Airflow question (?)

[les45]

On my current standy project I will have a Fantastic fan in the center of the roof but my windows will be fixed. The windows in the door can be opened for airflow but I would like to get some airflow over the front and rear ends to cover the bed area and the dinette area. I am contemplating some sort of existing trailer type vents but most of them are limited in size (about 3" diameter). My question is how is airflow affected by the reduced diameters? I know velocity would increase but how would the total volume be affected?

[Tomterrific]

I am not familiar with the Fan type vents as my vent is passive. I will say that it is my opinion, you can't have too much ventilation. More window opening might be your final solution. I have a way to open my home made doors a crack while we sleep. Ventilation is even nice when the night's are cool.

Tt

[FM82]

On my current standy project I will have a Fantastic fan in the center of the roof but my windows will be fixed. The windows in the door can be opened for airflow but I would like to get some airflow over the front and rear ends to cover the bed area and the dinette area. I am contemplating some sort of existing trailer type vents but most of them are limited in size (about 3" diameter). My question is how is airflow affected by the reduced diameters? I know velocity would increase but how would the total volume be affected?

The total volume would affected greatly in that case. Of course it would depend on how many of the 3" vents you installed, but, you would need to install enough 3" vents to equal the same volume opening as the fan-tastic vent for the air flow volume to be the same. Without that, the velocity would increase, but the volume would be reduced.

It's getting meticulous, but something else to consider with the louvers on the new vents. The space taken up by those also need to be taken into consideration. They actually reduce a 3" opening to less than 3 inches.

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[Modstock]

I'd probably re-think the fixed windows.
I've had nights with no breeze/wind even with my windows open and couldn't sleep. Which makes for a very tired/cranky next day.
Now I try to turn the trailer to get airflow if it's not getting inside.
Also picked up a 02cool battery powered fan.
Sometimes a spray bottle to get a mist on those hot nights.

Maybe try Coast. 12v Boat purge fans if you have to.


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[les45]

I should point out that we don't camp in the heat of the summer or the cold of the winter. With our moderate temps here in the Southeast, I've found that a fan with proper ventilation is really all we need in the fall and spring. I'm just trying to find something ready made to provide that ventilation with my existing Fantastic fan.

[me&z]

... you would need to install enough 3" vents to equal the same volume opening as the fan-tastic vent for the air flow volume to be the same. Without that, the velocity would increase ....

What FM said.

But you can probably get by with less. Think about the least open you've had your windows open while running the fan. How many square inches of open window was that? That would be the bare minimum (imo).

[Aguyfromohio]

Your plan sounds like the approach often used to cool enclosures full of electrical equipment. Install a single exhaust fan, and open intake vent holes wherever you need them.
That kind of airflow does not mix well at all, so you can easily get stagnant corners and areas with no flow. If a stagnant spot is bothering you, punch a new intake hole right there to let in a jet of cool outside air.

For the area questions, make the total square inches of intake vents equal the total square inches of the exhaust fan and you will be about right. As you add extra intake vents, the air velocities all go down together, at every intake, but so what? The air still moves through your cabin, just a bit slower.

[Cosmo]

I like bottom up airflow. My trailer came with these cargo trailer vents. In 4 years they have not leaked. Mine are mounted low near the floor in front. The air flows up to the roof vent and out. Good for active or passive ventilation.

https://www.mgtrailer.com/vents

Some old video of the vent. Lots of things have changed on the trailer since then - but not the vents.
https://youtu.be/F7HAlUdsYEE?t=286

Also a 12V stand alone fan can help. I have had it blowing directly on me both inside and outside the trailer in hot humid high temps. Maybe enough breeze for 2 humans close together.
https://www.amazon.com/gp/product/B0000 ... UTF8&psc=1


=Cosmo