AC commits pre-meditated murder on MPG

I have found it works great <90 degrees. After that the fan will run way too fast and you end up maxxing out the temp on HI before you can get fan speed under control.

 

I usually see approximately a 10% hit around town with the A/C on during my typical daily drive, which sucks for MPG regardless.

On the highway, it's roughly 5% hit to MPG depending upon speed, outside temp, etc. So, not much more of a hit highway compared to having it off. Granted, on the highway with the windows down you go deaf, lose your voice if you're trying to talk to anyone, and the drag from losing aerodynamics makes it a no brainer to just turn on the a/c then.

 

My wife never uses Auto because it blows the fan hard and she finds it too uncomfortable. I haven't tried toggle to Auto after cooling the car first.

I've used Auto once. I don't enjoy the high fan but if it's more efficient I'll take it.

It would be nice to be able to adjust the fan down to a comfortable level in Auto and have the Prius adapt to that as the upper limit.

 

Try opening the windows, especially the rear ones, a couple of inches on the highway. You'll get far more airflow than the fan can provide. But less wind noise and less aero drag than with the windows fully open. At speeds under 40mph in hot weather I open them all the way.

Ceramic tints help reflect infared out of the cabin, but unfortunately tinting the windshield, which is the biggest upward-facing window, isn't legal or sensible. I wish someone made a ceramic tint which would pass 90-100% of visible light but reflect infared.

 

Actually my MPG improves with A/C when comparing to driving with open windows. A couple tips:
- ECO mode
- recirculation
- keep A/C temp high (a few degrees below outside)
- run fan ~50%

Around here the biggest problem isn't high temps it is the humidity. Running 83F in 90F outside makes it comfortable. At highway speeds (55-65MPH) the amount electricity A/C drains from battery isn't big, the ECU keeps battery almost fully charged and the regenerative braking from traffic light stops is getting wasted anyways.

For reference the MPG we are getting is around 58-60.

 

Also you may wanna start using the windshield sun shade while parked, and leave windows cracked. After getting parked in sun the dashboard heats up so bad the air from vents will be +10F for at least 40min.

 

Your fan speed doesn't drop once the car reaches the setting temperature? It should. Or maybe you have the set temperature too low and the A/C can never get it that low so the fan stays on high? I could see if you have the temp set for below 65deg and it's 105degrees outside. lol

Between using the A/C, new 17" tires and giving up on mpg by driving 70mph I am currently seeing 39mpg after 252 miles on the trip gauge.

 

Temperatures have been hitting around 100 F here in the desert Southwest. Personally, I have the AC on all of the time. I do not notice any big hit on MPG.

Frankly, the AC is great, better than any car I have had. Since it is electric, it does not hit the MPG like other cars. I have to drive at least 20 miles to get to town and get about 48+ MPG on those short hops. I recently drove from Albuquerque to Denver and back, the long way through Four Corners, 1200 miles through the mountains. I averaged 53+ MPG.

If you want to roll in sweat w/o AC in order to perhaps save a couple of MPG, I guess that is your funeral. I'm for comfort.

 

There was a funny video of someone hypermiling a Civic hybrid and he would carry a small ice chest filled with cold water and use a wash cloth to cool himself off rather than using the A/C.

 

I can only speak for Gen 2 but you control the fan speed in Auto by raising the set temperature. The higher you set the temp, the slower the fan will run during initial cooling. It will automatically regulate lower as the inside cools. I usually find setting it at 73 is cool enough for me. If I am bothered by the high Auto fan setting when I get into a hot car, I merely raise the set temperature until I'm happy with the fan speed and then gradually lower the set point as the cabin cools.

Its false economy to drive around in a hot car by not using the AC as the traction battery is cooled with cabin air. Batteries especially when in use do not like heat, so run the air and be comfortable. Don't torture your main battery it may get you back in the future. As was stated previously in Auto the AC compressor and the fan will run slower as the cabin cools. When you set the temperature to LO the compressor will run full speed and consume as much energy as it can trying to reach the unreachable LO temperature.

 

For many drivers, Prius is 2 to 3x more fuel efficient for transport than their previous vehicle in combined traffic. While the AC is also more efficient, I've see no claim of 2-3x improvement.

An AC hit of 4.5 mpg on a Prius boosts fuel use from 2.00 to 2.20 gal/100miles, a cost of 0.20 gal/100miles.

A 1 mpg hit on a 20 mpg rig, about which hardly anyone would complain, boosts fuel use from 5.00 to 5.26, a cost of 0.26 gal/100miles. Though a smaller fraction of total use, it is a larger total cost.

Expressed in this style, folks would see Prius AC as more efficient than their previous vehicle, just not as dramatically so as the rest of the car.

 

I agree with you that MPG is a depressing way to express fuel economy (FE) for people driving lower-MPG vehicles. Been there.

But even if we could shift to gallons/100miles, I don't think doing so would help much, for several reasons:
- most non-hybrid vehicles aren't equipped with the instrumentation needed to monitor FE, and those that are have it in an inconvenient form (e.g., instantaneous and average MPG displays not shown simultaneously) - I once drove a Ram pickup that had an aMPG display all right: on the ceiling!! - and no iMPG display, so fairly useless (as well as depressing)
- most people don't pay much attention to their day-to-day FE (posters on PC are NOT a representative sample WRT FE consciousness) - at best they notice $$$$ flowing out of their wallets to pay for gas, and many don't care
- an unintended and unfortunate effect of EPA MPG standards is that most people think that a car "gets" a fixed MPG no matter what they do and expect that driving inefficiently, set the AC to run at full blast, etc, will not affect FE, no matter how it is expressed

As pointed out, many factors combine to determine the energy cost of running AC, among them outside temp and humidity, inside temp setting, speed, amount of sun, fan speed, recirc setting, whether AC is being compared to no AC with windows closed, cracked slightly, or open, etc, etc. So I don't think there is any exact % or MPG or gal/100 mile penalty to running the AC. STM the OP was running it in a way that might cost more energy, though I have no data.

FWIW, even though the Prius AC is electrical, running it will increase fuel consumption to recharge the battery - it isn't "free" energy.

But I think MPG works well as a measure for FE of more efficient vehicles: the numbers are in a convenient range to detect effects of different changes. If gal/100miles or l/100km were not single digits with a decimal they would be simpler for folks like me to use.

 

You are right but it is getting better. Owners of small cars are getting it and there is a lot of eco and mpg talk over on fiesta faction where I spend a lot of time too. Fiesta does not have an instant mpg gage but once you get used to a car you know when it is being efficient and when it isn't...heck, sometimes the instant is depressing too like when you are getting 10mpg going up a steep hill and you know you will be on throttle for the next 10 seconds minimum.

 

Auto mode.

I drive in high altitude, low humidity so our results should not be compared. My car gets 60-65 mpg on drives over 20 miles in 90F weather. Auto is set at 76-78F, and used after the car has vented for a couple of minutes. I make an effort to not let the car superheat when parked by looking for shade, always using a sun-block on the front windshield, and parking facing the sun.

 

I think many times I forget that I have a friend (HV battery/intake) in the back seat that needs to stay cool. If I'm hot the battery is probably hotter, so I try to keep the A/C going within reason to keep us both comfy. Which sometimes does murder mpg (vicious circle).

 

Early HCH's (and the Insight-I) have an AC compressor that works off the ICE, as in non-hybrids. So no AC if you want to shut down the ICE to coast. Later HCH's have a dual power AC that runs either off the ICE or off electricity. Seems like a clever solution.

When I do need to run the AC in the Insight-I I just pulse it on and off as needed. Unfortunately it's not a sophisticated system like the Prius has.