Everyone seems to be assuming that you have a big fan which actually changes the air flow in the whole room in a major way. If that's the case, great, put it any way you like - it doesn't matter. For people like me, who use a cheap fan in the summer. Put it in front of you facing towards you. You will feel cooler. If you are still interested in CFD I can give you a hand, but this is answer we are going to get from it…
I agree with you - it's similar to the principle of a space heater in the winter. You point it at yourself and heat only a small zone. In the summer, point the fan at yourself and use evaporative cooling to cool just a small zone.
In to room, via nice HEPA filter, for cleanliness.
Ignoring that, In to the room. Fan can not create much vacuum but can create much pressure.
Let me give you my most handy example. Imagine a queue. A push can cascade from last person to first person, but a pull can only be apply to last person.
The direction doesn't matter nearly as much as blowing the fan through a large-ish opening.
You want the air from the fan to accelerate other air on the way out/in. This is the same principle as turbofan engines, in which a higher bypass ratio (bigger fan) attached to the same fuel burning jet core is more efficient.
Why? Because the relationship between velocity and volume is not linear. Takes more energy to move the same amount of air the faster you accelerate it.
So ideally you want to position the fan in a large opening far enough back that the fast moving air can get a bunch of other air moving as well. Trade the high velocity fan air for a much higher volume.
I assume you want to move the cold air in and the warm air out. How to best achieve that completely depends on the shape of your room and the holes to the outside. You should probably do some computational fluid dynamics on a model of your place to see which blowing direction works better. It probably works best if you have separate inlets and outlets for the air that are maximally far apart, like on the ceiling and…
If you look at the design of windows on old houses from about 1700 to 1940 they facilitate exactly this. They open at the top and/or bottom to allow the circulation of air. Hot air will naturally rise and exit from the high up window. When air conditioning took off in the 1950s this became less important.
Also while extremely trivial here, higher pressure air has a higher capacity to transfer heat.
While this is technically true, the difference is very minor at the typical pressure ranges being used. The highest performing PC fans create about 10mmH2O pressure while typically you can expect about 1mmH2O pressure compared to 10mH2O of the atmosphere. This translates to densening of the atmosphere around components by 0.1% or 0.01%, respectively. Correct placement and design is by orders of magnitude more importa…
TIL about mmH2O. Is this common in HVAC? I thought pressure was mostly in mmHg or bars(millibars).
My 4rd grade teacher was convinced of the science of using two fans to cool off the classroom: one blowing cool air into the classroom from the hallway and one fan blowing hot air out of the classroom through a window. The kids that sat near the fan blowing in the room from the hallway were quite content, but the kids by the window were always complaining and they would secretly turn the fan in the window around so i…
If all the other teachers were doing this too, the hall might have been negative-pressure enough that the air blowing in was circulating right back out before reaching the rest of the room.
That would mean the kids near the outlet fan were getting air that was just pulled in from outside via the window seams.
My 4rd grade teacher was convinced of the science of using two fans to cool off the classroom: one blowing cool air into the classroom from the hallway and one fan blowing hot air out of the classroom through a window. The kids that sat near the fan blowing in the room from the hallway were quite content, but the kids by the window were always complaining and they would secretly turn the fan in the window around so i…
I should add that my teacher would think we couldn't understand the science or concept behind airflow going through the classroom to cool us off. He'd explain it over and over and get frustrated that so many students didn't seem to "get it." But really they did get it, it just wasn't working for them. I wonder if the arguments about scientific things nowadays aren't similar. It may not be that someone is stupid or doesn't get it, or even that they disagree, just that it's not working for them. The window kids understood that the room was supposed to be getting cooler, but it wasn't for them. They weren't against air flow, but it didn't seem to be working for them. Perhaps in theory the 2 fans in the classroom should have worked, but maybe the fans weren't strong enough, there were other places for the air to go (like the ceiling), etc. so that in practice it didn't actually work like the teacher claimed it would. Maybe there's a lesson there for public debates.
My 4rd grade teacher was convinced of the science of using two fans to cool off the classroom: one blowing cool air into the classroom from the hallway and one fan blowing hot air out of the classroom through a window. The kids that sat near the fan blowing in the room from the hallway were quite content, but the kids by the window were always complaining and they would secretly turn the fan in the window around so i…
I should add that my teacher would think we couldn't understand the science or concept behind airflow going through the classroom to cool us off. He'd explain it over and over and get frustrated that so many students didn't seem to "get it." But really they did get it, it just wasn't working for them. I wonder if the arguments about scientific things nowadays aren't similar. It may not be that someone is stupid or do…
We used to make paper fans and the teachers insisted "they just make you hotter" (due to energy expended waving them) but it sure didn't feel like it.
While this is technically true, the difference is very minor at the typical pressure ranges being used. The highest performing PC fans create about 10mmH2O pressure while typically you can expect about 1mmH2O pressure compared to 10mH2O of the atmosphere. This translates to densening of the atmosphere around components by 0.1% or 0.01%, respectively. Correct placement and design is by orders of magnitude more importa…
TIL about mmH2O. Is this common in HVAC? I thought pressure was mostly in mmHg or bars(millibars).
Yes, fans usually have a specification on the pressure they can create in inches of water or millimeters of water.
I think it is because you can measure it yourself with just a tube and water- open end manometer.
TIL about mmH2O. Is this common in HVAC? I thought pressure was mostly in mmHg or bars(millibars).
Yes, fans usually have a specification on the pressure they can create in inches of water or millimeters of water. I think it is because you can measure it yourself with just a tube and water- open end manometer.