Supply airflow Air changes

[Adnan86]

Hi everyone. I have a question regarding Air changes in occupied space. I am very much clear on Ashrae 62.1 Outdoor air requirements. My concern is about the total supply air changes that is to be maintained in any space. For example: A room has outdoor air requirement of 210 l/s following Ashrae. The total supply air required as per calculations is 270 l/s. The air changes obtained for 270 l/s is around 4.5ACH. Is there any requirement to maintain minimum ACH for supply air? If not then why most of the time we take 1cfm/sq.ft (5 l/s/sq.m) as minimum supply airflow rate in many applications.

 

[RossABQ]

I don't know of any Code-type requirements for SA rates; those are usually driven by cooling load (or in cleanrooms, cleanliness class).

 

[cdxx139]

There is no requirement for air change requirements, unless code required for healthcare, clean rooms or industrial spaces. The 1.0 cfm/sf is just a rule of thumb for typical cooling CFM for internal spaces for typical spaces such as an office spaces.

knowledge is power

 

[Adnan86]

Thanks Cdxx and RossABQ. Can I put the same question in other way. If I make load calculations for any space and if I get 0.5cfm/sq.ft as the supply air, Do I need to maintain minimum 1 cfm/sq.ft or the calculated airflow is enough. I read somewhere that minimum 1cfm/sqft (5l/s/sqm) is to be maintained.