Fall and Spring, prime Prius weather

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Old 19 Sep 2011, 03:40 am   #1 (permalink)
bwilson4web
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Default Fall and Spring, prime Prius weather

Over the years, I've plotted MPG vs temperature and found 80-85 F is
an ideal temperature. Temperatures below 55F require longer warm-up
and above 85F often require air conditioning. But between 55-85F, is
the Prius sweet spot.

So today I ran various errands around town: dogs to the nature trail;
shopping at Costco; late lunch at Ed's Pizza; and home again. Being a
Sunday, we didn't have enough pickup trucks towing lawn equipment in
trailers on the Parkway. So I pulled on to the access roads and just
enjoyed the day.

While I was enjoying the drive, I thought about how much we appreciate
our fuelish SUV and gas guzzler owners who pay so much in road taxes.
Of course, it is only fair because they tear-up the roads. There is
justice in their paying the price of their fuelishness.

Bob Wilson
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Old 19 Sep 2011, 06:02 am   #2 (permalink)
Leftie
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Default Re: Fall and Spring, prime Prius weather

bwilson4web wrote:
> Over the years, I've plotted MPG vs temperature and found 80-85 F is
> an ideal temperature. Temperatures below 55F require longer warm-up
> and above 85F often require air conditioning. But between 55-85F, is
> the Prius sweet spot.
>
> So today I ran various errands around town: dogs to the nature trail;
> shopping at Costco; late lunch at Ed's Pizza; and home again. Being a
> Sunday, we didn't have enough pickup trucks towing lawn equipment in
> trailers on the Parkway. So I pulled on to the access roads and just
> enjoyed the day.
>
> While I was enjoying the drive, I thought about how much we appreciate
> our fuelish SUV and gas guzzler owners who pay so much in road taxes.
> Of course, it is only fair because they tear-up the roads. There is
> justice in their paying the price of their fuelishness.
>
> Bob Wilson




Let's be realistic: most people are going to run their A/C long
before it hits 85F. In fact, you are *supposed* to do so, to keep the
battery pack cool. I've found that using the A/C in Eco mode (it cycles
less often and produces a more "cool," less "cold" air stream) makes
little difference in MPG, however. Above about 83F we can get 55MPG
average. below that it's 53-54. Below 50 the mileage starts to take a
real hit.
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Old 19 Sep 2011, 07:04 am   #3 (permalink)
Elmo P. Shagnasty
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Default Re: Fall and Spring, prime Prius weather

In article <1xDdq.22598$9w.21226@newsfe18.iad>, Leftie <No@Thanks.net>
wrote:

> Below 50 the mileage starts to take a
> real hit.


ever run several weeks at 10 degrees F? With high winds?
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Old 19 Sep 2011, 07:19 am   #4 (permalink)
News
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Default Re: Fall and Spring, prime Prius weather

On 9/19/2011 7:04 AM, Elmo P. Shagnasty wrote:
> In article<1xDdq.22598$9w.21226@newsfe18.iad>, Leftie<No@Thanks.net>
> wrote:
>
>> Below 50 the mileage starts to take a
>> real hit.

>
> ever run several weeks at 10 degrees F? With high winds?



What's the MPG hit in the northern winter? Are they still skittish in
cross-winds?
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Old 19 Sep 2011, 08:44 am   #5 (permalink)
bwilson4web
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Default Re: Fall and Spring, prime Prius weather

On Sep 19, 5:02*am, Leftie <N...@Thanks.net> wrote:
> bwilson4web wrote:
> > Over the years, I've plotted MPG vs temperature and found 80-85 F is
> > an ideal temperature. Temperatures below 55F require longer warm-up
> > and above 85F often require air conditioning. But between 55-85F, is
> > the Prius sweet spot.

>

.. . .
>
> * *Let's be realistic: most people are going to run their A/C long
> before it hits 85F. In fact, you are *supposed* to do so, to keep the
> battery pack cool. I've found that using the A/C in Eco mode (it cycles
> less often and produces a more "cool," less "cold" air stream) makes
> little difference in MPG, however. Above about 83F we can get 55MPG
> average. below that it's 53-54. Below 50 the mileage starts to take a
> real hit.


There is an excellent paper on traction battery cooling, NREL/
CP-540-31306, that covers traction battery temperature during the
emissions tests. Also, 202-01-1962, "Thermal Evaluation of Toyota
Prius Battery Pack." But a really important paper, "Thermal Behavior
of Small Nickel/Metal Hydride Battery during Rapid Charge and
DIscharge Cycles, Takuto Araki, Masato Nakayama, Kenichi Fukuda, and
Kazuo Onda, describes 'heat pumping.'

This last paper confirms what I found in a series of tests. How we
drive, especially if we are doing a lot of discharge-charge cycles,
can heat-pump our traction batteries. Charging is exothermic but
discharging also provides some ohmic heating. For example, I was
surprised to find a 'forced charge' can increase the traction battery
temperature by nearly 8-9C:
http://hiwaay.net/~bzwilson/prius/pri_batt_430.jpg

So if one is driving an NHW11 up tall hills at speeds above 60-65 mph,
the traction battery is at the edge of heat-pumping. All it takes is
to avoid this is to drive slower up the hills. Fortunately, many of
these grades have truck climbing lanes and no one blinks an eye if
you're in the climbing lane at 55 mph.

The other hill trick is to use "B" when descending a long, steep hill.
Often I'll just moderate the speed with the shifter and descend with a
minimum heating of the traction battery. But it took a while and
instrumentation to get metrics about this effect.

As for AC, I use it to stay comfortable. If it is dry and the sun
doesn't shine directly on me, up to the low 90s is OK. But some humid
days in the sun, even the upper 70s is too hot. But then I also drive
conservatively and pay attention to heat management. For example,
parking in shade instead of direct sun, using sun shields, and rain
guards on the windows.

A simple trick is to monitor the energy flows. If you are driving so
there is a lot of traction battery discharge and charge activity,
you're starting to 'heat pump' the traction battery. If you can change
to more modest, engine driven acceleration and hill climbs, the
traction battery will run cooler.

One of the reasons I upgraded my pack last year was for improved
thermal management. The modules after 2004 have much lower internal
resistance which reduces ohmic heating. They also have stronger
terminals, more resistant to internal pressure that increases with
heat. Heat is the enemy of long battery health.

Bob Wilson
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Old 19 Sep 2011, 08:56 am   #6 (permalink)
bwilson4web
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Default Re: Fall and Spring, prime Prius weather

On Sep 19, 6:19*am, News <N...@Group.Post> wrote:
> On 9/19/2011 7:04 AM, Elmo P. Shagnasty wrote:
>

.. . .
> What's the MPG hit in the northern winter? *


Here is my graph of MPG vs temperature:
http://hiwaay.net/~bzwilson/prius/pri_mpg_temp_030.jpg

But once we morning temperatures under 70F, I put my radiator block
back in:
http://hiwaay.net/~bzwilson/prius/pri_block_021.jpg

Not only does the engine warm-up faster but it reduces cooling air
drag. A lot of NHW20 owners use pipe insulation in the front grill.

> Are they still skittish in cross-winds?


I understand there is stiffening plate that can be bought for the
NHW20s that improves handling. I has not been a problem with our
NHW11, the sedan body, nor the 1.8L ZVW30. But then my driving tends
to be relaxed, less stressful.

Bob Wilson

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Old 19 Sep 2011, 09:02 am   #7 (permalink)
Elmo P. Shagnasty
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Default Re: Fall and Spring, prime Prius weather

In article <AtWdnRJvJZffuOrTnZ2dnUVZ_uAAAAAA@speakeasy.net> ,
News <News@Group.Post> wrote:

> > ever run several weeks at 10 degrees F? With high winds?

>
>
> What's the MPG hit in the northern winter? Are they still skittish in
> cross-winds?


Dunno about the 2010 on up models, but the 04-09 models are a bit
skittish. OTOH, I've learned to deal with it to the degree that I don't
notice it anymore.

Trust me, 10 deg F and high winds to drive against will pull that baby
down to between 30 and 35 mpg in the blink of an eye.
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Old 19 Sep 2011, 11:58 am   #8 (permalink)
Al Falfa
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Default Re: Fall and Spring, prime Prius weather

"News" wrote in message
news:AtWdnRJvJZffuOrTnZ2dnUVZ_uAAAAAA@speakeasy.ne t...

On 9/19/2011 7:04 AM, Elmo P. Shagnasty wrote:
> In article<1xDdq.22598$9w.21226@newsfe18.iad>, Leftie<No@Thanks.net>
> wrote:
>
>> Below 50 the mileage starts to take a
>> real hit.

>
> ever run several weeks at 10 degrees F? With high winds?



What's the MPG hit in the northern winter? Are they still skittish in
cross-winds?

I've experience a mileage hit of about 5% at temperatures as low as -30F.
No surprise considering the energy required to deal with fluids and cabin
heat at such extremes. Skittish in cross-winds? Nothing compared to the
SUV and Mini-Van I previously owned. As far as wind is concerned, the Prius
does well at minimizing the effect of a headwind and maximizing the effect
of a tail wind. You should drive one some time.



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Old 19 Sep 2011, 12:12 pm   #9 (permalink)
Elmo P. Shagnasty
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Default Re: Fall and Spring, prime Prius weather

In article <4e77682f$1@newsgate.x-privat.org>,
"Al Falfa" <crop@eastforty.fld> wrote:

> Now on my second Prius and living in an area with both wind and temperature
> extremes (western Minnesota) my worst tank ever was 48 mpg. Yes, one can
> achieve lower instantaneous readings. Perhaps this is what you mean by "in
> the blink of an eye."


No, I meant tank average.

Driving on the freeway against headwinds at 10 deg F, with the cabin
heat on becuase *I* want to be warm, is not the Prius's strong suit.

35mpg at best.
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Old 19 Sep 2011, 01:54 pm   #10 (permalink)
Al Falfa
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Default Re: Fall and Spring, prime Prius weather

"Elmo P. Shagnasty" wrote in message
news:elmop-07C3DB.12121019092011@news.eternal-september.org...

In article <4e77682f$1@newsgate.x-privat.org>,
"Al Falfa" <crop@eastforty.fld> wrote:

> Now on my second Prius and living in an area with both wind and
> temperature
> extremes (western Minnesota) my worst tank ever was 48 mpg. Yes, one can
> achieve lower instantaneous readings. Perhaps this is what you mean by
> "in
> the blink of an eye."


No, I meant tank average.

Driving on the freeway against headwinds at 10 deg F, with the cabin
heat on becuase *I* want to be warm, is not the Prius's strong suit.

35mpg at best.

I've never consumed an entire tank at high speed in cold weather against a
strong headwind. I once consumed an entire tank at high speed in warm
weather with a strong tailwind and averaged 70 mpg. I suppose the average
of our experiences would be 52.5 which is very close to the lifetime mileage
(only 20K miles) on my 2010.






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