Coach roof vents

[Ash1]

Following a small debate on a coach today, I turn to PH for help...
Some coaches have square air vents in the roof, one near the front and one near the back of the coach. They can be opened partially i.e. front or back end of the vent only or fully. On the coach i was on today it said ''ventilation'' with an up arrow underneath the vents. I said they should be opened fully, while somebody else said only the front end of them should be open otherwise the air will go straight out again. Who is right and what is the science behind it?

I'm sorry if this makes on sense, it's late.

[deviant]

I think you would open the front of the front vent and open the back of the back vent.

Front one will scoop air in and with the back of the rear vent open air should flow through the bus and flow out fairly easily. If both were open at the front air would not make its way in as it is to hard for it to escape again.

I remember on the school bus when somone tried to open one that also served as an emergency exit and they did something to it that caused it to come free of the bus, get caught by the air flow and blasted away

[S1_RS]

Do they not work on the airflow design, whereby there are air inlets at the fromt of the bus, therefore opening the roof events causes the air to flow from the front of the bus back to where the roof vent is. I would have thought the air pressure would be quite low over the vent which would tend to pull air out of the roof vents rather than force any in.

[mat13]

S1_RS said:

Do they not work on the airflow design, whereby there are air inlets at the fromt of the bus, therefore opening the roof events causes the air to flow from the front of the bus back to where the roof vent is. I would have thought the air pressure would be quite low over the vent which would tend to pull air out of the roof vents rather than force any in.

That would require a coach designer to consider passenger comfort.

[phumy]

Open the back end of the vent, with the faster outside air passing over the top of the vent will cause a lower pressure in the bus and sucks the "stale" air out, its called the venturi effect. This air will be replaced by vents in the front of the coach. If you open the front of the vent it will just blast air in making some people uncomfortable, plus if it rains the water may flow in too.

[Ash1]

But the stickers under the vents indicated that the whole thing should be opened, is this wrong?

[V88Dicky]

phumy said:

Open the back end of the vent, with the faster outside air passing over the top of the vent will cause a lower pressure in the bus and sucks the "stale" air out, its called the venturi effect. This air will be replaced by vents in the front of the coach. If you open the front of the vent it will just blast air in making some people uncomfortable, plus if it rains the water may flow in too.

This ^^^^^^


Ideal when travelling with a stag party and the lads want a tab on the bus. Draws the smoke right out