Extra power from 40 mph exhaust fan

In summary, the conversation revolves around the idea of harnessing the wind from an existing exhaust fan in a commercial building. The proposal suggests using a pipe with electric generators and a paddle wheel attached to the fan blade to generate power. Some people argue that this would decrease the efficiency of the fan and the amount of power generated would be negligible. Others suggest harnessing the heat loss from the fan motor instead. The conversation also touches on other unconventional ideas, such as using rainwater to generate electricity.
  • #1
tigershark
3
0
Say I have a commercial building that has a 24 inch diam. exhaust fan that is blowing approx 40 mph wind out of the building. I wonrder if I can make good use of this wind by mounting a 24-26 inch pipe that may be 6 to 10 ft long on the outside of the building. I imagine cutting out sections in the "tunnel" and setting up electric generators on the outside. The shaft to the generator would be extended and a fan blade such as a paddle wheel type would be attached. the paddle wheel blade could be set into the new wind tunnel so that half of it is inside and half outside. The wind would spin and generate useful power.

If anyone has any thoughts on this, I would like to hear them as well as possible details such as types of generators to use and what the output might be. Could enough generators be added to generate a significant amount of power?

Thx,

Jeff
 
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  • #2
While you're at it, put a wind turbine on your car to turn a generator that charges your battery. This should remove the load on the alternator on the engine and improve fuel efficiency. :rofl:
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Ok, yes that was a bit sarcastic, but if you can see how the car/wind turbine can't work then you should be able to see how the exhaust fan in a building proposal will fail.
 
  • #3
The exhaust fan already exists on the building. Why not harness that wind exiting the building?
 
  • #4
The same way that the wind is blowing by the vehicle? Why don't we harness that? It's the same thing.
 
  • #5
I think that your too rigid in your thinking. With a 6" x 4" paddle wheel design fan blade 50% of which is inside the tunnel, the resistance would be negligable vs. the potential power production. We all understand the prior concept noted but this is an existing exhaust fan with a harnessable resource, at least I think it is, up to a point where the resistance is too great and impedes the functionality of the exhaust fan.
 
  • #6
tigershark said:
I think that your too rigid in your thinking.

Nope. This is a basic law of physics. They are rigid and to think they can be bent is foolish.

tigershark said:
With a 6" x 4" paddle wheel design fan blade 50% of which is inside the tunnel, the resistance would be negligable vs. the potential power production.

So how far are you willing to take this? Negligible input with power output? You do realize what you are saying here right? Now I can understand that there may be more air flowing than necessary so a paddle wheel slowing things down wouldn't matter. If that's the case then it would be more efficient to change the fan or slow it down so there is less energy used by the fan which leaves more net energy to be used for something else which in your proposed generator would be produced but with a loss due to inefficiencies between the motor/fan and paddlewheel/generator.

tigershark said:
We all understand the prior concept noted but this is an existing exhaust fan with a harnessable resource, at least I think it is, up to a point where the resistance is too great and impedes the functionality of the exhaust fan.


There is no difference. Existing fan... Existing moving vehicle...
 
  • #7
Just in case Averagesupernova wasn't clear enough, the only way to have a negligible effect on the exhaust fan is to generate a negligible amount of power from it's airflow. If, for example, you want to generate 100w of power without decreasing the airflow of the fan, you'll need to run the fan faster, consuming an extra 100w of power (not including efficiency losses, of course).

Conservation of energy!
 
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  • #8
I fail to see your point unless you are trying to extract free energy. If you try and harness the exhaust fan power with a pipe you will obstruct the discharge air flow of the fan and decrease the efficiency of said fan. If the fan is discharging too much air then the thing to do is change the shiv (also known as sheaves or pullies) ratio and not try harnessing the excess air. Any thought of gain would be lost to friction. A good idea if you are not paying for the power, then you could steal the power with a chance of detection.
 
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  • #9
Instead of trying to harness the wind, harness the heat loss off the fan motor. Use thermals engines like sterling motors to turn tiny generators and trickle charge batteries. You don't get perpetual motion but atleast your system efficiency goes up.
 
  • #10
Averagesupernova said:
While you're at it, put a wind turbine on your car to turn a generator that charges your battery. This should remove the load on the alternator on the engine and improve fuel efficiency. :rofl:
-
Ok, yes that was a bit sarcastic, but if you can see how the car/wind turbine can't work then you should be able to see how the exhaust fan in a building proposal will fail.

Silly goose. A wind turbine would cause drag.
Ooops. I see you're being sarcastic.
Anyways, check out my solution to my serpentine belt idler arm going out one day, 12 miles from home:

http://home.europa.com/~garry/spc.jpg [Broken]
I'm glad the sun was shining that day. Barely made it home.

Btw, I was wondering if there was a depository of novel ideas that should not be tried because someone has done the math.

I calculated one day that the energy of the rainwater collected on my roof, run through tiny little water turbine electric generators, would be enough to cook about 2 packets of top ramen every year.
 
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  • #11
I've seen forums with a "trash bin" of crappy posts/ideas, but we don't have one.
 

1. How does an exhaust fan generate extra power at 40 mph?

An exhaust fan generates power by using the force of the wind to turn its blades. At higher wind speeds, the blades are able to rotate faster, thus generating more power. So, at 40 mph, the wind is strong enough to produce more power from the exhaust fan.

2. Can an exhaust fan generate power even when there is no wind?

No, an exhaust fan requires wind or air flow to generate power. It is designed to harness the kinetic energy of moving air, so without wind or air flow, there will be no power generation.

3. Are there any safety concerns with using an exhaust fan to generate power?

As with any electrical device, there are some safety concerns when using an exhaust fan to generate power. It is important to follow proper installation and usage instructions to avoid any potential hazards.

4. How much power can an exhaust fan generate at 40 mph?

The amount of power generated by an exhaust fan at 40 mph will vary depending on the size and type of fan. On average, a small exhaust fan can produce around 10 watts of power at this speed, while a larger fan can generate up to 50 watts.

5. Can the extra power from an exhaust fan be stored for later use?

Yes, the power generated by an exhaust fan can be stored in batteries or other energy storage systems for later use. This can be useful for powering small devices or for emergency backup power.

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