HEPA and ULPA Filters for Cleanrooms

A terminal filter sits as the last stage of air handling, mounted directly in a cleanroom's grid ceiling or in a filter housing, and it's what determines how clean the air actually is by the time it reaches the working area. Three of the four panels in this range – the NanoClass Square Pro Membrane KE, EF KE and EF FL – are stated to retain viruses, bacteria, toxic dust and aerosols as they pass through.

The range covers both panels for gel-sealed grid ceilings in cleanrooms and clean benches, and panels built for mounting in filter housings, terminals and ductwork.

Three of the four panels are classified under EN 1822, the European standard for HEPA and ULPA filters. The NanoClass Square EF KE spans the full range from E11 to U16 in three installed depths (86, 109 and 134 mm). The NanoClass Square EF FL is available in HEPA class H13 (>99.95%) or H14 (>99.995% at MPPS) in four installed depths from 30 to 150 mm. The NanoClass Square Pro Membrane KE is a dedicated H14 filter (>99.995% at MPPS) built around a pleated e-PTFE membrane instead of microglass fibre, giving an extremely low pressure drop at just 109 mm installed depth.

The fourth panel, the AirSquare Pro Flange HT, is not an EN 1822 HEPA/ULPA filter at all – it's classified ISO ePM1/ePM10 under ISO 16890, a fine-filter standard. It's built in microglass fibre with cotton-thread separators in a galvanised steel frame, rated to 120°C with high burst-pressure resistance, and is Eurovent Certified Performance. Its role in the range is as a pre- or final filter ahead of, or independent from, a HEPA/ULPA stage – not as a HEPA/ULPA filter itself.

Both the NanoClass Square Pro Membrane KE and NanoClass Square EF FL state their efficiency "at MPPS" – Most Penetrating Particle Size. It's the particle size at which a filter medium is least effective at capturing particles, because very small particles move diffusively while larger particles are caught by direct interception; somewhere between those two mechanisms sits a minimum in capture efficiency.

EN 1822 requires a filter's performance to be tested and stated at exactly that weakest point, rather than at an arbitrary or favourable size. An H14 rating of >99.995% at MPPS is therefore the filter's guaranteed floor – at every other particle size, capture is at least as good.

The NanoClass Square Pro Membrane KE and NanoClass Square EF KE both have an integrated knife-edge for gel-sealed grid ceilings: the frame's sharp edge presses into a gel-filled channel in the ceiling grid, forming a continuous, joint-free seal without gaskets or fasteners. That makes it fast to swap a panel without breaking the ceiling's integrity, which is common in pharmaceutical production and other grid-ceiling cleanrooms.

The NanoClass Square EF FL instead uses a flange frame for mounting in filter housings, terminals and ductwork, sealed with a neoprene gasket on one or two sides, with a protective grille available as an option. The AirSquare Pro Flange HT uses the same flange principle, in a galvanised steel frame.

The NanoClass Square EF KE and EF FL both specify a recommended pressure drop of 450 Pa (maximum 600 Pa), operating temperature up to 70°C (peak 90°C), and resistance to 100% relative humidity. The NanoClass Square Pro Membrane KE's e-PTFE membrane gives an extremely low pressure drop by construction, is 100% boron-free, and is supplied guaranteed leak-free (scan-tested). At the other end of the range, the AirSquare Pro Flange HT is built specifically for elevated temperatures, rated to 120°C with high burst-pressure resistance – well beyond what the EN 1822 panels specify.

Three of the four panels – NanoClass Square Pro Membrane KE, EF KE and EF FL – list ISO 14644 among their applicable standards. Cleanroom classification under ISO 14644 is based on measured particle concentration in the room, not on filter class alone, but a terminal filter's capture efficiency at MPPS is a precondition for which class is achievable at all: the stricter the required ISO class, the higher the demand on the filter's performance.

Exactly which filter class is required for a given ISO class depends on the room's full design – air changes, layout and process – and should always be checked against a complete cleanroom design rather than the filter class in isolation.