Article 30350 of alt.solar.thermal: Path: news.misty.com!not-for-mail From: nicksanspam@ece.villanova.edu Newsgroups: alt.solar.thermal Subject: Re: Overnight air heater thermal storage Date: 25 Apr 2008 07:38:33 -0400 Organization: Villanova University Lines: 63 Message-ID: References: NNTP-Posting-Host: acadia.ece.villanova.edu X-Trace: max.inside.misty.com 1209119903 28006 153.104.44.130 (25 Apr 2008 10:38:23 GMT) X-Complaints-To: abuse@misty.com NNTP-Posting-Date: Fri, 25 Apr 2008 10:38:23 +0000 (UTC) Keywords: sanspam Xref: news.misty.com alt.solar.thermal:30350 8' ------------------------------------------ | | | | | ----------- | | | | | | | | | --- | | | | | | | ^ | ^ | | | | | | | | | | | | | | | | | | | | | | |c | | | | | |h |o | | | | | |o |o | | | | |h |t |l | | | | |o | | | | |Cc |Ch |u |Tha|Tca| 8' south --> | | | |s | | | | | | |e |c |c | | | | | |a |a | | | | |w |v |v | | | | |a |i |i | | | | |l |t |t | | | | |l |y |y | | | | | | | | | | | | | | | | | | --- | | | | | | | | | ----------- | | | | ------------------------------------------ We might replace the corrugated polycarbonate glazing and window screen in Gary's nice 12/06 MEN air heater described at http://builditsolar.com and http://www.motherearthnews.com/multimedia/image-gallery.aspx?id=74688&seq=1 with a $64 4'x16'6.5" UPS-shippable 3-pound roll of 0.007" GE HP92W Lexan folded over a flat 2x4 at the top, with a bottom tensioning spring to make a 3.5"-deep outer cool cavity and a 2" inner hot cavity and solar thermal cogeneration, as above, viewed in a fixed font. An 8' cube with lots of simple assumptions and US Rv exterior surfaces and 2 8'x8' layers of Lexan with 92% solar transmission would have an approximate G = 6x8'x8'/Rv Btu/h-F thermal conductance to outdoor air on a cloudy day. Rv = 15 makes G = 25.6. If 1000 Btu/ft^2 of sun keeps the cube 70 F for 8 hours with 8h(70-30)G = 8.2K Btu on an average Phila December day and a Cc Btu/F cool mass supplies 16h(70-30)G = 16.4K Btu of overnight heat and 0.92^2x1000x8'x8' = 54.2K Btu = 8.2K+16.4K+8h(Tca-30)8x8/R1, the average cool cavity temp Tca = 88 F. If Cc is 70 F at dawn and 88+18 = 106 at dusk and 16.4K = (106-70)Cc, Cc = 458 Btu/F, eg 458/64 = 7.2 psf of water with a 12x7.2/62.33 = 1.4" waterwall depth. If the hot cavity gains 54.2K/8h = 6775 Btu/h at a 106+6775xR1/64ft^2 = 212 F max temp (boiling:-) and the hot waterwall supplies heat for 5 cloudy days in a row with 5dx24h(70-30)G = 122.9K Btu = (212-70)Ch, Ch = 865 Btu/F, eg 13.5 psf with a 12x13.5/62.33 = 2.6" depth. With more thermosyphoning airflow and exponential vs linear warming and finite airfilm conductance and passive thermal control details, we might end up with a 2x3 cool wall and a 2x4 hot wall, or thinner phase-change walls. Anna Edey made waterwalls with 55 gallon plastic film drum liners sandwiched between 10 cent/ft^2 2"x4" welded-wire fence walls over wood frames. Nick