6 CLEAN ENVIRONMENTS
Required number of HEPA filters
Required air flow
cubic feet per minute
Nb of HEPA filters
(1 HEPA = 500 CFM)*
13 333 CFM ÷ 500 CFM = 27 HEPA filters
1 000 CFM ÷ 500 CFM = 2 HEPA filters
* The amount of air (CFM) processed by a HEPA
filter differs for every model. Check the number of
CFMs your HEPA filters process.
Author’s tip: In our calculations, we always design
our cleanroom HVAC with a slightly higher number
of air changes per hour (ACH) and a higher number
than the average (but not the highest) of CFM the
HEPA filter can supply. Consider that the filters will
accumulate dust and therefore after some time will
require more power to maintain the flow.
2. 4) Low air return
Generally speaking, you need approximately the
same number of low air returns as the number of
HEPA filters. However, just like HEPA filters, every
air return model differs. The quantity of air returns
depends on their capacity, as every model on the
market is different. The number of air returns may
be higher or lower than the number of
HEPA filters, depending on whether
they can process more or less air than
the HEPA filters allow into the room.
2. 5) Pressurization
Cleanrooms are held in positive pressure, except when dealing with hazardous products, which must be held
in negative pressure. Positive pressure
will force the air flow out of the room
instead of into it. This means that the
air in the cleanroom will have a tendency to leak out of the room, instead
of in, thus preventing unfiltered air or
air particulates from entering into it.
To prevent contamination of rooms
from particles from an uncontrolled
environment, we add an anteroom
between the classified area and the
uncontrolled space, and increase the
pressure of this anteroom, which acts
as an airlock.
The pressure differential prevents
contaminants and particles from
moving from the lower pressure side to the high
pressure side. Therefore, the pressure cascade is
the key to the cleanliness of the cleanroom.
However, with hazardous products, we want
the opposite effect: the pressure is negative in
order to prevent air that might be contaminated
by hazardous products from escaping the room.
3) Full flush design to help you maintain your class
Full flush design isn’t mentioned anywhere in the
ISO 14464-1 norm; however, it is highly recommended for the lowest classes (ISO 7 and lower).
This will not only facilitate the validation process
but will also make your daily cleaning tasks much
easier. Reaching the desired cleanroom class at
commissioning and certification is one thing, but
keeping it clean day after day while your employees are inside working is a harder task. Easy to
clean walls and fully flush designs (wall-to-wall,
wall-to-ceiling. and wall-to-floor covings, windows, lighting, and air returns) will make the
maintenance task a much easier one.
Charles Lipeles is the VP of U.S. Business
Operations for MECART, a Canadian manufacturer
of modular cleanrooms. MECART also has its own
design and installation teams for a turnkey customer
solution. Charles has 25 years of experience in the life
science industry and in semiconductor manufacturing. firstname.lastname@example.org; www.mecart-cleanrooms.
The low air returns of
this ISO 6 cleanroom are
illustrated by the blue