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Solar heating small building  RSS feed

 
Dennis Tate
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I'm building a 14 x 16 building with an attic for storage and maybe my wife would use it for her crafts. Its on a concrete turn down slab, so I thought radiant heat in the floor, particularly a solar passive setup would be desirable. At this point I've poured the slab with a radiant barrier underneath and have about 140' of PEX tubing in the slab making one loop.
Obviously a collector panel is required, and maybe a circulating pump. I have some deciduous tree shading issues but not total blockage, and can set the collectors about 30 feet away from the building ground mounted for a better sun exposure if needed.
What would you recommend? What other components would I need for a simple setup?
I will have grid power to the building, and a buddy gave me a tankless electric HW heater.
Thank you for any suggestions you may have.
 
Ezrio Passetti
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I read about many solar collector concepts and got about thermostatic air collector. It was an elegant and simple thermostatic design uses only the buoyancy of heated air to create circulation through the collector, eliminating the cost, maintenance and power consumption of fans, sensors and controllers commonly used in other collector designs. So I suggest you to build this solar heater.
 
Brian Knight
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Location: Asheville NC
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Hi Dennis, congrats on your project. You seem to be using two forms of solar energy that sometimes share the same terms. I think its best to break the two up into: Passive solar design and Solar Thermal.

Passive solar design is simply shape, orientation and window design. For your structure, you would need about 20 to 30 square foot of high SHGC window facing south. This is the most affordable, simple and reliable way to use the sun to heat your dwelling.

Solar Thermal is the term used to heat water. Although there are passive ways to use solar thermal, its considerably more complicated and trouble prone than passive solar design.

If you have land that slopes to the south then its possible you will not need a circulator but you would have needed to run your radiant tubes in 3/4" to 1" diameter at least which is pretty unheard of. Even so, I think planning on a DC circulator (EL SID) powered by a PV panel is the best way to circulate fluids which is a more passive way of doing it. Such a system is immune to the dreaded parasitic energy flaw of most thermal systems and DC pumps are much more reliable and resilient than AC.

If you oriented your structure to the South, I would just plan on the windows to do what they can. If you have time, some spare money and like to tinker then it might make sense to start messing with a solar thermal system but be prepared for a learning experience..
 
Brian Knight
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Location: Asheville NC
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Forgot to mention that you shouldnt waste resources with radiant barriers under radiant floor slabs. Maybe in a framed floor situation but a radiant barrier (foil) needs an airspace to function. Radiant slabs on grade need insulation and I probably wouldnt go less than R10.
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