Check the image attached below. This is a typical evaporative air cooler design. My proposed addition to this design is to retrieve the water back. What if we guide the evaporated water through a tube. The vapor is then compressed and passes to a condenser, which condenses the vapor back to water. This water returns to the water tank for reuse.

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I am not an engineer and don’t have much experience in applying these ideas in real life. However, I would appreciate any help regarding if this would actually work and the problems that may arise.

Thanks in advance!

  • $\begingroup$ what will you do with the heat that is produced when the water vapor condenses? $\endgroup$
    – jsotola
    Feb 2 at 19:24
  • $\begingroup$ It will be ejected out of the room that is being cooled. In principle, I’m thinking of something like the normal AC condenser, which ejects the heat out of the room to the outside. $\endgroup$ Feb 2 at 19:47

2 Answers 2


Not only is it possible, it is the fundamental invention of effective "air conditioning"

Historically, an "air conditioner" was an invention that controlled the humidity of air. There were already coolers and heaters, but having the wrong humidity has the specific bad effect of making paper curl.

The first effective "air conditioner" worked by spraying water through air to reach 100% humidity (evaporative cooling), then cold-coil cooling the air (condensing out the water) to the temperature where the water content was the required value, then heating the air to the required temperature with the required effective Relative Humidity.

The 100% humidity stage cooled the air and gave it a fixed relative humidity, required to give the next two stages a known start point. The cooling and heating stages can be two sides of the same heat exchanger.

The next major invention of Air Conditioning was the invention of a better heat pump (smaller, cheaper, and more effective), but the fundamental invention was the realisation that humidity could be controlled as well as temperature, by using a two-or-three stage process.

Patent: https://patents.google.com/patent/US1085971A/en

One of the major advantages of simple modern residential "air conditioners" is that they don't require water supply and plumbing. And a two-stage process is always more expensive than a single-stage process.

The energy requirement of temperature change and humidity change is the same, regardless of which order you do them in, but the efficiency and cost will be different. I'm not an AC engineer, but I know that some buildings still use humidifiers and dehumidifiers, sometimes both are fitted, and used depending on load and time of year.

  • $\begingroup$ So, you are saying my so-called proposed “addition” is viable for use. However, what makes conventional ACs used rather than my mentioned addition. It seems that it will require a similar energy needs (correct me if I’m wrong), uses water rather than refrigerants which, mostly, have high ODP and GWP. Also, it is cheaper than modern used ACs. Is the efficiency the main reason here? and how different is the efficiency of this idea when compared to normal ACs. $\endgroup$ Feb 3 at 6:23

The diagram is the proper design diagram for a evaporative cooler, BUT you need to understand a few things:

  1. The 25 degree air will be close to 100% relative humidity. Most people will not find this comfortable. Places where these types of coolers ar eused are typically desert environments where the extra humidity in the air mixes with extremely dry air. Note that this design is exactly the same as an evaporative humidifier.

  2. You need make-up water to replace the water that goes into the outlet air.

  3. You need to treat the water. Everything here will turn nasty quickly. The pad will turn into goo, the water itself will get slimy as well. Commercial/industrial cooling towers use professional water treatment to combat this. Home humidifiers use an additive to keep the pad serviceable.

  4. You can't "retrieve the water back" without installing a dehumidifier, which is essentially an air conditioner. No one would ever do this, using two processes where only one is required. The evaporated water in essentially dissolved in the air. To get the water out of the cooled air, you have to cool the air below the dew point. There might be some small-scale dessicant-based processes to do this, but consider them all experimental.

  • $\begingroup$ Thanks for the comments. I’m just wondering why the vapor will be dissolved in air. Shouldn’t the hot vapor just move up? Please elaborate on that part. $\endgroup$ Feb 3 at 18:51
  • $\begingroup$ @BelalBahaa, this is just the way the physical world works, and why these things tend to be done by engineers who learned such things in school. And the vapor isn't hot, it cooled down just like the air. $\endgroup$
    – Tiger Guy
    Feb 3 at 21:09

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