# my wife's Prius



## smirnov3 (Sep 6, 2007)

ok, I know there has been a lot of back and forth on the Prius here in recent months, but we just got one, and I want to give you guys my take on it.

1) It's BIG.
Our other car is a Ford focus, and the Prius is roomier. The trunk is a little shallow, but since it's a hatchback, so it's tolerable.

2) I don't know what idiot came up with the rear window, but it's insufficient. And that second 'trunk' window doesn't help. And the 'back up camera' that comes standard is like looking through a keyhole.

3) We got decent gas milage - 50+ MPG cruising from Boston up into NH / White Mountains. And on city streets, it's in the high 50s. the ideal speed for this car is 40 MPH, with some stop & go.

4) the AC controls are a pain.  they are all controlled by the touch screen computer. But once I set the AC, I usually witch either to the music control, or the fuel economy display. 

You forget that the AC is on.  I wonder how many people drive around with their AC set on low & don't even know it.


All in all, it's a good family car - big enough to car-pool the kids, and still get better gas milage than most everything else on the road.

And Toyota is planning to release a smaller version (with mayde a diesel engine) in a couple of years for those of us that just need something to get to work and back.


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## R&D Guy (Sep 7, 2007)

I think the ultimate in MPG would be a diesel hybrid seeing how diesel's get such good mileage alone.  One thing I wonder about is how long the mileage stays good.  For example, rechargable batteries can put out power for a long time when they are new, but the older they get the more fequently you have to charge them.  I'd think at some point the MPG would drop in a hybrid and you'd need to replace all the batteries.  Seen any thing like that?


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## begreen (Sep 7, 2007)

The car, like any, has it's pluses and minuses. As you are discovering, there's a lot of relearning to do with it. The car is anything but conventional. 

It is quite roomy, and rated mid-sized. The back seat has nice legroom. Yep, rear vision sucks. You get very used to using the side mirrors extensively. Set them a little wider than normal and try it. Your mileage will increase as the engine breaks in. Set up the tire pressure to about 40 lbs. all around for a bit more. I don't like the digital a/c controls either. But because the a/c is electric drive, no worry with running it all the time. Your mileage is not affected by having it on. Rumor is there will be a plugin hybrid version coming next and maybe a wagon. That will be interesting.

Edit: I was wrong. The AC running does have a penalty. It can affect mileage by as much as 10-20%. Thanks Colin for pointing out this.


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## Metal (Sep 7, 2007)

I have heard that hybrids have been found to be a leading contributor to smug.  Have you noticed this?  They had a whole show about it on South Park the other night.


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## KeithO (Sep 8, 2007)

"Smug" you say ?   I guess at the pump one can be "smug" for sure...


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## begreen (Sep 8, 2007)

Hard to get smug around here. Too many Priuses to count. Our car is dusty and dirty and just doing it's job until I take the time to wash it.


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## PAJerry (Sep 8, 2007)

I'm beginning to treat mine like a bit of a truck. Real good for hauling lumber and downspouts with all the seats folded flat. Don't know about firewood, but after it hits 100k mi., I might give it a try. Should be there by next spring.


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## R&D Guy (Sep 9, 2007)

Metal said:
			
		

> I have heard that hybrids have been found to be a leading contributor to smug.  Have you noticed this?  They had a whole show about it on South Park the other night.



LMAO!  Yeah I saw that too - very funny.


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## DiscoInferno (Sep 10, 2007)

BeGreen said:
			
		

> I don't like the digital a/c controls either. But because the a/c is electric drive, no worry with running it all the time. Your mileage is not affected by having it on.



Is electric drive somehow much more efficient?  It may not directly load the engine or drive motor, but any a/c does require power which has to come from gasoline (barring a plug-in mod).  The net mileage loss might be small, but I wouldn't have thought it had much to do with how it's driven.


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## begreen (Sep 10, 2007)

The car is designed so that systems (power steering, brakes, a/c etc.) are not affected when the car is in all electric mode. The car can be running with the gas motor off for extended periods of time, when city driving, coming down a hill, etc., so it's important that these system work at all times, regardless of electric or gas mode. 

The electric power comes from the high voltage battery system which is charged by the engine, when running - and by regenerative braking. The braking charge is essentially free. It is using the power generation mode of the electric drive to slow the car down. In a conventional car, this braking energy is unused and dissipated as heat. This is pretty efficient, especially in stop and go traffic and in hilly areas. A nice side benefit is that the Prius gets great brake lifetime. I've read of folks with over 80k on their brakes and still going strong.


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## DiscoInferno (Sep 10, 2007)

Right, so using the a/c will run the batteries down faster, requiring the engine to run longer, consuming more gasoline.  There's no free lunch, although it may be a cheap lunch.  

On my little pickup the a/c only costs maybe 1 MPG, despite adding a quite noticeable load to the engine.


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## TMonter (Sep 10, 2007)

If Toyota release the Prius in a true Wagon, that will be our next car. If not we're looking into a Rav 4 or Highlander because of space considerations.

However, when we buy our next car I will be paying cash. I refuse to finance anything anymore.


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## begreen (Sep 11, 2007)

DiscoInferno said:
			
		

> Right, so using the a/c will run the batteries down faster, requiring the engine to run longer, consuming more gasoline.  There's no free lunch, although it may be a cheap lunch.
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> On my little pickup the a/c only costs maybe 1 MPG, despite adding a quite noticeable load to the engine.



Not necessarily, unless the car is sitting still. Did you read the part about regenerative braking charging? Not all charging is coming from the engine. And the Prius generator is not your typical belt driven affair. 

Regardless, I'm not sure running a car with the engine continuously to keep cool is more efficient than Toyota's electric A/C. Considering most engines are oversized in America, I doubt it.


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## DiscoInferno (Sep 11, 2007)

BeGreen said:
			
		

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Regenerative braking turns kinetic energy back into electric potential energy.  Where did that kinetic energy come from?  From the gas engine, or from the electric motor run from batteries charged by the gas engine.  Unless the prius has been modified, all power/energy ultimately comes from the gas engine.  The rest (braking, charging) is just shuffling that same power around.  The prius may be more efficient than traditional cars, but it still obeys the laws of thermodynamics.

So, I claim the following:

1.  Gasoline is the only external source of power for the prius
2.  The A/C uses power, and dumps it as heat to the environment (i.e. the power is lost forever)
3.  Ergo, running the A/C indirectly uses gasoline, and thus reduces mileage, however slightly.

What's more, if the prius has electric heat then it loses mileage there too.  (But is of course still far more efficient than a conventional car, which generates lots of heat whether you want it or not.)

BTW - A little googling found this discussion, which seems to indicate that running the A/C can cause a huge hit in hybrid mileage.
http://www.greenhybrid.com/discuss/f22/how-much-air-conditioner-affects-mpg-1001/


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## smirnov3 (Sep 11, 2007)

TMonter said:
			
		

> However, when we buy our next car I will be paying cash. I refuse to finance anything anymore.



Good for you!

But don't tell the dealer that until half way through the negotiations, especially if you are buying a used car - the auto dealers subside the cost of the loan by raising the price of the car (ie they will raise the sticker price so they can give you a better rate).

This is true for both new & used cars, but with new cars, it's set up by the manufacturere, so the dealer has very little control over it, but with used cars, it's often the dealership that's financing the loans, so if you pay cash, you save the dealer money, and he can pass that on to you.


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## smirnov3 (Sep 11, 2007)

DiscoInferno said:
			
		

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Yup, there is no Free lunch, not even with a Prius.

What the Prius does is recycle - it reuses energy that in other cars is wasted


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## cbrodsky (Sep 12, 2007)

One of the earlier posts said running the A/C doesn't hurt mileage on a hybrid because it's electric.

That statement is not true - if you run the A/C, you're using up electrical power that otherwise could be used to help propel the car, so your battery charge will not last as long.  That same power storage is what in theory gives you better mileage, but if you spend it elsewhere, you give up some of that benefit.

I will definitely be interested in an AWD plug-in hybrid if/when they come available because then they'll finally have adequate power storage to displace all these loads into renewable electric sources.  For now, I'd get nothing out of current hybrids on my 25 mile commute that is 95% highway driving in cruise control.  The fact that my brakes don't have any measurable wear after 50K miles tells me just how little opportunity I'd gain with regenerative braking alone.  That makes current hybrids a dubious case for us drivers with some of the longest commutes.

Audi is supposedly bringing in clean A4 diesels in the next year or so, as I'm sure others will.  They're already able to deliver low 30s on the A4 with a 200HP gas engine, AWD drivetrain and a not-so-light sedan with top of the line safety ratings.  If they get to high 30s with biodiesel and possibly offer an even smaller engine to push into the 40s as BMW is doing in Europe on the 320d, we will finally get some good green car options in the northeast where AWD is often a requirement for car buyers.

I suspect the current hybrid technology is only the first in a huge wave of options that are coming where we will choose between hybrid, plug-in hybrid, diesel, diesel hybrid, and the choice that is right will depend a lot on your driving habits vs today's limited choices that don't fit many people.

-Colin


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## begreen (Sep 12, 2007)

DiscoInferno said:
			
		

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No argument with your logic. You are correct. But the Prius and some other hybrids do it much more efficiently than the current standard passenger car that needs the gas engine running to get any A/C at all. Will there be better technologies coming? I sure hope so. In the meantime, Toyota has created a technological wonder. It is exceptionally reliable and efficient under a very wide range of daily driving circumstances. We need a lot more of this.


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## cbrodsky (Sep 12, 2007)

BeGreen said:
			
		

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I'm still not sure I buy the argument that having an electrical compressor is that much more efficient.  Most of the time, your engine is going to be on anyway in a Prius - it's not really an electric car.  Possible exception is the person that drives most of their commute in stop and go traffic.  So your gas engine is already on most of the time for a typical commuter.

Then the question is are you better off just adding another pulley to that already running engine for direct drive of an A/C compressor, or instead to an alternator that generates electricity, that in turn powers a compressor, possibly with losses as it goes through the battery charging cycle?  (remember, the "free" power in these cars from braking is needed to get any mileage benefit - if you burn it on A/C, then you're still paying a price)

I can't even measure a difference in mileage when I run with or without the direct drive A/C compressor on our car - I'm sure there is a fraction of a MPG impact, but if I eliminate 5% off that fraction of a MPG for the time I'm at a stoplight, did I really save much?  I don't think so - maybe 0.05 MPG at best.

I think when you get into plug-in hybrids where the car can truly propel itself off electric for extended periods, then the argument may be quite different.  But I think this is oversold in the current generation of hybrids.

-Colin


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## DiscoInferno (Sep 12, 2007)

One thing stacked against efficient cars is that the amount of power (gas) the A/C unit uses is basically fixed; thus it represents a higher percentage hit on mileage the higher the mileage of the car.  So if they ever make the mythical 100 MPG car, running the A/C will destroy its mileage.  One solution might be better insulation and low-e glass, just like in homes.


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## begreen (Sep 12, 2007)

NY Soapstone said:
			
		

> I'm still not sure I buy the argument that having an electrical compressor is that much more efficient.  Most of the time, your engine is going to be on anyway in a Prius - it's not really an electric car.  Possible exception is the person that drives most of their commute in stop and go traffic.  So your gas engine is already on most of the time for a typical commuter.
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> Then the question is are you better off just adding another pulley to that already running engine for direct drive of an A/C compressor, or instead to an alternator that generates electricity, that in turn powers a compressor, possibly with losses as it goes through the battery charging cycle?  (remember, the "free" power in these cars from braking is needed to get any mileage benefit - if you burn it on A/C, then you're still paying a price)
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The amount of time that the internal combustion engine is going is entirely dependent on one's driving. If one's driving is all freeway, then you are correct. But it is not so for hilly areas or urban driving. For us, living in hilly country, the engine shuts off a lot. Actually, you change your driving style to maximize the electric only cycles. On my normal trip into town I have it down to a science. As long as I stay under about 42 and the terrain is level, I can coast for about a mile or two on electric. Every downhill run is on electric only. If I were driving around Millbrook I know I would be on electric only a lot. Maybe not on the uphill sections of the Taconic or Rt. 22, but certainly on the downhill areas and some flats. 

From an energy consumption POV you are probably correct. An electric AC normally might not be that much more efficient. As stated, the purpose is to provide system continuity in non-ICE modes. That said, Toyota engineered every piece of the car to save weight and improve efficiency, so I wouldn't be surprised if the electric A/C system is state of the art to further extend efficiency. Also, no belts for the AC mean less loss due to friction, less weight too.

edit: Yes the Prius AC system is much more advanced than the average auto AC. It uses a high efficiency, variable speed, variable scroll, synchronous compressor to tailor the output to the load. So as the car cools down the AC uses less power. The computer management for the car's HVAC is pretty slick. In Auto mode it automatically reduces fan speed too. Initially it blast cold air out the foot and upper vents. Then as the car cools down it shifts the output to the top vents only. The system automatically monitors temperature and humidity.


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## TMonter (Sep 12, 2007)

Actually the original Prius didn't have an electric compressor.


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## begreen (Sep 12, 2007)

DiscoInferno said:
			
		

> One thing stacked against efficient cars is that the amount of power (gas) the A/C unit uses is basically fixed; thus it represents a higher percentage hit on mileage the higher the mileage of the car.  So if they ever make the mythical 100 MPG car, running the A/C will destroy its mileage.  One solution might be better insulation and low-e glass, just like in homes.



Good observations DI. There is no free lunch. We will pay for our creature comforts one way or the other. From what I can tell A/C on average will be about a 10-20% average fuel economy penalty. I can't speak from personal experience as we rarely run the AC. We use it more in the winter for defogging, than any other time of the year. For better economy, the best thing one can do is set the AC temperature higher. If it's 90 outside and 90% humidity, setting the the car temp to 78 degrees should feel balmy. 

http://www.hybridcars.com/gas-mileage-factors/airconditioning.html

PS: Colin, thanks for pointing this out. I've added a correction to the original post. If you poll users of Priuses in hot climates, that run AC all the time, they still are getting great mileage. FWIW, Priuses are very popular in the southern states. Especially southern CA and TX.


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