
Ask HN: How do I get a two-stage (indirect) evaporative cooler? - ladberg
Quick background on my thought process:<p>Air conditioning is amazing but uses a ton of energy, which is expensive and might eventually be unsustainable.<p>Evaporative cooling is the process of water separating into hot steam and colder water. Basically, evaporation is caused by a small fraction the water molecules moving at high speeds (which equals high temperature), which can be hot enough to effectively turn into a gas and leave the liquid body. When these molecules leave the liquid they take with it their above-average heat energy, leaving the liquid slightly cooler overall. This works well in arid climates because water in the air doesn&#x27;t re-enter the liquid body, and especially well when it&#x27;s windy out because the water molecules that evaporate are whisked away before they can condense.<p>A lot of people have evaporative coolers (swamp coolers) which cool you down by emulating sweat evaporating on your skin and use far less energy than AC. However, they actually slightly increase the temperature of the air and add humidity, which can be uncomfortable.<p>Enter: the two stage evaporative cooler. It harnesses the cooling effect of evaporation, but evaporates over a heat exchanger instead of your skin. The heat exchanger is used to actually cool the air in the building without adding any humidity and using very little energy.<p>The problem is that I can&#x27;t find anywhere to buy one or any instructions on how to build one myself. I have some vague sketches on how I would build one, but I&#x27;m not sure how I would go about verifying the design and eventually building it. Does anyone know where I could find one? If they don&#x27;t exist, is there any particular reason why? Am I missing a key complexity in the process?
======
Gibbon1
Swamp coolers actually reduce the temperature of the air. At the expense of
increasing humidity. Generally for residential units that's okay since they
work best in places where the weather is both hot and low humidity.
Humidification is seen as mostly an advantage.

Not a HVAC expert but I think larger commercial systems work that way you
describe. Rather than describe it poorly, here's a link to manufacturers
explainer for their evaporative cooling towers.

[https://www.evapco.com/technologies/evaporative-
cooling-101](https://www.evapco.com/technologies/evaporative-cooling-101)

I think these are often used to argument the condenser on commercial HVAC
systems.

~~~
ladberg
Sorry yep I was a bit wrong on the swamp coolers. The water can cool the air
through conduction down to the temperature of the tap, but the actual
evaporation process warms it. (I may still have it wrong, please correct me)

In the link you sent, it looks like even the direct evaporative cooler is
effectively working as a heat exchanger because it's cooling water down (not
air) to be sent elsewhere. This can cool below the temperature of the tap and
doesn't add any humidity. That's basically what I want so maybe I was using
the wrong terminology in the post, but it's still different than a swamp
cooler.

~~~
Gibbon1
I've been trying to figure out how to explain this. But basically what's going
on thermodynamically with a swamp cooler is a classic adiabatic process,
jargon for the total energy doesn't change.

When you evaporate water into dry air. The total energy doesn't change[1]. But
it take energy to evaporate water. So where does the energy come from? By
reducing the temperature of the air.

[1] I think the entropy increases which is why it's favorable.

