Gen2 Heat Pump power consumption observation

[phaduman]

* outside temp 41F. Inside temp 72F when I reached work. So it's at steady state 72F.
* plugged into ChargePoint 5.8kW system.
* Turned off AC.
* Charge rate showed 16miles/hour.
* turned on AC. Waited for heating to settle (1min-2mins).
* charge rate showed 12miles/hour.
* turned off AC. Charge rate went back to 16 miles/hour and stayed steady.

Maintaining 72F when outside is 41F in Gen2 consumes 1.45kW i.e. with heater on, the kW going to battery is 4.35 (5.8/16 * 12). At lower charging speeds, it's easier to measure vs. perhaps in DCFC where these would be rounding out...thought would be interesting to share.

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[mikehmb]

That's great data, thanks for sharing. Jives with what we figured was going on re: consumption, which was <50% of what the G1 trucks use (as they are powering a resistive heater).

 

[R1Tom]

That's great data, thanks for sharing. Jives with what we figured was going on re: consumption, which was <50% of what the G1 trucks use (as they are powering a resistive heater).

I would expect it to be somewhere around 1/3 or resistive but I don't know much about heat pumps in vehicles.

Ultimately the heat pump is nice add for sure....but it's benefit is somewhat limited in that the size of battery and power to move vehicle is many magnitudes greater than heating the cabin.

 

[HyperionMark]

I agree, the average heat pump should be 3 to 4X more efficient than resistive depending on ambient temps. But as mentioned, maybe vehicle heat pumps have to have different designs which would limit it closer to 2X.

FWIW, I have an extremely efficient cold weather mini split at home that can do about 2X even down to negative temps. More like 5X above freezing.

 

[KootenayEV]

* outside temp 41F. Inside temp 72F when I reached work. So it's at steady state 72F.
* plugged into ChargePoint 5.8kW system.
* Turned off AC.
* Charge rate showed 16miles/hour.
* turned on AC. Waited for heating to settle (1min-2mins).
* charge rate showed 12miles/hour.
* turned off AC. Charge rate went back to 16 miles/hour and stayed steady.

Maintaining 72F when outside is 41F in Gen2 consumes 1.45kW i.e. with heater on, the kW going to battery is 4.35 (5.8/16 * 12). At lower charging speeds, it's easier to measure vs. perhaps in DCFC where these would be rounding out...thought would be interesting to share.

I'd be curious what you see after doing this test in other conditions. I had a 2014 Leaf with heat-pump, which reported the HVAC usage in real-time on its own screen. In similar conditions, I would have an initial surge to 1.5kW as the system warmed up, but steady state in those conditions at highway speeds (with higher heat loss) would only be in the 0.3 to 0.5kW range for the rest of my 1hr commute.

 

[not_a_car_guy]

What's interesting with Rivians is that the battery capacity is so large and the power required to move the vehicle is so much higher than typical EVs (especially compared to something like a model 3), that the overall % spent on heating is much smaller.

On the model 3, the switch to heat pump will have a much more dramatic impact than on the Rivian.

For instance, let's say I'm driving at 70mph, and I'm getting 1.8mi/kWh with my winter tires. That means I'm using about 39 kW.

A 1.5kW space heater can get a small room REALLY toasty. You really only need about 750W to maintain a comfy temp. And the R1T cab is not huge.

But let's be conservative and assume we are using 1kW for resistive heat, and I save half of that with a heat pump, then 0.5/39 is only about 1% of actual saving.

I would give up that 1% to have the resistive heater blast us with hot air very soon after turning it on (no waiting like in a ICE car). In fact this is one aspect my kids and family love about the Rivian. We just use the heater indiscriminately because it's such a small percentage of overall usage.

For a model 3, that is getting 3.5 mi/kWh in the winter, the saving of 0.5kW is more like 2.5%. And if you have less range to start with , then that 2.5% could be more important too. My guess is the Rivian is probably much better insulated than the Model 3 as well ;-).

But for the Rivian, especially with Large or Max battery packs, I like the luxury of a resistive heater that is quiet.

One thing I've always wondered is if recirculating air vs. bringing in fresh air makes a big difference to how much energy is spent on heating over a long trip. I like using fresh air in general, but I'm not sure how much harder that is causing the heater to work.

 

[KootenayEV]

What's interesting with Rivians is that the battery capacity is so large and the power required to move the vehicle is so much higher than typical EVs (especially compared to something like a model 3), that the overall % spent on heating is much smaller.

On the model 3, the switch to heat pump will have a much more dramatic impact than on the Rivian.

For instance, let's say I'm driving at 70mph, and I'm getting 1.8mi/kWh with my winter tires. That means I'm using about 39 kW.

A 1.5kW space heater can get a small room REALLY toasty. You really only need about 750W to maintain a comfy temp. And the R1T cab is not huge.

But let's be conservative and assume we are using 1kW for resistive heat, and I save half of that with a heat pump, then 0.5/39 is only about 1% of actual saving.

I would give up that 1% to have the resistive heater blast us with hot air very soon after turning it on (no waiting like in a ICE car). In fact this is one aspect my kids and family love about the Rivian. We just use the heater indiscriminately because it's such a small percentage of overall usage.

For a model 3, that is getting 3.5 mi/kWh in the winter, the saving of 0.5kW is more like 2.5%. And if you have less range to start with , then that 2.5% could be more important too. My guess is the Rivian is probably much better insulated than the Model 3 as well ;-).

But for the Rivian, especially with Large or Max battery packs, I like the luxury of a resistive heater that is quiet.

One thing I've always wondered is if recirculating air vs. bringing in fresh air makes a big difference to how much energy is spent on heating over a long trip. I like using fresh air in general, but I'm not sure how much harder that is causing the heater to work.

This is similar to the analysis I went through in my head going from my Leaf to my 2018 Model 3. I have been generally good with that decision for the last several years, so I was happy to see a simple resistive heater in the Rivian and am happy I have it in mine.

For some reason the market (or marketing dep'ts?) has decided that people really want a heat-pump in EVs though, so I'm guessing at some point they will become ubiquitous.

 

[Skysurfer]

One thing I've always wondered is if recirculating air vs. bringing in fresh air makes a big difference to how much energy is spent on heating over a long trip. I like using fresh air in general, but I'm not sure how much harder that is causing the heater to work.

Forcing fresh air can require substantially more energy versus recirculation. Think of a situation where the cabin is up to temperature. In that case you are taking something more like 65F air and warming it to 80F coming out of the vent, so a delta of 25F, just dealing with the heat loss in the cabin. However, if are in fresh air only, you are trying to heat the outside air temperature to the same 80F. So if it is -10F outside that is a delta of 90F, requiring a substantial amount of additional energy to heat compared to the recirculated air. Which is why auto mode will mostly recirculate and occasionally switch to fresh air when the outside temperature differs from the set temperature.

 

[R1Tom]

This is similar to the analysis I went through in my head going from my Leaf to my 2018 Model 3. I have been generally good with that decision for the last several years, so I was happy to see a simple resistive heater in the Rivian and am happy I have it in mine.

For some reason the market (or marketing dep'ts?) has decided that people really want a heat-pump in EVs though, so I'm guessing at some point they will become ubiquitous.

Me too...for my use case....I would rather have G1 resistive heat. Faster...alot less noise...and less to break.

 

[phaduman]

Good analysis on resistive heaters on the R1s.
I guess Rivian wants to / rather needs to get some technologies buttoned down before putting them into R2s where I am sure heat pump will be more impactful.

They cannot afford to fail with R2.

 

[R1Tom]

Good analysis on resistive heaters on the R1s.
I guess Rivian wants to / rather needs to get some technologies buttoned down before putting them into R2s where I am sure heat pump will be more impactful.

They cannot afford to fail with R2.

Excellent point! Work on refining that stuff on R1 and execute perfectly on R2.

 

[ThirteenElectrics]

What's interesting with Rivians is that the battery capacity is so large and the power required to move the vehicle is so much higher than typical EVs (especially compared to something like a model 3), that the overall % spent on heating is much smaller.

A 1.5kW space heater in a room isn't perhaps the best comparison. A room is heavily insulated (especially the roof) and has real glazed windows with a vacuum in the middle. I don't think any EV has vacuum windows (though they do have acoustic glass with multiple layers). There is tons of glass in a Rivian. The Rivian is also moving at 60+ MPH, which enhances the heat loss as air smashes against the windshield. That forced convection effect is massive. The windshield is its own heat pump! I'm about to buy this product: https://evinsulate.com/collections/evglass/products/rivian-r1s

... and they claim:

"Precise testing using a common EV's diagnostic and recording data showed a 24% reduction in range loss at -10°C / 14°F, and the colder it is outside the greater the reduction in range loss."

... but of course, they are trying to sell me something. And they don't specify what the original range loss was. However, I expect the Rivian resistive heater to pull ~7.5 kW at full power, give or take.

 

[not_a_car_guy]

I expect the Rivian resistive heater to pull at least 7.5 kW at full power. Likely more like 10 kW.

Wow

 

[R1Tom]

A 1.5kW space heater in a room isn't perhaps the best comparison. A room is heavily insulated (especially the roof) and has real glazed windows with a vacuum in the middle. I don't think any EV has vacuum windows (though they do have acoustic glass with multiple layers). There is tons of glass in a Rivian. The Rivian is also moving at 60+ MPH, which enhances the heat loss as air smashes against the windshield. That forced convection effect is massive. The windshield is its own heat pump! I'm about to buy this product: https://evinsulate.com/collections/evglass/products/rivian-r1s

... and they claim:

"Precise testing using a common EV's diagnostic and recording data showed a 24% reduction in range loss at -10°C / 14°F, and the colder it is outside the greater the reduction in range loss."

... but of course, they are trying to sell me something. And they don't specify what the original range loss was. However, I expect the Rivian resistive heater to pull ~7.5 kW at full power, give or take.

7.5kw seems maybe a little large but maybe not with all the glass. But that would only come into play at warm up and then at design temps which I assume are something like -15 degF for these things maybe?

 

[MarkNorman]

Me too...for my use case....I would rather have G1 resistive heat. Faster...alot less noise...and less to break.

Actually, there is almost certainly more to break on a G1 with resistive heat. G1 has an AC and a heater. G2 only has a heat pump. G2 was all about simplifying, zonal architecture and heat pump were 2 big elements of that.

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