Theory 38/Society, Computation & Engineering /Infrastructure
Water Use Is a Wet-Bulb Ratio
Water efficiency is compared per technology. The weather may dominate.
Data centre water consumption is set by the ratio of cooling load to ambient wet-bulb depression rather than by the cooling technology, so a site with a favourable climate can use less water with a worse system.
01The evidence
Water use varies widely between sites with the same cooling design, and the variation tracks local humidity and temperature.
02The tension
Efficiency metrics are quoted per technology, which predicts consumption from the design and treats climate as a correction.
03The mechanism
Evaporative cooling consumes water in proportion to the heat rejected and inversely to how much the air can absorb, which is the wet-bulb depression.
That makes the ratio the determinant, and predicts consumption should track it rather than the technology class.
04What this is not
Those ratings compare designs. This compares climates, which explains variation within a class.
05Predictions
- P1Consumption should track the load-to-depression ratio.
- P2Favourable climates should beat better technology.
- P3Climate should explain more than design.
06Refutation
Consumption tracking technology at controlled climate would restore design ratings.
07What it changes
It would change site selection for data centres.