Hi Lawrence,
thanks a lot for your post, it is quite useful. I am going to test it on the actual BACnet device today. what I am going to do next is to split the Array message coming out of the BACnet Read node by the fix length
Split array message to different message and copy Key to Topic

Then to switch base on the message topic, after that each message is published to a broker via an individual MQTT Topic
really new to Node-red and not into Java Script and hope this can work, will post the result here for the knowledge sharing.
thanks