Influence of window opening vs. A/C use on fuel economy

On 6 Sep 2006 17:32:02 -0700, wrote:

>Great Post, it's something I always wanted to do but didn't.
>Question, during A/C winows closed, was the Vent on Re-Circulate of
>Fresh Air Position
>Thanks

Fresh Air.

"Elmo P. Shagnasty" > wrote in message
...
> In article > ,
> "R Flowers" > wrote:
>> Let me guess - you're not married?
>
> I am. I am fortunate to be married to a woman who doesn't worry about
> her hair.
>

That's nice. Does she have very short hair? My wife doesn't really 'do' her
hair, but still complains about the wind whipping it around her face.

-- R Flowers

Spdloader wrote:
> Windows down messes up my wife's hair.
>
> A few miles per gallon is cheap for my peace of mind.
>
> Just my .02

Yeah, you have to factor in the cost of a trip to the hairdresser too!

JXStern wrote:

> However, the numbers are small enough, say 2%, that on a $50 tank of
> gas we're talking $1.00. And you sure can't hear the radio with the
> windows open more than a crack at speed.
>
> I do guess the window numbers would be more significant for an Accord
> without the antlers and big slab sides, might get it up to, oh, who
> knows, 5%?!? But presumably the A/C numbers would be the same, which
> would validate the claim which your experiment did not, but would
> still be just about $1.00/tank in the other direction.
>
> OTOH, windows would impose less overhead at slow speeds, say in stop
> and go, ... oh, where will it end?!

I'm with you on this one - yeah, there's a MEASURABLE difference, but is it
really that NOTICEABLE to the average driver? And is the difference worth the
comfort?

It's kinda like the amusement I get from seeing people lining up or going out of
their way to go to a gas station that has prices a few cents less per liter -
with my 50 liter tank, a two-cent difference means a savings of a whole $1.00,
IF I have to fill up from empty. It's just not worth $1.00 of my time to sit
and wait in line or to go out of my way.

Gordon McGrew wrote:
> On 6 Sep 2006 17:32:02 -0700, wrote:
>
> >Great Post, it's something I always wanted to do but didn't.
> >Question, during A/C winows closed, was the Vent on Re-Circulate of
> >Fresh Air Position
> >Thanks
>
> Fresh Air.

I thought the compressor worked less when the Vent is not always
bringing in Warm air from outside, I wonder what difference that would
have made.
Personnally though, I worry about having it in Re-Circulate mode on a
long trip and not getting enought Oxygen and staying alert.
Bg

On 7 Sep 2006 14:03:30 -0700, wrote:

>
>Gordon McGrew wrote:
>> On 6 Sep 2006 17:32:02 -0700, wrote:
>>
>> >Great Post, it's something I always wanted to do but didn't.
>> >Question, during A/C winows closed, was the Vent on Re-Circulate of
>> >Fresh Air Position
>> >Thanks
>>
>> Fresh Air.
>
>I thought the compressor worked less when the Vent is not always
>bringing in Warm air from outside, I wonder what difference that would
>have made.
>Personnally though, I worry about having it in Re-Circulate mode on a
>long trip and not getting enought Oxygen and staying alert.
>Bg

I think it brings in some fresh air even in recirc mode.

Regarding your point on the compressor; This car does not have a
thermostat but I do sometimes sense that the compressor is shutting
off sometimes. Not so much that I can say for sure. Does anyone know
if this car cycles the compressor?

On Thu, 07 Sep 2006 19:11:40 GMT, Matt Ion >
wrote:

>JXStern wrote:
>
>> However, the numbers are small enough, say 2%, that on a $50 tank of
>> gas we're talking $1.00. And you sure can't hear the radio with the
>> windows open more than a crack at speed.
>>
>> I do guess the window numbers would be more significant for an Accord
>> without the antlers and big slab sides, might get it up to, oh, who
>> knows, 5%?!? But presumably the A/C numbers would be the same, which
>> would validate the claim which your experiment did not, but would
>> still be just about $1.00/tank in the other direction.
>>
>> OTOH, windows would impose less overhead at slow speeds, say in stop
>> and go, ... oh, where will it end?!
>
>I'm with you on this one - yeah, there's a MEASURABLE difference, but is it
>really that NOTICEABLE to the average driver? And is the difference worth the
>comfort?

The difference would be about $2 per tank for this vehicle or about
fifty cents an hour. Well worth it when needed - which it really
wasn't on this trip.

If this test were done in an Accord or Civic or even the Ody without
the roof box, the cost per hour might be similar but larger as a
percentage of total fuel cost.




>
>It's kinda like the amusement I get from seeing people lining up or going out of
>their way to go to a gas station that has prices a few cents less per liter -
>with my 50 liter tank, a two-cent difference means a savings of a whole $1.00,
>IF I have to fill up from empty. It's just not worth $1.00 of my time to sit
>and wait in line or to go out of my way.

Gordon McGrew wrote:
> On Thu, 07 Sep 2006 19:11:40 GMT, Matt Ion >
> wrote:
>
>
>>JXStern wrote:
>>
>>
>>>However, the numbers are small enough, say 2%, that on a $50 tank of
>>>gas we're talking $1.00. And you sure can't hear the radio with the
>>>windows open more than a crack at speed.
>>>
>>>I do guess the window numbers would be more significant for an Accord
>>>without the antlers and big slab sides, might get it up to, oh, who
>>>knows, 5%?!? But presumably the A/C numbers would be the same, which
>>>would validate the claim which your experiment did not, but would
>>>still be just about $1.00/tank in the other direction.
>>>
>>>OTOH, windows would impose less overhead at slow speeds, say in stop
>>>and go, ... oh, where will it end?!
>>
>>I'm with you on this one - yeah, there's a MEASURABLE difference, but is it
>>really that NOTICEABLE to the average driver? And is the difference worth the
>>comfort?
>
>
> The difference would be about $2 per tank for this vehicle or about
> fifty cents an hour. Well worth it when needed - which it really
> wasn't on this trip.
>
> If this test were done in an Accord or Civic or even the Ody without
> the roof box, the cost per hour might be similar but larger as a
> percentage of total fuel cost.

Fair'nuff... my Accord gives me usually 500-550km on a tank (80% city driving),
which works out to around 28mpg (alright for an '87 with almost 420,000km), so
it really isn't worth the difference for me.

>
> Regarding your point on the compressor; This car does not have a
> thermostat but I do sometimes sense that the compressor is shutting
> off sometimes. Not so much that I can say for sure. Does anyone know
> if this car cycles the compressor?
>
>


System pressure cycles the compressor, by nature of its design.

Spdloader

JXStern wrote:
> On Wed, 06 Sep 2006 19:41:47 GMT, (Gordon
> McGrew) wrote:
>> It has become popular lately to claim that turning on A/C uses less
>> fuel than opening windows. On a recent round trip to Kansas I used
>> my handy Scan Gauge to check milage under different operating
>> conditions. (What else is there to do driving across Missouri and
>> Kansas?)
> ...
>
> You sir are a gentleman and a scholar.
>
> However, the numbers are small enough, say 2%, that on a $50 tank of
> gas we're talking $1.00. And you sure can't hear the radio with the
> windows open more than a crack at speed.
>
> I do guess the window numbers would be more significant for an Accord
> without the antlers and big slab sides, might get it up to, oh, who
> knows, 5%?!? But presumably the A/C numbers would be the same, which
> would validate the claim which your experiment did not, but would
> still be just about $1.00/tank in the other direction.
>
> OTOH, windows would impose less overhead at slow speeds, say in stop
> and go, ... oh, where will it end?!
>
> J.


It is good information, but the true differences are difficult to assess, as
many segments are averaged together, so one cannot calculate the standard
deviations for each group. It does seem that on 9/7 there was less head
wind.....