Out of interest, do you know any commercial refrigeration engineers or installers? They might know a thing or two about ethernet relay control if they know their stuff. Most new installations of supermarket refrigeration has some element of ethernet control to it - in my shop the fridges have the canopy lights controlled by a central unit, and all the fridges communicate their data (temperature, humidity etc) to a central server, via ethernet. The central server can then alarm if any of the units go out of spec, and even communicate this to a remote monitoring centre via the burglar alarm peripheral interface.
I might be barking up the wrong tree, but I can certainly see similarities with what you want to do . . .
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