Cold Weather, Hot Data: Heater Power Usage and Exterior Temp

[Firn]

Hey everyone, we had a great conversation about heater usage the other day, so I thought I’d share my latest findings with you all.


Background:
I’m conducting some specific tests to assess the impact of tire pressure on efficiency (more on that later), and tracking heater usage is a key part of validating my data. Below are my findings so far.


Test Setup:
I drive a consistent highway route, maintaining a steady 70mph with cruise control (non-ACC) engaged, interior temp set to my normal 70 degrees. I’ve completed the route four times now. While I’ve tried to keep external temperature and wind speed as consistent as possible, there’s about a 12°F difference between my warmest and coldest test days. Plus side, we can see how the heater responds to different temps.


Results:
The exterior temperatures, as reported by the truck, are shown on the upper four lines of the chart, with coolant heater power usage overlapping on the lower section.

Note: This is my first attempt at using Microsoft Power BI, so I’m still refining the visuals.


Here are the average heater power usage figures for each day I tested. Averaging period is ~52 minutes.

• 12 Jan: 3.49 kW
• 22 Dec: 4.34 kW
• 5 Jan: 4.11 kW
• 9 Jan: 5.56 kW

Observations:

• I’ve noticed that using the HVAC on Auto 3 setting seems to increase power usage. Not only is the power consumption higher, but the cabin also feels warmer.
• Each test begins a few miles from my home. The truck is garage-kept and typically starts around 55°F when I get in.
• I haven’t observed the heater using any power to warm or maintain the battery temperature (there’s a specific PID for that).
• On 22 Dec, the higher power usage at the beginning of the test was due to the HVAC being off at home, and then turning it on shortly before starting the trip. The system was still warming up the cabin at the start of the test.

Since my primary focus is on efficiency and tire pressure, I’ve trimmed the data to only include the segments where I was traveling at 70mph.

I’ll continue testing and refining the data. If anyone has additional insights or suggestions, feel free to chime in!

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[Jseis]

I’ve played around with tire pressure, heating, speed, and finally concluded that the two lane rural highway I drive 90-100 miles a day in about 55 minutes rules. Headwinds (up to 10-15 mph), cooler temps (35-45 F), standing rain on the roads, all play their part, but speed rules them all. My speed outside of small town 30-35 mph zones is 53-58 and usually impacted by winter weather & summer traffic, both of which tend to slow me down. I’ve experimented w/120V 200-500 watt heaters (small under desk sized) and they’ve marginal gains if I don’t use the trucks heat and if I do, for brief periods (30 seconds a few times per hout) to get moisture out of truck. The Lightnings HVAC is excellent though somewhat of an energy hog. An oscillating 750 watt dash heater probably the way to go to heat cab and keep window de-fogged. Pump some leaf bags full of air in the back seat to reduce cab volume. Of course now we are into hyper-miler crazy. I’ve a tonneau for covering tools though not aerodynamic gains lol!

My winter average is ~2.4 mi/kWh and summer is right at 2.6 mi/kWh.

Space Heater I’m experimenting with. At 500 watt setting it pulls 490watts from cab power. Tilt switch. keeps 50% of window clear, and cab passably “warm”. Barely. I think I lose 1.2 miles of range in one hour. The gain is not running HVAC on 1 bar auto at 67 degrees. That sucks 10-12% of power and that translates into 15-20+ miles of range lost.

 

[Firn]

I’ve played around with tire pressure, heating, speed, and finally concluded that the two lane rural highway I drive 90-100 miles a day in about 55 minutes rules. Headwinds (up to 10-15 mph), cooler temps (35-45 F), standing rain on the roads, all play their part, but speed rules them all. My speed outside of small town 30-35 mph zones is 53-58 and usually impacted by winter weather & summer traffic, both of which tend to slow me down. I’ve experimented w/120V 200-500 watt heaters (small under desk sized) and they’ve marginal gains if I don’t use the trucks heat and if I do, for brief periods (30 seconds a few times per hout) to get moisture out of truck. The Lightnings HVAC is excellent though somewhat of an energy hog. An oscillating 750 watt dash heater probably the way to go to heat cab and keep window de-fogged. Pump some leaf bags full of air in the back seat to reduce cab volume. Of course now we are into hyper-miler crazy. I’ve a tonneau for covering tools though not aerodynamic gains lol!

My winter average is ~2.4 mi/kWh and summer is right at 2.6 mi/kWh.

Space Heater I’m experimenting with. At 500 watt setting it pulls 490watts from cab power. Tilt switch. keeps 50% of window clear, and cab passably “warm”. Barely. I think I lose 1.2 miles of range in one hour. The gain is not running HVAC on 1 bar auto at 67 degrees. That sucks 10-12% of power and that translates into 15-20+ miles of range lost.

Still working on the data, but from the data above even 70 degree interior with a 12 degree exterior, and JVAC at auto 3 is 11 miles of range lost per hour. 25 degrees outside, 70 inside, and auto 1 is closer to 7 miles per hour. But, more than a 500w space heater for sure.

Interior volume shouldn't ge a concern, just exterior losses. Once a volume of air is warm there is nowhere for the heat to go.

As far as speed, yes, certainly slower is more efficient. I plan to try various changes and see how they effect efficiency. At the end of the day I will drive as fast as I drive, if I can find more efficiency doing it then that's more range

 

[lightspeed]

Did you have recirc on? I would imagine that recirculating the warm air would be a significant addition to efficiency.

 

[Grumpy2]

Interior volume shouldn't be a concern, just exterior losses. Once a volume of air is warm there is nowhere for the heat to go.

I am sorry that I am not following your study completely, but this statement stuck me.

All exterior surfaces of the cabin are colder than the air inside the cabin. The volume of air in the cabin is never equal, there is instead a constant effort to heat all of the volume of air inside the cabin to be equal. The air immediately adjacent to all of the exterior surfaces are colder than the air in the center of the cabin.

 

[Firn]

Did you have recirc on? I would imagine that recirculating the warm air would be a significant addition to efficiency.

To be honest, I'm not sure. It's not a setting i change so I did not pay any special attention to it.

 

[Firn]

I am sorry that I am not following your study completely, but this statement stuck me.

All exterior surfaces of the cabin are colder than the air inside the cabin. The volume of air in the cabin is never equal, there is instead a constant effort to heat all of the volume of air inside the cabin to be equal. The air immediately adjacent to all of the exterior surfaces are colder than the air in the center of the cabin.

Yes. But the volume itself does not contribute to heat loss, only it's contact with the surfaces around the volume. Given two volumes of air, but the same amount of surface contact, the only difference would be a slight bit more energy to get the large volume UP to temp. The volume of air itself isn't losing heat simply because it is larger.

People worry about how much air they are heating, when instead they should worry about the exterior losses.

 

[StevenC56]

What is the difference between Auto 1, 2 and 3?

 

[TaxmanHog]

What is the difference between Auto 1, 2 and 3?

Fan speed, ironically it's not always linear, I've experienced "2" blowing harder than "3"

Note these three settings are minor adjustments of automatic fan control, if you want fixed value manually adjust the speed by touching the fan icon then twist the dial from off to 7

 

[Jseis]

Did you have recirc on? I would imagine that recirculating the warm air would be a significant addition to efficiency.

It would be if it stayed on. The 390 water fa-heat is essentially a recirculating fan w/heat.

 

[Jseis]

Fan speed, ironically it's not always linear, I've experienced "2" blowing harder than "3"

Note these three settings are minor adjustments of automatic fan control, if you want fixed value manually adjust the speed by touching the fan icon then twist the dial from off to 7

“1” is my fav setting or 1 bar auto

 

[21st Century Truck]

The presence or absence of the glass sunroof is likely another important factor for cold weather longer distance trips. On my former Mach E, the panoramic glass roof, although decently coated to minimize Summer UV insolation, was almost an open window in really cold weather for radiating cabin heat out until I insulated it with silver bubble insulation during Winter adventures.

This is one of several reasons why I made sure the Lightning I bought has a classic metal roof.

 

[Maineiac12]

What is the difference between Auto 1, 2 and 3?

I’m also curious if there are significant power consumption differences between auto 1 and auto 2.

I had been using 1 but moved it up to 2 when temps dropped below 10 this morning. Brrrr!

 

[Maxx]

I’m also curious if there are significant power consumption differences between auto 1 and auto 2.

I had been using 1 but moved it up to 2 when temps dropped below 10 this morning. Brrrr!

I have not compare the two but what I have seen is the SIGNIFICANT difference between initial cold power consumption and when cabin has reached the target temperature. Don't quote me on this but once when I looked at it, when it started, I think it was around 9-10 KW and when it got a little warmer around 500W. All of this assuming we are talking Lightning without Heat pump.

I have not made any scientific comparative experiments on this but logically speaking space heater and truck's heater both use heating elements. If you are not introducing cold outside air to the cabin, the only difference should be Truck heater is able to heat up the cabin much faster and may be a very small loss of heat in any non insulated tubes outside the cabin hot air travels through.

p.s. unless the leaf bag OP mentioned is well insulated, it should not make any difference on longer drives. Heat will be absorbed to heat up inside of it. I do I agree with his observation on speed. It makes a huge difference. I get 3.4 mi/KWh round trip on a good summer day.

 

[21st Century Truck]

Every really cold morning I preheat and precondition the truck during the final 30 minutes of my special EV-only Time of Use electric submeter's low rates window. I figure the mass of the truck's body and battery will keep a lot of the residual heat until I need to use the Lightning... better than starting from a cold soak, even hours later as it might be.

Also, on longer trips when I DC Fast charge I also set "cabin departure" for about 30 minutes after I plug in. I figure drawing juice for heat is better / cheaper / faster as a piggyback off the Fast Charging stream.

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