Yes, you are right the current NitroPC comes with an active cooling. But it is pretty silent during typical workloads (due to the "U" type CPU originating from Laptops), you can quite reliably configure it to be "nearly" fanless, if you restrict max cpu frequency and/or turbo mode, but this will obviously lead to performance limitations - just as a possible solution for you. Meanwhile I can also say that for upcoming product fan-less designs are also investigated.