Reversible Ceiling Fan: Benefits & Functionality

[DaveC426913]

(I think I've actually asked this before...)

I have a standard 3 speed reversbile ceiling fan. The reverse switch of course changes it from blowing air up to blowing air down.

What is the benefit of reversing the fan?

Most people seem to think that it constitutes a difference between drawing air into the room and blowing air out of the room. (without thinking it through about equalization of air pressure and the fact that you can't have and 'in' without also having an 'out'.)

Personally, I believe that the air flow is direction-agnostic. The flow - either way - forms a toroid, rotating either down or up around the outer edge, but otherwise having no in-the-room or out-of-room effect.

The only functional difference between 'up' and 'down' is whether the occupants feel a breeze. You'd use the 'down' on a hot day when a breeze would be nice, and you'd use the 'up' anytime you want to circulate the air without blowing on people, such as in the winter.

Am I right?

All opinions welcome, but I would be interested in the input of someone who can speak with authority about it.

 

[DaveC426913]

Yup. I did.

https://www.physicsforums.com/showpost.php?p=602551

Though I would still be interested in the input of someone who can speak with authority about it.

 

[brewnog]

Russ is our HVAC man, see if you can catch him in one of the Engineering forums instead.

 

[FulhamFan3]

In the normal mode it gives you a breeze which cool you through convection. The opposite isn't totally useless though. When it is cold outside the windows and other walls may be cold while the center of the room and the ceilling retains the warmer air. The reverse setting makes sure this air circulates throughout the room.

 

[DaveC426913]

In the normal mode it gives you a breeze which cool you through convection. The opposite isn't totally useless though. When it is cold outside the windows and other walls may be cold while the center of the room and the ceilling retains the warmer air. The reverse setting makes sure this air circulates throughout the room.

What I am trying to determine - specifically - is whether the circulation is symmetrical between forward and reverse. i.e. the cold walls will have air blown past them whether it is going up or going down.

 

[vadslram]

there is virtually no difference to a dry bulb thermometer for the fan direction.
both directions will mix the air, creating a more stable temp gradiant. Down force FEELS cooler because you feel the breeze on your skin.

 

[russ_watters]

Waaaay late (sorry) but just recently resurrected...

What I am trying to determine - specifically - is whether the circulation is symmetrical between forward and reverse. i.e. the cold walls will have air blown past them whether it is going up or going down.

No, the circulation is not symmetrical because the blowing side directs the air directly away from it, while on the suction side, the air comes in from all directions. You can test this by sticking your hand behind a desk fan - you'll feel little or nothing. With equal fan speeds, you'll get much less blowing across the walls with the fan blowing up because the fan is close to the ceiling and you kill the velocity by blowing straight at the ceiling.

In the summer, you want wind blowing across your skin, so you blow straight down. In the winter, you want even temperature throughout the room, without it feeling breezy, so you have the fan blowing up.