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Hi
One of the nasty things about fans is that there are a lot of spec's on them. Size and power input are pretty obvious. Noise level is one that is pretty easy to observe. There are at least two other very critical parameters. The first is the number of CFM (cubic feet per minute) the fan will move. More is better. Computer fans are *famous* for advertising numbers that are nonsense. It's a lot like eBay battery amp hours. The next parameter is back pressure. Block off a fan completely and it's not going to move any air. That's true of all of them. Block it partially and the fan has to work against the generated pressure. Some fans (or blowers) can move a *lot* more air at a given back pressure than others.
If you are doing a proper design on a tight fan ventilated enclosure, back pressure may be your biggest issue. Blowing air through a wide open computer case, it may matter much less . Volume of air is what you are after so one fan that moves twice as much may save you finding room for a second fan.
Just as on modern computers, fans can be set up to run faster when that's called for. It's not a perfect thing. You do need some sort of controller and controllers can break. Often it's the only way to match up the noise /power / air flow / back pressure needs in a rational fashion. Getting the sensors and firmware right in a controller is often a multi step process. The computer guys took a *long* time to get it even close to right.
Finding that fan A is the same size as fan B is only the start of swapping this for that fan. Unless the other important specs also line up ... who knows what will result. If there is a controller involved there are even more things to worry about. All the experiments over the summer have demonstrated that this isn't a easy thing to test quickly. Being sure that a swap is 100% .... not easy at all.
Lots of fun !!
Bob
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