What's going on here? Comsumers are confused by the "up to" ratings that manufacturers advertise, yet AHRI ratings tell quite a different story. By looking at AHRI ratings I've come to some generalizations:
1: EER is much more important than SEER since EER is based on a 15 degree difference (95OD/80ID) between indoor and outdoor tempatures vs. SEER 2 degree (82OD/80ID)difference. I want to know how efficient it's running when it's HOT outside.
2: There is a practical EER limit of about 14 for air source AC units, no matter what the SEER is. EER increases significantly going from lower SEER to higher SEER single stage units. The larger outdoor coils improve EER. once the larger coil is used, EER is only marginally improved when going to 2 stage units.
3: The highest EER ratings are given to the smaller sized unit within a particular line. Downsizing has a real advantage here if the AC can keep up with the load during peak conditions.
4: Airhandler and coils make a big difference in EER, even on lower cost single stage units. 2 stage units almost always require variable speed blowers to get thier rated SEER.
It seems to me that consumers are better off buying smaller high SEER single stage equiptment and using the extra money to fix ductwork/leaks in the house. A 16 SEER 2 ton Single stage AC has about the same EER as a 3 ton 2 stage 19 SEER unit. If the house only has a 2 ton load the customer wasted thier money on a 2 stage unit as far as reducing power bills is concerned.
Are customers real world power bills that much lower with 2 stage equipment only because thier old stuff was in poor shape? Would thier power bills been just as low with a higher SEER single stage unit? Is 2 stage equipment more about comfort and less about energy savings?