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Electricity-free way to cool a home?

 
pollinator
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Location: Clemson, SC ("new" Zone 8a)
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Mk Neal wrote:...I know on my block we actually get water quality problems from too LITTLE water usage (sediment builds up), so this might be worthwhile for my house.



Interesting.  I've never heard of such a problem.
 
pollinator
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Matthew Nistico wrote: It also won't work on a flat roof, like the tar or gravel roofs of some commercial buildings, or on the flat roof of an RV.



I’m thinking it would work just fine on those roofs (better, really, since they get hotter than sloped roofs) but you’d need a different way to disperse the water, like a sprinkler or soaker hoses. Flat roofs are not truly flat, they all have very slight pitches toward drains. But even if they didn’t, you just need to control the water flow so it keeps the roof wet but doesn’t create standing water, which would be wasted. On an RV, the water drains off the sides or ends. Again, just a slight misting to keep the roof wet is adequate. Where this will not work particularly well is on a steep metal roof, since the water will simply run off too quickly.
I like the idea of a solar panel to run the pump. Similar to the roof vent fan units that incorporate a solar panel to run automatically when the sun shines. If you have rain barrels, the downspouts are refilling them with any excess runoff. Once you had a sense of water usage, you could have spigot water on a timer to top them off, to compensate for evaporation loss.
The 12v RV pumps typically run a gallon per minute at 30 psi, which would be adequate. They draw less than 5 amps, which would be a 60 watt solar panel- less than $50 and not very large. So, yes, this would be very efficient compared to running A/C!
 
Matthew Nistico
pollinator
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Location: Clemson, SC ("new" Zone 8a)
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Julie Reed wrote:I’m thinking it would work just fine on those roofs (better, really, since they get hotter than sloped roofs) but you’d need a different way to disperse the water, like a sprinkler or soaker hoses.



Thank you for considering the idea so carefully.  You might well be right about the feasibility on flat roofs.  The idea of intentionally creating standing water - or as you point out, very very slowly draining water - even the thinnest layer of it on a flat roof just scares the hell out of me.

Yes, I also suspect that this concept would prove very efficient compared to central AC.  But the proof will (some day) be in the pudding, as they say.
 
Julie Reed
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Every time it rains hard you have standing water on flat roofs, nothing to be scared of. As I mentioned, they aren’t really flat, they have to be designed to drain! So they have multiple angles leading to drains, or sometimes simply one pitch to an edge which may have gutters or scuppers. Flat roofs are even more waterproof than pitched roofs, simply because they are designed to hold water for short periods of time. The only concern is snow load, in the north. (Interesting side point- our wasteful country, in the 60s, designed large buildings with deliberately poor insulation in the roof so that heat loss would melt the snow, which was considered far cheaper than constructing a stronger roof).
While the wet roof idea is obviously far less costly than A/C, it would be interesting to do a side by side comparison in 2 identical structures (storage sheds would make cheap test labs). I realize it would never lower inside temps as much as A/C does, but might be adequate. It could certainly reduce the cost of running A/C, and it would also be a great companion strategy with something like earth tube cooling.
 
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Matthew Nistico - here is a project that sounds very similar to your idea, complete with lots of data!  Night Radiation Cooling of Water Flowing Over Roof

And for everyone, while I'm linking one of my favorite sites, here's a whole list of interesting ideas, projects, plans, etc - Build It Solar passive cooling
 
Julie Reed
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Great links C Jones! Thank you, can’t wait to spend some time on those when the rain keeps me inside tomorrow.
 
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Location: SW Michigan
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When i lived in the desert of Joshua Tree, we had a very real heat problem. The flatish roof was covered in the tar and pebbles of yesteryear. It worked very well with the wind and harsh conditions. However, between 3pm and midnight, we could feel the stored heat coming from the roof in the house and above if you were on the roof.

A 110 F this is a major problem.

So, being a midwesterner, i found the solution.

Simply water.

Now everyone will scream I am wasting water. Yes and no. Grey water got used up and POOF! it was amazing ow well it worked. It would literally steam right off. Especially in the evening once the sun went below the mtn tops, a quick spray and problem went away. Thus less waste w the swamp cooler or ac unit.

The reverse in the winter.

Good luck.
 
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just a thought, but many of the very old, pre electricity houses in Florida were built with very high ceilings and wrap around covered porch and large or lots of windows built under the best and biggest shade trees.
 
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