2020 IMC Question on Ventilation

[jar546]

A commercial building is being retrofitted with a new ventilation system. The system design includes the use of both natural and mechanical ventilation. According to the 2020 IMC, what are the specific criteria that need to be met for this combined approach to be compliant, especially concerning the minimum airflow and control mechanisms?"

A) Natural ventilation openings alone must meet the entire minimum ventilation rate while mechanical ventilation serves as a supplement.

B) The combined system only requires the mechanical ventilation to account for 50% of the minimum required ventilation rate.

C) Natural ventilation can serve as a primary means only if equipped with automatic controls to activate the mechanical ventilation during insufficiencies.

D) The IMC doesn't permit combined natural and mechanical ventilation systems in commercial applications.

 

[Sifu]

E) Except for the either/or clause it is not expressly prohibited in intent but problematic. Little guidance. Logic must be dictate the design an effectiveness.

 

[steveray]

I thinking I looked into this once and "hybrid" ventilation was not addressed, but not prohibited...I'll have to look at 2021 to see if they addressed it

 

[Sifu]

I have seen it many times. Usually as a result of a comment that they have not provided enough outdoor air through mechanical methods. (They get real creative with ventilation schedules). Sometimes the answer is to demonstrate how a the combined mechanical and natural equal the required amounts. I have debated on the code language of either/or, but with the commentary guidance I have not prohibited it.

As far as I can tell the '21 code and commentary is the same.