I had a thought on how to build a solar water heating unit that would keep water warm at least over night, if not for days. I'm thinking that if you ran copper tubing through a box that was filled with sand, with the box obviously oriented to capture as much solar heat as possible, and with a double pane of glass to cover it, I would think that would heat the water quite efficiently as well as keep the sand hot at least over night.
I'm not currently in a position to test this, but does anyone else have any thoughts as to how efficient this might be?
Check this guy out!!!! Pretty awesome!!! He has Solar Hot Air and Solar Hot Water and Solar Space Heating. He even offers all the scientific mumbo-jumbo that you "guys" understand. (that part zims right past my simple brain LOL)
If you live around any stamp mills (associated with old mines) you may be able to get stamp sand which is black or dark gray and really soaks up the heat.
They use a heat box similar to what you're thinking. They use PVC pipe, wine bottles, garden hose and iron pipe and paint the heating pipes black to absorb the sun's rays.
The system is gravity fed. It's really low tech and cool!
They use a heat box similar to what you're thinking. They use PVC pipe, wine bottles, garden hose and iron pipe and paint the heating pipes black to absorb the sun's rays.
I like the design. But actually, what I was suggesting was a specific modification to this concept. Instead of using a storage tank for the resulting hot water, the tweak that I was specifically thinking of was to fill the box with the pipes with the darkest sand you can find (as another person mentioned, the black sand from around a mine would be perfect, although I don't know of any up here in the Portland, OR area). The sand would absorb the heat and release it to the water pipes throughout the night. I know it would make it heavy, but for this "over the head" heat box design, all you'd need to do is add a support to the middle.
The only thing you'd need to figure out is how much sand. You wouldn't want it too thick or the water would take too long to heat. I'm thinking just enough to come up to the top of the pipe. Maybe even leave the top inch or so exposed, but that would insulate the pipe so it would hold the heat over night.
Your thought is to use the sand as thermal mass to store heat. It could work. I wonder if the air spaces between the grains of sand might become an insulator and reduce the transfer of heat to the sand grains below the surface?
You could do a small scale experimental mock up to test the idea! Maybe build an alternate method at the same scale for a comparison.
Down here in Florida they re-nourish beaches from time to time. Well they re-nourished a beach near me with sand that had a lot of marine fossil material in it. The fossil material was jet black. The sand mix was sort of a grayish tan overall. The sand was so hot most of the time that you couldn't walk barefoot in it because it burned your feet. You left the beach and your feet were sore for several days. I never checked to see how far down the heat went into the sand though. I should have.
The sand was so hot most of the time that you couldn't walk barefoot in it because it burned your feet. You left the beach and your feet were sore for several days. I never checked to see how far down the heat went into the sand though. I should have.
I think the heat in the sand on the beach doesn't penetrate too deep because of all the moisture. Seems to me that the time I spent on the beach in southern CA, all you had to do was go down a couple of inches to get to pretty cool sand. On the other hand, with this system, even though there is no moisture and evaporation involved, the water would get hot and transfer that heat to the lower levels of the sand during the day. Man, I can't wait till I have a house again, so I can test some of this stuff!!
BTW, thanks for chiming in on the thread. I just wanted to engage people and get some thoughts as I think about what to experiment with when I have a chance. I will definitely post my findings when I get a chance to get some hands-on experience.
Metals were very high on the list and that makes sense because that's what we make cooking pots from. Copper is very high in terms of thermal conductivity while sand is very low. Maybe good combination would be thin walled copper pipe painted black with a bed of a dark colored moist clay underneath?
Temperatures in areas near a large body of water do not fluctuate as much as temperatures in other areas. This is because water acts as a moderator since it takes longer to heat up and longer to cool down. This makes me think that it would be more efficient to just heat water to use as a thermal mass rather than sand.
If you want your setup to work in the winter, you'll probably have to insulate all sides of the capture device except the side that receives sun.
Completion date - September, 2008. We just finished the project yesterday. We were able to raise the 75 degree inlet temperature to the mid 130s and briefly over 158 degrees (the max my digital thermometer reads) where it exits the outlet, with sunshine and a 79 degree outside temperature. I'll update this page when I get better data, but early results are exciting!
Update - October. With the outside temperature in the mid 50s, the collector is able to take 68 degree inlet temperature and consistently output 116 degrees at approximately 80 cubic feet per minute through the mid day hours. We will see how well it works when it is 20 degrees colder, but I'm very pleased so far.
Update - November 29th. An outside temperature of 46 degrees, an input temperature of 59 degrees and a sustained midday output of 107 degrees at 80 CFM. Assuming 280 BTUs per square foot, that works out to an efficiency of 62%! I understand that a 50% efficiency rating is typical for solar collectors.
Update - December 13th. We are within a week of the solar minimum, an outside temperature of 35 degrees, an input temperature of 61.7 degrees and a midday output of 101.8 degrees at 80 CFM. Assuming 263 BTUs per square foot, that works out to an efficiency of 55%! I am thrilled and consider this project a complete success!
I wonder how many codes he is violating? For one thing, he is blocking the basement window wells, which are escape routes for emergencies. They are not there for show.
UPDATE: Oh, geez, this guy is at 39.5 degrees latitude, somewhat warmer than my 44 degrees.
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