SS553 2016 7.5 refers to outdoor air treatment. The new changes are not new to most consultants, designers or engineers in which all PAU are already equipped with 2 layers of air filtration except in addition to cater to all fresh air intakes, ventilation fans(lift shaft /toilet intake) and resizing to cater the 2 layers of MERV6 and MERV14 and prefereable with gases removal (carbon) air filters either as permanent installation or the space and static pressure as required.

It applies to aircon/fans intake of outdoor air only and cater for the filters for them so they can be used when outdoor pollution level is in unhealthy range. The rational is logical as imagine during haze periods, there are fresh air or intake fans introducing the contaminants and polluted air right into buildings which is enclosed. Of course they can be partially or closed during emergency like a fire damper which closes/open when smoke is in. However, in the case the outdoor pollution comes, this might be a challenge to do it because it might not be so accesibile or feasible to seal or close all of them.

During Haze time, most of our customers/buildings should already have MERV13 mechanical air filters should not face any problems except for those cases who intake outdoor air without filtration (lift shaft intakes, fresh air intakes). Also they should have another layer MERV13 at the AHU side in which most outdoor pollution should not be a problem. To meet requirements, you can use the MERV14 instead, the slight increase in pressure drop about 20% is manageable for most systems.

The Estimated 9-10” inline duct depth with housing can cater both filters. Standby Secondary filter can be put in when required. Example, car park ventilation intake should not require these filters in normal circumstances.

  1. Carbon Pleated (act as gas phase filter and also prefilter MERV8) 24x24x2”t
  2. C90 Ccell 90-95% Merv14 24x24x4”thickness       (also available in 2” thickness but pressure drop is about 200Pa initial@3400cmh)

1. FC Frame with Synthetic Washable Media 24x24x1" thickness (can put carbon type media when required)

2. C90 Ccell 90-95% Merv14 24x24x4”thickness       (also available in 2” thickness but pressure drop is about 200Pa initial@3400cmh)

Initial Pressure Drop: 150Pa @2000cmh (1.5m/s) (system usually running at 70% at same face area 610x610mm)

Design or Recommended Final Pressure Drop: >250-350Pa @ 3400cmh (2.5m/s)

The standard PAU should have enough inline depth space, the most Ideally should be to cater 2-4" prefilter and 12-15” secondary filter slot.(can slot in the filter when required). 


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