In the summer, why do you want to pull hot air from the ceiling downwards instead of pulling up colder air to the ceiling?
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While hot air rises, there’s usually not a significant difference in air temperature between the air at the ceiling and the air at the floor, unless you’re in a very tall room or you have some way to trap the hot air up top (like an attic). So the effect of blowing the “hot” ceiling air down to the “cool” floor is not a concern. (If the air is trapped in an attic, your ceiling fan won’t move it down to you – it’s trapped.)
However, in winter you’re producing heat on the edges of the room via vents or radiators. The difference in temperature right next to the radiator versus the middle of the room is a lot greater than the difference between the ceiling and the floor in summer.
So, in winter, you want to mix the warm air coming from the radiators with the cooler air in the center. In summer, you don’t care about mixing the air because there aren’t any significant hot or cold spots, but you do want the air blowing over your skin.
(Actually, you might want to mix the air in summer if you’ve got air conditioning. So you can benefit from both the air-mixing and the breeze-on-skin effects.)
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