A Fresh Air Handling Unit (FAHU) is made up of several integrated components that work together to filter, cool/heat, dehumidify, and distribute 100% fresh outdoor air into a building.
1. Casing, Panels & Insulation
- Description: Outer body of FAHU, usually double-skin panels (inner & outer metal sheets with insulation in between).
- Purpose:
- Provides structural strength.
- Prevents air leakage.
- Reduces thermal losses and noise transmission.
- Insulation Type: PU/PIR foam or rock wool for thermal + acoustic insulation.
2. Air Filters
- Types:
- Pre-Filters: Capture large dust particles.
- Fine Filters (MERV 8–13): Remove smaller particulates.
- HEPA Filters: Used in hospitals, labs, cleanrooms (removes >99.97% at 0.3 µm).
- Purpose: Improves IAQ by removing dust, pollen, and microorganisms.
3. Mixing Box (Optional in Hybrid FAHU)
- Description: Section with dampers that mixes outdoor air with return air.
- Purpose:
- Controls the proportion of fresh and return air.
- Optimizes IAQ and energy consumption.
- Note: Pure FAHUs are 100% outdoor air, but in some cases they may include a mixing box.
4. Cooling & Heating Coils
- Cooling Coil:
- Chilled water coil or DX coil.
- Lowers air temperature and removes moisture (dehumidification).
- Heating Coil:
- Hot water, steam, or electric coil.
- Maintains comfort in cold climates.
- Purpose: Ensures thermal comfort and humidity control before air supply.
5. Humidifiers / Dehumidifiers
- Humidifier: Adds moisture in dry climates.
- Dehumidifier (via cooling coil): Removes excess humidity in hot-humid climates.
- Purpose: Maintains recommended 40–60% RH for comfort and health.
6. Fans / Blowers
- Type:
- Centrifugal fans.
- Plug fans or EC (electronically commutated) fans in modern FAHUs.
- Purpose:
- Move large volumes of air.
- Overcome system static pressure (ductwork, filters, coils).
- Control: Variable Frequency Drives (VFDs) for energy-efficient fan operation.
7. Drain Pan & Condensate Removal
- Description: Collects condensation formed on cooling coils.
- Purpose:
- Prevents water carryover into ducts.
- Drains condensate safely to waste lines.
- Design: Corrosion-resistant, sloped for easy drainage.
8. Silencers / Acoustic Attenuators
- Purpose: Reduce noise from fans and high-velocity airflow.
- Application: Important in hospitals, hotels, and office spaces.
9. Control Dampers & Actuators
- Types:
- Fresh air dampers.
- Return air dampers (if mixing box).
- Exhaust/relief dampers.
- Purpose:
- Control airflow volume and direction.
- Enable pressure balancing and energy efficiency.
- Actuators: Motorized for automatic control via BMS.
10. Sensors & Control Devices
- Types:
- Temperature sensors.
- Humidity sensors.
- CO₂ sensors (for Demand-Controlled Ventilation).
- Differential pressure sensors (for filter monitoring & pressurization).
- Purpose: Enable real-time monitoring and automation.
11. Heat Recovery Systems (Optional)
- Types:
- Energy Recovery Wheel (enthalpy wheel).
- Plate Heat Exchanger.
- Run-around Coil.
- Purpose: Recover cooling/heating energy from exhaust air → reduce energy consumption.
- Mandatory: In many local codes (UAE, Qatar, Saudi) for FAHUs handling large fresh air volumes.
12. Special Hygienic Design Features (for Healthcare)
- Antimicrobial coating on internal surfaces.
- Smooth, cleanable interiors.
- UV-C lamps for microbial control.
- HEPA filter housings with airtight seals.
13. Electrical & Control Panel
- Purpose: Controls fan motors, heaters, dampers, sensors, and communicates with BMS.
- Features: Local operation switches, overload protection, and emergency shut-off.
14. Access Doors & Inspection Windows
- Allow easy access for maintenance, filter replacement, and inspection.
- Often equipped with safety latches and viewing panels.
Summary Table of FAHU Components
| Component | Function |
|---|---|
| Casing & Insulation | Prevent leakage, heat loss, and noise |
| Filters (Pre, Fine, HEPA) | Remove dust, pollen, microbes |
| Mixing Box | Mix fresh + return air (if hybrid FAHU) |
| Cooling/Heating Coils | Temperature and humidity control |
| Humidifiers/Dehumidifiers | Maintain RH (40–60%) |
| Fans/Blowers | Move and distribute air |
| Drain Pan | Remove condensation safely |
| Silencers | Reduce noise |
| Dampers & Actuators | Control airflow and pressure |
| Sensors | Monitor IAQ, pressure, and system health |
| Heat Recovery Devices | Improve energy efficiency |
| Control Panel | Automation and BMS integration |
| Access Doors | Maintenance and inspection |
