6 replies to this topic

[ClownFish]

When I finished my observatory, I noticed that fine dust came in under the dome and along the edge of the shutter door.  I have a dusty dirt country road upwind of the dome, and cars kick up the dust which then blows all over the dome, and some enters it.  So I designed and built a filtered-air positive-pressure system to maintain a greater air pressure inside the dome vs outside.  This will blow air out the cracks and keep dust (and snow) from entering.

The system uses two 12-volt (6 amp) marine ventilation fans, that move 540 CFM of air from outside and through a filter.  The filter is an aluminum electrostatic washable filter, although I will be replacing that with a paper HEPA filter later.  The intake outride is eight inches in diameter and the output inside the dome are two four inches (x2) holes.  I power it off two 12volt Marine deep-cycle 100 AH batteries that are charged by two solar panels.  If I am using the observatory, I turn them off as soon as I open the shutter.

The first video link below shows the system in operation.  It’s quite loud but fortunately I don’t do much work in the dome itself, so it’s not a huge issue right now.  Plus at night when I am using it and the dome is open, I turn off the air system.

 

The second video shows final testing.  It works great!  What would be cool is to build a RPi controller to have the system slow down when there is no wind, and then speed back up when the wind speed increases.  I have to figure out to connect to my AAG Cloudwatcher system which also monitors wind speed.

 

Here's the pump being built.  I have since added a weather seal and lid.  Four hand-knob bolts secure the lid tightly.

 

Video 1:  Installation - https://youtu.be/CYYdD8mqo2s

Video 2:  Testing - https://youtu.be/KzZqeMaPiC8

 

 

 

[torsinadoc]

Nicely implemented

[BOSS3128]

Nice setup!!

[ClownFish]

Thanks!  I haven't has a spec of dust in two weeks!  

[Stozhary]

My two thoughts. 

First inside observatory should be positive pressure. To achieve that you should pump air from outside and filtered. you did that. 

I would use cheap box fan (20x20x4") from Walmart and use the same filter size like 20x20x2. it runs with three speed and need 110V.

You can install it into wall, preferably from "clean"side of building and if it possible from North side.

Second, use portable room air filter. Honeywell makes great units with HEPA filters. Its not cheap but worth.

And obvious cover optics with one side cut plastic bag.

Cheers

Stozhary.

[ClownFish]

I fit the filter system with paper filters and found that the metal reusable filter was not catching the finest dust.

 

But my main issue now is that one air pump is not pulling as much air as the other.  I tried each fan by themselves and they both work fine, but when I run them together one pushes out twice as much air as the other.  So I think I have a design flaw - in that one fan is lowering the pressure inside the box to the point that the second fan cant pull as much.  I'm not sure if separating them with a divider would help.  The intake is 8" diameter which is more than enough capacity for four output holes. 

 

Any thoughts?

 

PS:  I noted that running just one fan was enough to keep dust out when the wind outside was low.  But with a good breeze dust could still get in. So I need both fans running at capacity.  

[archer1960]

I fit the filter system with paper filters and found that the metal reusable filter was not catching the finest dust.

 

But my main issue now is that one air pump is not pulling as much air as the other.  I tried each fan by themselves and they both work fine, but when I run them together one pushes out twice as much air as the other.  So I think I have a design flaw - in that one fan is lowering the pressure inside the box to the point that the second fan cant pull as much.  I'm not sure if separating them with a divider would help.  The intake is 8" diameter which is more than enough capacity for four output holes. 

 

Any thoughts?

 

PS:  I noted that running just one fan was enough to keep dust out when the wind outside was low.  But with a good breeze dust could still get in. So I need both fans running at capacity.  

With two identical fans mounted symmetrically (looks that way, anyway), I would think they would share the load pretty equally. Have you inspected them to see if one is damaged, a vane is bent, or the bearings aren't as free as the other, or something like that? Failing that, check to be sure the electrical connections are all good on the weaker one. You could try a divider so each is pulling through its own half of the filter; that might equalize it a bit.