HVAC Redirecting Airflow with a Curved Surface

[iXod]

TL;DR

I want to change a fan's airflow direction

I want to change the direction of airflow from a fan. The fan is covering a window so as to bring fresh air into the workspace, exhausting warmer air through open windows throughout the workspace.

It would help cool those in the immediate area of the fan if it were blowing 90 degrees to the current orientation, but in order to draw in fresh air, the fan must remain where it is, covering the window.

I am considering building a simple curved surface (an arc of 90 degrees) sandwiched between 2 flat surfaces. The fan will blow onto this arc and the air will exit the arc, changes by 90 degrees.

For best effectiveness, should this curve be a constant-radius? Or some other shape?

Thank you.

 

[jrmichler]

The larger the radius, the less the restriction, and the more air will flow. The following chart, from my 1985 copy of the ASHRAE Handbook of Fundamentals shows the effect of the radius:

The restriction is a function of the Co number - smaller number is less restriction.

If space is tight, you can use a square elbow with turning vanes:

Turning vanes in a square elbow can reduce the restriction to almost the same as a large radius elbow. They give you the option of building a square elbow, installing it, and checking the airflow. If the airflow decreases too much from the fan without the elbow, just add turning vanes.

 

[Baluncore]

Keep the turning vanes some distance apart for access.
If there is no filter, they will need to be cleaned regularly.

 

[iXod]

Thanks for your replies. I’ve decided to use my original design, a simple 36” radius curved surface built with 1/4” plywood. The radius surface will be HDPE.

My next task is to determine what the max CFM this window opening can support.

What is the CFM limit (per sq.in. or sq.ft.) of common (1/8”?) window screen?

Thank you.

 

[Rive]

Just out of convenience I would suggest considering a sail instead of plywood. Can free up a lot of space.

 

[iXod]

Please explain. Is a sail a piece of fabric attached so as to give a radius when “inflated” by the fan’s air pressure? I’d never heard of this. Sounds simple.

 

[Rive]

Is a sail a piece of fabric attached so as to give a radius when “inflated” by the fan’s air pressure? I’d never heard if this. Sounds simple.

So simple that you came up with a plan just after hearing about it for the first time

Harder to make it anything 'optimal' than plywood, but can be simply stowed away in a bag at autumn.

 

[Lnewqban]

Considering reversing the flow of the existing fan outwards.
Fresh air will come in through each of the screened windows, sweaping the whole space at lower speed while collecting heat from persons and equipment, just to be exhausted, finally collecting the heat produced by the fan motor, through a single window (back draft damper or screen to keep insects out when the fan is off).

For areas that are not naturally reached by that flow of air, you could install ceiling fans or regular horizontally blowing fans.
I believe that you could make more workers comfortable that way, avoiding strong drafts of air inside the space.

 

[iXod]

Add to my previous post: there are vehicles around the building that idle while parking, loading, the exhaust from these can be drawn in through open windows. This was one of the main reasons for preferring a single inlet (it’s high in a loft) and multiple exhaust windows.

Were the neighbors different, the dongle outlet is preferable.

Thanks.

 

[Lnewqban]

Add to my previous post: there are vehicles around the building that idle while parking, loading, the exhaust from these can be drawn in through open windows. This was one of the main reasons for preferring a single inlet (it’s high in a loft) and multiple exhaust windows.

Were the neighbors different, the dongle outlet is preferable.

Thanks.

In that case, positive pressure is better.
Could you install a regular horizontal fan blowing 90 degrees across the airstream of the inlet fan?
Could your inlet fan collect the truck’s fumes as well?

 

[berkeman]

Add to my previous post: there are vehicles around the building that idle while parking, loading, the exhaust from these can be drawn in through open windows. This was one of the main reasons for preferring a single inlet (it’s high in a loft) and multiple exhaust windows.

Were the neighbors different, the dongle outlet is preferable.

Thanks.

Have you done any programming with Arduino or other microcontrollers so far? You could to a fairly simple system that senses the vehicles parked and idling causing the exhaust problem, and pause the system...

 

[rbelli1]

idle while parking

Put up "No Idling" signs

BoB