Thermal mass for solar heater?

[motoman465]

I am in the process of building my first solar heater.  I have reused wood from old pallets, the foam that comes in shipping boxes for insulation, Monster energy drink cans, and an old piece of plexiglass.

I just had an interesting thought and was wondering if any of the gurus on this board have thought of it and/or tried it.  What would happen if you lined the inside of the collector box with black ceramic tiles.  I would think it would produce usable heat even after the sun went down.  Is my thinking correct?

Todd

[zeusmorg]

 Not for long, and it would also delay usable heat when the sun came up..

Thermal mass needs to be huge to be able to "store" heat. You're better off just using aluminum for heat transfer in the collector, then get that heat inside your dwelling, and let the contents of your house act as the heat sink.

 The size of a solar collector wouldn't lend itself well to a heat storage unit.

[Dave B]

Todd,

  I think black tile would work fine but it will probably take longer to heat up and longer to cool down. I don't think you will produce any more total heat but there will be that lag time because of the mass of the tile which may not be objectionable. Go for it, aside from being heavy why not give it a go and experiment with your idea ? My opinion, but that's just me. Good luck with your project.  Dave B.

   

[motoman465]

Thanks for the input.  I hadn't thought about it taking longer to heat up, but I think I will make a carbon copy of the one I am working on just to see.  I'm having too much fun with it.  My project is generating some interest, my neighbor wants to build one to keep his shed warmer during the winter.

Todd

[Adam T]

Hi Todd,

 As stated above, adding any additional thermal mass to the collection area will simply slow the temperature fluctuation in both the rise and fall for the temperature curve on your collector.   When heating a medium, optimally the bulk of the thermal mass should be the actual medium, be it water/air/other.  Therefore the thinner the pipes or ductwork, the more quickly the heat moves through it to the media you are heating; water/air/other.

Adam T.

[Madscientist267]

It is not likely to make you much of a difference by adding thermal mass in that quantity. In relation to the space you are trying to heat, the amount they can hold is a drop in the bucket.

If you're going add thermal mass, add it to the space that you are heating, ideally passing the transfer medium through it. Remember that the tiles will be giving some of their heat off in the form of infrared, which will just go to waste in the evening/night sky. If it is in the space to be heated, some of the infrared will then be absorbed by items in the area itself, minimizing waste.

Also, you can optimize heat storage vs space by choosing a material with the highest specific heat you can find. Water is easy to come by, and has excellent thermal characteristics.

Steve

[Dave B]

Todd,

  I'm glad to see you are going to try it, you will certainly produce heat. I wasn't quite sure what I would get from all my work shown here either but when they kick on and produce about 1000 watts each in heat I get a good laugh every time.

  I know a bit about thermal mass also after building my log home over 16 years ago. I think you would benifit from your plan even more if you could use double pane glazing. You are going to want to wash all that stored heat out of your box when in the shade. The less heat you lose off the glass the better. I like your spirit, go for it and let us know how it works out.  Dave B.

[spinningmagnets]

You may wish to spend some time over at www.builditsolar.com, tons of great ideas there.

I'd use two layers of glazing, Glass on the inside (cheap, high heat-resistance, perhaps an old sliding glass door?) polycarbonate on the outside (good heat-resistance, great breakage resistance from branches, etc). I'll bet your plexi will half melt fairly quick. You will be suprised at how hot the collector gets.

For thermal mass, a dry-stack of masonry blocks absorbs heat quickly, but water drums will hold 5-times the BTU's per volume. On a cold winter day, if the sun only comes out for a short while, you need to absorb as much as possible as quickly as possible. Water drums absorb very slowly, but hold more BTU's.

A hybrid pile has been suggested to me as a cheap and useful option. The top half is water drums, and the bottom half is masonry block. During the day, the masonry absorbs whats available quickly. At night, the circulation stops and the masonry heat migrates to the drums above overnight.

In dry winter air, mold and fungus is not a big problem, but in cool but humid air the stack can get funky. In that situation, you can seal off the solar collector and heat-storage pile into a closed-loop, you can draw off the heat from the top of the pile by inserting an aluminum heat exchanger, such as an 18-wheelers turbo intercooler. Its a large aluminum air-to-air radiator.

More complex, but that would also allow your system to passively collect any time heat was available, but then you only draw off as much as needed from the storage box to keep the room comfortable.

Install one-way flaps on the bottom ports of the collector so at night it doesnt reverse flow and pull warmth away from the house.