Carol regarding the vent covers, If they are steel and not aluminum Lowes and Hope depot carry some magnetic covers that are made for indoor use they appear to be the same material used for the car magnet use to advertise a business on the side of a car. This might be OK but my personal experience would only last a year or two. The Arizona sun tears up the car magnets after a few years. WW Granger makes a more robust magnetic cover for $12 each. If it were me I'd get a coupla hinges and hook and eye and make a cover that would attach and just flop down when need out of 1/4 plywood. Maybe make a seal around the edges out of some of that foam striping stuff that made for that purpose.
They're plastic, Don, but I am not married to them. Have to figure out how the building performs when they are covered. The ridge will have to stay open as it is an exhaust vent. At least that is what I am reading this far. But it requires inlet air from some place so I can't block the vents off entirely. That suggests filtering that air which is problematic in terms of flow and clogging, which I am told takes less than 10 minutes. Interesting conundrum. (Sorry for the language, Vaughn.)
But it requires inlet air from some place so I can't block the vents off entirely. That suggests filtering that air which is problematic in terms of flow and clogging, which I am told takes less than 10 minutes.
Hmm, I'm dubious that the building is sealed well enough that putting dust covers over the vents would cause a real problem for shortish periods of time. Of course you probably want something you can leave on for longer periods of time so that might complicate the situation some if it causes the airflow to be low enough it raises the roof temperature significantly. Its possible that that wouldn't happen, I don't know enough to be positive.
What might would well enough would be adding a slightly convolute entrance akin to a fallout shelter vent (although in this case I'm thinking maybe a n shape not a u shape) might do more or less what you need in regards to keeping ~98% of the dust out. I suspect that that last 2% of dust is kind of a lost cause anyway because you'll get some infiltration around the doors and through the roof vents (having lived in AZ for 10 years I got pretty comfortable with resignation as far as absolute dust control goes). That would let you basically keep in it in place all of the time. Some experiments I did a couple of years ago with solat dehydrators showed that you can get a pretty significant airflow increase with a $10 solar panel and a similarily cheap ball bearing 6" fan which should, I think, more than make up for the loss due to inlet shape. You might want to wire the booster fan alongside the lights or something so you can turn it off so it's not sucking in dust when you don't want it to. You could also have a light flap that opens inwards which would let it auto adjust for pressure differential, those are pretty commonly available (I've seen them at the home stores.. can't remember what for though).
Agreed that the building is well sealed. It is not. There is gobs of space between the trusses. Enough so, it won't keep bugs out.
SO an idea that is rolling around would be to screen the soffets for bug control. Use the wall space between the studs as a duct from the vents to the attic. Shield the vents on the outside with the H shaped covers you suggested to interrupt the flow enough to drop the dust particles before entering the building. Assist the air flow throw the attic with a solar powered fan to keep air moving.
Sheet and insulate the ceiling. Run a through the wall swamp cooler mid way on the west wall (opposite the double door). Humidity regularly way below 15% here. Down the road insulate the walls and install A/C. Maybe use one of those motel type units that also heat.
I can spread out the investment and maybe have a relatively comfortable environment with low maintenance.
I think screening is a good idea in general. In addition to the bug issues you're in a moderate fire risk area so blocking incoming sparks is an A++ idea. California has adopted a somewhat stringent code on the matter that imho has a lot of good ideas, but even just using nonflammable materials would help a lot. A short overview is here: https://www.firesafemarin.org/home-hardening/vents
For just a swamp cooler, part of what makes them work is airflow.. so I might hold off on insulating the ceiling to much before seeing how well that does/doesn't work? It could be the extra upflow offers enough advantages to offset the possible insulation benefit. I remember when I had one I also had a big old up-duct that fed into the attic I'd open when running the swamp cooler.. and then I'd close that up in the winter for heating. So maybe seal and insulate but have a ceiling penetration for upflow when in the summer/running the swamp cooler? I think that might solve some/most of the other roof venting problems as well... Although ideally there you'd have the airflow coming in along the sides.. so maybe swamp cooler in the center of one end wall and then some attic vents along the side?