Climatology Lec 1

8/13/2019 Climatology Lec 1

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BUILDING SERVICES - III

climatology

B A h 3rd

S

CLIMATE AND IT’s ELEMENTS



Global climatic

factors

INDEX

•Global climatic

factors

•Elements ofclimates

•Classification of

tropical climates

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PAGE CLIMATOLOGY



• ELEVATION OR ALTITUDE EFFECT CLIMATE

Climate changes with increase or decrese in altitude.

• PREVAILING GLOBAL WIND PATTERNS

There are 3 major wind patterns found in the Northern Hemisphere and

also 3 in the Southern Hemisphere. These are average conditions and

do not essentially reveal conditions on a particular day. As seasons

change, the wind patterns shift north or south. So does the intertropical

convergence zone, which moves back and forth across the Equator.

Sailors called this zone the doldrums because its winds are normally

weak.

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c l i m a t o l o g y

INDEX

•Global climatic

factors



tropical climates



• LATITUDE AND ANGLES OF THE SUNS RAYS

As the Earth circles the sun, the tilt of its axis causes changes in the

angle of which sun’s rays contact the earth and hence changes the

daylight hours at different latitudes. Polar regions experience thegreatest variation, with long periods of limited or no sunlight in winter

and up to 24 hours of daylight in the summer.

• TOPOGRAPHY

The Topography of an area can greatly influence our climate. Mountainranges are natural barriers to air movement. In costal areas, winds off

the ocean carry moisture-laden air toward the coast. The Coastal Range

allows for some condensation and light precipitation. Inland, the taller

Plateau range rings more significant precipitation in the air. On the

eastern slopes of the Deccan plateau, sinking air warms fromcompression, clouds evaporate, and dry conditions prevail.

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• EFFECTS OF GEOGRAPHY

The position of a town, city or place and its distance from mountains

and substantial areas of water help determine its prevailing wind

patterns and what types of air masses affect it. Coastal areas may enjoyrefreshing breezes in summer, when cooler ocean air moves ashore.

In spring and summer, people in eastern ghats watch for thunderstorms,

these storms are caused where three types of air masses frequently

converge: cold and dry from the north, warm and dry from thesouthwest, and warm and moist from the Bay of Bengal- these colliding

air masses often generate storms.

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• SURFACE OF THE EARTH

Just look at any globe or a world map showing land cover, and you will

see another important factor which has a influence on climate: the

surface of the Earth. The amount of sunlight that is absorbed orreflected by the surface determines how much atmospheric heating

occurs. Darker areas, such as heavily vegetated regions, tend to be

good absorbers; lighter areas, such as snow and ice-covered regions,

tend to be good reflectors. The ocean absorbs and loses heat more

slowly than land. Its waters gradually release heat into the atmosphere,which then distributes heat around the globe.

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• Climate change over time

Cold and warm periods punctuate Earth’s long history. Some were fairly

short; others spanned hundreds of thousands of years. In some cold

periods, glaciers grew and spread over large regions. In subsequentwarm periods, the ice retreated. Each period profoundly affected plant

and animal life.

Since the turn of the 20th century, temperatures have been rising

steadily throughout the world. But it is not yet clear how much of thisglobal warming is due to natural causes and how much derives from

human activities, such as the burning of fossil fuels and the clearing of

forests.

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Elements of climates

INDEX

•Global climatic

factors



tropical climates

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PAGE

CLIMATOLOGY



• ELEMENT OF CLIMATE:

- TEMPERATURE

- HUMIDITY

- VAPOUR PRESSURE

- PRECIPITATION

- SKY CONDITION

- SOLAR RADIATIONS- WIND FLOW & WIND INTENSITY

- VEGITATION

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• TEMPERATURE :

• Measured in ° C (degree Celsius)

• Measured for dry air with the means of simple Mercury thermometer.

DRY BULB/ TRUE TEMPERATURE:

The dry-bulb temperature is the temperature of air measured by

a thermometer freely exposed to the air but shieldedfrom radiation and moisture.

Dry bulb temperature is the temperature that is usually thought of as air

temperature, and it is the true thermodynamic temperature. It is the

temperature measured by a regular thermometer exposed to the

airstream. Unlike wet bulb temperature, dry bulb temperature does notindicate the amount of moisture in the air. In construction, it is an

important consideration when designing a building for a certain climate.

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WET BULB/ TRUE TEMPERATURE:

The wet-bulb temperature is a type of temperature measurement that

reflects the physical properties of a system with a mixture of a gas and

a vapour, usually air and water vapour. Wet bulb temperature is thelowest temperature that can be reached by the evaporation of water

only. It is the temperature one feels when one's skin is wet and is

exposed to moving air. Unlike dry bulb temperature, wet bulb

temperature is an indication of the amount of moisture in the air.

Wet-bulb temperature can have several technical meanings:• Thermodynamic wet-bulb temperature: the temperature a volume of air

would have if cooled adiabatically to saturation at constant pressure by

evaporation of water into it, all latent heat being supplied by the volume

of air.

• The temperature read from a wet bulb thermometer

• Adiabatic wet-bulb temperature: the temperature a volume of air would

have if cooled adiabatically to saturation and then compressed

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HUMIDITY:

• Humidity is a term for the amount of water vapour in the air, and can

refer to any one of several measurements of humidity. Formally, humid

air is not "moist air" but a mixture of water vapour and other constituentsof air, and humidity is defined in terms of the water content of this

mixture, called the Absolute humidity. In everyday usage, it commonly

refers to relative humidity, expressed as a percent in weather forecasts

and on household humidity status; it is so called because it measures

the current absolute humidity relative to the maximum. Specifichumidity is a ratio of the water vapour content of the mixture to the dry

air content (on a mass basis). The water vapour content of the mixture

can be measured either as mass per volume or as a partial pressure,

depending on the usage.

• Measured in g/Kg or g/m3 (degree Celsius)• Measured by instrument called DRY & WET BULB HYGROMETRE

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A hygrometer is a device used for

measuring the humidity of the air

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RALATIVE HUMIDITY:

• It is the ratio of actual amount of moisture present, to that amount of

moisture the air can hold at a given temperature and is expressed in %.

RH=AH / SH X 100(%)

RH= RELATIVE HUMIDITY

AH= ABSOLUTE HUMIDITY

SH= SATURATION POINT HUMIDITY

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ABSOLUTE HUMIDITY:

• Absolute humidity on a heat basis is the mass of water in the unit

volume of air. The most common units are grams per cubic meter,

although any mass unit and any volume unit could be used.

• If all the water vapour in one cubic meter of air were condensed into a

container, the mass of the water in the container could be measured

with a scale to determine absolute humidity. The amount of water

vapour in that cube of air is the absolute humidity of that cubic meter ofair. More technically, absolute humidity on a volume basis is the mass of

dissolved water vapour, mw, per cubic meter of total moist air, Vnet:

AH= m (by volume) / V (net)

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• Absolute humidity ranges from 0 grams per cubic meter in dry air to

30 grams per cubic meter (0.03 ounce per cubic foot) when the vapour

is saturated at 30 °C.

• The absolute humidity changes as air pressure changes. This is very

inconvenient for architectural engineering calculations, e.g. For rooms,

where temperature can vary considerably.

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SATURATION POINT HUMIDITY / SPECIFIC HUMIDITY:

• Specific humidity is the ratio of water vapour to dry air in a particular

mass, and is sometimes referred to as absolute humidity or humidity

ratio. Specific humidity ratio is expressed as a ratio of kilograms of watervapour, mv , per kilogram of dry air ma .

• That ratio is defined as:

SH=m

(by

volume)

/ m (mass of air)

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EFFECT OF HUMIDTY:

• HUMAN COMFORT:

Humans control their body temperature mainly

by sweating and shivering. At high humidity, sweating is less effective,and we feel hotter. At low humidity, the risk for nosebleeds increases,

especially during cold winter seasons.

• Some people experience difficulty breathing in high humidity

environments. Some cases may possibly be related to respiratory

conditions such as asthma, while others may be the product of anxiety.

- Air conditioning works by reducing humidity in summer.

- In winter, heating cold outdoor air can decrease relative humidity

levels indoor to below 30%, leading to discomfort such as dry skin

and excessive thirst.

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EFFECT OF HUMIDTY:

• BUILDING CONSTRUCTION:

Traditional building designs typically had weak insulation, and it allowed

air moisture to flow freely between the interior and exterior. The energy-efficient, heavily-sealed architecture introduced in the 20th century also

sealed off the movement of moisture, and this has resulted in a

secondary problem of condensation forming in and around walls, which

encourages the development of mold and mildew.

Additionally, buildings with foundations not properly sealed will allow

water to flow through the walls due to capillary action of pores found in

masonry products. Solutions for energy-efficient buildings that avoid

condensation are a current topic of architecture.

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VAPOUR PRESSURE:

It is the partial pressure of water vapour present in the air.

The atmospheric pressure (P) is the sum of the partial pressure of dry

air (Pa) & the partial vapour pressure (Pv) :

P= Pa+Pv

• The air is saturated when the P v = the pressure of saturated vapour

presure of the same temperature (Pvs) .

• Relative humidity can also be expressed as the ratio of actual vapour

pressure to the ’ SATURATION POINT VAPOUR PRESSURE ’.

P= AH /SH X100 = Pv / Pvs X 100(%)• VP is measured in pressure unit : N/ m

2

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• Humidity data is basically used to state the futur eclimatic condition of a

specific location , as it is used to predict the :

- Monsoon trend

- Amount of precipitation

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SKY CONDITIONS:

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It is the PRESENCE/ ABSENCE of clouds in the sky.

On an average two observations are made per day:• DURING DAY

• DURING NIGHT

It is expressed in % of the sky hemisphere is covered by the clouds.

IMPORTANCE: Sky luminance values are needed if daylighting in

buildings is to be predicted.



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SOLAR RADIATIONS:

A simple sunshine recorded during the day time which is expressed in

NUMBER OF HOURS/ DAY , as an average for each month.

Average Daily Amounts of Solar Radiations for each month of year

would give a fair indication of climatic conditions, including seasonal

variations.



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WIND FLOW AND WIND INTENSITY:

Air movement is affected by the following:

• Differences in air pressure as air moves from areas of high pressure toareas of low pressure.

• Differences in temperature

o Thermal buoyancy- describes the action of air as it is heated. Because

heated air is less dense it rises, moving from a cool, high-density area toward a warm, low-density area.

o Convection currents- The movement of cooler air moving in to replace

rising warm air will establish convection currents any place in the building in

which temperature differentials exist, with main areas of concern being theliving space and attics. Supply and return registers are key points of

temperature differentials and also key points of pressure differences caused

by heating and cooling system hair handlers.

Climatology Lec 1

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