This is how I plan on ventilating my hive- with mesh covered holes in positions where the bees have access and can decide what they like.
The whole fan thing is just an idea- and if I implemented it - it would be filtered- and a very small fan. I understand all the arguments against it- I am just curious at this stage…
@Michael_Bush how about if you you inserted that fan- not randomly- but in accordance with what the bees want? Assuming you can figure that out? 
My new hive design has an insulated roof with an air space between the roof and the cover boards. I was thinking of using a fan to aerate that space- drawing fresh air up through the hive- (the air inlets at the bottom of the hive would have cloth filters to prevent dust being drawn in) and venting out of the roof vent. I am thinking a really tiny fan powered by a tiny solar panel- and only in use in the hottest months. It’s just an idea. I plan to make at least 3 identical hives in the coming weeks and I would only test a gimmick like this beside a hive without the gimmick.
Having read and appreciating your opionons concerning ventilation: I take it you think the product @bigB linked is probably crap- and the claims they make dubious? http://www.beecoolventilators.com15
However I have done more research about heating the hives in winter- and that seems a no brainer to me. If you can add a few degrees of heat to a hive in cold weather easily- I can’t see how it could be a bad thing for the bees? Whether it’s insulation, passive solar- or something a little more high tech.
I have come up with a way to turn my flow frames into heat sinks… and I will be incorporating that into one of my upcoming hives.