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Old 06-24-2011, 06:34 AM   #21 (permalink)
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Excessive heat is a major factor in driver fatigue.
A/C can counter that.

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Old 06-24-2011, 08:27 AM   #22 (permalink)
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per: http://www.rospa.com/roadsafety/info...tigue_2011.pdf
Crashes caused by tired drivers are most likely to happen:
*on long journeys on monotonous roads, such as motorways
*between 2am and 6am
*between 2pm and 4pm (especially after eating, or taking even one alcoholic drink)
*after having less sleep than normal
*after drinking alcohol
*if taking medicines that cause drowsiness
*after long working hours or on journeys home after long shifts, especially night shifts

Drivers most at risk
Young male drivers, truck drivers, company car drivers and shift workers are most at risk of falling asleep while driving. However, any driver travelling long distances or when they are tired, is at risk of a sleep related accident.

I don't know if I'm cool with listing AC as "safety equipment" given the extenuating circumstances where it would make a difference and the impact to efficiency. I'm sure there is some safety benefit to having your windows open in even more situations too (can hear better anyway...).
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Old 06-24-2011, 11:41 AM   #23 (permalink)
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It's been pretty hot here in Indiana recently (up in the 90's), and I've been doing without my AC. Usually, it's hottest when I'm leaving work. Here's what I do: Before I start I open up all the doors on my truck for a minute ot two to let it air out (just a minute or two makes a big difference). My first 5-10 miutes are in town, averaging ~20 mph so I crank down my driver's window most of the way. At the slow speeds I figure it's not going to make hardly any difference on aero. Once I get out of town (assuming it's still hot) I just roll down the driver's window an inch or so. For me, that blows air right on my face, so it's not that bad. I'm sure that does hurt my aero just a little bit (although I can't imagine too much), but I'm pretty sure it's a lot less than using the AC.
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Old 06-24-2011, 02:41 PM   #24 (permalink)
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I use the windows to as much as possible. But when the humidity gets high enough, you reach a point where the flow of outside air is not doing any good. So I've been up into the 90s and even low 100s when it is dry and I'm not in direct sunlight with just the windows. But earlier this week, it was 77F, saturation humidity and the sun beaming down on me. No choice, A/C but only set for enough to dry out the air.

Still, there are things to do with A/C:
  1. highest tolerable temperature - no need to have the compressor running all the time.
  2. recirculate - so it can dehumidify the air and keep it in the cabin.
  3. OFF when accelerating or stopped ... just use fan.
  4. Take the higher speed route - A/C is a smaller fraction of the fuel burn.
Well this is how I handle it.

Also in the summer, I park the car in the shade or where it will be shaded when I'm ready to leave. Of course there is a reflective sun-shield put up over the dash. Finally, I have 'rain guards' on both cars to let the hottest of the air escape. But once I get to the car, I turn the key to ignition and roll down all windows. Then I take down the sun screen and setup the iPad touch to play through the cassette adapter. During the car warm-up drive, no A/C until I can tell if it is really necessary.

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Old 06-24-2011, 05:59 PM   #25 (permalink)
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Here's what temp vs mpg looks like with no AC to skew the hot end of the chart. My 15-year-old AC has finally quit so there's no temptation.

This is the average of all my commutes in the last four years. That should be enough to smooth out any other effects and see a general trend.

The slight dip above 80 is because my morning commute is slightly downhill and more efficient, but morning temperatures never get above the low 80's.


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Old 06-24-2011, 06:26 PM   #26 (permalink)
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Quote:
Originally Posted by dcb View Post
Ok, now you are being Satan Nobody has ever tried to paint AC as safety equipment, that is just a little too soft for me. AC is the first thing I disable on my cars (so I can run the defroster fan w/out using the compressor)
(What follows is strident, but it is directed at the attitude among the FE conscious that A/C is somehow optional; not at the author of the quote)

You obviously don't live in a place where heat is a constant, nor have you dealt with heat prostration. Heat kill more North Americans than all other weather events combined. And, as todays vehicle are not designed for ventilation the way they once were, the lack of A/C makes them hotter than in decades past.

I submit that if you worked in a vehicle in the hotter parts of the U.S. that you'd find this premise foolish. Safety when behind the wheel has much to do with being alert. Being drowsy, groggy, hell, just plain sweaty isn't any form of being alert . . where one sweats through his clothing numerous times per day.

There are outdoor jobs advertised here where a requirement is that one is already employed in an outdoor position. The cull is only partly for those who find it uncomfortable.

The control for being cold is easy: add clothing. There is no such e-z control for high heat & humidity.

Let's also, for safety's sake, add in the ability of A/C to greatly reduce dust and other irritants, as well as greatly reduce sound levels. These both wear down any driver quickly. So . . . temps of 90+, high humidity and heavy unavoidable dust. This is no extreme state confined to one area or only a few occupations.

Let me also add that it assumes one will never be old, injured, ill or distracted. Any combination of those, and, in the heat, one will simply not drive (if one is at all smart). A/C is a lifesaver in a larger sense.

No, for A/C, it is better to investigate the operation of components and the system as dealer-spec is often "off". We have all heard of "tolerance stack" and in proper A/C operation, IMO, consider it a given that there is something in even a brand-new vehicle's HVAC system that warrants tuning. The best A/C is the one whose compressor operates for the shortest times; and the blower at the lowest energy draw. Knowing "how" to use it is just as important for longest term efficiency. (Think of this as improvements to rolling resistance, where use is likened to aero penalties; as shorthand). I touched on it in this thread.

HVAC use in a vehicle has to be factored for an enclosed vehicle on the highways, no differently than for cold weather warm-up.

For most of North America there are only a few months of the year where temps are "ideal" from this perspective of FE.

Thus my earlier question about "prediction": vehicle spec first, climate & terrain second, and driver use plus driver skill afterwards are the major determinants . . but is there a short-cut about temps? Vehicle logging seems to be the singular answer (given adequate warmup -- which I posit as being 30-miles, minimum, for any vehicle). Past that, past those, perhaps we can start to make more general statements on weather data.


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Old 06-24-2011, 06:30 PM   #27 (permalink)
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Another data point from the highway in the 04 Odyssey V6 5AT. I've driven this particular route "a few times".

100F and reasonable AC usage is more efficient than 70F and no AC. As soon as you leave the highway it's another story. The numbers swap around with the fuel-sucking AC dominating the equation. Honda engines seem to like warm weather.
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Old 06-24-2011, 07:26 PM   #28 (permalink)
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I've found that A/C in a CTD DODGE almost can't be tracked for highway use. Around town it is more a matter of keeping the interior from heating when doing errands. Someone seeking the final tenths is welcome to put paid to those statements.
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Old 06-24-2011, 10:38 PM   #29 (permalink)
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PaleMelanesian -- Q: what kind of LINEAR regression equation do you get through those data points?

...by my 'eyeball integration' it looks sorta like: MPG = 0.3(ºF)+50

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Old 06-24-2011, 11:02 PM   #30 (permalink)
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Quote:
Originally Posted by PaleMelanesian View Post
Here's what temp vs mpg looks like with no AC to skew the hot end of the chart. My 15-year-old AC has finally quit so there's no temptation.

This is the average of all my commutes in the last four years. That should be enough to smooth out any other effects and see a general trend.

The slight dip above 80 is because my morning commute is slightly downhill and more efficient, but morning temperatures never get above the low 80's.


Attachment 8797
Excellent. Really useful too, since I have the same car, though not the same mileage!

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