1. What is a FAHU?
A Fresh Air Handling Unit (FAHU) is a specialized type of Air Handling Unit (AHU) designed specifically to condition and supply 100% fresh outdoor air into a building. Unlike a regular AHU, which often handles a mixture of fresh and recirculated return air, the FAHU focuses solely on outdoor air to maintain indoor air quality (IAQ), occupant health, and comfort.
- Purpose: To supply filtered, cooled/heated, and dehumidified air into the building.
- Core Difference: FAHU = fresh air only; AHU = mixture of fresh + return air.
2. Importance of FAHU
- Indoor Air Quality (IAQ): Ensures fresh, clean, filtered air supply.
- Comfort: Maintains temperature and humidity within desired range.
- Health: Removes contaminants, odors, CO₂, and VOCs.
- Compliance: Meets international ventilation standards (ASHRAE 62.1, local codes).
- Safety: Helps in pressurization of critical spaces (hospitals, clean rooms, escape routes).
3. Applications of FAHU
FAHUs are commonly used in buildings that require strict IAQ or high occupant density:
- Hospitals & Healthcare Facilities – to prevent infection spread, maintain sterile environments.
- High-Rise Office Buildings – to maintain comfort and meet ventilation codes.
- Hotels & Residential Towers – to ensure fresh air supply in centralized systems.
- Industrial & Pharmaceutical Plants – to provide clean air for processes.
- Educational Institutions & Airports – for large occupant spaces with high air turnover.
4. Key Features of a FAHU
- Air Filtration: Multi-stage filters (Pre-filter, Fine filter, HEPA in healthcare).
- Cooling/Heating Coils: For temperature control and dehumidification.
- Humidifiers/Dehumidifiers: For humidity management.
- Fans/Blowers: To handle large air volumes at designed static pressure.
- Heat Recovery Devices: Energy recovery wheels, heat pipes, or run-around coils to save energy.
- Control Dampers & Sensors: For airflow, CO₂, temperature, and humidity monitoring.
5. FAHU vs. AHU
| Parameter | FAHU | AHU |
|---|---|---|
| Air Source | 100% Outdoor Air | Mixed Air (Fresh + Return) |
| Primary Purpose | Ventilation & IAQ | Comfort conditioning |
| Energy Demand | Higher (due to 100% conditioning) | Lower (reuses return air) |
| Typical Use | Healthcare, high-rise, clean rooms | General building HVAC |
6. Role of FAHU in HVAC System
- Acts as the first stage in the HVAC air distribution system.
- Works with chilled water systems or DX coils for cooling.
- Integrates with BMS (Building Management System) for control.
- Supplies air to ducted systems, AHUs, or directly to occupied spaces.
- Supports energy efficiency by using heat recovery and demand-controlled ventilation.
7. Case Example
In a hospital isolation ward, the FAHU is responsible for:
- Providing 100% fresh air supply to patient rooms.
- Maintaining positive pressure in corridors and negative pressure in isolation rooms.
- Filtering air through HEPA filters to prevent contamination spread.
- Ensuring compliance with ASHRAE 170 – Ventilation of Healthcare Facilities.
