AC Pre-Cooling Systems: Buyer Beware

AC pre-cooling systems have been on the market for years. Many claim they can reduce your air conditioning expenses by up to 30%. But buyer beware! These "misting" systems come with serious drawbacks.

What are AC Pre-Cooling Systems?

AC pre-cooling systems are relatively simple devices. They use a system of hoses to spray an air conditioner condenser with a light water mist during the operating cycle. This cools off the outside coils, and can make the air conditioner work more efficiently in hot weather.

So, Why Don't Manufacturers Put Misters on the Condensers?

Water is corrosive. And your outside condenser coil is made of metal. Metal corrodes. AC pre-cooling systems spray your coil with water over and over again.

Are you starting to see the potential issue here?

Yes, a misting device can reduce the outdoor air temperature around the coil to exhaust heat more effectively. And this would be a really great thing if it wasn't for the fact that the water evaporating on the surface of the coil will leave behind mineral deposits. Those mineral deposits will build up over time.

Which is bad.

Not only will those mineral deposits actually reduce the efficiency of your coil, but, as you may have guessed, they are magnets for corrosion. Even when ac pre-cooling systems integrate water filters into their design, this doesn't solve the problem. The water mist will capture airborne dust and contaminants before it hits your coil.

Now, all the effort your misting system put out to increase efficiency is getting counter-balanced by the fact that scaling and corrosion are decreasing efficiency and increasing the likelihood of a refrigerant leak. And nothing ruins operating efficiency like low (or none) refrigerant.

Our Advice On AC Pre-Cooling Systems

AC pre-cooling systems use very basic technology. HVAC manufacturers aren't stupid. They would love to be able to increase summer cooling efficiency with one easy trick. But, life isn't that simple. There is always a trade-off. Unfortunately, ac pre-cooling systems will give you short-term efficiency at the cost of long term performance and virtually certain mechanical failure.

Questions or Comments?

Is there more you want to know about ac pre-cooling systems? Let us know here, on Twitter, or over on Facebook.

3 comments (view/add)
  • Belevolk
    Posted on 8/16/2019

    Some companies try to avoid the condenser issues by putting an heat exchanger cooled by water in the refrigerant loop. In Arizona they were sold as "Hot Tap" hot water from cold air. Again water is corrosive and they lost a lot of compressors from leaks in the exchangers.
    Worked with a guy that used his swimming pool as a pre cooler for his ac's. He was using stainless steel marine exchangers, Still lost a compressor every couple of years due to leaking. Finally disconnected the system.

  • Kyle
    Kyle from Ingrams
    Posted on 8/16/2019

    That is an interesting approach to the problem. Makes sense why it wouldn't work out long term. But using a swimming pool as a pre-cooler is definitely a new one on me!

  • stuart
    Posted on 8/19/2019

    I installed a heat recovery unit to my ac 2 years ago and it works great. I turn off water heater from may to September. The really hot days the temperature would not go below 85 on those days when the night and day temperature would stay above 90 after heat recovery it would cool to 74 no problem. Increased tonnage effectively and free hot water awesome!

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