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Filter tips - selection, servicing and care

Filters are too often a neglected aspect of building maintenance, says Mark Bamforth
While a single new filter may cost less than £5 itself, it can have a great impact in determining the functionality of the entire system which will have a cost thousands of pounds. That's why filters need to be replaced regularly.

Keeping filter technology and selection at the forefront of engineers' minds, however, is a big challenge in an economic climate where belts are being tightened and companies seek ways to cut corners and save money. Ironically, the increased efficiency benefits of good air filtration regimes can deliver a major cost effect saving on any system, yet this is usually overlooked in favour of short term saving.

Keeping up to date with the optimum filter specifications for a building is no easy task, but there are some simple dos and don'ts to follow:

Selection and specification
The wrong choice of filters will impact on the whole air conditioning system. We often find dirty ducts and staining on grilles which can indicate a history of badly fitted filters or the wrong regime of filter changing. Cleaning is far more costly than prevention and issues like these can be resolved by ensuring that the filters used are fit for purpose.

  • DO - look out for evidence of incorrect filtration in visibly stained grilles and dirty ducts.


  • DO - consider what you need to achieve.


  • When Sick Building Syndrome became a big health issue a few years ago, the final filter grade stipulated for offices rose to finer grades F7 or F8 (where previously the requirement had commonly been for F5 or lower).

  • DO - consider what is available, including the latest technological innovations.


  • There have been refinements in how filter technology is used in relation to media area, pressure drop, energy saving and biocides. Pleated synthetic mats, spun glass fibres or glass paper, card framed panels and bag filters are the basic building blocks of typical air filtration systems and should provide a long term benefit over the lifecycle of the building. More filter media means greater cost, but it does result in a lower pressure drop and higher dust holding, which leads to a longer filter service life and fewer changes with consequential savings in overall energy costs.

    Rigid mid-range filters using pleated glass paper can cost twice as much as an equivalent conventional pocket bag filter, yet they offer savings in energy and change costs. Their shorter length can also result in savings to air handling unit manufacturers in terms of metalwork costs.

  • DO - pick the right size.


  • Whether through laziness or ignorance, we come across many badly serviced air conditioning installations where shortcuts have been taken, resulting in gaps which largely neutralise the effectiveness of the filter.

  • DO - ensure you compare like with like in terms of efficiency, flow rate, pressure drop and construction.


  • DON'T - assume that filters which look alike will have the same specification.


  • DON'T - re-order the same filter without checking there isn't a more suitable product available.


  • DON'T - pick the cheapest or a lower efficiency to save money.

  • The ongoing filter replacement cost needs to be balanced against the quality and ability of the filter to do the job for which it is designed. The lowest cost filters are designed to remove the great mass of large particles present in the air, acting as a pre-filter to more costly filters further down the system which protect more expensive parts such as fans, coils, humidifiers and keep supply ducts clean.

  • DON'T - over specify.


  • DO - ask the supplier for advice.


  • Servicing
    The temptation can be to reduce the frequency at which filters are changed in order to make a cost saving, but failure to replace filters correctly leads to deterioration in the system's efficiency and it is far more costly cleaning and replacement of expensive key parts.

    There is a choice when it comes to changing filters - according to the pressure drop of the system, or at set time intervals e.g. monthly/yearly regardless of other factors.

  • DO - consider all the variables including whole life costs and knock-on effects.


  • DO - take into account pre-filters and final pressure drops.


  • DO - think about disposal.


  • DON'T - take a shortcut and consider only the cheapest option.


  • The author is sales engineer at D & E Filtration Services
    16 July 2012

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