I can't answer your question, but the obvious advice is to try it each way and see what the result is...

 

The mileage drops fairly fast above 65. The wind resistance is quadratic with speed and it is very noticeable above 75. I am sure there is data around for miles per kwHR/ vs speed. I haven't seen how many kw are consumed by cooling a Bolt at 110 F. You could probably just sit still in the sun on a hot day with the air conditioning on and read it off the the power used on front panel in real time.

A year or so ago, there was a post on this forum where the mi per kWh vs were computed, but I can't tell you how to search for it. I think at 65 mph, my Bolt runs just above 4 mi/kWh. At 30 mph it is 5 mi/kWh or a little higher.



At 4 mi/kWh at 60 mi per hour that works out to a power of 15 kW. So you just need to know how how much power in kW is going into the air conditioning.

 

High speeds are worse by a massive margin. You won't save much time with the A/C on by driving faster, but you'll use a lot more energy.

 

We lose about thiry kms (about twenty miles) off our full charge range by using A/C. Driving 65 mph rather than 55 mph will reduce our range by considerably more than that. I don’t drive that fast often, but it looks like it would be about a sixty or seventy km reduction (maybe forty mile?) and as totaledJetta mentioned, as you increase speed more than that the range reduction will be exponential.

 

The A/C uses just a few kW, which is a lot less than the added drag from driving at 70 mph instead of 65 mph. The large drag coefficient on the Bolt (0.32) is Not Good.

I cannot imagine anyone can survive in 110 degree F heat without A/C.

 

...The large drag coefficient on the Bolt (0.32) is Not Good.

I cannot imagine anyone can survive in 110 degree F heat without A/C.

Just to clarify .... the 0.32 was an estimate from pre-production ... the production number was lower, at 0.308. Which is about what my BMW e90 LCI is (0.3).

http://www.hybridcars.com/2017-chevy-bolt-ev-is-less-of-a-drag-than-originally-believed/

When pre-production prototypes were revealed in January 2016 the wind tunnel testing was coming in at .312, as Car and Driver magazine reported at the time. With the final production headlight lenses and other exterior parts in place on the car it has since fallen to .308.

To the OP, this might be a useful reference ... We just got back from visiting family and the return trip was primarily interstate speeds ranging from 70-75 mph in 102F temps, with ~480 lbs of people and ~300 pounds of cargo, and we were running the A/C at 70F and a fan speed of 5, and the little EV had no trouble maintaining pace with traffic and keeping the cabin comfortable. I was impressed with how functional it was. Return trip was 85 miles and a slight elevation gain, and we averaged 3.8 mls/kWh for the return leg. There was basically no wind. We would've fallen a little short of the EPA rating, but this is a pretty extreme condition...

Yesterday we drove down at 95F temps, but took a slightly longer time (but shorter distance) route that had half interstate, and half predominately 55 mph roads, and more towns. We also used A/C, but averaged 4.4 mls/kWh. That day also had basically no wind. So ... speed trumps A/C in our experience.

If you want to get technical, drag force increases as velocity^2. And the rate at which this force is applied increases as velocity. So POWER drag increases as velocity^3.

 

This question needs to be clarified more, but what I think is being asked is, "will driving faster and getting to the destination sooner, thereby reducing the amount of time the AC runs, increase range".

The answer is no.

 

Yes. It reminds me of the old story about speeding to get to the gas station before you run out.

 

The good news is, at 110F the air density will be low so less air resistance. Air conditioning will run anyway to cool the battery so it might as well cool the payload too.

 

But then you need to figure in the resistance from all the dust in the atmosphere in Southern Arizona

 

I've never done extensive testing but when I run A/C I don't notice much of a drop in efficiency (maybe 0.1 less mi/kWh) but if I'm driving at 50MPH or above the economy takes a big hit regardless of if A/C is on or not. Instead of getting ~4.7 mi/kWh in town driving 35-40 I get closer to 3.7mi/kWh on the freeway at 65-70.

 

Driving at 65MPH will consume about 15 kWh per hour. AC consumes less than 1 kWh most of the time, and at most 2-3 kWh per hour.

 

I assume AC accounts for 5-10% of electrical consumption. In my Prius, it accounts for 10% since I only get 15 miles on a charge, so I only take short trips where the AC runs at full speed.

 

It should be pretty simple to determine maximum AC power draw. Sit in Park, with no lights, radio, or fan on. The DIC should show 1 kW over several minutes. Now turn the AC on at Max/65F, with the fan on high , and all three vent positions selected. Again watch the DIC kW reading for several minutes. The difference will be the maximum draw.

 

The problem with this is that the power meter is only accurate to a kWh. Does a reading of "1kWh" mean that the consumption is somewhere between 0.5 and 1.5, or does it mean somewhere between 1 and 1.9? And the A/C draw is not very large in comparison, so it's impossible to get a very accurate estimate this way. However it can be used to place an upper limit on the draw and to confirm that it's pretty small, especially compared to the power required to move the car at highway speeds.

 

There is a better way to determine AC energy

The kW power flow meter on the speedo panel is not much use for determining HVAC usage since it rounds to nearest kW. Other better ways:

1) Note the total kWh used since last charge on the energy info screen. Note also the percent attributed to HVAC. Use the average speed and miles driven since last charge info as follows:

Example - today, after charging overnight, I drove 100 miles and used 22 kWH. 10% energy went into HVAC, and my average speed was 25 mph. 10% of 22 kWh is 2.2 kWh. 100 miles at 25 mph works out to 4 hours. 2.2 kWh HVAC / 4 hours works out to HVAC using 550 Watts.

2) (This method works only at rest): Select info screen showing kWh used. It increments every 1/10 kWh. Sit in car, make calls, surf internet, read a Kindle, or nap...whatever. Note how often kWh used increments. I had a situation where a colleague ran late and I killed 30 minutes in a parking lot. The kWh meter incremented 0.1 kWh about every 10 minutes. That works out to 0.6kWh / hour or 600 Watts.

Finally, be aware that HVAC energy usage is not a fixed figure - it highly depends on outdoor temperature sunshine and "indoor" setpoint and fan speed. As outdoor temp rises the car needs more AC to maintain a given cabin temperature, and, at the same time, the refrigeration system works harder to reject cabin heat into the ambient air. More technically speaking, as outdoor temps rise, compressor refrigerant discharge pressure rises, system capacity falls, and compressor power rises to overcome the increase in discharge pressure.

I'm both an engineer and HVAC contractor, so I could bang on a bit more, but I hope y'all get the idea from the brief outline above.

One last point - I haven't actually examined my Bolt's HVAC system (it works well, so no need to mess with it), but I expect that it works better while moving than sitting still since movement almost certainly increases air flow across the condensing coil, improving efficiency.

Oh yeah - most of the foregoing doesn't apply to heating mode (other than measurement tips). Bolt heat comes from a purely resistive system...Btuh out = Watts in times 3.413. Perhaps future Bolt models will incorporate a heat pump for more efficient heating compared to resistance, but since I live in Florida, I don't much care...

 

The kW power flow meter on the speedo panel is not much use for determining HVAC usage since it rounds to nearest kW.

I wouldn't even assume that it rounds. It could well simply truncate - meaning that a reading of "1 kW" could be anywhere from 1 to 1.9 kW. We simply don't know, or at least I personally haven't seen anything to tell me.

 

Fair point...perhaps I'm too generous.

Upon reflection, perhaps it rounds up...it mostly displays 1 kW, sometimes 0.5kW, at "idle" even when not operating AC. I'm not sure what the car's true standby consumption is, but I'd guess somewhere in the vicinity of 100 Watts. I suppose that's another test one could run using the kWh used meter...how long does it take to use 0.1 kWh powered up but no HVAC running.

 

Fair point...perhaps I'm too generous.

Upon reflection, perhaps it rounds up...it mostly displays 1 kW, sometimes 0.5kW, at "idle" even when not operating AC.

Regardless of truncation or rounding, in average it should not matter as it happens both with and without A/C? Unless the strategy is something like "rounding (or truncating) with a minimum of 0.5 kW as we do not want to display 0".

I'm not sure what the car's true standby consumption is, but I'd guess somewhere in the vicinity of 100 Watts.

For an Outlander PHEV, 350 - 450 watts of idle power is quite normal.

 

There is a pretty good thread here:
http://www.chevybolt.org/forum/9-20...t-ev-general-discussion-forum/5866-speed-vs-energy-efficiency-2.html#post366586


As others have noted, I am now seeing about 10% energy usage how that Houston is in upper 90's this week.


This is a summary of my first decent length trip from Houston to Austin (175 miles), although I think I had a bit morerange efficiency.
On the way there atan average of about 75 mph for about 150 miles (@2.9 m/kwh) and about 25 milesin city driving (@5 m/kwh), I pulled up to DCFC charger with about 15 miles(estimating 3 kwh) of range remaining. By those calculations, I used 56.7 kwh,with 3.3 kwh in reserve. Way to close for comfort, and was glad to hitstop-and-go traffic through Austin.
On the way home, Ileft the same DCFC charger at 89% (say 54 kwh capacity), prepared to stop atanother charger on the route. But driving home at 65 mph for about 170 miles(@3.6 m/kwh) and about 5 miles in city driving (@5 m/kwh) I made it home withabout 25 miles (estimating 5 kwh) of range remaining (no stop needed). By thosecalculations, I used 48.2 kwh, with 5.8 kwh in reserve (starting with about 6kwh depleted).


Small note, it isslightly uphill to Austin and downhill to Houston, so that would affect therange efficiency numbers slightly.

 

BTW: It seems almost obvious that driving faster is less efficient. But driving (much) slower at some point also becomes less efficient. So, there must be a break even point. Pretty sure this is much slower than anybody is willing to drive.

 

On a tangent thought, I've always wondered where the breakeven point is for going up a hill. After all, it takes energy to merely maintain position on a hill (when the brakes aren't on), so going as slowly as possible up it isn't efficient.

 

I'd drive no faster than 60 mph with the A/C set at 78 degrees. Probably the most efficient combination. Also, stay away from driving Nissan electrics...

 

The most efficient speed for EVs is typically around 10 to 20 mph depending on the vehicle.

 

On the question of speed and it's effect on range, I see people complaining about lack of adaptive cruise control.... I don't care for my daily commute (virtually zero traffic = no need for adaptive cruise) but when I go on a long highway run and I slowly pull up behind a semi when I have cruise set on 70 and I watch my KW usage drop from 21 or 22 down to 16 or 17 it makes me long for adaptive cruise as a "drafting on trucks" tool

Keith

 

I see people complaining about lack of adaptive cruise control.... I don't care for my daily commute (virtually zero traffic = no need for adaptive cruise) but when I go on a long highway run and I slowly pull up behind a semi when I have cruise set on 70 and I watch my KW usage drop from 21 or 22 down to 16 or 17 it makes me long for adaptive cruise as a "drafting on trucks" tool

In general cruise control is going to be detrimental to efficiency because the system makes too frequent and too severe throttle adjustments in an effort to maintain speed as close as possible, this is especially true when going up even slight hills where the car will apply quite a bit of throttle to maintain the set speed when usually you would try to maintain a set throttle position and allow yourself to slow a bit or maybe only apply a little additional throttle to keep your speed from dropping too much on longer hills. I stopped using it years ago in my ICE vehicles because I can drive much more efficiently modulating the throttle myself. I do use it for brief periods on hours long drives to allow me to "stretch" my legs a bit and hive my calf muscle a brief respite.

Now of course it's certainly possible for a car company to design their cruise control to operate with economy in mind, but based on my limited experience testing it in the Bolt and other reports I've heard it does not seem that GM did so for the Bolt.

 

Great video for this topic.

Noticed his numbers at the end of the video indicate he has over 61 kWh usable...way more than my 56 kWh usable. :-(

He got the same calculated 61+ kWh usable on his winter run in February. I am soooo jealous. WTF GM.

 

If we're talking most time efficient speed on a long trip, I did the math and found somewhere around 75 MPH is the sweet spot assuming you can find a DCFC near to 10% remaining capacity.

That said, there are a lot of variables at play and 75 MPH isn't always the most time efficient speed.

 

Since I got Torque Pro up and running a few months back, my "Usable" has varied from 59.7 to 60.5. It's showing 60.0 today. Doesn't seem to be related to temperature, charge habits, driving habits, charge status, etc. It changes every week or so if it's going to change at all.

 

I have calculated our Bolt's capacity many times, using the info off the DIC, and energy screen. It has always been in the 55-57 kWh range. Last month I actually did a test from full to empty, and came up with 56 kWh. Pretty sad, but I know there is not a thing I can do about it. One of the beauties of buying an EV. You never know what you have, until it's too late.

Wouldn't it be great if they put the Torque Pro info on the energy screen, instead of that stupid chassis energy flow cartoon?

 

Wouldn't it be great if they put the Torque Pro info on the energy screen, instead of that stupid chassis energy flow cartoon?

Post of the month!

 

Did a little test today on the power draw when using AC while parked. I did this using Torque Pro and the Bolt PIDs. Below is the data showing the instanteous power consumption reported for when the car is off, then turning the ignition on and letting things "settle", then turning on AC (72F fan speed 4) until things "settle" (consumptions ramps up and then seems to ramp down and settle when the cabin gets close to the desired setting), then turning the AC and Fan OFF and letting settle, then turning on the ignition off.

Looks like the AC can draw considerable power if there is a large amount of cooling needed, but then settles down once the cabin is at/near temp. Maybe ~0.5-0.7kW consumption for a continuous draw (but I'm guessing this amount varies depending on how much hotter the outside is vs the cabin desired setting).

 

Looks like the AC can draw considerable power if there is a large amount of cooling needed, but then settles down once the cabin is at/near temp. Maybe ~0.5-0.7kW consumption for a continuous draw (but I'm guessing this amount varies depending on how much hotter the outside is vs the cabin desired setting).

It depends what you think of as considerable. From that graph, and what I gather from the kW load screen on the DIC, the car "idling" pulls between 0.5-1.0 kW. The AC at max output was pulling an additional 2 kW. That is pretty small compared to the heater's max of about 9 kW. Driving down the road at 40 mph takes 9 kW.

Using kWh/mi converted from miles/kWh, and average mph from the DIC, and the percent power to drive, climate, and battery conditioning, you can determine your average power use for each.

I did a ride in March, when it was in the mid to high thirties, rainy and overcast. Did 143 miles, averaging 45 mph. I set the heat to max/90F, and fan to 5. Heat averaged 3 kW, so was on about one third of the time to maintain 90F cabin temperature...more than the AC can pull on high.

 

I consider a 7000% increase "considerable"

That is like people talking about huge percentage increases in EV sales. Seven times nothin' is still nothin'.

Or you can just measure things directly from the OBD and isolate each variable and get better accuracy than relying on the DIC and it's coarse resolution.

I'd love to get one, just as soon as it is plug and play. I am no computer geek. I am terrified of screwing something up, playing with the OBD, and software. That is like a baby with a hand grenade. heck. I can't even figure out how to do a multi quote.

I'm not sure the AC can't pull more than 3 kW ... I'll have to test that. I could set the temp as low as it would go (instead of 72) and put the fan on high ... based on the pretty easy test I did this afternoon, it wouldn't take much more to move it above 3 kW consumption.

I look forward to your result. I did a ride last summer with the AC set to min/65F, but I forget the results, other than it was might cold.

 

I'd love to get one, just as soon as it is plug and play. I am no computer geek. I am terrified of screwing something up, playing with the OBD, and software. That is like a baby with a hand grenade.

It really is pretty much plug-and-play.

 

OK. I am looking at this spreadsheet from Telek. It doesn't look like plug-and-play to me.

http://bit.ly/ChevyBoltPIDs

I figure I'd go for the high end OBD2 unit? Low battery draw is good, given how poorly the 12 volt batteries are maintained in EVs, and high sample rate sounds good too, I imagine?

[ame]https://www.amazon.com/ScanTool-427201-OBDLink-Bluetooth-Professional/dp/B00H9S71LW/ref=sr_1_2?s=automotive&ie=UTF8&qid=1522253582&sr=1-2&keywords=obdlink+lx[/ame]

It comes with Android software so it should communicate with my LG VS501 K20 phone? Think the Tesla nut, kid at my Verizon store could load up/setup the app and PIDs for me?