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re: commercial alternative to flat water panels?
27 dec 2003
sundog wrote:
>> i like the idea of a solar trough in a 2:1 concentrating solar attic.
>
>is this something like a skylight with collectors below or a box that is
>placed on the roof?
it's likely larger, something like an attic with a transparent south roof
and a north roof that reflects sun down onto a greenhouse poly film air
distribution duct (about 40 cents per linear foot) filled with a few inches
of water during the day. it might have some standard pv panels under that.
this could be as simple as making the lower 4' of a roof transparent, with
a fresnel reflector kneewall to the north, eg a white wall or a few
reflective strips.
with a 1:1 slope, it might look like this, viewed in a fixed font:
shingles
transparent --
south t r4
t r3 4'
t ductr2
t pvs r1
------------------------ attic floor
| 4' |
if the bottom edge c of reflective strip r1 is screwed to the south side of
the kneewall (cv) and the top edge b reflects sun s onto line a on the floor
4' to the south at dawn, it needs to be spaced d1 inches away from cv:
v
t .
s t bd1. ---
t . . . 1'
t . .
a--------------------------c ---
| 4' |
angle cab = sba = atan(1/4) = 14 degrees, so abc = 90-14/2 = 83 and
bcv = 7 and d1 = tan(7) = 0.122', or 1.5", eg a 2x4 layed flat. for r2,
cab = atan(2/4) = 26.6 and d2 = tan(13.3) = 0.236' or 2.84", and so on...
a linear foot of attic like this with r1 glazing with 90% solar transmission
would collect about 0.9x4(1330+910) = 8064 btu on an average 46 f january day
in wichita falls, tx. at 120 f, it might lose 6h(120-46)4sqrt(2)/r1 = 2512,
for a net gain of 5552 btu.
>> >my interest is in heating water to provide underfloor heating in a partly
>> >passive solar house. there is no space for heat absorption walls inside
>> >but i have quite a bit of unshaded roof available (at least 24' x 12')
>> >that has a slope of 1 in 3 and faces roughly 15 dergees east of true south.
sounds workable... 15 dergees is ok. it might be steeper than 1/3 for heating.
where will it be? it might have enough south windows and sunspaces and air
heaters to keep itself warm on an average day of the worst-case month.
>> how about a sunspace and shelfbox on the south side of the house?
>
>there are two possible spaces on the first floor wall. one is likely to be
>shaded by (legally protected) trees but i'll have to visit the lot and check
>out how much. the house has not yet been built. the other space is about 7'
>wide and should have no shade, apart from late afternoon in winter. what
>depth - out from the house wall - would be needed?
a shelfbox might be 4' deep...
>is your email address still the same as in your usenet archives
>****@acadia.ee.vill.edu
for the moment... vill is soon to become villanova. both work now.
>i would like to discuss the possibility of your doing some design for me.
oooo. good...
nick
nicholson l. pine system design and consulting
pine associates, ltd. (610) 489-1475
821 collegeville road fax: (610) 831-9533
collegeville, pa 19426 email: nick@ece.villanova.edu
computer simulation and modeling. high performance solar heating and
cogeneration system design. bsee, msee, sr. member, ieee. registered
us patent agent. web site: http://www.ece.villanova.edu/~nick
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