Modern heat pumps are significantly more efficient than resistant heat down to -22F. People who think heat pumps don't work in cold climates are basing their information off 1990's knowledge.
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Reeler
Decade of Pure EV Driving
dgpcolorado
high altitude member
Really? Air source heat pumps? I wasn't aware of that.
I hardly ever use my heater. I just wish I had a heater-off button so that I could just blow outside air on the windshield to defog it, no heating needed. And I really hate it when I am too warm and I try to blow cool outside air in the car and it heats it even though I have the heater set to "Lo".
JohnnyG
Weee!
^^THIS!^^
I love fully automated climate control. That being said, sometimes I just want some fresh air through the vents. I can control (manually turn on/off) the A/C, so why not the heater?? I can manually control every aspect of the climate control system (fan, vents, a/c, etc) except the heater. I shouldn't have to turn the temp all the way down; and like @dgpcolorado states, if the temp outside is colder than "Lo", it's going to choose to heat the air coming in, regardless. And then if I put it on "Lo", and later hit the [Auto] button, my A/C goes into overdrive trying to turn my car into a deep freezer.
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It does this already, the first time you press defrost you get a blue icon.
dgpcolorado
high altitude member
Does that really not use heat? The manual is unclear, it just says that the second touch (red) operates "the heating and fan at their maximum level." it doesn't say that the first touch is no heat and, since the climate control system seems to be on whenever the defroster is on, my assumption is that the heater is being used. I'll try to measure it sometime.
llavalle
Member
It does. It also forces new air instead of recirculation and kicks in the A/C compressor. In cold climates, it'll also bump the PTC heater (electric heat) to compensate for the AC effect.
When you hit it twice and it becomes red, it bumps the heat and fan speed to maximum, like you said.
Reeler
Decade of Pure EV Driving
Tesla is going to have to add a heat pump to compete. The LEAF & Soul have one too.
Beating a dead horse. I dread winter again. The AC is so efficient compared to the heater. Luckily my family can take a bit of cold during long car trips. Our leaf is so toasty and so efficient but so not a road trip car...
Hyundai Ioniq has a heat pump too.
I'd love to know what air-source heat pump is actually more efficient than resistive heat at -22F, however, while producing anything remotely like its rated output. There have been multi-stage designs like the Hallowell Acadia that claimed to go that low, but they're inherently larger and less reliable than mainstream designs. Even the most efficient units from Daikin, Mitsubishi, etc. are rated only down to -15F, and while they might eke out a COP above 1 at those temperatures, they also produce far, far less heat than their rated capacity -- so unless they're massively oversized, supplemental (read "resistive") heat will still be required, basically any time you're at about 5F or below.
So a heat pump could certainly help efficiency but resistive heat will still be needed for climates in which a surprising number of people drive their Teslas. I've always assumed they didn't go for a heat pump because there were no off-the-shelf designs for automotive use, designing a very compact heat pump that is both highly efficient for cooling and which can heat at low temperatures is not a small task, new heat pump designs are often quite unreliable and require a lot of revision even after they're brought to market, and they would have still needed resistive heat anyway. Basically they'd have run up parts cost, bought themselves a big design nuisance in a discipline far from their core engineering competencies, and risked the reliability of the air conditioning too. I think they made the smart choice.
Now that several manufacturers are shipping automotive heat pumps though I suspect the calculus of the decision may have changed. I wouldn't hold out for a retrofit for existing cars. ;-)
Obviously it wouldn't be used at those temps. There would need to be resistive heat backup, as all these other cars have. The vast majority of us very very rarely see temps at that level though, and even those who do see temps in the 30s even more often. At that temp range a heat pump would have a enormous benefit.
And yes, it would increase the part count, cost and complexity, but really very minimally. The differences between a heat pump and an air conditioner are very minor. It's a clear case of Tesla just not having the resources to design an optimal system at the time. That was understandable in 2012, but its terrible that they haven't changed it by now.
stopcrazypp
Well-Known Member
I think you are missing the capacity. The COP may be better than 1, but if it is producing at significantly lower than the rated kW capacity, then the heat output (kW) will be lower (even though it is more efficient). Efficiency aside, that is what you feel in terms of how "strong" the heat is.
That's why the supplemental resistive heat must be used even though it has a lower COP.
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Or the capacity high enough not to care. None of the state-of-the-art heat pumps use backup heat. Backup heat is a 2000's problem, not a 2017 problem. I don't have backup heat in my house.
I like heat pumps, and am considering switch my house over to them, In a steady state winter use case, the heat pump may work well, but there are many automotive cases where it does not:
Defrost: The A/C runs to dehumidify the air, then the heater core warms the air back up. This would require 100% electric heat.
Temperature blending: Whereas the electric heating element is easily controlled from 0-100%, the heat pump does not have the same control level over its operating range (40-100 for one brand).
Split climate control: In the case where the driver is in the sun (A/C) but the passenger in the shade (heating). The heating will need to come from the PTC.
Changeover: Going from heating to A/C takes extra time/ energy to stop compressor, change valving, start up, achieve new operating point (temperature change of internal exchanger).
External operating point: Heat pumps often have an external heating coil to defrost the coil, system would need to revert to electric heat for both the interior and the heat pump unit. A quick search turn up HP that work to -25C, normal automotive testing goes down to -40C.
Complexity: the directional switching valving and TXV modification decrease the reliability of the system.
From a human factors POV, a more direct heating via seats and heated steering wheel allows the driver to feel warm with the least energy. Especially in a larger vehicle.
Edit: found -25C heat pump
Defrost: The A/C runs to dehumidify the air, then the heater core warms the air back up. This would require 100% electric heat.
Temperature blending: Whereas the electric heating element is easily controlled from 0-100%, the heat pump does not have the same control level over its operating range (40-100 for one brand).
Split climate control: In the case where the driver is in the sun (A/C) but the passenger in the shade (heating). The heating will need to come from the PTC.
Changeover: Going from heating to A/C takes extra time/ energy to stop compressor, change valving, start up, achieve new operating point (temperature change of internal exchanger).
External operating point: Heat pumps often have an external heating coil to defrost the coil, system would need to revert to electric heat for both the interior and the heat pump unit. A quick search turn up HP that work to -25C, normal automotive testing goes down to -40C.
Complexity: the directional switching valving and TXV modification decrease the reliability of the system.
From a human factors POV, a more direct heating via seats and heated steering wheel allows the driver to feel warm with the least energy. Especially in a larger vehicle.
Edit: found -25C heat pump
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stopcrazypp
Well-Known Member
Here's a link to the latest Mitsubishi model (first manufactured 2016):
The heating capacity at -25C (-13F) (figure 5 page 12) drops to 45% of rated.
https://nonul.mylinkdrive.com/files/PUMY-P60NKMU1_-BS_Service_Manual.pdf
It still has a aux heat setting.
Sure, you can buy one twice the capacity rather than use an aux heat, but I don't see how newer ones had eliminated the core issue of a massive drop in capacity at lower temperatures.
@mongo One other thing you missed: the cabin may need to be heated and the battery/drive-train may need cooling at the same time. Tesla currently uses the single A/C system to cool both. So the only option would be to add a heat pump to the existing system. Which makes things more expensive and take more space.
If getting 2x overcapacity on normal heating days for the worst case bothers you, then you'll be really really bothered by it having 4x, 8x, or more overcapacity for cooling in the summer. Just think about the workload, 95F to 72F, or -22F to 72F.
There is no problem here.
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