Gym Sulkinson Fork wrote:
On Thu, 25 Oct 2018 17:31:23 +0100, Rod Speed
wrote:


"Gym Sulkinson Fork" wrote in message
news
On Thu, 25 Oct 2018 17:09:56 +0100, Rod Speed
wrote:



"Gym Sulkinson Fork" wrote in message
news On Thu, 25 Oct 2018 16:25:20 +0100, Rod Speed
wrote:

Gym Sulkinson Fork wrote

Why are these fitted instead of just a stationary vent like you
see on caravans?

They act like a pump.

http://www.flettner.co.uk/van-roof-vents/

I don't see the point in using the wind to power a vent, when
the air was
already moving.

It isnt from the place you want to move it from.

Surely that's like fitting a generator to your bicycle to power
a motor
to
make you go faster?

Nope, more like using a wind generator to generate
electricity and using the electricity to drive a fan, but
without the losses involved with the electricity
generation and the electrical fan.

But the point is to move air into or out of (shouldn't matter
which, air still goes through the van) where the vent is.

It does actually, particularly when getting it to
remove the hot air in the roof space in summer.

but if you let the wind blow it in, then it goes out where it's
currently coming in.

Yes, but is going against the natural flow of the hot air
coming out of the roofspace, so doesn't work as well.

Think of electrically powered exhaust fans.

The work much getter moving the air out of the roofspace
than moving outside air into the the roofspace.

Makes no difference how that fan is powered,
still works better to move the hot air in the
roofspace in the way it wants to go by convection.

I tend to do that when designing desktop computers, but mainly
because of where the hot chips are and what needs the most cooling. I have
intake fans front bottom cooling the disks, then across the
graphics card, then over the CPU then out the top back and/or top.

You can't even design your own life.
You are a failure, always have been and always will be.
Peter Hucker, the clown of newsgroups.