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-   -   windows vs. A/C (https://ecomodder.com/forum/showthread.php/windows-vs-c-2065.html)

rocket 04-29-2008 11:20 AM

windows vs. A/C
 
As the weather warms up, I'll need more than my vents to keep from frying while i drive. Is fuel economy better w/ the windows down (increased drag) or w/ A/C on (increased engine load)? I don't have the $$$ to get a scangage II yet to test myself. I drive a 97 ford aspire 5spd :turtle:. THANKS!

MetroMPG 04-29-2008 11:27 AM

In city driving, windows down generally trumps A/C use.

At higher speeds, the difference may depend more on the vehicle and the speeds you drive, I'd bet that for your vehicle, windows partly down is still best.

See this thread for more information:
http://ecomodder.com/forum/showthread.php?t=190

DifferentPointofView 04-29-2008 10:29 PM

I took in account that I drive a brick, and big engines don't take such a big hit in MPG's from extra accesories because the amount of load put on it isn't very burdensome to the engine, whereas a small engine takes the burden more seriously.

So in the city, I drive with either vents on, or windows down.

On the highway, this is what I do. I don't see why more people don't do this, because it has shown me excellent results. Instead of running the a/c the whole time, I have the vents on, and when I get too hot, I press the A/C button, wait till the compressor has cycled twice, then turn off the a/c and use the vent again. The air remains cold for about 3 miles, and then goes back down to regular vent temps. I can usually stand it for about another mile, then i get hot (it's a good thing I'm cold all the time anyway :thumbup:) then I let it cycle on twice, and turn it off.

My drive is about 10-12 miles, so I only have to press the a/c button three times. a whole lot better than driving 10 miles with the A/C constantly cycling on and off.

I judge when it cycles on by the volt gauge, because when the volts go down about 1-2 volts, (from about 14) that's when the compressor is running.

When on the highway, I never have the windows down. brick+open windows=giant brick parachute.

Arminius 04-30-2008 12:14 AM

I do the same thing. Off, on, off, on.

boxchain 04-30-2008 12:18 AM

You can switch the AC on during in gear accelerations, taking advantage of DFCO. See: http://forum.ecomodder.com/showthread.php?t=1447

Works best for stop/go type travels. I've found a 5-10s decel will cool the air down for about a minute. It's free and better than nothing :D

trikkonceptz 04-30-2008 05:52 PM

I started doing this also and quickly realized something .... it would be awesome if we could run a/c without the fan. In vent mode as mentioned the a/c remains cold for a while before it become hot, yet you can't activate the a/c without the fan.

They should invent an a/c mode that work with the fresh air vent so when cruising you shouldn't have to use the fan ...

boxchain 04-30-2008 07:44 PM

Quote:

Originally Posted by trikkonceptz (Post 22479)
They should invent an a/c mode that work with the fresh air vent so when cruising you shouldn't have to use the fan ...

You don't want that, it's the same as running AC in your house with the windows open, you'll just pull in more hot humid air, making the AC work less effectively.

DifferentPointofView 04-30-2008 09:47 PM

Quote:

You can switch the AC on during in gear accelerations, taking advantage of DFCO. See:
I've found that when I do that, it isn't good, the volts drop down, and when they do I have less pickup and use more gas. the Jeep also shakes from lack of sparking power. I get the best mpg's when I'm running almost 15 volts. and at night my dash lights are brighter :D

boxchain 04-30-2008 11:59 PM

Guh, I meant decelerations.

Harpo 05-01-2008 07:39 PM

Both work well
 
I got my windows tinted (FormulaOne Pinnacle 35) and it makes a bunch of diffence on how much you have to touch the compressor button. I still use almost exclusively DFCO AC because with my city driving. The DFCO ops are very common, as timing events for long Neutral coasting is few and far between. I use recirc in traffic just to keep the exhaust gases at bay and retain dehumidied air inside.

After the tint install, I've been using the Drivers window down more as the heat load in the car is far lower. I can fix the FF at 1.00gph, and rolldown /rollup the window, and see no change in mpg running at 50mph, my favorite speed. 70% of my return trip in the afternoon are country roads with shade and scenery. I hit the Sirius Blues Channel, roll the window down and set the FF. I'm home before I'm ready to get there!

I had a best on my return trip home today, at ~75° OAT, and average IATs around 105°, window down, 24.9 miles, average 47mph, at 49.5mpg. Summer gas and calming blues, I reckon.

DifferentPointofView 05-01-2008 09:31 PM

I don't like the Tinting law in IL. I can't tint the windows I need most! the fronts!!!! I can tint the rears as dark as I want though, So when I do re-tint them (they're peeling and an awful blue color) I'm going midnight black. darker than 5% limo (2.5%VLT)

8307c4 05-03-2008 09:49 PM

As a general rule, below 55mph open windows, 55+ A/c

However, at 55+ one can also crack the windows vs. opening them completely.
Still doesn't work but so good, once the temps hit 95+ I mean...

DifferentPointofView 05-04-2008 12:28 AM

Quote:

As a general rule, below 55mph open windows, 55+ A/c
If your driving a car, but some cars with larger engines A/C is better than open windows, because the A/C doesn't hit as bad as the drag coefficient hit from open windows.

Trucks, vans and SUV's take the hit real bad from open windows at 55, even at 40. I usually close the windows after I hit 35 and turn on the fan (no A/C). Even from winds blowing the vehicle backwards makes it harder to keep speed, making your vehicle a giant parachute isn't any better.

Lazarus 05-04-2008 09:01 AM

Quote:

Originally Posted by DifferentPointofView (Post 23262)
If your driving a car, but some cars with larger engines A/C is better than open windows, because the A/C doesn't hit as bad as the drag coefficient hit from open windows.

Trucks, vans and SUV's take the hit real bad from open windows at 55, even at 40. I usually close the windows after I hit 35 and turn on the fan (no A/C). Even from winds blowing the vehicle backwards makes it harder to keep speed, making your vehicle a giant parachute isn't any better.

Do any of you have a source for this AC data or is just accepted practice?

DifferentPointofView 05-04-2008 11:38 PM

Mostly practice, but I'll try and show you a source when I have time. Kinda checking in on things real fast right now :D

PaleMelanesian 05-05-2008 10:30 AM

If you crack your window and also crack the right rear, you get a good amount of cross-flow. It gives you much more airflow than just cracking your one window.

Also, use a windshield reflector visor when you park - the car will start out much cooler.

Bror Jace 05-05-2008 10:06 PM

When I had my '95 Civic 5spd, I took it from Albany to West Point on the NY State Thruway to play paintball. On the return trip, it got quite warm so I intermittently used the A/C ... but only when going downhill ... and downhill stretches could be quite long ... lasting a minute or two.

When climbing hills, I turned it back off. With that 1.5L, you could feel the compressor kick in and out ... an obvious difference.

i_am_socket 05-06-2008 10:06 AM

They did a segment on Mythbusters about the window vs A/C thing and came to the same conclusing with windows are better < 45 and A/C is better > 45. I currently do the front passenger & left rear crossflow, but the temps are rising... going to have to get that windshield screen.

ebacherville 05-08-2008 12:18 PM

any one know about moon roofs or sunroofs.. being more efficient than say window use?

I have a moonroof in my benz and its adds a nice breeze but not overly windy like a windows open does.. seems very efficient... it has one of those 1" deflectors in the front that pops up when it opens to deflect the air over the opening in the roof to case a draft out instead of a draft in like a windows does...


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