What are the advantages of electric fans over clutch fans?
07-15-2005, 12:24 PM
#1
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What are the advantages of electric fans over clutch fans? Ok, I'm arguing about this with some people on another site, but they are completley failing to offer any compelling (it mathmatical) reason that electric fans are better than clutch fans.
I'm not saying this couldn't be true, I'd just like to be convinced of it
The claim is going that electronic fans are "more effecient", which would mean they flow more air while ultimating producing less of a parasitic power loss on the engine. However, my understanding of this is that any real gain in overall engine effeciency by switching to electric fans because of this would be very nill, because your alternator still has to produce power to drive the fans, which in turn creates the same load on your engine, hence still requiring what I am guessing would be very close to the same amount of power a clutch fan would take.
I am thinking that the logic behind utilizing electric fans as GM does FROM THE FACTORY (not aftermarket) is not primarily because it makes the engine more effecient, but because somehow it is more easily controlled by the PCM or something along those lines:
If anyone could offer me a technical explanation as to why electric fans are better and/or more effecient as far as an overall engine effeciency/overall power output argument goes, I would appreciate it.
I'm not saying this couldn't be true, I'd just like to be convinced of it
The claim is going that electronic fans are "more effecient", which would mean they flow more air while ultimating producing less of a parasitic power loss on the engine. However, my understanding of this is that any real gain in overall engine effeciency by switching to electric fans because of this would be very nill, because your alternator still has to produce power to drive the fans, which in turn creates the same load on your engine, hence still requiring what I am guessing would be very close to the same amount of power a clutch fan would take.
I am thinking that the logic behind utilizing electric fans as GM does FROM THE FACTORY (not aftermarket) is not primarily because it makes the engine more effecient, but because somehow it is more easily controlled by the PCM or something along those lines:
If anyone could offer me a technical explanation as to why electric fans are better and/or more effecient as far as an overall engine effeciency/overall power output argument goes, I would appreciate it.
07-15-2005, 12:31 PM
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Electric fans can draw more air through the radiator since you can place two small ones side by side vs. one large engine driven fan. In that respect they are more efficient.
I'd have to double check the size of the fan motors, but since they are relatively small and don't always run you can be safe in saying they take less HP from the motor.
The only way to be sure is to dyno two similar cars...one with a mech fan and one with electric.
I'd have to double check the size of the fan motors, but since they are relatively small and don't always run you can be safe in saying they take less HP from the motor.
The only way to be sure is to dyno two similar cars...one with a mech fan and one with electric.
07-15-2005, 01:05 PM
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A clutch fan ALWAYS turns. No matter how cool the engine is. It is always depleting HP from the engine, even if it is minimal.
An electric fan only operates when it is needed. A good controller can turn it off at highway speed. A dual fan can be controlled to only operate one if needed (such as when running your A/C) and start the other when over a certain higher temperature. This helps the efficiency.
An electric fan wil stay off immediately after engine start (unless the A/C is running) allowing the engine to come up to proper temperature faster.
OK, it takes electric power to drive the fan. Next time you're on the highway put your car in cruise. Now turn the stereo on and off while justing touching the accelerated with your foot. Does it react to the stereo? Maybe, but probably not enough for you to tell. I have amps (1200W worth) in my truck and probably pull 200w regularly when jammin' but turning it off and on doesn't effect my highway speed even momentarily when I turn it on and off.
Short of a dyno test there is no way to tell how much HP you save/gain.
Is it worth the money?
Keep in mind that it is all relative. If you are an avid racer 1 HP could be enough to get you a win. If you a daily driver 1 mpg improvement could be the difference (especially at todays fuel prices).
An electric fan only operates when it is needed. A good controller can turn it off at highway speed. A dual fan can be controlled to only operate one if needed (such as when running your A/C) and start the other when over a certain higher temperature. This helps the efficiency.
An electric fan wil stay off immediately after engine start (unless the A/C is running) allowing the engine to come up to proper temperature faster.
OK, it takes electric power to drive the fan. Next time you're on the highway put your car in cruise. Now turn the stereo on and off while justing touching the accelerated with your foot. Does it react to the stereo? Maybe, but probably not enough for you to tell. I have amps (1200W worth) in my truck and probably pull 200w regularly when jammin' but turning it off and on doesn't effect my highway speed even momentarily when I turn it on and off.
Short of a dyno test there is no way to tell how much HP you save/gain.
Is it worth the money?
Keep in mind that it is all relative. If you are an avid racer 1 HP could be enough to get you a win. If you a daily driver 1 mpg improvement could be the difference (especially at todays fuel prices).
Last edited by 007fl; 07-15-2005 at 01:12 PM.
07-15-2005, 02:24 PM
#4
Here's my take:
The electric fan may be more efficient when in pairs, but I doubt its more efficient than a direct drive since the electric fans require the mechanical energy to be converted into electrical energy, and then converted again back into mechanical energy. During the conversions energy is lost (mostly as heat) but I doubt theyre more efficient in that respect.
Where they pay off is here: First off, Theyre not always on. Secondly, and more importantly, the load placed by the alternator on the engine does not grow proportionally as RPM increases. That means the fans will be putting the same load on the engine (via alt) at redline as it will at normal cruise speed. A clutch fan will put exponentially more load on the engine the faster it is spun.
The electric fan may be more efficient when in pairs, but I doubt its more efficient than a direct drive since the electric fans require the mechanical energy to be converted into electrical energy, and then converted again back into mechanical energy. During the conversions energy is lost (mostly as heat) but I doubt theyre more efficient in that respect.
Where they pay off is here: First off, Theyre not always on. Secondly, and more importantly, the load placed by the alternator on the engine does not grow proportionally as RPM increases. That means the fans will be putting the same load on the engine (via alt) at redline as it will at normal cruise speed. A clutch fan will put exponentially more load on the engine the faster it is spun.
07-15-2005, 02:30 PM
#5
i was going to say exactly what 007fl said.
above 35mph (or whatever its set at in your PCM) you dont need the fans... so they kick off.
they only come on when needed. that alone is more efficient.
flex fans take alot of power. more power then is used by just the elec fans thru the alternator... think about this:
at LOW LOW RPMs, (engine idle) the flex fan has to move enough air to keep the car cool.
a electric fan only has to be efficient in the narrow operating range of the electric motor speed.
at higher RPM the electric is off. the car is moving. but the flex fan is still moving a HUGE amount of air. so much that those STIFF metal blades are being flattened out by air pressure. (hence flex fan)
now the clutch fan, isnt as bad.. but its still turning the fan some do to drag. and it has all the same problems as the flex fan... the order of efficiency (from least to greatest) is like this: fixed fan, flex fan, clutch fan, elec fan
if you want real world proof, goto the dragstrip in a mechanical fan car (or truck)... one thats consistent... make some baseline runs, then, take the fan off and run again... you'll see a gain in the slip. you'll also see a MPG diff.
above 35mph (or whatever its set at in your PCM) you dont need the fans... so they kick off.
they only come on when needed. that alone is more efficient.
flex fans take alot of power. more power then is used by just the elec fans thru the alternator... think about this:
at LOW LOW RPMs, (engine idle) the flex fan has to move enough air to keep the car cool.
a electric fan only has to be efficient in the narrow operating range of the electric motor speed.
at higher RPM the electric is off. the car is moving. but the flex fan is still moving a HUGE amount of air. so much that those STIFF metal blades are being flattened out by air pressure. (hence flex fan)
now the clutch fan, isnt as bad.. but its still turning the fan some do to drag. and it has all the same problems as the flex fan... the order of efficiency (from least to greatest) is like this: fixed fan, flex fan, clutch fan, elec fan
if you want real world proof, goto the dragstrip in a mechanical fan car (or truck)... one thats consistent... make some baseline runs, then, take the fan off and run again... you'll see a gain in the slip. you'll also see a MPG diff.
07-15-2005, 03:13 PM
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I think that you all forgot one thing an electric fan can do that the clutch one can't. High HP engine run hotter and need more CFM of airflow to cool them down. The electric fan runs full RPM even if the engine is at idle which allows for maximum cooling where as the clutch fan is turning slower due to low engine crank RPM. So the clutch fan will allow the engine to run hotter during idle than an electric fan would. Electric fans are superior in all aspects so why waste your time with a clutch driven fan?
Also, from a PCM standpoint it allows for greater flexibility to control temps with an electric fan. You can easily adjust the temp the fans activate, make the fan activate when other devices engage (A/C), etc. Technology makes things easier to control and monitor hands down. Better fuel economy by removing the parasitic loss from the crank. Ability of the PCM to control the fans on/off only when needed instead of the constant load. Kinda like saving energy by turning off the lights in your house when your not home and don't need them.
Also, from a PCM standpoint it allows for greater flexibility to control temps with an electric fan. You can easily adjust the temp the fans activate, make the fan activate when other devices engage (A/C), etc. Technology makes things easier to control and monitor hands down. Better fuel economy by removing the parasitic loss from the crank. Ability of the PCM to control the fans on/off only when needed instead of the constant load. Kinda like saving energy by turning off the lights in your house when your not home and don't need them.
Last edited by UnleashedBeast; 07-15-2005 at 03:23 PM.
