What an oxymoron:wind turbine. That is exactly what it isn't:wind driven.
Here's the dynamic. Cut a hole in your roof and the hot air rises(if you have intake)but rain gets in. So you put a cap over the hole which slows the escaping air but keeps the fierce Dallas storm out.
You want more air to escape so you put on a turbines whose cap size has been effectively reduced to the small plate all the fins have been spot welded to. I know because one of my winter jobs, when roofing was slow, was to build turbines for Mr. Vernon Johnson at Coolcrafters in Arlington Texas on South Peycos Drive.
The escaping hot attic air makes the turbine spin even on still days. Of course "even" but especially on still days. That is because a wind spun turbine won't let the air out as fast, if at all.
You don't believe me so I'm going to prove it to like Aristotle proved to me the world was flat.
Imagine that we live on a large planet like Jupiter and the gravity is so dense the air is as thick as water. If the flowing water above your roof is spinning the turbine then the hot water in your underwater attic cannot get out as fast because of the pressure of the flow of water over the roof.
This makes sense and the fluid dynamics are the same. The hot air's escape is impeded by the wind spinning the fins rather than rising air spinning the fins.
Other attic ventilation systems like vent ridge and low profile vents have a better "down wind" side because the turbine makes air flow around it, it being elevated and spinning, thereby making airplanes fly.
Did I skip something? Oh yeah, that Italian dude who predicted that F-16's would lift off the ground when they got moving fast because of the vacuum caused by the shape of the wing, was proven right. The Wright Brothers knew it and started a roofing company in Irving over a hundred years ago. Their roofs flew and flew.
Here's what Wikipedia says about his theory:
In fluid dynamics, Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy. Bernoulli's principle is named after the Dutch-Swiss mathematician Daniel Bernoulli who published his principle in his book Hydrodynamica in 1738.
Bernoulli's principle can be applied to various types of fluid flow, resulting in what is loosely denoted as Bernoulli's equation. In fact, there are different forms of the Bernoulli equation for different types of flow. The simple form of Bernoulli's principle is valid for incompressible flows (e.g. most liquid flows) and also for compressible flows (e.g. gases) moving at low Mach numbers. More advanced forms may in some cases be applied to compressible flows at higher Mach numbers (see the derivations of the Bernoulli equation).
Bernoulli's principle can be derived from the principle of conservation of energy. This states that in a steady flow the sum of all forms of mechanical energy in a fluid along a streamline is the same at all points on that streamline. This requires that the sum of kinetic energy and potential energy remain constant. If the fluid is flowing out of a reservoir the sum of all forms of energy is the same on all streamlines because in a reservoir the energy per unit mass (the sum of pressure and gravitational potential ρ g h) is the same everywhere.
Fluid particles are subject only to pressure and their own weight. If a fluid is flowing horizontally and along a section of a streamline, where the speed increases it can only be because the fluid on that section has moved from a region of higher pressure to a region of lower pressure; and if its speed decreases, it can only be because it has moved from a region of lower pressure to a region of higher pressure. Consequently, within a fluid flowing horizontally, the highest speed occurs where the pressure is lowest, and the lowest speed occurs where the pressure is highest.
See, I told you so. Don't confuse him with his evil cousin Venturi, who squeezed air into small pipes and made it hurry.
That's why, when those storms blow in from Lewisville and north Carrollton into Irving and Dallas, turbines start to fly.
So if you want turbines, go get a real job. They are about the least effective form of roof ventilation you can buy for your attic. The only thing worse is a roof exhaust vent without matching intake vents.
That behind the times roofer who wants to add a turbine on the lower ridge on the back of the house is your attics worst enemy and he is going to cost you a lot of money.
Attic ventilation is my mantra and passion. If it isn't your roofing company's passion then he shouldn't be your roofer.
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