Peak Cooling Reductions

Peak Cooling Reductions Q: Don't get me wrong, I love rebates. However, a few days ago I attended a meeting with other HVAC contractors called by my state energy office. They announced $125 per ton rebates for us to upgrade air conditioner installations from a unit with a seasonal energy efficiency ratio (SEER) of 10 to an Energy Star SEER-12 or better. I asked if there were any requirements for sealing the ducts or installing the air conditioner correctly. They said: "No, we just want peak reduction." Wouldn't they get more peak reduction with their money if the installation was good and the ducts were sealed?

--I Love Rebates

John Proctor, P.E. is the developer of the CheckMe! programs.
A: You are right. A 3.5-ton SEER-12 unit has an energy efficiency ratio (EER) at peak of 7.6. For a similarly sized SEER-10 unit, the EER at peak is 6.5. Upgrading the SEER-10 to a SEER-12--and doing nothing further to improve the A/C system's performance--will save the utility about 0.6 kW on peak. (This figure assumes a duty cycle averaged over all units, including ones that are not on, ones that are cycling, and ones that are running continuously.) With a per-unit upgrade cost of $500 (including 15% administration), the cost per kW saved approaches $900.

If you make the same installation upgrade and verify correct installation--measuring air flow and refrigerant levels--the peak reduction would be 0.9 kW. At a $260 cost for verified charge and air flow, the cost per kW drops to $835. In addition, this system would be much better for you and your customer in the long run.

The real peak reductions come not from upgrading from a SEER-10 to a SEER-12, but rather from removing the "running dogs." Running dogs are old inefficient air conditioners that are running during peak periods, generally defined as between 2 pm and 4 pm. When a bounty is put on them--$500, for example--on top of any other applicable incentives, significant cost-effective peak reduction is possible. The replacement of a running dog with an Energy Star unit that has a correct charge and air flow reduces peak by 2.9 kW at only $470/kW. If you also sealed the ducts and sized the air conditioner properly, you would have peak reductions exceeding 3 kW for running dogs at a similar cost per kW.