thomas rubino wrote:Although not cheap, the heat fans that sit on your wood stove produce a significant breeze, using no electricity at all.
They have a Thermo Electric Generator (TEG) inside them powered by the heat of the stove. Technically you could rig something up to power them with heat for cooling purposes, but with that much cost it would be cheaper to add more capacity/production to whatever off-grid energy source is being used.
I don't know how useful this idea would be for a multitude of reasons, there is a really good video about more efficient ceiling fans here:
If you already have a decent plan for powering a ceiling fan then finding a BLDC fan is a good option. It's possible to find out the specs of the motor and get a different motor controller that hooks up directly to DC power, but that's pretty technical and probably not worth it if you are only running on a 12V or 24V battery system.
I have taken a bunch of used PC fans and hooked them up in various ways to provide cooling. If you have appropriately sides hole saws, you can mount them to a piece of wood and make a duct to move cool air in or hot air out. I had my bedroom set up this way for several years. Especially when using old fans, they sometimes make annoying resonant sounds at certain speeds. Rather than buying individual speed controllers, I just found a voltage that they would run at without being too loud (such as 9V) and powered them with that. Since they were free, I could use a few extra to make up for the loss of airflow by undervolting them. They are already long lived, and running them slow prolongs that life further. Keep them clean and they can run non-stop for several years.
I was also using this for drying clothes. The rain is pretty much daily and sporadic around here, so just leaving a line out in the sun can be problematic. I had a free sheet of steel roofing that I covered a small rack inside a plywood box and used one of those USB power banks to run 4 smaller fans at 5V to exhaust the moisture laden air. I only used what I had on hand just to see if it worked. Nowadays you can find USB-C power banks that are capable of giving multiple voltages, such as 5V, 9V, and 12V which could be used to power a number of fans. You would have to figure out the current draw of the fans and the rated output of the power bank. They make various adapters (trigger boards and cables) to get a consistent output since USB-C needs to communicate with something to output the correct voltage.
You could also use any type of battery with an appropriate buck/boost converter to give what you need. The benefit to this is you can have a small number of quiet fans closer to you and perhaps a few more fans elsewhere for intake and exhaust. I had some small wires going around my bedroom for fans and lighting, but it would be easy to use separate batteries. Of course this is from the viewpoint of someone that can make battery packs for dollars instead of hundreds of dollars.
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