Solar PV, Solar Thermal and Radiant Heating

[earlgrey]

I think this is the best forum to drop this.

I have a 660 square foot home in Eastern Washington (so it's clear and sunny pretty much year round, but still stays ~20 degrees for 3 months). The house is built on a concrete slab with no crawl space or basement. Shading is not an issue.

We are planning the installation of a solar water heater and a small PV system, and switching from electric in-wall heaters to radiant since we're re-doing the floors as well.

The simple question is this: Do y'all think it would more cost-effective to install electric radiant heating running off the panels with a smaller solar thermal system for hot water, or should I get a larger solar thermal water heater that services both our hot water needs as well as a hydronic radiant heating system and offset our other energy uses with the PV system?

[Mike90250]

Are you going to be able to bury hydronic loop coils in the slab, or just perimeter base board heat radiators ?

Hydronic floor needs only a small thermal differential, but baseboards will need much hotter fluid. Check out the solar collector & storage shed at buildit solar for some great ideas

http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm

[J.P.M.]

Are you going to be able to bury hydronic loop coils in the slab, or just perimeter base board heat radiators ?

Hydronic floor needs only a small thermal differential, but baseboards will need much hotter fluid. Check out the solar collector & storage shed at buildit solar for some great ideas

http://www.builditsolar.com/Projects.../solarshed.htm

As a first cut, I'd consider solar thermal and hydronic radiant floor heat. but before I did that I'd add perimeter insulation to the slab to a depth of wherever the frost line is and a bit more.

PV for the non HVAC electric loads and fossil fuel for the backup HVAC, or propane if CH4 is not available. Depending on in/out temp. differential and common winter outside temps., maybe a heat pump.

I'd not use PV to supply electric resistance for a heating method.

BTW: on grid ? If so, what do you pay for a kWh of electricity ?

[earlgrey]

The slab is pre-existing. I suppose we could pour cement over the hydronics but would like to avoid that.

We are on-grid. Our electrical is real cheap @~8 cents per kWh. We're considering solar for a few reasons, one of which is a $0.54 per kWh rebate on PV produced electricity for three years, which with the fed credit about pays for the system. Plus solar is cool.

Anywho, resistance heat is inefficient regardless of rates which is why we'd like to subsidize it a bit.

On another note, there is no gas hookup to the property so our water heater backup would be electric (I don't really feel like messing with anything else).

JPM, thank you for the link. I think we'd like to progress to a 100% system like that but it probably isn't presently feasible; nonetheless that site has great inspiration and ideas. I'd like to set the system up so we can add to it over the years.

Thanks all for the ideas and thoughts!

[J.P.M.]

JPM, thank you for the link.

You're welcome, but I believe that was Mike's link.

As to the slab, regardless of how building heat is provided, I'd still insulate the holy grail out of the the perimeter if not already done.

BTW, welcome to the neighborhood.

[earlgrey]

You're welcome, but I believe that was Mike's link.

Whoops, sure enough! Thanks Mike. I found a few more projects on that site that are definitely more applicable to the size of our project, so again thanks for the link. His above slab hydronic installation was especially helpful.