I would like to improve the sub floor ventilation of my house and am thinking of installing forced air fan system. Does any one know of any company in NZ that install this kind of system? Here is a website I found:
Try buying a cheap system without the filters on Trademe and position the ducting around the basement and suck air from the outside into the fan. get a decent sized fan, not the DVS type but something that does 800m3+ per hour to do a proper job.
Improving sub floor ventilation is also on my to-do-list. I've been advised that I don't have enough ventilation bricks in place. The recommendation is to double the number of ventilation bricks around the sub-floor. I don't know your specific situation, but I'd be surprised if you'd need to resort to installing a fan-based system down there. I'd look into getting someone in to knock some extra ventilation grilles/bricks in there.
Also address the cause of any excess moisture. We had a problem with water under the house and got a drainlayer in to sort this out. We're also looking at installing a plastic vapour barrier on the ground.
If you've still got problems after that, then installing a fan may be an option.