I am a home automation integrator and I was approached by a client about implementing a controller for a system that with a solar thermal HW system as the primary source and a tankless water heater as the secondary source.  This system will provide hot water to a 6000 sq. ft. house and pool.

I was curious if there is a system that is able to automate the primary and secondary source.  Before I go through the process of creating a system to integrate the solar and tankless systems, valves and pumps, I wanted to see if someone else had already done this type of thing using existing products.  I believe there are some DDC control systems utilized in commercial properties but I can't seem to locate any.

Any suggestions or ideas would be greatly appreciated.

There is at least one set of solar controllers, the Resol BS Plus I believe, that can monitor the temperature coming back from the radiant heating system and then "decide" whether to recirculate that water, or to push that water into the solar tank and get new solar tank water instead. (Most of the other Resol controllers can do the same thing, I believe.) If you combine that functionality with the possibility of always running the selected water through a condensing, modulating boiler that stays off if the water is already warm enough, this should answer your requirement, I believe. Jeff

Here's what I do... all domestic hot water currently gets "pre-heated" by a desuperheater when our ground source heat pumps are running (evacuated tube SHW system has been ordered, but has not yet arrived).  "Final" temperature is regulated by an on demand Noritz system.  The Noritz unit (as with most on-demand units) modulates to add just the right number of BTUs to the water in order to reach the desired final temperature.  If the water entering the Noritz is - already - at final temperature, the unit doesn't run.  If water enters at any temperature below 125F, then it adds the required BTUs to reach the set point (in our case 125F).  Quite simple really.

Hope this helps.
Ed