318ti.org forum

Go Back   318ti.org forum > Technical, Maintenance and Modifications > HVAC

Notices

HVAC Heating, ventilation and air conditioning.

.
» Recent Threads
1999 M-Sport For Sale
12-31-2023 05:10 PM
Last post by Coop540iT
03-23-2024 06:39 PM
1 Replies, 99,239 Views
Once again 318ti owner...
03-20-2024 12:39 PM
Last post by two30grain
03-22-2024 02:04 PM
1 Replies, 62,197 Views
What brakes do I...
03-20-2024 03:27 PM
Last post by huirtera
03-20-2024 03:27 PM
0 Replies, 59,464 Views
Reply Share/Bookmark
 
Thread Tools Display Modes
Old 04-24-2011, 03:18 AM   #1
vsonix
Senior Member
 
vsonix's Avatar
 
Join Date: May 2010
Location: Southwest England
Posts: 379
Vehicles
iTrader: (0)
Default Aircon - impact on fuel economy?

Sorry if this has been touched on before but couldn't find anything when I searched. I've just had my aircon fixed (wasn't working when I got the car); the car is now icy cool when I want it to be; however I am worried if I start using it a lot my fuel economy will suffer. I don't mind maybe losing 1 or 2 mpg tops on long runs since the cabin is a quieter, nicer place to be with it on, but I need to know if I should be sparing with its useage I guess. Anyone found the ti's aircon to be better/worse than other cars in that respect?
vsonix is offline   Reply With Quote
Old 04-24-2011, 08:00 AM   #2
John Firestone
Senior Member
 
John Firestone's Avatar
 
Join Date: Nov 2004
Location: Bremerhaven, Germany
Posts: 977
iTrader: (0)
Default

The increased consumption depends on how much cooling you ask of the air conditioner. Typical averages for Germany might be 1-2 liters/100 km during cool down and 0.5-1 liters/100 km thereafter. How that converts to mpg depends on the car's realized mpg as those units are non-linear. If you are getting 10 mpg, the air conditioner won't be very noticeable. If you are getting 100 mpg, using the air conditioner might prove a financial hardship.

Using my long term average of 8.6 l / 100 km (32 mpg UK) for the base consumption, I convert the above to 4-7 mpg during cool down and 2-4 mpg thereafter. Perhaps someone someplace hot can give you some better figures from their consumption records. I'm not sure I use my air conditioner enough to have the data for a calculation

Judging by the last few days, this will be a good summer to have it in northern Europe. I think I'll be glad I got mine fixed.

Last edited by John Firestone; 04-24-2011 at 08:46 AM.
John Firestone is offline   Reply With Quote
Old 04-25-2011, 01:11 AM   #3
vsonix
Senior Member
 
vsonix's Avatar
 
Join Date: May 2010
Location: Southwest England
Posts: 379
Vehicles
iTrader: (0)
Default

yeah, the last few days it's hit the low 20s in the afternoon, unprecedented this early in the year in these parts!
vsonix is offline   Reply With Quote
Old 04-25-2011, 06:51 AM   #4
pdxmotorhead
Senior Member
 
Join Date: Mar 2005
Location: Portland Or
Posts: 2,666
iTrader: (1)
Default

In every test I've seen, the AC is lower impact than the windows being down.
I played with mine on a road trip, used the cruise and drove 100 miles on AC and 100 with windows and sunroof open. The windows cost me 3 MPG vs the AC.

The OBC even was able to tell.

Dave

Dave
__________________
Dave - PDX
1995 318ti - Active Black and Tan.
2005 330xi - Mtech 1 - 6spd - Orient Blue/Black
pdxmotorhead is offline   Reply With Quote
Old 04-25-2011, 01:54 PM   #5
vsonix
Senior Member
 
vsonix's Avatar
 
Join Date: May 2010
Location: Southwest England
Posts: 379
Vehicles
iTrader: (0)
Default

thanks Dave that's what I was kinda hoping.
Roughly what kind of speeds were you averaging? At the moment I tend to be windows open and aircon off up to about 60mph and above that the windows up and aircon on
vsonix is offline   Reply With Quote
Old 04-25-2011, 02:52 PM   #6
John Firestone
Senior Member
 
John Firestone's Avatar
 
Join Date: Nov 2004
Location: Bremerhaven, Germany
Posts: 977
iTrader: (0)
Default

The German automobile club (ADAC) needed another 0.2 l/100 km (less than 1 mpg) with the windows open, between 80 and 100 km/h. Using the A/C to modestly cool the car from 28 deg C to 22 was 2 to 10 times more costly in town.

Their test vehicles were a Ford Fiesta 1.4, a Mazda 6 2.0 MZR, an Opel Vectra 2.2, an Audi A4 1.8 T and an Audi A4 2.0 TDI. Using the AC was between

Last edited by John Firestone; 04-25-2011 at 03:12 PM.
John Firestone is offline   Reply With Quote
Old 04-26-2011, 09:11 AM   #7
pdxmotorhead
Senior Member
 
Join Date: Mar 2005
Location: Portland Or
Posts: 2,666
iTrader: (1)
Default

Quote:
Originally Posted by vsonix View Post
thanks Dave that's what I was kinda hoping.
Roughly what kind of speeds were you averaging? At the moment I tend to be windows open and aircon off up to about 60mph and above that the windows up and aircon on
Hmm. Well,, I suppose the statute of limitations is up by now......
This was a unique area, I was setting the cruise at 90MPH its a REALLY out of the way road in eastern washington (Ie See for > 7 MILES!)

I had to drive it 4 times in 1 day 55 miles each direction... So I was able to use the same fuel and get a couple of nice long high speed runs on it. Got 24MPG on the OBC doing it... There is only 1 turn in the whole road that required dropping cruise and resetting.

Couple other interesting tidbits, the water temp stayed the same. The outside air temp was 95F and The car was empty except for me. I was running 32 rear and 28 front cold tire pressure. I got both runs done between 1 and 4 PM and the Air temp on the OBC stayed within a couple degrees all 4 trips.

Dave
__________________
Dave - PDX
1995 318ti - Active Black and Tan.
2005 330xi - Mtech 1 - 6spd - Orient Blue/Black
pdxmotorhead is offline   Reply With Quote
Old 04-26-2011, 09:32 AM   #8
cooljess76
NOBODY F's with the Jesus
 
cooljess76's Avatar
 
Join Date: Oct 2006
Location: Ventura California
Posts: 7,824
iTrader: (6)
Default

Mythbusters actually tested this. Here's the thing though, according to the "quiz" on their website, windows up A/C on gets better fuel economy than windows down A/C off:
http://dsc.discovery.com/games-quizzes/driving-myths/

However, according to their test, it's the exact opposite by a significant margin:
http://dsc.discovery.com/videos/myth...-minimyth.html
cooljess76 is offline   Reply With Quote
Old 04-26-2011, 10:19 AM   #9
pdxmotorhead
Senior Member
 
Join Date: Mar 2005
Location: Portland Or
Posts: 2,666
iTrader: (1)
Default

Did they use a BMW? LOL

I have noticed that my car seems optimised for side windows up.
Bmw went to all the trouble to make that fancy little spoiler pop up in front of the sun roof, yet did not seem to do squat about the side windows, the buffetting ad the lack of cover on the seatbelt riser makes it NOISY as all hell at highway speed. I find that on vent with the sunroof in popup mode I'm the most comfortable.

I heard a great line from the engineer who designed the Audi diesel for the lemans races.

"Noise is energy, if you get rid of noise you save energy."

My little bonzai run is not a scientific test by any means, but what it proved to me was that It does not make enough difference for me to care....

Damn the dinosaurs full steam ahead... !!

Dave
__________________
Dave - PDX
1995 318ti - Active Black and Tan.
2005 330xi - Mtech 1 - 6spd - Orient Blue/Black
pdxmotorhead is offline   Reply With Quote
Old 04-26-2011, 06:30 PM   #10
John Firestone
Senior Member
 
John Firestone's Avatar
 
Join Date: Nov 2004
Location: Bremerhaven, Germany
Posts: 977
iTrader: (0)
Default

Quote:
Originally Posted by pdxmotorhead View Post
"Noise is energy, if you get rid of noise you save energy."
Well, I suppose if you equate a symptom to the cause. An object that produced one acoustical watt, 0.0001% of the M42/M44 engine's 103 kW peak power, would rupture your eardrums, with the windows up or down.

As to the Mythbuster's quiz and the program (assuming I could view it), both could be true or false simultaneously, without recasting them as postulates in monetary economics. As the engineers found in the ADAC test I linked to earlier, which is more efficient, windows down or the air conditioner, depends, for a start, on the air conditioner technology and the vehicle speed.

Last edited by John Firestone; 04-26-2011 at 06:35 PM.
John Firestone is offline   Reply With Quote
Old 04-26-2011, 07:14 PM   #11
vsonix
Senior Member
 
vsonix's Avatar
 
Join Date: May 2010
Location: Southwest England
Posts: 379
Vehicles
iTrader: (0)
Default

Quote:
Originally Posted by pdxmotorhead View Post
Hmm. Well,, I suppose the statute of limitations is up by now......
lol, if ever the long arm of authority tries to pull me up for anything said online the official line I stick to is that I was exaggerating to make myself look cooler
vsonix is offline   Reply With Quote
Old 04-26-2011, 07:32 PM   #12
vsonix
Senior Member
 
vsonix's Avatar
 
Join Date: May 2010
Location: Southwest England
Posts: 379
Vehicles
iTrader: (0)
Default

Quote:
Originally Posted by pdxmotorhead View Post
Bmw went to all the trouble to make that fancy little spoiler pop up in front of the sun roof, yet did not seem to do squat about the side windows, the buffetting ad the lack of cover on the seatbelt riser makes it NOISY as all hell at highway speed.

Dave
my fave design flaw is the way water comes in the windows when you wash the windscreen at >10mph
vsonix is offline   Reply With Quote
Old 08-31-2013, 12:40 AM   #13
Honolulu
Junior Member
 
Join Date: Jul 2013
Location: Honolulu, Hawaii
Posts: 8
iTrader: (0)
Default

Unfortunately, I call the mythbusters "attempt" Bad Science. Nice try, but too many potentially significant variables have not been addressed. Even the test itself is flawed, thusly.


One: true that the engine (indirectly) measures intake air flow through the AFM. But the engine computer does know how much fuel the engine is getting, via the pulse width signal sent to the injectors. Some cars will report the mpg to the driver using that data... of which no mention was made.


Two: the "test" was only run once, with one car using AC, the other using windows. We can't/don't know the state of tune of these two vehicles, surely they are not identical. Therefore, for the test to be valid, the "AC versus windows down" test should be run with the vehicles reversed.


Three... even if the test was run correctly (see item two above) the test is only valid for the vehicles used. Aerodynamics for other vehicles will of course vary. The coefficient of drag for these SUVs was not mentioned. The results will be different for vehicles with a different Cd, ECU, state of tune, and numerous other factors.


Overall, this was a pretty lightweight attempt to address the question, and in my opinion the "results" are meaningless.
Honolulu is offline   Reply With Quote
Old 09-01-2013, 09:21 PM   #14
M-technik-3
Senior Member
 
Join Date: Aug 2008
Location: Globally
Posts: 1,162
Vehicles
iTrader: (1)
Default

The way we work it, if it's too humid and hot the AC is on. Otherwise around town windows open but for freeway the windows up and AC on.

We get 29-31 combined MPG so it's much easier to fill the Ti vs our Tahoe which gets 15/20 mpg and my E30 M3's the R12 has been dry for a couple of years so it doesn't matter in that respect.
M-technik-3 is offline   Reply With Quote
Reply

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Fuel economy L84THSKY Maintenance 22 10-08-2020 03:06 PM
Aircon belt question oakley Engine 3 06-08-2008 06:11 PM
Do you have side impact air bags? TiPerformance Interior and ICE 52 10-25-2007 06:54 PM
Impact on overall forum of inappropriate posts pdxmotorhead Site Feedback 6 11-19-2006 05:44 AM
left quarter panel m-tech impact strip iananderson02 US and North America 7 10-29-2006 03:39 PM


All times are GMT +1. The time now is 09:43 PM.


.
Powered by site supporters
vBulletin Version 3.8.8
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©1999 - 2024, 318ti.org
© vBadvanced CMPS v3.2.2
[page compression: 128.54 k/151.73 k (15.28%)]

318ti.org does not warrant or assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information or products discussed.