Room control
BACnet: planning an interface between building systems and AV
If you want to display building data in an AV interface, first define the information you need and the decision it should support. The building management professional can then identify an available point and a way to share it while preserving the existing system logic.
Start with the PICS and exact model
The PICS is the manufacturer’s statement of the BACnet capabilities implemented in a product. Use it to review object types, properties, services and network options. Match it to the installed model, firmware and protocol revision.
The BTL listing identifies the tested product version and functions. It supports component selection; the specific AV combination also needs an agreed point list and planned checks.
Prepare a point list that can be interpreted
| Item | What to request | Why it matters |
|---|---|---|
| Identity | Device, object type and instance, and property | Avoid selecting a point by display name alone. |
| Meaning | Description, data type, unit and scale where applicable | Distinguish a measurement from a setpoint or indication. |
| Access | Required reading and approval from the system professional | Separate displaying information from changing it. |
| Freshness | How it updates and when to show unavailable data | Avoid presenting the last received value as current. |
| Verification | Expected value, reference source and reconnection behavior | Define what to observe in a later test. |
What Present_Value means
As a specific reference, Beckhoff TF8020 documentation for BACnet Revision 14 describes Present_Value as the current object value. It distinguishes analog, binary and multistate data. Its Analog Input table separates required and optional properties and write access; do not transfer every field unchanged to another product.
For a reading, also agree on the state information accompanying the value and how the platform indicates missing updates. The presence of Present_Value does not establish that the data has the unit, meaning or freshness your interface needs.
Proposed example: displaying an environmental reading
Suppose the BMS can share a noncritical environmental reading. The AV interface would display the value, its unit and an indication of freshness. If updates stop, it should mark the reading as unavailable or stale according to the agreed criteria. This reading would not operate HVAC equipment or establish an occupant count.
- Building professional → approved point and meaning.
- Documented BACnet interface → available value and state.
- AV interface → data, unit and missing-update indication.
What to confirm with the building professional
Ask which communication option the installation uses and which option the AV platform supports. Ethernet ports at both ends do not establish shared support for every BACnet function. Start with documentation; network access and any testing require specific coordination.
This scope covers noncritical AV information. Fire systems, evacuation, access control, machinery and safety functions are excluded from the proposed interface. The building professional retains responsibility for building operation and control.
- Manufacturer, model, firmware, PICS and applicable BTL listing.
- A point list you can share without passwords or private network topology.
- Required reading, unit and stale-data criteria.
- AV platform and the maintainer at each end.
Questions to define the inquiry
Is a BACnet label on both devices enough?
No. Compare the documented functions of both products and the specific point to be shared. The protocol name does not replace that review.
Does displaying a point allow its value to be changed?
Reading and writing are different functions. To display information, agree on read access and scope; do not assume or request write access when the function does not need it.
Can I inquire without a complete point list?
Yes. A label photo, a description of the information you need or a preliminary diagram can help identify which documents to request from the building professional.