Filtering out confusion
December 1st 2005 Higher standards of filtration, coupled with rigorous attention to filter selection and maintenance result in cleaner, purer air and fewer indoor air quality problems. Graham Bentley of Jasun Filtration explains
Good indoor air quality depends on a number of factors, including effective filtration, that provides the primary defence for building occupants and HVAC equipment against particular pollutants. Selecting HVAC filters based on the needs of the facility instead of simply their initial cost will lead to a review of filter efficiency as a determining factor.
Filtration efficiency defines how well the filter will remove contaminants. Low-efficiency filters are typically used to keep lint and dust from clogging the heating and cooling coils of a HVAC system. Medium and high efficiency filters are typically used to remove bacteria, pollen, soot and other small particulates.
There are many types of HVAC filters. In most buildings, the best choice is a medium-efficiency pleated filter, that has a higher removal efficiency than low-efficiency filters, and more adequately removes the particles that cause IAQ problems, unlike high-efficiency filters that would clog.
The pleated air filters used in HVAC systems are made with a wide range of media, including fibreglass, polyester, cotton, paper and synthetic non-woven materials.
Advances in non-woven technologies have allowed a stepchange improvement in both performance and value of synthetic media over the standard cotton/poly blends used for years in HVAC filters. The synthetic media can be made of thermally bonded, continuous hydrophobic polyolefin fibres that resist shedding and do not absorb moisture.
This is important in resisting bacterial growth, and it keeps shed fibres from getting into HVAC coils or into breathing air. Synthetic media can be made without the use of chemical binders, so humidity will not affect the web structure and will not cause the glue to soften and, thus, fibres to shed.
Unlike cotton/polyester filter media that are made with a surface-loading structure, synthetic filter media can be made with a gradient density structure that provides a solid mechanical foundation to maintain high efficiency over the useful life of the filter. After specifying a filter media and selecting a filter, it's important to pay close attention to correct installation. The goal is to avoid bypass air by making sure that all the air in the system goes through the filter. Bypass air causes contamination in housings, coils, fans and ducts. Air filters should be monitored and maintained to provide maximum filtration, while not overtaking the supply fan capability or leading to blow-out situations with no air filtration. Proper filter maintenance is crucial to keeping the ductwork clean. If dirt accumulates in the ductwork, and if relative humidity reaches dew point (so that condensation occurs), bacteria and mould may grow. This is especially the case in HVAC systems with acoustical duct liners, that are frequently used in air handler fan housings and supply ducts to reduce sound transmission and provide thermal insulation.
It is crucial to establish the appropriate filter change strategy. Filters should be changed immediately if they become wet, if microbial growth on the filter media is visible, or when filters collapse or become damaged to the extent that air bypasses the media. Make the job as easy as possible. One tip is to place labels on the housing units with information, such as number and type of filters, date changed, and pressure drop. Air handlers that are located in hard-to-access places are more likely to suffer poor air filter maintenance. Therefore, quick release and hinged access doors for maintenance are desirable when security is not an issue. When changing the filter, make sure that the replacement is of the correct size and comparable with your housing. Review the performance value of the filter to ensure the pressure drop will not be too great, especially as the filter loads. The greater resistance will reduce the air flow to the unit, creating a negative impact on the unit's heating/cooling efficiency and energy efficiency. Time filter change-outs for when the facility is unoccupied, this will help avoid problems associated with disruptions in the HVAC system, and possible distribution of odours or emissions. If this is not possible, turn off the supply fans to prevent debris entering the ductwork downstream of the filters. When removing a spent filter, take care to avoid dropping contaminants into the ductwork.
It is important to follow the recommendations of the filter manufacturer to determine proper procedures and frequencies for maintaining and changing filters. And don't forget to document all inspections and corrective actions.
Remember, correct filter selection and maintenance can contribute greatly to better indoor air quality.
Bulletin
Established in 1972, Jasun Filtration believes it is the UK's oldest independent air filtration manufacturer.
Managed by Graham Bentley and Colin Hitch, the company manufactures a wide range of filtration products, that it distributes to a spectrum of customers in both the industrial and commercial sectors.
The company operates from two sites in Bridgewater and a third in Sittingbourne Kent, that specialises in producing air filters for the commercial kitchen ventilation industry.
For more information, contact: Graham Bentley, Jasun Filtration Riverside House Parrett Way Bridgewater somerset TA6 5LB Tel: 01278 452277 E: info@jfilters.com More articles from Jasun Filtration Plc: | 
