Windows Down vs A/C

Aye, I was expecting to see a max load of 1500 watts like you did. I think the main difference was Power Mode vs. Eco Mode and the fact is was much hotter than when you performed your testing. I tried turning on Eco Mode to see if it changes the current draw but it was way late into the trip so current draw dropped from 600w to 500w. I then turned Power Mode back on and the draw went back up to 650w but turning Eco Mode on again made no difference so I am hesitant to draw any conclusions.Either way, 1500-1800w of draw for 5-10min is a lot of power and should make a dent in your mpg. Even a 1000w? average for 38 miles is pretty huge.

I think our next round of testing should include Eco and Power mode testing.

 

Don't know if any of you have seen the August, 2012, Consumer Report issue? There's a sidebar: "Debunking Fuel Economy Myths." One of the "myths" is A/C vs windows down.They tested a Honda Accord at 65 MPH. Using A/C reduced the gas mileage by 3 MPG. Opening the windows had no measurable effect.

There's no info on how they conducted the test, how long they drove, etc.

edited to correct month.

 

I've read it. Even without all of the details the information jives with what we know about the Prius. The main difference is the amount of loss. It is not a static loss. It changes with ambient temp, cabin temp and AC settings. My personal opinion is a minimum of a 2mpg loss in ideal conditions and a 10mpg loss in maxed out scenarios.

 

My GenII is at least a 5mpg loss for AC in the 90F+ temps. AC takes lots of power....

 

OK but you also should state what is the difference btw your A/C setting and the ambient temp and what fan level you put ... HUGE differences ... if you always put (say) 68F and you get into the car on an 99F+, like we had here in New York last week sure you will see even more mpg loss (engine will not even stop regardless of SOC seem to me over certain load ICE will not stop )... but if you start out with A/C 82-85F and gradually lowering to 75F which is more than bearable you will not see that much loss ... (same goes for the winter ...)

In other words prius can not make miracles ... physics rules

 

Please have a look at these diagrams - they show how heavily the fuel consumption increases caused by the Air Condition. Fuel Economy diagram with and without Air Condition | PriusChat

I have experimented with the aerodynamic parameters in Wayne Browns simulator, the effect is much lower in any case. I recommend: open the window. Switch AC off as much as you can. The aerodynamics is not damaged by open windows.

Best regards
Rainer

 

Very impressive charts no question and there some sweetspots

Well what speed do you think is the cut off point (I know every one has some opinion on this ) but. Aerodynamics doesn't play really big role till highway speed comes in .. you can go on authobahn speed there. But 65mph and above open windows will start to play quite a bit ... and the noise (wind and tire) is just way too much ...and again 99F lowering windows and going city speed also doesn't help much ... I do not use A/C under 80-85 depending humudity .. here in New York humiditiy could be very high on top of the temp. But my wife wouldn;t stand that ...

 

so I tried this on my Wed commute and saw immediate increase in mileage. I normally use AC in the morning too since it is around 80F. But I found cracking the two windows mentioned works great and with just the fan on (no AC)....I have ample cooling to be comfortable. In the afternoon it is out of the question...nearly 100F every day. But it seems I can cut my AC impact on mpg in half. I already matched my best mpg during this tank...so will add this technique to my next full tank to see where it will take me so I can see exactly how much it helped. Thanks for the tip!

 

No problem, my friend! I'm glad it worked for ya.

I have been using this technique in the 100F heat and it gets a bit uncomfortable but when trying for a record tank it's worth it. Today it was 106F and I kept staring at the interior temp reading at 114F and thought to myself are you out of your mind? Thankfully it cooled down to 110F fairly quickly and then to about 105F towards the middle of the trip. I bested my previous best evening commute by 4.2mpg, however. When I parked and the trip summary read 90mpg (49miles) I almost fainted and not just from the heat. LOL

FWIW, I wasn't able to use the solar roof ventilation nor could I crack my windows today so most of the excess heat would not have been there on a normal day.

 

What were batt temps like?

And nice trip btw.

 

Much higher today. Interior temp was 114F and battery temp was 96F or 98F. After driving for awhile the battery temp mirrored the outside temp (ambient = 102-106F). The highest it got was 106.8F and that was with the interior temp in the 108F range. keep in mind I turned off the solar cooling, the windows were not cracked and I started the trip at about 10F hotter.

Thanks.

 

F8L...you only did that for testing, right? In reference to no AC.

 

Has anyone done experiments for battery temp for (1) mild A/C fan on Auto (2) no A/C fan on high windows up (3) Windows down.

I suspect the battery cools the best with the blower and the windows up and that is the real reason you should not drive with the windows down. The other argument is there is NO air filter for the HV battery. If you use the cabin filter and the ducting you are not getting as large of debris and filtered air.

 

does it reference anything in the manual about cabin cooling and the battery temp? I am curious since it seems that from an engineering standpoint, they left that door open. Meaning that there is no dedicated cooling system for the battery. We are digging into this...but many owners will never pay it any mind.

 

The battery does have a cooling system, but the air intake for the battery vent is located inside of the cabin. The assumption is that people will keep that cabin at a temperature tolerable to humans, which is also tolerable for the battery.

Tom

 

That is understood. So for example...on days I go to the beach. It is mid 90's...I have the windows down and the sunroof wide open. Ideal for windy beach weather...not ideal for the battery. From an engineering standpoint...if the battery was at risk in such conditions then they would have to have dedicated cooling system to take over. Or is it so that the percentage of cycles with the battery in this condition are small in comparison to your overall driving habits and do not add significant risk to the battery life. My best guess is there is no immediate risk...but long term repeated behavior such as that will deplete battery life in the long term.

 

No. I almost never run the A/C when I am alone. I am monitoring battery temps in this car, however, so if it appears I am doing the battery harm then I will turn on the A/C. Because I have the solar roof, sunshade, tinted windows, etc etc. my battery should stay cooler than those cars without these features. Thus if I run a little higher battery temp during my 1hr commute I am not going to freak out over it since most people would be cooking their battery for many hours throughout the day. I just need to figure out what that battery temperature threshold is.

 

I'm going to show this post to my wife the next time she starts to complain when the house temp goes over 85F.

"This guy turns on the heater if the temp drops below 90F."

 

I have not conducted such tests but I did notice that on a 35mile trip last weekend I had the A/C on and despite setting it on Auto at 76F the cabin temp never got below 86F according to Torque. I would assume the battery would be at least that temperature if not a tad higher. Air temperature at that time was mid 90s if I remember correctly. I do not feel comfortable with battery temps over 100F but I figure there won't be too many days where I would subject it to such heat.

 

Where is the cabin sensor ? I notice that the AC in auto mode responds very quickly to changes in radiation from clouds -- way faster than the cabin temperature actually might change.