RACA Journal March 2022 | Página 29

Feature

changes per hour ( ACH ). The required air flow from the HVAC system is then calculated using the ACH and room volume . In comparison with a conventional commercial HVAC system , cleanrooms can reach as many as 250 air changes per hour , or more . It has been said in illustration , the effectiveness of these filter ’ s efficiency is extremely high , and the very next best thing is a brick wall . No matter what type of classed room an engineer is dealing with , the filter configuration will be of great importance .

* Some references state : ‘ particulate absorption or particulate arrestor ’

Table 1 : Example of required air changes per hour ( ACH ) per ISO Class

Once the ACH requirement is known as well as the room size , the air flow can be calculated as well as the filter configuration , and how many filters are required . Each filter ( and there are

Something that is highlighted quite often from a clientperspective is that a request comes through for an ‘ ISO 7 cleanroom ’ as an example . An ISO classification does not define a cleanroom in terms of function and layout . It only defines the cleanliness level of the air that needs to be met , or the maximum quantity of air particles allowed in a space .

The cleanroom classification will , however , influence the layout of a facility . For instance , you can enter certain classed rooms directly from an uncontrolled environment . Conversely , you will need at least one airlock before entering an ISO 6 environment , and so on . These aspects of facility design are important to keep in mind from the planning phase as well as to ensure the correct pairing of air filtration .

A cleanroom is also not simply the floor , walls , and ceilings . Cleanroom HVAC systems differ from conventional commercial systems due to significantly increased air supply , specific engineered airflow patterns , the use of high efficiency filtration , room pressurisation needs ( positive or negative ), and air extraction .

In order to meet the required ISO class , air must pass through either high efficiency particulate air ( HEPA *), or ultra-low particulate air ( ULPA *) filters . Essentially , the lower the ISO class , the more often the air need to pass through the filter ( s ) – the air