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<DIV>Inflatables have more promise for air than water heating, IMO, altho</DIV>
<DIV>"solar siding" seems better for that purpose. Polyethylene film has</DIV>
<DIV>high IR transmittance, ie not much heat-trapping greenhouse effect,</DIV>
<DIV>compared to glass or polycarbonate, so a 140 F water heater would be </DIV>
<DIV>inefficient, but an air heater could double as an attached garage:
</DIV>
<DIV> </DIV>
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<DIV>gggggggggggggggggggggggggggggggggggggggggggggggground </DIV>
<DIV> </DIV>
<DIV>|
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<DIV> </DIV>
<DIV>With 28' in the east-west direction, it needs 2x28'x16' = 896 ft^2</DIV>
<DIV>of film for the walls plus 265 for endwalls, totaling 1161 ft^2, eg</DIV>
<DIV>a $136 16'x75' 4-year roll from <A
href="http://www.greenhousemegastore.com">http://www.greenhousemegastore.com</A></DIV>
<DIV> </DIV>
<DIV>The south wall would receive 580sin60+430cos60 = 717 Btu/ft^2 on</DIV>
<DIV>an average December day with a 32 F daytime temp in South Bend, IN,</DIV>
<DIV>ie 0.9x717x16'x28' = 289.1K Btu. With 70 F air inside for 6 hours,</DIV>
<DIV>it would lose 6h(70-32)16'x28'/R1 = 102.1K Btu to the outdoors, for</DIV>
<DIV>a net gain of (289.1K-102.1K)/6h = 31.2K Btu/h (140 F air inside </DIV>
<DIV>real R1 film for 6 hours would lose 6h(140-32)16'x28'/R1 = 290.1K</DIV>
<DIV>Btu/day, more than the solar gain.) </DIV>
<DIV> </DIV>
<DIV>With a dark mesh screen ("s" above) and polyiso foamboard behind it,</DIV>
<DIV>the film might be the main south wall heat loss, with a net gain of</DIV>
<DIV>187K Btu/day. (A less expensive and less efficient version could </DIV>
<DIV>have film vs polyiso foamboard behind the mesh.) </DIV>
<DIV> </DIV>
<DIV>With a few layers of gauzy mesh or felt to keep the surface near</DIV>
<DIV>the film cooler and increase its thermal resistance (a wall can't </DIV>
<DIV>lose much heat by convection to an airstream approaching the wall,</DIV>
<DIV>see equation 1 on page 4 of <A
href="http://www.cibse.org/pdfs/8cimbabi.pdf)">http://www.cibse.org/pdfs/8cimbabi.pdf)</A>,</DIV>
<DIV>we might collect and store higher temperature heat in water as well,</DIV>
<DIV>using a car radiator, despite the high IR loss of the polyethylene</DIV>
<DIV>film, ie keep a cloudy day heat store warm as well as solar heat </DIV>
<DIV>air for the house. The film's high IR loss can help prevent melting</DIV>
<DIV>the mesh or felt under stagnation conditions.</DIV>
<DIV> </DIV>
<DIV>If 100 ft^3 of 140 F water in a 30" diameter x 25' polyethylene film</DIV>
<DIV>duct inside a 2'x2'x25' bench with 108 ft^2 of R20 surface (bags of</DIV>
<DIV>dry leaves?) loses 24h(140-29)108/20 = 14.4K Btu on an average day,</DIV>
<DIV>we can keep it warm with 14.4K/6h = 2400 Btu/h for 6 hours with 1000</DIV>
<DIV>cfm of air at T = 140+2400/1000 = 142 F with a 1000 Btu/h-F car </DIV>
<DIV>radiator. With C cfm of airflow and (T-140)C = 2400 Btu/h,</DIV>
<DIV>C = 2400/(T-140). </DIV>
<DIV> </DIV>
<DIV>Heating C cfm from 70 to T (F) requires (T-70)C Btu/h. If the same</DIV>
<DIV>air flows into the mesh at 70 F and into the radiator at T (F) and</DIV>
<DIV>through the house and back into the mesh, and 31.2K Btu/h = (T-70)C</DIV>
<DIV>= (T-70)2400/(T-140), then T = 145.8 F and C = 411 cfm. (Or more,</DIV>
<DIV>since the radiator will be more efficient with less than 1000 cfm</DIV>
<DIV>of airflow.) </DIV>
<DIV> </DIV>
<DIV>A 1000 Btu/h-F car radiator inside a house with a G Btu/h-F thermal</DIV>
<DIV>conductance can keep it 65 F on a 29 F day with a minimum water temp</DIV>
<DIV>Tm = 70+(65-29)G/1000. If 100 ft^3 of 140 F water cools to Tm over</DIV>
<DIV>5 cloudy days and 5x24h(65-29)G = (140-Tm)100x62.33, G = 96 Btu/h-F,</DIV>
<DIV>or more, with some help from indoor electrical use.</DIV>
<DIV> </DIV>
<DIV>The garage might also supply 289.1K-102.1K-14.4K = 173K Btu of warm</DIV>
<DIV>air for the house on an average day, enough to warm a 200 Btu/h-F</DIV>
<DIV>house with no windows or electrical use, which would require another</DIV>
<DIV>100 ft^3 of water in the garage to stay warm for 5 cloudy days with</DIV>
<DIV>a solar heating fraction close to 100%.</DIV>
<DIV> </DIV>
<DIV>Nick</DIV></DIV></DIV></BODY></HTML>