Why exactly do you think this? Just logically - why would tesla move to a heatpump if it was really only helping effiency at 50-60 degrees ambient air temp? Everything that has been written about the model y contradicts what you've said.
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Heat pump
- Thread starter jbdvm1988
- Start date
Why exactly do you think this? Just logically - why would tesla move to a heatpump if it was really only helping effiency at 50-60 degrees ambient air temp? Everything that has been written about the model y contradicts what you've said.
We really do not do much super range testing trips in winter. The heated seats work
rather well and heating the rest of the car is rather small. In our Leaf (24kwh) it was rather
tricky for both heating and more on the A/C side. You can always wear a coat but there is
just so much you can take off in the summer (I guess). A few percent really does not make
a big deal for most.
rather well and heating the rest of the car is rather small. In our Leaf (24kwh) it was rather
tricky for both heating and more on the A/C side. You can always wear a coat but there is
just so much you can take off in the summer (I guess). A few percent really does not make
a big deal for most.
I didn't say it only helps at 50-60. I said it helps the most at 50-60.
That's just about how heat pumps work - as the temperatures fall, the heat pump has to work harder to get the same amount of energy transferred, making it less efficient. In Tesla's case, they apparently put a cutoff at -10C (Around 14F) - below that it won't try to draw heat from the outside air at all.
Which means that unless you've conveniently got a warm battery pack to pull heat from somehow, you're generating heat with resistance just like the older cars.
So at 50-60, it might reduce the HVAC part of your energy usage by 75%; below 14 it probably won't reduce it by any significant amount, and in between it's in between.
(The HVAC portion of usage, which at 50-60 might only be 5 or 10% of total usage.)
So if Tesla's cutoff is 14F, what do they use for cabin heating below that? As I understand it, they don't include the PTC heater on the Model Y...?
They run the heat pump and HVAC fan inefficiently. They, also, have two small 12v heaters in the cab. (mainly for the dual-zone climate control.)
They can, also, run the drive units inefficiently and use that heat as well.
A combination of deliberate inefficiency in motors, controlled pumping losses, and resistive heating. When It can't steal battery and motor heat.
Thank you both! The drive unit heat I figured would be in play - on the 3 I believe it's only used for the battery and not the cabin, but, well, Octovalve.
Will be curious to see how this all plays out when we get to the depths of winter. The 14F cutoff is news to me; I had mentioned in another thread that heat pumps are notoriously inefficient below freezing... I kinda got the "you're not buying into the Tesla magic" treatment so it's curious (and reassuring for my ego) that there is a low-temp cutoff. Physics be physics.
I care much more about the cabin comfort than the range, to be honest! Just want to make sure that cabin can get nice and toasty warm... Happy wife, happy life.
HyperionMark
Member
I get the thought process behind your rationale, but I believe with the octovalve they are able to achieve some heating from the battery and/or motors into the cabin. I could be wrong, but I think there is a little bit to be gained even at the most bitter temps.
If you somehow have a warm pack in the freezing cold, absolutely. Usually in those temperatures you’re having to heat both the cabin and the pack.
HyperionMark
Member
I definitely agree those situations aren't super common and I can't pretend to know exactly how the octovalve works either.
A couple situations I can think of:
1. Preconditioning the vehicle in a warm garage before you take off. There would likely be some battery heat to work with. Not a ton, but some.
2. Supercharging. There would almost definitely be some waste heat that could be used for heating the cabin.
It's physics. Heat pumps are not some new invention. Heat pumps transfer heat from one side of an environment to another. If it is 0 degrees outside, it will have to work harder to transfer heat from this cold environment in to the car than if the outside temperature was 40 degrees.
However, if there's heat outside, it will need less energy to move that heat inside than a resistive heater that only has a 100% efficiency. Heat pumps could have efficiencies up to 300%.
They can. The issue is that when it’s so cold, say 10F, and you’re on a road trip, the battery can’t retain enough heat for very long.
This is still a big help when it’s 40F outside and you want to travel a long distance.
As a prospective buyer, I consider this to be a 10% range increase down to maybe 40F and even 30F, but more importantly, greater comfort. I might be okay wearing a jacket and relying on seat heaters, but passengers aren’t always as forgiving. The heat pump should make these cars more useful to those of us who live in colder areas.
Yes, I think the heat pump can probably increase efficiency between 5-10% in mild winter temperatures, 30F to 55F.
Sorry, if "if and buts were candy and nuts we would all have a merry xmas"
I am sorry, "I think" and "maybe" just not my form of "Data Lets see real data
over a range of temps before we all become one of those people.
I am sorry, "I think" and "maybe" just not my form of "Data Lets see real data
over a range of temps before we all become one of those people.
SageBrush
REJECT Fascism
What is the difference between a 'real world' test and a robust physical model ?
The 'real world' drive has unspecified conditions, e.g. a dopey driver
I try very hard to avoid becoming one 'of those people' who do not understand that 'real world' tests cannot be generalized.
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