AC operation - parasitic loss?
 

Does the hybrid suffer from this since the accessories are powered by an electric motor v belt driven? I just don't notice the typical sensation you feel in throttle input and engine performance. Thank you.

Re: AC operation - parasitic loss?
 

Great question. The 2 Mode AC compressor is powered by the high voltage DC battery directly. No belt.

That's why you can have relatively good cool with the engine OFF in Auto Stop.

The typical system like my 2001 Suburban has a compressor that is a little too small at engine idle so it warms up a little at stop lights. Then the compressor is too BIG at freeway speeds.

Your Tahoe compressor is variable depending on load not engine RPM. So in other vehilces the too BIG compressor cycles on and off. You can feel the change in engine drag as it starts abruptly. In a Chevy Tracker I had, I would use the AC as a poor mans Jake Brake on long down grades in the Blue Ridge mtns.

So in Coral Gables Florida on a 95 degree 95% humidity day, your compressor may draw 5 kW. Then out on the freeway after cabin cool down it can drop to 300 W or 0.3kW. Burning gasoline with the engine and taking the ~20% gasoline to electricity efficiency drop is made up by the much wider dynamic range of the HV electric compressors. Same for electric steering. My Suburban is stealing 200 watts on flat straight roads just spinning the belt and pump. Your 42V electric steering = 0W straight and flat.

Energy and time is still power and it ain't FREE! It's all about optimizing your power. Now if that CD or DVD would come out cooler than a fresh baked pizza... there is some more energy to optimize.

Re: AC operation - parasitic loss?
 

So mpg is in fact decreased by some slight amount but on the hybrid you won't notice that power loss or sensation when the ac compressor kicks in?

In my smaller gas only car, I can definitely tell. Shift points are different when rev matching. Starting from a stop I can feel the engine slightly bogged down. Wot it's all good.

Thank you.

parasitic loss?
 

Idoubt that there is ANY parasitic loss for the ac.

Re: AC operation - parasitic loss?
 

so do you gents keep ac on all the time in auto?

Re: AC operation - parasitic loss?
 

I keep A/C on all the time in auto mode. no difference in power or loss. the only time I noticed and nearly turned off the A/C is when I was in traffic in NV for almost three hours at 105F in idling traffic. I was cycling the DIC to check tranny and engine temp and it was the highest I have recorded and noticed. the hybrid did not lose steam or overheat but I know sooner or later in gridlock it will. The A/C was on 68F all the time!

Re: AC operation - parasitic loss?
 

Some of the most efficient gasoline engines today use about 86 grams of fuel per kilowatt-hour. Assuming 80% engine to HV DC generation that’s 86 grams for 800 watt-hours. Now the HV DC to AC compressor motor is about 75%. Now that 86 grams buys you 600 watt-hours to run AC. On the new Texas Interstate at 85 mph and AC on 68F you might burn 43 grams of fuel in the 85 miles to supply the approximate 300 watt-hours to run the compressor. ~ 2736 grams per gallon means 1/63 of a gallon.
Doubtful most reading this can measure that. Now in Laughlin NV on a cabin pull down you might need 5 kW of compressor power. Coral Gables Florida on a 95F 96%RH day 6 kW. But only for a short time.

Re: AC operation - parasitic loss?
 

I'm lost with all the numbers. but I know even with the electric compressor the A/C is still cold like a regular one.

Re: AC operation - parasitic loss?
 

Most don't care how it works. Just that it works! :shade:

But energy like pennies adds up to something significant if you let too many pile up.;)

Re: AC operation - parasitic loss?
 

i've noticed that in cold weather, the ac doesn't automatically light up when set to auto. what's the threshold?