Fan Filter Unit (FFU)

What is an FFU?

An FFU (Fan Filter Unit) is a motorised air-filtration device.

It supplies clean air to cleanrooms, laboratories, medical facilities, and minienvironments by removing harmful airborne particles during air recirculation. FFUs are installed in the ceiling grid or floor grid of the system. Large cleanrooms typically require a correspondingly large number of FFUs — sometimes from a few hundred to several thousand. FFUs are equipped with a HEPA or ULPA filter depending on the cleanliness class of the room, plus an internal fan-driven air distributor.

FFU housings are typically constructed in steel, aluminium, or stainless steel. The FFU draws air, filters it through the embedded filter, and discharges it into the room or enclosed work zone. Fan speed is controlled in one of two ways: by direct switch, or by computer over LAN.

The achievable cleanliness depends on the embedded filter:

• HEPA — removes 0.3 µm or larger particles at 99.97% efficiency
• ULPA — removes 0.12 µm or larger particles at 99.999% efficiency

Sizing Formula

nFFU = (V × N) / S

• V — room volume (m³)
• N — air changes per hour
• S — airflow rate of one FFU (m³/h)

Worked Example

Calculate the number of 575 × 1175 × 240 mm FFUs required for a room measuring 50 m × 20 m × 2 m (length × width × height):

• V = 50 × 20 × 2 = 2,000 m³
• Required air changes: N = 54 changes/h
• FFU airflow: 18 cmm × 60 min = 1,080 m³/h
• nFFU = (2000 × 54) / 1080 = 100 units

Air Changes by Cleanroom Class