1. Casing (Enclosure)
- Definition: The external structure or housing that holds all FAHU components (filters, coils, fans, dampers, etc.).
- Function:
- Provides mechanical strength and stability.
- Prevents air leakage (should meet international leakage class standards).
- Protects internal components from environmental damage.
- Reduces heat transfer and noise to/from the surrounding environment.
- Construction Materials:
- Galvanized steel (most common).
- Stainless steel (for corrosive or hygienic applications such as hospitals, pharma).
- Aluminum (lightweight, corrosion-resistant).
2. Panels
- Definition: The side walls, roof, and base plates of the casing, usually built as modular panels.
- Types:
- Single-Skin Panels: Simple metal sheets; used for small/low-cost FAHUs.
- Double-Skin Panels: Two metal sheets with insulation sandwiched between.
- Importance:
- Double-skin panels improve thermal insulation (reduces energy loss).
- Provide acoustic insulation (quieter operation).
- Ensure durability and better IAQ (no condensation, no microbial growth inside).
3. Insulation
- Purpose:
- Prevents heat gain/loss through FAHU casing.
- Reduces condensation risk on panels.
- Provides sound attenuation (reduces fan/airflow noise).
- Types of Insulation:
- Polyurethane Foam (PUF): Excellent thermal insulation (k ≈ 0.020–0.024 W/m·K).
- Polyisocyanurate (PIR): Higher fire resistance than PU foam.
- Rockwool / Mineral Wool: Fire-resistant, good acoustic performance, slightly lower thermal efficiency.
- Thickness:
- Typically 25–50 mm depending on climate and application.
- Thicker insulation for hot-humid climates or healthcare projects.
4. Performance Standards
- Thermal Break Design: Prevents condensation at metal joints by using insulating separators.
- Leakage Class: Complies with EN 1886, SMACNA, or Eurovent standards.
- Panel Strength: Must withstand fan pressures and external loads.
- Fire Resistance: Insulation material should be fire-rated for safety.
5. Example: Hospital FAHU
- Casing: Stainless steel for hygienic surface.
- Panels: Double-skin with 50 mm PIR insulation.
- Internal coating: Anti-microbial coating to prevent bacterial growth.
- Result: Maintains sterile, energy-efficient, and quiet operation.
6. Example: Commercial Office FAHU
- Casing: Galvanized steel with powder coating.
- Panels: Double-skin with 40 mm PU insulation.
- Extra feature: Acoustic lining to reduce fan noise in open-plan office supply ducts.
