A/C Usage and Impact on FE

[R.I.D.E.]

In some cases like the hypermiling Insight owners who average close to 100 MPG, the AC penalty is 30 MPG !!!!!!.

I drove my Insight to my step daughters this weekend. Started out with 72.5 MPG for 45 miles.

Drove it 76 miles at speeds not over 57 MPH and ran AC at minimal fan, reciriculate, and econ mode. Mileage dropped to 63.4 MPG when we arrived at her house.

Drove back later in the afternoon and did not run the AC. Mileage increased to 66 MPG overall.

Not sure how good my math still is, but from 72.5 @ 45 to 63.6 @ 121 is a significant drop. Normally I would average about 70 on that trip.

To increase the overall trip mileage to 66 @ 198 would require the mileage to be back near 70 MPG on the return trip.

A guess would be at least a 15 MPG hit for minimal AC use in the Insight, but remember this, still better than 55 MPG if the whole trip would have been with AC.

Thats a 15 MPG hit for minimal AC use.

Fan speed 1, recirculate, with econ mode which allows the engine to still shut off at stops. That is the absolute minimum AC use on the Insight, and it still costs almost 15 MPG!!!!!

Now you must consider that thei Insight will burn one gallon of fuel every two hours at a constant 40 MPH under ideal circumstances. That's the same amount of fuel an average V8 uses just idling!!!!!

Bottom line is the more efficient cars become the much greater the cost of running the AC. It's more exponential than linear and if we ever build mega mileage cars we will also have to address the gross inefficiency of conventional AC systems, even with the best modern designs of compressor.

regards
gary