[Whitelighting1!]

We have a 2017 with 17,000 miles logged and live in Phoenix. Can anyone give us feedback on our question as to what drains the battery more - using A/C or traveling at speeds over 65 MPH? We are trying to maximize our range for our highway commute while driving in 110 degree heat.

 

[Sean Nelson]

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

 

[TotaledJetta]

We have a 2017 with 17,000 miles logged and live in Phoenix. Can anyone give us feedback on our question as to what drains the battery more - using A/C or traveling at speeds over 65 MPH? We are trying to maximize our range for our highway commute while driving in 110 degree heat.

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.

 

[Vertiformed]

We have a 2017 with 17,000 miles logged and live in Phoenix. Can anyone give us feedback on our question as to what drains the battery more - using A/C or traveling at speeds over 65 MPH? We are trying to maximize our range for our highway commute while driving in 110 degree heat.

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.

 

[Chwkev]

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.

 

[GlenandhisBolt1!]

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.

 

[redpoint5]

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.

 

[shocker]

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.

 

[GJETSON]

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.

 

[TDIwyse]

...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.

 

[Sean Nelson]

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.

...whereas A/C usage increases linearly (once the cabin has cooled down). Driving for 2 hours vs. 1 hour merely uses twice as much A/C. But driving twice as fast uses WAY more than twice as much power.

 

[raitchison]

We have a 2017 with 17,000 miles logged and live in Phoenix. Can anyone give us feedback on our question as to what drains the battery more - using A/C or traveling at speeds over 65 MPH? We are trying to maximize our range for our highway commute while driving in 110 degree heat.

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.

 

[demart]

We have a 2017 with 17,000 miles logged and live in Phoenix. Can anyone give us feedback on our question as to what drains the battery more - using A/C or traveling at speeds over 65 MPH? We are trying to maximize our range for our highway commute while driving in 110 degree heat.

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.

 

[redpoint5]

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.

 

[GJETSON]

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.

 

[Sean Nelson]

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.

 

[JaxEVLyftUber]

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...

 

[Sean Nelson]

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.

 

[JaxEVLyftUber]

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.

 

[Ampera e]

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.