I have a Philips Hue lighting system and a Heatmiser multi room heating control system. Both use Zigbee RF mesh technology to talk their devices. In this context I am interested in the answers to these questions…
a) in general do the two Zigbee networks interact in any way?
b) might the two networks interfere with each other?
c) could they enhance each other e.g. forming a common mesh with more resilient routing paths?
No - under any sort of normal conditions, they should not interact. All ISM systems are meant to only use a small amount of the available bandwidth and should therefore interoperate fine. I’m aware of a system that uses ZigBee in large hotels - each room has a separate network, and this works well.
No - separate networks are completely separate. Nodes on different networks will not even be aware of each other (as per my answer to question a)).