Windows down or A/C on?

I'd think the main power sapping culprit is the AC compressor. It cycles on and off. The lower you set cabin temp, and the higher the ambient temp, the more often, and longer, it'll be running.

A racing cabin fan isn't as big a power sap, but it is symptomatic of a running near capacity, with an oft cycling compressor.

Also, the AC system is throwing out a lot of heat through its front grill radiator, taxing the effectiveness of the engine and inverter radiators.

I'm not sure the AC has a net benefit, at any time. With the temp set relatively high, at higher speeds where open window drag is more of a factor, it's a close race, other than that....

 

Obviously none of you have bad allergies like I do. Windows open is never an option for people like me, no matter where or when.

Bill the Engineer

 

I agree -- it is not your driving style.

AC however, can be anywhere from a BIG user of energy to not-too-bad, depending how it is used. If you are motivated, find F8L's thread discussing smart AC use. Here is the Cliff notes version:

1. Prevent the car cabin from heating up past ambient when the car is parked
2. Drive with windows open for the first 5 - 10 minutes, then turn on the AC
3. Set AC to auto and temp to ~ 77F when in use in the summer

Not complicated, but it is a different behavior for some people. If your climate is humid the AC demands go way up. And of course the shorter the drive the bigger the fuel economy hit.

 

All of the comments posted are very good ones. Of course, if you have a garage or car
Carport, keep it out of the sun.

 

Here are couple things that affect your mpg that relate to AC:
1. If your trip is 10 miles or less, you will see big drop due to cool the car down. Same go for winter when you heat up the car. Nothing you can do about it.
2. How hot is outside and what your setting temperature will make a big difference. For me I set at 78F. If it is 90 outside, I lost about 5mpg. If I set at 74F, I could lost another 2 mpg.
3. How hot is the car before you drive. My car tinted except for the windshield. If I park the car facing the sun, I lost another 2 mpg to cool down the car and the blazing hot seats. And this is 14 miles trip. The number will be different, depend how far is the trip.

 

Well it was 85 degrees out, A/C set on low, fan halfway, drove 25 minutes and got 70 MPG. Nothing you stated makes sense....

 

The first 8 miles of my drive to work are P&G speed range.Today w/o AC I hit 88.7 mpg, although corrected for elevation it calculates out to 73.5 mpg.

So your result makes sense to me: about a 4% fuel economy hit from AC. That is what I see too, but it is something of a minimum in my experience and requires use of the tactics I've mentioned before, and my dry climate.

 

If 'low' MPG is 45 and 'high' is 90 MPG, then a 5% fuel economy hit at 45 mpg = 10% at 90 mpg. This is just simple math assuming the AC load is the same.

On the way to work I hit 88.7 mpg for the first 8 miles starting from a cool engine. The same return route starting from a warmed up engine was ~ 66 mpg*. This calculates out to 75.7 mpg for a 16 mile rountrip starting from a cool engine w/o AC use. Compared on Orenji's 70 mpg with AC, we are talking about a 6 - 7% fuel economy cost.

The meter said 66.6 mpg, but I was traveling 20 mpg when I started the trip meter and my net battery SOC dropped at least one, and maybe two bars.

 

Think again.

 

Or not.....

 

You have to consider the problem in terms of consumption.
Let's say AC costs 10 units (of energy) a mile;
'poor' fuel economy without AC costs 100 units a mile,
and 'good' fuel economy without AC costs 50 units a mile.

Now figure the percentage increases in fuel consumption:
In the first case consumption increases from 100 -> 110 units per mile,
While in the second case consumption increases from 50 -> 60 units per mile.

 

It will asymptotically approach 100%. More accurately, as the fuel consumption without AC approaches zero, the fuel consumption with AC will approach the consumption of AC.

That seems intuitively obvious.

 

Who are you responding to ?

 

Highroller.

 

Its like a burning cigar, the ratio of O2 × amount of draw will act like or the same as the A/C of a C. The more A/C used in a C the colder the air in the cabin and less fuel in the tank