Does using a 'water mister' on my outdoor house a/c system's condenser make sense ?

Question

I've only recently discovered the WONDERS of a patio mister. I'm no physics major, but the fine mist of water lands on your skin and evaporates, making you feel cooler 20-30 degrees. I then found a very expensive outdoor a/c unit water mister and I further researched that this is also done for commercial roof-top HVAC units.

Assuming I can safely figure out when the outdoor a/c fan kicks on (it's one wire), to then allow the misters to turn on (rigging one of those battery powered water timers) - would this make my outdoor ac unit work 'less hard' and save more in electricity, than the very small amount I'll lose in water. If so, uhm... why don't more people do this ?? (I live in hot San Antonio, Texas)

Answer 1

Manufacturers would have incorperated this long ago if this was feasable.

Units will rust and corrode over time and this will only add to it.

Water cooled condensers were used in the past but cost more to operate than air cooled.

Any warranty left on the unit could be voided when you change the design of its operation.

If your intent on using it you could use a current relay (Johnstone Supply) to energize your water supply.

Answer 2

Rough one to answer...commercial units are water cooled for they handle huge amounts of air. Your unit will benefit only slightly, and then only on dry days...humid days will make little difference. AC units are designed to work with air cooling, and although is seems that by cooling with water, it would work more efficiently, I doubt that the savings in electric power would be offset by addtion of water...AND constant water on the aluminum fins could, and will, over time, have an adverse effect on the condensor!  If you had wanted a geothermal cooling system, the time to install it would have been when you purchased and installed the original unit, not after the fact. Good luck and peace. Goldwing

Answer 3

Sure you a/c would run more efficiently.  The cooler the condenser coil is the discharge pressure would be lower. The lower the discharge pressure is the more efficient the compressor is.

Now for the bad news, Running water on the condenser would cause scale on the coil. You would have to use a strong chemical to keep it clean. You would probably have to clean it every other day. If you don't keep the coil clean less air wil pass through it and the discharce pressure would get higher. The higher the discharge pressure the less efficient the unit operates.

So the answer is it is not a good idea to run water on the a/c condenser coil during operation.  If you want to save money keep that coil as clean as possible.

Answer 4

I think the people talking about the perils of using water to cool the system/scale buildup, etc. miss the point.  Remember, your AC's heat exchanger sits out in the weather all the time, and runs when it rains; water is sucked directly into the unit with no detrimental effect.

Regardless, when misting, you are NOT cooling with water.  When an ultra-fine mist of water is released into the air, it evaporates almost instantly, sucking heat out of the air as it does so.  It's called "adiabatic saturation".  Adiabatic saturation causes a drop in the ambient temperature of the air left behind after the ultra-fine mist has evaporated.

It is that cooler air which is then drawn into your heat exchanger.  Since the air being drawn in is cooler, the efficiency of the heat exchanger is greater, saving you money.

Look into a coolnsave unit.  It uses a flapper switch which is activated when the unit comes on and the hot air is blown out.  That switch activates the misters.  No electricity used at all.

I've recently started throwing a couple of plastic jugs of water in the freezer, then setting them around my heat exchanger during the hottest part of the day.  The air being drawn into the unit goes across the frozen water and is cooled before it enters the heat exchanger.  I haven't seen any utility bills yet, and don't expect a measurable difference, but it was 104 degrees here today, and my house was cooler using the jugs (for the two hours they lasted) then it was last week when the highs were 98 and 99.

Answer 5

The answer is No. Your AC was designed to be run with an Air cooled condenser. So the area of condenser was calculated accordingly. Using mister would mean that the cooling of the condenser can be done more efficiently but the spare capacity of the cooling fins can anyway not be used. Moreover you would be spending some energy running this mister which is going to cost you additionally. So it is best to let these things be the way they are. What you can do however is to take other measures to keep the load on your AC low. Like making sure that the outside unit is in a shaded area and not exposed to direct sunlight.