Immediate difference between C5 and Xantia

[nick]

(5) Again from (3) and has nothing to do with engine temperature per se. An A/C system is basically a fridge. Go to the back of your fridge and check the heat. It is that heat and any heat from ancillaries in maintaining the correct temperature of your engine which increases your carbon footprint.

I agree that any additional fuel used by the engine in running an a/c system will contribute to CO2 emissions, but how does the heat coming out the back of a fridge or from an aircon condensor contribute to it?
This is not addditional heat that has been produced, merely heat that has been moved from one place to another by a heat pump. The only net heat production by a fridge is from its 100 watt (or so) motor. The majority of the heat coming out the back is what its removed from the inside of the cabinet.

The way I look at it is, I bought a smaller car which uses less fuel with the aircon on than a larger car would with the aircon off!
Do you necessarily need a car as big as a C5??

[frenchcarnut]

I agree that any additional fuel used by the engine in running an a/c system will contribute to CO2 emissions, but how does the heat coming out the back of a fridge or from an aircon condensor contribute to it?

The principle behind a fridge is no different to that of an A/C system in that the differences in pressure within a system are utilised to lower temperature. A fridge operates by absorbing heat and then transferring it from a cooler to a warmer region using latent heat transfer, compression and expansion of vapour. However, the cooler you want a fridge the more power has to be used in creating the heat differential. To a degree this is supplied by the engine, but unfortunately there is loss through transfer inefficiencies and thus overall more heat is produced, more power required thus more fuel is consumed.

I get the feeling that most who have argued against this point have suggested that these inefficiencies are minimal or have improved over the years. Well the latter may be the case and the former might be insignificant to the individual motorist as I have already alluded to with my C5, but collectively it still promotes a problem.

The way I look at it is, I bought a smaller car which uses less fuel with the aircon on than a larger car would with the aircon off!

Totally agree.

Do you necessarily need a car as big as a C5??

Yes, but since I have one, it will be converted to use SVO once the warranty has expired with less reliance on the A/C

[Kowalski]

Alan is right that an air-con system works most efficiently when its properly maintained, when it gets low on gas the efficiency isn't great. My Dad used to work with refrigeration equipment and when I've quoted the pressures and temperatures that the car uses he said that the car system has been designed to be very efficient, but you'll only get the right temperatures and pressures if there is the right amount of gas in the system.

I can't seem to find where I read about fuel consumption increasing with air conditioning being turned on, the energy to run the system doesn't come for free, some cars used to have a switch to turn off the air-con when you fully opened the throttle....

I couldn't find the a site on the 'net that quoted the fuel consumption cost for using air-con but I did find the following on the AA website...

Drive smoothly – driving hard can increase fuel consumption by a third
Don’t exceed speed limits – regularly exceeding the speed limit (eg 80mph instead of 70mph on a motorway) can add up to 30 per cent to fuel bills
Carrying an empty roof rack can add 10 per cent to fuel bills
Low tyre pressures, open windows, air-conditioning, harsh acceleration, inappropriate gear changes and excessive loads all increase fuel consumption
Plan journeys carefully – much fuel is wasted by motorists who either get lost or do not take the best route to their destination

The addition in fuel consumption for air-con seems small compared to the other things you could be doing to burn excess fuel. Driving a smaller car isn't mentioned, I do believe that not driving a gas guzzler has some benefit on your fuel consumption.

[rowanmoor]

I have read something (thought it was AA or RAC) that said that typically 40mph is the point at which the efficiency balance tips from open windows to air-con.

ie. below 40mph you use less fuel driving with the windows open rather than air-con on, but over 40mph you use less with air-con on rather than windows open.

That will of course be an average and specific car and engine variants will be different.

Of course windows closed, no fan and no air-con would be the most efficient, but how many people can put up with that on a hot day. I don't have air-con and love the heat, but I know I couldn't cope with that, so I have the blower on full and (if at low speeds) the windows open. My driving style, air-con would be least of my worries when it comes to fuel consumption.

[jeremy]

It never ceases to amaze me how poor the ambient ventilation is on our Citroens. I have BX TD and a ZX Avantage - both of which have dashboards full of vents - but both only seem to provide stuffy air in warm weather - and so I have to start opening the windows and roof.

Life would be much more pleasant if they would give a good blast of ambient air, like my old Hillman Hunter did. I'd also welcome the removal of the fascia vents from the heating system so as to allow cooler air at face level when the heater was being used.

(Water valve does shut off on BX and ZX heater is in good order)

[nick]

I'd also welcome the removal of the fascia vents from the heating system so as to allow cooler air at face level when the heater was being used.

The very early BXs did have that, the two outer dash vents were totally seperate from the heater. The downside was if you had them open a lot of engine noise came in as they were basically just a hole through the bulkhead into the grille below the wiper!

[jeremy]

You've got me thinking there Nick. I seem to remember that BL Mini's used an insulated tube to get over that problem (well it looked good), and Jaguar used inlets over the headlights for a foot level vent.

[nick]

All the BX version used was a thin piece of mesh across the holes to keep debris out. It seemed to be only early base models that had these. My A reg 14E had them, but the C reg 16RS I owned later didn't, the vents were plumbed into the heater on the later car. (Both with the PRN dash)
The original 1.4 was never a quiet engine and having the vents open made it even more noticeable.

[frenchcarnut]

It never ceases to amaze me how poor the ambient ventilation is on our Citroens. I have BX TD and a ZX Avantage - both of which have dashboards full of vents - but both only seem to provide stuffy air in warm weather - and so I have to start opening the windows and roof.

Life would be much more pleasant if they would give a good blast of ambient air, like my old Hillman Hunter did. I'd also welcome the removal of the fascia vents from the heating system so as to allow cooler air at face level when the heater was being used.

(Water valve does shut off on BX and ZX heater is in good order)

I used to hate my petrol Xantia for that, always fogging up in wet weather, always needing the A/C on to shift it or the windows down and the windscreen fan full blast. Happens a lot less in the C5

[Mandrake]

I used to hate my petrol Xantia for that, always fogging up in wet weather, always needing the A/C on to shift it or the windows down and the windscreen fan full blast. Happens a lot less in the C5

Hi,

Are you sure the inside of the windscreen didn't just need a damn good clean ? My Xantia was like that when I first got it too - window looked clean, but it would always fog up inside on a cold day unless I used the A/C - I gave the inside of the windscreen a thorough clean with a cloth and meths and no more fogging

A year or so later it started fogging again and I had to clean it again - my suspicion is that there is a tiny amount of leakage in the heater matrix and the heater gradually coats the inside of the windscreen with invisible gunky film from something in the coolant, which "fogs" very easily in cold weather...

Regards,
Simon

[TehAgent]

The differences between a xantia and C5?

You need to convert a C5 to run on Veggie, where as my Xantia just drinks it strait from tesco's / costco

At the moment I'm running my Xantia on 100% rapeseed oil. runs fine, its performance is better and goes for longer than when run on the diesel equivalent, and its almost half the price.

When my Aircon was working (before the compressor blow its bearings) and i was driving around on diesel, there was no difference in the mileage i could get.

To understand this, you have to look at how the compressor is attached to the car and how it functions, its mounted under and just forward of the engine, beneath the fuel pump (on my model anyway) a belt runs around the AC compressor then around the Hydraulic pump and then the alternator and so on, and is driven by the engine,

When the AC switch on the dash is pressed, the ECU tells it to engage the clutch on the AC compressor and this in turn, makes it rotate, The only part of the compressor to be electric is the clutch which from what i can gather is a electromagnetic brake. But you may correct me if I'm wrong.

I cant see how something of this design can use more fuel as the compressor is very easy to rotate by hand (trust me Ive done it) this would have minimal effect on the actual engine rotation its self and a electromagnetic brake wouldn't need that much from the battery to engage with enough force to hold the wheel in place while it rotates.

Then we have the heater matrix, when the engine is running and the AC is off, my car idles at just below 1000rpm, when the AC was on, it still ran at just under 1000rpm. so it wasn't having any effect on engine rotation and thus not using anymore fuel than it was at idle, (as a example car, my friends mondeo 2.0si, creeps above the 1000rpm mark soon as the AC is on, and thus does have a effect on fuel consumption)

IIRC, a car battery draws in 14amps from the alternator when it is running, to keep the battery charged, this would be plenty and the AC would not need to draw more from the battery than what the battery is getting (or your battery would go flat pretty fast)

As for carbon foot prints,

Well as I'm on 100% pure rapeseed, I'm releasing back the same carbon from my car that the plant took out in its life time. when i have to start mixing it with diesel, it will be a little higher, but still below what your C5 will be kicking out so...i shall be sticking to my trusty Xantia

Now all i need to do is get that AC working again.

Some of what i said might be wrong, but the principle is the same, things have progressed since AC became more main stream and the only true test is by those who own the car and not by someone who gets paid to type road tests for a day.

but at the end of the day, when all is said and done, one thing that no one can calculate is other peoples driving styles and the temperament of another's car. and its here that its going to be very diverse with figures and opinions.

[RichardW]

Sorry mate, but most of that (about the A/C) is frankly bollox

I cant see how something of this design can use more fuel as the compressor is very easy to rotate by hand (trust me Ive done it) this would have minimal effect on the actual engine rotation its self and a electromagnetic brake wouldn't need that much from the battery to engage with enough force to hold the wheel in place while it rotates.

Whilst the clutch might be an electromagnetic brake, the compressor is not - it HAS to take energy from the engine to run it. After all your fridge doesn't get cold unless you plug it in does it?

Then we have the heater matrix, when the engine is running and the AC is off, my car idles at just below 1000rpm, when the AC was on, it still ran at just under 1000rpm. so it wasn't having any effect on engine rotation and thus not using anymore fuel than it was at idle, (as a example car, my friends mondeo 2.0si, creeps above the 1000rpm mark soon as the AC is on, and thus does have a effect on fuel consumption)

Diesel engine has a governor - as the A/C loads the engine up the governer injects more fuel to keep the engine revs the same. You will notice a slight shudder as the compressor kicks in, and then tend to find you need more revs to pull away - this is the effect of the work the engine is doing to turn the compressor.

IIRC, a car battery draws in 14amps from the alternator when it is running, to keep the battery charged, this would be plenty and the AC would not need to draw more from the battery than what the battery is getting (or your battery would go flat pretty fast)

The load on the alternator varies depending on the electrical load. On a dry day with no blowers, once the start charge has been replaced the alternator will be doing little. On the other hand on a wet, dark, day just after a cold start with the blower on full the alternator will be working hard. Diesel engine alternators are usually rated somewhere around 80 amps. When you are running the A/C the engine cooling fans run all the time too - this will increase the load on the alternator by a not insignificant amount. It used to be the case that A/C cars had bigger alternators and batteries than non A/C cars - this is possibly still true for petrol cars, but probably not for diesels (bigger alts and batts to compensate for high starting currents required).

Some of what i said might be wrong,

8)

What ever anyone says using A/C WILL use more fuel. It simply has to - you don't get something for nothing (well unless you increase the boost on a diesel engine, when this IS possible ). How much will depend on the sort of driving you do, the ambient temp, the state of the A/C system, the size of the engine, etc etc etc.

[frenchcarnut]

Are you sure the inside of the windscreen didn't just need a damn good clean ? .....

I used to use 'Mr Muscle' kitchen degreaser on my windscreen quite regularly. Perhaps that wasn't quite enough but you provide an interesting theory which I hadn't considered.

As for the Xantia, it's someone else's problem now, lest it be consigned to the scrap yard, but you never know the same might eventually apply to the C5, so thanks for the tip!

At the moment I'm running my Xantia on 100% rapeseed oil. runs fine, its performance is better and goes for longer than when run on the diesel equivalent, and its almost half the price.

I think I'd like another Xantia (but diesel this time) to tinker with and do all my veggie driving around town. Should be able to pick one up from ebay for 50 quid where the owner has abandoned it because of the suspension, heater blower and wheel sensors

What ever anyone says using A/C WILL use more fuel. It simply has to - you don't get something for nothing (well unless you increase the boost on a diesel engine, when this IS possible ). How much will depend on the sort of driving you do, the ambient temp, the state of the A/C system, the size of the engine, etc etc etc.

That's the way I see it and have experienced it. I was told on numerous occasions that the A/C was fine on my petrol Xantia but that it was much better on diesels both with respect to performance and consumption.

[dnsey]

I cant see how something of this design can use more fuel as the compressor is very easy to rotate by hand (trust me Ive done it) this would have minimal effect on the actual engine rotation its self and a electromagnetic brake wouldn't need that much from the battery to engage with enough force to hold the wheel in place while it rotates.

Was the clutch engaged when you tried this, and did you turn it long enough to build up pressure? The energy absorbed by the a/c is evident by the drop in idle speed when it engages (unless compensation is used, as it usually is nowadays).

[Kowalski]

I cant see how something of this design can use more fuel as the compressor is very easy to rotate by hand (trust me Ive done it) this would have minimal effect on the actual engine rotation its self and a electromagnetic brake wouldn't need that much from the battery to engage with enough force to hold the wheel in place while it rotates.

Unless you can spin it quickly enough by hand so it produces pressure in the system the resistance will be very low, it's not actually doing anything meaningful. To get resistance you have to create flow, create pressure and actually cool the evapourator so that the TX valve closes a little....