indian climatic zones

8/22/2019 Indian Climatic Zones

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Climatic zones in India &

Learning how energy flowsthrough human bodies or

buildings


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The various climatic zones in India

Buildings in differentclimatic zones require

different passive features to

make structures energy-

efficient. Some features that

can be adopted in particular

zones are listed below.


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Hot and dry

The hot and dry zone lies in the western and the

central part of India; Jaisalmer, Jodhpur and Sholapurare some of the towns that experience this type of

climate.

In such a climate, it is imperative to control solar

radiation and movement of hot winds. The designcriteria should therefore aim at resisting heat gain by

providing shading, reducing exposed area, controlling

and scheduling ventilation, and increasing thermal

capacity. The presence of water bodies is desirableas they can help increase the humidity, thereby leading

to lower air temperatures. The ground and surrounding

objects emit a lot of heat in the afternoons and

evenings. As far as possible, this heat should be

avoided by appropriate design features.


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Warm and humid

The warm and humid zone covers the coastalparts of the country, such as Mumbai, Chennai

and Kolkata. The main design criteria in the

warm and humid region are to reduce heat gain

by providing shading, and promote heat lossby maximizing cross ventilation. Dissipation of

humidity is also essential to reduce

discomfort.


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Moderate

Pune and Bangalore are examples of cities

that fall under this climatic zone. The design

criteria in the moderate zone are to reduce

heat gain by providing shading, and topromote heat loss by ventilation.


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Cold

Generally, the northern part of Indiaexperiences this type of climate. the design

criteria are to resist heat loss by insulation

and controlling infiltration. Simultaneously,

heat gain needs to be promoted by admitting

and trapping solar radiation within the living

space.


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Energy in Buildings

The purpose of energy management in buildings, and

hence the role of the building energy manager, is to

identify the areas in building stock where energy is

used in excess.

Energy consumption in building is required for the

following uses:

Heating

Cooling

Ventilation

Lighting Equipment and machinery

Domestic hot water


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Objectives1. Explain the relationship between temperature and thermal

equilibrium.

2. Explain how heat flows in physical systems in terms of

conduction, convection, and radiation.

3. Apply the concepts of thermal insulators and conductors to

practical systems.4. Describe free and forced convection and recognize these

processes in real-life applications.

5. Identify the relationship between wavelength, color, infrared

light, and thermal radiation.

6. Calculate the heat transfer in watts for conduction, convection,

and radiation in simple systems.

7. Explain how the three heat-transfer processes are applied to

evaluating the energy efficiency of a house or building.


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Heat Transfer can be transferthrough:

Heat Conduction

Convection

Radiation


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Heat Conduction

Key Question:

How does heat pass

through different

materials?


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Heat Transfer The science of how heat flows is called heat

transfer.

There are three ways heat transfer works:

conduction, convection, and radiation.

Heat flow depends on the temperature difference.


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Thermal Equilibrium Two bodies are in thermal

equilibrium with each

other when they have thesame temperature.

In nature, heat always

flows from hot to cold untilthermal equilibrium is

reached.


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Heat Conduction Conduction is the transfer of heat through

materials by the direct contact of matter.

Dense metals like copper and aluminum are very

good thermal conductors.


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Heat ConductionA thermal insulatoris a material that conducts

heat poorly.

Heat flows very slowly through the plastic so thatthe temperature of your hand does not rise very

much.


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Heat Conduction Styrofoam gets its

insulating ability by

trapping spaces of airin bubbles.

Solids usually are

better heat conductors

than liquids, andliquids are better

conductors than

gases.


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Heat Conduction The ability to conduct

heat often depends more

on the structure of a

material than on the

material itself.

Solid glass is a thermal

conductor when it isformed into a beaker or

cup.

When glass is spun into

fine fibers, the trapped air

makes a thermal insulator.


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Thermal Conductivity

The thermal conductivity of a material describes

how well the material conducts heat.


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ThermalConductivity

Heat conduction insolids and liquids

works by transferring

energy through

bonds betweenatoms or molecules.


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Heat Conduction Equation

PH = k A (T2 -T1)L

Area of cross section (m2)

Length (m)

Thermal conductivity

(watts/moC)

Heat flow

(watts)

Temperature

difference (oC)


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Variables for conduction


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Calculate Heat Transfer

A copper bar connects two beakers of water at different

temperatures.

One beaker is at 100C and the other is at 0C.

The bar has a cross section area of 0.0004 m2 and is one-half

meter (0.5 m) long.

How many watts of heat are conducted through the bar from

the hot beaker to the cold beaker?

The thermal conductivity of copper is 401 W/mC.


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Convection

Key Question:

Can moving matter carrythermal energy?

*Students read Section 26.2

AFTER Investigation 26.2


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Convection Convection is the transfer of

heat by the motion of liquids

and gases. Convection in a gas occursbecause gas expands when

heated.

Convection occurs because

currents flow when hot gas

rises and cool gas sink.

Convection in liquids also

occurs because of differences

in density.


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Convection When the flow of gas or

liquid comes from

differences in density and

temperature, it is called

free convection.

When the flow of gas or

liquid is circulated by

pumps or fans it is called

forced convection.


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Convection

Convection depends on

speed.

Motion increases heat

transfer by convection in

all fluids.


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Convection Convection depends on

surface area.

If the surface contactingthe fluid is increased, the

rate of heat transfer also

increases.

Almost all devices made

for convection have fins

for this purpose.


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Forced Convection

Both free and forced convection help to

heat houses and cool car engines.


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Convection and Sea Breezes

On a smaller scale near

coastlines, convection is

responsible for sea breezes. During the daytime, land is much

hotter than the ocean.

A sea breeze is created when hot

air over the land rises due toconvection and is replaced by

cooler air from the ocean.

At night the temperature reverses

so a land breeze occurs.


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Convection Currents Much of the Earths climate is regulated by giant

convection currents in the ocean.


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Heat Convection Equation

PH = hA (T2 -T1)

Area contacting fluids (m2)Heat transfer coefficient

(watts/m2oC)

Heat flow

(watts)

Temperature

difference (oC)


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Calculating convection The surface of a window is a

temperature of 18C (64oF).

A wind at 5C (41o

F) is blowingon the window fast enough to

make the heat transfer

coefficient 100 W/m2C.

How much heat is transferredbetween the window and the air

if the area of the window is 0.5

square meters?


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Radiation

Key Question:

How does heat from thesun get to Earth?

*Students read Section 26.3

AFTER Investigation 26.3


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Radiation Radiation is heat transfer by

electromagnetic waves.

Thermal radiation iselectromagnetic waves

(including light) produced by

objects because of their

temperature. The higher the temperature

of an object, the more

thermal radiation it gives off.


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Radiant Heat

We do not see the

thermal radiation

because it occurs atinfrared wavelengths

invisible to the human

eye.

Objects glow different

colors at different

temperatures.


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Radiant Heat A rock at room

temperature does not

glow.

The curve for 20Cdoes not extend into

visible wavelengths.

As objects heat up they

start to give off visiblelight, or glow.

At 600C objects glow

dull red, like the burner

on an electric stove.


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Radiant Heat As the temperature rises, thermal

radiation produces shorter-

wavelength, higher energy light.

At 1,000C the color is yellow-orange, turning to white at 1,500C.

If you carefully watch a bulb on a

dimmer switch, you see its color

change as the filament gets hotter.

The bright white light from a bulb is

thermal radiation from an extremely

hot filament, near 2,600C.


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Radiant Heat

The graph of power

versus wavelength

for a perfect

blackbody is called

the blackbody

spectrum.


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Radiant HeatA perfect blackbody is a surface that reflects

nothing and emits pure thermal radiation.

The white-hot filament of a bulb is agood blackbody because all light from

the filament is thermal radiation and

almost none of it is reflected from other

sources.

The curve for 2,600C shows that

radiation is emitted over the whole

range of visible light.


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Radiant Heat A star is a near-perfect

blackbody.

The distribution of energy

between different wavelengths

(colors) depends strongly on the

temperature.

Sirius is a hot, young star about

twice as big as the sun and 22times as bright.

Because its temperature is

hotter, Sirius appears bluer than

the sun.


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Radiant Heat

The total power emitted as thermal radiation by ablackbody depends on temperature (T) and

surface area (A).

Real surfaces usually emit less than the blackbodypower, typically between 10 and 90 percent.

The Kelvin temperature scale is used in the

Stefan-Boltzmann formula because thermalradiation depends on the temperature above

absolute zero.


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Stefan-Boltzmann formula

P = sAT4

Surface area (m2)

Stefan-Boltzmann constant

5.67 x 10-8watts/m2K4)

Power

(watts)

Absolute temperature(K)


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Calculate Radiant Power The filament in a light bulb has a

diameter of 0.5 millimeters and

a length of 50 millimeters.

The surface area of the filament

is 4 10-8 m2.

If the temperature is 3,000 K,how much power does the

filament radiate?


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Radiant Heat When comparing heat

transfer for a pot 10 cm

above a heating elementon a stove, radiant heat

accounts for 74%

How is heat transferredwhen the pot sits on the

element?


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Application: Energy-efficient Buildings

indian climatic zones

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