Windows Steaming Up

[martswain]

I concur, the use of A/C makes a very marginal difference to fuel consumption on modern cars, it cannot be nothing but your feet make the greatest difference to MPG (no offence intended to those with hand controls)

Being lucky enough to always change to a brand new vehicles, I have found that the inside of all the glass needs a good clean even if it appears clear, I am convinced some of that "new car" smell is actually chemicals that contaminate the glass and encourage misting.

The problem seems to go away after a couple of months.

[Catlover]

Cleaning inside windows with soapy water will leave a soap film on the glass, reducing the effect of fogging. Also works on spectacles when wearing a face mask.

[Mick F]

I see that Stivino is confused.

i'll try and be clearer.

He is correct of course, that you don't get something for nothing and aircon requires power to drive it.

The issues are: ............................  how much power, and is it actually detectable in all the other power requirements of a modern vehicle on modern roads?  Does it actually make any difference? What are the huge advantages of aircon as opposed to the minimal cost of running it?

I maintain that running aircon permanently makes no appreciative difference to fuel consumption.  In fact so small a difference, it's undetectable in the real world of real driving on real roads.

Mick.

[Satsuki]

1 hour ago, Mick F said:

I see that Stivino is confused.

i'll try and be clearer.

He is correct of course, that you don't get something for nothing and aircon requires power to drive it.

The issues are: ............................  how much power, and is it actually detectable in all the other power requirements of a modern vehicle on modern roads?  Does it actually make any difference? What are the huge advantages of aircon as opposed to the minimal cost of running it?

I maintain that running aircon permanently makes no appreciative difference to fuel consumption.  In fact so small a difference, it's undetectable in the real world of real driving on real roads.

Mick.

The fact is, the power consumption is highly depending to the AC model and the age of the car (the older ACs tend to consume more energy for being less efficient). Back in 2000 there was an article published by NREL [1] showing the fuel economy can be decreased by almost  0.4 km/L (1 mpg) when using the AC. 12 years later, another research in 2012 [2] showed that about 80% of the fuel consumption is by the AC compressor and depending on the vehicle speed it can affect the fuel efficiency up to 90% (when the car is idle) and down to about 9% when driving at 120k/h (75miles/h). Later in 2015 a research [3] showed that ACs with electrical compressors (versus belt driven compressors) are up to 54% more efficient and can reduce the fuel consumption by almost 14%.

Since the last published report in 2015, the cars are considerably improved and are more efficient and optimised. The technology is also advanced considerably. If the fuel consumption was a big issue you would see a lot of research and publication about it. So to sum up the discussion, as the main fuel consumption is by the AC compressor, it really depends on what temperature/power the AC is set to and the outside temperature. The warmer outside temperature leads to higher consumption. Also if you spend most of your time in traffic jams then the fuel consumption by AC will be more obvious. Finally, the older the car technology is the more fuel consumption for the AC.

I personally do not feel much different in fuel consumption with my Yaris Hybrid 18 reg and I am able to get about 65-70mpg with AC on during winter. However, I don't leave the AC constantly on, but as soon as I feel the windows are fogging I switch it on and leave it on.

 

[1]: https://www.nrel.gov/docs/fy00osti/28960.pdf
[2]: https://journals.sagepub.com/doi/full/10.1177/0954407012455973
[3]: https://iopscience.iop.org/article/10.1088/1757-899X/100/1/012028

[mrpj]

On 10/8/2020 at 9:55 AM, Catlover said:

If your Yaris is a hybrid (you not given details) then the air con would be electrically driven so not using petrol. 

Not directly, no. But it will be using energy from somewhere which needs to be replaced by the engine running, fuelled by ------

I wish I could devise a way of patenting free energy!

Sadly Elaine hasn't returned to interrupt this free energy topic.

[Mick F]

14 hours ago, Satsuki said:

The fact is, the power consumption is highly depending to the AC model and the age of the car (the older ACs tend to consume more energy for being less efficient). Back in 2000 there was an article published by NREL [1] showing the fuel economy can be decreased by almost  0.4 km/L (1 mpg) when using the AC. 12 years later, another research in 2012 [2] showed that about 80% of the fuel consumption is by the AC compressor and depending on the vehicle speed it can affect the fuel efficiency up to 90% (when the car is idle) and down to about 9% when driving at 120k/h (75miles/h). Later in 2015 a research [3] showed that ACs with electrical compressors (versus belt driven compressors) are up to 54% more efficient and can reduce the fuel consumption by almost 14%.

Since the last published report in 2015, the cars are considerably improved and are more efficient and optimised. The technology is also advanced considerably. If the fuel consumption was a big issue you would see a lot of research and publication about it. So to sum up the discussion, as the main fuel consumption is by the AC compressor, it really depends on what temperature/power the AC is set to and the outside temperature. The warmer outside temperature leads to higher consumption. Also if you spend most of your time in traffic jams then the fuel consumption by AC will be more obvious. Finally, the older the car technology is the more fuel consumption for the AC.

I personally do not feel much different in fuel consumption with my Yaris Hybrid 18 reg and I am able to get about 65-70mpg with AC on during winter. However, I don't leave the AC constantly on, but as soon as I feel the windows are fogging I switch it on and leave it on.

 

[1]: https://www.nrel.gov/docs/fy00osti/28960.pdf
[2]: https://journals.sagepub.com/doi/full/10.1177/0954407012455973
[3]: https://iopscience.iop.org/article/10.1088/1757-899X/100/1/012028

Thanks for that fulsome reply.

in all the years of using aircon in UK, the only time it made any appreciable difference to fuel use, was when the car was boiling hot whilst parked, and then having the aircon on fully cold until the car internals were happy.  Only happened a couple of times, and generally we find parking under trees or in the shade and have done for years now.

Since making sure the cars haven't been parked in full summer sunshine, all has been easy and cheap.  in fact, the fuel consumptions haven't been affected in the slightest when using it.

First car was  Renault 1.6 16v Clio bought brand new in April 2001 and had her for 12years before parting with her.  Aircon on permanently and the car had done 100,000miles by the time we sold her.

Mick.

[Biomecanoid]

On 10/8/2020 at 3:13 PM, Mick F said:

Of course not.  Plain physics.

I was replying to the assumption that "aircon uses more petrol".

There are many things - or driving styles - that use "more petrol", and aircon doesn't use any more petrol than driving badly, in fact far far less.

Once the car is dry, and once the car is running and the engine is warm, the aircon demand is minimal, and perhaps miniscule.   It's a myth that "aircon uses more petrol"  because it doesn't.  Hybrids use electricity and non-hybrids use a belt driven from the engine.

This is me.  Speaking as a long-term aircon user with conventional ICE cars and as a hybrid user too.  Believe me or not, it's up to you.

Mick.

Aircon steals power from the engine, hurting acceleration, top speed and fuel consumption . It is very evident on all cars unless you have a big engine like 2000cc 

[Catlover]

Dont notice it in my car.

[bathtub tom]

46 minutes ago, Biomecanoid said:

Aircon steals power from the engine, hurting acceleration, top speed and fuel consumption . It is very evident on all cars unless you have a big engine like 2000cc 

So when you see BTCC cars putting on their headlamps to intimidate the car in front, they're compromising their chances of passing because they're reducing their available power to the transmission?

[martswain]

It will hurt top speed a little, but as most cars can easily exceed 90 mph, you'll never notice unless you are on a track.

Unless you are using full throttle every time you accelerate, there will be plenty of excess power to overcome the 1-4 HP that a typical modern A/C unit consumes, acceleration in normal driving will be exactly the same.

@Biomecanoid you won't even notice it, you'll just have to plant your right foot a little harder in your little Sirion.

Of course you use more fuel, but you'll only really notice it in stop-start traffic on a hot day.

[Patrick O'Kane]

On 10/8/2020 at 9:55 AM, Catlover said:

If your Yaris is a hybrid (you not given details) then the air con would be electrically driven so not using petrol. 

As the gent above says - you don't get something for nothing. The A/C system is electric yes - the electricity comes from the alternator which, regardless of whether car is hybrid or not, is driven by the petrol engine. The more power that's required in the car, even from batteries, the greater the alternator load is on the engine to recharge those batteries. However, any fuel consumption impact from this load is very minimal......fractions of an mpg impact

 

 

[scannerman]

On 10/8/2020 at 1:13 PM, Mick F said:

Of course not.  Plain physics.

I was replying to the assumption that "aircon uses more petrol".

There are many things - or driving styles - that use "more petrol", and aircon doesn't use any more petrol than driving badly, in fact far far less.

Once the car is dry, and once the car is running and the engine is warm, the aircon demand is minimal, and perhaps miniscule.   It's a myth that "aircon uses more petrol"  because it doesn't.  Hybrids use electricity and non-hybrids use a belt driven from the engine.

This is me.  Speaking as a long-term aircon user with conventional ICE cars and as a hybrid user too.  Believe me or not, it's up to you.

Mick.

On some cars with belt driven AC pumps, you may notice that when the AC pump clutch engages to drive the pump, the idle speed will be increased. This in itself will make very little difference to fuel economy but the effort to drive the pump will be a slight drain on engine power, so to maintain previous performance to when the AC pump was disengaged, you will need to push the gas pedal a bit further, hence less economy. Whether this is significant I leave others to decide but you don't need a degree in engineering to work it out.

[Mick F]

The issue here, is driving along and then switching the aircon "on".

If it's on all the time, the car is always dry and clear.  Most - if not all - systems have a temperature control.  You can have aircon on and be warm if you want.  All aircon does, is dry the air.  You can have any temp you want, but if you want an extreme, the system has to do more work ............. hence the load.

Once it's at the desired temp, the load is minimal.  Ours is on permanently, and last time we drove the car - day before yesterday - it was set to 22degC.  As the weather out there is typical December weather, the heater took the brunt of the engine power and certainly not the aircon.  We had dry heat at 22degC coming in and clear windows.

Mick.

[TonyHSD]

This with aircon and lost power is only noticeable in small engine underpowered cars, in bigger engine cars you can’t notice any lost of power and engine pulls the car as usual. In Toyota hybrids AC is electric and uses power from high voltage hybrid Battery and does affect efficiency especially in hot summer days where more power is needed to cool down the cabin. Driving in town with AC ON and mostly on electric power you will notice how ice kicks in more often to recharge the hybrid Battery. I personally never use air conditioning in winter season unless really need to clean the windows quickly, and in summer only when over 20C° outside. Air conditioning doesn’t necessarily mean better quality air in terms of purity and humidity, at least not in these cars we are talking about but if you like it ON all the time that’s no problem at all, efficiency would not suffer that much, driving style makes for good or bad fuel consumption.👍🚗