What a Data Center Chilled Water Buffer Tank Does (and Why It Matters) A chilled water buffer tank is a small-volume, thermally insulated storage vessel placed on the chilled-water side of a data center cooling plant. Its job is to decouple chiller run-time from instantaneous load swings so the compressors do not start and stop too often. For a data center, where IT load and free-cooling share shift minute to minute, the buffer tank is one of the cheapest reliability upgrades