I've been researching options for cooling a south facing exterior wall on my house. One thing I've been thinking about is what if I just spray the wall with water and let it evaporate?
The wall is wood siding, 1.5 stories. I say 1.5 stories because the top story is a bonus room over a garage. On the bottom story is a 3 car garage (two garage doors).
The idea is not to use misters, because I'm not trying to cool the air, but to use something like drip micro sprinklers to wet the whole surface of my south facing wall (maybe mounted under the eaves pointing at an angle downwards). The sprayers would turn on for x seconds, then turn off to allow time for the water to evaporate and cool the house. This would repeat on some interval (maybe based on the temperature of the wall).
Apart from the cost of the water, do you see any issues with this plan? I've considered the mineral deposit problem, I'm hoping I can just put an extra calcium filter on there?
Update
After doing more research, apparently this is known as "Spray Cooling", and not "Evaporative Cooling", because what we are cooling is what we are spraying down, instead of cooling air through evaporation. I've found several published papers on the application of this in manufacturing, electronics, etc… Papers like this one, Spray Cooling Using Multiple Nozzles: Visualization
and Wall Heat Transfer Measurements, have some interesting charts showing the cooling curves based on temperature.
Then I came across someone with a slightly similar idea to me, 1977 Patent US4175703A, "Spray cooling system for gable roof".
From the patent:
Periodically, the valve is operated whereupon water is forced through
the pierced holes in the pipe and sprayed as a sheet of water in an
overlapping pattern directly from the pipe onto the building roof.
Thereupon solar heat evaporates the water upon the roof absorbing some
8500 BTUs of heat in the process for each gallon of water employed.….
they have not met with any marketed degree of acceptance in the
residential building market. Probably the foremost reason for lack of
success here is attributed to the absence of system aesthetics.
🙂
Update 2
I finally found a few DIY examples online. These are for roof cooling, which is what I'm starting to lean towards. I think that continually spraying down wood siding might not be the best option… https://www.builditsolar.com/Experimental/RoofCooling.htm.
Best Answer
Evaporative cooling is less effective in places with high humidity. There are mathematic formulas for how much water will be needed to cool a specified surface area by some number of degrees and they are not simple. The wiki article on this has some good information. It would be good to get some idea how much water will be needed before heading down that road.
Before I went that direction I'd look into something that is a one time cost vs. a recurring cost:
Or some combination of the above.