Filter replacement criteria for supply air ceiling filters (4 determination methods, priority: pressure difference > leak detection > appearance > usage duration)
1. Core determination: Pressure difference value (the most standard, GMP / hospital mandatory basis)
Each filter is equipped with an independent pressure difference meter. If the pressure difference exceeds the limit, it should be replaced immediately, regardless of the usage time.
Primary efficiency filter (G3/G4)
Initial pressure difference: 40-60 Pa
Final resistance threshold: ≥ 100 Pa
Treatment: Can be disassembled for water washing. If the pressure difference remains high after washing, it should be replaced.
Intermediate efficiency filter (F7/F8/F9)
Initial pressure difference: 70-110 Pa
Final resistance threshold: ≥ 200 Pa
Treatment: Cannot be washed. If the pressure difference meets the standard, it should be replaced immediately.
HEPA/ULPA high-efficiency filter (H13/H14)
Judgment rule: Actual pressure difference ≥ initial pressure difference × 2
Example: Newly installed high-efficiency filter with an initial pressure of 120 Pa, rising to 240 Pa, must be replaced.
Supplement: The fan automatically increases frequency, the air volume significantly decreases, and the room fails to reach the set cleanliness level, which are basically caused by filter blockage and increased pressure difference.
2. Leak detection determination (specific to high-efficiency filters, replace immediately if leakage occurs)
Only for the end HEPA/ULPA filters, no leak detection is required for the primary and intermediate efficiency filters.
Annual third-party PAO/DOP aerosol leak detection;
Single measurement point leakage efficiency not up to standard, frame sealing leakage;
Filter body has penetrating leakage points.
Any one of the above conditions is met, regardless of the pressure difference, it must be replaced immediately, otherwise the cleanliness level will not meet the requirements and the acceptance cannot be passed.
3. Visual inspection of appearance (quick judgment during daily inspection)
Primary / intermediate efficiency visible features
Large areas of blackening on the filter surface, thick accumulated dust, water washing cannot restore transparency;
Filter material damage, frame deformation, sponge sealing strip detachment;
Moisture, mold, water stains, oil stains adhering.
High-efficiency filter appearance abnormal (replace immediately)
Filter paper collapse, wrinkles, damage, holes;
Water accumulation inside the box, filter material moldy and yellowish;
Sealing glue cracking, filter edge and corner deformation and leakage;
Long-term fumigation disinfection causing filter material brittleness and powder shedding.
4. Supporting judgment based on environment and operating conditions
The following phenomena indicate that the filter has failed or is severely clogged:
The particle concentration in the clean area continuously exceeds the standard, and the settled bacteria and airborne bacteria are not up to standard.
The air velocity at the supply air ceiling outlet is uneven， with no wind in some areas；
Under the same fan frequency， the indoor pressure difference continuously decreases， unable to maintain positive pressure；
Fan noise increases， severe heating， long-term full-load operation.
5. Time is only an auxiliary reference (cannot be the sole basis for replacement)
Only when pressure difference， leak detection， and appearance are all normal， it serves as a management warning：
Primary efficiency： The longest 3 months without cleaning is recommended for maintenance；
Intermediate efficiency： After 12 months， it is recommended to check the pressure difference；
H14 high-efficiency after 1.5 years， H13 after 2 years， ULPA after 5 years， conduct comprehensive leak detection and pressure difference measurement.
6. Summary of replacement priority (operational sequence)
Pressure difference exceeds limit → Replace immediately (the first standard)
PAO leak detection exceeds standard → Replace immediately
Filter material damage， mold， deformation → Replace immediately
Long-term non-compliance with cleanliness level， insufficient air volume → Investigate the filter and replace
Reaches the preset usage period → Check the pressure difference， replace as needed