We left a 1.5 ton window unit exactly where it was and added a handful of sensors and a small controller. A model of how the room and the unit respond to cooling forecast the next few hours, and an optimiser scheduled the compressor against that forecast instead of waiting for a thermostat to trip.

The building was a bedroom, not a data hall, and we have never pretended otherwise. What carried across was the loop: measure a few points, predict what happens next, act before the heat arrives, all computed on site on the controller itself. That is the same loop now running at rack scale with Imperial College Estates.