Air conditioning vs DRL

At one point, it was suggested that disabling DRL's was a fuel saving issue,
and calculations
show that for a large numbers of cars and miles driven, there is a finite
savings in fuel. This
might be statistically and regulatorially significant when combined with
other techniques which
yield small incremental savings.

On the 'Mythbusters' television show (yeah, I know...not scientifically
rigid, but interesting) the
presenters evaluated automobile air conditioning contributions to fuel
consumption. The premise
was that driving with the windows down and air conditioning off should give
better mileage than
driving with the AC on.

In the first test, the fuel economy was estimated using a computer model
which measured an
airflow parameter on the moving car. This test showed that driving with the
windows down
gave somewhat poorer mileage than driving with windows up and AC on.

The second test was more practical. They charged two nominally identical
SUVs with exactly
5 gallons of fuel, and drove them at 45 mph until they went dry. The one
with the AC off and the
windows down continued to lap for 15 miles after the AC on version went
dead.

Whether the results are significant or not is hard to tell. It might,
however, hint that we are less
worried about fossil fuel consumption than we are about keeping cool in a
nice new guzzling SUV.

And if petroleum rises to $80 per barrel as some are predicting, we will
hear the un-cool scream of those who believe it is God's will that Americans
pay $1.00 per gallon for gas.;>)

wrote:

> At one point, it was suggested that disabling DRL's was a fuel saving issue,
> and calculations
> show that for a large numbers of cars and miles driven, there is a finite
> savings in fuel. This
> might be statistically and regulatorially significant when combined with
> other techniques which
> yield small incremental savings.
>
> On the 'Mythbusters' television show (yeah, I know...not scientifically
> rigid, but interesting) the
> presenters evaluated automobile air conditioning contributions to fuel
> consumption. The premise
> was that driving with the windows down and air conditioning off should give
> better mileage than
> driving with the AC on.
>
> In the first test, the fuel economy was estimated using a computer model
> which measured an
> airflow parameter on the moving car. This test showed that driving with the
> windows down
> gave somewhat poorer mileage than driving with windows up and AC on.
>
> The second test was more practical. They charged two nominally identical
> SUVs with exactly
> 5 gallons of fuel, and drove them at 45 mph until they went dry. The one
> with the AC off and the
> windows down continued to lap for 15 miles after the AC on version went
> dead.
>
> Whether the results are significant or not is hard to tell. It might,
> however, hint that we are less
> worried about fossil fuel consumption than we are about keeping cool in a
> nice new guzzling SUV.
>
> And if petroleum rises to $80 per barrel as some are predicting, we will
> hear the un-cool scream of those who believe it is God's will that Americans
> pay $1.00 per gallon for gas.;>)
>
>
I would gladly pay $1 a gallon..................

Bob

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That particular Mythbusters segment was particularly bogus
(even for a program that engages in a lot of bogusity) for
several reasons:

1) No two vehicles are ever "identical." We are talking
about relatively small potential differences in gas mileage.
5 gallons of fuel (less than 100 miles of driving and in two
different vehicles is not statically significant.
Particularly when I know from personal experience that the
fuel mileage of an Expedition increases as the vehicle is
"broken-in." It takes at least 5000 miles of driving to
achieve maximum fuel economy.

2) The maximum speed used was only 45 mph. At this speed
aerodynamics is relatively unimportant.

3) AC usage depends on the heat load. On a relatively cool
cloudy day, with a few passengers, the power consumed by the
AC will be greatly reduced. On a long trip, once the vehicle
has been cooled down, the load on the AC is less.

4) The Mythbusters used Expeditions. Close to a worst case
vehicle for this test (I suppose a V-10 Excursion would have
been worse). Expeditions get horrible gas mileage at best.
They have very large interiors and lots of glass, which
translates into increased loads on the AC. They are
relatively non aerodynamic, so opening the windows might
have less of an effect that opening the windows on a Honda
Accord.

5) They completely ignored the comfort of the driver and
passengers. To do a fair comparison, they should have
adjusted the AC to provide the same inside temperature as
opening the windows. Riding around with the A/C adjusted for
an inside temperature of say 80 degrees and the windows
closed is not the same as riding around with an inside
temperature of 72 degrees with the windows closed.

BTW, I actually enjoy the program and am a regular viewer.
Lots of cool stuff to complain about. I only wish I had been
smart enough to have come up with the idea and sold it to TV
myself.

Regards,

Ed White

wrote:
>
> At one point, it was suggested that disabling DRL's was a fuel saving issue,
> and calculations
> show that for a large numbers of cars and miles driven, there is a finite
> savings in fuel. This
> might be statistically and regulatorially significant when combined with
> other techniques which
> yield small incremental savings.
>
> On the 'Mythbusters' television show (yeah, I know...not scientifically
> rigid, but interesting) the
> presenters evaluated automobile air conditioning contributions to fuel
> consumption. The premise
> was that driving with the windows down and air conditioning off should give
> better mileage than
> driving with the AC on.
>
> In the first test, the fuel economy was estimated using a computer model
> which measured an
> airflow parameter on the moving car. This test showed that driving with the
> windows down
> gave somewhat poorer mileage than driving with windows up and AC on.
>
> The second test was more practical. They charged two nominally identical
> SUVs with exactly
> 5 gallons of fuel, and drove them at 45 mph until they went dry. The one
> with the AC off and the
> windows down continued to lap for 15 miles after the AC on version went
> dead.
>
> Whether the results are significant or not is hard to tell. It might,
> however, hint that we are less
> worried about fossil fuel consumption than we are about keeping cool in a
> nice new guzzling SUV.
>
> And if petroleum rises to $80 per barrel as some are predicting, we will
> hear the un-cool scream of those who believe it is God's will that Americans
> pay $1.00 per gallon for gas.;>)

> 4) The Mythbusters used Expeditions. Close to a worst case
> vehicle for this test


Well, its the BEST vehicle for rigging the test so that AC appears to
dominate :-)

In a very aerodynamic car (say a 1993-up Chrysler LH car) where opening
the windows makes a significant difference in drag, you might get a
completely different result. A car like an Expedition's aero drag is
totally dominated by frontal area, so that opening the windows isn't
going to add much drag, but turning the A/C on will consume more power.

wrote:
> At one point, it was suggested that disabling DRL's was a fuel saving issue,
> and calculations
> show that for a large numbers of cars and miles driven, there is a finite
> savings in fuel. This
> might be statistically and regulatorially significant when combined with
> other techniques which
> yield small incremental savings.
>
> On the 'Mythbusters' television show (yeah, I know...not scientifically
> rigid, but interesting) the
> presenters evaluated automobile air conditioning contributions to fuel
> consumption. The premise
> was that driving with the windows down and air conditioning off should give
> better mileage than
> driving with the AC on.
>

Mythbusters... funny to watch, but they're NOT scientists. Period.

Wife's car - 90 Beretta. Digital dash with instantaneous and average
fuel economy meters. highway driving is about 1-2 mpg better with the
AC on and the windows up. YMMV. (I don't believe in air
conditioning... but on the highway it does appear to use less gas.)

Her parents live 60 miles away in the country so I have driven it lots
and it's a rather boring drive... lots of time to play with the onboard
mpg meter some days...

*** once again - this is for OUR 1990 Beretta. not your car.
Ray

"C. E. White" > wrote in message
...
> That particular Mythbusters segment was particularly bogus
> (even for a program that engages in a lot of bogusity) for
> several reasons:

I second your objections and agree with every one of them.

"At one point, it was suggested that disabling DRL's was a fuel saving
issue,
and calculations show that for a large numbers of cars and miles
driven, there is a finite
savings in fuel. This might be statistically and regulatorially
significant when combined with
other techniques which yield small incremental savings. "

JS> They would have to figure out what the net savings would be. From
the savings in gasoline they would have to subtract the cost of people
injured and killed because they ran into a car that was not visible
because the DRL's were off. Consider not only the4 direct medical
costs but lost wages too.

And as far as saving gasoline by turning the AC off, sure you could
save a little. A far more effective way of saving gasoline is to buy
smaller vehicles with more fuel efficient engines. It doesn't take a
PHD in math to figure out that a Toyota Camry will use a whole lot less
gasoline than a Navigator or Suburban. There will be enough savings to
turn the AC on.

"John S." > wrote in message
oups.com...
> And as far as saving gasoline by turning the AC off, sure you could
> save a little. A far more effective way of saving gasoline is to buy
> smaller vehicles with more fuel efficient engines. It doesn't take a
> PHD in math to figure out that a Toyota Camry will use a whole lot less
> gasoline than a Navigator or Suburban. There will be enough savings to
> turn the AC on.

Very true...Horsepower comes at a price. Even Nissans, Toyotas, and Hondas
now come with engines approaching 300 ponies, and ponies eat.

I hope to find better numbers about the range of energy requirement to drive
typical
automotive air conditioners. I know that heat load, basic design, etc can
widen this
band of data considerably, but there should be studies out there.

As another poster mentioned, the type of vehicle and the speeds involved are
also
part of the equation.

When I was a young boy, air conditioning did not exist, at least in the
homes here. Temperatures
near 100F and humidity levels of about the same number were common. It was
miserable. I
certainly hope we dont have to live that way any more.

John S. wrote:
>
> And as far as saving gasoline by turning the AC off, sure you could
> save a little. A far more effective way of saving gasoline is to buy
> smaller vehicles with more fuel efficient engines. It doesn't take a
> PHD in math to figure out that a Toyota Camry will use a whole lot less
> gasoline than a Navigator or Suburban. There will be enough savings to
> turn the AC on.
>
Yeah, but what mpg will your Camry be getting while it's towing my race
car? (Probably about the same once the hitch tears off....)

"When I was a young boy, air conditioning did not exist, at least in
the
homes here. Temperatures near 100F and humidity levels of about the
same number were common. It was miserable. I certainly hope we dont
have to live that way any more."

JS>, oh yes, I remember that too, although you can get used to quite a
bit. More than once I drove through the California desert towards
Needles in the summer with no air conditioning.
Although I do remember having poor mans AC for about 10 years...a swamp
cooler.

I do think it is a bit silly to spend any time worrying about tiny
reductions in milage when there are obvious ways to make a big dent in
our fuel usage. It's all about buying cars that are appropriate to
usage rather than desire. We've all seen the Navigators and Suburbans
in traffic with one occupant, or the 350hp 2 seat sports cars. There
is no excuse for that kind of excess if making the most of our limited
fossil fuel is a concern. I think the gas guzzler tax is a very good
way to induce people to make the most of their transportation dollars.
It could be applied at the pump...say $1.50 per gallon. Or it could be
applied annually on a scale that is graduated based on EPA combined
milage. And all vehicles should be included.