Would you trade your frunk for a heat pump?

[TheCats]

I'd like the pro-heat pump people to chime in, because there seems to be confusion (including my own). You want the heat pump to heat the a) cabin, or b) battery?

You want the heat pump for both heating tasks.

Even in the mildest parts of southern California you'll need to heat the battery before DC fast charging. The optimal battery temperature for charging is likely 35-40C, with some variance with the undisclosed details of the battery chemistry and structure. Charge acceptance and cycle wear will be degraded outside of that range.

Most people, even in California, don't live in the mildest parts. A heat pump isn't a make-or-break feature, but it's worthwhile efficiency boost.

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[bellyer]

Heck no. Now that I've had a frunk, I won't go back to not having one. That is what is stopping me from putting in a Fisker Ocean order.

 

[iankellogg]

it really seems most people here don't understand what a heat pump is. The Mach E already has a heat pump, it just can't be reversed. ALL ford needs to do is add the valves and condenser/evaporator pair. Very minimal weight to use the existing heat pump to heat the cabin.
Also the mach e uses the same coolant loop to heat the cabin as it does the battery. Motors aren't on that circuit as far as i know. Ford could improve cold weather quite a bit there.

The resistive heaters can stay there too and can boost the BTU output.

 

[Njia]

Where does that cutoff lie? Ability to hold 1 grocery bag? 1 can of V8? 1 shrimp? When does it lose its usability?

A regular sized business envelope laid flat.

 

[Jppumper]

With it getting colder, the thermal requirements of Battery Electric Vehicles is evident in the reduction of range (real world range not GOM displayed range). This reduction is dependent on many factors in each individuals climate.

The benefits of heat pumps have been debated ad nauseam.

The merits of frunk storage have also been discussed at extreme lengths.

The question is: Would you trade your frunk for a heat pump?

Let the debate begin!

What is a heat pump, besides the HVAC unit outside my house?

 

[AEtherScythe]

I live in Michigan. Below 40°F heat pumps begin to require more energy than traditional heaters.
From about 25°F down, they are worthless.

 

[MaineSailor]

I haven’t been very excited about the heating system in our MME. One of the only issues I have with the car! I have been highly discouraging my son from purchasing a Lightning for this very reason, he’s in Alaska so this is serious stuff. But being a true Alaskan he has a solution for this. If it works on a boat it ought to be fine in a pickup.

Interesting thought, but I don't think having a live propane heater in a car would pass muster with the safety regulators!

 

[Avelli]

No to the heat pump. No need to add one more mechanical thing that could potentially fail.

Interesting thought, but I don't think having a live propane heater in a car would pass muster with the safety regulators!

It'd be fine. LP, Hydrogen, and CNG cars are already sharing our roads.

 

[ARK]

With flexible valving, such as Tesla's octovalve, a resistive heating element isn't needed. The electric motor is simply run less efficiently (the rotor is magnetically locked at 0 RPM) and heat is extracted from the motor cooling loop.

Apart from the relatively light valve array, a heat pump just uses a compressor very similar to an AC compressor. It's best done with a clean sheet design, but it's not inherently more expensive to manufacture than any other electrically driven compressor.

Doesn’t Tesla still include a resistive heater though on all its vehicles that also have a heat pump?

I’d be curious as to how efficient heating through a resistive heater is versus using the motor in this way.

I think Tesla does this with the motors but only to heat the battery (not the cabin) before supercharging and only on the Model 3 and Y. The Model 3 and Y have a relatively inefficient induction motor in the front (that is not helping move the car except when needed when traction is low), and this relatively inefficient motor type generates a lot of heat. The Model S and X, and also the Mach-E, have the same more efficient type of motors, i.e. a permanent magnet synchronous motors, in the front and rear and can’t create heat in the motors in the front to nearly the same extent as a Model Y or 3.

 

[TheCats]

Doesn’t Tesla still include a resistive heater though on all its vehicles that also have a heat pump?

I’d be curious as to how efficient heating through a resistive heater is versus using the motor in this way.

I think Tesla does this with the motors but only to heat the battery (not the cabin) before supercharging and only on the Model 3 and Y. The Model 3 and Y have a relatively inefficient induction motor in the front (that is not helping move the car except when needed when traction is low), and this relatively inefficient motor type generates a lot of heat. The Model S and X, and also the Mach-E, have the same more efficient type of motors, i.e. a permanent magnet synchronous motors, in the front and rear and can’t create heat in the motors in the front to nearly the same extent as a Model Y or 3.

Teslas with heat pumps use generated or residual heat from the motor(s) and battery. If there is no residual heat, the system uses the radiator. Only if the radiator isn't keeping up, in extreme cold, will the motor be run less efficiently. If the motor isn't turning, that means running it at 0 RPM -- using power to magnetically lock the rotor, which generates waste heat.

The front induction motor isn't that much less efficient than the rear permanent magnet motor from a battery use point of view. But the difference between 99% efficient and 98% is a factor of two in generated heat.

The reason for using a front induction motor is that the freewheel losses are lower -- when unpowered it spins with much less drag. Since most of the time the rear motor is the only one providing power, the front motor efficiency isn't a big deal. That also means that it's not a significant heat generator.

VW will be using PM motors on front and rear, with a clutch (or clutches?) decoupling the front motor. That is extra complexity for what might be a negligible gain.

 

[ARK]

Teslas with heat pumps use generated or residual heat from the motor(s) and battery. If there is no residual heat, the system uses the radiator. Only if the radiator isn't keeping up, in extreme cold, will the motor be run less efficiently. If the motor isn't turning, that means running it at 0 RPM -- using power to magnetically lock the rotor, which generates waste heat.

The front induction motor isn't that much less efficient than the rear permanent magnet motor from a battery use point of view. But the difference between 99% efficient and 98% is a factor of two in generated heat.

The reason for using a front induction motor is that the freewheel losses are lower -- when unpowered it spins with much less drag. Since most of the time the rear motor is the only one providing power, the front motor efficiency isn't a big deal. That also means that it's not a significant heat generator.

VW will be using PM motors on front and rear, with a clutch (or clutches?) decoupling the front motor. That is extra complexity for what might be a negligible gain.

I think the induction motors are also a bit cheaper, the S and X jettisoned them with Raven, and again with the new dual motor LR and tri-motor Plaid variants that came out last year.

 

[Chicago-E]

I live in Michigan. Below 40°F heat pumps begin to require more energy than traditional heaters.
From about 25°F down, they are worthless.

This is simply not accurate when it comes to the heat pumps installed in cars these days. Actually far from accurate.

 

[TheCats]

This is simply not accurate when it comes to the heat pumps installed in cars these days. Actually far from accurate.

Modern home heat pumps are effective down to about -20C (-4F). Below that they still work, but they don't move enough heat to keep the house warm. The supplemental heat isn't because the heat pump stops working or is inefficient, it's just because it's not powerful enough to keep the house at the target temperature.

The lowest effective temperature is related to the output temperature. A heat pump can be effective to well below -20C if it's just trying to keep the battery above 0C, as might be need to keep the battery able to charge or put out enough power for highway speed.

 

[Chicago-E]

Modern home heat pumps are effective down to about -20C (-4F). Below that they still work, but they don't move enough heat to keep the house warm. The supplemental heat isn't because the heat pump stops working or is inefficient, it's just because it's not powerful enough to keep the house at the target temperature.

The lowest effective temperature is related to the output temperature. A heat pump can be effective to well below -20C if it's just trying to keep the battery above 0C, as might be need to keep the battery able to charge or put out enough power for highway speed.

Good thing a Mach-e is a lot smaller than a house

 

[VegStang]

They could add the heat pump once they clean up the mess of hoses & boxes they have in the front (see Munro video.) With all the new EVs coming out this year I suspect Ford will have to advance their game with the MME and any subsequent vehicles in the space.

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