Greetings with my first question: DHW as radiant zone?

I am designing my home for Western Washington state. 2400 sq. ft. 1-level, slab-on-grade, house with hydronic in-floor heat and no cooling. Heat loses in the house come out to 22000 btu/hr in the winter. I'd like to use a 3 ton geothermal water-to-water to give me room for DHW. Read about Desuperheaters, which are great for summer A/C waste heat, but are less of a great thing in the winter. It's not an expensive add on, but I was wondering if anyone has just heated a DHW preheater tank (that supplies tankless DHW heaters) off the manifold that feeds the in-floor tubes? I would still have a buffer tank between the geothermal unit and the floor manifold to limit cycling.

 

DSHs work also great in the winter, making DHW with the efficiency of the geo system.
Running the DHW off the same heatpump as a zone is more elegant, but more expensive solution.

Some older designs without the more efficient buffer tank bypass/load direct principle, but the idea is the same.

http://welserver.com/WEL0383/

http://welserver.com/WEL0664/