The air-handling system serving a cleanroom is called a purification air-conditioning system in China's GB 50073-2013 Code for Design of Clean Rooms. Unlike comfort air conditioning, it cannot manage temperature and humidity alone; it must hold three targets at once: cleanliness, temperature/humidity and room pressure differential. The core equipment of a central system is the modular air handling unit (AHU).
GB/T 14294-2008 defines a modular AHU as air-handling equipment assembled from functional sections, for systems with a resistance of at least 100 Pa. By application, the standard divides units into general, fresh-air, clean (purification) and special-purpose units; clean plants use the clean type.
1. Choose the system layout first: three common routes
| Layout | Typical use | Characteristics |
|---|---|---|
| AHU with single return air + ductwork + HEPA terminals | ISO Class 6-8 | Low investment; temperature and humidity are controlled jointly in one return-air loop |
| MAU + FFU + DCC | ISO Class 1-5 and high-precision spaces | The MAU (make-up air unit) sets the dew point, the DCC (dry cooling coil) handles sensible heat, FFUs (fan filter units) cover the ceiling |
| MAU + RAU (recirculation units) | Multi-room plants with very different zone conditions | One recirculation unit per zone; flexible zoning |
Most electronics assembly and pharmaceutical support areas use the first layout, so the rest of this article follows the single-return-air AHU route.
2. Sections are combined as needed, but their order follows a logic
An AHU has no fixed set of sections. GB/T 14294-2008 lists mixing, flow equalizing, filtration, cooling, primary and secondary heating, dehumidification, humidification, supply fan, return fan, water spray, sound attenuation and heat recovery; each project selects them by l