[Mobile Master Tech]

There are too many variables to accurately gauge effectiveness by seeing how quickly the house temp goes down. It would be better to check amp draw with an inexpensive clamp-on ammeter ($20 or less on ebay). Do this after the unit has stabilized, then switch on the misting system and check after stabilized again. The system will also go up in btu/hr capacity when you do this since the temperature "lift" from evaporator temp to final condenser temp will be less. You could measure the actual efficiency gain by comparing the power draw to the calculated btu/hr removed by the system if you measure airflow and enthalpy before and after the evaporator, but that may be more work than you want.

I manually wetted a swamp cooler pad strapped around my condenser to test this idea and got a 5-7% lower amp draw depending on outdoor temp/humidity. I didn't calculate the btu/hr to get an actual efficiency gain but it was probably around 10%, allowing for slightly higher btu/hr capacity from the lower condensing temp.

The other factor is water usage, since water is a precious resource. To get the best bang for the buck, I plan on using a swamp cooler pad only on the lower third of my condenser, kept wet whenever the condenser is on by a circulator pump pumping condensate water from the indoor unit. It will dribble water onto the top of the pad and excess will be collected in a tray channel at the bottom, just like a swamp cooler. I can add nearly mineral-free water from my reverse osmosis system if the condensate isn't enough, probably with a modified toilet fill valve. This way I will use only 1/3 the water, very little of which is makeup water I pay for. I won't have to worry about mineral buildup, which is harder to completely remove than you might think. Spaced away from the coil far enough, there won't be any liquid on the condenser to cause corrosion problems down the road, either.

Why only the bottom third? My condenser coil has multiple flow paths in the upper 2/3, but all the refrigerant then flows through a single final loop in the bottom third. This way, there is less airflow restriction.The full flow of ambient air will do the initial cooling/condensing in the upper 2/3, but the compressor will only "see" the lower condensing temperature of the water cooled lower 1/3, regardless of the temp of the upper section. This assumes of course that the system is charged properly so the refrigerant is still partially a gas by the time it reaches the lower third. Otherwise, there will be no power draw benefit, only extra subcooling.