Craig Chapman explores the impact of the new EN779:2012 standards and Eurovent 4/11 passive energy ratings on filter products
Numerous far-reaching and much-needed changes in both product testing and representation have hit the air filter world during the last 18 months. EN779:2012 supersedes the 2002 version, while Eurovent 4/11 passive energy ratings have been introduced from A to G, in much the same manner as those displayed upon kitchen white goods.

Both moves will have a positive effect upon the health and hygiene of the mechanical ventilation system, with most air filters manufactured using synthetic, nanofibre and polypropylene media now being downgraded to a new and lower 'M' rating, or creating unsustainably high resistance to air volume.

These synthetic filters rely upon an electrostatic charge to catch and hold particulates. That charge then encounters problems in an urban environment where the airborne carbons present in traffic and factory pollution neutralise it, which in turn sees filters drop from typical initial 75%-80% filtration efficiency at 0.4µm, to below 20%, according to Eurovent test figures.

Microfine glass filter media passes the new standard and test procedures consistently well, however such products tend to be more expensive to purchase, if not to use.

With energy costs typically ranging between 9p/kW and 12p/kW, the phrase, 'it costs a lot more to use an air filter, than it does to buy one' is most relevant.

Purchasing managers should discuss filter budgets with energy managers, because in many cases the ability to achieve nett free filter supplies, within the overall costs of running a HVAC system, are very possible.

Finance and energy
It is quite feasible to save over £200 with each 592mm x 592mm filter over a course of 18 months compared to previous practices, through using higher capacity, lower resistance filters within inverter controlled air handling units (AHUs) - with back-up temperature systems - while also vastly improving air hygiene.

The Eurovent 4/11 passive energy formula and resulting ratings, refer to how much fan energy is required to move air through different types of air filter. As they are graded by their filtration standard, a better - denser and more efficient - air filter will typically require more fan energy to move the required air volume, than for a lower efficiency filter.

Many designs of higher efficiency filter will catch more and therefore fill up faster, increasing resistance to air flow.

The dust holding capacity of the filter also comes into play as higher capacity filters fill slower, the resulting lower resistance to airflow is vastly more beneficial to the user if it can be sustained over the longest period.

GVS Filter Technology UK (formerly Nationwide Filter Company) believes that the test standard of 100g dust loading is perhaps a little low to represent the long-term sustainability of an air filter, and works within the spirit of an advisory energy rating.

It has also been noted that many AHU inverters reach their 50Hz peak rate long before typical filter 'change' resistance is reached. In such circumstances, changing the filter is the cheaper option as opposed to running a falling air volume for the next few months.

The Eurovent fan energy formula can also be used to demonstrate that the common practice of keeping air filters for an additional six months to 'save money' can cost three to four times more than the overall cost of installing clean, lower resistance filters and running the AHUs at slower fan speeds, while the air hygiene levels will of course benefit from such a practice.

Physics and biology
Other movement within the air filtration industry is to consider both the physics and biology of air filtration. The physics aspect of air movement is of course important, however the product is called a 'filter', which will determine the air hygiene of the building for the next six to 12 months and therefore should be selected with this fact in mind.

The air filter is located within the air handling unit, which draws in all manner of trace-level, airborne micro-organisms along with the required air volume.

Within four to five metres, the temperature and humidity levels of the incoming air are changed dramatically and perhaps future test standard updates could refer to what effect these climatic changes have on the airborne bacteria, fungi, algae and yeast which settles within the filter and around any front-end frost coils.

The air handling unit creates what is essentially a micro-climate, while the dark, warm, moist location of many designs of air filter forms a virtual incubation chamber.

During warmer months, air handling units are cooling warm, moist air. High filter resistance can slow the air speed significantly which, if not compensated by effective inverter systems, typically sees the output from chiller systems increase, creating condensation within the AHU while also wasting energy.

Drip channels can drain away low levels of condensation, however the air filters will also become damper, accelerating the cell growth rate of various micro-organisms caught within them.

Numerous studies are available regarding how volatile organic compound forms and the effects it can have within a sealed ventilated building.

Many building engineers carry out regular checks for legionella and pseudomonas in AHU condensation traps. However the likes of aeromonas hydrophilia, klebsiella, listeria, proteus and alcaligenies will thrive under such conditions within the air filters and even an F8 filter, under constant air pressure, has a permitted 10% penetration rate. These, and many other micro-organisms can have a profound effect upon certain products and of course, upon the health of the building occupants, especially in health care buildings where many patients have lowered immune systems or take blood-thinning medication.

Likewise, autumn spores such as Cladosporium Sp, which can severely affect those with even minor respiratory ailments, will enjoy a significantly longer lifespan protected from frost within an air filter, than they will in the atmosphere.

Historically in the UK, the FM contractor supplies the filters along with other replaceable parts, while the client pays the energy bill. The Eurovent 4/11 ratings are designed to help bring together both sides to discuss the best approach.

Several filter manufacturers have been working hypothetically along these lines for a few years, even perhaps against the wording of the 2002 standard, however the Eurovent 4/11 ratings now give much needed recognition to what can be achieve by a well-planned approach to air filtration.

// The author is sales engineer at GVS Filter Technology (formerly Nationwide Filter Company) //