Azero-energy building (ZEB) is a popular term to describe buildings with zero net energy consumption and zero carbon emissions annually. A ZEB is basically a residential or commercial building with greatly reduced energy needs through efficiency gains.
These ZEBs will need effective ventilation supplying high indoor air quality (IAQ), which in turn will require the use of high-quality air filters.
Evolution of filter classes
Over the years, the filter industry has seen the basic purpose of air filtration shift. Air filters used to be selected to protect ventilation equipment - today, their main function is to improve the indoor climate and protect the health of people. Today's polluted air in urban environments may cause headaches, cardiovascular and respiratory problems. Clean filtered air, on the other hand, leads to improved work performance, reduced absenteeism due to illness and enhanced well-being.
Filter classes have also progressed from low filter levels, such as G4 and F5, to today's high filtration classes, F7 and F9, with F7 being the most common and minimum class for guaranteeing acceptable IAQ.
Unfortunately, there is a paradoxical relationship between filter classes and energy savings because the better the filter, the higher the energy consumption since a filter's resistance to air flow and pressure drop often increase.
Due to their resistance to the air flow, air filters account for at least 30 per cent of a ventilation system's energy consumption today.
With energy costs spiralling, the cost of cleaning, supplying and exhausting air in buildings has consequently become a major concern today and the choice of the right filters important. Improving the energy efficiency of HVAC systems is one way to make buildings greener and combat climate change.
Within Eurovent, the European Committee of Air Handling and Refrigeration, the issue of pressure drop has been discussed considerably and the energy classification of filters. The Eurovent Guideline 4/11 - Energy efficiency classification of air filters for general ventilation purposes, is ready and published on the Eurovent web site.
Starting in January 2012, Eurovent Certification will certify all fine filters, that will be assigned an energy efficiency class (A to G) tested according to EN779:2011. They will also be classified according to their annual energy consumption, initial efficiency and minimum efficiency (ME).
A welcomed initiative
The new European standard for air filters (EN779:2011) comes into force in autumn 2011. Its purpose is to classify air filters based on their minimum filtration efficiency (ME) on 0.4µm particles. The industry has now voted for tougher requirements for air filters and the standard has been published in August this year. National versions will be available in mid-November, after which the former standard will no longer apply.
The new standard will help eradicate a number of problems related to filter performance. One of these problems is associated with electrostatic-charged synthetic filters. These filters usually demonstrate good initial filtration efficiency while they keep their charge, but tend to discharge extremely rapidly, often after just a few weeks of operation. F7 performance in the lab for an electrostatic-charged filter can therefore decrease to F5 in real operating conditions, and sometimes even more. Their cleaning ability deteriorates considerably as a result. Unfortunately, far too many European buildings are now using electrostatic-charged F7 filters that have medium efficiency (ME) values between 5 and 10 per cent.
As a consequence, as much as 90 to 95 per cent of the contaminants in outdoor air find their way into buildings and pollute the indoor environment.
By basing classification on an ME of at least 35 per cent for F7, the new EN779:2011 standard will force these filters out of the market. At the same time, it will contribute to the development of synthetic filter materials offering considerably higher particle separation.
Not all filters are the same
Regrettably, the price for this will include higher pressure drops and increased energy consumption.
There is one major concern about the new classification: while the 'worst' filters will vanish from the market, there is a possibility that "good" filters will be made 'worse'. Although energy savings can be achieved by having the lowest possible pressure drop, such development could be retrograde.
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Richard Ringström is Product Manager, Gas Turbine Filters, Camfil Farr Power Systems, Boras, Sweden. www.camfilfarr.com/ps