Anyone try those mist-n-save ac condenser sprayers supposed to save money?

D107

Just heard of these units--spray heads put out mist that gets sucked into condenser, cooling the air going into it. Comes with calcium filter to ensure fins don't get coated with calcium. I have seen misting systems in European restaurants that work great with people, but not sure about this. Some online comments I've seen from HVAC people:

"A piston metering device controls Freon flow with pressure difference. Spraying water on the outdoor coil lowers the head pressure. Therefore lower pressure difference, therefore lower flow through a fixed oriface. Therefore less cooling. However efficiency can go up, so compressor amps drop. If you use water spray, you will need to add Freon to get enough cooling. If you have a TXV, you will have less trouble. "

"water fills up the condenser fins creating less heat transfer un less the water is 50* lower than the ambient temp you are pissing in the wind .......and on your unit! "

ratio

Dunno about what they're saying, but my Old Guy says when he lived in TX, you'd come across solenoid valves tied in to pressure switches on the liquid line & plumbed in to a hose to give the condenser a squirt if the pressures ran too high.

Jamie Hall

This works -- if, and only it, the dewpoint of the air is very low. Then the water spray does evaporate and, in the process, cools the air. It would also work on a hot condenser, provided the dewpoint was low enough -- again, the evaporation will cool the condenser (it will also cool your car's radiator if it overheats and you have a hose handy -- but you may crack it...). In the southwest it's common to have units which just spray water into the air for cooling a house -- they're called swamp coolers. Also outdoor restaurants and the like will have spray mists overhead.

bob_46

Rheem-air , installed a bunch of them in the 60's. Beautiful equipment, well made, a 3 ton had a 11/2 hp compressor . All copper condensing coil including fins sitting in a SS pan with a float and a pump to spray the coil. Squirrel cage blower belt driven and a semi hermetic compressor "quiet". Water quality and maintained cost killed them. Spraying an aluminum coil would be a disaster.

newagedawn

in the south west, people call that a "swamp cooler"

ChrisJ

Please no.

Don't do it.

JUGHNE

I worked on a 16 ton Roof Top Unit where the maint man was perhaps too lazy or just didn't know that you must clean coils at least once a year when you are surrounded by cottonwood trees.
(I lean more towards the former reason).

Compressors were kicking out on high head on hot days.
He put a lawn sprinkler on the roof for the water to be sucked into the coil. This kept the AC on line for several years.
But when he left the job and I show up to correct the plugged coils the fins were plugged with water deposits.
In order to back flush correctly many hours were spent fin combing the deposits out of the coil. Acid could not be used because of rubber roof.

Our water has only 5 grains of hardness. There may be only 3 water softeners on our muni water system. (One is mine, wife said we need one....who am I to argue...Christmas present.....deductible as a demonstration unit isn't it??)

If there is a calcium filter that would prevent deposits on anything it seems that it would cut into the water softener business drastically.

JohnNY

I've installed rooftop misting systems specifically to cool AC units on Manhattan high-rises, as per the building engineers' request. I have no idea if it works, but I've installed them for at least two people that have asked for them.

Gordy

There is the common sense part that says if they were beneficial enough to bother with, manufacturers would offer it as an option at least.

Seems gimmicky to me.

ChrisJ

Gordy said:

There is the common sense part that says if they were beneficial enough to bother with, manufacturers would offer it as an option at least.

Seems gimmicky to me.

Oh, no, I think they do work.
But I think they also cause a ton of problems that will cost far more to fix than the thing can ever save.

There's a reason large commercial buildings use water cooled condensers, but it's not some cheap POS slapped on a typical residential aluminum/copper condenser.

D107

Which all goes to show how easy it is to sell something to a public that rarely cares to scrutinize the product. If it sounds good we buy it. We definitely need more science education going on here, teach us all to think more critically. Can always count on this forum to set the record straight.

KC_Jones

On large industrial air cooled units they will install an adiabatic pad system. Basically water absorbing pads (cellulose type material) that has water dripped down over it. The air flows through and is cooled through evaporation which then boosts capacity.

I say boosts, but these are typically only used to bring capacity back when ambient temps rise beyond the unit rating. So if the unit is rated with 90° ambient temps and the temp rises to 100, they run the adiabatic system to get the air over the coil back to 90. Those are just random numbers, but that is the basic concept.

Some companies to make spray systems that spray water directly on the finned coil, but they don't look very good after a while (IMHO).

Harvey Ramer

The answer is not mister systems. Inefficient, wasteful and problematic.

The better solution is desuperheating or refrigerant waste recovery via a condensing water tank or a coaxial refrigerant to water heat exchanger. This requires tapping into the compressor discharge pipe, but the benefits are substantial. The condenser head pressure is easily controllable via water temp and variable flow rates. The waste heat is captured and can be used in concert with the hot water production equipment onsite.

Even if the water were dumped, it should still be more effective and use less water than a mister.

ratio

I should note that what my Old Guy described wasn't for normal operation, but for the 1% cooling when things just can't keep up.

ChrisJ

Everyone's talking about how to cool the condenser off more and I'm over here trying to warm mine up.

Seems like I'm always going in the opposite direction.

ratio

ChrisJ said:

Seems like I'm always going in the opposite direction.

Perhaps one of those ceramic heaters, on a thermostat, a foot or so back from the unit?

ChrisJ

ratio said:

ChrisJ said:

Seems like I'm always going in the opposite direction.

Perhaps one of those ceramic heaters, on a thermostat, a foot or so back from the unit?

Wow that sounds wasteful.
I'm sure the ICM controller will do just fine. If I ever get time to put it in!

Harvey Ramer

@ChrisJ
Shutters on the condenser are also an option if you want a hands on approach.

ratio

It's my firm belief that efficiency and comfort are in fact opposing concepts; to achieve one the other must be sacrificed in proportion.

ChrisJ

ratio said:

It's my firm belief that efficiency and comfort are in fact opposing concepts; to achieve one the other must be sacrificed in proportion.

Found this in my thermostat manual today.

ratio

Yup, it's called dehumidification. Not sure how it would work with a fuel burning furnace, generally the order is wrong.

bob_46

@ChrisJ I think you should spend some time with the psychiatric chart oops I meant psychrometric chart.

bob_46

Here is a blowup of the Rheemaire condensing unit I was talking about, this one shows a tin can instead of the semi hermetic.
Back in the day almost all high quality residential condensing units had belt driven squirrel cage condenser fans super quiet semi hermetic compressors potential relays ,start condensers , crankcase heaters, high and low pressure switches etc. You could hardly hear them run but they were expensive , only rich people had AC.

unclejohn

Seems to me if water is cheaper then electricity it would be ok. You don't have much control over it unless you use a temp sensor. But now your moving away from cost efficiency. I once keep a 10 ton condenser running at 1789 rest. in Georgetown over night with a garden hose.

Gordy

Gimmick.....