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re: solar closet water heat storage medium
17 sep 2003
joe fischer   wrote:

>thomas  wrote:

>: i have a good, not great, southern exposure on the end of a split level
>: rancher.  the interior space on the south side of the house is the kitchen
>: and the living room.  there are 440 sq ft. floor and 3520 cubic ft of space.

the volume isn't very important here...

>: the building is slab on grade with the kitchen and living room on the upper
>: floor.

how big is the building? how much insulation?
>: my thought is to make a sunspace on the south side on the ground
>: approximately 15 feet wide by eight feet high x eight feet high.  

sounds good. you might make it bigger. you might collect 0.9x980x8x15
= 106k btu of sun from the south and 0.9x610x8x15 = 66k of overhead sun
and lose about 6h(100-30)200ft^2/r1 = 84k btu on an average december day,
for a net gain of 88k btu/day, a bit less than a gallon of oil. how does
that compare with your fuel bill?

>: i have yet to calculate the number of bottles and water volume.

a 2 liter bottle is about 4" d x 12" high. hexagonal vs square stacking
adds about 10% to the number of bottles...

>       figuring 4 pounds in each bottle, a pound of
>water will hold 1 btu for each degree of temperature rise,
>and even 30 degrees rise during the day would only amount
>to 120 btu per bottle maximum. 

you might store overnight heat in 120k/120 = 1000 bottles...
a few years ago, the local 7-up bottling plant gave me about 1200
2-liter bottles on a 4'x4'x8' tall shrink-wrapped pallet, way more
than a pickup truckful, loose. but water vapor permeates through
pet bottle walls over time, esp when warm, so the bottles
might need topping up every year... 

>       eutectic salts can be mixed to melt at 75 degrees, which would
>store about considerably more heat in the phase change...

but they get tired of changing phase.

>: <  south
>: -------------------
>: |         --> warm out
>: |       |
>: |       |___________kitchen level _________
>: |  b    |
>: |  o    |
>: |  t    |
>: |  t    |
>: |  l    |
>: |  e    |
>: |  s    |
>: |         <-- cold in
>: |____________________slab on grade________

the cold and/or warm vents need one-way plastic film dampers to prevent
warm house air from flowing into the sunspace through the top vent and
cooling and returning to the house via the bottom vent at night.

and this is just a crippled sunspace, not a solar closet. in this picture,
the bottles store heat during the day, but a lot of that heat goes back out
through the glazing at night.

you might sprinkle some sand above the kitchen ceiling, under the attic
insulation. or stack the bottles inside the kitchen, on a wall, as in
a large wine rack. or put bottle gabion columns around the house: place
one bottle vertically on the floor, surround it by 8 radial bottles, necks
inward, wired in a ring, put another radial layer on top, and so on. build
one around a pole lamp for more interior drama. this water could come in
handy if well pump power fails during a hurricane.

>a window can let in as much as 1500 btu per hour per square meter (yard)

a single layer of polycarbonate with 90% transmission might pass 0.9x800
= 720 w/m^2 of am2 sun, ie 2456 btu/m^2 or 2055 btu/yd^2. 

>and solar black chrome on copper foil will help heat the air quickly,
>providing a lot of heat during the day.

black paint or black window screen is cheaper, but that foil (where can
we buy it?) can help a trombe wall, another form of crippled sunspace...

>depending on the material that the south facing wall is made of, some
>consideration of having a glass wall outside the existing wall, to create
>a trombe wall, and any amount of mass that could safely be added would help.

maybe, with that unobtainium foil. 

>it might help to make small models and use thermometers to measure
>the effects. 

pe norman saunders says you can learn with a cardboard box and saran wrap. 


   in our home solar heating system we used water as the thermal storage
   medium for an air-transfer unit, the water being contained in 1000
   one-gallon polyethylene bottles stacked so that air could flow between
   them. they worked satisfactorily until some desert pack rats invaded
   the storage bin, making nests of the insulation and chewing holes
   in the water bottles. 
                                 p 468, _applied solar energy_, by
                                 aden b. meinel and marjorie p. meinel
                                 addison-wesley, 1976

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