What is BACnet?

BACnet gives every controller in a building a common vocabulary. A zone temperature is an Analog Input object, a fan command a Binary Output, an occupancy schedule a Schedule object, and every object has standard properties such as Present_Value, Units and Status_Flags.

Because the vocabulary is standard, a supervisor can discover devices it has never seen, list their objects and read or command them without a custom driver per manufacturer.

Key functions

• Device and object discovery (Who-Is, I-Am)
• Read and write object properties
• Change-of-value subscriptions
• Schedules, calendars and trend logs
• Alarms and event notification
• Prioritized commands through a priority array

BACnet is the reason a building can mix controllers from different vendors and still be run from one screen. Most commercial buildings in North America have BACnet somewhere, which makes it the main way outside software reaches HVAC and lighting.

For energy work it opens the largest flexible loads in a building. Reading BACnet points shows what the HVAC system is doing; writing them, carefully and at the right priority, lets software shift that load for tariffs or grid events.

A BACnet device holds objects; each object has properties; clients use services to act on them. ReadProperty and WriteProperty read and change values, SubscribeCOV asks a device to report when a value changes, and Who-Is and I-Am find devices on the network.

Writable outputs have a priority array of 16 slots. Life-safety functions write at the highest priorities and normal operation lower down; the device acts on the highest-priority value present, and a writer releases its slot when it is done. BACnet runs over several networks: BACnet/IP on UDP, MS/TP on RS-485 serial wiring, and BACnet Secure Connect (BACnet/SC), which uses TLS over WebSockets.

1. 01→

   Supervisor

   Who-Is, ReadProperty

2. 02→

   BACnet/IP or MS/TP

   Routed through the building

3. 03→

   Controller

   Objects and properties

4. 04

   Equipment

   AHU, VAV, chiller, lights

Voltra discovers BACnet devices and points on a building network and maps HVAC, lighting and metering points into the same device model as chargers, solar and storage. It reads alongside the existing BMS, so building alarms and energy alarms sit in one list.

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  BMS

  BACnet discovery and building points next to energy assets.

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  Voltra Edge

  The on-site runtime that reaches local BACnet networks.