Air conditioner performance measurement

[Jerry Liebler]

Now that I've 'optimised' the charge in my newly installed ductless split I wanted to find out just how many BTU/h it is moving. In doing the charge optimisation I saw the temperature drop across the evaporator go from 16 to 24 degrees and the current drop from 12 to 11 amps so I knew that the capacity has improved substantially.  I searched the WWW and found three formulas and an on line interactive psychometric table.  The table is at http://www.linric.com/webpsy.htm.  I found the CFM for each blower speed on the AC sellers web site.  The formulas are: 1. sensible heat flow in BTU/h Qsens=1.08 * CFM * (temp in- temp out)  2. total heat flow in BTU/h  Qtot=4.45* CFM * (enthalpy in - enthalpy out),for this one you need the  psychometric table.  3. latent heat flow in BTU/h  Qlat= 0.68 * CFM * (gr moisture in - gr moisture out),  for this one you'll also need the psychometric table.  You need the indoor wet bulb and dry bulb temperatures and the temperature (dry bulb) of the air coming out of the unit.  I used my handy dandy infrared digital thermometer to make the measurements, getting wet bulb by pointing it at a wet sponge that's been sitting a while, incoming dry bulb by measuring a similar  but dry sponge hanging in the air going into the indoor unit.  For temperature of the air out of the unit I pointed the thermometer at the louvers in the air stream.  The outdoor temperature was 80 f.  I took readings at the end of the unit's cycles on each fan speed.  The results were always a Qtot between 19,900 and 21,900 Btu/h.  My inverter panel showed it was using 11 amps at 121 volts.  I'm now waiting for an outside air temperature of 95 which is where the ratings are supposed to be taken, but I do believe that for once a manufacturer actually understated performance.  Certainly not bad for a unit that's rated as 18,000 BTU/h and 1480 watts to deliver 19,900 while using under1331 watts.  But the factory had definitely 'overcharged' it making it's capacity about 15,000BTU/h,and well under the rating.
Regards
Jerry 4107 1120

[Nick Badame Refrig/ACC]

Hi Jerry,

Good calculations!

One point I want to correct you on, "Wet Bulb" meaning that your tempature bulb, or probe, needs to be submerged in the liquid for a reading.

This may have thrown off your readings if you were pointing your infared at a wet sponge.

Nick-