Don’t worry, just a little bump - $70 is just around the corner. Short traders just keep making those margin calls, mortgage the house if you have to. Fortunes await you! PO is for pansies and doomers. At $70 short some more ..... it is going back to $22 .... the world is awash with oil ........ reality has nothing to do with it, its all in those charts!!!!!!!!!!
Joined: May 17, 2005 Posts: 386 Location: Northeast Ohio
Posted: Thu Jul 20, 2006 8:06 pm Post subject: Mythbusting: AC and it's effect on gas consumption
Well I see a lot of people mention about how wasteful AC is for gas consuming, and I saw this tidbit today. I thought it made sense as far as drag vs. AC usage.
Quote:
MYTH 5 - Air conditioning wastes gas
Temperatures are in the triple digits in some places nationwide and if you have air conditioning, of course you're going to use it.
But you don't have to feel guilty about cranking up your car's AC. According to Edmunds.com, the air conditioning compressor does pull power from the engine wasting some gas, but the effect is minimal in modern cars. On the other hand, driving with your windows down at high speeds can create an aerodynamic drag.
Several studies say driving without a lead foot results in the most significant gas savings of all. A European study cited by Natural Resources Canada's Office of Energy Efficiency found that rapid acceleration from stoplights and hard braking reduced travel time by just four per cent in city driving – the equivalent of just over a minute every half-hour – but resulted in a 37 per cent jump in fuel consumption and a five-fold increase in toxic emissions.
Edmunds.com, a U.S.-based automotive website, also put this tip to the test four times in November 2005 and found similar savings to be had. "Chances are you've got hybrid-style mileage in your gas pedal foot," the testers concluded. Their recommendation: "Stop driving like a maniac."
Quote:
Minimize air-conditioning use
The experts part company slightly on this one. The CAA advises motorists to use their AC "sparingly." So too does Natural Resources Canada's website, which advises people to instead use their flow-through ventilation on the highway and open a window when driving in the city.
Edmunds.com, however, wasn't completely convinced. Its testers drove almost 100 kilometres in two cars at just over 100 km/h – one had the A/C on and the windows up, and one had the A/C off and the windows down. "The effect [of having the A/C on] appears to be fairly minimal in modern cars," it said.
This has got to take you back to the days with the family on vacation. Dad says, "Turn the A/C off! It wastes gas!" And Mom says, "We can't roll the windows down or everyone on the highway will think we can't afford A/C." And you're in the back roasting, hoping someone will win the argument so you can cool off.
Well, family psychology aside, if dads are still saying this, they aren't necessarily right. While the A/C compressor does pull power from the engine wasting some gas, the effect appears to be fairly minimal in modern cars. And putting the windows down tends to increase drag on most cars, canceling out any measurable gain from turning the A/C off. But this one depends on the model you're driving. When we opened the sunroof in our SUV, the mileage did decrease even with the A/C off. Still, in our experience, it's not worth the argument because you won't save a lot of gas either way. So just do what's comfortable.
_________________ Reality is agreed perception. Unfortunately there is also a reality imposed by nature.
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Joined: Sep 16, 2004 Posts: 4248 Location: Southwest WI
Posted: Thu Jul 20, 2006 8:37 pm Post subject: Re: Mythbusting: AC and it's effect on gas consumption
I use mine all the time in my little 4cyl car. Its a 5 speed and the only bad thing is that i lose a LOT of accelerating power when the AC is on. I turn it off if i need a boost! I pull a boat around quite a bit (around 800pounds) and i hardly even take a hit there (still avg over 30mpg my last tank and that was with a lot of pulling).
Posted: Thu Jul 20, 2006 11:26 pm Post subject: Re: Mythbusting: AC and it's effect on gas consumption
I've done experiments with my car, and at highway speed I haven't been able to detect any difference in gas milage based on whether the AC is on or off. So I'm inclined to agree.
Posted: Sun Jul 23, 2006 10:00 am Post subject: Re: Mythbusting: AC and it's effect on gas consumption
I have a 2004 Civic hybrid that provides real time mpg. The difference on a flat stretch of road with low traffic, consistent speed, low winds with the ac on or off is about 1 mpg. Thats at 55 mph. By the way I average around 60 mpg at 55, 55 mpg at 60, 48 mpg at 65, 40 at 70, and 36 mpg at 75. I think its interesting the effect of wind resistance on efficiency. I get better efficiency in the city then on the interstate at 70 mph
Posted: Tue Jul 25, 2006 7:10 pm Post subject: Re: Mythbusting: AC and it's effect on gas consumption
Those mythbuster guys ran a test of ac vs windows down, and found that it is more efficient to have the windows down:
Episode 22 Mythbusters wrote:
Jamie's A/C car ran out of gas first -- Adam's windows down SUV ran for another 30 laps -- completely contradicting the computer mpg estimate. Computer estimate based on air flow into the engine, so it would appear that it is unable to properly model the difference between A/C and windows down.
There are many factors involved, such as driving style, aerodynamics, efficiency of ac system, etc, so it is difficult to conclusively prove which is more efficient. Highly efficient vehicles like the Honda Insight might have a completely different result compared to a SUV. _________________ "I eat the pretzel, it get stuck in the throat and I pass out..." - George W Bush
March 7, 2007 Remarks by the President to Political Appointees
Last edited by gw on Tue Jul 25, 2006 7:23 pm; edited 1 time in total
Posted: Tue Jul 25, 2006 7:21 pm Post subject: Re: Mythbusting: AC and it's effect on gas consumption
I have done quite a bit of milage testing on my motorcycle and I have found my best milage is at 45 mph. This is the slowest speed that I can maintain in 5th gear without lugging. My milage goes from 40 mpg at 65 to to 58 MPG when driving at 45 mph.
Posted: Tue Jul 25, 2006 7:50 pm Post subject: Re: Mythbusting: AC and it's effect on gas consumption
Etalon wrote:
Why would you have the windows down anyway if the AC is off? Just use the fan without the AC on.
Because a car with closed windows is fundamentally the same design as a solar oven and I don't like being well done. Besides my dog would have heat stroke if I closed the windows. Little heater fan doesn't push nearly enough air. _________________ "I was born in a deep forest
I wish I could live here all my life
I am made from stones and roots
My home, these woods and roads
All my life I loved this sound
Of the woods all around
Eagles fly where the winds blow free" -Korpiklaani
Posted: Sun Aug 06, 2006 9:10 pm Post subject: Re: Mythbusting: AC and it's effect on gas consumption
I have never studied any actual numbers for car AC, but in general:
One Ton of Refrigeration (12,000 Btu/Hr) requires about 1 Horsepower, this is a rule of thumb for an older system that is not very efficient. So modern systems can do betther than that, and one ton is about enough for 400 square feet of office space (high internal loads) or maybe 800 square feet of typical residential space. How many tons refrigeration for a car AC? I have no idea, but 1/2 ton would seem generous for a typical car.
So 1/2 Ton x (max) 1 HP per ton = maybe 1/2 HP and that is at "peak" load or the hottest worst condition.
Compare that to a car engine - maybe 105 HP for a small car engine - and you can see that its a small percentage.
Posted: Mon Aug 07, 2006 7:35 am Post subject: Re: Mythbusting: AC and it's effect on gas consumption
In nearly every car I've personally driven, I can feel the drawdown on the engine when the A/C is engaged vs. not engaged. From crappy little foreign cars, to big American cars, to sports cars.
In addition ... A/C vs. windows down? Where was the "control" group, meaning no A/C and windows up? The proper test would have also involved variations in outside temperature, and variations in the models of cars.
All these tests show is that for the model tested, energy "lost" to A/C is equivalent to efficiency lost in increased aerodynamic drag.
This is nowhere near a scientific test. It's pablum designed to soothe the masses, encouraging driving when it's really hot outside. _________________ "We have seen the enemy, and he is us." -- Walt Kelly
Posted: Mon Aug 07, 2006 7:52 am Post subject: Re: Mythbusting: AC and it's effect on gas consumption
JustinFrankl wrote:
All these tests show is that for the model tested, energy "lost" to A/C is equivalent to efficiency lost in increased aerodynamic drag.
But that's the point, isn't it? When it's hot, you're either going to use A/C or pull the windows down. Nobody is going to voluntarily bake in the car.
I always thought it was around 10-15hp, but I learned that way back when, when automotive a/c compressors were large and inefficient (compared to today's), like the cars and engines of that time.
6hp sounds about right to me, if not a little on the low side.
On the highway, my car shows a roughly 2 mpg decrease on the Inst MPG with a/c on vs. off.
Around town that decrease becomes much more pronounced (~5 mpg). And I can feel the power loss when I turn on the a/c. This is with a 260hp engine/manual transmission in a 3100 lb car.
A 1hp difference is not noticeable to a driver in "seat of the pants" terms. I say this from years of experience in drag racing, and analyzing elapsed times and trap speeds. My personal threshold is about 8-10 hp, as far as being able to "feel" it while driving a car, based on experience. I can go into more detail about how I determined that number if desired.
I can definitely "feel" my a/c slowing the car down, except at full throttle where the computer disengages the compressor for maximum acceleration.
My car always gets better mileage with the a/c turned off. That has been true with every car I've owned that had a/c. More powerful engines seemed to show less effect on mpg than less powerful engines (ie V8 vs I4).
Posted: Mon Aug 07, 2006 10:18 am Post subject: Re: Mythbusting: AC and it's effect on gas consumption
Doly wrote:
JustinFrankl wrote:
All these tests show is that for the model tested, energy "lost" to A/C is equivalent to efficiency lost in increased aerodynamic drag.
But that's the point, isn't it? When it's hot, you're either going to use A/C or pull the windows down. Nobody is going to voluntarily bake in the car.
Of course not. My point was that they weren't going to address that both of these things decreases fuel efficiency, and the real reason is driving in the heat. One could choose to not drive, or bicycle, or walk, or take public transporation, move closer to work, work from home, drive when it's not so hot. That one could choose to organize his/her life in a different manner, a manner that didn't depend on immediate gratification and dependence on the car, was not going be addressed here. _________________ "We have seen the enemy, and he is us." -- Walt Kelly
Joined: May 24, 2004 Posts: 3428 Location: California, USA
Posted: Tue Aug 08, 2006 5:46 am Post subject: Re: Mythbusting: AC and it's effect on gas consumption
For me it comes down to 1) driver safety and 2) arriving on client's sites in a fit condition to do work that demands heavy brainpower.
Without AC, I get worn out and tired, sleepy and spaced-out from the heat. With AC I can stay alert and safe and fit to work. Studies of commercial truckdrivers show similar results.
I do not have AC in my house because, unlike on the road, I can get up and drink unlimited amounts of cold water and take other steps to stay cool (aside from which the house never gets as hot as the vehicle) that aren't possible on the road.
There are other steps that can improve efficiency on the road without impairing safety or job performance. Driving as slowly as the road and traffic conditions allow is the most obvious one. Driving less by whatever means are possible, is the other.
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