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Name: Donna F.
Status: Student
Age: 10
Location: N/A
Country: N/A
Date: February 2004


Question:
What determines the air flow in a room?



Replies:
What determines the air flow in a room? The "goesinta" and the "goesoutta", in my opinion. Very important. A room with one small window open has little airflow. Open a door on the other side, and air will probably flow in through one and out through the other.

Each opening has its own amount of resistance to airflow, and the pressure outside the two openings are usually a little different than each other. Strength of the total flow will be = [pressure difference] x [sum of resistances] x [some fixer-upper-number].

A window facing upwind sees a higher pressure. Air will come in there.
A window facing downwind sees a lower pressure. Air will go out there.
A window facing sideways to a fast wind may have the lowest pressure of all, surprisingly. Pressure at doors to the rest of the house, is pretty much controlled by the open doors and windows and leaks around the rest of the house. In our house on hot summer nights, warm house air tries to rise and leak out through the attic, while heavier cooler night air comes in all the windows. Especially if I open the attic hatch.

Air can go around in circles inside a room too, but slower. Often there will be one warmest wall and another coldest wall. Air will rise at the warm wall, travel across the ceiling, fall at the cold wall, and creep across the floor, back to the warm wall. If you do not like sleeping with cold drafts, perhaps your bed should not be next to the cold wall in winter. That situation is what bed-canopies are good for. Other than style, that is.

Cordially,
Jim Swenson



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