[alcook]

Does the Aircon cool only?

I was convinced AC's could heat as well.... (though the snow flake on the button may give the game away....)

Mine seems sadly lacking in heating and I have to effectively wait for the engine to warm up with the temp on 28.... Oh, and the seat on level 3.....

Is it broke or am I a plonker???

[grey man]

Thats a good question. I believe some air con systems can operate as a 'heat pump' to provide early (after a cold start) heat, but very few do this, the recent Honda Accord being the only one I have heard does this. Honda's 2.2 diesel is very efficient and consequently very slow to warm through. It may be that spray freezing onto the front evaporator (in heat mode, normally the condenser) is probably an issue. Not sure how this is avoided.

BMW in the X5 diesel use a Webasto fuel fired heater. It is supposed to assist rapid warm up in cold weather. Optionally it can have a remote switch on that also turns on the heater fan so that you can turn on the heat whilst you have breakfast and get into a warm car. This may also be used/optional in the 5 series diesel too? Unfortunately, although my X5 has one, it has never worked, and this seems a quite common trouble. As ever - its expensive to diagnose (as it only operates when the ambient temperature is low and the engine cold) and I'm told expensive to replace.

[M3-FAST]

Originally Posted by alcook

Does the Aircon cool only?

I was convinced AC's could heat as well.... (though the snow flake on the button may give the game away....)

Mine seems sadly lacking in heating and I have to effectively wait for the engine to warm up with the temp on 28.... Oh, and the seat on level 3.....

Is it broke or am I a plonker???

MMM, never really thought about this but good point!

I have an aircon unit in my conservatory at home. It is one with the outdoor unit and an indoor mounted wall blower. In the summer it chills the room and gives out cold air almost immediately if called for, However, when set to warm the room, the outdoor unit powers up and runs for a good 3-5mins before the indoor unit starts blowing warm air. Not sure what it is doing though but it is unable to dispense warm air as quickly as it can cold.

Maybe the setup in the car is similar, and you are not waiting for the engine to warm, but for the aircon unit to blow warm air?

Maybe someone will be along soon to enlighten us - where is Squeeze? He may know!

[NFS]

'Air conditioning' as a term encompasses heating, cooling and de-humidification.

The systems we have in cars are actually for 'comfort cooling'. Although they are heat pumps they only operate in one direction. Taking heat from the internal space and dumping it outside.

I would imagine that this is done to save money on the controls and because cars already have an alternate 'waste' heat source freely available (the engine).

If you used the heat pump for heating, then the engines waste heat would be dumped to atmosphere and energy would be wasted in driving the AC compressor. Using air tempered with engine heat would mean that the compressor isn't operating all the time, which would then reduce fuel consumption.

A lot of buildings work this way, with 'mixed mode' systems. For example an office comfort cooling 'split system' is often combined with a low pressure hot water (LPHW) traditional radiator heating system.

The split system could be specified to provide heat as well as cooling, but LPHW would typically be cheaper and more energy efficient. Because per unit gas fired heating would work out better than elec power for the compressors.

[alcook]

Thanks mate. Excellent technical answer on AirCon (most of which was new on me - so thanks)

Unfortunately I read it 4 times and still don't know if the answer is 'Yes' or 'No'....

[- Paul -]

No - if aircon is on - the heating still works if thats what you mean?

[alcook]

Hi Paul.

No, I was asking if the Aircon system in my car can also provide direct heat, rather than simply passing it through from the engine (which takes time to warm up on these cold mornings).

i.e I can get instant cooling.... but not warming.

From NFS's answer, it appears it has a cooling function only and only.

[NFS]

Originally Posted by alcook

Hi Paul.

No, I was asking if the Aircon system in my car can also provide direct heat, rather than simply passing it through from the engine (which takes time to warm up on these cold mornings).

i.e I can get instant cooling.... but not warming.

From NFS's answer, it appears it has a cooling function only and only.

Yes you are right, BMW in car AC is cooling only.

The system works by circulating a 'volatile' liquid around internal pipework. 'Volatile' just means that it's likely to change state from liquid to gas at temperatures close to ambient, when it's pressure is altered by the pump.

The liquid is 'pumped' by a mechanical compressor powered by the engine. This additional load is why the fuel economy is reduced with AC on.

When it changes from gas to liquid and vice versa the refrigerant either takes in or gives out heat.

By this process the AC system can take heat from the internal space and dump it outside.

It's perfectly possible to build a system that operates in reverse (to provide heating) because the process is the same either way. However this would require additional controls and would make the system more expensive.

Main reason (I think) why this isn't provided in cars though is that the waste heat from the engine is freely available. This can be used to heat the interior WITHOUT having to run the pump, which means that you can provide heat without reducing fuel economy.

[alcook]

Originally Posted by NFS

Main reason (I think) why this isn't provided in cars though is that the waste heat from the engine is freely available. This can be used to heat the interior WITHOUT having to run the pump, which means that you can provide heat without reducing fuel economy.

Thanks mate, that one I understood...

Shame it's not an option too, as cold days are as common here as hot ones and that extra heat in the mornings would be a welcome addition (especially if remote controlled) rather than waiting a good 5 mins or more for the engine to warm up enough to start warming the cabin...which then takes another 5 mins or so..

[squeezebm]

Originally Posted by NFS

'Air conditioning' as a term encompasses heating, cooling and de-humidification.

The systems we have in cars are actually for 'comfort cooling'. Although they are heat pumps they only operate in one direction. Taking heat from the internal space and dumping it outside.

I would imagine that this is done to save money on the controls and because cars already have an alternate 'waste' heat source freely available (the engine).

If you used the heat pump for heating, then the engines waste heat would be dumped to atmosphere and energy would be wasted in driving the AC compressor. Using air tempered with engine heat would mean that the compressor isn't operating all the time, which would then reduce fuel consumption.

A lot of buildings work this way, with 'mixed mode' systems. For example an office comfort cooling 'split system' is often combined with a low pressure hot water (LPHW) traditional radiator heating system.

The split system could be specified to provide heat as well as cooling, but LPHW would typically be cheaper and more energy efficient. Because per unit gas fired heating would work out better than elec power for the compressors.

Unless of course the A/C compressor was Inverter drive so your nearly right

[grey man]

Originally Posted by alcook

Thanks mate, that one I understood...

Shame it's not an option too, as cold days are as common here as hot ones and that extra heat in the mornings would be a welcome addition (especially if remote controlled) rather than waiting a good 5 mins or more for the engine to warm up enough to start warming the cabin...which then takes another 5 mins or so..

Its certainly an option on X5 and I think 5 series saloon/estate too. Controlled from either a timer set in the i-drive - or as an additional (i.e. more £££) a remote thing like a key fob

[xenon]

Originally Posted by grey man

Its certainly an option on X5 and I think 5 series saloon/estate too. Controlled from either a timer set in the i-drive - or as an additional (i.e. more £££) a remote thing like a key fob

But it's not done from the A/C. The auxilliary heater on the timer or from the fob, is only available on diesel cars as it burns some of the diesel in a Webasto heater to provide heat. I had it on my 5 and it was very useful.

Back to the original question, the A/C compressor cools and dries the air and then the heater warms it back up. That means that you get warm DRY air as opposed to warm moist air which would steam the windows up like mad. BUt the A/C itself does not operate in reverse, as has been said.

[squeezebm]

Originally Posted by redE93cab

MMM, never really thought about this but good point!

I have an aircon unit in my conservatory at home. It is one with the outdoor unit and an indoor mounted wall blower. In the summer it chills the room and gives out cold air almost immediately if called for, However, when set to warm the room, the outdoor unit powers up and runs for a good 3-5mins before the indoor unit starts blowing warm air. Not sure what it is doing though but it is unable to dispense warm air as quickly as it can cold.

Maybe the setup in the car is similar, and you are not waiting for the engine to warm, but for the aircon unit to blow warm air?

Maybe someone will be along soon to enlighten us - where is Squeeze? He may know!

[Porscha!]

May I just ask is it true or not that having the AC on while demisting the front screen will mean it will demist quicker? It appears to do so on my 5 Series also less likely for the car to steam up with the AC on.

The car has a Climate Control system (I think) well it is set in temperature rather than just hot - cold.

Thanks.

[NFS]

Originally Posted by Porscha!

May I just ask is it true or not that having the AC on while demisting the front screen will mean it will demist quicker? It appears to do so on my 5 Series also less likely for the car to steam up with the AC on.

The car has a Climate Control system (I think) well it is set in temperature rather than just hot - cold.

Thanks.

Yes because the AC also dehumidifies the air.

[Porscha!]

Originally Posted by NFS

Yes because the AC also dehumidifies the air.

Thankyou