Most submetering guides stop at "pick an accurate meter." But a meter that cannot talk to your building automation system or analytics platform is a stranded asset. The integration protocol — usually Modbus or BACnet — determines how your data gets out of the meter and into something useful. Picking the wrong one means gateways, translators, and integration headaches later.
What These Protocols Do
A communication protocol is the shared language that lets a meter, a controller, and software exchange data. Modbus and BACnet are the two dominant options in commercial buildings. They are not interchangeable, and many meters speak only one of them natively — so how many submetering points your building actually needs and where they live drives the protocol decision as much as the BAS does.
Modbus — Simple, Fast, Everywhere on Meters
Modbus is a lightweight, widely supported protocol that comes in two main flavors: Modbus RTU, which runs over serial (RS-485) wiring, and Modbus TCP, which runs over Ethernet/IP. It is simple to implement, inexpensive, and extremely common on submeters and power monitors. Its limitation is that it carries raw register data with little built-in context — the integrator must know what each register means.
BACnet — The Building Automation Native
BACnet is the protocol designed specifically for building automation, and it dominates HVAC and BAS environments. It comes as BACnet MS/TP (serial, RS-485) and BACnet/IP (Ethernet). Its advantage is rich, self-describing objects: devices expose named points with units and metadata, which makes large-scale integration and interoperability far cleaner. The tradeoff is more complexity and typically higher cost.
The Real Decision — Follow Your BAS
The practical rule is to match the meter to the system that will consume its data. If your data is destined for a building automation system, choosing BACnet-native meters usually eliminates a translation layer. If your meters report to a dedicated energy dashboard or analytics platform — or you have a simple, meter-only network — Modbus is often the cheaper, simpler path. Mixing protocols is common and workable, but each boundary you cross needs a gateway.
Gateways and When You Need Them
A protocol gateway translates between Modbus and BACnet (or onto MQTT/cloud platforms). Gateways are routine and reliable, but each one is a device to buy, configure, and maintain, plus a potential point of failure. The cleanest designs minimize protocol boundaries; if every meter and your BAS already speak BACnet, you may need no gateway at all.
Serial vs. IP — A Wiring Decision Too
Within either protocol, you choose serial (RS-485 daisy-chain) or IP (Ethernet). Serial is cheap and proven for runs of modest distance and device count; IP scales better, integrates with existing network infrastructure, and simplifies remote access — at the cost of network engineering and security considerations. Many buildings run serial at the meter level and bridge to IP at a gateway.
Specification Tips
In your spec, state the required protocol and physical layer (e.g., "BACnet/IP" or "Modbus RTU over RS-485"), the register or object map, the polling rate, and any gateway requirements. Confirm the meter's native protocol before purchase — and pair the protocol decision with the right CT and meter accuracy class for the use case. Retrofitting protocol support after the fact is where budgets break, especially in no-shutdown retrofit deployments.
There is no universally "better" protocol. Modbus wins on simplicity and meter ubiquity; BACnet wins on building-automation interoperability. Decide based on where your data needs to land, minimize protocol boundaries, and specify the physical layer explicitly.