What differentiates cleanroom HVAC to conventional systems?

Cleanroom HVAC design encompasses much more than conventional temperature and humidity control. Typical office building air contains from 500,000 to 1,000,000 particles (0.5 microns or larger) per cubic foot of air. A Class 100 clean room is designed to never allow more than 100 particles (0.5 microns or larger) per cubic foot of air. Class 1000 and Class 10,000 clean rooms are designed to limit particles to 1000 and 10,000 respectively. A clean room differs from a normal comfort air conditioned space, in the following ways.

Increased Air Supply:

Whereas comfort air conditioning would require about 2-10 air changes/hr. A typical clean room would typically require 20 – 60 air changes and could be as high as 600 for absolute cleanliness. The large air supply is mainly provided to eliminate the settling of the particulate. And dilute contamination produced in the room to an acceptable concentration level.

The use of high efficiency filters:

The use of high efficiency particulate air (HEPA) filters having filtration efficiency of 99.97% down to 0.3 microns is another distinguishing feature of clean rooms. The HEPA filters for stringent clean rooms are normally located at the terminal end and in most cases provide 100% ceiling coverage.

Room pressurization:

The clean room is positively pressurized (to 0.05 in-wc) with respect to the adjacent areas. This is done by supplying more air and extracting less air from the room than is supplied to it.

There is much more into the design of clean rooms in terms of details of technology of equipment. The type of filtration, efficiency, airflow distribution, amount of pressurization, redundancy, noise issues, energy conservation etc…etc…