A/C on Fuel Economy

i figure 5-10% depending on hwy or city driving.

 

I see no reduction in fuel economy, I use the AC more in my Prius than any other car I owned.

 

Obviously air conditioning uses some energy, but the amount is hard to predict. The Prius uses a variable speed electrically powered A/C compressor, so the compressor is used as little or as much as needed. Light use means a very small mileage hit. Heavy use more.

Keep in mind that open windows also hurt mileage, and a hot HV battery is not a happy battery. My advice is to use A/C to keep comfortable and not worry about it. The mileage hit is small.

Tom

 

I'm not sure this has been answered yet for the Gen III.

See this thread with some data for the Gen II (shouldn't be very different for the Gen III).

JimboK used Wayne Brown's Prius Simulator and came up with these numbers (Gen II):

So, with this theoretical tool: from a nominal 3.7-3.9L/100km, it can go up to 4.0-4.1L/100km, a difference of 0.2-0.4L/100km, or 0.9-1.7 gal/1000miles.

I guess it depends on many things. Last week, I got stuck in traffic (stop&go) with a 30°C outside temp and left the A/C on to 23°C. It quickly drained my traction battery and the ICE started to run periodically to charge the battery. My fuel consumption for this commute went from 4,2L/100km to 5L/100km (around 3,5gal/1000miles difference).

The UK's "Prius Brief Guide" indicate Air Conditioning can result in 10-25% extra fuel consumption, but it also states that shifting up gear can result in 8% saving (and the Prius as no way to change gears...), so I'm not sure if these numbers are Prius specific:


PS. I can personally confirm that the Luggage Rack and Bicycle Rack fuel consumption impact is right (or maybe even too optimistic), as seen on vacation last summer (mostly highway).

 

With about 90°F OAT the last two days, I was getting similar fuel economy to when it was about 20°F OAT in the winter. The "sweet-spot" for fuel economy seems to be around 75°F, which, coincidentally, is mine as well.

 

Just been looking at the UK Prius Brief Guide and I think the section on a/c is generalised. Perhaps they use the same wordings for all their models and somebody hasn't updated/corrected it for the Prius.

The part on page 16 states that you should switch off your engine if stood for longer than 30-60 seconds! Hmmm, correct me if I'm wrong, but I do remember the Prius already does this itself

 

With my daily 52 mile commute with 40 miles highway driving at 60 mph, I have seen about a 1 to 1.5 mpg decrease when using A/C versus not. This is with about an average OAT of 80-85 F in the afternoon. The morning commute lately has been in the 65-70 F range so no A/C.

 

Can you specify to what MPG number this 1-1.5 MPG decrease apply?

A x MPG difference means nothing by itself (MPG = 1/fuel consumption, it is not linear).

 

Good point. I average about 51 mpg without the A/C and 49.5 mpg with the A/C.

 

40 degree weather with heat on, 42-46 MPG.

80 degree weather with ac on 52-56 MPG,

calculated mpg not computer generated.

warm is good

cold is bad

alfon

 

I live in TX (100+ in the summer so AC is ALWAYS on, although I do drive in Eco Mode in the summer months to control the air flow) and have had this car since last July of 09. I do not notice any significant drop in MPG. I average 51-54 MPG with a 90 mile a day RT commute once the temp gets above 80 degrees. During the winter months (okay, it's Texas, so winter is relative) when temps avg around 40-50 degrees my MPG dropped to around 49-50 MPG.

I know this is not a scientific answer, but I do concur that any mileage drop is quite insignificant.

 

On the principle that the A/C burden is mostly in bringing down the cabin temp initially; the longer your commute, the less impact it will have on your gas consumption (the impact is then diluted on a longer distance). Shorter commutes will therefore see a more important impact in MPG, even if both have the same initial burden.

 

I know this is a technical conversation but let me put this in the context of economics and physiology with a real life example. My commute today was 11 miles each direction to and from work, DC area. In the am, nice cool morning, no ac needed. My MID showed increased MPG from 61.2 (first round trip 22 mi, no ac used) to 61.8 for trip to carpool lot in am, first leg. On the trip home, 90F and very hot cabin on entry. I ran ac most of the way home, some p&g ac along the way, but always a cool cabin temp range of 77-80 F. In driveway, I was at 60.5mpg on MID. My 22 mile round trip cost me about $1.00 in gas costs. My .7mpg drop for roundtrip commute of 22 mi, using ac when I needed it, cost me about a penny or two extra over steady state mpg, or 1-2%. Physiology tells us the body operates very effectively within certain temperature ranges. Less so as the range varies too hot or too cold. Driving is always a safety hazard, so comfortable temperature range in cabin is safer right. It's a no brainer to run the ac when needed and don't sweat the very negligible pocket change or diminimus mpg diff. Comfort, safety first. You'll smell better when you get home too. Always a good thing.

 

My non-scientific answer is also that the A/C has a surprisingly small impact on mpg. If you switch the AC on and off repeatedly and watch the mpg gage, there is no effect. But on my Tacoma, when the AC compressor kicks on or off, you can feel it. The truck surges (AC off) or lugs back (AC on). It feels like an automatic transmission shifting gears.

 

The Prius A/C compressor doesn’t work like what you knew on other cars. As you describe, usually, the compressor is mechanically attached or detached from the engine, as it is turned on/off.

On the Prius, the compressor is electric and works on the high voltage system (like the electric motors that moves the car). It can then run even if the engine is stopped.

It still draws is energy from the engine, but indirectly (engine generates electricity from gas, which is stored in the main battery). Turning it on/off will not show on the instant MPG gauge. You will only see it over a longer period of time on your trip MPG.

The compressor is also of variable speed rather than simply on/off. It is true that it is quite efficient though.

 

I just returned from a 4500 mile trip down south .... A/C on the entire trip (90's outside temperature). First, the A/C unit in the Prius is wonderful!! Second, my overall fuel average was 50.3 mpg .... Cannot beat that.

Logically, there is a small dip in fuel efficiency .... but a
"hit" I am more than willing to take in 90 plus degree temperature.

 

On a long distance, the dip will not show. On a short commute, it becomes visible.

 

This has been exactly my experience. MPG for the Prius (higher or lower) seems much more related to the outside temp.

 

Ours has dropped from around 53 MPG to about 48.5 since we started using the A/C in sunny So. California. We are disappointed, but this is still great mileage.