AHU Filter Selection and Calculation

AHU Filter Selection and Calculation

Understanding AHU Filter Selection in HVAC Systems Filters are critical components in an AHU because they remove dust particles and help maintain indoor air quality. Proper filter selection improves system performance, protects cooling coils, and reduces maintenance costs.

Common Filter Types in AHU:

• Pre Filter - Removes larger particles (5-10 µm )
• Fine Filter - Removes medium particles (1-5 μm )
• HEPA Filter - Removes very fine particles for clean environments

Typical applications:

• Office AHU → Pre + Fine Filter
• Clean Room → Pre + Fine + HEPA
• Pharmaceutical Area → Multi-stage filtration

Filter Area Calculation Formula:

Required Filter Area = Airflow ÷ Face Velocity

Example:

Airflow = 5000 CMH

Convert airflow:

5000÷3600 = 1.39 m³/s

Assume filter face velocity:

2.5 m/s

Filter Area:

1.39÷2.5

Required Filter Area = 0.56 m²

A=QVA=\frac{Q}{V}A=VQ

Where:

A = Filter area (m²)

Q = Airflow (m³/s)

V = Face velocity (m/s)

Recommended Face Velocity:

• Pre Filter → 2.0-2.5 m/s
• Fine Filter → 1.5-2.0 m/s
• HEPA Filter → 0.45-0.6 m/s

Typical Pressure Drop:

• Pre Filter → 30-60 Pa
• Fine Filter → 70-150 Pa
• HEPA Filter → 150-300 Pa

Correct filter selection helps achieve:

• Better air quality
• Lower fan energy consumption
• Reduced maintenance frequency
• Longer equipment life