Energy management starts two floors above the fan

"Whoever is closest to the equipment manages energy best"

I heard this recently from a respected BMS manufacturer — at a joint meeting with a customer. A competitor. He said it without irony.

He developed the thought: you have to know the blade geometry of the fan in that specific air handling unit and tune the controller algorithm to that specific geometry. That, he said, is where the savings come from.

He may well have been right about the blade. I am no expert on fan aerodynamics. But that is not energy management. That is the optimisation of one parameter of one device.

Optimising a device is not the same as managing energy

Energy management is a business process. It starts two floors above the impeller. It connects the invoice, the tariff or the PPA contract, tomorrow's price forecast and the customer's production process — and only at the very end does it reach down to what the fan in the air handling unit is doing.

The difference is simple. Optimise the blade and you squeeze a few percent more efficiency out of the fan. Manage energy and you decide whether that fan should be running today at 17:00 or better at 19:00 — or whether it should stand still in a given hour, because the spot price is spiking and the carbon intensity of the grid will be low over the next few hours.

Let us put numbers on it

Picture the fan of an air handling unit rated at 30 kW, running a few hours a day.

Optimising the blade gives you, say, 3% less consumption. In practice — a few percent off the bill of that one device. Worth having. But marginal, and one-off.

Now the second lever. On a dynamic tariff, the gap between the most expensive and the cheapest hour of the day can be several-fold. If that same fan (and dozens of other loads in the facility) is simply switched off when it is not needed, or shifted (because you ventilated the space properly earlier) — without touching a single blade — you cut the cost of the same work by tens of percent. The same work, the same efficiency, a different hour. And a lever that works every day, not once.

3% from the efficiency of one device against tens of percent from the decision of "whether, and at what price". Those are two completely different orders of magnitude — and two different people in the customer's organisation who answer for them.

Where the savings really come from

Both things are needed. But they are different categories of problem. Let the blade specialists deal with the blades — they do it well.

A company's energy is not the sum of its optimised fans. It is the decision of when, and at what price, to run them — or not to run them.

"The closer to the equipment, the better" is true if the equipment is your business. If your business is a company — energy management starts two floors up.