DIY Attic Fan(s)

[ggrant3]

Okay, so I am very new to this but want to start diving into some solar projects.

I currently have a 110v attic fan. I saw a solar version at a local store and that got me thinking.

I've done some searching online and seen a few DIY versions made with car radiator fans. So I thought that would be a good start as my first project.

The existing 110v attic fan helps keep the attic temps a little lower, but I'm in South Florida and it gets hot in the attic. What I have though of doing was adding two 12v fans connected directly to a solar panel (no batteries). Most likely having one exhaust hot air outside through a gable (that I would be installing so sizes can easily be matched to the fan I choose). Then having a second fan on the other end of the attic just circulating air throughout the attic. Then maybe in the future, removing the 110v attic fan and replacing it with a 3rd 12v fan. The goal is to move much more hot air out of the attic compared to the existing 110v fan

That's about the limit of my research and concept. The questions I have are:

1. Are there any articles that could be recommended from people that have already done something like this?
2. Some people have stated they put a fuse inline, how would I calculate the proper fuse size for this?
3. If I bought a 75-100 watt panel, could I just tie all the fans to that one panel (all +'s tied together and all -'s tied together)? Or would I need some kind of splitter coming off of the panel? Or separate panels for each fan?
4. How would I find out about adding a thermostat to this setup?
5. In one of the videos I watched, it said something about adding fans for attic ventilation having a negative affect on your a/c? Has anyone heard about that? Since all of our a/c lines are run through the attic, I would assume the lower temperature environment would be better. Not sure how it could have a "negative" effect.
6. Best places to look for pieces/parts for this system and types of panels (if there are different types)
7. Other tips, tricks, or advice is welcomed too

 

[snoobler]

Ensure you understand the performance of the 12V fans. Is their cfm meaningful, and can you mount them with the shrouds as unshrouded fans perform poorly?

What is their current draw? Their current draw * 12V = Watts of power, e.g., if they pull 10A @ 12V, they need 120W to work. To get a meaningful run time, you should increase that by at least 50% when sizing your panels.

Automotive fans tend to be small and noisy.

3. Only if the panel provides enough wattage to power the fans. Something like this should be put between your panels and your fans:

https://www.amazon.com/dp/B07B4HLLWH/ref=sspa_dk_detail_5?pd_rd_i=B07L7M82WF

This will take 18-35V input and convert to regulated 12V power at up to 30A.

Select panels with a Vmp and Voc in the 18-35V range.

The converter could be used to supply all your fans up to 30A provided you have enough panel power to do so.

5. excessive flow can disturb insulation that's permeable to forced air, so it can diminish the effectiveness of the attic insulation. Situation dependent.

 

[boondox]

Agree that the 12V fans I have encountered don't move enough air to be useful. One good fan at either end, one in and one out will probably provide the best cooling. That's what I do with my greenhouse.

 

[svetz]

With any attic, the most important thing to do first is check that the air intakes aren't blocked with decades of dust or blown insulation (look at the screening under the eaves, if you can't see through it air isn't flowing through it). The best fan in the world won't move much air if there's no inlet for the air. Natural convection works well if you have enough openings.

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