Considering a Mist n Save?

A good friend of mine recently asked about the Mist n Save (it’s named COOL-N-SAVE) add on component which claims to reduce your electrical usage.  He wanted to know if it worked and if it was worth it.

He was doing right by being cautious about adding any component to the air conditioning system and there is no short answer to this question.  The following is my personal opinion only since I have never installed one, nor have I ever seen one in use on a system here in south Texas.  (That alone should tell you something.)

I went to their website to find out if there have been any studies done that proves the effectiveness or any information on how to properly install and maintain one.  It’s not that I needed to know if reducing the temperature of the condensing coil would increase efficiency and reduce electrical consumption, that’s a no brainer for a true AC technician.  What I wanted to know is if the company cares about their consumer or if it’s just another gimmick.

Their website cited studies but the links to those studies were no good and I hope that’s just a lack of maintaining their web site instead of a shifty way to influence potential consumers.  The only instructions they had were fuzzy snap shots of the package the product comes in and there certainly was no information on the truly important things you need to know.

First of all, there is the hard water issue and to give them some credit, a banner popped up on their website right away, telling of the locations they won’t ship to due to hard water problems.  Anyone who deals with hard water knows that when the water evaporates it leaves behind the minerals, causing a buildup rather quickly.  If you spray that water on a hot condensing coil the buildup is going to be essentially baked on and very difficult to remove.  If a buildup of minerals is allowed to occur on the condensing coil you will lose way more efficiency than you ever saved and shorten the life of your unit.  You can’t just rinse those minerals off either, it takes a harsh cleaner to do so and that cleaner will likely damage your coil, reducing efficiency even more and maybe even voiding any warranty rights for a leaking coil.

The unit comes with a calcium filter and that’s a good thing, but what about all the other minerals found in hard water? There is no mention of other minerals on their filter and since this is starting to look like a gimmick, I must assume the filter is only for calcium.

The unit is designed to spray water on the coil when the fan comes on, by means of a flap that is pushed up when the fan pulls air through the coil. That’s an ingenious way to allow a homeowner to install it but one thing they don’t address is the installation on a heat pump system. During the heating mode you will need to make sure that the water supply to the unit is turned off. If you don’t, the system won’t heat for very long at all and you will end up with a huge block of ice on the coil. Left unattended this would use massive amounts of electricity as the system goes through defrost cycles to heat the home.

Now for the deal breaker for me. The reason this component would work to reduce electrical usage is because it reduces the liquid line temperature leaving the condensing unit. The measurement of this is called sub-cooling and it is something that every manufacturer looks closely at when they engineer an AC system. When you change the sub-cooling of a system you can thereby also change the super-heat which is a measurement of the indoor coil’s evaporation of that liquid.  If the superheat is too low, you will slowly damage your compressor which is the heart of and also the most expensive component of your AC system.  Most units today have a thermostatic expansion valve at the evaporator coil which regulates the super-heat but not all of them do. The fact that this company does not mention the importance of making sure your system is inspected for proper superheat after it is installed tells me that this is a gimmick. By that I mean it’s about making money for them and not about saving you money.

#1. You may end up spending as much in water filters and water as you save on electric bills.

#2. This component cannot be used in the heating mode on a heat pump system.

#3. You should have your system checked by a licensed AC company when one of these is installed.

#4. Making sure the Cool-N-Save is functioning properly will require frequent inspections and maintenance.

Overall, I think it is a fantastic way to reduce electrical usage but it’s not for everyone. If you are considering installing one I suggest asking your AC service company first and then have them check the system’s operation after wards. As well, be sure to check with the manufacturer to make sure you won’t void any warranty by having one installed.

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