Prius Air Conditiner Management

dagerlach · Jun 20, 2006

Does anyone know if the air conditioner compressor is cycled relative to the temperature selected at the AC Control or does the air conditioner use a â€˜mixing boxâ€™ that just cycles the AC compressor at a preset temperature and mixes warm air from the engine coolant system to achieve the selected cabin temperature?

I am wondering if selecting a comfortable temperature will work just as well as manually turning the compressor on and off at the appropriate times to minimize engine and battery loads. For example, descend hills running the AC, or parked at a stoplight, and accelerate w/ the AC off.

Thanks!!

hobbit · Jun 20, 2006

The compressor is a variable-speed synchronous motor, so it doesn't
really "cycle" in the classic sense. Thus, as cabin temp starts
reaching what you asked for, it can gradually draw less power.
.
_H*

TonyPSchaefer · Jun 20, 2006

Let me tell you that I was impressed with the Prius air conditioning system right off the bat. Working for a building controls engineering company, I immediately related with what the Prius was thinking. There are some differences in the details between building controls and car A/C systems, but the basics are pretty much the same.

Basically, it works like this: if the interior of the car is hot and you want it cold, the fan and compressors come on full-bore. On the other hand, if it's cool in the car and you want it slightly cooler, then they all come on slightly. As the temperature in the car reaches the desired setpoint, Prius recognises that it's getting closer and adjusts the compressor and fan accordingly. In that way, it eases into the proper temperature rather than running the fan all-out and then suddenly stopping (which is what most residential air conditioners do).

In an over-simplistic way of thinking of it, think of the fan speed as the proportional difference between SETPOINT and CUR-TEMP. For example:
SETPOINT=65Âº and CUR-TEMP=90Âº creates a high proportional difference resulting in a high fan speed.
SETPOINT=65Âº and CUR-TEMP=70Âº creates a lower proportional difference resulting in lower fan speed.
The Prius most likely recalculates several times per second (I'm guessing)

Secondly, you might notice that the vents blowing the air change. Rather than blowing a bunch of air out of the dashboard vents and straight into your face, Prius will adjust so the air is coming out of the windshield vents and at your feet. As the airflow rate decreases, Prius will reroute the air to the vents. This is very smart since the sensation of comfort is a combination of temperature and air movement. Doing this, Prius can keep you comfortable simply by moving air, chilling it a little less and using less energy.

Just like the variable transmission, you can think of the A/C as a variable system. Basically, if allowed to do it's thing without human interferance, it will work extremely efficiently.

jeromep · Jun 21, 2006

Tony, that is by far the best explaination about A/C logic and operation ever posted here.

SCDrJ · Jun 21, 2006

I am also quite impressed with the system in our new Prius. Automatic AC is a blessing in this car - it works without huge drains on the FE. If you want to preserve more energy for motive force, just adjust your setpoint higher! Our car is getting great FE with AC set 72-74 most of the time. If you can tolerate 78 (or higher), do it! I look at the AC like I do the cruise control... The car tends to know how to control itself better that we do.

Alternatively - you can do what this "extreme" Honda Civic Hybrid owner does (from GreenHybrid):

Re: keeping cool

Ok I've been a bit extreme in the past and have tried many things to avoid summer A/C including pumping ice water through a vinyl hose which is placed against the skin. Although that worked to a limit, I was using a hand pump and was too much distraction for safety.

Summer heat here in GA is hot and very sticky.

What I did....and will surely do this summer as well is to bring one of those small Coleman 6-pack coolers filled 1/3 way with ice & water, but mostly ice.

I also bring a 10 inch square dabbing cloth and swab the head, arms etc as needed.
Really, it worked rather well.

I bring my cooler when its over 90. Next month I'll bring it almost every day.
That's for my own driving solo of course.

With family along I'll cycle the AC as needed while coasting or rolling down a hill.

I'll never turn the compressor on while climing a hill or accelleration.

If friends are along and I want to impress them with the car I'll blast it in full auto for a full "Auto stop" effect. It gets them every time.[/b]
Click to expand...

Not making this up... http://www.greenhybrid.com/discuss/keeping...149.html?page=1

I say you're making a solid conservation effort by having the hybrid in the first place, is 1-2MPG (if that) worth being comfy and arriving to work not being a sweaty mess? Probably.

mattleb · Jun 21, 2006

<div class='quotetop'>QUOTE(TonyPSchaefer @ Jun 20 2006, 02:58 PM) [snapback]274303[/snapback]</div>

Just like the variable transmission, you can think of the A/C as a variable system. Basically, if allowed to do it's thing without human interferance, it will work extremely efficiently.
[/b]
Click to expand...

Just out of curiosity, does this description also apply to the Classic Prius? Since the engine needs to run to keep the AC going in my classic I have acquired the habit of turning off the AC at lights and then turning it back on once moving to keep the engine from turning on and off frequently. In theory it doesnâ€™t hurt the engine to do that but I still donâ€™t like to have it turning on and off at lights just to keep me cool. (I live in Seattle so itâ€™s not THAT hotâ€¦)

AnOldHouse · Jun 21, 2006

Re: keeping cool

Ok I've been a bit extreme in the past and have tried many things to avoid summer A/C including pumping ice water through a vinyl hose which is placed against the skin. Although that worked to a limit, I was using a hand pump and was too much distraction for safety.

Summer heat here in GA is hot and very sticky.

What I did....and will surely do this summer as well is to bring one of those small Coleman 6-pack coolers filled 1/3 way with ice & water, but mostly ice.

I also bring a 10 inch square dabbing cloth and swab the head, arms etc as needed.
Really, it worked rather well.

I bring my cooler when its over 90. Next month I'll bring it almost every day.
That's for my own driving solo of course.

With family along I'll cycle the AC as needed while coasting or rolling down a hill.

I'll never turn the compressor on while climing a hill or accelleration.

If friends are along and I want to impress them with the car I'll blast it in full auto for a full "Auto stop" effect. It gets them every time.[/b]
Click to expand...

After reading this, I'm going to enjoy my fully automatic climate control even more. Really, what does this guy think he's saving by going to this extreme?

Let's say you get 50 MPG without A/C, okay?. Now, let's say the economy hit using A/C is even a full 10% or 5 MPG, so now you're getting 45 MPG. I think that even this is an extreme example, I don't honestly think the hit is anywhere near that large, just using it for argument's sake and to prove my point. Over the period of driving 5,000 miles, that would be an economy loss of 500 miles, or approximately one extra fill up for every 10 you would have made otherwise. I do nearly 30K miles a year myself. I use A/C about 1/3 of the year here, so that's 10,000. So, using A/C would cost me an extra 2 full tanks of gas or about $60 in this obviously way overstated example. So now, is it worth $60 a year for my personal comfort on those hot 10,000 miles or approximately 222 HOURS using an overall an average of 45 MPH? Damn right it is!!!

Lil Mo · Jun 21, 2006

<div class='quotetop'>QUOTE(AnOldHouse @ Jun 21 2006, 07:01 PM) [snapback]275010[/snapback]</div>

After reading this, I'm going to enjoy my fully automatic climate control even more. Really, what does this guy think he's saving by going to this extreme?

Let's say you get 50 MPG without A/C, okay?. Now, let's say the economy hit using A/C is even a full 10% or 5 MPG, so now you're getting 45 MPG. I think that even this is an extreme example, I don't honestly think the hit is anywhere near that large, just using it for argument's sake and to prove my point. Over the period of driving 5,000 miles, that would be an economy loss of 500 miles, or approximately one extra fill up for every 10 you would have made otherwise. I do nearly 30K miles a year myself. I use A/C about 1/3 of the year here, so that's 10,000. So, using A/C would cost me an extra 2 full tanks of gas or about $60 in this obviously way overstated example. So now, is it worth $60 a year for my personal comfort on those hot 10,000 miles or approximately 222 HOURS using an overall an average of 45 MPH? Damn right it is!!!
[/b]
Click to expand...

Here is a price comparison to your $60:

Coleman Quart Blue Take 6 Cooler (also comes in red): $8.99
Bag of Ice: $1.99
Splash of Water from Neighbors Hose: $0.00
Small cloth: $0.50
Swabbing yourself: priceless

AnOldHouse · Jun 21, 2006

<div class='quotetop'>QUOTE(Lil Mo @ Jun 21 2006, 10:24 PM) [snapback]275015[/snapback]</div>

Here is a price comparison to your $60:

Coleman Quart Blue Take 6 Cooler (also comes in red): $8.99
Bag of Ice: $1.99
Splash of Water from Neighbors Hose: $0.00
Small cloth: $0.50
Swabbing yourself: priceless

[/b]
Click to expand...

:lol: :lol: :lol: :lol:

windstrings · Jun 22, 2006

I found that giving a little more charge to my airconditioner made it run cooler, but I have never done it to the prius.

Has anyone charged thier own system before to add more?

ken1784 · Jun 22, 2006

FYI,

Following is detail technical information of the AC from Denso.
http://www.epa.gov/cppd/Presentations/Mats...%20inverter.pdf

Enjoy,
Ken@Japan

daronspicher · Jun 22, 2006

In early experimentation, I tried 'auto' a/c and got the idea I was going to suffer decent mpg penalties. I then went to manual intervention and seemingly notice little or undetectable impact on mpg.

I set the fan on low or the next one up, and I turn on the A/C (not auto, but the lower left AC button). I usually have the temp on 'low'. If I still need a/c and low fan is giving more than I want, I'll bring it up to 68 or 70.

I keep the air location set to feet - vent.

This seemingly doesn't impact much... my 5 minute bars are typical, my overall mpg seemingly hangs in there... I guess I need to run a week on auto and see if the overall impact on the tank is noticeable.

windstrings · Jun 22, 2006

<div class='quotetop'>QUOTE(ken1784 @ Jun 22 2006, 01:01 AM) [snapback]275145[/snapback]</div>

FYI,

Following is detail technical information of the AC from Denso.
http://www.epa.gov/cppd/Presentations/Mats...%20inverter.pdf

Enjoy,
Ken@Japan
[/b]
Click to expand...

Wow..nice manual....

If no one has ever told you Ken... its nice having your input from the other side of the big Pond.

You always seem to be privy to info not easily assessible.

And also a different viewpoint than the trend.

I consider you a valuable asset to PC.

thanks for your input in all your posts!

BVISAILMAN · Jun 22, 2006

The following may be Priceless, but it is also IDIOTIC.......

If you drove 15,000 miles per year, and used your AC for the entire time, and it affected your mileage by 2MPG (most probable), at $3.00 per gal your additional annual fuel cost would be $37.50.

If you mileage was affected by 5mpg (not very likely) your additional annual fuel cost would be $99.00

Now in all probabilty, you would use your AC only for a maximum of half the time so the numbers above would be half......

So in conclusion...for for under $20.00 per year you could be very comfy using your AC...Your bags of ice will cost you more than that each month.

WHAT ARE YOU THINKING? DUHHHHH

Here is a price comparison to your $60:

Coleman Quart Blue Take 6 Cooler (also comes in red): $8.99
Bag of Ice: $1.99
Splash of Water from Neighbors Hose: $0.00
Small cloth: $0.50
Swabbing yourself: priceless

[/quote]

TonyPSchaefer · Jun 22, 2006

Believe it or not, the guy who's using the ice to cool his car is really dead-on accurate and not insane at all. There are many large companies with large cooling requirements that use a strategy known as "Ice Storage" for cooling. And it works exactly the way he says it does but on a considerably grander scale.

Basically, since large installations are charged per kWh and since electricity is cheaper at night, they literally freeze vast amounts of water overnight and store it. Then they use the evaporative properties of the melting ice to pull heat from water pipes and chill the water inside (just like you do with ice in a cooler). That chilled water is passed through the air ducts where the cold water and pipes pull the heat and humidity from the air thus creating cold air to come out of the vents. So: ice chills water, water chills air, air chills occupants. That way, all their electrical expenses come at night during the cheap rates.

I am always amazed at how the same principals can be applied across multiple platforms.

daronspicher · Jun 22, 2006

<div class='quotetop'>QUOTE(TonyPSchaefer @ Jun 22 2006, 12:34 PM) [snapback]275326[/snapback]</div>

Believe it or not, the guy who's using the ice to cool his car is really dead-on accurate and not insane at all. There are many large companies with large cooling requirements that use a strategy known as "Ice Storage" for cooling. And it works exactly the way he says it does but on a considerably grander scale.

Basically, since large installations are charged per kWh and since electricity is cheaper at night, they literally freeze vast amounts of water overnight and store it. Then they use the evaporative properties of the melting ice to pull heat from water pipes and chill the water inside (just like you do with ice in a cooler). That chilled water is passed through the air ducts where the cold water and pipes pull the heat and humidity from the air thus creating cold air to come out of the vents. So: ice chills water, water chills air, air chills occupants. That way, all their electrical expenses come at night during the cheap rates.

I am always amazed at how the same principals can be applied across multiple platforms.
[/b]
Click to expand...

Help me make the leap from cooling this skyscraper to applying it in the prius with a cooler full of ice... Do you get cheaper gas if you fill up at 3am?

richard schumacher · Jun 22, 2006

Ice Chest man is nuts. One accident caused by the distraction of his screwing around with that portable swamp cooler will exceed his fuel savings by orders of magnitude. Does he also cook road kill on his exhaust manifold, I wonder? Sheesh.

tochatihu · Jun 22, 2006

<div class='quotetop'>QUOTE(mattleb @ Jun 21 2006, 06:39 PM) [snapback]274998[/snapback]</div>

Just out of curiosity, does this description also apply to the Classic Prius? Since the engine needs to run to keep the AC going in my classic I have acquired the habit of turning off the AC at lights and then turning it back on once moving to keep the engine from turning on and off frequently...[/b]
Click to expand...

The classic Prius is somewhat different. The compressor is driven by an engine pulley belt, not a dedicated electric motor. Whenever its clutch is engaged, the compressor speed is totally controlled by engine speed.

There is little need for you to shut off the A/C at traffic lights. It will not cause the gas engine to run more (or maybe only a little tiny bit). However if you also push the 'max A/C' button, that will make the gas engine run 'as much as needed' to maintain the cabin temperature that you have selected. That is where the mpgs begin to drop.

brighamwj · Jun 23, 2006

<div class='quotetop'>QUOTE(tochatihu @ Jun 22 2006, 05:47 PM) [snapback]275458[/snapback]</div>

The classic Prius is somewhat different. The compressor is driven by an engine pulley belt, not a dedicated electric motor. Whenever its clutch is engaged, the compressor speed is totally controlled by engine speed.

There is little need for you to shut off the A/C at traffic lights. It will not cause the gas engine to run more (or maybe only a little tiny bit). However if you also push the 'max A/C' button, that will make the gas engine run 'as much as needed' to maintain the cabin temperature that you have selected. That is where the mpgs begin to drop.
[/b]
Click to expand...

I have been turning my new prius a/c off after short periods, but am still only averaging 38 mpg.. I only have 300 miles on the car, but what am I doing wrong? I was hoping for at least 44.

Wildkow · Jun 23, 2006

<div class='quotetop'>QUOTE(richard schumacher @ Jun 22 2006, 01:21 PM) [snapback]275416[/snapback]</div>

Ice Chest man is nuts. One accident caused by the distraction of his screwing around with that portable swamp cooler will exceed his fuel savings by orders of magnitude. Does he also cook road kill on his exhaust manifold, I wonder? Sheesh.
[/b]
Click to expand...

:lol: :lol: :lol:

It was 105F today and will be 109F tomorrow our road kill is already cooked when we pick it up!

Wildkow

p.s. I keep my temp set at 80F and have seen as much as 4 mpg dif playing with the AC. The Valley is pretty flat in these parts so I think it is pretty accurate reading. Just ordered the front sun shield from the online store and seriously thinking of getting the windows tinted.

Wildkow

<div class='quotetop'>QUOTE(brighamwj @ Jun 22 2006, 09:13 PM) [snapback]275638[/snapback]</div>

I have been turning my new prius a/c off after short periods, but am still only averaging 38 mpg.. I only have 300 miles on the car, but what am I doing wrong? I was hoping for at least 44.
[/b]
Click to expand...

Patience with some more breakin miles on the ODO and a little more experience you will get 44+.

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