Excuse me fellas if my questions appear dense...

I'm working on a site where they are using vrv iv's for space heating / cooling, but they are also connected to hydroboxes for hot water (showers & taps - not heating)

I've never actually worked on such a system before (or any Altherma for that matter) which has these hydroboxes.
I managed to take the covers off and have a very brief look inside one today.

The first thing I could not understand is why this hydrobox has a secondary system on 134a with it's own rotary compressor. I would have assumed it's using mainly discharge gas from the outdoor unit to heat the water in the primary circuit?

Unless I've been looking in the wrong places, I've struggled to find anything that shows exactly how these things work with a decent schematic.

Could anyone explain how these work, or point me in the right direction?

Any help appreciated.

Cheers