Posted by Morris Dovey on December 17, 2007, 1:02 pm
I was pondering how to go about storing excess daytime heat for use
after the sun sets, and came up with an idea for a "heat storage
closet" immediately behind the collector panel. Whatever it lacks in
originality, it makes up for with simplicity. :-)
My notion is to stack pairs of 55-gallon barrels filled with water
across the width of the panel(s) and put a movable "lid" on the closet
to control the flow of heated air in bypass, deposit, or withdrawl
modes.
Bypass mode would be used whenever there's solar input and the air
temperature of the space is below the lower limit of a comfort range.
Deposit mode would be used whenever the air temperature of the space
is above the upper limit of a comfort range.
Withdrawl mode would be used when there's no solar input and the air
temperature of the space is below the lower limit of the comfort
range.
I've posted a sketch/schematic of the closet at
<http://www.iedu.com/DeSoto/Projects/ThermStore/ThermStor.jpg> (the
panels are left of the closet and the heated space is to the right),
and would like to invite your thoughts as to _any_ low-cost
improvements that might be made to this method.
--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/
Posted by Jeff on December 20, 2007, 7:32 am
Morris Dovey wrote:
> I was pondering how to go about storing excess daytime heat for use
> after the sun sets, and came up with an idea for a "heat storage
> closet" immediately behind the collector panel. Whatever it lacks in
> originality, it makes up for with simplicity. :-)
Have you tried this yet?
I have some questions about charging the drums. A WAG about the
convective heat transfer in would be about 5 BTU's F / SF. Nick, do you
have a better number?
Perhaps a delta T of 20F, 20 SF (2 drums, front surface) yield 2000
BTUs/ hr. Those same two drums would store 15,000 BTU at delta 20F.
That may be about right...
I don't know what radiative losses will be in bypass mode, it may be
worth considering since the bottom is open.
Jeff
>
> My notion is to stack pairs of 55-gallon barrels filled with water
> across the width of the panel(s) and put a movable "lid" on the closet
> to control the flow of heated air in bypass, deposit, or withdrawl
> modes.
>
> Bypass mode would be used whenever there's solar input and the air
> temperature of the space is below the lower limit of a comfort range.
>
> Deposit mode would be used whenever the air temperature of the space
> is above the upper limit of a comfort range.
>
> Withdrawl mode would be used when there's no solar input and the air
> temperature of the space is below the lower limit of the comfort
> range.
>
> I've posted a sketch/schematic of the closet at
> <http://www.iedu.com/DeSoto/Projects/ThermStore/ThermStor.jpg> (the
> panels are left of the closet and the heated space is to the right),
> and would like to invite your thoughts as to _any_ low-cost
> improvements that might be made to this method.
>
> --
> Morris Dovey
> DeSoto Solar
> DeSoto, Iowa USA
> http://www.iedu.com/DeSoto/
>
>
Posted by nicksanspam on December 20, 2007, 8:34 am
>I have some questions about charging the drums. A WAG about the convective
>heat transfer in would be about 5 BTU's F / SF.
You probably mean 5 Btu/h-F-ft^2 (Btu per hour per degree F per square foot.)
>Nick, do you have a better number?
About 2+V/2 Btu/h-F-ft^2 for a rough surface, with V in mph.
> Perhaps a delta T of 20F, 20 SF (2 drums, front surface) yield 2000
>BTUs/ hr.
... 2Btu/h-F-ft^2x20Fx20ft^2 = 800 Btu/h.
>Those same two drums would store 15,000 BTU at delta 20F.
...2x55gx8.33Btu/F-gx20F = 18,326 Btu.
Nick
Posted by Jeff on December 20, 2007, 10:42 am
nicksanspam@ece.villanova.edu wrote:
>
>> I have some questions about charging the drums. A WAG about the convective
>> heat transfer in would be about 5 BTU's F / SF.
>
> You probably mean 5 Btu/h-F-ft^2 (Btu per hour per degree F per square foot.)
Yes. I'm just going to have to write that down somewhere as I always
forget it...
>
>> Nick, do you have a better number?
>
> About 2+V/2 Btu/h-F-ft^2 for a rough surface, with V in mph.
OK, Here is what I get. If the drums are just between two walls.
There will be enough area to dilute the air speed down to 1 mph or less.
50 CFM through 5 ft^2 is 10 f/*minute* and that ain't a lot of mph
(closer to 0 than 1).
I'm thinking those barrels will never charge unless you can radically
improve contact area or air speed.
Which brings up another point, I'm assuming Morris's collectors are
thermosyphon. How does he intend to withdraw heat, he'll have a worse
convection problem then?
Jeff
>
>> Perhaps a delta T of 20F, 20 SF (2 drums, front surface) yield 2000
>> BTUs/ hr.
>
> ... 2Btu/h-F-ft^2x20Fx20ft^2 = 800 Btu/h.
>
>> Those same two drums would store 15,000 BTU at delta 20F.
>
> ...2x55gx8.33Btu/F-gx20F = 18,326 Btu.
>
> Nick
>
Posted by Morris Dovey on December 20, 2007, 11:04 am
Jeff wrote:
<good stuff snipped>
| Which brings up another point, I'm assuming Morris's collectors
| are thermosyphon. How does he intend to withdraw heat, he'll have a
| worse convection problem then?
How so? Remember that (I think) I'd like the withdrawal to take place
slowly and steadily.
--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/
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> after the sun sets, and came up with an idea for a "heat storage
> closet" immediately behind the collector panel. Whatever it lacks in
> originality, it makes up for with simplicity. :-)