We have a lot of the "silliest" answers here, from people who have no datacenter or AC experience. You put up a bounty, you get stupid spammers and beggars.

You basically have two choices:
- Traditional refrigerant air conditioning with a condensing outdoor unit,
- Evaporative "Swamp coolers", where facilities allow large outside berth for building flow-through, and the local weather is favorable.

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Evaporative cooling is measured a different way, in the temperature drop from intake air temp, with accompanying increased humidity. You can make 100F outside air into 75F inside air. However, you will need to look at the cubic feet per minute ratings of the systems to see what can keep up with your heat load. You may decide that 85F will be the maximum "output" temperature rise after air goes through your racks - for this much cooling, you will be looking at garage-door sized walls of fans from the outside and gallons of water per minute.

However, the evaporative cooling does have the advantage that you are putting in a massive outside air circulation system - the 75% of the day and year when outside air is below 75F, you will need nothing more than to run the fans.

Inside a closed air conditioned building, evaporative cooling may enhance efficiency a bit. AC removes humidity, to the point where the IDUs need to pump water out. You could add some humidity back to pre-cool the hot AC intake air (you can't humidify cold air AC output). The humidity would have to be strictly monitored to not go overboard or add more humidity than the AC can remove.

Whatever system is implemented, you need to direct airflow through your facility and systems, ideally in a typical contained hot/cool-aisle system:
*cut*