Typically you should expect your cooling systems to consume approximately 20% of the total amount electricity consumed by the miners. Less of course during the winters. Properly cooling 400 miners is not simply an equation as there are many external factors that must be considered. Humidity levels, deviation of outside temperature during the day and night, and consideration for heavy rain environments. The most cost effective way of cooling 400 miners is to do a wall separation between the "cold", and "hot" isle. This wall should have cut-outs for each ASIC miner. You want to do this because air will take the least path of resistance, and much of your airflow will go around your miners on the rack.

So let's talk numbers. 400 Antminer s9s will require 48,000 CFM of exhaust for proper cooling in warm environments. You should do five 10,000 CFM fans. They key is to be able to turn off individual fans to lower your CFM when days are cooler. You NEVER want to assume pushing a lot of air is a good thing for the miners. Too much air can cause the fan guards to get too cool and build condensation. This will lead to corrosion on the heat sinks. Typically for this amount of miners, you should also include a fan that can re-inject the hot exhaust air back into the cold isle. You will want to do this in the winter and keep the "cold" isle around a constant 80 degrees F. There are automatic systems that can be designed to do all of this for you.

Your intake side will not require fans. Your exhaust fans will pull the majority of the airflow into the mine. You will want to use 5 or 6 48" weather hoods where the intake square cutouts are. You will then use metal pre-filters followed by "sock" disposable filters. You will want to change out your filters once every 4 months and clean your pre-filters once a year.