How much HP does the A / C actually draw?

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Originally Posted By: Nick R
I don't know how much power it draws, but it is a LOT. Seriously, anyone who's ever driven a small 4cyl car (especially one that is underpowered to begin with, ie a cavalier) knows that Turning on the A/C makes it dangerously slow. I have to turn it off to merge onto the highway or it just takes way too long to get anywhere. I actually am thinking maybe it isn't the horsepower it takes, rather it's the resistance to change speed.

I know that feeling. I never would set it to max, always to Vent or something so I could hit the A/C button if I needed it to actually go. It doesn't help there is no WOT A/C Disable. If a '88 Mustang has WOT A/C cutout, why doesn't a '98 Chevrolet? I tried to figure out a method to install a WOT cutout on the Cavi before I got the Vic. The only way would be to tap the TPS signal and setup another circuit to pull a normally closed relay open. Unfortunate, as it would have been nice.
Its the lack of torque, I think. Like you said your Expy or Mustang dont really notice.. More cylinders to spread the load.
I read somewhere that Car A/Cs were REALLY oversized for the cabin space, due to people wanting to cool it as quick as possible. I think it was 1-1.5ton?
 
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Originally Posted By: CaspianM
It would would be hard to say how many HP w/o knowing actual BTU/h for a given car. Size of the compressor varies.
But ball park numbers are:
1 ton cooling power =12k btu/h

If it is a two tone unit then it draws 24k btu/h of energy.
1 ton=12k btu/h
1 hp=2,544 btu/hr
therefore for a 2 ton unit it draws 12k/2544=9.4 HP
3 ton unit 36k/2544=14 HP
There are also mechanical losses as well such as noise, heat& belt on top of that.
I did not include the power drawn by the fan either.


Are you assuming an automotive AC unit? Because those numbers are awfully inefficient. A modern 5 ton home AC unit has 60k BTU of cooling and uses around 6-10hp depending on its efficiency.
 
I would estimate a small car's AC uses 3-4 hp. 25 is so outrageous your car would barely move if it were true.

The reason 3-4 hp seems like a lot is because most of the time you engine is turning around 2000-3000 rpm, and at those speeds it is making a small fraction of its rated power. That 100 hp engine is producing about 35-40 hp at 2500 rpm. So the AC is sucking up 10% of the engine's output. That's why it has such a large impact on small engines
 
Originally Posted By: Colt45ws

I read somewhere that Car A/Cs were REALLY oversized for the cabin space, due to people wanting to cool it as quick as possible. I think it was 1-1.5ton?


They have to oversize a car AC's because a car is all glass and uninsulated metal, and many cars are a dark color, plus there's a huge heat-producing object called the engine 1 foot away. Contrast with your home which probably has dual-pane glass and insulated walls and attic.
 
car units are actually better considered as refrigeration units, not 'air conditioners', due to the extreme temp drop they produce.
 
Originally Posted By: tonycarguy
Originally Posted By: CaspianM
It would would be hard to say how many HP w/o knowing actual BTU/h for a given car. Size of the compressor varies.
But ball park numbers are:
1 ton cooling power =12k btu/h

If it is a two tone unit then it draws 24k btu/h of energy.
1 ton=12k btu/h
1 hp=2,544 btu/hr
therefore for a 2 ton unit it draws 12k/2544=9.4 HP
3 ton unit 36k/2544=14 HP
There are also mechanical losses as well such as noise, heat& belt on top of that.
I did not include the power drawn by the fan either.


Are you assuming an automotive AC unit? Because those numbers are awfully inefficient. A modern 5 ton home AC unit has 60k BTU of cooling and uses around 6-10hp depending on its efficiency.

No assumptiom. They are universal. No matter what system it is always 1 ton=12k btu and 1 hp=2544 btu/h.
 
Originally Posted By: SteveSRT8
car units are actually better considered as refrigeration units, not 'air conditioners', due to the extreme temp drop they produce.


All are refrigeration systems in core with some additions.
 
Originally Posted By: tonycarguy
I would estimate a small car's AC uses 3-4 hp. 25 is so outrageous your car would barely move if it were true.

The reason 3-4 hp seems like a lot is because most of the time you engine is turning around 2000-3000 rpm, and at those speeds it is making a small fraction of its rated power. That 100 hp engine is producing about 35-40 hp at 2500 rpm. So the AC is sucking up 10% of the engine's output. That's why it has such a large impact on small engines


Ding, ding, ding, we have a winner!!!!!!!!!!
25.gif



Most modern 4 cyl. engines produce their peak HP at around 6-7k rpm, and peak torque at around 4-5k RPM, but AC power draw is pretty much constant when the compressor is engaged, that's why these engines feels so slow because there is really little torque available below 4k RPM, but any V8 or turbo diesel with lots of torque at 2k RPM will not even notice the AC kicking in.
 
In a typical sedan about 10k btu heat needs to be removed which is about 4 hp but then again we have larger cars.
 
Originally Posted By: DreamerGT
On both my cars It doesn't feel like it takes any HP.


Same here on all our Panthers...We just leave it on all the time all year long...It saves a ton of money on window regulators.
 
Originally Posted By: CaspianM

No assumptiom. They are universal. No matter what system it is always 1 ton=12k btu and 1 hp=2544 btu/h.


The measurement of output is universal. What it takes to produce that output is variable, depending on the efficiency of whatever system you are looking at.
 
I feel it real BAD on the Civic and slightly on the MPV. I cut the A/C when I go uphill. Need the power.
 
Originally Posted By: tonycarguy
Originally Posted By: CaspianM
It would would be hard to say how many HP w/o knowing actual BTU/h for a given car. Size of the compressor varies.
But ball park numbers are:
1 ton cooling power =12k btu/h

If it is a two tone unit then it draws 24k btu/h of energy.
1 ton=12k btu/h
1 hp=2,544 btu/hr
therefore for a 2 ton unit it draws 12k/2544=9.4 HP
3 ton unit 36k/2544=14 HP
There are also mechanical losses as well such as noise, heat& belt on top of that.
I did not include the power drawn by the fan either.


Are you assuming an automotive AC unit? Because those numbers are awfully inefficient. A modern 5 ton home AC unit has 60k BTU of cooling and uses around 6-10hp depending on its efficiency.


I recall 12HP in readings many years back for the average full size sedan.

Automotive A/C is not going to be an efficiency-optimized system because it has to function at a wide range of rpms. it cycles also, unlike a home unit. home systems may use adjustable orifice to regulate cooling performance whereas I'm not aware of any vehicles that do. plus they can't fit in the evap/condensors with large surface areas either.
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other points-

Chrysler dealer told me our 01 T&C had the same tonnage as a 1,500ft² house. that's what.. 2 tons?

trying to get a small engine to accelerate when it's out of it's powerband while the A/C is pulling a load kills acceleration. Heck, I even feel it in my small v6.
 
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Originally Posted By: CaspianM

But ball park numbers are:
1 ton cooling power =12k btu/h

If it is a two tone unit then it draws 24k btu/h of energy.


That's not quite right. There is no properly functioning AC unit that is so inefficient that it needs one BTU of energy to move a BTU of energy.
 
Originally Posted By: brianl703
Originally Posted By: CaspianM

But ball park numbers are:
1 ton cooling power =12k btu/h

If it is a two tone unit then it draws 24k btu/h of energy.


That's not quite right. There is no properly functioning AC unit that is so inefficient that it needs one BTU of energy to move a BTU of energy.


It actually is the other way around. If it take 1 unit of work to produce 1 unit of work then it is 100% efficient. Eff=output/input.
I just posted theoretical values and also said that mechanical losses such as internal loss and belt are extra which reduces eff of the unit.
 
Originally Posted By: CROWNVIC4LIFE

Same here on all our Panthers...We just leave it on all the time all year long...It saves a ton of money on window regulators.


Living in Miami, this would make sense.

I can really feel it on my 140hp Duratec as well as all 4 cyl I've owned. I don't notice a thing with 376hp
19.gif
 
Originally Posted By: CROWNVIC4LIFE
Originally Posted By: DreamerGT
On both my cars It doesn't feel like it takes any HP.


Same here on all our Panthers...We just leave it on all the time all year long...It saves a ton of money on window regulators.
It prolongs the life of the A/C system as well!!!
 
Originally Posted By: TooManyWheels
Originally Posted By: CaspianM

No assumptiom. They are universal. No matter what system it is always 1 ton=12k btu and 1 hp=2544 btu/h.


The measurement of output is universal. What it takes to produce that output is variable, depending on the efficiency of whatever system you are looking at.


I believe those numbers are what they are in the industry. Efficiency is factored in once the base unit size is determined depending on BTU requirement.
 
Originally Posted By: CaspianM

It actually is the other way around. If it take 1 unit of work to produce 1 unit of work then it is 100% efficient. Eff=output/input.
I just posted theoretical values and also said that mechanical losses such as internal loss and belt are extra which reduces eff of the unit.


The air conditioning is not producing anything, it's moving heat from one place to another.

In the real world, air conditioners move much more than one BTU of heat for each BTU of energy used.

Ditto for heat pumps, which is why they use less energy per BTU output than resistance heating coils (which use one BTU of energy input for one BTU of energy output).
 
Originally Posted By: CaspianM
Originally Posted By: brianl703
Originally Posted By: CaspianM

But ball park numbers are:
1 ton cooling power =12k btu/h

If it is a two tone unit then it draws 24k btu/h of energy.


That's not quite right. There is no properly functioning AC unit that is so inefficient that it needs one BTU of energy to move a BTU of energy.


It actually is the other way around. If it take 1 unit of work to produce 1 unit of work then it is 100% efficient. Eff=output/input.
I just posted theoretical values and also said that mechanical losses such as internal loss and belt are extra which reduces eff of the unit.


1 ton cooling = 12k BTU/hr | units conversion

one BTU/hr = 0.293 watts of heat | unit conversion (not power consumed)

one ton cooling = 3.516kw of heat | unit conversion (not power consumed)

in generic numbers, 1 ton household A/C requires 1.4 kw/hr, which equates to ~2+hp in an efficient 1 ton system...

Which thus suggests that vehicle A/C is grossly inefficient when engine-driven compressor is used. maybe the electric-pumped A/Cs can optinmize for greater efficiency...

Are they really installing electric compressors in cars as posted above? I thought electrical systems were going to 36 or 48 volts in order to support that, which I haven't yet seen? hello 300+ amp alternator...
 
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