Real world mpg

(04-05-2012 10:51am)Donny Dog Wrote:  The handbook recommends that the air con and 'auto' be left on as a 'default' setting,. I had assumed that the actual cooling function (requiring the compressor to run) would only operate when the internal selected temperature could not be achieved using cooler air from outside, and that the air con would not actually run other than in hot weather. Is this not the case? If it is cold, and presumably the air is being warmed rather than cooled, what is the air con doing? Does the heater consume electricity? (I had assumed it was the normal type of heater which operates off the engine cooling system, and that the heat was therefore 'free').

The air-con compressor does more than just cool the air - it also dehumidfies it too. The Evoque has an Eco setting I expect? In Eco the system regulates the temp without the compressor or dehumidifying the air - its pretty OK unless the ambient air is warmer than the desired temp inside the car.

Back in my motor industry days we used to reckon that an air-con compressor consumed 10% of engine power...that's a lot. They are probably more efficient these days.

I think I read here in one of Tim's posts that it is an electric heater - not water.

It is better for your car to leave the CLIMATE control on (it isn't just AC as Straydox points out) humidity inside the cabin can cause loads of problems with the electronics so best to leave it on the auto setting and keep the interior damp free, especially helpful when you get into the car when it is pouring with rain or you have snow on your shoes too.

The heater is a PTC system using a ceramic element, you can read all about it here http://www.dbk-usa.com/ptc-heaters/ptc-heater-facts

(04-05-2012 12:16pm)Straydox Wrote:  The air-con compressor does more than just cool the air - it also dehumidfies it too. The Evoque has an Eco setting I expect? In Eco the system regulates the temp without the compressor or dehumidifying the air - its pretty OK unless the ambient air is warmer than the desired temp inside the car.

So, leaving aside when it's warm enough to require refrigeration to control the interior temperature, how often would the compressor run, do you reckon?

(04-05-2012 12:16pm)Straydox Wrote:  Back in my motor industry days we used to reckon that an air-con compressor consumed 10% of engine power...that's a lot. They are probably more efficient these days.

That would be one big compressor if it consumed 19 hp (in my SD4)!

(04-05-2012 12:16pm)Straydox Wrote:  I think I read here in one of Tim's posts that it is an electric heater - not water.

I thought I'd read that, but wasn't sure. Maybe modern cars don't use waste heat any more, but why??

(04-05-2012 02:32pm)Donny Dog Wrote:  So, leaving aside when it's warm enough to require refrigeration to control the interior temperature, how often would the compressor run, do you reckon?


That would be one big compressor if it consumed 19 hp (in my SD4)!


I thought I'd read that, but wasn't sure. Maybe modern cars don't use waste heat any more, but why??

It's hard to be specific about when the compressor will run because its dependent on air temp and humidity and that's variable - our UK air is really damp in winter for example. Personally I drive most all of my cars in Eco mode (and will with the Evoque too). As Tim has said when you get into the car in the rain or have snow cover boots running full A/C will dry out the interior (and your head too - have you noticed your nose gets all dry inside with full climate on?).

An air-con compressor can apply quite a load - in some cars you can see the rev counter needle twitch at idle when the compressor kicks in (engine management detects it and adjusts the idle speed to compensate). Some cars have electromagnetic clutches in the aircon compressor pulley - so whilst the pulley rotates all the time it may not be actually be connected to the compressor.

The change to electrical heaters is probably driven a desire to have the smallest amount of coolant in the engine as possible so it will warm up very quickly and be more efficient.

(04-05-2012 02:48pm)Straydox Wrote:  It's hard to be specific about when the compressor will run because its dependent on air temp and humidity and that's variable - our UK air is really damp in winter for example. Personally I drive most all of my cars in Eco mode (and will with the Evoque too). As Tim has said when you get into the car in the rain or have snow cover boots running full A/C will dry out the interior (and your head too - have you noticed your nose gets all dry inside with full climate on?).

An air-con compressor can apply quite a load - in some cars you can see the rev counter needle twitch at idle when the compressor kicks in (engine management detects it and adjusts the idle speed to compensate). Some cars have electromagnetic clutches in the aircon compressor pulley - so whilst the pulley rotates all the time it may not be actually be connected to the compressor.

The change to electrical heaters is probably driven a desire to have the smallest amount of coolant in the engine as possible so it will warm up very quickly and be more efficient.

OK, thanks very much. Is there an 'Eco' button, then (if so, I haven't spotted it yet!) or do you just mean cancel 'Auto' and 'AC'?

(04-05-2012 02:32pm)Donny Dog Wrote:  Maybe modern cars don't use waste heat any more, but why??

They still use the waste heat but just to heat the engine block and because the blocks are so thermally efficient for modern diesels the cabin takes for ever to warm up. This and to help reduce cold start emissions in cold weather is why Freelander, D4,RRS and FFRR have fuel burning heaters which also can be specced with a remote timer to pre-warm the block so you can drive off with warm air quicker on cold mornings. When the first LR were launched with these heaters there were lots of phone calls to dealers and Land Rover Assist on the first morning when the temperature dropped below 5c because of smoke coming out from under the front bumper or the nearside front wheel arch..................... it was the exhaust of the diesel powered heater! Must admit that I wasn't impressed with the timed heater that was fitted to my last FFRR, it never seemed to warm much and the seat heaters and heated steering wheel were better at warming me until the car was up to normal operating temperature. Evoque doesn't get the FBH because it has the PTC heater

(04-05-2012 03:38pm)XFullFatTim Wrote:  They still use the waste heat but just to heat the engine block and because the blocks are so thermally efficient for modern diesels the cabin takes for ever to warm up. This and to help reduce cold start emissions in cold weather is why Freelander, D4,RRS and FFRR have fuel burning heaters which also can be specced with a remote timer to pre-warm the block so you can drive off with warm air quicker on cold mornings. When the first LR were launched with these heaters there were lots of phone calls to dealers and Land Rover Assist on the first morning when the temperature dropped below 5c because of smoke coming out from under the front bumper or the nearside front wheel arch..................... it was the exhaust of the diesel powered heater! Must admit that I wasn't impressed with the timed heater that was fitted to my last FFRR, it never seemed to warm much and the seat heaters and heated steering wheel were better at warming me until the car was up to normal operating temperature. Evoque doesn't get the FBH because it has the PTC heater

I must say I never use the heated seats (and I've had them in several cars), but the heated steering wheel is great. I have problems with the circulation in my fingers (due to previous injuries, largely) and they turn blue when they're cold, especially if placed high up on the steering wheel, so the heated wheel is a real boon. A bargain at £180 really.

I have an ECO button but it's nothing to do with heating, it's to do with Start/Stop on the Manual version. I think ECO in this context means turning off your heater and A/c...?, I did this (heater) and it's saved me 3mpg on 20 mile journeys. But will soon turn it on again if we have another 7 deg morning!

I'm not sure if this thread is still on topic but a recent holiday meant I could drive decent distances on a mix of motorways and decent A and B roads where the Evoque did alright. She returned 42 mpg on both the out and return runs and this was driving normally, rather than sportily and the majority of time in Sport mode.

Went out for a run in the country today for lunch.

4 adults 80 mile round trip, used economy route setting on nav, using A & B roads to restaurant, on a reset trip, outward journey 39.1 mpg, on the return, sought out the motorway, back home overall journey was showing 40.2 mpg.

No dawdling, kept up with the speed limits.

Happy with that.