Get a stop watch and time the spinning disk on your electric meter for 30 seconds or so when only you AC unit is running. Then time it when it's not running and no other major appliances or on, or when the "base" load is constant and subtract the two. I think one revolulution of the disk is maybe 1/1000th of a kw-hr, but it should say on the meter. TO get a more accurate value, you'll need to time it for 1 minute, then multiply by 60.
Does that make sense?
However, to calculate the actual delivered efficiency, you'll need ot know totla capacity. You'd have to measure the temeprature drop fom the return to the supply, then know the wet bulb temeprature (dewpoint) indoors and use the mfg data sheets to determine the approximate percentage of latent capacity under those conditons. All you need is the ratio. Then take hte tmeprature differential, multiply it by the CFM and by 1.08 and divide by the ratio of sensible to latent capacity and you have you measured total capacity in BTU's. Now divide that by 1000 and by the measured killowatts and you have your EER value. Divide by 3.413 and you have COP.
I think I have thsoe last calculation right. Another pro wantot check my numbers.
