How much energy does an air conditioner with an 9.7 eer save as opposed to a 10.7eer?

Question

How much energy does an air conditioner with an 9.7 eer save as opposed to a 10.7eer?

Answer 1

OK here's a definition and an example from a web page:

http://www.cwlp.com/Energy_services/effi...

The formula for calculating EER is:

  EER = (Btu/hr of cooling at 95°) / (watts used at 95°)

For instance, if you have a window air conditioner that draws 1500 watts of electricity to produce 12,000 Btu per hour of cooling when the outdoor temperature is 95°, it would have an EER of 8.0 (12,000 divided by 1500). A unit drawing 1200 watts to produce the same amount of cooling would have an EER of 10 and would be more energy efficient.

So then suppose you have a given amount of cooling you want to achieve:  C = 10,000 BTU/hr

Let E1 be the energy used by the first air conditioner and E2 be the energy used by the second air conditioner

Then 9.7 = C / E1  and 10.7 = C / E2

or E1 = C/9.7 and E2 = C/10.7

E2 will be more efficient, so a higher efficiency rating means a more efficient air conditioner.  (Ideally your efficiency rating would be infinite, so you could get your air cool without using any energy at all, but that is not actually possible.)  

The air conditioner with a 9.7 eer would actually use more energy, not save energy.

The 10.7 EER would use this much less energy than a 9.7 EER:

100% * (C/ 9.7 - C / 10.7) / ( C/9.7 ) =

100% * (1 / 9.7 - 1 / 10.7 ) / ( 1 / 9.7 ) =

100% * ( 1 - (9.7 / 10.7) ) = 9.3%

You'd save 9.3% of your energy, with the 10.7 EER, compared to what a 9.7 EER would use.

Looking at it the other way, you'd use this much more energy with the 9.7 EER over what the 10.7 EER would use:

100% * ( (10.7 / 9.7) - 1 ) = 10.3%

Answer 2

A 10.7 EER unit is more efficient than one with an EER of 9.7.

BTU rating ÷ watts = EER

If the two units are exactly the same BTU rating, then the incremental efficiency of the 10.7 EER unit is:  (10.7 - 9.7) ÷ 9.7 = 10.3% more efficient than the 9.7 EER air conditioner.

The actual energy savings will depend on the BTU rating of the AC unit.