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re: solar collector design for a solar closet?
7 nov 2002
rob  wrote:

>hello,

hi rob,

>i came across nick pine's solar closet and it seemed very interesting.
>it seems like a relatively simple way to store solar heat in a house
>and have a reasonably normal looking and normally constructed house. 
>are there any houses constructed using this system?

not that i know of, yet. there have been a few starts and abandonments.
one of the (largely unrecognized, even by me until lately) problems is 
that it's hard to store overnight heat for a house, starting with warm
air from a sunspace, unless the thermal mass in the house has lots of
surface exposed to the warm air. lots of insulation helps... 

>in reading mr. pine's usenet postings, it seems he prefers a very
>sunspace made from half a quonset style greenhouse as the collector
>because it is much cheaper than "built" solar collector.

commercial plastic film greenhouses are quite very, with kits for about
50 cents/ft^2. standard labor to put up a 30'x100' version from scratch
is 3 people, 1 day. mine is a lean-to, 16' tall x 12' deep, made from
steel pipe half-bows. 

>it seems the problem with the sunspace is the vulnerability of it
>to hail, wind, and over heating in the summer, although mr. pine
>reports no problems with his system.

so far, so good. it could use more shading and ventilation in summertime. 
my biggest problem has been maintaining homeowner's insurance. state farm
came out to inspect and cancelled when they saw the plastic film, even
after 20 years with no claims. this may be illegal, since it was built to
the boca code, with a township permit. ever looked at the statefarmsucks
web sites? :-) mostly gripes from plaintiff attorneys...

>somewhere i read he recorded a temperature of 143f in the summer.

that was in my dynaglas-covered attic.

>i wondered if vertical solar collectors attached to the outside
>insulated) of a basement foundation could be made using the same
>materials as the greenhouse solar sun space?

sure, altho "collectors" don't add useful living or storage or
growing floorspace to a house. 

>a 10 year mylar film attached at the edges of a solar collector.

or 49"x50'x0.020" rolls of replex polycarbonate...

>a 50% black sunshade hung in the middle and some sort of dampers
>to hold the heat in the solar closet.

sounds a bit vague. recall that solar closets (tm) live inside
sunspaces. they aren't the same. a sunspace has no heat storage. 

>
>                / roof slope
>              /
>            /
>          /
>        /
>      /
>    /
>  /
>/------ 3-4 foot eaves
>	|
>	|
>	|
>	|
>	|
>	|
>	|
>	|
>	|
>	|
>	|-----------------3-4 ft overhang over basement
>               |    >>>>>>>>> hot air in |
>               |       | f |             | 
>               |       | o |             |  insulation 
>   collector	|       | u |   solar     |  outside wall of solar
>   glazing -->	|       | n |	closet    |  closet and underside
>               |       | d |   (battery) |  of basement slab.
>               |       | a |             |
>               |       | t |             |
>               |       | i |             |
>               |       | o |             |
>               |       | n |             |
>               |  <<<<<<<<< cool air out |
>               |-------------------------------

the tabs make this hard to read, but there appears to be only one
layer of glazing, vs sunspace and closet glazings... perhaps the sun
could make this a "frost-protected warm foundation" with no digging.
 
>it is also seems a relatively simple process to hang some fin tube in
>the solar closet to at least pre-heat domestic hot water...

lately, i'm drawn to hydronic slabs and thomason trickle collectors...

>how deep should the collector be?  a couple of inches deep or
>something like a foot.

steve baer suggests 1/15th of the height for natural air circulation.

>i have seen it recommended that the 50% black solar cloth should start
>at the outside of the collect and slope back towards the inside at the
>top so the air flows through it.

sounds good to me.

>should the back of the collector be flat or have a triangular corrugation
>/\/\/\/\/\/\/\ ?

i'd say flat's good enough.

>will a solar closet work have the capacity to provide adequate heat,
>or given the climate, would a solar cistern be a better solution.  the
>solar cistern seems to be a more active and complex system.

toby's solar cistern concept seems a bit hairbrained to me. 
 
>btw, here is some data for my area:
>
                   jan... dec 	year

>average high      33.1   33.0  56.2
>average low       11.9   11.9 	29.8

looks pretty cold. how much solar energy falls on a square foot of south
wall on an average jan/dec day? what's the nearest town and state? 

nick




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