Windows Down vs A/C

I don't blame her. I mean I love the feeling of a cool house but when I get in the car and my mpg is on the line I turn into an endurance athlete. I think of all the time I spent baking in a racing jacket and helmet while waiting my turn to run down the 1/4mile. That was easy compared to this. I feel like I am accomplishing something by just enduring, staying in control and adapting to changing traffic and terrain. Hypermiling is not for the weak! Hahaha

 

Then whatever you do, DO NOT look at your home electric meter.

 

holy crap. If I clear 85F...I am looking for the AC button.

 

This is what my question boils down to.

 

Justin,
It would be interesting to know if battery performance trailed off at high(er) temperatures. That is my excuse for using AC, although I also mention safety issues (falling asleep at the wheel) and long term reliability when I am feeling guilty about being a wimp.

 

Here? #23

2010 TOYOTA PRIUS HVAC Interior Temperature Sensor

If this is it it looks like it is somewhere between the center console and the power button.

 

This may help although it is for a Gen I Prius.

http://www.nrel.gov/vehiclesandfuels/energystorage/pdfs/2a_2002_01_1962.pdf

 

It appears battery performance is fine up to at least 45C (113F). Somewhere around 52C (125.6F) the HV battery fan should come on to help cool the pack. It sounds to me like pack performance is hindered by cold temperatures and not hot temperatures but pack longevity may be compromised and damage may occur in very hot temps. This is just going off of older data on the first Gen Prius. Battery design and casings have changed since then so I may be way off base.

 

Some of those hot days when I was testing different A/C scenarios I saw my battery get to around 110. :/ And seems like even when it is pretty nice outside and the car is somewhat cool it has no problem getting into the upper 90's. Maybe your higher speeds of driving, on average, are pulling more air across it keeping it much closer to ambient air?

 

It's possible. With the cross flow method you are pushing air from the driver's side window to the rear passenger side rear window where the vent is located. It doesn't seem like it would do much unless the rear window was more than just cracked 4" or so.

 

Go look at the charts of lifetime NiMH % life of battery vs. discharge temp. It is worth the few dollars in gas to keep the HV battery as low temp as possible. I personally think the HV fan is improperly set probably due to testers complaining about fan noise. I think everyone should always have the cabin fan on high and fresh air, always, and judicious use of the A/C when it is over 90 ambient.

 

Well that is the rub. My experience with computer case fans and having the case side open versus closed with intake and exhaust fans kind of leads me to believe that air isn't going to just flow across the HV battery with the windows open. I'm pretty sure you need the cabin sealed and the cabin fan to force air out, but I also don't have any data to confirm it.

Is there a post where someone shows ambient temp / battery temp / windows up/down / cabin temp with A/C / cabin fan mode.

 

i always do windows down as first choice but sometimes there is simply too much exhaust fumes to make that a "happy" choice. as far as efficiency goes; windows down have proven to be a minimal impact on MPGs despite what Mythbusters said BUT, the more efficient your car based on Cd, the more windows will affect your performance.

so all in all, it really depends on
1) how fast you are going
2) how hot it is
3) what you are willing to put up with

 

Maybe I'm wrong, but windows down pushs pollen and bugs and gunk into your HV battery that has no air filter. Windows down may not force air over the HV battery and it may have to get hot enough for the HV fan to come on.

Windows up with cabin fan on high keeps the HV battery cool and extends its life.

 

Just curious if you have actual evidence of what certain temps can do to a Prius battery. Also, are you watching your battery temps like most of us are?

 

There's a grill beneath the blank-out that's straight down from the power button on my '11. If you look from the floor up, you'll see it. I would bet that's where the sensor is. The knob on the top right of the dash is probably the sun load sensor.

 

Speaking of this. I drove home today with my windows cracked at high speed and all the way down at low speeds. My battery temp stayed at around 8F to 10F higher than ambient temp and pretty close to in-cabin temp. The temperature stayed right around 96F for most of the 60mile trip with a peak of 98F. The ambient temp was 93F but dropped down to 80F by the end of my trip. Battery and cabing temp slowly declined with ambient temp.

When I tested A/C on in-cabin temp last week it never dropped below about 86F. Even so, I suspect the battery temp would also drop down closer to the cabin temp. Thus with the A/C you may be able to keep the battery 10F cooler when ambient temps are 90F+. I'm not sure this is really a big deal until temps are 100+, however. I'm not a battery expert.

 

That's interesting and pretty much matches a lot of the stuff I've seen on Torque. I, also not being a battery expert, would agree that you probably can run windows down no problem until it is 100+ outside. I think it's pretty telling that even when the battery temps are a little over 100 you still don't hear the battery fan running at full speed. That tells me that Toyota has no problem with the batteries being at that temp.

 

That's what I was thinking or hoping. I've never heard the fan yet. It supposedly comes on at 52C in the GenI. What is the temp setting for the GenIII? Maybe I'll set up a gauge for fan speed and start watching it.

Oh, despite the wind picking up today and blowing against me (Grrr) I managed to increase my tank from 68.2mpg to 68.5mpg 527miles).I had to take the river road and drive slow to get those numbers though. My avg speed dropped from 48mph to 44mph. In hindsight I think I may have done better just sticking to my usual freeway route. lol

 

that will be an amazing tank for that speed!

I don't want to say what I'm at right now or hope to be at when the tank is empty because I don't want to jinx myself.