Roof ventilation simply cannot be explained and/or measured by calculations for openings, by volume or claiming 5 to 10 air changes per hour – what does 5 to 10 air changes per hour mean to the end consumer, really nothing.
The fact is that effective roof ventilation can only be dictated by the forces and elements of nature incorporating the principles of fluid dynamics – fluid dynamics the study of air and gases in motion including aerodynamics, density, pressure, flow velocity and temperature functions.
Fluid dynamics in relation to roof ventilation – airflow, thermal currents, wind, aerodynamics. Convection – Newton’s Law of Cooling, in layman’s terms hot air rising cold air falling.
The venturi effect causing air to move through a constriction the average flow speed of air doubles increasing the air’s velocity as the air diverges to leave the constriction.
So therefore it would be desirable for an effective roof ventilation system to be designed to use and harness the elements of nature incorporating fluid dynamics. This is what an effective roof ventilation system should be calculated by.
It is simply not a matter of punching a hole in a roof and covering it with a ventilator that has no design elements within to harness the principles of fluid dynamics and claiming 5 to 10 air changes per hour. This is simply pie in the sky and really inconceivable.
MANY ELEMENTS COME INTO PLAY WHEN CONSIDERING THE CONCEPT OF ROOF VENTILATION
Consider this a house surrounded by houses and trees is obviously going to receive a different result to a house in the middle of a dusty paddock in the height of summer.
So taking all possibilities into consideration when designing an effective roof ventilation system the ventilator should be aerodynamically designed with the elements in mind and fluid dynamics incorporated with inlets and outlets within the roof to allow the ambient temperature to circulate the roofspace 24/7. Then the roof in question at the time of installation should be broken up into zones with an inlet and an outlet in each zone, this is the concept for effective roof ventilation.