Article 61565 of alt.solar.photovoltaic: Path: news.misty.com!not-for-mail From: nicksanspam@ece.villanova.edu Newsgroups: alt.solar.photovoltaic,alt.solar.thermal Subject: Re: What color house? Date: 27 May 2008 16:04:02 -0400 Organization: Villanova University Lines: 56 Message-ID: References: <1gho34h85cheb9u1k62a0q4k9k3v46jeqt@4ax.com> <483c5020$0$89399$815e3792@news.qwest.net> NNTP-Posting-Host: acadia.ece.villanova.edu X-Trace: max.inside.misty.com 1211914988 29646 153.104.44.130 (27 May 2008 19:03:08 GMT) X-Complaints-To: abuse@misty.com NNTP-Posting-Date: Tue, 27 May 2008 19:03:08 +0000 (UTC) Xref: news.misty.com alt.solar.photovoltaic:61565 alt.solar.thermal:30544 Morris Dovey wrote: >Vladimir Vladimirovich Nabokov wrote: > >> I assume a dark color will absorb the heat and awhite will reflect heat, so if >> you live in the Midwest, what's a good compromise? >> >> Pure white would seem perfect in the summer to keep out the solar heating, but >> in the winter you would welcome the heat gain. Am I stuck with middle gray, or >> is there an established scientific answer? > >The color or the paint is nowhere near as important as the insulation >inside the wall and the caulking around openings like doors and windows. > >There's a link below to photographs a white building (not a house) that >was kept comfortably warm through the winter by two vertical black solar >panels set into it's south wall. What happened on cloudy days? >I doubt the building would have been much better heated if it'd been >painted black. NREL says 930 Btu/ft^2 falls on a south wall in Des Moines on an average 24.4 F December day, so 1 ft^2 of white R20 south wall with a U2 airfilm conductance would lose about 24h(65-24.4)1ft^2/(R20.5) = 47.5 Btu/day. We could model a dark south wall like this, viewed in a fixed font: 930/24h = 38.75 Btu/h --- 20 |--------|-->|------------www--- 65 F --- | | 1/2 | 24.4 -----www------- which is equivalent to: 1/2 20 ---------www-------------www--- 65 F | | 24.4+38.75/2 = 43.78 F --- - | - with a heat loss of 24h(65-43.78)1ft^2/20.5 = 24.8 Btu/day. With an 8'x48' wall, the difference is 8x48(47.5-24.8) = 8698 Btu/day. If a single-glazed air heater gains 0.9x930 = 837 Btu/ft^2 and loses 6h(80-24.4)1ft^2/R1 = 334 on an average December day, for a net gain of 503, the dark wall is equivalent to 8698/503 = 17 ft^2 of air heater. Nick