Filters in FAHU

1. Importance of Filters

• Protect occupants by removing dust, pollen, smoke, bacteria, and harmful particles.
• Protect downstream HVAC components (coils, ducts, diffusers) from clogging and fouling.
• Improve Indoor Air Quality (IAQ) and comply with ASHRAE 62.1, EN 779, ISO 16890 standards.
• Different spaces (office vs. hospital) require different filtration levels.

2. Types of Filters in FAHU

🔹 a. Pre-Filters

• Efficiency: Low efficiency (MERV 4–8 / G2–G4 in EN standard).
• Particle Size Removed: Large particles >10 µm (dust, lint, pollen, hair).
• Material: Washable synthetic fibers, aluminum mesh, or nonwoven fabric.
• Purpose:
  • First line of defense against coarse dust.
  • Extends life of fine and HEPA filters.
• Applications: Used in all FAHUs as the primary stage.

🔹 b. Fine Filters (Secondary Filters)

• Efficiency: Medium to high (MERV 9–13 / F5–F9 in EN standard).
• Particle Size Removed: 1–10 µm (smaller dust, bacteria carriers, smoke).
• Material: Pleated synthetic fiber or glass fiber media.
• Purpose:
  • Improves IAQ by removing smaller particles.
  • Protects sensitive areas and equipment.
• Applications:
  • Offices, malls, airports (F7–F8).
  • Healthcare general areas (F9).

🔹 c. HEPA Filters (High-Efficiency Particulate Air)

• Efficiency: ≥99.97% at 0.3 µm particle size (H13, H14 in EN 1822).
• Particle Size Removed: Very fine particles including bacteria, viruses, smoke, allergens.
• Material: Ultra-fine glass fibers arranged in pleats.
• Purpose:
  • Critical for sterile environments.
  • Ensures protection from airborne infections.
• Applications:
  • Hospital operating rooms, isolation rooms, ICUs.
  • Pharmaceutical production & cleanrooms.
  • Labs requiring contamination-free environments.

3. Filter Arrangement in FAHU

Filters are arranged in stages to maximize efficiency and lifespan:

1. Pre-Filter (Coarse) → Captures large particles.
2. Fine Filter (Secondary) → Captures medium to small particles.
3. HEPA Filter (Final) → Installed only in critical applications.

🔹 Example:

• Office FAHU: Pre-filter + Fine filter (F7).
• Hospital FAHU: Pre-filter + Fine filter (F9) + HEPA filter (H13/H14).

4. Pressure Drop & Maintenance

• Each filter creates resistance (pressure drop) to airflow.
• Pressure drop increases as the filter gets dirty.
• Differential Pressure Gauges or sensors are used to indicate replacement time.
• Maintenance:
  • Pre-filters → washable, replaced every 3–6 months.
  • Fine filters → replaced every 6–12 months.
  • HEPA filters → replaced every 1–2 years (depending on usage).

5. Comparison Table

6. Practical Example

• Hospital Operating Room FAHU:
  • Pre-filter (MERV 8) → removes dust/pollen.
  • Fine filter (F9) → removes bacteria carriers.
  • HEPA filter (H14) → delivers sterile air to OT.
• Office Tower FAHU:
  • Pre-filter (MERV 6).
  • Fine filter (F7).
  • No HEPA (not required, saves energy).