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

Gordon McGrew wrote:
> On Thu, 07 Sep 2006 19:11:40 GMT, Matt Ion <soundy@moltenimage.com>
> 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.

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

>
> 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

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

>
> 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

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

>
> 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

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

JXStern wrote:
> On Wed, 06 Sep 2006 19:41:47 GMT, gRmEcMgOrVeEw@mindspring.com (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.....

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

JXStern wrote:
> On Wed, 06 Sep 2006 19:41:47 GMT, gRmEcMgOrVeEw@mindspring.com (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.....

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

JXStern wrote:
> On Wed, 06 Sep 2006 19:41:47 GMT, gRmEcMgOrVeEw@mindspring.com (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.....

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

Michael Pardee wrote:
> A/C is essentially a "minutes per gallon" question while driving
> represents more of a "miles per gallon" cost. I think it's certain
> that at low speeds the efficiency is better with the windows open and
> A/C off while at high speeds the opposite is true. Where that
> changeover point is undoubtedly varies widely from model to model,
> and the "high speed" regime may start above the speed limit for many
> cars.
> When the Mythbusters ran their test they used SUVs which drank a lot
> of gasoline anyway and probably didn't suffer much when the windows
> were open. In addition, the speed was so low A/C would be a clear
> loser.
> Mike

I don't believe the original gas mileage matters, only the differences.

Maybe one can assume that windows open would be less of an effect on a
vehicle with more mass and available torque (unless the vehicle allowed a
higher volume of air)?

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

Michael Pardee wrote:
> A/C is essentially a "minutes per gallon" question while driving
> represents more of a "miles per gallon" cost. I think it's certain
> that at low speeds the efficiency is better with the windows open and
> A/C off while at high speeds the opposite is true. Where that
> changeover point is undoubtedly varies widely from model to model,
> and the "high speed" regime may start above the speed limit for many
> cars.
> When the Mythbusters ran their test they used SUVs which drank a lot
> of gasoline anyway and probably didn't suffer much when the windows
> were open. In addition, the speed was so low A/C would be a clear
> loser.
> Mike

I don't believe the original gas mileage matters, only the differences.

Maybe one can assume that windows open would be less of an effect on a
vehicle with more mass and available torque (unless the vehicle allowed a
higher volume of air)?

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

Michael Pardee wrote:
> A/C is essentially a "minutes per gallon" question while driving
> represents more of a "miles per gallon" cost. I think it's certain
> that at low speeds the efficiency is better with the windows open and
> A/C off while at high speeds the opposite is true. Where that
> changeover point is undoubtedly varies widely from model to model,
> and the "high speed" regime may start above the speed limit for many
> cars.
> When the Mythbusters ran their test they used SUVs which drank a lot
> of gasoline anyway and probably didn't suffer much when the windows
> were open. In addition, the speed was so low A/C would be a clear
> loser.
> Mike

I don't believe the original gas mileage matters, only the differences.

Maybe one can assume that windows open would be less of an effect on a
vehicle with more mass and available torque (unless the vehicle allowed a
higher volume of air)?

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

"L Alpert" <alpertl@xxgmail.com> wrote in message
news:mZxMg.23979$kO3.6534@newssvr12.news.prodigy.c om...
>
> I don't believe the original gas mileage matters, only the differences.
>
> Maybe one can assume that windows open would be less of an effect on a
> vehicle with more mass and available torque (unless the vehicle allowed a
> higher volume of air)?
>
Vehicles with lower fuel economy are less sensitive to differences, because
the losses are already pretty high. In the Toyota Prius fora people are
shocked to find that running the heater can decrease the in-town fuel
economy 10 mpg... the finer the edge the more quickly it dulls.

Mike

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

"L Alpert" <alpertl@xxgmail.com> wrote in message
news:mZxMg.23979$kO3.6534@newssvr12.news.prodigy.c om...
>
> I don't believe the original gas mileage matters, only the differences.
>
> Maybe one can assume that windows open would be less of an effect on a
> vehicle with more mass and available torque (unless the vehicle allowed a
> higher volume of air)?
>
Vehicles with lower fuel economy are less sensitive to differences, because
the losses are already pretty high. In the Toyota Prius fora people are
shocked to find that running the heater can decrease the in-town fuel
economy 10 mpg... the finer the edge the more quickly it dulls.

Mike

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

"L Alpert" <alpertl@xxgmail.com> wrote in message
news:mZxMg.23979$kO3.6534@newssvr12.news.prodigy.c om...
>
> I don't believe the original gas mileage matters, only the differences.
>
> Maybe one can assume that windows open would be less of an effect on a
> vehicle with more mass and available torque (unless the vehicle allowed a
> higher volume of air)?
>
Vehicles with lower fuel economy are less sensitive to differences, because
the losses are already pretty high. In the Toyota Prius fora people are
shocked to find that running the heater can decrease the in-town fuel
economy 10 mpg... the finer the edge the more quickly it dulls.

Mike

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

On Sat, 09 Sep 2006 11:43:49 GMT, "L Alpert" <alpertl@xxgmail.com>
wrote:

>JXStern wrote:
>> On Wed, 06 Sep 2006 19:41:47 GMT, gRmEcMgOrVeEw@mindspring.com (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.....

Better check the date. Tests were run on 8/31, 9/4 and (mostly) 9/5.

The behavior of the Scan Gauge is a little flaky in regards to
measuring fuel consumption. I recalibrate it at every fuel stop and
it can vary by 10% or more. Since the calibration changed between
test sessions, you can't compare the absolute milage figures between
sessions. Also, gradually changing terrain, elevation, wind and
different test speeds complicate the situation. That is why I looked
at relative fuel economy between the sessions. Below is the
individual session data in case you or someone else wants to do more
sophisticated analysis. Just keep the above in mind.

Test 1 8/31 76 mph

A/C Window m/g miles
on closed 18.2 10.0
off closed 19.5 10.0
off wide opn 20.2 10.0
off closed 21.2 10.0
on closed 17.4 10.0
off closed 18.9 10.0
off wide opn 18.7 10.0
on closed 18.8 10.5
off closed 19.7 10.0
off F3 R3* 19.3 10.0
on closed 19.1 10.0
off R6 18.5 10.0


* F3 R3 = front window down 3", Rear window down 3"


Test 2 9/4 75 mph

A/C Window m/g miles
off closed 21.0 10.0
off R4 20.0 10.0
off closed 22.5 8.7
on closed 20.9 10.0
off closed 22.4 11.4
off F2 R4 22.4 10.0
off F2 R4 21.4 11.4
off closed 21.7 10.0
off closed 21.0 10.4

Test 3 9/5 75 mph

A/C Window m/g miles
off closed 19.6 10.0
off R4 20.5 10.0
on closed 18.5 7.8
off closed 20.0 10.0
on closed 19.2 10.2
off R4 20.8 10.1
off closed 21.7 10.0
on closed 20.1 10.0

Test 4 9/5 73 mph flatland

A/C Window m/g miles
off closed 21.6 10.0
off F3 R4 21.1 10.2
on closed 21.2 10.0
off closed 22.5 10.0
off F2 R4 22.4 10.9
on closed 20.6 11.6
off closed 21.4 10.0
off F3 R4 21.7 10.0
on closed 20.6 10.0
off closed 22.8 13.7
off F3 R4 21.4 10.1
on closed 20.3 10.5
off closed 21.6 12.0
off F3 R4 21.8 11.0
on closed 21.4 10.0
off closed 23.4 13.0

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

On Sat, 09 Sep 2006 11:43:49 GMT, "L Alpert" <alpertl@xxgmail.com>
wrote:

>JXStern wrote:
>> On Wed, 06 Sep 2006 19:41:47 GMT, gRmEcMgOrVeEw@mindspring.com (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.....

Better check the date. Tests were run on 8/31, 9/4 and (mostly) 9/5.

The behavior of the Scan Gauge is a little flaky in regards to
measuring fuel consumption. I recalibrate it at every fuel stop and
it can vary by 10% or more. Since the calibration changed between
test sessions, you can't compare the absolute milage figures between
sessions. Also, gradually changing terrain, elevation, wind and
different test speeds complicate the situation. That is why I looked
at relative fuel economy between the sessions. Below is the
individual session data in case you or someone else wants to do more
sophisticated analysis. Just keep the above in mind.

Test 1 8/31 76 mph

A/C Window m/g miles
on closed 18.2 10.0
off closed 19.5 10.0
off wide opn 20.2 10.0
off closed 21.2 10.0
on closed 17.4 10.0
off closed 18.9 10.0
off wide opn 18.7 10.0
on closed 18.8 10.5
off closed 19.7 10.0
off F3 R3* 19.3 10.0
on closed 19.1 10.0
off R6 18.5 10.0


* F3 R3 = front window down 3", Rear window down 3"


Test 2 9/4 75 mph

A/C Window m/g miles
off closed 21.0 10.0
off R4 20.0 10.0
off closed 22.5 8.7
on closed 20.9 10.0
off closed 22.4 11.4
off F2 R4 22.4 10.0
off F2 R4 21.4 11.4
off closed 21.7 10.0
off closed 21.0 10.4

Test 3 9/5 75 mph

A/C Window m/g miles
off closed 19.6 10.0
off R4 20.5 10.0
on closed 18.5 7.8
off closed 20.0 10.0
on closed 19.2 10.2
off R4 20.8 10.1
off closed 21.7 10.0
on closed 20.1 10.0

Test 4 9/5 73 mph flatland

A/C Window m/g miles
off closed 21.6 10.0
off F3 R4 21.1 10.2
on closed 21.2 10.0
off closed 22.5 10.0
off F2 R4 22.4 10.9
on closed 20.6 11.6
off closed 21.4 10.0
off F3 R4 21.7 10.0
on closed 20.6 10.0
off closed 22.8 13.7
off F3 R4 21.4 10.1
on closed 20.3 10.5
off closed 21.6 12.0
off F3 R4 21.8 11.0
on closed 21.4 10.0
off closed 23.4 13.0