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Roof sprinklers

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mike_belben:
I built an open sided tin lean-to off the shack to have some sheltered workspace from the rain and blazing sun.  The gutter is plumbed to a collection tote for garden  water. I dropped a sump pump in and hosed the tin rooftop down on an oppressively hot noon day.  Other than evaporative losses the free rain water was being collected and recirculated.  


The gravel temp in the sun was in the 90s.  The gravel temp under the shade of the enclosure was 70ish and air temp was around 83 and stuffy feeling from the ceiling area. The underside of the tin was 125-130F before wetting. After a few minutes of hosing the top of the roof, underside temps dropped to 88-90 and the feeling of coolness from above was a notable relief, like a welcome breeze.  


The sump pump draws .05 amps @115vac when pushing up to the roof through an unthrottled hose.

The collection water out the downspout was easily hot enough for a good shower the entire cycle.  20 minutes later the roof was back to 130F so there is certainly all the hot water you can want on a tin roof during a sunny day.  This is only 12x24

 If that roof was over an air conditioned space i am certain it would reduce the heat that the air handler is having to work with.  Water is ~830x denser than air which means it can carry away and/or store much more BTU than the same cubic volume of air.  Hence the 40 temp drop in minutes.


Cooling and hot water for the electrical cost of a window fan.  Im going to use it to heat the kids pool and cool my workspace. 

stavebuyer:
Along the same line I have an old desert tan shade cloth that I used to block the morning sun from my sawmill building. I am tempted to stretch it over the roof of my garden shed(12x24) that is in full sun to see what difference a little shade would make.

HemlockKing:

--- Quote from: stavebuyer on July 26, 2021, 07:09:52 PM ---Along the same line I have an old desert tan shade cloth that I used to block the morning sun from my sawmill building. I am tempted to stretch it over the roof of my garden shed(12x24) that is in full sun to see what difference a little shade would make.

--- End quote ---
Shade makes all the difference I find, I hate working in the sun actually. Unless its a warm early spring thawing day lol 

stavebuyer:
Curious as to how the cooling would be reduced once the water in your tote had been heated after a cycle or two across the roof? Would you need a larger tank or long buried loop for the system to remain effective?

mike_belben:
The tote was just a numbers run for today to see if it was worth the effort.  Im gonna use an 18ft round pool that we just stood up.  about 7,000 gallons of water.  I think it would take about a week to raise that 5 degrees.  


I stuck my hand in the top of the tote and couldnt feel any temp rise.  As the delta T shrinks it will get less effective at cooling the roof down.  A 20g water heater tank or something however could probably stay at 120f all the time.  Be handy for an offgrid gravity fed hot water supply.  Solar could easily run the pump. Tank in the rafters.



I always kinda thought about cooling my future cabin roof with a recirculated coi pond.  Keep the water turning over and help keep out solar attic gains during the noon sun.  

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