Take advantage of evaporative cooling to boost AC unit efficiency

An air conditioner mister is a very straightforward device. It releases a fine spray of mist around your central air conditioner condenser unit (the outdoor unit) while the compressor fan is running. This fine spray of mist evaporates into water vapor as it moves through the air.

As you may have learned in high school physics, evaporation is a cooling process – the state change from liquid to gas (water droplits to water vapor) increases the energy level in the water vapor molecules, by absorbing some of the heat energy in the surrounding air. By misting the air around your condenser unit, you cool the surrounding air. The cooler the air going into the condenser unit, the less energy the condenser requires to pump heat out of the air conditioning system, and the less you pay in electricity bills.

You may have seen a garden mist cooler on display outside your local building center. My Home Depot has one on display all summer, showering a fine mist into the air and lowering the temperature around the entranceway. You could just place one of these water misters beside your air conditioning condenser unit and let it run all the time while the unit is on. One problem with that is that you’ll waste quite a bit of water, since much of the time that the mist flows from the mister, the condenser fan is not running so the cooling effect of the evaporating water provides no energy savings. Another is that some of that water won’t evaporate, and the longer the mister runs, the more water you’ll have all over the ground around your condenser unit.

A new product called the Cool-N-Save is designed to do exactly this: whenever the condenser unit fan starts running, the Cool-N-Save lets out a fine mist around the sides of the outdoor unit to cool the air that is then drawn into the unit. The Cool-N-Save connects to an outdoor water supply by the provided hose, and its misters connect around the top edges of the condenser unit.

The misting switch is activated by a paddle that sits atop the condenser unit. When the condenser unit fan goes on (indicating the active part of the cooling cycle), the airflow from the fan causes the paddle to rise from its horizontal resting position, which turns on the flow of water to the misters. When the fan shuts off at the end of the active part of the cooling cycle, the paddle falls back to its resting position, shutting off the supply of water.

The following video provides a good illustration of how the Cool-N-Save works. Take a look now if you like – then read on to find out whether this system is the right system for you, or whether a DIY system might be within your technical ability.

Quality of the Cool-N-Save system

I am always careful, on my website, to qualify my recommendations for energy efficiency products based on feedback from previous purchasers of the product. The Cool-N-Save system seems to work well for most of those who provided product reviews, but a couple of qualifications are in order. First of all, the Cool-N-Save appears to be a relatively simple system that probably cost far less than $70 to manufacture. That may be fine by you – you’re paying for the convenience of easy installation and the thought that went into the design. But if you pay $70 you probably expect high quality components that last a long time. Based on the customer reviews, it appears there are a couple of minor quality issues with the Cool-N-Save air conditioning mister that may need to be addressed by the manufacturer.

First, as with any mist cooler, the nozzles of this air conditioner mister can occasionally clog up due to impurities in the water supply, particularly if you have hard water. The Cool-N-Save does come with a water filter to remove these impurities; it’s important to run the system for at least a minute or two with the mister section detached to flush out any impurities in the filter before you start. If the nozzles do become clogged, you may be able to flush them out by detaching the hose just after the filter, and using a funnel to pour some distilled white vinegar into the hose, then reattaching the hose and running the misters again. (You can activate the misters by pulling up on the air paddle, if the condenser fan isn’t running.)

Second, some reviewers have reported poor quality of the flapper valve and the spray arms, with slow leaks developing in both after a few months, and with the flapper valve sometimes sticking in the near-upright (on) position, or sometimes falling back to the horizontal (off) position without fully shutting off the misting.

Finally, as one reviewer pointed out, the industrious tinkerer can probably build a system themselves for a fraction of the cost of the Cool-N-Save, with potentially better quality and a better end result. I’ve provided an outline of how I think this can be done below, although since I don’t personally own a central air conditioner, I can’t attest to how well it works.

Overall, customers who bought the Cool-N-Save air conditioner mister seem to be reasonably satisfied with its operation and with the savings it provides (or, in some cases, the improved cooling capacity it provides in very hot weather), but the system does seem to work better in dry climates than in muggy ones. This is because the cooling power of evaporating mist is much greater in a dry climate; in a humid climate the air may already be saturated with moisture, so less of the mist actually evaporates.

Building your own air conditioner mister

As I mentioned above, you could probably build your own air conditioner mister for quite a bit less than the Cool-N-Save. Given my poor success rate with home-built systems I can’t claim to have a foolproof design, but the following illustration should give you some starting ideas.

DIY air conditioner mister system

You could build this air conditioner mister system (I am not claiming it will work!) from components like the following:

Orbit outdoor misting system: This provides most of the misting components you need to build your air conditioner mister, including a self-draining water filter, coupler from standard garden hose to the mister piping, the piping for the mister, and five misters (save one for a clogged one later). Total cost: about $24 as of current writing. Orbit makes a wide range of misting products, from simple misters to complete professional systems for creating a whole-patio or whole-yard mist cooling system. Click on the image to see more details on this product or to see similar products available at Amazon. Note that this system may not operate optimally at lower water pressures. You can use the water filter to clean particulates out of your water before it goes into the misting system; the misting tubing, and possibly some of the feed tubing. Tie the tubing in place with cable ties or by some other means.

Hand-made paddle: I am guessing this can be easily constructed by the typical handyperson out of a 2′ length of rigid PVC pipe and a flat or slightly curved piece of rigid plastic, for example one cut from a 2.5 or 5 gallon HDPE bucket. Fasten the two securely together and connect the base of the paddle to the outside edge of the condenser unit, in such a way that it can pivot. The paddle may need to be weighted so that it has enough weight to pull the shut-off valve to the closed position once the condenser fan stops running. I assume the cost for this is about $2-5

Length of steel rod: Connect the steel rod between the paddle and the shut-off valve handle, in such a way that when the paddle is up, the valve is fully on, and when the paddle is down, the valve is fully off. Through experimentation you should be able to find a rod length and connection point on the paddle such that when the paddle lies flat against the condenser unit, the shut-off valve for the air conditioner mister is in the off position, and when the paddle is at about a 30-45 degree angle, the shut-off valve is fully turned on. I assume you can find a length of steel rod suitable for this task for under $2.

Metal shut-off valve: You’ll want a sturdy brass or aluminum shut-off valve with a longer lever so that you have enough lever to secure the steel rod to. The one pictured here should do the trick for an air conditioner mister. The current price is around $15. You may be able to do better at your local building center but I would not recommend going with a valve with plastic components.

Garden hose: If it weren’t for the fact that the shut-off valve needs to be right near the paddle, you would not actually need a garden hose for your air conditioner mister, as the Orbit outdoor misting system comes with plenty of hosing to reach a nearby faucet. The trouble is that the hosing is narrower than standard garden hose diameter, which means you would need to find a specialty shut-off valve to fit that hose. I’ll assume you have the garden hose lying around or can find one for $10 or less.

Cable ties and miscellaneous hardware: If you’re a handyperson you probably already have most of the smaller parts you’ll need to complete such a DIY air conditioner mister project. You’ll need cable ties or some other means of attaching the misting hose to the condenser unit, and the paddle to the top of the condenser unit.

That’s about all you should need to build your own air conditioner mister. All told, about $50-60 worth of materials, and if you shop around you may be able to do better. Undoubtedly it will take you longer to (A) assemble all the materials from different places, and (B) connect it all together – the Cool-N-Save system can be installed in under 10 minutes if you know what you’re doing. But if you enjoy the challenge, go for it!

I encourage the adventurous visitor to give it a try and let me know (through the “Contact” link on each of my pages) what the outcome was – and what exact design you used. You could even build a less thorough version of an air conditioner mister using a simple standalone mister such as the one shown here, but you’ll need to find a way to get it to shut off when the condenser is not running.

8 replies
  1. Barry Miller
    Barry Miller says:

    An inexpensive 24 volt automatic sprinkler system valve would be easy to attach to the 24 volt relay on the ac unit, instead of using the paddle and manual valve.

  2. C Vegas
    C Vegas says:

    I got a coolnsave – $85. Comes with a water filter that keeps the scaling off the coils. Now in my 5th year of using it and it’s still working great. All I have to do is replace the filter every year. Automatic water sprinkler? Are you kidding? No way. And why go through the hassle of building your own – this works. Seriously… I have too much to do with my life to quibble over the $85 cost of a kit.

    • Robin
      Robin says:

      I agree that it seems a bit absurd to try to build a system from scratch from parts you have to buy, when a new system costs under $100, especially when you have no guarantee the DIY system will work. I guess I was just getting carried away with how one COULD build it from scratch – I haven’t done it myself.

  3. B Frost
    B Frost says:

    You can count me as a happy Cool-N-Save customer. I bought one about 3 years ago. The first one was damaged – it leaked quite a bit. But the customer service guys were really helpful and sent me a replacement unit right away. No hassles. My HVAC guy was really upset with me about the idea of spraying mist all over my ac unit. Predicted all kinds of problems – none have come true. And now he’s a convert. Told me that he got one for his home. To me… this IS a DIY cost control thing. One thing – it’s really important to keep up with replacing the water filters – order from Cool-N-Save. I let it go one season and my unit looked like a snowball. I had the unit cleaned up and got a new filter – “snow” is gone.

  4. JB
    JB says:

    I used a 24 volt irrigation valve and connected it to the 24 volt relay as mentioned by Barry above and it works great. Using PVC and the brass misters I was able to customize it for my ac with 10 misters. The water in my area has a lot of calcium so I use softened water. The ac misting system uses only a fraction of the total household softened water so I notice no change in the consumption of salt.

  5. Dave H (@seymourgomez)
    Dave H (@seymourgomez) says:

    I experimented on these for an Arizona power company I worked for in the late 1970s. They are incredible energy savers and extend the life of the compressor.

    BUT watch out for hard water buildup on the coils. They will destroy the coils and you have a very high cost to replace. Best to put in an RO water filtration unit beside the A/C and pipe your water through it. Change out the water filters once a year.

    Also, don’t run these evap coolers when the outside air drops below about 80 degrees, as a CYA for warranty. That would translate to a cooled air temperature of about 55, which is not a good idea. The way to do it is to put a temperature switch on the water line or the solenoid that can can be adjusted to about 80-85 degrees.

  6. xsellr8
    xsellr8 says:

    Yeah would be great if you could “still” get one for under $100 bucks but Coolnsave is “sold out” for 2017 (or can’t stand the heat from above?) and several similar low priced options have magically disappeared from Amazon etc (pressure from above no doubt) but you can now get setups that cost several hundred dollars, or you can even rent them. Looks like the powers-that-be have stepped in to maximize profits and get it back in the pockets of those who are losing the revenue on electricity because of it. We get screwed coming and going…..and those who can’t see it are blind fools.


Leave a Reply

Want to join the discussion?
Feel free to contribute!

Leave a Reply

Your email address will not be published. Required fields are marked *