First, consider the design of modern day automatic climate control systems. The incoming airflow is initially CHILLED to as low a temperature as is possible, as low as 34F, in order to have the highest probability that dehumidification will occur. THEN a selected portion of the CHILLED airflow is routed through the HOT heater core and then remixed with the other bypassed, non-diverted still chilled portion to have a resulting outflow that is very close to the temperature setpoint so as to NOT discomfort the passengers.

So, HOT water flow is always required unless/until the entire modern day concept, design, of automatic climate control systems is rethunk.

A second, not insignificant issue, is the fact that the A/C functionlity is very hard to closely modulate, moderate, absent the above reheat/remix procedure.

So there is no real benefit, for the moment, from having the A/C compressor powered by the hybrid battery.

 

An electric powered AC compressor can be sized closer to the capacity needed by the AC system. The compressor will always run at it's optimum speed, and does not need to be oversized to allow for idling and low rpm operation.

I don't know if these advantages result in a net energy savings or not; but believe it to be a net savings, even when taking into account the need to generate the AC power to run the compressor. However, in my opinion the efficiencies of AC electric motors and generators is in the high 90s, and I believe only a small percentage of power is lost (guessing 10%).

If anyone has real numbers on energy cost or savings I would be interested!

 

True.... but 0.9 (generator) x 0.9 (motor) and you are already down to 81%, factor in the loss for storage and recovery from the battery and you are further down than you might think (only matters when the engine is off admittedly)

I'd be interesting in seeing the actual numbers myself. I'm very curious which way comes out better, but I wouldn't be surpised to find out its better as a direct drive, just inconvenient because its not on when the engine is off. If you are going to leave the engine in MAX setting all the time, then its definitely more efficient to have the electric motor, because you don't have an ICE running JUST to drive the A/C. But in those other two modes.... I'd love to see the numbers.

 

Just some observations:

With the current A/C setup, I either have to A: sweat at long stop lights while the fan recirculates air that is warming rapidly (a car can reach 130F in 15 minutes on a sunny day) because the engine shut off to save gas or B: I can totally negate the point of owning a hybrid while I let the engine idle just to run the A/C system.

If the A/C compressor was electric, like in most newer Toyota vehicles, the A/C would stay cool at stop lights until the battery (either 12V or HV, not sure which) got low enough to trigger an ICE startup. That would still save more gas on hot days compared to running the compressor off of the ICE alone on.

I'm no expert, but I do remember from high school physics that internal combustion engines are far from efficient, about 40%, at turning the energy in gasoline into rotary motion. The rest of the energy is lost as heat. Also, much of the energy that is being output from the engine as torque is being wasted , since it doesn't take the full output of an engine at idle to drive the compressor. The rest is lost as heat if the HV battery can't take any more charge.

While it wouldn't be totally free energy, if the compressor was run off of the HV battery it would still be the most efficient way to do it. Even taking into account conversion losses, HV A/C still has to be more efficient than ICE A/C when the vehicle is in a situation where it would normally run in EV mode. No ICE=saving gas=saving $$. When driving, ICE A/C would be marginally more efficient, but only due to the fact that conversion losses are minimized because it doesn't have to convert to electric energy.

 

When the car is idling.... yes... its a terribly inefficient system. But when the car is going down the road with the engine running at non-idle? Now how often is the car stopped at an intersection or on EV vs going down the road with the engine on?

The 40% loss of the gas engine is irrelevant because either way you get the 40% loss.... every watt of electricity in that battery was created by a wasteful 40% conversion from gasoline. Theres no free electricity. Even regen braking was created initially by the wasteful gas engine pulling you up to speed first, so you could recapture that energy with a loss. If you use it for A/C you are just getting less than 81% of your 40% (that would be a 32% efficiency calculated VERY roughly with no loss for battery conversion). Whereas with a direct drive off the engine you'd be getting the original 40% (minus whatever losses through the clutch).

I'm pointing out its not immediately easy to see the better setup, despite what everyone thinks.... its alot more complicated than that.

When it prevents the engine from going off, you are clearly correct, an electrical system is better. But if you are on a highway? If you can manage to stay off the MAX A/C? The ideal system would be probably be one that can use BOTH an electrical motor and the ICE for power, but that would be more complicated.

 

Ford engineers are smart people.

IF an electric A/C were an advantage, and the advantage out-weighed the cost, then it would have been included. I do not like it when people think they are smarter than a whole team of engineers.

The FEH is the way it is, because it is the BEST way to do things, for the majority of users, in the majority of situations, in the majority of climates.

YOU may be an exception, in the minority, and it may not be best for you.

But if you look at the whole fleet, world-wide, then an ICE based A/C is the best answer, and has the lowest environmental impact to the planet. And isn't that what you really want?

Isn't it better for you to burn an extra ounce of gas at a stoplight to run the A/C a couple months a year, than for 9 others to burn 9 extra ounces of gas to re-charge the battery from using an electrical A/C? ( Plus what if an electrical A/C meant you got a 6 year battery warranty??? Still want it? )

Remember, the A/C in your HOME is the largest power user you own.
Cool air isn't cheap folks. Most (small) home A/C are rated at 10,000 watts.

-John

 

"... a whole team of engineers....."

You apparently forgot an important element...

Plus a whole team of beancounters that have absolute VETO power.

 

Good point willard! Engineers are smart but they're certainly not in charge.

 

I have been an engineer now for over 25 years. I have yet to see anything remotely like that ever happen.

If nothing else, schedule comes into play. Too many times, a better design is forfeited simply because it could not be completed at the same time.

Engineering is compromise, always.

 

Is it possible that Toyota just wanted the occupants of the car to be comfortable?

When I had a Prius, I noticed that the elec AC drained the battery quickly when sitting. And the system, overall, was not nearly as effective as the one in my 2008 FEH. But despite this, it sure was nice to have cooling (even weak cooling) when the ICE was off.

Most of these posts have been about efficiency, but I wonder if comfort was not a big motivator for Toyota? Maybe they justified the cost of elec AC based partly on the comfort factor. Maybe the no-AC-at-stoplights problem was on their "to do" list.