Hello all: I am a newbie here so may this question was brought up. We have a building with a canteen for workers. 

The canteen uses AHUs to provide outdoor air, but the total cfm does not comply with ASHRAE 62.1 requirements. It also has operable windows, and the operational area comply with natural ventilation requirements. I was wondering if this situation can fulfill with the IEQ P1?  Or should I do a Mixed-Mode Design Calculations with CIBSE Applications Manual 13?

Because the 62.1-2010 Section 6.4 said, “Natural ventilation systems shall be designed in accordance with this section and shall include mechanical ventilation systems designed in accordance with Section 6.2 and/or Section 6.3.”.

But the CFM of mechanical systems is not enough, I am not sure in this case if it is in accordance with Section 6.2?   If I use the exception for mechanical ventilation, it requires “. Natural ventilation openings that comply with the requirements of Section 6.4 are permanently open or have controls that prevent the openings from being closed during periods of expected occupancy. Does this mean I should add some window control?

Thanks