I'm curious, where did you get a heat pump that uses R744? As far as I know, none of the major manufacturers offer one for residential use. I'm also curious about how well it works for you.
You'll see them sold under the EcoCute name. Daikin, Panasonic, and Corona (no relation) make them. They get used for homes meant to only have water and electricity hookup, called "all electric" homes.
As user Danieru replied the heat pump is a a Japanese import (although the tank and rest of the system is locally made).