Filtration is too often a Cinderella service. Mark Bamforth offers an overview
Filters are often out of sight and out of mind. However, neglecting them can also leave the user of an air handling (AHU) system out of pocket. While a single new filter may cost less than £5, it can have a great impact on the functionality of a system which costs thousands of pounds.

Filter selection is the first step in improving efficiency to make cost savings. So:

• DO - look for evidence of incorrect filtration. (Are the grills visibly stained and the ducts dirty?)
• DO - consider what you need to achieve
  When Sick Building Syndrome became an issue, 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 Filters are a mature product, but refinements have taken place in how they are 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 the air filtration system available to provide a benefit over the lifecycle of the building.

More filter media means more cost, but it also means a lower pressure drop and higher dust holding, which in turn leads to a longer filter service life and fewer changes with savings in overall energy costs. This provides a valuable opportunity to demonstrate energy savings.

Costing twice as much
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 offer savings to AHU 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 negate the use of the filter.
• DO ensure you compare like with like in terms of efficiency, flow rate, pressure drop or construction
• DON'T assume that filters which look alike 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 lower efficiency filter to save money; it's a false economy. The lowest cost filters, generally media pads or panels, are designed to remove large particles in the air, acting as a pre-filter to more costly filters further down the system. A well-made, well fitted and regularly monitored panel filter will save on plant maintenance, increasing energy efficiency and reducing cleaning costs.
• DO over-specify on the basis that it can only improve your whole system with knock-on effects
• DO ask for advice
  Replacing filters at the right time intervals translates to real cost savings. The temptation can be to reduce the frequency of changing in order to save money, but failure to replace filters correctly leads to deterioration in the system's efficiency and it is far more costly to clean and replace key parts.
• 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 - shortcut to consider the cheapest option

// The author is sales engineer at D&E Filtration Services //