BACnet for running a site

4 posts in this topic

Hey all,

Was wondering if any one can help me think through a project!

I come from the HVAC world, but pretty fresh in the industrial automation world.

The site as follows

  • 24X Growth ponds;  split into pairs (12X PLCs with IOs)
  • Central processing plant
  • Spread across 1sq km

Each pond pair will have its own PLC and IO with basic controls and loops.

Each pond relies upon the main plant, they are not independent system [require resources stored at the central plant]

The control processes are slow, the fastest cycle time is around 45mins (with longest being weeks) - I'm not looking for fast response.


I know BACnet quiet well, is there any reason not to use it for a job like this? That way I can have a simple setup, and run Niagara ax for easy as reporting, alarming and remote access.

Thanks for your time, any input would be appreciated :)




Edited by lizard.brain

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I've never used BacNet but if you're familiar with it, why not? 

The alternative is probably Modbus, but why switch mid-stream if you'd had success with Bacnet in the past?

I have seen several comments on Linkedin from those in the HVAC world who are migrating, when possible, to Modbus from Bacnet because of issues with inter-operability of Bacnet produc', but having to experience, I can't comment.

If you consider Modbus, RTU over RS-485 has an inherent issue with grounding and might require an RS-485 repeater Isolator to eliminate ground loops between points at long distances, where the earth grounds are at different potentials.   Ethernet is inherently isolated by design, although the spec for distance is 100m, although the signal doesn't die at 100m, you're on your own as to whether it works and how well beyond that point, so people put in a switch as a repeater at 100m intervals.

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Very few PLC's use BACNET. I actually can't think of a single one.

If you have to deal with engineering approvals I doubt they'll go with  Niagara  .

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@lizard.brain I have checked at Niagara AX sites at They can use with Modbus too then you should select device on Modbus and connect at Niagara AX. Differrent on BACnet and Modbus are BACnet use variable name but Modbus use numerical address such as 40001 to represent variable. Most Modbus Master could use maximum 32 devices on 1 nodes (for extended may be use repeater).

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