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<DIV>"Bob Waldrop" <bwaldrop@cox.net></DIV>
<DIV> </DIV>
<DIV>>I recently came across this interesting take on the traditional solar
window heater.</DIV>
<DIV>http://blog.imehrle.com/2011/02/10/solar-heating-made-easy----very-easy.aspx</DIV>
<DIV> </DIV>
<DIV>>In discussing this elsewhere, however, someone mentioned that since it
hangs on the inside of a window, it blocks sunlight from the window.</DIV>
<DIV> </DIV>
<DIV>Views too.</DIV>
<DIV> </DIV>
<DIV>>That person thought that the heat resulting from the flow of sunlight
into a room without any obstruction in the window would be greater than the heat
resulting from the operation of this device in a window, which would have the
incidental effect of blocking some sunlight from the room.</DIV>
<DIV>Is that correct? </DIV>
<DIV> </DIV>
<DIV>Yes, but it also increases the heat loss from the window when the sun is
shining. </DIV>
<DIV> </DIV>
<DIV>http://rredc.nrel.gov/solar//old_data/nsrdb/1961-1990/bluebook/data/14821.SBF
says 780 Btu/ft^2 falls on a south wall on an average January day in Columbus,
OH with a 26 F outdoor temp. With no solar heating panel, a 1 ft^2 R2 window
with 80% solar transmission in a 70 F house would gain 0.8x780 = 624 Btu and
lose 24h(70-26)1ft^2/R2 = 528, for a net gain of 96 Btu/day. With a 143 F
panel next to the glass for 6 hours, it would lose 6h(143-26)1ft^2/R2 +
18h(70-26)1ft^2/R2 = 747 Btu, for a net loss of 123 Btu/day, or
more, if the panel reflects some sunlight back out of the window. </DIV>
<DIV> </DIV>
<DIV>And how can Mike circulate solar warm air through the rest of the house
with the furnace blower if he leaves the return vent open but closes the supply
vents to the solar room? Airflow requires return and supply paths. Where's the
supply path to the room?</DIV>
<DIV> </DIV>
<DIV>If Mike knew more about airflow or heatflow, he might suggest hanging huge
ugly boxes and cutting holes in house walls or turning a south window into an
air heater with a foamboard insert that collects less solar heat than the window
but greatly reduces the heat loss at night...</DIV>
<DIV> </DIV>
<DIV>If a 2' wide x 3' tall window gains 6ft^2x624/6h = 624 Btu/h by day and a
1" R10 foil-foamboard panel with 1.5" slots at the top and bottom with dark
high-temp BBQ paint facing the window and foil facing the room loses about
18h(70-26)6ft^2/R12 = 396 Btu at night and
16.6(24in^2/144in^2/ft^2)sqrt(3’(70+dT-70)) = 7.2dT^0.5 cfm of 70+2dT (F) air
flows out of the top slot and provides (70+2dT)-70)7.2dT^0.5 = 14.4dT^1.5 Btu/h
to the room and 624 = (70+dT-26)6ft^2/R2+14.4dT^1.5 = 132+3dT+14.4dT^1.5, ie dT
= ((492-3dT)/14.4)^(2/3). Plugging in dT = 10 F on the right makes dT = 10.07 on
the right, then 10.07, with 23 cfm of 80 F airflow and 230 Btu/h of heatflow,
for a net gain of 6hx230-396 = 984 Btu/day, vs 96x6ft^2 = 576 for the window
alone, or a net loss of 738 with Mike’s panel. </DIV>
<DIV> </DIV>
<DIV>Nick </DIV></DIV></DIV></BODY></HTML>