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