idea of a fan in the roof for the purpose of venting the heat
out is a seemingly attractive one.
the fan being used here is a 240v axial or centrifugal fan not
an erratic solar whiz bang
is, 'a fan sucking the heat out'...... fantastic...modern day
roof ventilation......if only the Romans had them.
sucks the heat out of the roof, (I say sucks as it's the term
the sales people use when creating a negative pressure) and
it obviously draws ambient air in, as a consequence to replace
that which has been removed, using the path of least resistance.
in principle, the ingress points have to be further most distance
away from the fan, so as to air wash the distance in between
the two points, and the ingress or eaves vents themselves need
to have minimal resistance, the efficiency of which is going
to affect the fan efficiency.
In the case
of a ventilating the roof space of a skillion roof, where the
distance between ceiling and roof lining can be as little as
200mm having a dedicated ingress with a fan at the opposite
end, there would be some benefit in both relieving the heat
gain and offsetting the saturation of the ceiling insulation.
in mind that the average roof space temperature is around 68
degrees and the heat transfer via conduction of the steel roof
will be proportional to the airflow of the fan.
long is the fan going to last?.....given that manufacturers
such as EBM Papst
Abegg do not recommend their fans be used in conditions
above 60 degrees