Air conditioning fuel consumption?

DaveyDave

Hi all,

I was wondering how much fuel does AC actually use? Searching online leads me to articles on random websites and I don't see anything consistent.

Driving a 151 i30 automatic diesel but unfortunately it's not actually the 2015 model so has the older 6 speed torque converter instead of the 7 speed DCT so it has very poor fuel economy. Struggle to get 37MPG driving as efficiently as possible and I'm wondering how bad the AC would effect it as filling the car is draining my wallet...

punisher5112

Ac will use around 10% or so extra but so will driving with windows open maybe even more so knowing when to use either way.

punisher5112

What type of driving are you doing?

Ubbquittious

If the car is sitting there idling and you switch on A/C is there a ferocious drop in revs followed by the revs picking up significantly?

There might be a trip computer that will show the number of litres per hour you're burning so you can try that with the A/C on and with it off. If its warm and you have the blower turned up to the end the A/C clutch will be engaged for longer as well

mickdw

Drive on. I leave my aircon to do it a thing all year round. By all accounts you are less likely to have issues with the system by doing this so that more than cancels out the extra fuel consumption. Certainly in my case, I've been driving cars with aircon for 15 years and have not had an issue.

DaveyDave

punisher5112 wrote: »

What type of driving are you doing?

Fairly even mix of urban and dual carriageway I think. Fairly straight back roads to work, outside of rush hour with little to no traffic then the odd journey to the city centre on the N4 at night.

colm_mcm

punisher5112 wrote: »

Ac will use around 10% or so extra but so will driving with windows open maybe even more so knowing when to use either way.

10%? I'd say more like 2%

Maybe 30 years ago, but newer systems are way more efficient.

Foxhole Norman

Haven't noticed any real change of MPG with A/C on, both on a 2.5 6 Cylinder and 4.4 V8, yes it idles a bit higher but I'd say I might lose 0.1mpg or the like.

Del2005

colm_mcm wrote: »

10%? I'd say more like 2%

Maybe 30 years ago, but newer systems are way more efficient.

+1. Drove with both AC on and off and never noticed much difference in the amount when refuelling.

_Brian

Del2005 wrote: »

+1. Drove with both AC on and off and never noticed much difference in the amount when refuelling.

Same here, 2.0 Tiguan TDI, always leave it on as it makes no difference.

That's atrocious MPG for OP with the i30, I'd have expected that car to be doing 50+, is it the automatic that is killing it or is there something wrong.

My Tiguan is 4Motion 4wd version and it does 43MPG regular driving, more if I go in granny mode. A 151 car doing 37mpg is awful, truly awful.

bmwguy

_Brian wrote: »

Same here, 2.0 Tiguan TDI, always leave it on as it makes no difference.

That's atrocious MPG for OP with the i30, I'd have expected that car to be doing 50+, is it the automatic that is killing it or is there something wrong.

My Tiguan is 4Motion 4wd version and it does 43MPG regular driving, more if I go in granny mode. A 151 car doing 37mpg is awful, truly awful.

In my recent quest to change cars I had a 2006 530d 6 cylinder big car 3 litre diesel and it was averaging 37mpg in mixed driving. I would expect a 520d to be at least 5mpg higher and the likes of OPs car to be another 5 on top of that pushing up towards 50 like you said yourself

digitaldr

I think it's better to leave AC on to avoid bacterial growth which lead to smelly welly odours.

bladespin

punisher5112 wrote:

Ac will use around 10% or so extra but so will driving with windows open maybe even more so knowing when to use either way.

What car is that? No noticible difference on mine (2014 Passat) or any pervious cars I've driven.

JoeA3

_Brian wrote: »

Same here, 2.0 Tiguan TDI, always leave it on as it makes no difference.

That's atrocious MPG for OP with the i30, I'd have expected that car to be doing 50+, is it the automatic that is killing it or is there something wrong.

My Tiguan is 4Motion 4wd version and it does 43MPG regular driving, more if I go in granny mode. A 151 car doing 37mpg is awful, truly awful.

My 152 does 27 on a good day :pac:

Air conditioning makes no discernible difference to mpg in a modern car. As already stated, better to use it than not, as the system does not like being left idle for long periods.

GerryDerpy

digitaldr wrote: »

I think it's better to leave AC on to avoid bacterial growth which lead to smelly welly odours.

And to prevent the system from loosing refrigerant and to keep the compressor moving and lubed. You will notice cars will lose 10-20% refrigerant a year from lack of use.

biko

Mythbusters did an episode on this
http://www.discovery.com/tv-shows/mythbusters/videos/air-conditioning-vs-windows-minimyth/

Phonicks

most people are usless with heating

Its simple
Do....
1)Turn on aircon
2)Turn on fan (not to loud)
3)Set temperature to about 21 (or heat it half way)
4)Give it 5 mins
5)if its too hot turn temp (heat) down a bit,
6)if its too cold turn temp (heat) up a bit
7) repeat steps 4-6 for the rest of your life

DONT....
1) if cold set heat to full
2) if hot set heat to min
3) turn fan on at a noisy setting
4) when temp is now too much the other way turn fan off
5) repeat steps 1-4

The_Honeybadger

No noticeable difference at all in my Passat. I usually leave it on all of the time now

jca

Phonicks wrote: »

most people are usless with heating

Its simple
Do....
1)Turn on aircon
2)Turn on fan (not to loud)
3)Set temperature to about 21 (or heat it half way)
4)Give it 5 mins
5)if its too hot turn temp (heat) down a bit,
6)if its too cold turn temp (heat) up a bit
7) repeat steps 4-6 for the rest of your life

DONT....
1) if cold set heat to full
2) if hot set heat to min
3) turn fan on at a noisy setting
4) when temp is now too much the other way turn fan off
5) repeat steps 1-4

I just use auto (22-23°) on mine when the engine is up to temperature maybe a bit less heat in warmer weather. There's no difference in fuel consumption whether AC is used or not so I just leave it on continuously.

Wibbs

biko wrote: »

Mythbusters did an episode on this
http://www.discovery.com/tv-shows/mythbusters/videos/air-conditioning-vs-windows-minimyth/

That's what I would have thought myself. Maybe more modern systems are better regarding fuel consumption? With my car I most certainly notice the A/C when it engages periodically when I have it on. The engine note definitely changes and it's doing more work, which I can feel(even passengers have noticed it).

Which stands to reason. There is increased resistance from the A/C compressor and paraphernalia doing its heat exchange thing. Unless we're ignoring the laws of physics it will of course use more fuel, by how much is the thing.

That depends on a few factors. Efficiency of system for a start. I'd imagine it would also be far less noticeable on a big engine that already uses more fuel than say on a 1 litre engine. As for increased longevity by using it? I dunno. maybe. I'd rarely run mine in the summer, but would use it on frosty morning to clear the windows, still, maybe ten times a year and it still blows cold air nearly two decades on(well it did until the idler pulley bearing pooed itself. Added to list of summer tinkering )

_Brian

I'm just astonished that no one else seems to think 37mpg for a modern hatchback size car is madness.

No offence intended to OP but who in their right mind would buy this !!

bmwguy

_Brian wrote: »

I'm just astonished that no one else seems to think 37mpg for a modern hatchback size car is madness.

No offence intended to OP but who in their right mind would buy this !!

It's been said at least twice that I can see

jca

_Brian wrote: »

I'm just astonished that no one else seems to think 37mpg for a modern hatchback size car is madness.

No offence intended to OP but who in their right mind would buy this !!

37 mpg from a torque converter type auto is brilliant. A relative had a Passat with the same setup and it regularly dipped into the 20's MPG.

Foxhole Norman

jca wrote: »

37 mpg from a torque converter type auto is brilliant. A relative had a Passat with the same setup and it regularly dipped into the 20's MPG.

I have a torque converter 525 and 540, petrols the 525 has returned up to about 38MPG on a long cruise and even the 540i returned 30 ish MPG cruising with some added fun, 37 from a diesel hatchback be it torque converter or not is rubbish.

colm_mcm

Agreed, the old model i30 with the older torque converter was a good bit better on fuel than 37mpg.

JoeA3

_Brian wrote: »

I'm just astonished that no one else seems to think 37mpg for a modern hatchback size car is madness.

No offence intended to OP but who in their right mind would buy this !!

Lol. A "hatchback" covers a huge range of vehicles and engine choices. And what type of driving the owner is doing is also a huge factor!

A diesel shopping trolley doing school runs, I'd say high 30's low 40's is probably about right. Same car doing the motorway all day will probably hit 50+ mpg easy.

I also drive a hatchback. 27mpg is average. 37mpg is the dream :pac:

heroics

I leave aircon on all the time. don't notice any difference in my current 520. My old a6 or the e240 before it. Average Low 40s mpg in the 520

colm_mcm

colm_mcm wrote: »

10%? I'd say more like 2%

Maybe 30 years ago, but newer systems are way more efficient.

I always thought it was 10% but your post explains why I haven't really noticed much difference when I switched it off. thanks

Anjobe

Wibbs wrote: »

That's what I would have thought myself. Maybe more modern systems are better regarding fuel consumption? With my car I most certainly notice the A/C when it engages periodically when I have it on. The engine note definitely changes and it's doing more work, which I can feel(even passengers have noticed it).

Which stands to reason. There is increased resistance from the A/C compressor and paraphernalia doing its heat exchange thing. Unless we're ignoring the laws of physics it will of course use more fuel, by how much is the thing.

That depends on a few factors. Efficiency of system for a start. I'd imagine it would also be far less noticeable on a big engine that already uses more fuel than say on a 1 litre engine. As for increased longevity by using it? I dunno. maybe. I'd rarely run mine in the summer, but would use it on frosty morning to clear the windows, still, maybe ten times a year and it still blows cold air nearly two decades on(well it did until the idler pulley bearing pooed itself. Added to list of summer tinkering )

A couple things about the Mythbusters test stand out to me. First, they used SUVs which are already poor aerodynamically, and 45 mph may be just too slow for opening the windows to make much difference. Second, I suspect cars made for the US market have more powerful A/C compressor pumps than those sold here. I believe that modern A/C pumps in European models use less than 2 bhp, so I suspect the fuel it uses would be barely noticeable even for small engines. Perhaps Mythbusters would have come to a different conclusion if they had tested small Euro-market hatches at 80 km/h plus.

bmwguy

Anjobe wrote: »

A couple things about the Mythbusters test stand out to me. First, they used SUVs which are already poor aerodynamically, and 45 mph may be just too slow for opening the windows to make much difference. Second, I suspect cars made for the US market have more powerful A/C compressor pumps than those sold here. I believe that modern A/C pumps in European models use less than 2 bhp, so I suspect the fuel it uses would be barely noticeable even for small engines. Perhaps Mythbusters would have come to a different conclusion if they had tested small Euro-market hatches at 80 km/h plus.

The one thing that seemed to be a massive variable in myth busters was they used 2 separate vehicles. I would have thought using the same vehicle would have been a much more accurate way. Remove all variables.

Dial Hard

Edit: was posting about the Mythbusters episode but it's already been covered.

CalamariFritti

Del2005 wrote: »

+1. Drove with both AC on and off and never noticed much difference in the amount when refuelling.

I know how you meant it but this is kinda funny all the same.

bmwguy

Well folks in the name of science I have tested it i had a bit of a motorway journey on the n4 to do, all flat no hills. Stuck the car in cruise control at 120 kmph on the way to my destination about 20 kms away with at 120kmph I a/c on and reset trip computer. Motorway was pretty empty and i didnt have to brake at all and I only reset computer once up to speed.
When I exited motorway stage the computer was showing 7.9 l/100km or about 36mpg.
I did the exact same test on way back, reset computer with driver side front window open and I will admit I had to brake once but as I was doing so the computer was showing 8.0 l/100km . It stayed at 8.0 for the rest of way home.

So, nothing in it at all really. Everything like for like on a 20km journey except for cooling method.

Car is a 2006 525i e60 automatic by the way.

nice_guy80

drove a hire Nissan Tiida in Australia a few years back
the car actually slowed down when the A/C was turned on.

Cee-Jay-Cee

I had the air con on most days over the last 2 weeks and it's made zero difference to my MPG. The car is still averaging 32mpg for my short 8km commute each day.

Unless your doing huge mileage and have the air con on all the time I don't think it's going to make any noticeable difference

OP I'd be more concerned as to why your fuel economy is so poor. 37mpg is piss poor for that car regardless of it being automatic which shouldn't make a massive difference, maybe 2/3mpg at the most over a manual version.

bmwguy

Cee-Jay-Cee wrote: »

I had the air con on most days over the last 2 weeks and it's made zero difference to my MPG. The car is still averaging 32mpg for my short 8km commute each day.

Unless your doing huge mileage and have the air con on all the time I don't think it's going to make any noticeable difference

OP I'd be more concerned as to why your fuel economy is so poor. 37mpg is piss poor for that car regardless of it being automatic which shouldn't make a massive difference, maybe 2/3mpg at the most over a manual version.

It's 37 in a mix of urban and dual carriageway. I would guess going by my own he is getting 32 urban and 42 dual carriageway. Still poor for a 151 diesel in a small hatchback. What's the quoted figures? I am guessing 55-60mpg combined anyway or about 5l/100kms?

It's getting about 8-10 mpg or 25-30% higher than my car in the same mix of driving which is much bigger, also automatic, petrol and older tech (possibly I am not sure about the last one).

Is that what you would expect? Quoted figures for cars recently are a joke for most drivers.

I see the new AMG and M cars from Merc and BMW quote better figures than I get in a 525i which is not a performance car at all. Pie on the sky stuff.

Fireball14013

I did a test many years ago, about 12 or more. Had a gen 7 Celica. Used to drive a fair bit at weekends. Brimmed the tank, left Air Con off all week end, got 430 miles by the time it was on the last bar of the digital fuel guage. Did the same the following weekend, except with air con on all the time. Got about 415 miles. Bear in mind the amount I used to get out of brim to empty varied by about 10 miles most of the time anyway, maybe up to 15, so minimum difference was my conclusion.
I think the bigger the engine the less you'll notice it, more torque to turn the compressor. Remember renting a small petrol car on holidays and on steep hills the air con would have to go off!! Then again, maybe in warmer countries they fit more powerful units.

jca

Mine is only a 1.4 TSI and there's no difference in consumption, my figures are measured using the full tank method.

demanufactured

nice_guy80 wrote: »

drove a hire Nissan Tiida in Australia a few years back
the car actually slowed down when the A/C was turned on.

That's because it's a Nissan tiida

freddieot

37 mpg in a 2015 i30 sounds bad. Is this the norm ?

I do lots of 10km urban trips combined with some M50 and a long trip to Portlaoise or Tullamore about every two weeks. I'm getting 35 mpg.

However that's in an X5 x25d with AWD and air con and toys on all the time. Just makes no sense that a smaller and lighter car of the same year only manages 37.

_Brian

The whole air con Vs open window is mute in this discussion.
Op's car is maybe 20mpg off where a family sized hatchback diesel should be performing.
This is either a design flaw or there is something seriously wrong. I can't imagine how you would research buying a car and see such terrible mpg figures and think' "yep, that's a good buy"

heroics

_Brian wrote: »

The whole air con Vs open window is mute in this discussion.
Op's car is maybe 20mpg off where a family sized hatchback diesel should be performing.
This is either a design flaw or there is something seriously wrong. I can't imagine how you would research buying a car and see such terrible mpg figures and think' "yep, that's a good buy"

I agree that mpg is poor for the OPs car. Just because it seems that mpg is the basis for you buying your cars does not mean that it is for everyone. For some it matters for some it doesn't.

heroics

Just to add OP if you look at https://www.honestjohn.co.uk/realmpg/hyundai/i30-2012 they reckon real world mpg is between 39.7-45 for the automatic depending on which version you have. so you are probably about right compared to other drivers of the car.

Looking at that site the real world mpg drops by about 10mpg for the auto compared to the manual of the same model/engine which is crazy.
Allthough I just looked at a Kia Ceed as a comparison and it drops by 15mpg for the auto over the manual.

I had a look at my own then as you got me interested and the BMW 520D for example on that site the real world mpg is practically the same in the auto as the manual.

_Brian

heroics wrote: »

I agree that mpg is poor for the OPs car. Just because it seems that mpg is the basis for you buying your cars does not mean that it is for everyone. For some it matters for some it doesn't.

I take your point, I do high enough mileage as does the missus, 90-100k between us so it is a factor, plus I need something to pull a trailer and caravan with ease.

I just presumed all modern diesel cars were hitting 50+mpg, mine were hitting that 20 years ago.

Sleeper12

DaveyDave wrote: »

Hi all,

I was wondering how much fuel does AC actually use? Searching online leads me to articles on random websites and I don't see anything consistent.

Driving a 151 i30 automatic diesel but unfortunately it's not actually the 2015 model so has the older 6 speed torque converter instead of the 7 speed DCT so it has very poor fuel economy. Struggle to get 37MPG driving as efficiently as possible and I'm wondering how bad the AC would effect it as filling the car is draining my wallet...

I just got rid of a 2.9l Jeep 20MPG in the city & 30MPG on the motorway if I kept it around 60MPH. I'm in a Ford Connect getting 55/60MPG now. I don't know myself.

I saw a test done on Mythbusters or something like it. You use more fuel with your window down,

To hell with the little extra cost. Comfort is what it's all about. Same with heating in my house in winter. You'll never be cold in my house.

JoeA3

_Brian wrote: »

I take your point, I do high enough mileage as does the missus, 90-100k between us so it is a factor, plus I need something to pull a trailer and caravan with ease.

I just presumed all modern diesel cars were hitting 50+mpg, mine were hitting that 20 years ago.

They will - but you cannot apply that criteria with a paint brush! Mpg depends heavily on typical journeys and driving style. A modern humdrum diesel hatch will get 50+ up and down the motorway all day long. It will not get anything like that if the car is used in more typical driving - school runs, work commutes, city stop/start. High 30's for that kind of driving sounds about right to me.

jca

heroics wrote: »

Just to add OP if you look at https://www.honestjohn.co.uk/realmpg/hyundai/i30-2012 they reckon real world mpg is between 39.7-45 for the automatic depending on which version you have. so you are probably about right compared to other drivers of the car.

Looking at that site the real world mpg drops by about 10mpg for the auto compared to the manual of the same model/engine which is crazy.
Allthough I just looked at a Kia Ceed as a comparison and it drops by 15mpg for the auto over the manual.

I had a look at my own then as you got me interested and the BMW 520D for example on that site the real world mpg is practically the same in the auto as the manual.

The 520 is a direct drive box a completely different beast to the slushbox used in that era of Hyundai.

jca

_Brian wrote: »

The whole air con Vs open window is mute in this discussion.
Op's car is maybe 20mpg off where a family sized hatchback diesel should be performing.
This is either a design flaw or there is something seriously wrong. I can't imagine how you would research buying a car and see such terrible mpg figures and think' "yep, that's a good buy"

Maybe the op needs an auto and didn't realise that Hyundai used the old type auto box. There's a huge difference between the two types, the rate of tax (on the co2 system) is a great indicator.

DaveyDave

Hi all,

Thanks for all the responses Just wanted to note regarding my MPG. It's actually my mam's car, she needs an automatic due to a foot injury. She had a 2013 model but had a number of people drive into it in car parks and it seemed to have a bit of a curse after some pretty bad cosmetic damage kept occuring.

She got a 2015 model as they have a 7 speed DCT transmission which has much better MPG but unfortunately it was the same 6 speed torque converter, so in essence is a 2014 model? Or the UK just didn't get them at the beginning of 2015. Unfortunately she didn't check as she was expecting it to be 2015 spec.

I've heard diesel engines are inefficient for short journeys and I drive 15 minutes to work, I haven't heard anyone complain about this (or maybe I'm blind) so I'll take it with a pinch of salt but I've read numerous articles online saying they will have poor MPG for the beginning of a journey and won't be of much benefit.

I just know when I get a car in a few months it will be a petrol

JoeA3

Yep. You'll never get near claimed mpg figures if you're driving a diesel on such short and/or stop-start commutes.