# Does the battery coolant ever heat the cabin air?



## michigantesla (Mar 9, 2019)

Tech Question:

Will the battery coolant ever directly heat the cabin air? Example the outside air temp is 30 degrees F and the Battery Temp is 100 degrees F. If you set the HVAC to heat can the M3 use this relatively warm coolant to heat the air? To do this there would need to be a radiator of battery coolant that the HVAC air is blown across I suppose.

Part 2: If the heat in the battery coolant can be used to heat the cabin air, then is there a way to turn on heat but not use the resistive heater?


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## Bokonon (Apr 13, 2017)

michigantesla said:


> Will the battery coolant ever directly heat the cabin air? Example the outside air temp is 30 degrees F and the Battery Temp is 100 degrees F. If you set the HVAC to heat can the M3 use this relatively warm coolant to heat the air? To do this there would need to be a radiator of battery coolant that the HVAC air is blown across I suppose.


The battery coolant loop is isolated from the HVAC system, so the battery cannot heat the cabin, nor can the resistive heater warm the battery.

Even if they were connected, in 30F weather, you'd have to drive the car for a bit to generate enough heat to warm the pack sufficiently for it to heat the cabin, especially in the case where the battery was cold-soaked (i.e. also close to 30F)... So you'd probably be using resistive heat at the beginning anyway. And by the time the battery warmed up, the heater would require less power to maintain temperature, so the relative gain in efficiency wouldn't be as great.



michigantesla said:


> Part 2: If the heat in the battery coolant can be used to heat the cabin air, then is there a way to turn on heat but not use the resistive heater?


Alas, no. It would be nice if the Model 3 had a heat pump for mild temperatures (40s - 50s), but you'd still need the resistive heater for colder temperatures, and that would add cost and manufacturing complexity.


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## michigantesla (Mar 9, 2019)

Bokonon said:


> The battery coolant loop is isolated from the HVAC system, so the battery cannot heat the cabin, nor can the resistive heater warm the battery.
> 
> Even if they were connected, in 30F weather, you'd have to drive the car for a bit to generate enough heat to warm the pack sufficiently for it to heat the cabin, especially in the case where the battery was cold-soaked (i.e. also close to 30F)... So you'd probably be using resistive heat at the beginning anyway. And by the time the battery warmed up, the heater would require less power to maintain temperature, so the relative gain in efficiency wouldn't be as great.


Ahh bummer. In the winter my garage is kept at 55 degrees F. Figured if I charged before leaving in the morning the battery would be significantly warmer than the outside air. So using the heat in the coolant would be nice.

But I understand that it would add complexity and another point of failure. Anyway good to know thanks.


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## Bokonon (Apr 13, 2017)

michigantesla said:


> bummer. In the winter my garage is kept at 55 degrees F. Figured if I charged before leaving in the morning the battery would be significantly warmer than the outside air. So using the heat in the coolant would be nice.


Agreed... Though as someone who has no garage at all, I can tell you that charging before you leave to warm the battery in winter definitely has benefits, such as making more regen (and sometimes power) available at the beginning of your drive. So I'd say you're thinking along the right lines.


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## JWardell (May 9, 2016)

Not through the HVAC system. But the battery absolutely radiates a lot of heat into the cabin. A 20 minute supercharge on a day in the teens and I was sweating inside!


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## Frully (Aug 30, 2018)

I was lead to believe before launch that the motor/battery coolant system would secondarily heat the cabin. Today I learned that is not the case.


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## garsh (Apr 4, 2016)

michigantesla said:


> Will the battery coolant ever directly heat the cabin air?


Not yet. But it will in a future version of Tesla vehicles.
@MelindaV spotted this recent patent filing:
https://patents.justia.com/patent/20190070924

And my reaction after reading through it:



garsh said:


> I finally got around to reading that patent.
> *Holy crap, this is going to be awesome!*
> 
> They're not simply replacing the cabin air conditioner with a heat pump. They're integrating the cabin heating/cooling heat pump with the rest of the car's cooling system! This thing is going to great!
> ...


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## michigantesla (Mar 9, 2019)

As a follow up to the original post here is some more info. Now that it is cold here in Michigan I am understanding the issue more. Even though I park in an attached garage most nights the pack never stays warm at all for any period of time. 

My garage stays above freezing but since the pack is low to the ground it gets the coldest part of the garage which may be below freezing. I can turn the heat on in the garage but all the warm air stays up higher. Then I park outside at my work and that really cools it. I have scan my Tesla app and can look at the temps. Pack usually is less than 50 degrees. Many time way less. Driving it normally barely puts in any heat at all. 

So my Regen is really limited and worse yet the power is limited also. I can live with it as it is what it is. Really the batteries and driveline are so efficient they don't make much heat. 

A heat pump off the fluid would be good but it actually may COOL the fluid pretty fast in cold conditions. 

So not sure the answer other than a bigger kwh pack so I can run the heater without even thinking of the range reduction. Of course regen and power would still be limited unless the cells are warmer . 

Even though it doesn't cost much I find myself driving with heat off just on principle. Blasting the heat adds about 30 percent to usage. As time goes on I am getting better at using the heat. 

Driving in cold does hurt efficiency all by itself compared to warmer weather. But only about 10 to 15 percent is what I observe. The resistive heating is a big load at 6kw when cranking. 

I guess if there was an ez answer Telsa would already be doing it.


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## Feathermerchant (Sep 17, 2018)

Electric overalls....

https://www.revzilla.com/heated-motorcycle-gear


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## garsh (Apr 4, 2016)

michigantesla said:


> Even though it doesn't cost much I find myself driving with heat off just on principle.


I did that during my first winter with the Tesla. But I had a Nissan Leaf for 6 years prior, and I _had_ to do it with that car in order to make it to work, so it had become habit.

This winter, I've settled on the following:

Set climate control to manual.
Set temp to 67° F (19.5° C).
Have the air come out on the windshield to prevent fogging - maybe on the feet too.
Set fan to a very low speed - 2 or 3.
Set my seat heater to high.
It still uses noticeably more energy than having it off, but it's not too excessive, and it's enough to keep my feet and nose from getting too cold while the rest of my body is too hot from the seat. 


> I guess if there was an ez answer Telsa would already be doing it.


@MelindaV discovered a patent that Tesla filed a while back that includes some even more extreme ways to capture & use waste heat, and it sounds like they're planning to get rid of the resistive heating altogether when they have this new system in production.


MelindaV said:


> and already in the works...
> https://patents.justia.com/patent/20190070924





garsh said:


> I finally got around to reading that patent.
> *Holy crap, this is going to be awesome!*
> 
> They're not simply replacing the cabin air conditioner with a heat pump. They're integrating the cabin heating/cooling heat pump with the rest of the car's cooling system! This thing is going to be great!
> ...


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## Frully (Aug 30, 2018)

michigantesla said:


> As a follow up to the original post here is some more info. Now that it is cold here in Michigan I am understanding the issue more. Even though I park in an attached garage most nights the pack never stays warm at all for any period of time.
> 
> My garage stays above freezing but since the pack is low to the ground it gets the coldest part of the garage which may be below freezing. I can turn the heat on in the garage but all the warm air stays up higher. Then I park outside at my work and that really cools it. I have scan my Tesla app and can look at the temps. Pack usually is less than 50 degrees. Many time way less. Driving it normally barely puts in any heat at all.
> 
> ...


garsh already answered...but worth adding - with your tesla login you can look at all the parts at epc.tesla.com 








In this drawing it really seems like there aren't any coolant lines to the heater core.

I really like going through the drawings just to better understand how stuff is strapped in there, in case I ever need to pull anything apart.

Aside: I want to (but it would void warranty) add a heat exchanger (closed loop) to the coolant loop so that I could use ground-source heat (near, but above freezing) to keep the battery 'warm' during our obscenely coldest month (-40c worst). It's overkill but (pre)conditioning the battery is almost worse for me with short commutes than hvac heat. There is a LOT of battery mass to keep happy.


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## Feathermerchant (Sep 17, 2018)

You may be better off building a coil and putting it up against the bottom of the car in cold weather. The battery enclosure would transfer the heat to the cells. It could be removed to drive.

Or build a 'garage' to enclose the car and heat the garage with your source.


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## Frully (Aug 30, 2018)

I have a 3 car garage that I don't heat much, and would be far more efficient to only heat the battery. 
As for putting the coil on the battery, yes, but I want minimal weight, and the battery is insulated from the outside world (remember the factory robots that couldn't figure out how to install the battery blanket?)


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## Feathermerchant (Sep 17, 2018)

If the garage is insulated it wouldn't take much. What is your source of heat you are planning to use?


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