[Greenbuilding] [BULK] Re: Air Conditioning for Phoenix

[Ben Pratt]

OK--i'm really a dunce compared to most of you on this list--but now 
i'm feeling a little smarter because i had this same idea--metal roof 
on purlins.
	I love metal roofs. I built a garage ten years ago--the only 
thing i ever built--and used a metal (pole barn style) roof. Only had 
to put trusses every 8 feet (i did every 6) instead of every 2 for a 
"normal roof). Never held any snow (8/12 pitch). I put the screws in 
very carefully, so they  made a nice grid pattern. Thought it looked 
great and so did most of the neighbors.
    So I was considering doing this to my new (1929) house when a new 
roof is needed in a few years. Actually wanted to do the purlins 
thing to keep my roof cooler--and i would love to get overhangs out 
of the deal (my house has none). Couldn't you do it right over the 
shingles (in case it rained during the construction and to save time)?
    What would the cost be to get someone to do this--compared to 
removing and replacing the shingles. Unfortunately, it's not a simple 
roof. I imagine the price of the material has gone up a lot. Hasn't 
steel gone up, like 700% in the last ten years?
   Also, i'm in minnesota, not arizona, so another option could be to 
insulate (foam sheeting) on top of the existing roof and put the 
purlins and steel on top of that. My attic is finished, so I can't 
insulate it any better without demo-ing the ceiling.

-Ben




At 9:43 PM -0500 1/30/07, Keith Winston wrote:
>Hi there,
>>  I'm going to push the limits of what he can handle as it is.  A metal
>>  roof makes a lot of sense in Phoenix, and that is the second part of
>>  this project that I didn't mention.  Living roofs are great, but involve
>>  structural mods that I'm not willing to consider on someone else's
>>  house. 
>>  
>What about: put your metal roof on purlins (not all mftrs allow it, but
>some do) to create an air channel underneath, vented top and bottom
>(hopefully it's a simple roof -- include insect barriers in the vents).
>Use a radiant barrier under it, pointing up.
>
>Insulate the roof from within the attic with spray foam, in the meantime
>sealing up the attic so if there are any ducts in there they are inside
>the envelope. Sorry, he has to move the nesting dolls. Check with your
>local foam contractor to see how willing/able he/she is to work around
>crap, but probably it needs to be empty. Hire a few young people to
>clean it out! Leave the insulation that is probably already on the
>floor, to make the attic a lightly conditioned space. Then you get the
>reflective metal roof, a radiant barrier properly installed, a
>convective air space to keep the whole assembly from getting TOO hot, a
>tightly insulated roof, interior ductwork... have I missed anything?
>
>Say, did you ever find indirect evaporative coolers? We can't really use
>them here in DC, too humid. I see that Mastercool has an indirect
>modification available http://www.adobeair.com/masterCool.html, I can't
>find it on their website but call and ask them. The other one is here:
>http://www.oasysairconditioner.com/, which looks impressive.
>
>Another possibility is a Freus water cooled evaporative air conditioner,
>quite different from a direct or indirect/2 stage evaporative cooler. It
>is a compression-cycle machine that uses a spray of water on the
>condenser coils to improve performance.
>
>http://www.freus.com/
>
>They don't have a good website. You'll probably gain more information here:
>
>http://www.toolbase.org/TechInventory/TechDetails.aspx?ContentDetailID=793&BucketID=6&CategoryID=6
>http://ezinearticles.com/?Evaporative-Water-Cooler---This-Water-Cooled-Condensing-Unit-Is-No-Swamp-Cooler&id=269729
>http://www.ecosmartinc.com/productdocs/1-Freus-Overview.pdf
>
>I'm not sure whether it makes more sense to use less electricity, or
>spray the Ogalala into the air to be whisked away...
>
>Also, I have used/installed the Fujitsu 12RLQ mini-split heat pumps,
>which are 21 SEER units. If you have an open floor plan and can get away
>with just one or two sources, it's a good prospect. Of course, you may
>need to consider ventilation, though with swamp cooling it's part of the
>picture. See if an HRV is justified in there, it might remove a bunch of
>the moisture while still cooling makeup air. I like the Venmar units.
>
>Warmly, Keith
>
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-- 
B  e  n  j  a  m  i  n   P  r  a  t  t
Professor
Department of Art and Design
University of Wisconsin-Stout
Menomonie, WI 54751
715 232 1537