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[–]Tom_Bombadil 5 insightful - 1 fun5 insightful - 0 fun6 insightful - 1 fun -  (4 children)

My educated guess:

This addition would likely require regular cleaning so contamination (dust, pollen, etc.) doesn't accumulate in the radiator cooling fins.

Plus the evaporation rate depends:

  • on the RH of the air.
  • exposure to sunlight
  • Air temp.
  • Air flow

So you'd want a way of controlling the rate of water flow; adjusting for these floating variables.

Also, the water would generally need to be drawn through the sides, and blown up/out. This isn't an difficult obstacle, but it would change the design.

Plus, the liability of water damage from:

  • poor installation
  • leakage
  • neighbor kids screwing with it
  • Damage/wear from increased thermal cycling (cold water of hot surfaces) literally rinse and repeat.
  • etc.

Plus the warranty risks associated. Adding water to anything creates problems.

Also, it reduces profitability for the energy companies.

It's a good idea. On hot days you could momentarily boost you efficiency by spraying down you external ac unit, but it will evaporate quickly.

If your ac fins are bent then you could buy one of these to straighten bent fins and increase the air flow.

You could also winterize your windows to reduce leakage and basically add an extra insulating later to your windows.

This is all shooting from the hip guesses.

I'm not an AC engineer...

Good luck!

Edit:.

https://en.wikipedia.org/wiki/Evaporative_cooler

Evaporative cooling is especially well suited for climates where the air is hot and humidity is low.

[–]magnora7[S] 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (3 children)

Interesting analysis.

Maybe it could only be activated on super-hot days, when the efficiency gains would be particularly high? And the high heat would also guarantee the water would all evaporate quickly so it wouldn't hang around for too long, which seems the source of a lot of the problems.

[–]Tom_Bombadil 3 insightful - 1 fun3 insightful - 0 fun4 insightful - 1 fun -  (2 children)

And the high heat would also guarantee the water would all evaporate quickly so it wouldn't hang around for too long

Not necessarily. It depends on the weather conditions.

If it's a humid day then the evaporation rate drops quickly,. Adding water on a 90 deg day with 85 deg dew point won't get you much.

All machine efficiency depends on your ∆T. So it will always work better on hot days with cooler water. If it's extremely humid then the evaporation rate will be lower.

Evaporation absorbs the most heat energy. 1cal raises 1g of liquid water 1deg C.
The latent heat required to evaporate 1 g of 100 deg C water to 1g of 100 deg C steam is 540 Cal/g. Same situation with ice to water is 80 Cal/g.

Do you have insulation in your attic? Check the R value for efficiency.

If not, then that helps quite a bit. Also, attic ventilation. Get a attic fan that you can use to increase ventilation. Particularly at night when the outside is much cooler.

Moving air transfers heat away if. Static air insulates (tiny pockets is air in Styrofoam). Sometimes the attic fan works against you. It depends.

[–]magnora7[S] 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (1 child)

So I looked it up, it takes 2.45 Wh to raise the temperature of one gallon by one degree F. So if the water goes from 80F to 120F, that's 98 Wh. That's remarkably close to the 100 Wh break-even.

So if you had access to cheap water, or had expensive electricity, this might actually save money and use less energy overall. Or if the water delta is more than 40 degrees, that'd made it cost effective too.

[–]Tom_Bombadil 2 insightful - 1 fun2 insightful - 0 fun3 insightful - 1 fun -  (0 children)

It's way better than that.

That method is for heating water. Evaporation draws many times more heat energy away. Many.

The transition from liquid to gas is 540x the energy to raise the same mass 1 deg C.

You get the best results from evaporation. Your body cools when sweat evaporates. If it doesn't evaporate then you're hot and miserable.

Fans don't cool, but increase the rate of thermal transfer (increased air mass in physical contact per unit time), which also increases the evaporation rate. Moving air can also hold more moisture (from memory, needs verification).