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.

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