A friend of mine has proposed a similar system, but I had concerns about the usable capacity. Out of curiosity, I ran your 1,000 gallon scenario through the calculations to see how much that could hold. The basic theory is that the specific heat of water is 4.2 kJ/kg*K (kilojoules per kilogram degree kelvin), meaning that you must add 4.2 kJ to raise 1 kg of water by 1 degree K (or degree C) and vice-versa. Convert 1,000 gallons to 3,800 kg, and assume that you can raise the temperature all the way to 200F (93C) and continue using it to heat your floor all the way down to 90F (32C). Therefore, you could extract a total of 970,000 kJ from a fully-charged tank. This is equivalent to 0.9 MMBTU (million BTUs) or 1 mcf of natural gas (10 therms or ccf if you prefer). A home the size of yours in a northern climate will typically require tens of thousands of MMBTU for a full winter's heating; you can convert last year's fuel bills for an estimate.<br>
<br>If I didn't drop a few zeros along the way, I'd say that your 1,000 gal tank should be able to get you through a cold night if you have good insulation. How much capacity do your panels have? You can use that info to calculate how long it will take to charge the tank. If you can get 10^9 kJ out of your panels in a typical winter day, this system might be able to handle the diurnal swing.<br>
<br>Feel free to check my calculations here:<br><a href="https://docs.google.com/spreadsheet/ccc?key=0Aly4mhoYtT8jdHpEZnZnNmFkWm01Skdta01FUlE5SXc">https://docs.google.com/spreadsheet/ccc?key=0Aly4mhoYtT8jdHpEZnZnNmFkWm01Skdta01FUlE5SXc</a><br>
or try this calculator:<br><a href="http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/spht.html">http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/spht.html</a><br><br>Filling the tank with a phase-change solution could store much more energy, but would add considerable cost and complexity.<br>
<br>Sorry that I don't have any advice about the mechanics of the system, and I hope I didn't throw (pardon the pun) cold water on your plans!<br><br>Ethan<br><br><div class="gmail_quote">On Wed, Jul 4, 2012 at 4:24 PM, Corwyn <span dir="ltr"><<a href="mailto:corwyn@midcoast.com" target="_blank">corwyn@midcoast.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="im">On 7/4/2012 3:36 PM, Clarke Olsen wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Corwyn,<br>
Thank you for your considered advice.<br>
1. 1000 gal was the biggest (5'x10'x4' low boy concrete septic) tank that I could squeeze in the crawl,<br>
before the house went on.<br>
2. Bottom to top is obvious, though it seems that loops pulling heat out should be high in the water,<br>
and one putting heat in could stay on the bottom.<br>
</blockquote>
<br></div>
You will get better stratification if the incoming water from the collector, is heating the warmest water at the top of the tank, it will also be a more efficient heat exchanger.<div class="im"><br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
3. I have no calculation.<br>
</blockquote>
<br></div>
I suggest you get some. You could probably give enough information to this list to get someone to do most of the heavy lifting for you.<div class="im"><br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
4. My collectors will mount on ground level frames against the south wall, making adjiustments easy,<br>
and inviting drain back.<br>
</blockquote>
<br></div>
My concerns are weight, and water connections.<div class="im"><br>
<br>
Tilting back to catch summer sun inceases the effective area by 50%.<br>
<br></div>
Not really. For my location, adjusting tilt by +/- 15 degrees, twice a year, gets me 5.05% more solar (804 kBTUs vs 765 kBTUs per square foot per year).<div class="im"><br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
5. The house went through last winter with just the booster to heat the floor. Oh, yeah, and a wood stove.<br>
</blockquote>
<br></div>
Well, if you already have the booster, you might as well keep it, but controlling it is still going to be tricky. I would expect to only use the wood stove for supplemental heat.<div class="HOEnZb"><div class="h5"><br>
<br>
Thank You Kindly,<br>
<br>
Corwyn<br>
<br>
-- <br>
Topher Belknap<br>
Green Fret Consulting<br>
Kermit didn't know the half of it...<br>
<a href="http://www.greenfret.com/" target="_blank">http://www.greenfret.com/</a><br>
<a href="mailto:topher@greenfret.com" target="_blank">topher@greenfret.com</a><br>
<a href="tel:%28207%29%20882-7652" value="+12078827652" target="_blank">(207) 882-7652</a><br>
<br>
<br>
<br>
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