re: Help find an old thread—Cooling the roof with sprinklers

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For it to work I would think you’d need water running on your roof all day.

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First, you really don't want "running water" for an efficient system. You want a system that keeps the entire roof surface covered with just enough water to be constantly evaporating to take advantage of the high latent heat of vaporization of water. In the perfect system no water would drip off the roof surface at all.

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If you started in the afternoon your attic would already be too hot for the watering of the roof to make a noticeable difference.

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This really makes little sense. To illustrate that mist down a section of extremely hot patio in the sun and check the temperature delta before and after, you will see a HUGE drop almost immediately.



Again, there are a huge number of variables and it will be more efficient for some homes than others. Just a single example is the better your attic insulation is the less effect it will have.