Thursday, June 21, 2012

Ceiling Fan Effectiveness

While investigating why my home is not cooling evenly, I ran a quick test.  Using my infrared thermometer, I ran some scans on two rooms.  The test was done at noon, with the air conditioner enabled, set on 85.  The outside temperature as measured by the air conditioner (in the shade) was 89.

In room one (R1) the temperature at the junction of an outside wall, an inside wall, and the ceiling, was 85.9 degrees Fahrenheit.  In the room two (R2) the temperature at the junction of the same outside wall, same inside wall, and same ceiling, was 86.4 degrees.  Needless to say, a temperature variation of half a degree might seem negligible, certainly within an acceptable margin of error, except for one thing:

In R1, the ceiling fan had been running four hours.

This raises an interesting question, if running the ceiling fan for four hours only cools the room by half a degree, is it really working?  Yes, because its not a ceiling fan's job to cool a room: its job is to circulate air.

But wait!  It get's more interesting. 

The temperature of the fan's motor housing was 97 degrees.  This means that the fan was acting as a heat source.  Of course the ceiling fan is equipped with a light kit.  With the light illuminated for one hour, the temperature of the globe around the single incandescent bulb increased from ambient to 95 degrees.  This means the light was also acting as a heat source.  (The four bulb "tulip" light kit in R3 was 103 degrees, using CFL bulbs.  The three bulb halogen fixture in R2 was 118 degrees.)

This experiment causes me to question the value of ceiling fans.  In both R1 and R2 the temperature at the baseboard was 81 degrees.  Conventional wisdom dictates that the fan in R1 would pull cooler air up, or push hotter air down.  By circulating the air, the room would be more evenly cooled.  Yet, the measurements indicate the effect of circulation is not significant.  On top of costing electricity to operate, its possible that the fan is adding heat, not subtracting.

So why do people use ceiling fans if they don't work?  One word: breeze.  People think ceiling fans work, because they can feel a breeze, which seems to have a cooling effect.  (In reality, a breeze is only effective on bare skin because it assists evaporation of perspiration.)

Thus, I will conclude with this philosophical question:  
If a ceiling fan is running in a room,
and there is no one around to feel it,
does it do any good? 
No.

4 comments:

  1. Another stupid question - Did you check the direction of the blades and the rotation?

    But yeah, if no one is in the room - turn it off.

    I am sure you checked wikipedia :)

    ReplyDelete
  2. The blades are spinning in "the correct" direction. Oh... and I fixed the Wikipedia article.

    ReplyDelete
  3. Always see to it that your fans are clean, as it would help in its efficiency, and help you save energy costs. Be certain to remove accumulated dirt in the fan motor itself. You may use a paintbrush to clean it, so that the motor would not have a hard time working.

    Staci Severns

    ReplyDelete