What DOES the direction of a ceiling fan do?

[DaveC426913]

Please pardon my interjection but:
... launched one of the most heated (and unquotable) responses I ever received from a long past girl friend when she asked "Which is the best direction for the ceiling fan to blow, up or down" and I started my response with: "Well, it depends ..." but never got any further than that.

Is there a reason?

My hypothesis is that running a fan one direction versus the other direction has little direct effect on circulation - the air moves in a toroidal shape - either upward or downward either way - the only real difference is that downward creates a direct draft/breeze, whereas upwards diffuses the draft/breeze.

You might prefer a breeze in the summer, and you might prefer no draft in the winter.

 

[berkeman]

At least for me, the difference is whether I want to feel the breeze or not.

 

[sysprog]

The objective in each case is the greater comfort of the room inhabitants. Various factors influence that objective. Those include whether there are open doors or windows in the room, the temperature and humidity of the air, and related seasonal differences.

From https://www.hansenwholesale.com/ceiling-fans/fan-direction-summer-winter:

Evaporative cooling by sweating in the summer is not the same phenomenon as wind chill in the winter is; however, the illustrations and associated explanations seem otherwise reasonably accurate to me.

 

[Keith_McClary]

Which way will accumulate less dust on the blades?

 

[DaveC426913]

OK, thanks. I should clarify why this is a thread at all.

When I first started encountering reversible fans, I had no idea myself what the reversible function was for, so I sort of deferred to those who were more familiar with them, and just sort of assumed they knew how to work them.

I have heard people opine on this issue - there are those who think that
- one direction warms the room and the other direction cools the room, or
- one direction draws air in while the other direction pushes air out.

It wasn't until I started thinking about it myself that I couldn't make sense of that - both directions simply circulate the air. I concluded myself that the only net effect was the breeze.

 

[sophiecentaur]

I have heard people opine on this issue - there are those who think that
- one direction warms the room and the other direction cools the room, or
- one direction draws air in while the other direction pushes air out.

I have an idea that the speed of the fan needs to be adjusted to get the optimum effect in each case. In winter, I suggest that a slow downward air movement could help suppress the natural downward flow over the cold walls and bring any warm air down from the roof onto the user. That's the same stated reason for putting radiators under windows.

A strong downwards flow in summer could just help you lose heat through sweating. Bot both settings should, by that rule, be downwards.

Another point - why would anyone want extra draught when it's cold?

 

[DaveC426913]

Another point - why would anyone want extra draught when it's cold?

Exactly. Which is why I think you oughtn't do this:

Bot both settings should, by that rule, be downwards.

 

[sophiecentaur]

Exactly. Which is why I think you oughtn't do this:

I wouldn't disagree for winter conditions except on a very sunny winter day. The hot air in the apex of the conservatory won't find its own way down to you, so a slow down draught could help to get some value from the Sun. That would involve some tinkering to find the optimum and that's always good sport.