|
|
re: a stupid question
3 feb 2004
george ghio wrote:
>what shape ducts?
flattish... 30" 6 mil uv poly film greenhouse air distribution ducts
(about 40 cents per linear foot) laid flat on top of the pv panels
so they are about 44" wide and 2" tall when the sun is shining, and
empty at night.
>what are the losses through a couple of inches of water and two layers
>of plastic?
almost none for the water itself. the air-plastic interface would have
a fresnel loss of about 4%, with a lot less for polyethylene-water and
polyethylene-glass interfaces, with some sort of matching goo. you might
look up the refractive indices and work this out.
>how much energy is lost to pumping the water and moving the panels or
>mirrors?
...70 watts max, as mentioned below. the panels and mirrors don't move.
>what is the duty cycle of these pumps?
perhaps 8 hours per day in july. less in winter, when more heat is needed.
>> with a basement heat store, this might also provide some
>> wintertime space heating or hot water for showers.
>
>"might" have several lbs of frozen water sitting on the panels.
intelligent control.
>> it could have a building underneath.
>
>love this bit. a building under the basement.
you may be confused, my good man. pick one:
1. basement heat store with pvs on a ground rack, or
2. no basement heat store, with a building under the rack.
nick
...something like this on the ground, made from 15 18' pieces of unistrut,
viewed in a fixed font:
|
. |
f| at dawn, in full sun, the panels might
. r| see about 0.9x0.9x0.9x800w/m^2x16'/6' =
e| 1555 w/m^2... 6 62"x32.5" 165 w sharp
dynaglas . s| panels might produce 1539 watts, if
n| they are cooled by a few inches of water
. e| flowing through plastic film ducts on top.
18' l| 16'
. | the floor would receive about 6x16x1555/10.76
r| -1539 = 12.3kw of net heat. two attwood v1250
. e| 24v 35w bilge pumps could move 42 gpm of
f| water through the ducts, keeping the panels
. | about 12.3kx3.41/(42x8x60) = 2 f above the
duct duct | 24-hour shaded-pool wet bulb temp.
. panel panel |
-----------------|------evap pool-----
| ~6' | ~8' | ~1'
.....................................................
--------------------------------------
| | |
| | |
| p p | |
|-----------------| |
| v v | |
| | |
| p p | 10' wide |
|-----------------| epdm rubber | 16'
| v v | |
| | |
| p p | |
|-----------------| |
| v v | |
| | |
| | |
--------------------------------------
with sun elevation theta, the panels would see approximately
800x0.9x0.9/3.28(6+16x0.9) = 1185(sin(theta)+2.4cos(theta)) = 3082 w/m^2
(3 suns max), when theta = 26.2 degrees, producing about 3051 watts
of electricity with about 83.4k btu/h of net heat on the floor, so
the panels might be about 83.4k/(42x60x8) = 4.1 f warmer than
the 68.4 f (20.2 c) 24-hour wet bulb temp in phila in july.
strip # bottom (ft) top (ft) spacer (in) tilt (deg)
1 0 1.329988 0.069425 0.2492357
2 1.331271 2.653542 1.718152 6.180075
3 2.718412 4.021652 3.185456 11.51298
4 4.207816 5.485535 4.430827 16.11825
5 5.845247 7.095126 5.455744 19.98893
6 7.676832 8.899349 6.285437 23.19267
7 9.75055 10.94771 6.952877 25.82627
8 12.11791 13.29236 7.489846 27.98812
9 14.83565 15.99017 7.923422 29.76574
height= 15.99017 conc= 1.995 ohb= 11.00475 %
|
|
