wind systems
The basic passive measure in wind systems is to allow for ventilation such that there is cooling in the summer and air flow is blocked in winter to protect from chilly winds. Some basic forms of passive wind systems are:
1. WINDOWS AND OPENINGS
  • Basically the placement of the window opening , has an effect on how much air flows through a shelter. In order to let air flow through a space, both inlet and outlet openings are required. Inlet openings control the amount of air flow and the outlet openings direct the air stream. Acording to Givoni, when the wind angle is perpendicular to the inlet window, windows on adjacent corner walls work better and if windows are positioned 45 degrees to the wind direction,the average indoor air velocity is increased and better indoor air circulation is provided.
  • The size of inlets also effects the air speed. The inlet should be related to the flow pattern in order to catch the incoming air movement. The interior air velocity is increased if the outlet is larger and inlet smaller, which is known as the Venture effect and used commonly in hot-arid climates. Conversely if the outlet is smaller than the inlet, the interior space will receive a decreased air velocity.
  • An unobstructed straight flow ensures the speediest air movement. Partitions affect flow patterns only when they are placed in the air stream. Placing partitions in the air flow stream will slow movement and reduce the ventilative ability. The velocity is lowest when the partitions is in front of, or near the inlet window, as the air has to change direction upon entering.
2. WIND TOWER

The basic idea of a wind tower is to catch unobstructed high level breezes. It is popular in hot arid areas such as the Persian Gulf and North Africa. In areas where wind is mainly from one direction, the tower forms a scoop with only one opening facing the that direction. In areas where wind is from several directions, the tower has openings in all directions.
 

The wind tower functions in the following manner:
The air entering the tower from the windward opening with positive wind pressure coefficient, leaves through any opening which has a pressure coefficient smaller than that at the windward opening. That is, part of the air which has entered the tower is lost through the tower openings, (which has negative pressure coefficient) and the rest enters the house. The portion entering the house may be partially cooled by the structure, if a sufficient amount of coolness has been stored in the structure from the night before. When air flows over moist surfaces, it is further cooled evaporatively. During the night, when air is flowing through the tower and the building , the ambient air coolness is also stored in the building mass. With heavy structures, this energy plays an important role in providing thermal comfort.


The disadvantages of traditional wind towers are:
  • Dust, insects and small birds can enter the building.
  • A portion of the air admitted in the tower is lost through the other tower openings and never enters the building.
  • The amount of coolness which can be stored in the tower mass is very limited compared to the cost of the tower.
  • It does not find any application in areas with a low wind speed.
ROOF AND DOME VENTILATION
Increasing roof surface helps increase the rate of heat loss. In many hot arid areas, curved roofs are widely chosen over flat roofs. The curved roof s increase the ability of heat transfer and hence are easily cooled.  Warm air which is less dense, then rises within the domes or vaults away from the living space and since the hot air is kept within the curved roof, the heat transfer from the roof is minimized . As the velocity of air increases when it flows over a curved roof, the pressure decreases. The reduction of pressure the draws the hot air out from the dome, then the cooler air enters the lower openings.