109 degrees + A/C running + City driving = mileage drop

[wamba2000]

One of the "joys" of living in Phoenix is the dry heat, even when it gets to 109 in early June.

Had to fill the C-Max this weekend, reset the trip mileage, and ran a bunch of places in the heat with A/C running.  Mileage for the trip was in the 40.5 range, where the usual has been 46-47 mpg for me using the Trip mileage ( funny, actual mileage is lower, see my Fuelly average.)

 

Anyone have much experience on the amount of the drop from A/C?  I will still run it, but my lifetime mileage will level off ( currently shows at 43.8).  Will see how Lifetime is affected on this tank by running A/C

 

 

[obob]

Your location seems to be a good candidate for a windshield shade.

[plus 3 golfer]

wamba2000, how long was each leg of the trip?  Did you see my post here.  I said it wouldn't surprise me if for shorter trips, high temps, the FE hit would be as much as 15%.

[salsaguy]

if you have the new version of MFT i believe you can see the power distribution on the main screen if you hit the hybrid road symbol (shows a full screen pix of the car and the hybrid system lines), and you can also change your my view display panel in the driver's side to show how much your accessories are taking up your fuel and battery.

Edited June 4, 2013 by salsaguy

[asb]

Though it's hot where you live, the humidity here is killing me.  It's 73 degrees outside in the morning, but I have to run the air because it's so humid, it feels like 90 degrees outside.

 

Anyway, what I've done with the ac is keep it set between 73 and 75 degrees.  It cools the car well enough for me and doesn't put a lot of drain on the system.  My mileage isn't suffering as much as when I had it set lower.

 

Roll the windows down when you first get in and max the ac for a few minutes.

[wamba2000]

Plus 3, yes, the trips were a few miles in nature, making stops etc.  Figured it would take the hit.

ASB, I keep the temp set on 75 or so, have noticed the car stays cool enough.  However when my wife gets in, the passenger setting goes to 70....oh well, happy wife, happy life!

Can't say much on that one.

Thx

[plus 3 golfer]

Though it's hot where you live, the humidity here is killing me. ...

....

Roll the windows down when you first get in and max the ac for a few minutes.

Rolling the windows down does little with the outside air at 109 F because the inside air temp will quickly drop below 109 F using AC.  It's that everything else inside the car is at say a sun-baked 120+ F and takes a while to cool down.  When the outside temp is significantly lower (usually below mid 80's), I will open the windows (usually until my wife complains about the windows being open) and then turn on the AC. :)   With the lower humidity in AZ, I can drive fairly comfortably with the windows cracked open in the mid 80's using no AC but 74 cabin temp is still better.

 

Also, the effect of humidity on FE can be significant.  For example, the ratio of the enthalpy (total energy content) of air at 80% relative humidity over 10% RH both at 100 F and both cooled to 10% RH at 45 F (assumed evaporator core temp) is about 3 times.  In other words, three times as much work has to go into removing the heat content of air at 80% vs 10% RH both at 100 F.  This is a significant reason why it in makes sense to use Max AC (includes recirculation), especially in areas with high RH.  Why keep expending energy to remove water vapor from the outside air over and over again.

 

Let's take the example one step further.  Once the cabin temperature reaches the set point say 75 F, the AC has to now run to maintain cabin temperature from the heat gain from solar and convection.  So, if one continues using recirculation (pushes the recirculate button) in both cases above, the difference in enthalpy (80% RH vs 10% RH) is over 5 times because now the input air to the evaporator core has been reduced to near the set point temperature with low RH.  

 

Bottom line, I always used recirculation back East where low humidity was 40%.  But in AZ,  I very rarely use recirculate except during the Monsoon season (usually July and August) where RH might be 50 - 60%. When monitoring the climate usage, I can barely detect a difference in recirculate vs non recirculate use.  This is likely because the vast majority of climate use once the cabin is initially cooled is to remove the heat gain from the outside sources.  I would expect the results of using recirculate to be much different in high RH areas 

[ScubaDadMiami]

I'm doing the same thing as asb, and it seems to be working pretty well.  Tinting has helped a lot more than I expected that it would help.  I haven't resorted to using a sun shade inside of the windshield; I hope that I can avoid this.

[wamba2000]

Plus3 thanks for the explanation on humidity.  I normally have outside air entering rather than re-circluate engaged.  Only use recirc to cool down initially.

 

I did not get the Panoramic roof tinted as others have done - in fact, had tint installers say it would cause breakage.  Alternative, I purchased vinyl tint film and using a little non-ammonia window cleaner and a squeegee, managed to position the film and get the bubbles out, then trimmed the edges with an razor blade.  Acts like tint, but is not permanent, and hopefully won't cause an issue in the heat of AZ.  It does help a bunch on the temps, but I also have the motorized screen closed.  Lucky I get a covered spot at work!

 

Summer is just our burden in AZ, let's see, we have only 3.5 more months of 100+??

[ctford]

I deliberately didn't get the panoramic roof (although I kinda wish I had it) because I saw no purpose in it when I found out it wouldn't open!  Living in Houston and having black leather, I knew it's only purpose would be to help my car bake in the sun.  

 

The temperature gauge on my car when I left work yesterday said 101.  And it's only the first couple days of June.  (I admit, I HATE living here, but not just for the heat!)  In any case, I always read in car manuals that using recirculate will run use more fuel, so I tried to avoid it.  Then I came to realize that that only counts in the majority of the country where my temp gauge doesn't read 112 in the summer.  Recirculate keeps the cold air circulating which takes less fuel than forcing the car to try to cool the ridiculously hot outside temps to a decent inside temp around 73 or 74, where I've been keeping it.

 

Houston can have no humidity days and 100% humidity days, depending on which way the winds blow off the ocean.  For my purposes in these conditions, recirculate has helped my mileage creep back up a bit.  Just my $.02.

 

Colleen

[fotomoto]

I  In any case, I always read in car manuals that using recirculate will run use more fuel, so I tried to avoid it.  

 

Good points Colleen but remember that those old manuals were referring to traditional a/c systems.  Most of those old belt driven compressors were run full time when recirc (MAX a/c) buttons or dials were selected; thus the poor FE.  The CMax system is electric and especially in Auto mode will try and balance cooling with energy use.   

 

Here in the hot, humid south, I use recirc to lessen the a/c load for both temp and humidity.  In our winters, I don't need recirc as it will fog windows PDQ without a/c or even light a/c use.  

[mtb9153]

Plus3 thanks for the explanation on humidity.  I normally have outside air entering rather than re-circluate engaged.  Only use recirc to cool down initially.

 

I did not get the Panoramic roof tinted as others have done - in fact, had tint installers say it would cause breakage.  Alternative, I purchased vinyl tint film and using a little non-ammonia window cleaner and a squeegee, managed to position the film and get the bubbles out, then trimmed the edges with an razor blade.  Acts like tint, but is not permanent, and hopefully won't cause an issue in the heat of AZ.  It does help a bunch on the temps, but I also have the motorized screen closed.  Lucky I get a covered spot at work!

 

Summer is just our burden in AZ, let's see, we have only 3.5 more months of 100+??

that's why they named it Arizona...Arid-zone-a I call your wonderful state. :)

[mipmapped]

The Energi left dash display can show the power draw for the climate control system. From my experience, starting off in 100F heat after being parked in the sun, the AC at 72F Auto starts off around 4KW and over a period of a few minutes drops to about 0.5KW where it stays. Since the AC draws from the HV battery, and the engine would be needed to replenish that in Hybrid mode, you would expect a drop in MPG. On a long trip, the 0.5KW shouldn't be a big impact.

 

Parking with a windshield sun shade does help a lot. It's a big piece of glass...

 

FYI, AC isn't nearly as bad as heating when running an Energi in EV only mode - that appears to draw a constant 4-5KW. When possible we tend to use the seat warmer instead. For the Hybrid the engine heat would be used.

[plus 3 golfer]

The Energi left dash display can show the power draw for the climate control system. From my experience, starting off in 100F heat after being parked in the sun, the AC at 72F Auto starts off around 4KW and over a period of a few minutes drops to about 0.5KW where it stays. Since the AC draws from the HV battery, and the engine would be needed to replenish that in Hybrid mode, you would expect a drop in MPG. On a long trip, the 0.5KW shouldn't be a big impact.

 

Parking with a windshield sun shade does help a lot. It's a big piece of glass...

 

FYI, AC isn't nearly as bad as heating when running an Energi in EV only mode - that appears to draw a constant 4-5KW. When possible we tend to use the seat warmer instead. For the Hybrid the engine heat would be used.

Did you read my post here.  Yes, actually in the same 109 F temp, my climate usage initially was close to 5 kW, dropped to 4 kW and settled in at about 0.5 - 0.75 kW.  In cooler temps, my usage would settle in at less than 0.5 kW.  

 

We can estimate the FE effect of a 500 Watts continuous load on FE.  The energy to replace that 500 Watts of load, assuming a conversion efficiency of 80% and an engine efficiency of 35% would be about 1800 Watts or 6100 Btu/hr. One gallon of E10 contains about 110,660 Btus.  About 0.055 gallons of fuel will be used every hour to keep us cool once the cabin has cooled down (based on my observations with set point = 74 F).  So now, if we know the average speed and mpg, we can estimate the FE hit.  Let's use cleanmpg.com speed vs FE graph shown below.  Based on that speed vs FE chart, one can constructs a table of the the FE hit shown below for steady cruising once the cabin temperature has stabilized.  Also, one could correct the FE vs speed chart for higher temperature as the chart is based on 70 F as FE likely will be higher because as the temperature increases due to lower air density, aerodynamic drag will be less.  Bottom line, IMHO the FE hit from AC is not bad once the set point temperature is reached.  It's the shorter trips (% of initial AC use higher than longer trips) amd stop and go traffic that will kill FE when using the AC.

 

 

 

 

Edited June 7, 2013 by Plus 3 Golfer

[mtb9153]

if you have the new version of MFT i believe you can see the power distribution on the main screen if you hit the hybrid road symbol (shows a full screen pix of the car and the hybrid system lines), and you can also change your my view display panel in the driver's side to show how much your accessories are taking up your fuel and battery.

ok with that remark is the car image in your power distribution screen a CMax?  Right now mine is a Focus per my remarks yesterday after Ford Techs screwed up my upgrade to 3.5.1.  See the attached picture.

Edited June 6, 2013 by mtb9153

[salsaguy]

mtb, i dont own a C-Max just yet.:) just here to learn a lot before we buy one for my wife.

i heard from others it should be showing a c-max not a focus so they messed it up for sure.

[PWBarrett]

So that works out to about 7 ounces of gas to run the AC for an hour.  Sounds like a bargain to me.

 

[plus 3 golfer]

So that works out to about 7 ounces of gas to run the AC for an hour.  Sounds like a bargain to me.

 

Or less than 20 cents an hour to stay cool.  Hardly worth moving the set point up to save a few pennies. ;)  Comfort over economy for me.  I may move it down a few degrees now.

 

Or about 132 ounces to go 50 miles.  Not many cars can do that. :)

[fotomoto]

+1 on keeping things cool.  Remember:  the hybrid battery is only cooled by cabin air.