A/C vs MPG

Yes. Basic physics. It uses energy.

 

The A/C on the Gen II is electrically driven too. The direct electrical variable speed drive allows for a more efficient system, but still there is no free lunch.

Tom

 

Depends on the system (what kind of vehicle) and how much regen you are doing in the Prius.

I think the general consensus is this: Dirving with the A/C vs. the windows down is a wash. So if you must cool down you might as well use the A/C. The A/C will also work to keep you tracion battery (hybrid battery and inverter?) cool and less likely to fail in very hot temps.

So in the grand scheme of things just to the simple math and decide if it is worth losing maybe 1mpg and baking in your car or using the A/C and being comfortable. Even a 2mpg difference in our cars equals VERY little money when you calculate it over a year. 1-2mpg loss on a 16mpg equals a lot more.

Soooo IMO be comfortable and enjoy your car.

 

Probby much less.

 

A non-technical observation. If it was a direct drive off the engine as in the past it uses horsepoer and energy all the time

If it's electric as in now, it still uses energy all the time but it would seem to me that it at times uses "excess" energy at no cost. Granted the batttery takes energy to charge, but if it won't go above 80% anyway then it looks like using the A/C simply means the regen occurs a little longer or more often before the ICE is needed.

In the TCH, the engine at times was propelling the car and charging the battery at the same time when there was spare horsepower generated that was not needed. That seems like free energy as well since you would waste it if it were not being saved in the battery.

 

I find that it doesn't suck the battery power like before ... probably has to do with it moderating itself b/c I stay in "ECO" mode most of the time though. In general driving down the road gliding ... I don't feel like it sucks the battery like it used to.

 

+1. I see that as the only really significant change relating to the A/C. I also see it as a noticeable change, because with the Eco Mode selected the A/C will not run at full out. It may take a bit longer to cool down, but you won't do a big run on the battery. This is pretty significant, because the time the A/C would be running full out is also the time the HSD is focussed more on ICE temp than on battery management. You'll more quickly draw down the battery and require the ICE to run longer without using the A/C with the Eco Mode selected.

I think it is an elegant little solution. Pretty much the opposite of those "Max" settings for A/C in many other cars.

 

Isn't the new ejector, replacing the expansion valve, also a significant change?

 

That's one factor in my reasoning to seek out a plug in conversion. I can charge up the battery and there will be such a huge improvement in capacity that it will compensate for things like that. I guess the drivetrain takes full advantage of the battery when it thinks it's full too. I also heard that a company has unlocked the ability to use both electric motors for driving all at once so that they can reach highway speeds using just the electric motors, safely. (Ewert?) Something like that. I'm going to wait until I see it done with the 2010 though.

 

It looks like a significant engineering change, yes. A 25% reduction in power use also would be significant. What it means in terms of real effect on mileage -- I don't know. I know that a governor on the fan speed and A/C output is going to use considerably less energy at the most critical time.

You bring up a great point, though! I don't have a measure of the energy savings of either one. Perhaps they aren't as one-sided as I had assumed! Thanks for point out yet another step forward found in the 2010 Prius.

 

It's been a while since I had a new car, so perhaps they all do this now, but: I've noticed that the Prius has fairly fine-grained control over fan speed, so you can point the vents at yourself directly without it being too much. WHich lets you run the fan at lower speed and keep the temp at a higher setting, presumably lowering A/C energy consumed.

 

No - even on cars with engine driven compressors there is an electrically operated clutch (that takes only a small amount of power) that controls when it is driven and the belt takes very little power when the clutch is not engaged. However the compressor cannot be driven at optimum speed as with the Prius system and that can improve efficiency.

The compressor is only driven as hard as it needs to be - for example I have a scanguage and with the A/C on full blast it consumes about 12Amps from the battery but when it is running slowly it might only take 2-3 Amps since it not working as hard.

The only case where there is excess energy that will be thrown away is when going down a long steep hill or during braking.

There is NEVER any spare horsepower generated or free energy - if the power is not needed the engine is controlled to produce less power (and so consume less fuel). If electricity is being generated it puts a load on the engine, so the engine has to run harder and consumes more fuel.

The same arguments apply to people who attempt to use EV mode to use "Free energy" - the car will automatically mix in electrical power from the battery with the output of the ICE as needed (in general better than you can).

kevin