Building management systems and why they under-deliver

Before you replace it, find out what it is doing

Most BMS problems are not hardware problems. They are a schedule left in place after a tenant moved out, a sensor that has failed and is reading a constant, a manual override somebody applied in 2019 to fix a cold complaint, or heating and cooling fighting each other in the same zone.

None of those cost anything to find and little to fix, and they are extremely common. A day of a competent controls engineer interrogating an existing system is routinely the highest-return spend available in a building that has one.

Time schedules that match how the building is actually occupied now.
Set points that are not fighting: a dead band between heating and cooling, not an overlap.
Sensors that are reading reality, calibrated and in sensible positions.
Overrides and holds reviewed and cleared, with a record of why each remaining one exists.
Optimum start, so the building reaches temperature at opening rather than at four in the morning.

Why it under-delivers so often

A BMS is commissioned once, by somebody who then leaves, for a building that then changes. Occupancy changes, tenants change, plant gets replaced, and the control strategy stays as it was on handover. Within a few years it is managing a building that no longer exists.

There is also rarely anyone whose job it is. The system sits between facilities, the maintenance contractor and the original installer, and the gap between them is where it stops being looked after.

What it does to a rating

Controls are credited in the assessment, so a building with proper zoning, scheduling and control is modelled more favourably than the same building without. The larger effect, though, is on what you actually spend, which is a different question from the certificate and frequently the one that gets the budget approved.

When replacement is genuinely the answer

When the hardware is obsolete and parts are no longer available, when the system cannot be interrogated or reported on, or when it is so fragmented that nobody can see the building as a whole. Those are real situations and they justify the capital.

What does not justify it is a working system nobody has tuned. Tune it first and then decide.

Questions we get asked

Is a new BMS worth the money?

Sometimes, but tune the existing one first. Most BMS underperformance is stale schedules, failed sensors, forgotten overrides and heating fighting cooling, and all of those are cheap to find and fix. Replacement is justified by obsolete hardware or an unreportable system, not by neglect.

How do I know if ours is set up badly?

Common signs are the building warm long before anyone arrives, heating and cooling running in the same zone, areas that are always too hot or too cold, and schedules that match a tenant who left. A controls engineer can usually tell you inside a day.

Does a BMS improve the EPC rating?

Controls are credited in the assessment, so proper zoning and control is modelled more favourably. The bigger effect is usually on what you actually spend, which is a separate question from the certificate.

Last updated 8 October 2026.