Ceiling Fans Running in Unoccupied Rooms Save Energy

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Ravenvalor

Ravenvalor

Senior Member
Location
Triad region of NC
Occupation
Electrician
Hello,

I've got a customer who just opened up a music instrument store. He has a store room where he has to keep the temperature at 74 and the humidity at a certain level also. Since we are in central NC the air conditioner and de-humidifier run alot. He has two ceiling fans in the room. Will running those fans continuously help with the cooling and humidity control?

Thanks and have a great Independence Day !!!
 
Cieling Fans

Cieling Fans

Ceiling fans don't provide any benefit unless the room is occupied where person(s) can
feel the movement of air. Otherwise they just use energy and produce a small amount of heat.
 
The question is whether the stratification of temperature and humidity without the fans, when the heat or AC is cycling, will be enough to cause a problem.
Do you have guitars, woodwinds or drum heads stored near the ceiling? :)
Some simple thermometer and hygrometer readings at different heights should tell you.
 
The space was just remodeled with a new central AC unit and a new dehumidifier.
There are only guitars there and they store at about 5' high at the highest point.
There are also 2 - ceiling fans in the room and he was wondering if he should run them continuously.

Thank you,
 
Ravenvalor said:
The space was just remodeled with a new central AC unit and a new dehumidifier.
There are only guitars there and they store at about 5' high at the highest point.
There are also 2 - ceiling fans in the room and he was wondering if he should run them continuously.

Thank you,
Click to expand...
Measure the temp at floor and at 5' (fans off). If they are close, the humidity will be close too.
 
Where, in the room, are the air registers that supply conditioned air to the room? Where are the return air vent? Where is the thermostat (and humidistat, if there is one) located?

Ceiling fans provide two benefits:
  1. For people in the room, the air moving over them provides convection cooling as well as evaporative cooling (as perspiration evaporates off their skin).
  2. The ceiling fans homogenize the temperature of the air in the room by mixing it.

For example, if the air registers and the return air vent are both low to the ground, then cooled air will stay close to the floor: it will come out the registers, travel along the floor, and return to the heat pump by way of the return air vent. Likewise, if the air registers and the return air vent are both on the ceiling, then heated air will stay close to the ceiling: it will come out the registers, travel along the ceiling, and return to the heat pump by way of the return air vent. In each of these cases, you will get stratified layers of air: a stagnant zone of hot air over the chilled air in the first example; or a stagnant zone of cold air below the heated air in the second example.

The ceiling fans will mix the air so that it will be more uniform in temperature (and humidity) from floor to ceiling. This will also allow the thermostat -- which is almost always mounted midway up a wall -- to more accurately respond to the correct temperature of the room. The celing fans do not need to be running at high speed to achieve this! Considering the value of the guitars in storage, I'd err on the safe side and run the ceiling fans. Their lowest speed should be sufficient, unless the ceiling is very high. If you can feel the air moving at the ground level, then that is all you need. I suspect that the owner may also see a decrease in his energy bills.
 
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I will forward this to my customer and let him run with it. Thanks for the good advice and the new definition for the day :).


hys?ter?e?sis

?hist??r?sis/
nounPhysics

noun: hysteresis

  • the phenomenon in which the value of a physical property lags behind changes in the effect causing it, as for instance when magnetic induction lags behind the magnetizing force.









 
It's going to cost him a very low amount per year to keep a ceiling fan on low. It will require energy to spin the fan and the electric motor in it will also produce some heat for a benefit in the winter and an expense in the summer.

Considering the (assumed) value of the contents of the room, and considering that leaving an air handler running 24/7 is known to freeze up a hvac system, I'd leave the ceiling fan on low 24/7. You don't want any musty pockets in that room where mold can grow, etc.
 
I run mine when not home. Here's my reasoning;

Human nature is to be reactive. In general, people's heads are at or above 5 feet. So when someone walks into a room in which the heat is stratified, the first thing they feel is the warm air around their heads, so they react by altering the thermostat (or like my wife, yelling at me to "fix it"). That leads to over compensation and excessive cycling / waste. I have found that by leaving the fans running in the room even when nobody is home, she comes home to a house that does not feel as warm as when they have been off all day, so when I get home, I don't find the fricken t-stat turned down to 65 degrees!
 
Other things to consider, HVAC outlets are high on the wall or in ceiling and returns are low or in floor, you get more stirring of the air in the space when HVAC blower is running, if you have a newer air handler with variable speed blower, leaving that fan on all the time will always stir the air, but it will run at a low speed when not heating or cooling - a ceiling fan may have no benefit at all in this situation.
 
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