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What is the effect of air-conditioning on battery mileage?

What is the effect of air-conditioning on battery mileage?

Does anyone know, or have an educated opinion, of the effect of air conditioning on the battery mileage of a Tesla M3; or alternatively, how many kilowatts the air-conditioning uses at hypothetically 95°?

Bighorn | 11. August 2017

2kW max

JAD | 11. August 2017

Very little. A/C affects ICE more, but the heater is very draining on an EV.

jordanrichard | 11. August 2017

I wouldn't worry about it. Cold winter temps make the biggest difference. Both you and the battery want/need to be heated......

bmz | 11. August 2017

Muchas gracias.

bmz | 11. August 2017

The reason why I didn't ask about heating is because in the wintertime you have a coat and gloves on; so I figured that heating would not be as big an issue. But tell me about having to heat the battery.

Bighorn | 11. August 2017

Heat is up to 6kW People tend to opt for seat heat if they need to conserve. Battery warmer can consume another 6kW. Sometimes frosty windshields/windows necessitate defroster heating--avoid driving with wet hair:)

ron369 | 11. August 2017

If you go to the Model-S page on Tesla's website, there is a range estimator. You can play with outside temperatures and turn AC or heating on and off, and see Tesla's estimate on how it impacts the range of the car.

jordanrichard | 11. August 2017

The battery pack, or more specific lithium-ion batteries like to operate in a certain temperature range and 10 degs. is not one of them..... :-) So the battery pack heats it self up so as to operate more efficiently, but that eats up range. Here in CT, when it gets down to the 60's, I notice an increase it energy usage. If you go to the range estimator tab on the Model S page, you will see the default outside temp set to 70. Change that to 60 and you will see the estimated ranges drop. Conversely, if you bump the temp to 100 the range increases dramatically.

Carl Thompson | 11. August 2017

@JAD

Why would AC affect ICE vehicles more than an EV?

Thanks,
Carl

gavinmcc | 11. August 2017

Just ride an electric motorcycle...never have to worry about AC or heat. :)

Like everybody else, I have noticed range is lessened by cold temps....interestingly really high temps give me extra range. We had a week of over 100 degrees and my battery saw almost 20% increase in range...but daily riding at 104 degrees is not really much fun. Those weeks (and Jan/Feb when it can be in the teens when I ride in the mornings) I am super jealous of people in San Diego...perfect year round riding.

G

sosmerc | 11. August 2017

Carl's question is a good one I think. I can't wait for someone with real knowledge to explain it. I think we have different types of AC system used on vehicles, but engine power or battery power has to "run" the unit. Could be belt driven or gear driven or independent electric current driven. HVAC system for commercial or residential use electric power (heat pumps) that provide either cooling or heating depending on what is needed. I think some cars are now starting to use this type of system. So a comparison of these systems and their "energy" costs would be interesting.
I'm sure we'll get some interesting answers to the question.

Rocky_H | 11. August 2017

I wanted to wait for @JAD because I feel like I've been hard on @Carl in that other thread, but this is just too interesting of a question, and I can't wait.

I do get that question a lot from gas car drivers, asking how much the A/C takes off of the range. I explain how very surprising and different it is that with an electric car, heating is much more of an energy draw. With a gas car, all of the heating is "free". The car is working very hard to get rid of two thirds of the energy of the gasoline as waste heat through the tailpipe, radiator, and heating vents. So that is never an energy loss. But the A/C compressor is a spinning load that has to be driven somehow, so it takes a little extra energy, requiring burning a little more gasoline.

Electric cars are so efficient that they have very low excess heat generated from running. There is a little bit, and that is collected in the Tesla system, but it's not really enough to warm up the inside of the car. So they have to run straight-up resistive coil heaters to adequately heat. Technically not all cars, though. Some of the later Leaf models and maybe some others do use a heat pump--like a reverse air conditioner--which is more efficient, since it's more like "moving" heat energy, rather than just converting it straight from electricity.

Sorry, @JAD, couldn't resist.

carlk | 11. August 2017

gavinmcc has a good point. Just wear a lot of clothes if you want to preserve energy. It can't be worse in the car than walking outside or riding a bike.

Frank99 | 11. August 2017

The Model S range calculator suggests that it's almost a wash - you get more range when the temperature is hot, but you lose a similar amount by turning on the A/C:

At 70 MPH in a Model S75:
A/C Off
Temp Range
50 234
70 241
90 244
110 253

A/C On:
Temp Range
70 228
90 230
110 216

So, about the same range at 70F and 90F with A/C as at 50F, and about an 18 mile hit at 110F.

carlk | 11. August 2017

Answer of that question is A/C in ICE cars are mechanically driven by the very inefficient car engine.

carlk | 11. August 2017

BTW you can use electric A/C compressor in an ICE car but it will still still be getting electricity from alternator mechanically driven by the very inefficient ICE engine.

Carl Thompson | 11. August 2017

@carlk

But AC in electric cars is also mechanically driven by the motor I thought? In other words pretty much the exact same way as ICE cars. Or do some EVs run a separate motor for their AC compressors?

Thanks,
Carl

noleaf4me | 11. August 2017

Carl - EVs have a separate motor that runs the AC. Only runs when it is needed

Carl Thompson | 11. August 2017

@noleaf4me

Why have a separate motor when you already have the main motor and you could just slave off of that like an ICE would? Conversely if having a separate motor is somehow better why don't ICE cars do this?

Thanks,
Carl

Frank99 | 11. August 2017

Because you can run the A/C with the car parked?

If you tried to use the main motor, you'd have to have a more complex transmission, and you'd still have the ICE problem of the A/C getting warm at low speeds/stopped. With a seperate motor for the A/C, you can run it at the most efficient speed you need, all the time

ICE vehicles don't do it because it's an extra cost. They have an engine turning all the time, and a long history of running accessories off the engine. It wouldn't surprise me to find out that some high-end vehicles have an electric-driven A/C, but that's outside my range of experience.

JAD | 11. August 2017

Sorry, occasionally work and life prevent me from living on the forum :)

As has kinda been stated, ICE cars simply run a compressor off the engine. It is a pretty cheap and simple system that works. EV's use an electric system that cost more but EV's are all about maximizing range and efficiency now so manufacturers put in the more expensive system. In an ICE car, the cost/benefit analysis doesn't justify the cost. I don't think the EPA ratings would change much based on their testing procedures, so only the end user would see a gas savings, but probably wouldn't sell more cars at the $100/car (or whatever) cost increase.

Some high performance cars actually turn off the A/C at wide open throttle. Serious racers immediately remove the A/C compressor for track work as it saps so much power even when off, plus weigh a lot.

Now ICE engines inefficiency works for them with heating, as they make LOTS of heat. Thus the radiators and hot exhausts. Air cooled Porsches just had a fan that blew air over the exhaust system to heat the cabin. Worked REALLY well once the car warmed up. EV's are too efficient and don't make excess heat so they have to burn energy to create the heat the ICE cars just vent to the air, much like ICE brakes versus regen. Regen would actually save some gas by reducing the demand on the alternator, but not enough to justify the added cost.

Bighorn | 12. August 2017

Electric motors don't continuously idle so running a belt for the AC is a non-starter.

Tesla2018 | 12. August 2017

Do electric vehicle batteries generate a lot of heat? Reason Im asking is because my garage door is facing the sun in the afternoon and I am in FL. If its 95 degrees outside my garage temp is about 90 when I get home from work. When I put my car in the garage and close the garage door, the tempeature of the garage goes up to about 96 degrees from the engine heat and from the car being blastrd by the sun on the way home making the hood, roof and doors all hot.
Will a Tesla put off as much heat. The garage is below a bedroom which is always warmer than other rooms next to it due to the heat. Yesterday morning at 8am it was 86 inside the garage and 80 degees outside so it doesnt even get a chance to cool down. Im afraid to keep the garage door open at night because I dont want mosqquitos, mice, snakes, turtles, squirrels, lizards and other critters getting in.

Frank99 | 12. August 2017

There will be heat generated from charging, but I don't know how much you might expect.

There won't be as much heat stored in the car when you get home as there is with an ICE, so the garage shouldn't heat up as much in the hour or so after you get home.

I'm considering adding some ventilation to my garage to cool it down in there. It's over 90 in the summer (Phoenix), which really hasn't bothered me before (the car is much cooler coming out of the garage than sitting in the driveway), but I'm thinking a thermostatically controlled fan that brings air into the garage whenever it's cooler outside than inside would be a good addition.

TeslaTap.com | 12. August 2017

Left out of this decision is the real world impact of heating and A/C. Yes, it will affect your range, but as you get used to the car and the long range it already has, it quickly becomes in the noise for most users. It becomes far more critical in EVs that have limited range (i.e. under 100 miles), since it takes about the same power to cool/heat the cabin no matter the battery size. The larger the battery, the less concern you'll have. In 4+ years now with my Teslas, I never needed, nor bothered to sacrifice comfort for range. My first Tesla was also a 60, with an EPA range of 208.

Rocky_H | 14. August 2017

The other good efficiency thing about a separate electrically driven A/C is that there are A/C compressors that can do variable speed operation so they can scale the cooling as needed, so it can scale up and down to save some energy.

But yeah, the biggest thing is the kickass feature of being able to turn on your A/C from the phone app while your car is parked and the main motor doesn't have to be spinning to drive it.

Haggy | 15. August 2017

An ICE uses an engine. It spins at a speed that makes sense for the operation of the vehicle, not what's optimal for the AC. When the AC doesn't need the compressor to run, an ICE has a solenoid that disengages the clutch, so that part has nothing to do with it. When the engine has to run faster than the AC needs, the AC is still a drag on the system. It's simply not an efficient use of the engine.

Tesla has a battery that's powerful enough to move several tons of car up a mountain. Turning a small motor that's optimized for an AC compressor isn't really a big deal. It won't have to match the speed of an ICE engine. It has to do less work than a small window AC unit for a small bedroom that's still many times larger than a car. You won't have times when the motor is too slow and the AC isn't working at capacity or it's too fast and wasting energy.

PeterPlt | 15. August 2017

Range is affected by a number of variables: Speed, Wind, Altitude (air density), Elevation changes, as well as what power you are pulling for heating/air conditioning, etc. I live in the Sun Belt and have driven my S85D for over 52,000 miles on local and long range trips. My average real world road range versus meter range distance after a charge is between 87-85%. In other words, if the car charges to 234 miles, I can plan on being able to drive 199 miles to "0" range remaining. I suspect the Model 3 will perform similarly.

By the way, these are the same kinds of performance issues aircraft incur. Trip planning for your Tesla is very similar. I like to arrive with at least 10% reserve, just in case of detours or other factors. Happily enough (unlike ICE vehicles) traffic delays do not dramatically affect your range.

I hope this helps!

bmz | 15. August 2017

You guys are great--thanks.

andy.connor.e | 15. August 2017

@Bighorn

A/C: 2kW
Heat: 6kW

Are they really????

LostInTx | 15. August 2017

Ancillary question - when charging at an SC location, can I leave the air conditioning on while the car is being charged? Reading through there seems to be a separate motor for the car and the AC. I'd love to keep the car cool while charging on a hot summer day. Can do?

KP in NPT | 15. August 2017

LostinTx - yes.

Bighorn | 15. August 2017

@andy
Umm, yes?

Carl Thompson | 15. August 2017

@Haggy

Good points. But it doesn't seem like there's anything inherent in an ICE design that says it must use an AC compressor driven by the engine and can't use a separate motor. And it doesn't seem like there's anything inherent in an EV design that says it can't have an AC compressor driven by the motor and must use a separate motor. It's just that most (but not all) ICE cars drive the AC compressor by the engine and most (all?) EVs use a separate motor.

Carl

Ehninger1212 | 15. August 2017

@carl

The Prius uses an electric motor to drive its AC compressor so yes.

No, the EV doesn't need a second motor to drive the AC compressor. But when stopped the AC would stop working. This is the same reason the Prius does not use the ICE engine the Prius ICE would have to always be running.

A lot of variables to this question.

But if we look at the same type of compressor drivin by an ICE or an electric motor. The electric motor drivin compressor would be more efficient simply because electric motors are more efficient than ICE.

Just think how crazy I would be running my home AC off of a diesel gen set.

andy.connor.e | 15. August 2017

bighorn

Lol are you unsure? Thats great to know. Can literally calculate battery usage. Im going to be the "can i make it there without it" kind of person.

Bighorn | 15. August 2017

No, not unsure though those are maximums. The 6kWs the battery heater can draw must also be factored in some circumstances. You can monitor non-driving draws looking at the power meter while in neutral.

andy.connor.e | 15. August 2017

Even better

Sandy’s 3 | 15. August 2017

Carl, At idle an ice motor is capable of still turning the AC compressor. An EV at idle is not turning therefore could not run the AC. So if the AC ran of an EV main motor you would not get AC when stopped (think traffic jam on a 90 dog day) and not have the ability to pre-condition.

andy.connor.e | 15. August 2017

Its been stated that the AC and heat does not take away from the performance of the car. That clearly indicates the main axle motors do not power these systems. Also, as FLHX13 points out.....

Carl Thompson | 15. August 2017

@FLHX13:
"An EV at idle is not turning therefore could not run the AC."

This is also true of many modern ICE cars, right?

"So if the AC ran of an EV main motor you would not get AC when stopped (think traffic jam on a 90 dog day) and not have the ability to pre-condition."

This is also true of ICE cars that don't run the engine when idle. I'm just pointing out that this is not an inherent property unique to EVs.

Carl

andy.connor.e | 15. August 2017

Carl

For vehicles like that, the AC is run off a separate motor. There is a prius in my family, and you can hear a motor running when the engine is off at a stoplight. Good point though

jordanrichard | 15. August 2017

Being that the AC motor in our cars is said to spin up to 16,000 RPMs, that would shred/melt any belt to a traditional AC compressor. Besides, looking at the DU as it is, where exactly would you place this belt driven compressor? Another point is that if the compressor is in the back, then you have to have the AC plumping going all the way to the front of the car to have it then piped in through the dash.

andy.connor.e | 15. August 2017

the belt drives a large gear, which spins a smaller gear at the 16,000 rpm. The belt could spin at 1000rpm, and the gears have a 1:16 ratio.

Rocky_H | 15. August 2017

That is kind of funny about different types of hybrids. We had a Prius, and yes, it has the separate drive for the A/C, since the main engine is off a lot of the time. We have a hybrid Honda Civic now, though, and the A/C is run from the main engine. The engine will only be off at a complete stop because of its more limited hybrid system. And yeah, if you let the engine stop like that, the A/C shuts off, and within a few seconds, you're blowing hot air. So there is a button to disable the "ECON" setting, so that it will keep the engine from shutting off at stops to be able to keep your A/C running.

carlk | 15. August 2017

Carl Thompson | August 11, 2017
@carlk
"But AC in electric cars is also mechanically driven by the motor I thought?"

Compressor in Tesla is driven by electrical motor that takes energy from battery. That has probably 90% or higher efficiency. The compressor in an ICE car is driven by belts and pulleys connected to the engine that has at most one third of that efficiency. Even worse, which is the fundamental problem with ICE, is the engine has to be designed for the worst case scenario, meaning bigger and more powerful to take care of A/C, and will use more energy even when it is not used or needed.

jordanrichard | 15. August 2017

Andy.connor.e, so again, where would all of this extra gearing go? Look at a picture of the drive unit assembly, where would you put this additional set up?

More and more ICE cars are coming with electric AC compressors as a way to reduce the engine load that a belt drive creates, which in turn reducing MPG. Similarly a belt driven AC compressor would reduce our car's range.

andy.connor.e | 15. August 2017

Sorry i dont really care to figure that out. What i said was in response to thinking that the belt would snap from moving at 16,000 rpm. If the AC requires that speed, you would gear up the belt from a lower RPM.

jordanrichard | 15. August 2017

Ok, but the belt coming off the motor to this gear reduction gear you suggested would be the one that would have to handle the up to 16,000 rpms and the massive torque of the car's motor.

andy.connor.e | 15. August 2017

Its just an example. Its not any different than having an electric compressor to run the AC. Where is that getting its power from? Most likely from the alternator, which also puts a load on the engine because the belt drives the alternator. I notice a performance change when i turn my AC on, what the actual numbers are i dont know but i'd only be trying to explain the concept.

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