Would you trade your frunk for a heat pump?

[GoGoGadgetMachE]

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. my home's heat pump is turned off right now as I type this for that reason.

Sponsored

 

[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.

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.

My original comment isn't so much about whether a heat pump in a car "can work" but rather there comes a point at which the amount of energy required to operate the heat pump exceeds the benefits of heating the battery and/or cabin. It takes more energy at lower temps to warm the battery than it would to just use an electric heater to warm the battery.

Heat pumps in colder climates only make sense if you have very cheap electricity, or better yet solar, so that you don't care how much energy you throw at them to get the job done.

For an electric car you maybe don't care about the cost of that energy but you certainly should care about the effects of inefficiently using the energy, because it costs you range. Net net at lower temperatures heat pumps are less efficient than direct use of energy to warm the battery.

 

[ChuckA]

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

This insulated 36 can cooler bag bought on eBay for $29 fits perfectly in the frunk. It leaves a foot on either side for tools, charger, washer fluid. FYI, 2 liter soda bottles fit standing up.

 

[Ride_the_lightning]

My original comment isn't so much about whether a heat pump in a car "can work" but rather there comes a point at which the amount of energy required to operate the heat pump exceeds the benefits of heating the battery and/or cabin. It takes more energy at lower temps to warm the battery than it would to just use an electric heater to warm the battery.

Heat pumps in colder climates only make sense if you have very cheap electricity, or better yet solar, so that you don't care how much energy you throw at them to get the job done.

For an electric car you maybe don't care about the cost of that energy but you certainly should care about the effects of inefficiently using the energy, because it costs you range. Net net at lower temperatures heat pumps are less efficient than direct use of energy to warm the battery.

my understanding is heat pumps (if implemented like Tesla does) cannot be less efficient than resistive heaters. By definition, a resistive heater turns 1kW of electricity into 1kW of heat output . A heat pump in a car, at its worst, would also turn 1kW of electricity into 1kW of heat output (less the small amount of energy to run the mechanical pumps and move the refrigerant). Where else does the energy go? If it isn’t mechanical, it’s heat or light. Not much light coming from a heat pump.

The variable that matters then is the “size” of the heat pump. It would need to be pretty beefy in order to generate warm air at -20F. In a house that would be cost prohibitive. You would need like a 15 or 20 ton unit. Makes more sense to put in a 4 ton unit, and kick on an Aux heater for extreme cold. A car cabin is tiny compared to a house, so those numbers may actually make sense (Tesla seems to think they do).

 

[Jimrpa]

I think we determined from my question about being stuck with a BEV that the resistive heater isn’t really a significant consumer of energy in the vehicle. So why go to the trouble of adding the complexity of the pumps and valves of a heat pump, which is just going to be less efficient at low temperatures and require that resistive heater to help it anyway? I’d rather the engineering team work on more useful things - like getting the remote frunk release working ???

 

[Ride_the_lightning]

I think we determined from my question about being stuck with a BEV that the resistive heater isn’t really a significant consumer of energy in the vehicle. So why go to the trouble of adding the complexity of the pumps and valves of a heat pump, which is just going to be less efficient at low temperatures and require that resistive heater to help it anyway? I’d rather the engineering team work on more useful things - like getting the remote frunk release working ???

Have you read any of these replies? It’s not less efficient, and you already have most of those pumps and valves because you have an air conditioner.

Edit: that being said I only want a heat pump if they also have a resistive heater, or if they make it an option like Volvo does on the XC40. I will take the reliability of resistive heat over the range of a heat pump. But if the MME was our only car I could see why the range gains would be worth it. I’ve spent $1500 replacing AC units in way too many cars. I can roll the windows down in the summer for a few days if the AC goes out, but if the heat stops working in the winter it’s downright miserable.

 

[Chuck]

It'll be 71 here today so why would I want to change?

 

[Jimrpa]

Have you read any of these replies? It’s not less efficient, and you already have most of those pumps and valves because you have an air conditioner.

Two points: going by personal experience with heat pumps, they most certainly are less efficient, particularly as temperatures go below 32 degrees F. Second, yes, I know a car air conditioning system already has “most of” the bits and pieces required for a heat pump. My point is that I’d prefer not to introduce any further mechanical complexity. You’ve said yourself that you’ve had to replace car AC systems. Things with moving bits and pieces, pipes and valves carrying fluid wear out and break. I don’t want them if I don’t need them.

 

[Ride_the_lightning]

Two points: going by personal experience with heat pumps, they most certainly are less efficient, particularly as temperatures go below 32 degrees F. Second, yes, I know a car air conditioning system already has “most of” the bits and pieces required for a heat pump. My point is that I’d prefer not to introduce any further mechanical complexity. You’ve said yourself that you’ve had to replace car AC systems. Things with moving bits and pieces, pipes and valves carrying fluid wear out and break. I don’t want them if I don’t need them.

We need to be more specific. A heat pump is less efficient at 20F than a heat pump at 45F. That doesn’t meant it’s less efficient than a resistive heater. Those are different things.

 

[Jimrpa]

We need to be more specific. A heat pump is less efficient at 20F than a heat pump at 45F. That doesn’t meant it’s less efficient than a resistive heater. Those are different things.

Fair enough - let me frame it from a user experience perspective: there comes a point where a heat pump just stops producing warm air. That point, in my experience, is around 32 degrees F. At that point, I’m not going to quibble over relative efficiency of the two systems, since it’s been established that the resistive heating system isn’t a huge draw on power. I want to stay WARM. ? YMMV as always ?

 

[Mosworthy]

If I can't do this, it ain't worth it

 

[mfbrown]

Given the choice Frunk or HP, Frunk! Of course, I'm in San Diego where the heated seats and steering wheel are sufficient - though the cabin conditioning is very nice on those cold mornings. As someone mentioned; they will continuously improve efficiency in these EVs and heating will be an important one if range is going to be pushed during the winter - not to mention the stories of people stuck for hours in the cold on the I-95.

I use my Frunk all the time, though more often than not, I use the internal latch. My late build has the button in FP, but it sounds awful going through the double release mechanism. Most of the time, I'm getting out of the car anyway when I want to get a hat, coat, or something out of my backpack that I store in there.

 

[Chicago-E]

Fair enough - let me frame it from a user experience perspective: there comes a point where a heat pump just stops producing warm air. That point, in my experience, is around 32 degrees F. At that point, I’m not going to quibble over relative efficiency of the two systems, since it’s been established that the resistive heating system isn’t a huge draw on power. I want to stay WARM. ? YMMV as always ?

They work to much lower temps than 32F in cars. Read about Tesla heat pumps. They are not comparable to home heat pumps systems. Stop making that comparison. Its flat out wrong.

 

[Jimrpa]

They work to much lower temps than 32F in cars. Read about Tesla heat pumps. They are not comparable to home heat pumps systems. Stop making that comparison. Its flat out wrong.

Ok, suppose I stipulate that for a moment. Is it really the best investment of resources to “optimize” a system that consumes 5Kw and is only used part time by a subset of the fleet?
As I said, I’d rather resources be spent on getting the remote frunk operational and BlueCruise working first ?

 

[mmap]

A heat pump in a car, at its worst, would also turn 1kW of electricity into 1kW of heat output (less the small amount of energy to run the mechanical pumps and move the refrigerant). Where else does the energy go? If it isn’t mechanical, it’s heat or light. Not much light coming from a heat pump.

If the compressor is inefficient then it will turn electricity into heat sort of like the resistive heater, thats true. BUT that heat does not go in the coil, it is exhaust heat... basically this heat would remain under the hood, heating the frunk and not the cabin. It's totally possible to have a heat pump draw a lot of energy, and generate waste heat, but not put enough warmth through the coil.

Sponsored