[De Clarke]

So, obviously driving with windows open (even a little) increases drag and hence degrades efficiency.

The unanswered question for me is "how much", i.e. how expensive a luxury is it to tool around in warm weather with windows down and enjoy the wind in one's hair?

Does anyone have back-of-envelope numbers for the reduced efficiency cost of fresh air?

Oh and while I'm on the subject, is there a straightforward way to get the "climate control" system to simply let outside air in, without trying to heat or cool or anything intelligent? In the old days we had a lever or knob that allowed outside air to come in, pushed by the vehicle movement, and blow out of the vents. I liked that. Every time I try to interact with the air/fan/vent system it seems to turn on the climate control computer which then starts the AC or the heater (as the case may be) which is not what I wanted.

Someone will probably tell me to go read page 200 and something in the manual, but I then would have to comment that no one needed to go RTFM to get outside air into cars 30 years ago, and that this was actually a right and proper state of affairs

 

[SGW]

In my 2017, just turn the fan to any speed, tap the “heat/AC” button (they share a button in the 2017) so the orange light is off, and tap to turn off the “arrow in the car button”(“recirc?”).

It should remember the way you leave it, so when you start up next time, the AC will stay off unless you hit that button or hit “auto.”

 

[Packard V8]

Windows down around town won't be noticeable decrease in range. Windows down on the highway at 70, too much buffeting, wind whip and noise for me to tolerate long enough to get a reading.

jack vines

 

[XJ12]

In my 2017, just turn the fan to any speed, tap the “heat/AC” button (they share a button in the 2017) so the orange light is off, and tap to turn off the “arrow in the car button”(“recirc?”).

It should remember the way you leave it, so when you start up next time, the AC will stay off unless you hit that button or hit “auto.”

also need to manually select the vent setting and use the fan setting. I don't think you'll get outside air to flow into the car otherwise. at least I can't feel it being forced in on its own. I use this setting all the time to get outside air. especially cool outside air.

 

[Stovebolt6]

I seem to recall someone (Car and Driver? Mythbusters?) running a test and some calculations and they came up with 45MPH as the upper limit for leaving the windows open. This was based on an ICE car, of course. When the weather's nice I usually have one front and one rear window open about an inch or so at the speeds I usually drive at. The air comes in at the rear window and blows out at the front window, so I get a nice circulation without too much noise. When the weather turns hot the A/C will get a workout.

 

[Mivo]

I found, during the winter, that my car was using heat on occasion even with the Heat-A/C button disengaged. Not sure if it would do the same in warmer weather with A/C.



I almost never use my A/C unless I'm on the freeway for a while and then only because it's too noisy to keep the window down. But it would be interesting to compare the energy cost of increased drag against the cost of running the A/C for those that want to squeeze every bit of mileage between charges.

 

[GlenandhisBolt1!]

The tradeoff between windows up or windows down (usually considered as a function of speed) varies with every model of car. One thing that the Bolt has going for it is the air conditioner is more efficient than an air conditioner on an ICE car. ICE cars use a compressor driven by a belt connected to the engine through an electrical clutch, so the compressor speed varies with the speed of the engine. Pumps are typically most efficient over a narrow speed range, so the ICE engine's pump is not at it's best at many engine speeds. But the Bolt's air conditioner compressor is driven by it's own motor, and we can be sure it's most efficient at that fixed operating speed. And there are no losses due to a belt drive or clutch. The air conditioner in my Bolt appears to use about 1kW to 2kW. I have heard that a typical ICE car uses around 5 hp (3.75kW) to drive the air conditioning.

The speed threshold for the Bolt is likely to be higher than many cars, since it has a relatively high drag coefficient (0.32). The difference in the drag coefficient for windows up and windows down is likely to be less significant than in a nicely streamlined car like the Tesla Model 3 (0.23 drag coefficient).

 

[KeithMoon]

The tradeoff between windows up or windows down (usually considered as a function of speed) varies with every model of car. One thing that the Bolt has going for it is the air conditioner is more efficient than an air conditioner on an ICE car. ICE cars use a compressor driven by a belt connected to the engine through an electrical clutch, so the compressor speed varies with the speed of the engine. Pumps are typically most efficient over a narrow speed range, so the ICE engine's pump is not at it's best at many engine speeds. But the Bolt's air conditioner compressor is driven by it's own motor, and we can be sure it's most efficient at that fixed operating speed. And there are no losses due to a belt drive or clutch. The air conditioner in my Bolt appears to use about 1kW to 2kW. I have heard that a typical ICE car uses around 5 hp (3.75kW) to drive the air conditioning.

The speed threshold for the Bolt is likely to be higher than many cars, since it has a relatively high drag coefficient (0.32). The difference in the drag coefficient for windows up and windows down is likely to be less significant than in a nicely streamlined car like the Tesla Model 3 (0.23 drag coefficient).

.32 cd for a car as high and short as the Bolt is incredibly low. Do not underestimate that achievement. Engineering an optimal vehicle is a trade-off between a constellation of different variables and for an Urban/suburban family utility vehicle (which is what the Bolt is) the optimization is as close to perfection as one could imagine.

The interior volume (and more importantly the geometry of that volume) is near perfect. It is immeasurably more useful than something like the Model 3 which (absurdly) traded-off utility for efficient highway speed where the average person spends less than 20% of their travel time. People buying a model 3 as their family vehicle is every bit as stupid as people who buy a Ford F-150 as their daily commuter vehicle (oh yeah, people do it but that is just more evidence that the intellect associated with the average IQ of 100 is to put it mildly, disappointing).

 

[XJ12]

just for the record, 0.32 was the design goal for the Bolt. They actually achieved 0.308

 

[Vertiformed]

How much power the A/C needs depends on how hot it is outside and what your thermostat setting. If it's 80 ℉ outside, cooling the cabin down to 74 ℉ doesn't need that much energy. On the other hand, if it's 105 ℉ and you tell it to cool the cabin down to 68 ℉, that requires more energy.

If it's cool enough that not running the A/C would be fine, or opening the windows would be good enough to having you feeling cool, running the A/C will have negligible impact.

You can explore all of this yourself since the Bolt provides all the tools you need to measure the impact of running the A/C on mildly hot days.

 

[Raymondjram]

This is a good post for future reference when some manufacturer offers an electric convertible.

 

[surgeonFWW]

How much power the A/C needs depends on how hot it is outside and what your thermostat setting. If it's 80 ℉ outside, cooling the cabin down to 74 ℉ doesn't need that much energy. On the other hand, if it's 105 ℉ and you tell it to cool the cabin down to 68 ℉, that requires more energy.

If it's cool enough that not running the A/C would be fine, or opening the windows would be good enough to having you feeling cool, running the A/C will have negligible impact.

You can explore all of this yourself since the Bolt provides all the tools you need to measure the impact of running the A/C on mildly hot days.

Good info. My wife & I drove the 226 miles necessary to get from our home to the nearest DCFC going east (Lexington, VA). We did not charge along the way. It was summer (~ 80-85 degrees F) and we charged to full at home (Huntington, WV). We drove at 60 mph on the interstate, staying in the right lane. We set the A/C at 76 and alternated between driving with the windows open 2" and with the A/C on. We arrived with 24 miles of range remaining. We were never worried about running out of electrons. We charged to full (because it was free and because we had the time, enjoying a relaxing meal at an outdoor restaurant (~ 1/2 mile away) and exploring the historic town a little). We were full in <2 hours, and proceeded to Washington DC (200 miles, but with many DCFC along the route).

 

[ArizonaJon]

This is a good post for future reference when some manufacturer offers an electric convertible.

Actually there is one BEV convertible you can buy today. The smart.

 

[StanJ]

Every time I try to interact with the air/fan/vent system it seems to turn on the climate control computer which then starts the AC or the heater (as the case may be) which is not what I wanted.

When I first driven the 2017 Bolt from dealer, I noticed the AC and heat went on when I needed to defog the windshield. It was August (in NJ). After arrival, I went through all the climate defaults and changed them such that when I direct air to windshield, the AC/heat does not come on automatically. If the outside air does not remove condensation, I turn on the AC and dial temperature down to prevent heater turning on. The windshield clears in a few second. Then, I shut the AC off and cycle as needed. Defogging is a safety feature so, you need to understand, what you are doing. With the proper setup, the AC/heat will never turn on just because the fan is on.
I don't open windows for climate control too much because I have problems with the noise. !-2 inches at speeds up to 40 MPH is OK. I think you are correct that with fan set to zero, there is no passive air circulation.
The Bolt is really great car.

 

[JC Bolt]

Actually there is one BEV convertible you can buy today. The smart.

Well, actually, not any more:

https://www2.greencarreports.com/ne...end-of-the-fortwo-has-been-a-long-time-coming

 

[GregBrew]

When I first driven the 2017 Bolt from dealer, I noticed the AC and heat went on when I needed to defog the windshield. It was August (in NJ). After arrival, I went through all the climate defaults and changed them such that when I direct air to windshield, the AC/heat does not come on automatically. If the outside air does not remove condensation, I turn on the AC and dial temperature down to prevent heater turning on. The windshield clears in a few second. Then, I shut the AC off and cycle as needed. Defogging is a safety feature so, you need to understand, what you are doing. With the proper setup, the AC/heat will never turn on just because the fan is on.
I don't open windows for climate control too much because I have problems with the noise. !-2 inches at speeds up to 40 MPH is OK. I think you are correct that with fan set to zero, there is no passive air circulation.
The Bolt is really great car.

You can get air circulation and eliminate the 2Hz air pressure cycling warble by cracking front and rear opposite side windows about an inch. I crack the front passenger side and the rear driver's side, so as to not muss the hair on the morning work commute. I've been doing this for decades, and it's worked on every vehicle I've ever owned, (except my S2000).

As an aside, I used this phenomenon in my physics class sound unit to demonstrate how a wind instrument like the flute and piccolo work by pressure buildup and collapse as moving air passes over an opening in a cavity. (Frequency being a function of cavity size.) I suggested that they try it on the limo they rent for prom, and tell their friends "It's a science experiment". Should get some extremely low frequencies with that large of a cavity. Caution, though, in some vehicles, opening only one back window at freeway speeds can be painful.:nerd:

 

[StanJ]

You can get air circulation and eliminate the 2Hz air pressure cycling warble by cracking front and rear opposite side windows about an inch. I crack the front passenger side and the rear driver's side, so as to not muss the hair on the morning work commute.

Thank you for your science addition, which I really enjoyed reading. I agree with you. However, early in my driving experience I discovered and further confirmed with every next sedan/hatchback, that the circulation is better when passenger and right rear window are crack opened (1-2 inches), so not the opposite rear window. It sounds counter-intuitive but from some reason, there is a light circulation coming around the driver in this configuration. The cross-ventilation tends to go on the driver's rights side but the left side is without any ventilation. :nerd: