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So I tried to use my shiny new GDS2 tool (the same diagnostics tool that GM mechanics use) to look at what the car reports for HVAC power usage. There's a TON of data in here, including a lot about power usage.

Unfortunately, it looks like the A/C power details are completely incorrect. I don't know what data it's pulling, but it doesn't seem to be pulling the correct data. Power usage for the A/C floats between 0.4 and 1.1kW pretty much any time the HVAC system is on, even if it's on full blast heat. A different A/C power usage metric shows up to 7.2kW used by A/C - when heater is on full blast... so, yeah, those numbers aren't reliable.

So, I took a look a different way. The main HV battery current usage seems reliable, and flips between 0.3A and 0.6A (it only has 0.3A increments), meaning that idle power draw is somewhere around 100-250W when the car is idle. Note that there would be at least some 12V battery charging with this as the car had not been turned on for a day. This is the same metric that you can pull via OBD2, however in this tool it updates live so that you can see it more accurately.

With the heater cranked full power "HI", I can see 22A maximum at 370V and, while still at maximum, it settles down to about 18.6A after a minute. That's 6600-8000W taking out the idle power - right around where we expect it since the maximum heater power reports as 7500W. The average draw will vary significantly, but is usually in the 2000-3500W range depending on how cold it is outside and how warm you want it inside.

Now using the A/C at full blast "LO", it will only go up to 2.4A peak, and settles in at 2.1A. That's 750W. I couldn't get it to go any higher than that, and it was getting cold quickly in the cabin. Having said that, even turning up the temperature a little only dropped it to 1.5A. I'd have to do this again during the summer to figure out what the average power draw would be, but I'd hazard it probably won't vary that much. Let's call it 500W average.

So, this answers a couple questions - first, the A/C takes 1/10th the power as the heater at full blast, and around 1/4th to 1/7th the power as heat for normal usage.

However, that doesn't mean that having a heat pump would only cost 1/4 to 1/7th the power...

The second answer is - putting in a heat pump instead of a resistive heater means that it would require a much larger unit.

A heat pump is generally about "300% efficient" - meaning that it could put out 2250W of heat at a cost of 750W. However, this is only in good conditions - meaning only about a 10C/18F temperature rise. It gets exponentially worse as you need more heat. Considering that your heater needs to work when it's cold, a 20C/36F delta drops that to 150% efficient, and a 30C/54F delta drops that to 100% efficient - in other words, it could only put out 750W of heat at a cost of 750W.

So there's the crux - the time that you want it the most, it's useless. When it's 0F outside and we are upset with losing 30-40% of our range, at the time when we need the most range savings, a heat pump is an expensive paperweight, and won't save us anything.

This data is backed up even by manufacturer claims - According to Bosch, a heat pump drawing 1kW will generate the heat equivalent of between 2-3kW - but looking at their data sheets also shows about a 60F maximum heat delta.

Since we know that, at minimum, we'd want at least 3500W of heat available, we'd need a heat pump unit 3-4x the size as our air conditioner, or we'd need one 2-3x the size plus still have a resistive heater.

This would definitely increase the cost - Nissan charged $1400 USD for this option (and still needed to have a resistive heater too), and doesn't heat up as quickly as the Bolt. During mildly cold weather you really only save half of the heating energy needed (1-2kW), and during really cold weather you don't save anything. Since the Leaf had half the range as the Bolt, that's double the impact.

Considering how Big the Bolt battery is, It's not hard to see why GM just decided that it wasn't worth making it an option.
 

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I don't know about vehicle heat pumps, but Fujitsu and Mitsubishi make house air source heat pumps that have a COP of just under 2 at -15 F, a bit above 2 at zero F, and iirc, above 3 at temps around 30 F for a house temp setting of 70 F.
 

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Data is from this study:
US Dept of Energy, Jon Winkler, Ph.D.
Laboratory Test Report for Fujitsu 12RLS
and Mitsubishi FE12NA Mini-Split Heat Pumps

Approximate values from a graph in the paper for the Mitsubishi are:
-10 1.8
+20 2.5
+30 3.0

Degree F, and house temperature was 70 F. These units certainly would not fit in a car. Don't know how the more compact vehicle ones perform.
 

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Heat pumps work by taking energy from outside, and moving it inside. When it is too cold outside, heat pumps are useless. That's why every home heat pump also has a hot-wire heater, designated Stage 2, to heat the house when the outside temperature is too cold to give up energy to the heat pump.
 

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...first, the A/C takes 1/10th the power as the heater at full blast..
Thank you for this!
I try to explain this to rookies, but it's nice to see the empirical evidence backing my statement.

The takeaway is.. feel free to use the A/C in summer, spare the heat during the winter!
 

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Heat pumps work by taking energy from outside, and moving it inside. When it is too cold outside, heat pumps are useless. That's why every home heat pump also has a hot-wire heater, designated Stage 2, to heat the house when the outside temperature is too cold to give up energy to the heat pump.
This is why I just had a ground source heat pump installed for my house. Where a heat pump would work better for an EV is if there's waste heat in the vehicle from the electronics. Getting it only from the air will not be enough for all circumstances.
 

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A beanie and a heavy jacket.. is how I stopped worrying.
A beanie? They stopped making those in the 60’s. Probably due to the stupid little toy propellers on top of them.
 

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I don't speak Kanukistanian. A "knit winter cap" whatever you call it in your locale. :p


If you've ever commuted on two wheels, bicycle, scooter, motorcycle.. the idea that having to wear a cap and coat inside your car is a hassle.. Well that thought is laughable. I don't mind at all. Of course, it only helps so much if you're in a place where it gets really cold. I am not.

I didn't intend to take this off track, I do appreciate the heat pump info shared here!(y)
 

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I don't speak Kanukistanian. A "knit winter cap" whatever you call it in your locale. :p


If you've ever commuted on two wheels, bicycle, scooter, motorcycle.. the idea that having to wear a cap and coat inside your car is a hassle.. Well that thought is laughable. I don't mind at all. Of course, it only helps so much if you're in a place where it gets really cold. I am not.

I didn't intend to take this off track, I do appreciate the heat pump info shared here!(y)
I believe that's what they call it in Capistan.
 

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Ok I looked it up, knit "toque" is what it is. Never heard of that word in my life.
 

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I don't speak Kanukistanian. A "knit winter cap" whatever you call it in your locale. :p


If you've ever commuted on two wheels, bicycle, scooter, motorcycle.. the idea that having to wear a cap and coat inside your car is a hassle.. Well that thought is laughable. I don't mind at all. Of course, it only helps so much if you're in a place where it gets really cold. I am not.

I didn't intend to take this off track, I do appreciate the heat pump info shared here!(y)
oh those. Those are properly called “Touques”.
 
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oh those. Those are properly called “Touques”.
I used to do that in college...but never before calculus...or physics...or thermo....oh heck, never before class, period. Tried it once. Didn't work out too well...
 

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Now using the A/C at full blast "LO", it will only go up to 2.4A peak, and settles in at 2.1A. That's 750W. I couldn't get it to go any higher than that, and it was getting cold quickly in the cabin. Having said that, even turning up the temperature a little only dropped it to 1.5A. I'd have to do this again during the summer to figure out what the average power draw would be, but I'd hazard it probably won't vary that much. Let's call it 500W average.
I highly recommend that you do this test again in the summer. I have easily observed the idle power consumption shooting up to 4kW (as opposed to 1kW that you normally see) on a hot (>30C) day when I turn the A/C on my Bolt at a LO setting. It then slowly settles down after about 10 to 20 minutes.
 

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I highly recommend that you do this test again in the summer. I have easily observed the idle power consumption shooting up to 4kW (as opposed to 1kW that you normally see) on a hot (>30C) day when I turn the A/C on my Bolt at a LO setting. It then slowly settles down after about 10 to 20 minutes.
What you are seeing is the heater coming on to deal with the humidity. I have found no way to prevent the heater from coming on with the AC, and the AC coming on with the heater. Turning off all automatic features, and even turning the temperature knob all the way up or down will not prevent mixing these two, if there is any significant humidity. I see this with Torque Pro.
 

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Two thoughts:

1) While the current heat pump technology doesn't do very well at -20C that's 253 kelvin so there's really still plenty of heat in the air for a heat pump to work with. Just as home air-source heat pumps have improved so we now see decent COPs at these low temps, I expect automotive heat pump technology to follow. Having a heat pump that could deliver 4kW of heat with a COP > 2 at -20C would probably do the trick and looks like it should be possible now. Although using that money for more battery capacity probably makes more sense.

Then again, automotive heat pumps are new technology, so we should expect the cost to come down as the volume goes up. Since the car already has a 'one way' heat pump and a low cost resistive heater, swapping to a two way heat pump with a resistive heater shouldn't really add that much cost.

2) I bet the EV winter heating problem could be solved with insulation. Because an ICE has so much waste heat available cars didn't need to be insulated. But for a cold climate EV it makes sense to develop automotive insulation technologies. Imagine what double pane glass, insulated body panels, and a heat recovery ventilator would do for the heating energy cost in a car. My bet is we see this stuff show up in EVs sooner than later.
 
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