Perforated Pipes forced air ventilation under slab of warehouse

I have warehouse working at -20c
with heave frost protection system
consist of perforated pipes 4 inch diameter and 34 meter lenght 9 holes around the diameter
the number of pipes is 50
I need to calculate the required air flow for this system

Why have holes in sub structure ventilation pipes ? I think the holes will allow moisture ingrees to sub structure where you do not want it.

it’s around always good to go with complete heat load and heat gain calculation to find the actual Air flow