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Heat System Stress Test

doct89

Member
Jul 5, 2020
28
20
Boston, MA
So today it's 34 degrees in Boston, with ~1" of snowfall. I figured it was a perfect time to stress test the heat pump and see what the car can do. I turned preheat on HI and have kept it on for a bit over an hour and made the below observations. I'm not sure if this is normal or not, so I could use some help:

  1. 1 Hour of preheat on HI, while plugged into NEMA 5-20 drained 7% battery. I'm ok with this, but I believe it represents ~7kw draw for both cabin heating and battery conditioning. (7%*74kw)+1.760kw
  2. The interior maxes out at 80 degrees on HI. Which is about 45 degrees above ambient. I'm wondering if that means the interior temp will max at 60 degrees when is is 14 degrees out, and 46 degrees when it is 0 degrees....
  3. The glass roof turns into a rainforest due to the humidity inside and the snow on the roof, the rear headliner is moist from the condensation dripping towards the rear of the roof
  4. The windshield defroster is terrible. It defrosts about 80% of the driver side and 50% of the passenger side, pictures below, you can see where the condensation remains fogging the view. Also, the defrost heat did not feel warm compared to the 80 degree interior temp, it was actually cold.
What does everyone think? None of these are really bad in my opinion except for #2. I thought the car has resistive heaters in addition to the heat pump for situations like this.

Thanks!

IMG_0546.jpeg
IMG_0547.jpeg
IMG_0550.jpeg
 
  • Informative
Reactions: LionelHutz

srlawren

Member
Aug 3, 2020
554
361
Vancouver, BC, Canada, Eh?
@doct89 thanks for sharing these observations, they are indeed helpful.

One that stands out to me as big concern is #3, where you have condensation that is causing the headliner to be noticeably wet. I hope this doesn't turn into mold [or mould in Canada, lol] or mildew concern, especially after a full winter.
 

doct89

Member
Jul 5, 2020
28
20
Boston, MA
@doct89 thanks for sharing these observations, they are indeed helpful.

One that stands out to me as big concern is #3, where you have condensation that is causing the headliner to be noticeably wet. I hope this doesn't turn into mold [or mould in Canada, lol] or mildew concern, especially after a full winter.
Yeah, I’m going to keep an eye on it. It could just be that the air was very humid since it was snowing and the hour preheat was excessive. Preheat doesn’t seem to dehumidify the air (ac button is off)
 

Mike_TV

Member
Apr 29, 2020
471
343
Chicagoland
The inside humility can be caused by excessive amounts of snow or water in or on the mats. If you have winter mats installed it's easy to wipe down and soak up any water with some old towels, once the car is warm, to remove the moisture. Carpeted mats will just hold the water, refreeze when the car is cold and then melt again raising the humidity inside.
 

hcdavis3

HCD3
Mar 3, 2019
1,834
1,069
02571
Yeah, I’m going to keep an eye on it. It could just be that the air was very humid since it was snowing and the hour preheat was excessive. Preheat doesn’t seem to dehumidify the air (ac button is off)
I suspect you’re right. It was very humid before the temperature plummeted.
 

LNL_HUTZ

Member
Aug 3, 2020
299
230
San Francisco
The windshield defroster is terrible. It defrosts about 80% of the driver side and 50% of the passenger side, pictures below, you can see where the condensation remains fogging the view. Also, the defrost heat did not feel warm compared to the 80 degree interior temp, it was actually cold.
My recollection is that it has separate defrost and defog settings. Did you try both?
 

Adkrenew

Member
Oct 10, 2020
16
6
Ny
Did you put your AC on when you defrosted it for heat that gets rid of condensation. Also not having it in recirculation mode is good I’m up in the mountains and was 15° this morning preheated the car and it worked like a charm
 
  • Helpful
Reactions: srlawren

zannman

Member
May 15, 2019
133
101
Ohio
The interior moisture is very specific to this time of year. If it was 60*F yesterday at 80% humidity, the air holds 2-3x more humidity than it can below freezing - see this psychrometric chart for reference
https://i.stack.imgur.com/GLwoY.png
https://i.stack.imgur.com/GLwoY.png

You won't get these kinds of temperature swings later in winter, so interior humidity won't continue to be this much of an issue as winter continues.

As per Question 2 above on the heat pump, there's a balance point temperature on all heat pumps where they are no longer as efficient as simple resistance heat. For instance the balance point could be 20*F, under which most to all heat would be resistive heater. No need to worry about the system being able to maintain a comfortable temperature near your setpoint at low exterior temperatures. Have driven electric for years and you'll enjoy the quick heating available at -20*F outside, but your range will suffer a good bit.
 

NE_Runner

New Member
Nov 1, 2020
1
0
New York
I end up bringing my new model y to tesla services centers. I put my car on HI and no heat was generated at all. The weather was around 20 degrees. I went and brought some gloves and drove for 80 miles to head to the services center. They tried to reboot it and it did not work. It seem to uncommon issue. Hopefully I will get my car back this week but it seem like both the A/C and Heat doesn't work. The defroster wasn't working for me and I was stopping every 20 minutes or so to wipe off the wind shields.
 

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