And keep in mind the weight disparaty between the Prius and the FEH/MMH, the latter clearly needs more battery in reserve.

"...I wonder if comfort....motivator.....Toyota..."

Actually the FEH/MMH climate control system has a greater ability for comfort insofar as the climate control is concerned. To properly moderate, modulate, the A/C, COOLING aspects it takes HOT water from the engine cooling water jacket. In the majority of A/C systems as the refrigerant transistions from a liquid to a gas within the evaporator sub-freezing temperatures are ALWAYS the result and that can be VERY discomforting if the reheat/remix method is not used.

When I want to raise the efficiency of the A/C functionality of my automatic climate control dramatically I lower the setpoint to max cooling and then use the blower speed to regulate my overall comfort level, effectively bypassing the reheat/remix function. Since the exiting airflow in this mode is then always so cold I always route it through the footwell vents.

 

I can't disagree with that.... I think the "rub" being expressed is more where its stated in some posts that an all electric system IS DEFINITELY more efficient than a mechanical one, usually stating that an ICE has much less efficiency than an electric motor (which it does... but misses the point that the gas engine losses figure in either way). The argument has come up several times. Its simply NOT OBVIOUS that that an electric system is better efficiency wise. Its entirely possible the ICE system is more efficient in normal use (not during "idle" of course) and that Toyota chose an electric system for passenger comfort reasons (as mtberman says). I can't tell you one way or the other without alot more knowledge and work on the topic.... so it is presumptuous of us to make a blanket assumption that the Ford engineers chose the more inefficient way.... They may have... for the exact reasons you state, but they might not have.

 

At least the way I am seeing it, it isn't electric motor vs. ICE PTO, it is all in the compressor design.

A compressor designed to work off of an ICE PTO, has all sorts of other problems to over come. These are such as an electro-mechanical clutch, and having to effectively work at all sort of vastly different RPM's. Being physically attached to the ICE itself, the compressor has to endure a lot of shacking and vibrating, without blowing a seal or ring.

That all goes away with a dedicated electric motor driven compressor.

Then that opens up a lot of enhancement possibilities, such as having a variable speed electric motor, that varies the compressor speed as per the current cooling load requirements (less power for 85 deg days, more power for 110 deg days). I know that, by itself, it adds a lot of efficiency and that's why it is now found in home central A/C system's compressors.

 

And a 2000 sq/ft home requires an electrical A/C rated at 10,000 watts.
The car system would be smaller, but then again,
How big is the FEH battery?
I ask again, would you trade an electrical A/C for a 6 year battery pack?
( Vs a 10 year one )

 

There is another consideration. There's a strong possibility Toyota has patented the electrically powered AC system they are using. IIRC it is powered by the high voltage system, not by the 12v system (the power steering and the brake accumulator are 12v) to get better efficiency, which also makes it a pretty unique (thus patentable) idea. Since electric AC didn't appear in Prius until the 2004 model year, it's likely the patents for it were not included in the licensing negotiations between Toyota and Ford.

Also consider that Toyota uses a larger capacity battery than the FEH and you have another reason not to use electric AC. Personally I think it'd be an improvement to use a fixed speed compressor running off the high voltage system, it could be more conservatively sized and still be effective.

 

Hello all,
Just FYI, following is good presentation slides about electric A/C for Prius.
http://www.epa.gov/cppd/Presentation...20inverter.pdf
All Toyota hybrid vehicles use such electric A/C.

Ken@Japan

 

Nice to see some data.... If I'm reading it right it seems like they say it saves MPG, but on slide six its shown that it takes slightly MORE energy to run a very well built, efficient A/C electrically (In my opinion I'd call it a wash its so close) but it doesn't save energy when the ICE is running.

So how do they say it saves MPG....My guess would be If you are going to set the temp to 70F and HOLD it there no matter what even when the engine is normally off, they are saying the engine having to kick on kills you and the electric A/C ends up more efficient because the engine has to idle to power it. But overall the conversion of energy is a loss when the engine is on.

For those of us that can stand warming up a bit at intersections it might not be so clear.

In any case, just so I don't get flamed more than necessary... YES if they put that kind of time in it and designed an electric system like THIS, I would want it in my FEH. Comfort has its advantages, and it looks like a wash when the ICE is on.

Incidentally, for those that say our system blows hot air almost immediately when the engine shuts off. In recirculate mode I find it stays pretty cold for a decent amount of time.... the problem is that the system freezes me out so bad when the ICE is running that I turn the heat selector up a bit, now when the ICE kicks off I'm actually blowing HEATED air into the cabin .... I have to reach over and twist the control to complete cold to stay cool for a bit. It would have been nice to have the mixing baffle flop to complete cold when the ICE kicked off.

 

From a second-hand point of view, it looks like even Toyota had to leave the task of developing an electric AC to its second-generation hybrid design. Obviously Ford had to limit some of the features it was able to design into its first-generation hybrid...in order to get it to market as soon as it did. I don't think Ford was "shopping Toyota's patents" for things to license as it developed the FEH. The possible infringement on some of Toyota's patents was realized after Ford finished the FEH. Licenses were traded between Toyota hybrid technology and Ford diesel technology at that point.

 

FWIW the 08's automatic setup partly addresses this concern by making changes as you drive. On ICE shutdown, outlet air warms and it sets the fan to medium-low. When the ICE comes back on and outlet air cools, it increases fan speed and then moderates it as the cabin temp stabilizes again. Not perfect, but less hassle and only noticeable on relatively hot/humid days and during longish periods of ICE-off.

We have not had any seriously hot weather in my area yet, but that's what I've noticed so far.

I would much prefer an elec compressor for the comfort factor. Not having one was the #1 reason I didn't buy a '05-'07 FEH. Once I tried the '08 setup with the "ECON" button, I made peace with it and bought one. Although I'm still not thrilled with the engine-driven AC, I will say that it's an excellent system as long as the engine's on.

 

I believe we have to refer to the slide five(engine running rate) as well, then the result is on slide seven, 19% overall gain.

My Prius experience is...
During parking waiting for a person in sunshine, the HV battery went low when A/C was on. The ICE run for a while to charge the battery when battery SOC became below 50%.
I don't have actual measurement, but my feeling is the ICE runs 10-15 seconds every 1-2 minutes, so the ICE runs only approximately 5-10% of time during such stand still.

The classic Prius had an engine driven A/C, now all Toyota hybrid vehicles have the electric A/C. I believe the electric A/C is very efficient, therefore Toyota decided to use it.

Ken@Japan