What is a good Indirect HW tank for a Water to Water HP?  SuperStor indirect tank?  Tanks with heat exchangers used for solar? 

A indirect HW tank is not a good idea for a water to water HP.

What do you suggest for heating both domestic hot water and hydronic heat (radiant floor)?

Maybe with a few isolation valves the heat pump heat exchanger could serve both tanks directly, radiant buffer tank, and dom hw tank, one at a time, with a flush cycle inbetween (when switching from buffer to dom, run X gallons of clean water through heat exch to flush out any possible contaminants).  Radiant system is clean with bronze pumps and no cast iron.

A gentleman in MD is running a W-W GSHP with great success, to supply both DHW and radiant floor hydronic heat, without any intermediate or indirect storage tank(s) - see http://www.ourcoolhouse.com/monitor/monitor.htm .

An ideal way to ask questions is via his forum, at http://www.ourcoolhouse.com/go/forum/post .

Hope this helps.

Best regards,

Bill

Due to market size, it's actually cheaper in general to pick up an electric water heater to use as a water storage tank than it is to use an indirect tank for HW storage.

I agree with Senecarr. Indirect tanks tend to be very expensive, likely both because of limited sales compared with conventional electric storage water heaters, and also possibly owing to the cost of the internal heat exchanger.

An additional benefit of using an electric storage heater in this manner is the ability to energize it for additional / backup hot water capacity.

Thanks for the good ideas.  I did look at the real time screen for OurCoolHouse, very nice system.  He seems to be doing an "open" radiant system where you treat the whole radiant system as plumbing and therefore OK to run domestic water through.  This concept is a little controversial, but done in some areas.  I think one key is to not let the radiant part stagnate over the off season, run the pumps every day or two to keep the water moving.

I'm not sure I'm ready to do a fully open system, I am concerned with maintaining some isolation between heating and domestic water. 

However, the downsides of the indirect are numerous: Besides the additional cost for the indirect, you have a loss of something like 10 degs in usable water temp (120 deg HP loop might give you 110 water with a big heat exch), so this is not the best solution. 

Using a less expensive Elect Tank (see Lowes) directly from HP water would be good all around, I just think I need some isolation from the heating water, hence the flush idea... any other thoughts??

The gentleman in MD that I referred you to encountered similar 'downsides.'  The original design included some kind of mixing valve, and other things, if I remember correctly.

He then made changes that resulted in implementing what you're referring to as an 'open' radiant system, as it's shown in the reference I provided above.

I recommend you ask him, via his forum, what the details were of his 'downsides' that he encountered, and ask questions to see if you too can get comfortable with an 'open' system.

Best regards,

Bill

Thanks Bill, you talked me into it.

I posted a question for Phil.

I'll let you all know if I get any good responses!

Bill,

Our friend in MD does have an open radiant system now, however, he says if he did it again, he would go to a closed system using an electric HW tank and plate heat exchanger.  He hasn't told me yet why he wouldn't use the open system. 

PBG, glad that Phil could be helpful.  He's a very smart person.

I suspect he wouldn't use the open system again because of having similar concerns you and others have voiced on code compliance.  I don't know, though, if this is indeed specifically the case for Phil.  Perhaps he'll elaborate if/when he responds to your further question.

Phil is the designer of the Web Energy Logger device ( http://www.welserver.com/ ) that I and many others use ( http://welserver.com/ww/ ) to obtain and publish instrumentation information on energy usage for our homes / businesses (my data is at http://welserver.com/WEL0043/ ).

Best regards,

Bill