TexasLeaf
Posts: 52
Joined: Wed Mar 21, 2018 5:37 am
Delivery Date: 21 Mar 2018
Leaf Number: 303111

Using air conditioning to reduce battery pack tempature

Tue Jul 31, 2018 9:07 am

I watched a video recently where Lemon Tea Leaf tested whether cabin temperature affected battery temperature.

https://www.youtube.com/watch?v=-7tKdylLMvo

Lemon Tea Leaf's test results where inconclusive but I think there may be value in employing this battery temperature controlling strategy on long trips when the battery temperature is already very hot. The theory is that a cold cabin, sitting directly above the battery pack, will increase heat transfer from the pack and help cool the pack.

Lemon Tea Leaf started out with a cool battery pack and then turned the AC on while the pack was fast charging. Lemon Tea Leaf compared the battery temperature rise with a Leaf that did not have the AC on. The battery temperature rise was about the same for the two Leafs.

In Lemon Tea Leaf's test the ambient temperature was about 60 degrees F and the average battery temperature was about 70 (60 with rise to 80) degrees F. 10 degrees F is not much of a driving force for heat transfer. When it's a 100+ degrees outside and your battery pack is already cooking on a long trip after several fast charges, turning down the cabin temperature while charging might make a signicant difference.

I actually tested this theory this last weekend. I drove almost 500 miles in my 2018 Leaf with four CHAdeMO charges. The goal of my trip was to test several battery temperature control strategies for long trips with multiple fast charges. The strategies were fairly successful, I really didn't start to see really high battery temperatures unit my fourth and last fast charge when the ambient temperature rose above 100 degrees F.

During the fourth charge I was just sitting there with a reduced charging speed and I thought about Lemon Tea Leaf's video. I turned the AC down and opened the hood to let the heat coming off the condenser escape. It's hard to say how much the cabin AC helped cool the battery pack but I have a feeling it helped keep my car from going into "turtle" mode when I finished this last hot, fast charge.

I don't thing turning on the AC while your driving helps, the moving air would just push out the cold air before it can have an impact battery temperature. But the bottom of the cabin is a large heat transfer surface and a heat transfer surface that is sitting directly above the battery pack and is 50 degrees F colder than the battery pack temperature has to create some kind of heat transfer. I think next time I try this theory I will start cooling down the cabin temperature 30 minutes before I start fast charging and I will be sure to bring along a sweater or jacket so I don't freeze myself out of the cabin.

TexasLeaf
Posts: 52
Joined: Wed Mar 21, 2018 5:37 am
Delivery Date: 21 Mar 2018
Leaf Number: 303111

Re: Using air conditioning to reduce battery pack tempature

Tue Jul 31, 2018 11:48 am

I read in another forum that the cabin air leaving the cabin actually blows across the battery pack when the air conditioning is in Fresh Air mode. Cold cabin air blowing across the battery pack would be much more efficient at cooling the battery pack than depending on heat transfer through the floor board. I know the fresh air has to go somewhere but I can't find any link or definitive information on how the fresh air leaves the cabin.

Does anyone have any information and/or link on how the fresh air leaves the cabin and whether the fresh air leaving the cabin gets blown across the battery pack?

LeftieBiker
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Delivery Date: 31 May 2013
Location: Upstate New York, US

Re: Using air conditioning to reduce battery pack tempature

Tue Jul 31, 2018 12:25 pm

There is supposedly a pressure relief flap where the emergency power disconnect is located, to let air leave the cabin when all the windows are up. This exhausts into the cooling tunnel above the pack, I've read.
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.

Reddy
Posts: 1510
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Leaf Number: 006828
Location: Pasco, WA

Re: Using air conditioning to reduce battery pack tempature

Tue Jul 31, 2018 1:05 pm

LeftieBiker wrote:There is supposedly a pressure relief flap where the emergency power disconnect is located, to let air leave the cabin when all the windows are up. This exhausts into the cooling tunnel above the pack, I've read.
Some months (years?) back there was a MNL user who piped a flexible 6" A/C duct from his garage, through an open window, directly into that disconnect. He found that he could reduce the pack temperatures from 90s down to 70s. Not super easy to do, but definitely shows that A/C can be used to keep the temps down.
Reddy
2011 SL; 9 bar, 45.80 AHr; 45,000 mi; rcv'd Aug 18, 2011
Long: http://www.mynissanleaf.com/viewtopic.p ... al#p226115"
Cold: http://www.mynissanleaf.com/viewtopic.p ... 60#p243033"

TexasLeaf
Posts: 52
Joined: Wed Mar 21, 2018 5:37 am
Delivery Date: 21 Mar 2018
Leaf Number: 303111

Re: Using air conditioning to reduce battery pack tempature

Tue Jul 31, 2018 3:38 pm

I'm pretty sure the cabin air relief vent for the 2018 Leaf is behind the bumper. I watched a few videos of repairs on older Leafs and behind the bumper is where the vents were. It's still possible there is a vent to the battery well but I don't know where it is.

I don't see how the cabin pressure relief vent behind the bumper could help cool the battery pack but I did also look at the cover plate for the HV disconnect above the battery pack. It does appear that there are vents around the cover plate that would allow air to pass but they are pretty small vents. I wouldn't count on much cooling air getting through that cover plate.

I did see a discussion related to removing the HV disconnect plate and using the open to force cool air through during fast charging with the AC in Fresh Air mode. This would be a simple enough mod to improve battery cooling and it could easily be reversed once there was no longer any need for additional cooling. I might try to remove the plate some time to see if I can improve battery pack cooling during charging on a long trip.

That little opening above the battery pack brings up a lot of opportunities for cooling the battery pack. You could use a little 12V fan to force cool air from the cabin to the battery pack. You could even run a garden hose through the opening and cool the battery pack with water.

I saw one chart that showed how someone was able to add additional cooling just by putting is AC in Fresh Air mode. I don't see how this would work but it might be worth a test to see if I can repeat his results. Anyway, I would be reluctant to try anything that might void my warranty but if any of you want to give some of these ideas a go, God Speed.

LeftieBiker
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Location: Upstate New York, US

Re: Using air conditioning to reduce battery pack tempature

Tue Jul 31, 2018 6:06 pm

There are likely two vents, one with the disconnect and one in the rear.

I saw one chart that showed how someone was able to add additional cooling just by putting is AC in Fresh Air mode. I don't see how this would work but it might be worth a test to see if I can repeat his results.


Fresh air mode pressurizes the cabin slightly, while recirculate does not. Having a way to remotely block and unblock the rear vent would be the most effective simple way to use cabin air to cool the pack. Beyond that you're back to piping in cold air and directing it to the inside vent.
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.

TexasLeaf
Posts: 52
Joined: Wed Mar 21, 2018 5:37 am
Delivery Date: 21 Mar 2018
Leaf Number: 303111

Re: Using air conditioning to reduce battery pack tempature

Tue Jul 31, 2018 6:42 pm

LeftieBiker wrote:There are likely two vents, one with the disconnect and one in the rear.

Fresh air mode pressurizes the cabin slightly, while recirculate does not. Having a way to remotely block and unblock the rear vent would be the most effective simple way to use cabin air to cool the pack. Beyond that you're back to piping in cold air and directing it to the inside vent.


The ventilation air paths are complicated and not direct. One thing that having the vents behind the bumper does is cool the trunk area. Cooling the trunk area may help cool the large battery pack modules in the rear.

When you turn the AC on in Fresh Air mode, there is a lot of air that comes out of the vents and it's all outside air. Once it gets into the cabin all of that air has to go somewhere. Air flow will follow the path of least resistance and I think removing the HV disconnect cover plate and placing the AC in Fresh Air mode might be a very effective way to add additional cooling to the battery pack.

LeftieBiker
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Location: Upstate New York, US

Re: Using air conditioning to reduce battery pack tempature

Tue Jul 31, 2018 8:50 pm

You misunderstood me, and then gave me back my own suggestion. Let me rephrase and expand:

Fresh air mode pressurizes the cabin slightly, while recirculate mode does not. Having a way to remotely block and unblock the rear vent, and then using the A/C with Fresh air selected (and fan on a higher speed) would be the most effective simple way to use cabin air to cool the pack. Beyond that you're back to piping in cold air and directing it to the inside vent.
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.

Evoforce
Posts: 820
Joined: Wed Mar 04, 2015 9:58 pm
Delivery Date: 28 Feb 2015
Location: Fountain Hills Arizona

Re: Using air conditioning to reduce battery pack tempature

Wed Aug 01, 2018 2:33 am

But...If the outside ram air is more powerful than the high fan setting, opening that plate might introduce more powerful ram air and drown out any cooled air inside as well as where that top of battery HV connector is located at half pack. Uneven cooling of the pack just doesn't make sense either. In my climate, engineered cabin air cars are also needing to have their batteries replaced. Most people only drive their cars around 4% of the time. So during the off time here, it still stews in the heat, especially after driving and charging. That doesn't even address people here that then park in their hot garage.
*2011 Leaf 1 bought 2/28/15 @ 28,000ish mi 10 bar (8 bars @ 11/25/15 @ 37,453 ) (New lizard @ 39,275 mi @ 1/20/2016) Now 52,166 mi.
*Tesla Model S 61,000 mi
*2011 Leaf 2 bought 4/28/15 @ 24,000ish mi 12 bar (new lizard Dec. 2014 @ 22,273 mi) Now 35,485 mi

LeftieBiker
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Joined: Wed May 22, 2013 3:17 am
Delivery Date: 31 May 2013
Location: Upstate New York, US

Re: Using air conditioning to reduce battery pack tempature

Wed Aug 01, 2018 4:17 am

But...If the outside ram air is more powerful than the high fan setting, opening that plate might introduce more powerful ram air and drown out any cooled air inside as well as where that top of battery HV connector is located at half pack.


I have never driven a car in which "outside ram air" is more powerful than the ventilation blower. Having the windows open produces more airflow of course, but that air isn't cooled. I also think you are confused about what I proposed, which is CLOSING the rear vent in order to direct the cooled cabin air down the battery cooling tunnel. Unless you are actually referring to the cooling tunnel when talking about "outside ram air" in which case the effect could be anything from increased cooling, through no net effect, to actual warming, depending on the ambient air temp.

In short, it isn't clear to me exactly what you are talking about...
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.

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