Ator,
Nice find. Even better value. If you use hot water, the return on investment will be super short. I hope you keep this thread updated on the actual performance and running cost, maintenance issues, and such over time.
The picture looks real nice, but what do you really own? I saw Panasonic has been producing a line called Aquarea, which this product would fit into. What line and model number of product do you actually have?
http://www.aircon.panasonic.eu/GR_el...c-aquarea-dhw/
It would be nearly impossible for me to justify building a custom made unit if I could buy a new one for the price you quoted. For 100 euro, I would spend some of the savings on having the unit installed by a licensed contractor.