HVAC for cleanroom

FAVEA builds HVAC systems for cleanrooms in accordance with GMP standards.

Cleanrooms maintain particulate-free air through the use of either HEPA or ULPA filters employing laminar or turbulent air flow principles. Laminar, or unidirectional, air flow systems direct filtered air downward in a constant stream towards filters located on walls near the cleanroom floor or through raised perforated floor panels to be recirculated. Laminar air flow systems are typically employed across 80 percent of a cleanroom ceiling to maintain constant air processing. Stainless steel or other non-shed materials are used to construct laminar air flow filters and hoods to prevent excess particles entering the air. Turbulent, or non-unidirectional, air flow uses both laminar air flow hoods and non-specific velocity filters to keep air in a cleanroom in constant motion, although not all in the same direction. The rough air seeks to trap particles that may be in the air and drive them towards the floor, where they enter filters and leave the cleanroom environment.

Selected ISO 209 airborne particulate cleanliness classes for cleanrooms

numbers (N)	Maximum concentration limits (particles/m3 of air) for particles equal to and larger than the considered sizes shown below
	0.1mm	0.2mm	0.3mm	0.5mm	1mm	5.0mm
ISO 1	10	2
ISO 2	100	24	10	4
ISO 3	1 000	237	102	35	8
ISO 4	10 000	2 370	1 020	352	83
ISO 5	100 000	23 700	10 200	3 520	832	29
ISO 6	1 000 000	237 000	102 000	35 200	8 320	293
ISO 7				352 000	83 200	2 930
ISO 8				3 520 000	832 000	29 300
ISO 9				35 200 000	8 320 000	293 000

The table is derived from the following formula:

C_n = 10^N x (10/D)^2.08

where:

C_n represents the maximum permitted concentration ( in particles/m³ of air ) of airborne particles that are equal to or larger than the considered particle size. Cn is rounded to the nearest whole number.

N is the ISO classification number, which shall not exceed the value of 9. Intermediate ISO classification numbers may be specified, with 0.1 the smallest permitted increment of N.

D is the considered particle size in mm.

0.1 is a constant with a dimension of mm.

The table shows a crossover to the old FS 209 classes e.g. ISO 5 is equivalent to the old FS 209 Class 100.

The standard also gives a method by which the performance of a cleanroommay be verified i.e. sampling locations, sample volume etc.. These are similar to FS 209. It also includes a method for specifying a room using particles outside the size range given in the table 5. Smaller particles (ultra fine) will be of particular use to the semiconductor industry and the large (³ 5mm macro particles) will be of use in industries such as parts of the medical device industry, where small particles are of no practical importance. Fibres can also be used. The method employed with macro particles is to use the format:

'M(a; b);c'

where

a is the maximum permitted concentration/m³

b is the equivalent diameter.

c is the specified measurement method.

An example would be

'M(1 000; 10mm to 20mm); cascade impactor followed by microscopic sizing and counting'.