Testing the Efficiency of Fan Models

Testing the Efficiency of Fan Models

Amy O’Connell


My project involved finding the relative efficiencies of different fan models in terms of power used and volume of air flow produced. To do this I first measured the power usage of each fan in Watts using the Watts Up Pro. I then used the anemometer to measure the air velocity generated by the fan. This step was particularly difficult, as the air velocity produced is generally not uniform over the surface of the fan. To account for this, I measured the air velocity at many individual locations on the surface of the fan by setting the lab quest to collect two measurements per second, and scanning the surface of the fan for three trials of thirty seconds. I then averaged these values to arrive at one uniform air velocity for the entire surface. I found the volume air flow produced by multiplying the surface area of the fan, pi(radius)^2, by the average air velocity produced. Using these values, I calculated the efficiency of each fan in volume of air flow produced per second divided by power consumed. To give the data a more practical application, I compared the calculated efficiency to the price of each fan model.

I also designed two fans of my own, and used a small motor made from a battery, magnet, and copper coil to test them out.

The first model was made from an index card, had six blades, and measured 1 cm in radius:

The second model I 3D printed in plastic using a 3Doodler pen. It measured 3cm in radius, had two blades, and was modeled after a small drone repeller.

Both were attached to the end of a simple motor, pictured here, and tested for air velocity produced over ten seconds.



Design Volume Air Flow Produced (m^3/s)
Card stock (index card), 1cm radius, 6 blades 0.00013644461
Plastic (3D printed), 3cm radius, 2 blades 0.00307510048

What this means:

The results indicate that the most efficient model tested was the O2COOL 10-inch Portable Fan, with an efficiency of 0.0274 cubic meters per second produced per watt. This was more than 4 times more efficient than the next most efficient model, the Lasko 1827 (as seen in room 205 of Sander’s Physics). This was followed by the generic table fan from Rite Aid, and finally the Vornado 573, with an efficiency of just 0.0028 cubic meters per second produced per watt. The O2COOL also had the highest efficiency compared to price, at 0.0012 units of efficiency per dollar. Again, this was more than 5 times the efficiency vs. price of any of the the other models tested.

As for my fans, I could not measure the efficiency because the power used by each model was unknown, but the plastic propeller- like model produced an air flow that was more than twice that of the paper model.

Were my results as predicted?:

My results were not at all as predicted. I assumed going into this project that more expensive fans would be more energy efficient, as a product of a more intelligent design and higher quality building materials. What I found was that there is a negligible relationship between the price of a fan and its relative efficiency. I also found that one aspect of a fan design, the type of current it uses, most significantly impacts the efficiency. The reason the O2COOL model has such a high efficiency was because the power it consumed was significantly less than that of any other model (around 6 times less than the next lowest power used). I believe this is because the O2COOL is also capable of running on batteries. Batteries by nature produce less power than a wall outlet, so the fan must be able to use very little power in order to run efficiently on batteries. This efficiency then translates to very little power consumed even when plugged in.

For my own fan design, I am not surprised that the plastic propeller-type model produced more airflow than the card stock model. I modeled my design after the propellers found on small drones, which must produce a large amount of airflow in order to counteract the force of gravity on the drone.

What science did I learn?:

While completing this project, I learned about a variety of topics. Taking data for the fans and calculating efficiency values taught me about air movement, and how the design of an air moving device impacts its function. I also learned about electricity and power, and how different sources of power are capable of powering different devices. In my fan designing, I learned about how radius, weight, blade rotation, and materials can affect the function of a fan. I also learned a great deal about simple motor design, and how electricity and magnetism combine to perform tasks of increasing complexity, from rotating fan blades to running a motor vehicle.

Relation with current science/technology?

Energy use is one of the most pressing topics in science and technology, and has been for several decades, because it has many implications. As developing countries become more industrialized, the global demand for energy continues to rise. This creates many problems, such as air pollution, environmental destruction, and climate change. It is important to conserve energy as often as possible, and creating more efficient devices for household use like table fans or kitchen appliances is important for conserving energy and minimizing global damage from energy consumption.
What I would do differently:

If I were to repeat this project, I would try to develop a more accurate system for calculating the air velocity produced by the fan. I probably would have better accounted for the various velocities produced at different locations as well as fan faces curvature by computing the volume of air flow in a manner similar to the computation of a surface integral. I would use a grid to section off the surface of the fan into individual squares, measure the air velocity at each individual square, multiply this by the area of the square, then sum the values at each square to arrive at one cumulative volume air flow produced.
What would I do next?:

Obviously efficiency is not the only thing to consider when assessing the quality of a fan model. If I were to continue this project for another 6 weeks I would collect data for other potential selling points for fans, like sound produced and size. I would also work on improving my own fan designs, and attaching them to a motor capable of faster and more predictable rotation for better results.


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