Types of wind turbine

The most commonly used type of wind turbine is the horizontal axis wind turbine (HAWT), the following picture shows a typical HAWT;

http://www.airfoils.com/apps.html

http://www.eia.doe.gov/kids/renewable/wind.html

A horizontal axis wind turbine consists of a rotor, a frame upon which the rotor stands and a generators to produce electricity and a tail. A standard HAWT consists of three blades. VAWT such as the Darrieus wind turbine are not neatly as common as there HAWT counterparts, the main reason for this is the their small operating ratio. The main advantage of VAWT is that they are easier to manufacture and have a lower noise level. picture > http://aerolab.virtualave.net/wind/ (picture of darriues)

As this web page is mainly devoted to the integration of generation technology toward zero emission buildings the decision has been taken to disregard the further consideration of either horizontal axis wind turbines and vertical axis wind turbines and to focus further investigation into ducted wind turbines. The reasons for this decision among others include the inherent complexity involved in the installation of HAWT and VAWT on the building envelope. For one; the size of turbines which would need to be installed in order to produce a significant amount of power would require additional planning permission and would likely interfere with reception as well as creating a substantial amount of noise. In some cases the installation of a HAWT can actually be economically feasible, in these cases is it very likely that the turbine is placed away from obstructions which would affect turbulence and thus wind speed.

Other consideration of the installation of a wind turbine are the aesthetics of the installation which must be carefully considered, it is of no doubt that the installation of a large HAWT or VAWT or top a building would have significant negative impacts on the building aesthetics and architectural considerations.

Ducted Wind Turbines (DWT)

The original idea for DWT was developed by an engineer from Glasgow in 1979; the original intention was for modular application. It was later investigated by the mechanical engineering department at the university of Strathclyde for the integration into the building design. A picture of the ducted wind turbine is shown below. One of the key differences between the DWT and standard wind turbines is the effect of the aerofoil on the wind turbine, this is very similar in the way in which the air flow over a wing on an aeroplane. Figure 2 DWT shows the effect on the flow characteristics around the edge of the building and through the DWT. It can be seen that the pressure on the edge of the building is positive and through the DWT the pressure is negative. The desired effect if for higher-pressure differential, without the top plate (on which there are PV’s mounted) the pressure difference would be less. The higher the pressure difference the higher the velocity through the turbine blades and thus more power is produced. For further information of ducted wind turbines refer to http://www.esru.strath.ac.uk

One main features of the turbine is that is does not start until the wind speeds are less than 5 m/s. The power output from the ducted wind turbine should be greater than from a horizontal axis wind turbine of similar scale to the effects of the aerofoil. DWT’s are very much in there infancy as a technology and are not currently being mass-produced by any major manufacturer. There is ongoing investigation into the fluid flow characteristic using programs such as Fluent Commercial. It is likely that the installation of DWT will not be seen for several years until the optimum settings for the aerofoil and other parts of the machine come out of the current ongoing analysis.