BACnet: why “compatible” does not mean it will work

In a modern building, heating, ventilation, lighting and security all talk to each other through a shared language: BACnet. It is what allows these systems — even from different manufacturers — to understand one another and to be operated from a single supervision screen.

On paper, almost every device on the market claims to be “BACnet compatible”. In practice, it is more nuanced than that.

The problem

Two devices can both be “BACnet compatible” and still work together badly. It is a little like two people who speak the same language, one of whom knows only a very limited vocabulary: the conversation is still possible, but incomplete.

In practice this shows up during the commissioning of a building: an alarm that never reaches the supervision system, a time schedule that has to be reprogrammed by hand, a sensor whose value never appears on screen. Nothing is broken — the system simply never received the right instructions to communicate properly, because the point had not been clarified before purchase.

What to check before buying

The answer is not to trust the words “BACnet compatible” on a datasheet, but to require two things before placing the order:

• a detailed technical document — called the PICS — in which the manufacturer lists precisely what its device can actually do in BACnet: not a general promise, but a concrete list.
• an independent certification, the BTL mark, issued by a third-party laboratory that has genuinely tested the device, rather than a manufacturer's own declaration.

That is the difference between asking “does it speak BACnet?” and asking “what can it actually say, and who verified it?”

Both acronyms, and the rest of the BACnet vocabulary, are explained in our express BACnet glossary. Our BACnet object reference then lets you check, function by function, what a device needs to support.

Why it matters

A project specified properly from the outset avoids weeks of expensive fine-tuning at the end of the site, when every manual adjustment has a cost and the schedule is tight. That insistence on clarity, rather than blind trust in a marketing claim, is the difference between a system that works from day one and one you spend months catching up on.

It is also a question of independence: a device whose real capabilities are documented and verified stays replaceable tomorrow, by another brand, without rebuilding the whole installation. We made the same point when asking who really holds the keys to your building.

At Workswell this is a requirement we build systematically into our specifications and into our BMS supervision and integration projects, precisely to avoid these unpleasant surprises.