Home: Temperature: Heating
Solar Heating   (+4, -2)  [vote for, against]
Save it for a rainy day.

OK, so the rayfo reminded me of all the half baked uses for solar power I used to think about, with his "Better conmposting" scheme. Heat can be stored in thermal mass - the problem most places is that you need the heat in the winter, but the sun shines mostly in the summer. So where to store the heat? One of my schemes involves hydronic heating of a large thermal mass most people already have - the driveway.

Pipes are buried in the earth beneath the slab, through which water, superheated either through mirror concentrators, or fresnel lenses, circulates. in the winter time, valve would redirect this water to circulate between pipes buried in the driveway and the crawlspace beneath the house. Heat stored in the thermal mass beneath the driveway will continue to heat the driveway, which will then be transferred to thermal mass beneath the house, perhaps just buried in the dirt, if you dont have a slab foundation.

I havn't gotton around to experimenting with this yet, it's an idea more suited to new construction. The main drawback is the cost of the pipes. A large fresnel lens, approxomately two by three feet, can generate tmperatures at it's focal point of around 1200) F. or better. A ceramic baffle could be used as a collector, and heat could be controlled through flow rate, and/or defocusing. Add a constant orientation platform, and a pump, all available from Edmund Scientific, and you could put this heat pump together for around $500. The cost of the tubing might be the real expense, as it imposes an upper limit on the water temperature, which at any rate, would have to be below boiling point. Glazed ceramic pipe would be ideal, aside from the joints, although high temp RTV gasket compound might work. In-slab hydronic heating typically uses a type of flexible, heat resistant hose, although I don't think it's designed for temperatures this excessive.

An alternative to this is to drill a series of holes in the ground, using a large earth bore/auger, coiling the pipe in the bottom, and filling with river rock, gravel, or other suitable thermal mass. This would make for an easier retrofit, and gets below the frost line. Once again, this would require copper pipe, or another, as yet unknown to me, material. A really halfbaked idea I had was to produce ceramic pipe using a solar kiln, powered once again, by a fresnel lens, and extruding clay though a the stationary kiln. I am currently investigating the properties of ceramic cloth hoses, brought up in another discussion, as this material might lead to fewer potential maintainence headaches. Any investors? I'm giving it away anyway, in light of the projected heating oil shortage - so get busy!
-- Scott_D, Sep 19 2000

Radiant floor heating. http://www.radiantheat.net/newcnst.htm
Something similar is available for driveways and sidewalks, etc. [StarChaser, Sep 19 2000, last modified Oct 21 2004]

When and if anybody annotates this, bear in mind that total cost should exceed no more than about ten thousand dollars, preferably about half that, for a basic system, for this to be cost effective - as ten years is about the usual time to reasonably expect such a system to pay for itself.
-- Scott_D, Sep 19 2000

This is pretty well covered in the literature on solar heating, but here we go:

First of all, it's not really useful to characterize the "temperature achieved" (1200ºF or whatever) of a solar collector. You can achieve that much temperature with a magnifying glass, after all, if you just focus the light tightly enough.

Really, big Fresnel lenses aren't very useful. It's better to make a lot of water somewhat warm (with a big collector, or at most a mirrored pipe enclosure) than to make a little bit of water extremely hot. The hotter the water is, the more heat you lose to radiation, so unless you're trying to generate steam (or power a kiln!) there's no need to go overboard.

Finally, it's generally a better idea to put your thermal mass indoors, that way it can slowly radiate heat into your house at night (and keep your house cool during the day!), rather than losing it into the surrounding soil. Just make one of your interior walls a thick masonry slab with pipes buried in it. (Water is the best thermal mass of all, but masonry can double as a structural member of the house!)
-- egnor, Sep 19 2000

All very true, egnor, but where I live, the difference between day and night temperatures during the summer is the difference between running the air conditioner full blast, and on low - I don't want any solar gain in the house in the summer time, cooling is a much greater problem. You're right - massy walls cool as well as heat and insulate, the very essence of the efficiency of adobe structure - unfortunately I can't really do that with this particular structure, although I may increase the wall and roof thickness with a double insulating external wall of two or even one by fours on four foot centers, or in whatever maximum width I can get insulation in.
-- Scott_D, Sep 19 2000

I was basically thinking about further North and East as well, where summers are hot day and night, but relatively short, and heat might be better stored away from the house during the peak of summer - the high temperatures capable of being generated by the lens arrangement is intended to heat the ground itself in a sort of artificial geothermal kind of way - costing little to operate, radiation would not be a huge problem, you could even use it to extend the growing season for your garden. In the fall, as temperatures drop, the heat could then be transfered under the house. Might not last all winter, but it would definitly conserve fuel. The idea behind the fresnel lens arrangement is that the temperature could be regulated by water flow, through, as I said, a ceramic element - the slower the flow, the hotter the water.

Given that such high temperatures are temperatures unneccesary, and even unwanted, as many smaller ones as are needed could do the trick - it just needs to be as hot as possible to store as much heat as possible in a short period.

Would you belive me if I told you that this idea started as a scheme to keep ice off my North facing driveway?
-- Scott_D, Sep 19 2000

Were working on 1/2" Solid core Fiber Optic Cable at my lab, click on name to fine me. We have tested the cables and they provide enough light to light areas of a home, the trick is in the output refraction fixture! Down with the Light bulb!
-- Fiberdude, May 15 2001

Hello, and welcome to todays episode of 'What the hell was that?'.

This isn't about light, it's about heat...
-- StarChaser, May 15 2001

There are some ideas here which have to do with light pipes; maybe Fiberdude somehow annotated the wrong one?
-- egnor, May 15 2001

I don't see that in the logs; I think this is just a case of a man with a hammer to whom everything looks like a nail. (Updated version: "To a guy with a 1/2" solid core fiber optic cable, everything looks like a ray of sunlight.")
-- jutta, May 15 2001

Must pave over a 40'x30' backyard spot. Would like to find some sort of inexpensive heat source to put under the blacktop as I am too disabled (and elderly) to shovel snow. Anyone know of a heating pad (light/hot water, whatever) etc. that might work? Kt
-- Cosmickt, Jun 11 2001

Wrong idea, [Cosmickt]; there's another one here for you (if I could just remember what it's called).
-- egnor, Jun 11 2001

There are ways to set up pavement to be self-snow clearing. One involves hot-water hoses being laid before the pavement goes down, then you turn on the hot water and it melts the ice. This shouldn't be too hard to run from a solar panel, although living in Florida I have zero practical experience with it. See the link for an example.
-- StarChaser, Jun 11 2001

So, Starchaser, you think I could run a regular plastic (or should it be stronger?) hose from my hot water heater through the backyard and then attach a trickle hose on the ground to be paved over? Thanks also egnor, let me know if you remember.
-- Cosmickt, Jun 17 2001

No. I said 'hot water hoses being laid before the pavement goes down'. The idea is to heat the pavement from beneath. Trickling water over it will just give you ice.
-- StarChaser, Jun 17 2001

Many large hvac systems already use the soil as a long term heatsink
-- DanDaMan, Dec 20 2007

[Fiberdude]'s lightpipes may be able to provide a solution that doesn't require liquid... your fresnel lens(es) feeding a lightpipe(s) which feeds a system of lightpipes under the driveway, terminating in all that nice black heat absorbing tarmac.
Do remember to cover the lenses over in the summer or you have ashphalt soup.
-- FlyingToaster, Dec 21 2007

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