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Old 11-09-09, 12:24 PM   #19
AC_Hacker
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Default Thermal Mass, Water Storage, PCMs...

If you can combine structural requirements with thermal mass, it's a win-win.

BuildItSolar has lots of pages illustrating work that has actually been done on thermal mass being used for heat storage.

Quote:
Originally Posted by Daox View Post
Wow, I didn't know there was THAT big of a difference between water and concrete.

Thanks for the chart AC Hacker.

Now, I need to find an elegant way of storing water in rooms...

Yeah, water is a really good medium for heat storage. It has the added advantage that it can be pumped through pipes, so it may be possible to locate your heat storage tank somewhere else.

So water storage is used as a 'heat battery', and energy is stored when there is too much energy (sunny day) and withdrawn when there isn't enough energy (cold night). One of the problems in making this work is insulating the 'battery' so the heat energy isn't lost. There are water storage tanks available in the US with claimed loss rates of a few degrees per day. There are water storage tanks available in Europe with claimed loss rates of a few tenths of a degree per day.



BuildIitSolar has several pages illustrating progress that has been made along these lines, regarding water storage of heat.

In the 70s there were experiments with water filled tubes for heat storage:


Nobody ever said that they didn't work, but the idea didn't gain public acceptance.

Currently there's still work being done along this line. Here's a guy who is using water-filled windows:



And you could also get a very large aquarium. Goldfish are able to survivie a wide range of temperatures.

Then there is the Phase Change Material thing... Here is a graph that I made to illustrate the sudden increase in the heat storage of water when ice is warmed from 27 degrees to 37 degrees:



What this illustrates is that it takes about a BTU to move a pound of water (ice) from 27 to 28 degrees, and from 28 to 29 degrees, but to move it from 32 degrees to 33 degrees, it takes 144 BTUs. This is huge! it's over 100 times increase, no battery, no moving parts. It happens on the molecular level and is completely reversable. The water doesn't wear out.

What's not so useful here is that it's happening at 32 degrees, and we're trying to stay warm.

But there are other materials that will do a phase change at a point nearer to our comfort level:

So there have been problems with the reversibility (AKA: incongruous melting) of glauber's salt incongruous melting, also with Calcium Chloride Hexahydrate, but for Calcium Chloride Hexahydrate the problem appears to have been solved. Paraffin doesn't seem to have the reversibiity problem, and is being micro-encapsulated and put into things from gloves to sheetrock. BASF of Germany is moving ahead in this.

Here is an interesting paper, where PCMs are combined with a flat plate solar collector to store and release heat on a daily basis.

We live in very interesting times...

Best Regards,

-AC_Hacker
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