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Model S Overall Thermal Management

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scaesare

scaesare

Well-Known Member
Mar 14, 2013
10,913
25,774
NoVA
#1
In another thread, a reference was made to yet an earlier thread with this pic of a diagnostic screen :

attachment.php?attachmentid=20088&d=1365905905.png


Looking at this picture, it appears that there are three thermal management loops: one for the battery (green) one for the drivetrain/charger (red), and one for the cabin HVAC (black). There are a few places where they seem to interact, such as the valve that thes the green loop in to the black loop for providing battery cooling, and the where the red and green loops both bass thru a "parallel" block for some reason.

I got to wondering about a few things, and have the following thoughts/questions for discussion:

1) Any thoughts as to what that "parallel" block does? Perhaps a valve to change the system from a parallel one to a serial operation? (the lower left corner reads "Current Mode: Parallel", hence my suspicion that it can be changed)

2) It appears that the drivetrain can generate some significant heat, with the motor having a temp reading of 162°C. If that is the case, I'd guess that putting the system in "serial" mode would allow the motor to provide battery pack heat in cold climates, helping reduce the need for the electric pack heater.

3) It appears the red drivetrain loop has it's own heat exchanger for cooling that can be switched in and out of the loop. When in "serial" mode, I'm assuming the black-loop chiller might provide additional cooling capacity.

4) I wonder if the excess drivetrain heat can also provide cabin heat? As the "normal" cabin heating is done via electric heaters, they appear not to be represented here. I'm assuming that the black HVAC loop is NOT representing Freon (otherwise the valve in to the green battery loop doesn't make sense), so perhaps the heat from the pack can provide cabin heat...

5) Are the charger(s) thermal managed with coolant? I'm assuming that "Heatsink" value to the left of Charger 1 is a passive device for the charger(s). Any ideas what "Magnetic" there means?

6) The "whistle shaped" symbols are pumps. What are the "bow-tie shaped" symbols below the HVAC heat exchangers? Louvers?

Any thoughts appreciated...
 
#2
scaesare said:
6) The "whistle shaped" symbols are pumps. What are the "bow-tie shaped" symbols below the HVAC heat exchangers? Louvers?

Any thoughts appreciated...
Click to expand...

I think the "bow-ties" are fans with the % reading next to them indicating fan speed.

As I noted in the other thread, it's interesting that the Model S battery runs quite a bit hotter than the Roadster. Active cooling kicks in at 55C, compared to 40C on the Roadster, which explains why people rarely hear the HVAC during charging or on hot days. The pack heater target of 10C is also a lot higher than the Roadster, and explains why it draws so much power in the winter.
 
#3
scaesare said:
2) It appears that the drivetrain can generate some significant heat, with the motor having a temp reading of 162°C. If that is the case, I'd guess that putting the system in "serial" mode would allow the motor to provide battery pack heat in cold climates, helping reduce the need for the electric pack heater.

That would be my guess... to accommodate both heating and cooling scenarios.

6) The "whistle shaped" symbols are pumps. What are the "bow-tie shaped" symbols below the HVAC heat exchangers? Louvers?

Maybe they represent controls that support the driver and passenger side temperature selection? I've always wondered if those are just airflow based or if they regulate temp somehow.

All good questions. I can't wait until someone really tears one of the cars apart (ok, gently dismantles one :) ) and gives us a breakdown.
Click to expand...
 
#4
djp said:
I think the "bow-ties" are fans with the % reading next to them indicating fan speed.
Click to expand...

That makes sense...

It is also indeed interesting that the battery is seemingly allowed to "passively" cool at up to 55°C. That's 131°F so... Yeah, I'd imagine it won't be lots of circumstances we'll hear the thermal systems kicked in when parked except in the hottest of climates...

I wonder how much thermal energy the battery pan will absorb from a hot stretch of asphalt in the Arizona dessert....
 
#5
I actually would have thought there was more interest in trying to understand the thermal systems here. Perhaps everybody is busy watching that OTHER thermal event thread, "The Great Exploding Tesla!". Or maybe other people aren't a big geek like I am...

In any case... at the risk of reinforcing that geek status by responding to my own thread questions, I found this Tesla Thermal Management System patent summary online.

It appears to shed light on a few things. Namely:

1) The drivetrain waste heat IS specifically utilized for passenger cabin heat. As a matter of fact its the first source mentioned, with the electric heater being secondary.

2) No mention is made of the chiller section actually cooling the drivetrain. So it may be that the passive radiator that can be switched in at the top of the red loop and cooled by ambient outside air is all that's necessary.

3) There is no discussion of the excess drivetrain heat being used to provide battery pack heat. As a matter of fact the patent summary describes the dirvetrain loop as only coupled to to the chiller loop, with no direct heat exchanger coupling to the battery loop. So perhaps the idea there is that once the motor has gotten up to operating temps, the pack itself has as well. (I will note that the schematic pic at the top of this thread still has the "Parallel" block... which implies a serial mode is also possible... so perhaps the final implementation is different than the patent describes?)

Interesting stuff...
 
#6
scaesare said:
1) The drivetrain waste heat IS specifically utilized for passenger cabin heat. As a matter of fact its the first source mentioned, with the electric heater being secondary.
Click to expand...

Yeah, I figured that one out for myself. The heater sucks large amounts of power when the battery pack is cold, but as soon as everything warms up the power draw drops drastically. The only conclusion I could come to is that they were using the battery pack as a thermal reservoir for the heat pump.

scaesare said:
2) No mention is made of the chiller section actually cooling the drivetrain. So it may be that the passive radiator that can be switched in at the top of the red loop and cooled by ambient outside air is all that's necessary.
Click to expand...

The Roadster clearly does it. Heck it'll switch off the cabin air conditioning to cool the battery. I'm pretty sure the Model S can still do it. However I'm wondering if the battery chemistry in the Model S runs warmer than that in the Roadster.

scaesare said:
3) There is no discussion of the excess drivetrain heat being used to provide battery pack heat. As a matter of fact the patent summary describes the dirvetrain loop as only coupled to to the chiller loop, with no direct heat exchanger coupling to the battery loop. So perhaps the idea there is that once the motor has gotten up to operating temps, the pack itself has as well. (I will note that the schematic pic at the top of this thread still has the "Parallel" block... which implies a serial mode is also possible... so perhaps the final implementation is different than the patent describes?)
Click to expand...

They can connect the two loops in series as well as parallel, so in that case the motor and battery are sharing the same thermal loop.
 
#7
Doug_G said:
The Roadster clearly does it. Heck it'll switch off the cabin air conditioning to cool the battery. I'm pretty sure the Model S can still do it. However I'm wondering if the battery chemistry in the Model S runs warmer than that in the Roadster.
Click to expand...

I was referring to the drivetrain (red loop). Certainly it cools the battery pack (green loop), as described in the patent summary and as appears in the diagnostic screen pic.


Doug_G said:
I suspect that isn't necessary. They have a separate pack heater to bring it up to operating temperature, and once you're underway the pack generates a fair bit of heat on its own.
Click to expand...

Yeah, that's what I was thinking when I mentioned that the pack itself will have already come up to temp by the time the motor has.

- - - Updated - - -

It looks like maybe you were editing your post as I was replying...

It does indeed look like the serial mode is possible... so that appears to be capability not described in the patent. In that case, I wonder if the HVAC system ever attempts to cool the drivetrain... or if it's just for allowing excess drivetrain heat to bring the pack and cabin up to temp simultaneously.


Also, to your point about the comparison to the Roadster... I do notice that the cabin HVAC does have it's effectiveness reduced at times... I am assuming that's when the battery cooling load is switched in. But I never feel like it's turned completely off.

There's also been some discussion in other threads that point out that the Model S pack seems to call for cooling at 55deg C, and pre-heating at 10deg... which seems a warmer range than the Roadster... so indeed the batteries may be designed to run warmer in the S...

Thanks for your feedback.
 
#8
scaesare said:
I was referring to the drivetrain (red loop). Certainly it cools the battery pack (green loop), as described in the patent summary and as appears in the diagnostic screen pic.
Click to expand...

The system has multiple modes. There's a little block at upper left in your picture marked Parallel. When it switches to Series mode, the two loops are connected together. The same fluid then circulates through the battery and drive train.

Then there are all the valves. There's an adjustable valve just under the chiller, which can hook the chiller into the battery loop. There are valves to the right of the chiller and the HVAC EVAP. And also an adjustable valve for the front radiator.

I can only guess at how many operating modes there are in this system, and under what conditions each is used. It's pretty sophisticated.
 
#9
Doug_G said:
The system has multiple modes. There's a little block at upper left in your picture marked Parallel. When it switches to Series mode, the two loops are connected together. The same fluid then circulates through the battery and drive train.

Then there are all the valves. There's an adjustable valve just under the chiller, which can hook the chiller into the battery loop. There are valves to the right of the chiller and the HVAC EVAP. And also an adjustable valve for the front radiator.

I can only guess at how many operating modes there are in this system, and under what conditions each is used. It's pretty sophisticated.
Click to expand...

Right. You'll note I mentioned that block in my post:

(I will note that the schematic pic at the top of this thread still has the "Parallel" block... which implies a serial mode is also possible
Click to expand...

What is unknown, is of that implies the chiller system is designed to ever attempt to cool the drivetrain... or if the intention of series mode is to heat the pack with excess drivetrain heat. Or perhaps both.

It is indeed sophisticated.
 
#11
patn said:
All good questions. I can't wait until someone really tears one of the cars apart (ok, gently dismantles one :) ) and gives us a breakdown.
Click to expand...

I've been trying to understand this as well so I can properly modify it. My car is apart enough that I can determine some things.

scaesare said:
4) I wonder if the excess drivetrain heat can also provide cabin heat? As the "normal" cabin heating is done via electric heaters, they appear not to be represented here. I'm assuming that the black HVAC loop is NOT representing Freon (otherwise the valve in to the green battery loop doesn't make sense), so perhaps the heat from the pack can provide cabin heat...
Click to expand...

From what I see I'd say the black HVAC loop is freon. The battery chiller is a small heat exchanger with coolant and freon lines. The same set of freon lines are in parallel with a valve on the firewall presumably to turn passenger AC on and off. I see no sign of any reversing valves as would be needed if it were a reversible heat pump, so my thought is that the freon only provides cooling of the battery and passenger compartment.

EDIT: Pictures of the chiller are In This Post.
 
Last edited:
#17
Cottonwood said:
Here is the same picture from 5.12; the target temps on the battery have changed a little...
Click to expand...

Do you know if this snap shot is from the P85 model? I've read somewhere on the Forum JB quoted to say that cooling for P85 is dispatched more agressively then other models. May be the target temperatures did not change with changes in software, and this is just a snap shot for P85...
 
#18
vgrinshpun said:
Do you know if this snap shot is from the P85 model? I've read somewhere on the Forum JB quoted to say that cooling for P85 is dispatched more agressively then other models. May be the target temperatures did not change with changes in software, and this is just a snap shot for P85...
Click to expand...

Interesting point. The picture was from a P85 with 5.12.

Mere mortals should have access to this info...
 
#19
Cottonwood said:
Interesting point. The picture was from a P85 with 5.12.

Mere mortals should have access to this info...
Click to expand...

Really interesting. The battery in P85 then should degrade slower, as it is maintained at a lower temperature. That is if one one does not drive it as a P85...
:smile:

It would also mean that energy consumption in P85 should be slightly higher as lower target temperatures for the battery would require cooling system to run more frequently/for longer periods of time.
 
Last edited:
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