re: passive solar cooling in the desert
16 sep 2004
>"auntie em" wrote in message
>> >i've been told that an above ground super-insulated house can be
>> >less expensive to build than an underground home and yet still
>> >cost the same to heat and cool.
>> well, if you can come up with a url or other reference for this i
>> would love to read it. i cannot imagine that this is accurate. i
>> have not been able to locate a quote for a stick built house, even
>> roughed in, which is less than $80 a foot, coupling that with the cost
>> of "super insulation", it would seem impossible to be able to build it
>> for less than an earth sheltered, or even adobe home.
what's the nearest big town to your desert home? august looks like the
worst-case month for cooling in phoenix, with a 24-hour average 91.5 f
and a 79.2 f nightly min and humidity ratio w = 0.0113, which makes the
ambient vapor pressure pa = 29.921/(0.62198/w+1) = 0.534 "hg with a dew
point temp 9621/(17.863-ln(pa)) = 520 r or 60.3 and a nightly wet-bulb
temp tw = 9621/(22.47-ln(79.2+460+100pa-tw) = 530, 524.8, 527.1, 526.1,
526.5, 526.3 r or 66 f, after a few iterations.
>have you costed a sip panel home with superinsulation thrown in as part of
>the structure? these virtually eliminate the invidious thermal bridging.
good idea. look at www.pbspanels.com. for very low cost and good insulation,
you might order your house in 8'x24'x12" r48 $5/ft^2 solid panels with holes
cut for doors and windows, and ask them to leave the hole material in place,
so you can spray paint everything on both sides when the panels arrive and
screw on hinges inside to make doors and interior shutters for "windows"
consisting of single layers of polycarbonate film over the outside holes.
you might "rough in" a single story 48'x48' house with 20 panels for about
20x8x24x5 = $19.2k in materials, ie $19.2k/48^2 = $8/ft^2.
you might put a layer of epdm rubber over a 2x4 perimeter berm over the
flat roof to make a pond with stones or old tires to hold it down and
provide shade and circulate cool water through old auto radiators or
thermosyphoning pvc pipes under the ceiling, as in zomeworks cool-cells.