Start out with a flat reflective roof (aluminum or reflective white paint coating) with a 2" barrier around three sides, and a 1" barrier along the fourth side. A few feet lower at this fourth side is a trough for catching water, and a pump and piping that goes to the other side of the roof. Fill roof with water.
In the summer, the water is pumped on hot days. The waterfall should lower the water temperature to near the wet bulb temperature, which is generally lower than the dry bulb temperature (what is normally referred to just as "the temperature"). Roofs are where much of summer heat enters your house, and when I lived in Northern California I measured my roof temperature at 130F.
In the winter, drain the roof.
This setup will work best for climates that: 1. Have access to inexpensive water. You'll go through a lot of water in the summer, and if water is expensive you may just want to use traditional air conditioning instead. 2. Get reasonably hot. 3. Aren't terribly humid. It should still work for humid climates (95F sure beats the 130F+ you'd get without water), but would work better for dry climates.
Alternate method: use a black roof and tint the water white. This will absorb heat in the winter (when you've drained the water), but still reflect in the summer.-- Worldgineer, May 07 2004 Roof Waterfalls http://www.halfbake...Irrigation_20Cooler [spacemoggy, Oct 04 2004, last modified Oct 05 2004] Look Ma, no fences. http://www.oldcount...rket.com/goats.html [2 fries shy of a happy meal, Oct 04 2004, last modified Oct 21 2004] You don't need a flat roof. Just pump the water to a distribution pipe at the top, and use the gutters to collect it. Eventually, this will create a moss roof.-- ldischler, May 07 2004 So, fill the roof with milk in the summer is what you're really saying... or just keep a cow up there.-- k_sra, May 07 2004 Ooh, and have it function also as a cheese machine. On second thought I'm not sure if it's wise to keep warm milk on your roof for more than a day or two.
(besides, I'd call this "Roof Milk" if that's what I really meant)-- Worldgineer, May 07 2004 I never know what you really meant. ; )-- k_sra, May 07 2004 And with a milk roof, you’ll have a problem with roof cats. And then dogs will get up there and chase the cats. And the dog owners will stand in your yard and yell things. Then, angry at their disobedient animals, they will throw rocks. And the rocks will make holes in your roof. And the cats and dogs will fall in the holes. And then it will begin to rain...-- ldischler, May 07 2004 ... cat and dog milkshakes.-- k_sra, May 07 2004 Sorry, [Worldgineer], looks like this is redundant. See link.-- spacemoggy, May 07 2004 Ah, in home:temperature rather than home:roof, that's how I missed it. I think my idea is significantly different - if nothing else because mine doesn't let the water just run off (sounds very wasteful).-- Worldgineer, May 07 2004 Attic insulation and ventilation can seriously reduce the effect a hot roof has on interior temperatures.
In the climate to which you refer, many use evaporative coolers instead of air conditioning much of the cooling season. A 6500 cfm evaporative cooler is not uncommon. Also a common practice is to vent the 6500 cfm of cooled air (drop of 30 degrees below ambient is easy to attain) through the ceiling in to the attic and out the attic vents. The 3/4 hp blower motor is a significantly cheaper to run than my 5 ton 12 SEER scroll compressor A/C unit.
On the other hand, if I had to live in the attic I might implement this very halfbaked idea.-- half, May 07 2004 They only let him out half by half.-- k_sra, May 07 2004 You could just have a few inches of soil on the roof (and it could still be sloped) and grow grass on it. This is a very good and low tech way to keep the roof cool in hot summers and still insulate over winter.-- desperado, May 09 2004 ...and if you are going to go that far then fresh milk can be kept on a roof almost year round, as long as it's still in the cow. Or goat, [link]-- 2 fries shy of a happy meal, May 09 2004 Particularly in the dry climates you recommend this for, you are going to lose a ton of water through evaporation. To avoid that you could change it to a closed system with pipes snaking across the roof. Simply dump the collected heat somewhere or recover its energy (the water heater, your pool, etc).
But that's baked, it is called a solar collector system.-- krelnik, May 10 2004 I just thought about how much it would suck to mow the roof...-- yabba do yabba dabba, May 10 2004 [krel] Yes, you definately will lose a lot of water through this system. But the good news is it doesn't have to be potable water. I know of at least one building that has to constantly pump water from it's basement because of high groundwater. There's no reason such water couldn't be pumped to the roof in this case or several others I can think of.-- Worldgineer, May 10 2004 Maybe it is just me, but I don't think there are many hot dry climates that have access to a lot of water. It seems that most hot dry climates have limited water supplies.-- GenYus, May 10 2004 True, but I was describing an ideal situation. This would still work for areas that only get hot for a few days a year.-- Worldgineer, May 10 2004 ...either close the loop... or, open it more, and take the cool water from public water supply, run it across your roof, and take the heated result and water your lawn and plants... problem is, your plants don't need nearly that much water.-- feet1st, Oct 12 2004 random, halfbakery