Keep in mind that ‘anything’ Node-RED can do, we can do on a groov Box.
So in effect, this is a 99% Node-RED question, not a groov question (and I might move this post to the Node-RED category to get more appropriate eyes on the question).
That said. It would seem that DF1 only has light support in Node.JS and none in Node-RED.
Looking at the usual flows.nodered.org does not show anything.
BUT, there is this node on NodeJS…
To use this npm module you will need to follow this guide; http://jamesthom.as/blog/2016/01/04/npm-modules-in-node-red/
There is also this project (from 6 years ago) that might be worth a prod; https://github.com/leicht/Df1
Also this project for the Pi claims that it can run DF1 over RS232; https://sourceforge.net/projects/advancedhmi/ You might get some tips from following some clues from it.
BUT, all that said, why not just use Opto?
Once its in a PAC Controller, it is dead nuts easy to hook that to groov… Skip Node-RED all together.