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Passive Solar Cooling in the Desert - Page 5

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Posted by nicksanspam on September 16, 2004, 12:52 pm

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.

Good idea. Look at www.pbspanels.com. For very low cost and good insulation,
you might order your house in 8'x24'x12" R48 $/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 = $9.2K in materials, ie $9.2K/48^2 = $/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.  


Posted by Auntie Em on September 18, 2004, 3:34 am

um, well, there isn't one.

Here is some information I got about the immediate area though,

Average temp. (F)
Jan  50.4,  Feb 56.0,  Mar 63.3,  Apr 70.7,  May 79.0,  Jun 84.4, Jul
84.6,  Aug 83.0,  Sep 78.7,  Oct 69.8,  Nov 58.7,  Dec 51.4

High temperature (F)
Jan 66.1, Feb 72.4, March 80.2, April 87.5, May 94.8, June 98.8, July
97.7, August 95.7, September 91.7, October  84.3, November  74.3,
December  66.7.

(Even though this is the "measured" high temps, I can tell you that I
have read where a week of 110 degrees is NOT unusual).

Precipitation (in)
Jan 0.4, Feb  0.4, Mar 0.2, April 0.4, May 1.1, June 1.6, July 2.2,
August 1.9, Sept1.8, Oct 1.3, Nov 0.4, December 0.3

Morning humidity (%)
Jan 73, Feb 69, March 65, April 64, May 68, June 70, July 73, August
74, Sept 77, Oct 76, Nov 74, Dec 74.
Afternoon humidity (%)
Jan 50, Feb 46, March 41, April 40, May 43, June 44, July 43, Aug 45,
Sept 49, Oct 48, Nov 49, Dec 51.

 So what does it all mean anyway?


Be careful what you wish for....

Posted by nicksanspam on September 18, 2004, 7:51 am
 Auntie Em  <Auntie Em> wrote:

A nearby NREL weather station with an average measured humidity ratio
might help evaluate the potential for evaporative cooling.

The yearly average (deep ground) temp is 67.5. Could be comfortable, with
dehumidification to w = 0.012. How can you do that without electricity?

Looks like July is the warmest. The daily high exceeds the average by
97.7-84.6 = 13.1 F, so the daily low would be about 84.6-13.1 = 71.5,
not very cool for a desert.

Only 12" of rain per year. I see why you call this a desert.
Are you sure these are all average numbers from the same location?

A 43% RH is not very dry for a desert. Pa = 0.43e^(17.863-9621/(97.7+460))
= 0.793 "Hg, which corresponds to a 9621/(17.863-ln(Pa))-460 = 71.7 dew
point with humidity ratio w = 0.0169. Very humid.

Direct and indirect evaporative cooling won't work well. You might enjoy
a SIP house with a LiCl/CaCl2 roofpond under a greenhouse still with an
open hatchway to allow humid house air to rise up and dry at night.
Would this work with an indoor greywater wetland?


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Posted by Auntie Em on September 19, 2004, 2:42 am

Yeah, why?  does it seem strange to you?


scroll down.

Be careful what you wish for....

Posted by Auntie Em on September 19, 2004, 2:50 am

My God, you're amazing.  The average low for July is EXACTLY 71.5.  I
have absolutely no understanding whatsoever of any of these
calculations, but apparently they work, eh?

Be careful what you wish for....

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