I wonder how the RS4 thing works?

Could be some peltiers and a fan powered by solar/battery. Not as efficient as a compressor system but quite small and scalable.

Personally I would rather have electric compressors along with electric water pump and PAS. Yes having to generate more electricity seems to add more inefficiency into the system but electric means you only need them on when needed, you can have them running with the engine off and you can boost them independent of engine speed. It also does away with parasitic serpentine belts and tensioners and idlers and means you can put things in accessible places and free up room around the cambelt for access. As well as not taking out your cambelt when something fails (eg water pump).

The new peugeot/bmw turbo charged petrol engines use electric water pumps so the pump does not run when the engine is warming up and can continue pumping water when the engine is turned off.

Another benefit of electric items is they can be shut down easier when accelerating so instead of needing a 120hp engine you can get away with a 110hp engine for the same acceleration response. Small savings which are all helping push up MPG figures.

You can also reduce the engine electricity generation load by extracting more energy during braking which helps reduce brake wear (slightly) and utilises waste energy.

Some mechanical aircon systems do this already (the old peugeot 306 one does) in that the magnetic clutch releases during hard acceleration to free up engine power.

If I had ‘just’ air-con I probably wouldn’t have it on all the time – only when needed

Modern ones do that for you anyway – even if they aren’t climate control.

30.5mpg – Astra’s baseline fuel economy
30.4mpg – Two front windows a third open
30.3mpg – Roof bars and laden roofbox
30.2mpg – Two front windows totally open
29.7mpg – Four tyres down to 20psi
28.0mpg – Air-conditioning on
27.2mpg – Three large adult males in the back seat
24.1mpg – Roof bars and laden roofbox, plus three adults in the rear, a bike carrier with two adult bikes and air-con

So

A) When I haul around a full tank of fuel its costing me money

and

B) Even when she is sat in the passengers seat … the wife is costing me money !!!

molgrips – Member
If I had ‘just’ air-con I probably wouldn’t have it on all the time – only when needed

Modern ones do that for you anyway – even if they aren’t climate control.

Eh? I don’t get this.
I mean with normal air-con I’d only turn it on when it got hot & stuffy inside the car or I wanted to clear the screen.
If it was a comfortable temp/cold outside/a bit warm/I wanted to drive with the windows open/I was just popping to the shops then i wouldn’t turn the air-con on. So it would be off.

I don’t mean that the air-con will regulate somehow, I just mean I wouldn’t actually turn it on.

Like her indoors’ 58 plate Pug 308. If you turn the air-con off, it is off. If it is on, it is on
It doesn’t turn on when needed, as it doesn’t know when ‘needed’ is. Whereas the climate control ‘knows’ that it is constantly trying to achieve 20 deg. C. or whatever it’s set-point is.

There can be benefits of having it always keeping a check on temps as keeping the temp in check requires much less instant power than trying to cool from a very high temp. You can then potentially get away with a much smaller system which can be better optimised. It also ensures the system is kept in good working order as seals need to be lubricated which happens when the gas is flowing.

I do agree that you should be able to turn it off though. Just don’t keep turning it on and off thinking you are saving power. If you want it on leave it on and keep it ticking over. If you are doing a short trip and/or have windows down etc then leave it off.

What I meant was that I think there is some kind of ballast in the system. So the compressor comes on, chills the coolant, then goes off again – like a home fridge. You won’t notice the actual switch coming on or off, or the air temperature changing – to you, it’s ON all the time but the compressor is not actually running the entire time.

This is only a supposition tho based on a few bits of reading on forums and such.

Personally I would rather have electric compressors along with electric water pump and PAS

The new Prius has no belts at all, not even a cambelt – for the reasons you describe. Mine only has one on the water pump. You’ve got as much electrical power as you need at any given time, so you might as well take advantage of it.

Some mechanical aircon systems do this already (the old peugeot 306 one does) in that the magnetic clutch releases during hard acceleration to free up engine power

Even really old cars have this – my crappy old 94 Passat had, if you had one with AC which I didn’t. It was built into the injector pump.