Dry cooler

Rejects heat to outside air through a closed loop rather than through evaporation, so the site trades some efficiency, a dry cooler works less well on a hot day than a cooling tower, for not consuming water at all. Warm-water direct liquid cooling makes this trade viable: because the water arriving at the chips is already 30-45C, the loop can be closed all the way to outside air without needing water's higher latent heat of evaporation to reject it. Sites that publish a water-usage figure alongside a PUE figure are usually running dry coolers, or running towers and wanting credit for not needing to.