Contacts PlasmaClean www.plasma-clean.com Novatron www.novatroninc.com Technovation Systems www.cleanroomsys.com Quest International UK www.airmanager.com DOP Solutions www.dopsolutions.com SciTech Engineering www.SciTech.com
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