Optimum start and stop: the cheapest energy saving most buildings ignore

Walk into most plantrooms and you'll find heating that starts at a fixed time — five o'clock, say — chosen years ago by someone cautious, on the coldest morning they could imagine. That caution now runs 365 days a year. On a mild April morning the building hits temperature by half six and then holds it, fully heated and completely empty, until people arrive at eight. Multiply those wasted hours across a year and a portfolio, and fixed start times quietly become one of the largest avoidable costs in the building.

What optimum start actually does

Optimum start turns the question around. Instead of "when should the plant come on?", it asks "when is the latest I can start and still be comfortable for the first person through the door?" The system learns the building's thermal response — how quickly it warms from a given inside temperature at a given outside temperature — and calculates the start time fresh each morning. Cold snap: it starts early. Mild spell: it might not start until seven. Nobody notices anything except the bill.

Optimum stop is the mirror image. Buildings hold heat; the fabric coasts. Stopping the plant a controlled period before the building empties lets the stored warmth carry comfort to close of day, shaving another slice of run time — and the same logic applies to cooling in summer.

What it needs to work

Three honest inputs. Sensors that tell the truth — an inside sensor mounted above a photocopier will teach the algorithm nonsense. Occupancy schedules that reflect reality rather than a calendar from two tenants ago. And plant that responds when asked: valves that actually close, actuators that actually move. Optimum start amplifies the quality of what's underneath it, which is why it's often the finishing move of a good commissioning visit rather than a box ticked in software.

Where it fits in the bigger picture

Pair optimum start and stop with night setback, weekend and holiday calendars, and honest zone schedules, and you have the cheapest energy programme available to any building: no new plant, no capital case, just the system you already own doing arithmetic on your behalf. It's rarely glamorous. It's reliably worth it.