aircon power consumption

[paranoid airbag]

I would've thought this was more easily available information, but apparently not - roughly how much power does a typical modern car use for its aircon? Are they still driven by a clutch or do they take power from the battery now? From what little I have found out from googling it seems very high - given that AFAIK household aircon works off a standard mains unit I'd expect no more than 1-2hp, and I think the US fuel economy test at least does include aircon use so there's an obvious incentive to make them efficient?
Cheers.

[FiF]

The power taken is variable these days, there might be some which have the old electric clutch in / out, but most run all the time have a variable output compressor and do just enough to keep the temperature correct. Thus on a hot day when working flat out to get the temperature down a typical European system takes about 12 bhp aiui, but once it's down to temperature then that drops significantly. I believe that in addition to monitoring vehicle internal temperature they also monitor the coolant circuit.

No doubt a proper a/c engineer could explain much better, but this variable output compressor malarkey results in the situation where it's more efficient to drive with the a/c on than with the windows open.

[mr.man]

Previous discussion on this subject concludes that 4-5 hp(3-4 kw)is accurate for
most modern "average " cars.

[Mr Sparkle]

Didn't realize it would be so much, seems like a huge amount.

[Justin S]

Not sure on variable loading compressors on cars personally. Inverter driven compressors are common on modern split a/c and industrial compressor systems. But a cars compressor runs variable but directly linked with the engine speed. As a whole, with normal thermostatic temperature control ( hot to cold dial), most people just wind it round to bloody cold. While this makes the car cool, it will generally mean the compressor will continually run without disengagement. Meaning continual power consumption from the engine. If a system using climate digital control, people usually set it at 22 or 21 deg. Meaning the system will reach temp and the compressor disengage and now run with now engine power consumption. It will take a reasonable amount of power consumption to run, but if you use it for a decent journey and the car reaches temperature internally,the car and occupants will be at a constant temp and the system will be more economical, as disengaging the compressor at regular periods. Our Honda we had was actually a heatpump, so giving heat on the dash to defrost the screen before the engine warmed up to temperature and swapped over. Clever stuff, but lots to go wrong.

[anonymous-user]

Typically, for an average sized passenger car:

Pull down = 6 to 7 kW of cooling power (~3kW of input mech power)
Maintain = 1.5 to 3 kW of cooling power (~1kW average mech input power)


(remember, the input power is approximately half the actual cooling power that the system delivers)

[FiF]

Justin S said:

Not sure on variable loading compressors on cars personally.

I have worked on material developments to facilitate this with the clutchless wobbble plate /flapper valves and thus avoid the clutch engage / disengage which used to be the case ten years or so back.

Read this link