I'll start off by saying I'm not HVAC expert, but I've spoken to several and read a bunch while researching this blog and learned something alarming. Ads circulating on social media trying to sell you a mister device for your outside air conditioning condenser, promising to save you huge money, may actually cost you many thousands in damage in the end.
First the science: Your condenser uses coils like a car's radiator, to offer huge surface area which radiates heat in a relatively small space. Simply put, when you spray tap water on your coils, they may temporarily cool (due to evaporative cooling processes), but water also has minerals which will over time, add scale to your coils. This coating of minerals will insulate the coils, severely reducing your AC's cooling ability. Some misting units do offer filters for these minerals, but no filter can stop all scaling and the risk is too great.
If your condenser gets coated in deposits, you may need to replace it years early due to irreparable damage, which can cost around $3,000-5,000 for a typical 5 ton unit for a 2,500 square foot house. While evaporative cooling misting devices can speed up your condenser's efficiency in the near-term, in the medium to long term it could cost you a whole lot more. (Side note: Why doesn't rain water cause scaling of lime and calcium deposits like tap water does? Rain drops are composed only of evaporated water, free from other minerals which get mixed when water is acquired from surface-based locations like springs, rivers and reservoirs. So, if your AC unit gets wet from the weather, don't worry.)
If you want to save money this summer, get an AC pro to swing by for a tune-up to make sure your system is working at top efficiency. -Brooks
