Renewable Energy Questions/Discussion > Solar (heating or electric)

Passive solar air heater - for home

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eidolon:
I'm at a disadvantage of not knowing your location and other circumstances.  A relative bought a solar home and the first thing they did was tear all that stuff out. The great thing about the world is everyone has their own ideas and criteria for success. An interesting read on PV heating is electrodacus.com.  Dacian is a strong proponent of it. One advantage is it can at least do something in the summer.  Of course his approach is almost impossible to duplicate unless starting from the beginning with new home construction.  Not trying to discourage you.  Implementation of any system comes down to the details.  I heat water with PV and almost everyone thinks I am wrong.

MadScientist267:
Wrong is only wrong if it tries to circumvent the laws of physics, or doesn't work. Everything else is somewhere on the practicality line.

I use peltier to do thermal management for my batteries in the truck, I can only imagine the sneering and snickering that took place over that, before I proved it to be viable for my situation.

Truth of the matter is, in my experience, it's never been so much the "what" as it has been the "how".

Implemented wrong, ideal concepts can prove totally useless if not even (as mentioned) have a negative impact.

With some experimenting and careful planning, concepts that are blindly shot down by the masses because of perceived and propagated issues with them, can prove not only viable, but even exceed expectations.

It's all in how it's done. The key is to figure out what is what before you either blow a bunch of cash up front on a concept that isn't going to work, or find yourself having to blow a bunch of cash undoing damage.

All that said, PV is cheap now. And surplus PV is the best kind of PV. That's not to say that it's the end all solution, but sure is a lot more viable than it was once upon a time...

Just my 2 cents...

Steve

welshman:
Maybe this?

MadScientist267:
Welshman -

On paper, that's pretty much where it begins... There's a few gotchas associated with that tho, and really just with passive of this nature in general.

The biggest has already been mentioned, and is very easy to overlook... What happens when it's cold out and the sun isn't shining... Convection is a two way street...

Ultimately, I've found that one way or another, fans have to be involved with anything like this because even if the surface is insulated to reduce conduction losses to the outside ambient, the energy will just "shape shift" and radiate as IR, still cooling the air in the plumbing, inducing the reverse flow, still causing a draft.

Flaps of whatever sort also seem minimally effective at preventing the reverse flow, and also provide some opposition to the desired direction of flow when the sun is shining.

Several revisions of the airflow and thermal management concepts have come and gone in the truck (and I'm sure I'm not completely done, as long as I'm still occupying the thing full time)... and just so happens winter is the "most conquered" of the big seasons... The scheme in play now, while not explicitly designed for direct heating via solar-to-air, IS designed to minimize the negative impact of night losses when it's cold. It's probably best described as "passive self inhibiting convection with active management"... A diagram would help clarify this, tho I don't have one on tap as of the moment, but I'll try to describe it...

Basically, my intake and exhaust ports leading to the outside are at more or less the same level, and up high on the outer box, forming a loop that naturally tends to cancel convection. Both ports have fans associated with them, but the important ones for the concept at hand are in what was originally considered to be the "intake", which forms the self canceling part of the big loop. There's also an additional port between the inner and outer boxes, but largely, it doesn't apply much to this.

I have plans to experiment more with the fine tuning, but will need another round of winter to do so... However as it sits, it's very effective at being able to confine heat inside. To accomplish this, a small fan opposes convection, trying to pull a negative pressure on the inner box (living space), with its source being down low all the way at the floor. This results in 2 things: 1, allows the air trapped inside the pipe/air handling chamber(s) to get cold, without being able to form a draft that would let it into the inner box... and 2, tries to prevent the warmer air toward the ceiling from escaping into the void between the ceiling and roof (essentially what would be the "attic" in a house).

In my specific situation, I can bring small amounts of extra heat in the "attic void" into the inner box during the day when the sun is beating on the roof as well, but the effect has minimal impact because outside on the roof, the PV shades the roof skin too much to be of real use in this way.

That said, I don't think I'd run it in the direction of natural convection where an explicit solar-to-air collector scheme is involved anyway, but that begins to fringe very heavily back into theory and away from "tried and true". Someone with more solar-to-air experience would need to chime in there, as from what I can tell with what I *do* know of it based on other things I've encountered with the truck, the ability to be able to move the air in both directions, and variably, would likely be important.

I'll try to get a pic or two soon and possibly a little diagram drawn up with some annotations to clarify what's happening if it might help... but hopefully this gives you a general idea of what I'm getting at.

At the very least, I hope it illustrates that while "pure passive" sounds good at first, it's not really possible by itself (at least as far as I've been able to tell with anything I've tried with it). Fans are my best friends, and yes, I spend a little energy moving/controlling air, but it's not extreme. In fact more often than not in winter, finesse is the key word.

Steve

welshman:
very interesting, esp about the negative pressure aspect of it.

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