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Kachadorian's air-core slab consists of hollow concrete blocks forming ducts under the floor. Kachadorian claims that air in these ducts would be warmed by the heat stored in the thermals mass of the hollow concrete blocks, create air movemnet and allow warmed air to float into the room above via duct openings in the floor.
I have always wondered would this design be improved if hydronic pipes were above the blocks in a cement screed. Any heat lost beneath the heated screed would heat the blocks and hence air in the ducts underneath. This must create air flow out of the ducts into the room above. Sort of re-claiming heat that may be lost.
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News wrote: ...

I'm not familiar with the details of Kachadorian's design but it seems to me that a good bit of insulation under the floor, hydronic pipes on top of that, and flooring on top of the pipes, would be the most sensible arrangement. Why let heat get lost beneath anything? If the flooring is more or less directly on top of the pipes then the floor itself would heat the air and create air flow directly in the room. Cleaning a floor certainly would be easier than cleaning air ducts in blocks under it.
Anthony
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Problem is that the floor isnt a very good source of lower grade heat. Its got its real downsides even with electrical heating embedded in the concrete floor.
Even without carpet, its not ideal and worse with carpet.
And the problem is that how warm the room feels is mostly due to the surface temperature of the walls and the air temp, and its non trivial to get those up to reasonable levels with any form of heated floor. Even with an electrically heated floor, you can get a situation where the floor is hotter than is comfortable while the room still feels too cold.
Corse another way of looking at it is to not attempt to do all the heating using solar, but to use that to minimise the heating fuel costs.
Still got some real downsides with just a uniform floor surface that the solar heat is being supplied thru tho.
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Wrong again Rod. A hydronic floor with lots of surface and a low water-air thermal resistance in an airtight house with lots of insulation works fine. Ignoring the R1 radiation conductance, the min floor temp required to keep a house with a 200 Btu/h-F conductance and a 2400 ft^2 floor 70 F on a 30 F day with a U1.5 slow-moving airfilm conductance is 70+I/(2400x1.5) = 72.2 F.
Nick
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Ken how do you insulate under the floor piping-Radiant floor heating, here we use foamboard. What R value are your 4 pane windows, are they sold in the US What R value do you use in walls and ceilings
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Best ignore him.
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I'll take a dump on him instead, thanks.
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Best ignore him.
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Best ignore him.
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Best ignore him.
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Best ignore him.
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Mr Troll, you will find we are not all disciples of Nick. Do a Google and see the conflicts. ..err is it worth saying that to him? Probably not.
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Some gutless fuckwit pom desperately cowering behind
wrote

Master gutless fuckwit pom, I never said you were.

Not interested in gutless fuckwit pom shit thanks.
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I know of a few installations of PVs where the underside of the PVs is ducting with air florced through. A heat pump collects the heat from the panels and house exhaust air. It wasn't that brilliant. I think it could have been better thought out.
How much heat do PV cells emit on the back and front of the cells?
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News wrote: ...

You could think of it this way. Typical PV panels are around 12% efficient at converting sunlight into electricity. This means that the other 88% is converted into heat. Clearly they are much better at making heat than electricity.
Anthony
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...

I thought around 30% was reflected? This would leave about 50% as heat.
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Nope, that would only be true if they were a perfect black body absorber of all energy that falls on them.
In practice quite a bit is just reflected off them.

But then so is say black roofing material.
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Well, maybe 16 and 84%, eg 0.84x800 = 672 W/m^2 in AM2 sun.

Buth they are better than that. Rich Komp says the silicon is almost transparent to IR, and the aluminum contact beneath is shiny, so PVs are a selective surface.
Nick
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I think that has a lot to do with whether there is an antireflective coating on the surface or not. Silicon is very shiny in the optical, (and I think the reflectivity is a function of doping), where most of the energy comes in, so, especially if the sun is at a substantial angle to the array, a lot of the energy is reflected from the top surface. What gets in and is not absorbed or reflected from the top surface metalization (around 10-20% I think for typical cells) passes through the active cell and what isn't absorbed there then passes through the rest of the bulk silicon used as a handle. The back side metalization would be under all this heavily doped handle. Very thin cells would be very different from the currently more common thick cells. I am not sure about the ones that are epi deposited on material other than silicon. If they are thrown down on a metal contact they are probably very reflective.
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