A/C and Mileage

[darth_vad3r]

So, AC has roughly a 5% hit on efficiency.

On one specific test/trip. It depends on your speed. If you are stuck in stop and go traffic for 2 hours to go 10 miles, A/C would have a 100% hit on efficiency.

The most consistent way to think about the hit would be in mi/hr ... e.g. blasting A/C might consume 5mi/hr (5 dashboard miles consumed per hour of A/C).

 

[darth_vad3r]

I think that hit may be more for a LR RWD as we usually are much lower wh/mi to begin with. Assuming it's a relatively steady 16 wh/mi to run the AC that is.

No, see above. 16 Wh/mi was specifically for a 1hr trip of 60 miles. If it was a 1hr trip of 30 miles it would have been 33 Wh/mi.

You need to think about energy use. If A/C uses 1kW of power, and you need 250 Wh to move one mile (250 Wh/mi), then 15 minutes of A/C would burn 1 dashboard “mile” of your battery’s energy. 1kW x 0.25hr = 250Wh. i.e. 1kW is 4mi/hr for a 250Wh/mi car.

5mi/hr is probably a safe upper bound for A/C. At least in the rough ballpark.

 

[AlanSubie4Life]

So, AC has roughly a 5% hit on efficiency.

The data in the video doesn't really make much sense, but 5% seems like a good rough estimate (at typical speeds). The efficiency hit in the video should be less at higher speeds (but it's not) for two reasons:

1) You're going faster so the Wh/mi due to the AC is less (Wh/mi = Power / speed)
2) Overall consumption is higher at higher speed so the % hit will definitely be smaller.

So: I don't believe the video data. My guess is his methodology is off: 1) You need to reset the trip meter once you get up to speed 2) You need to make sure the car is at temperature before you begin the test - these items are not detailed in the video so there is no way to assess his methodology. Anyway these things can substantially impact the results for small differences like this.

Anyway, 5% probably good as a rule of thumb if it's hot at "typical" speeds. In mild temps where you're using it for humidity control only, it can be pretty insignificant.

Just remember that the rule of thumb is just that and one % cannot accurately characterize the effect of AC (or heat for that matter). The actual effect will be highly dependent on outside temperature, inside set point, travel speed, humidity, etc.

 

[darth_vad3r]

The data in the video doesn't really make much sense, but 5% seems like a good rough estimate (at typical speeds). The efficiency hit in the video should be less at higher speeds (but it's not) for two reasons:

1) You're going faster so the Wh/mi due to the AC is less (Wh/mi = Power / speed)
2) Overall consumption is higher at higher speed so the % hit will definitely be smaller.

So: I don't believe the video data. My guess is his methodology is off: 1) You need to reset the trip meter once you get up to speed 2) You need to make sure the car is at temperature before you begin the test - these items are not detailed in the video so there is no way to assess his methodology. Anyway these things can substantially impact the results for small differences like this.

Ya, he critiqued the Mythbusters for using two different cars simultaneously, which is a fair point, but then by him using the same vehicle for all 6 test runs, the outside temperature and sun angle could have changed a significant amount.

I think the test results are half-decent to compare adjacent tests, but comparing from test 1 v 2 % change vs test 4 v 5 % change ... way too many uncontrolled environmental variables to try to do that.

He did say he waited for cabin temp to drop before starting the A/C test run. I remember him saying that at least once, probably on the 2nd AC run (70kph with AC).

 

[Magnets!]

“auto” does all this for you automatically, deciding when to keep recirculate on based on exterior temperature (most of the time if it’s hot ) and starting with high fan speed then lowering automatically once the set temp is reached (and raising again later if necessary).

True, but the OP seemed to be using manual since his fan setting was very high for a long period of time. For me, I liked auto when it worked, but it is not functioning right now.