Air conditioner condenser coil emissivity
I checked the air conditioner discharge with my flir. The coolest spot was 52'F from 10 feet away. The evap coils air inlet temperature was 72'F (digital temp display).
That is a temperature drop of 20'F. After checking several times 19 to 21 degrees F seemed to be the temperature drop this A/C liked to produce with todays outside temperature.
I turned the air conditioner off. Took my can of flat black engine paint and sprayed each pass of condenser coil with opposing 45 degree sweeps the third sweep normal to the coils.
Powered the air conditioner back up and the inlet air was reading 75'F and the discharge was almost immediately went down to 51'F and only kept getting colder.
Once the evap inlet temperature was showing 72'F the discharge air was 44'F.
That is an 8'F temperature differential improvement, now its discharging air 26'F to 28'F cooler than the inlet temperature (the discharge air is staying between 44'F and 46'F from 10 feet away according to the flir. I am guessing the expansion valve is kicking in to prevent evap freeze up? (If it even has one)
I was expecting a 2'F to 4'F improvement, not 8'F.
Now this AC faces east, points at the house next door and is shaded by several trees and under the roof over hang. The top of the AC might see direct sun light for maybe an hour a day a little before noon.
If you have a west facing AC and get sun rays directly onto the condenser coils painting them black might be really bad. I will let someone else test that.
Now should everyone run out and paint their shinny condenser coils black? No because every mechanical engineers who design these things are well aware of ideal black body emissivity, so if they are not black, then it stands to reason they are not black for a reason such as really bad overall performance if facing direct sun light.
Now according to Boltzmann's law a 1 square meter typical black surface, at room temperature will give off around 400 watts of energy. A shinny aluminum surface will give off only 1/3 of that or less.
Then a few days later...
I tried it on another air conditioner, this time one that was a few years old.
The coldest air on the discharge it picked up before the paint was 52'F, then after the paint was 47.5'F.
This time I had the kill-a-watt meter plugged in. It was drawing the same wattage before and after. I expected it to draw a little less. It might be drawing <1% less but appears to be in the range of its normal fluctuations.
So this mod looks like it wont save any power aside from getting you down to temperature that much faster and cycling the compressor off that much sooner.
I should have known, the compressor should draw the same wattage unless the expansion valve kicks in to prevent freeze up. Since this is an older unit, it may not be in danger of freezing up the evap coils at in these temperature ranges.
It kept using around 540watts before and after, but now its moving more heat with those 540 watts. Moving more heat with the same energy input, more efficient, I can live with that.
I originally posted this here:
There have been some replies an another test on a much larger centeral A/C.
Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.
Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.