You are totally correct for default OCs, but he underclocks them really hard, it could be viable to use AC with a single hole (let's say 10cm2) and small industrial fan.
He can reduce power consumption by a modest 30-40% but that will result in a much lower hashrate, the more efficient the less the hashrate, and since his power is free and most likely very limited he should utilize the power used by ACs to run a few miners instead, the only scenario in which he would be forced to use an AC would be for noise reduction where a large hole in the wall with a large duct fan attached to it will be noisy.