Heating — In a 15 °C hall, one extra degree adds 6.7% to the heating bill. ➤
Ventilation — Air pulled out of a heated hall is heat you paid for. Off, at 30%, at full: you see which. ➤
Lighting — An aisle nobody walks, a hall lit through lunch, a switch nobody flipped on Friday. All paid for, none of it useful. ➤
Left running — A machine that is on but doing nothing costs nearly as much as one doing work.. ➤
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A control system runs equipment. It was never built to find waste.
A thermostat exists to hold one point at one number. It does that job perfectly while the building around it runs four degrees too warm — because the rest of the building was never its business.
Most control systems store little or nothing. Without history there is no trend, no comparison between this winter and last, no proof — only the number on the panel right now — no way to know whether it is still true.
Heating knows nothing about the gate left open. Lighting knows nothing about the empty aisle. No controller knows that a machine has been running with nothing to do since lunch.