wind control (2)

8/11/2019 Wind Control (2)

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WIND CONTROL

WIND CONTROL


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ORIENTATTION FORWIND

PATH OF WIND-REFERENCE TO SEASONAL

WIND AND

PREVAILING WINDPATTERN IN INDIA AND ITSRELATION TO A BUILTSPACE.

SUB TOPICS


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WIND


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What causes the wind to blow?As the earth is affected by an unequally of heat energy from the

sun, the state of the air differentiate between different regions.Warm air expands and rises up while cold air condenses andsinks, hence resulting the flow of air and forms wind.

As the sun warms the Earth's surface, the atmosphere warms too.Some parts of the Earth receive direct rays from the sun all year

and are always warm.Other places receive indirect rays, so the climate is colder. Warmair, which weighs less than cold air, rises.Then cool air moves in and replaces the rising warm air. This

movement of air is what makes the wind blow.In meteorology, unless otherwise specified, wind means thehorizontal motion of airflow and signifies with wind directionand wind speed (wind force).


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Winds are commonly classified by

their spatial scale,their speed,the types of forces that cause them, the regions in

which they occur, and their effect.winds are often referred to according to their

strength, and the direction from which the wind isblowing.

Strong winds of intermediate duration (around one

minute) are termed squalls. Long-duration windshave various names associated with their averagestrength, such as breeze, gale, storm, hurricane,and typhoon.


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Mountain wave schematic. The

wind flows towards a mountainand produces a first oscillation(A). A second wave occurs furtheraway and higher. The lenticularclouds form at the peak of thewaves (B

Near mountains

Over elevated surfaces, heating of the ground exceeds the heating of

the surrounding air at the same altitude above sealevel, creating anassociated thermal low over the terrain and enhancing any thermal lows

that would have otherwise existed, and changing the wind circulation of

the region. In areas where there is rugged topographythat significantly

interrupts the environmental wind flow, the wind circulation between

mountains and valleys is the most important contributor to the prevailing

winds.
http://en.wikipedia.org/wiki/Sea_levelhttp://en.wikipedia.org/wiki/Sea_levelhttp://en.wikipedia.org/wiki/File:Vol_d'onde.svghttp://en.wikipedia.org/wiki/File:Vol_d'onde.svg


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Prevailing Winds

The direction of wind is measured in terms of where

the air is coming from. A northerly wind blows airfrom north to south.A southwesterly wind blows air from the southwest tothe northeast.The prevailing wind is the wind that blows most

frequently across a particularly region. Differentregions on Earth have different prevailing winddirections which are dependent upon the nature of thegeneral circulation of the atmosphere and thelatitudinal wind zones.In general, the following prevailing winds across theEarth may be identified, although variations arise dueto the positions and differential heating rates ofthe continents and oceans.


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What are the trade winds?The trade winds are just air movements toward theequator. They are warm, steady breezes that blowalmost continuously. The Coriolis Effect makes thetrade winds appear to be curving to the west, whetherthey are traveling to the equator from the south or

north.

What are the doldrums?The doldrums is an area of calm weather. The trade

winds coming from the south and the north meet nearthe equator. These converging trade winds producegeneral upward winds as they are heated, so there areno steady surface winds.


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Latitude Direction Common Name

90-60N NE Polar Easterlies

60-30N SW Southwest Antitrades

30-0N NE Northeast Trades

0-30S SE Southeast Trades

30-60S NW Roaring Forties

90-60S SE Polar Easterlies

Prevailing winds in the Indian Oceans are northeasterly. Duringthe summer months however, a larger low-pressure systemdevelops over southern Asia due to continental

heating. Winds in this region now reverse to form theSouthwest Monsoons, which bring a prolonged wet season toSoutheast Asia and the subcontinent of India.
http://www.ecoca.ro/meteo/tutorial/climate/older/Continental_Climate.htmlhttp://www.ecoca.ro/meteo/tutorial/climate/older/Continental_Climate.html


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Effect of prevailing wind on a coniferous tree


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The use of natural winds to enhance theliving environment is another solution offered by climaticdesign. "Air movement is essentially a design issue. One of theeasiest things to do is close the building and air-condition it.

A place like Bangalore does not need air conditioning for mostpart of the year. So using air movement and ventilationeffectively can cut down energy needs. To improve cooling, abuilding's windows should be placed and designed to captureprevailing winds. And also suggests the use of 'venturi effect'.It is essentially about looking at design in volumes i.e. when

you force a wind to move into a narrow opening and expandinto a larger volume, the effect can be quite incredible.This design strategy creates what is referred to as wind tunnelsand keeps the living spaces cool and airy.


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Local winds around the world. These winds are

formed through the heating of land (frommountains or flat terrain)
http://en.wikipedia.org/wiki/File:Diagrama_de_formacion_de_la_brisa-breeze.svg


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A: Sea breeze (occurs at daytime),What is a sea breeze?

On a warm summer day along the coast, this differentialheating of land and sea leads to the development of local windscalled sea breezes. As air above the land surface is heated byradiation from the Sun, it expands and begins to rise, beinglighter than the surrounding air. To replace the rising air, cooler

air is drawn in from above the surface of the sea. This is the seabreeze, and can offer a pleasant cooling influence on hotsummer afternoons.


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B: Land breeze (occurs at night)In coastal regions, sea breezes and land breezes can beimportant factors in a location's prevailing winds.

The sea is warmed by the sun more slowly because of water'sgreater specificheat compared to land.

As the temperature of the surface of the land rises, the landheats the air above it by conduction. The warm air is less densethan the surrounding environment and so it rises.

What is a land breeze?A land breeze occurs at night when the land cools faster thanthe sea. In this case, it is air above the warmer surface water thatis heated and rises, pulling in air from the cooler land surface.
http://en.wikipedia.org/wiki/Specific_heathttp://en.wikipedia.org/wiki/Specific_heat


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Type & Description of wind Effects observed on the sea

Calm Sea is like a mirror

Light air Ripples with appearance of scales;no foam crests

Light breeze Small wavelets; crests of glassyappearance, not breaking

Gentle breeze Large wavelets; crests begin to break;scattered whitecaps

Moderate breeze Small waves, becoming longer;numerous whitecaps

Fresh breeze Moderate waves, taking longer form;many whitecaps; some spray


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Strong breeze Larger waves forming; whitecapseverywhere; more spray

Near gale Sea heaps up; white foam frombreaking waves begins to be blownin streaks

Gale Moderately high waves of greaterlength;

Strong gale High waves; sea begins to roll;

Storm Very high waves with overhangingcrests

Violent storm Exceptionally high waves; sea

covered with white foam patches;Hurricane Air filled with foam; sea completely

white with driving spray


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All of these winds are part of a global air circulation systemthat acts to balance temperature and pressure around theworld. We already know that different parts of the worldreceive different amounts of heat from the sun.This differential heating in turn results in differences intemperature and air pressure around the world whichdrives theworldswinds.The equator receives the Sun's direct rays. Here, air is heatedand rises, leaving low pressure areas behind. Moving toabout thirty degrees north and south of the equator, the

warm air from the equator begins to cool and sink. Betweenthirty degrees latitude and the equator, most of the coolingsinking air moves back to the equator. The rest of the airflows toward the poles.


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As equatorial areas are heated most, the air

above them warms and rises as it becomes

lighter than the surrounding air, causing an

area of low pressure. In cooler areas, theair sinks because it is heavier and results in

an area of high pressure. Winds will blow

as air is squashed out by the sinking cold

air and drawn in under the rising warm air.

Any difference in temperature like this will

always cause a difference in air pressure

and therefore winds will blow. A good

expression to remember is that:

"winds blow from high to low" (ie: from

high pressure to low pressure)


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What is a monsoon?A monsoon is a seasonal wind, found especially in Asia that

reverses direction between summer and winter and often bringsheavy rains.In the summer, a high pressure area lies over the Indian Ocean

while a low exists over the Asian continent. The air masses move

from the high pressure over the ocean to the low over thecontinent, bringing moisture-laden air to south Asia.During winter, the process is reversed and a low sits over theIndian Ocean while a high lies over the Tibetan plateau so airflows down the Himalaya and south to the ocean. The migrationof trade winds and westerlies also contributes to the monsoons.Smaller monsoons take place in equatorial Africa, northern

Australia, and, to a lesser extent, in the southwestern UnitedStates.


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The wind direction is not the same throughtthe year . It changes from season to season.Over Pondicherry , the wind will be from either

west or southwest duringsouthwest monsoon season,ie June to

September.

It will be from northeast or north duringNortheast monsoon season,ie October toDecember. However , Sea breeze plays an

important role as Pondicherry is a coastalstation . When westerly winds areweak(particularly during south west monsoonseason) sea breeze over rides and blows fromthe east in the afternoon timings on most of

the days.


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During northeast monsoon season the sea breeze strengthens

the already prevailing easterly winds . Thus easterly winds

blow most of the days in a year particularly in the afternoon .However the sea breeze can penetrate only upto a maximum of

20 kms inside the land.


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CAUSE OF WINDS:


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Wind is caused by differences in atmospheric pressure. Whena difference in atmospheric pressure exists, air moves from thehigher to the lower pressure area, resulting in winds of variousspeeds. On a rotating planet, air will also be deflected by

the Coriolis effect, except exactly on the equator.Globally, the two major driving factors of large-scale windpatterns (the atmospheric circulation) are the differential heatingbetween the equator and the poles (difference in absorption

of solar energy leading to buoyancy forces) and the rotation ofthe planet.

Outside the tropics and a loft from frictional effects of thesurface, the large-scale winds tend to approach geostrophicbalance.


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Why does the wind blow?There are three forces that cause the wind to blow in the direction that it does:

1. Pressure Gradient Force2. Coriolis Force3. Friction

Friction

Coriolis Force


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Near the Earth's surface, friction causes the wind to beslower than it would be otherwise. Surface frictionalso causes winds to blow more inward into lowpressure areas. A new, controversial theory, suggestsatmospheric gradients are caused by forest induced

water condensation resulting in a positive feedbackcycle of forests drawing moist air from the coastlineWinds defined by an equilibrium of physical forcesare used in the decomposition and analysis of wind

profiles. They are useful for simplifying theatmospheric equations of motion and for makingqualitative arguments about the horizontal and

vertical distribution of winds.


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The orientation can defend undesirable effects of worse

weather. While planning to build a new house, ask yourarchitect to design building in such a way that energy loss isminimum.

Benefits of building orientation :

Energy savingOrientation of building is energy efficient approachas thebuilding orientation saves heating, cooling and lighting cost.Breeze/Natural Air

Orientation of building provides breeze is in warm and humid

climates. On the other hand, the orientation prevents hot windsin hot and dry climates.Natural ventilation

Building orientation provides natural ventilation and light

which is beneficial to the health of inhabitants of the house.


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Wind load:

Wind acts horizontally on the exposed vertical surfaces

of walls, columns and inclined roof of the structure.


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Orientation of building is to design building in such a wayas it receives maximum ventilation and natural light inall climatic conditions.It provides comfortable living

conditions inside the house/building and saves energy billsalso.


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Cross ventilation is yet another idea.

It involves a window that opens to the wind allowing breezes into

the building and another window on the opposite side that lets

stagnant air to be flushed out.

This strategy creates continuous air movement in a space.


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A windmill style ofanemometer
http://en.wikipedia.org/wiki/File:Young_wind_monitor.jpg


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Measurement of wind:

Wind directionis usually expressed in terms of the

direction from which it originates. For example,a northerlywind blows from the north to thesouth.Weather vanespivot to indicate the direction ofthe wind.

At airports,windsocksindicate wind direction, and canalso be used to estimate wind speed by the angle.

Wind speed is measured by anemometers, mostcommonly using rotating cups or propellers. When a

high measurement frequency is needed (such as inresearch applications), wind can be measured by thepropagation speed of ultrasoundsignals or by the effectof ventilation on the resistance of a heated wire.

A i d d
http://en.wikipedia.org/wiki/File:Young_wind_monitor.jpg


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Average wind speeds

prevailing and local winds are not spread evenlyacross the earth, which means that wind speedsalso differ by region. In addition, the wind speedalso increases with the altitude.


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Potential Damage with Prevailing wind in relation To Built Spaces

Moderate damageMinor or no damage Considerable damage

Severe damage Extreme damage Total Destruction

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