solar_heating.ppt

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Solar energy for heating

SUBMITTED BY

ALOK DUBEY (07BEE019)

AJAY SHANKAR NAIR (07BEE016)

ALOK KUMAR(07BEE020) ANEESH OBEROI

(07BEE024)

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Cloudy, mixed and clear weather radiation 0 2 4 6 8 10

1 2 3 4 5 6 7 8 9 10 11 12

Months k W h /m 2 ,d a y

The upper curve shows kWh/m2 on a day when the weather is clear, the lower curve when it is cloudy,

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Solar absorbers

 The simplest solar heating elements are

windows in a house, that let visible light through, but do not let the longer

wavelengths through.

 In this way we get the “greenhouse effect”.

The reason for this can be seen in an infrared spectrum. Glass absorbs most wavelengths above 3 um, but not those below.

 Visible light is around 0.4 – 0.9 um, while

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Windows

Impact from the Sun

1-8 kWh/m2,day

0.2 0.4 0.8 4 50 um

Absorbance in glass

UV VIS IR(heat)

Visible light passes through glass without loss, while IR- light (heat) is absorbed by the glass.

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Glass

Copper or Alumina absorber

Insulation

Liquid flow

Solar radiation

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Concentrating absorber

Very high sun elevation is not absorbed to avoid overheating in the middle

of the summer

House wall

Semi-permeable mirror

Part of the light passes through Here hot water

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Storage

 Normally hot water storage

heaters for family houses are dimensioned to buffer the heat demand for 2-3 days. In some

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Solar absorber system

 There are two principally different

solar absorber systems.

 The first has self recirculation

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System with self recirculation

Cold water Hot water

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System with pump

recirculation

Cold water Hot water

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Solar absorber in a Swedish

house

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The storage tank with

recirculation pump and

control

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Solar absorber element

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Building your own absorber

Glass window Wooden frame Protection list

Insulation

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The absorber

Cold water in

Hot water out

Cover to avoid rain water from getting under the absorber

Absorber

Wooden fastening to the roof

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The elements in parallel

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Active Solar Heating

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Parts of the Active Solar

Heater

 Solar systems consist of

collectors and electricity to distribute the Sun’s Energy

 The heart of a solar

collector is black

 Heat is moved by

circulating water, antifreeze, and air

 Applications include

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Types of Active Solar

Heating

 Two types

◦ Liquid ◦ Air

 Both systems collect solar

radiation, then distribute and store heat

 If the system does not provide

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Liquid Systems

 Use water, antifreeze, or methyl

alcohol

 Components are hydronic collectors, a

storage tank, pumps, pipes, a heat exchanger, and controls

 Liquid Systems of have three

operating modes

◦ Primary mode

◦ Secondary mode

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Storing Heat for Liquid

Systems

 Store solar heat in tanks or in the

masonry mass of a radiant slab system

 Storage tanks require 3.8-7.6 L of

water for 0.093 m (1 square foot)

 Tanks are usually made of steel,

concrete, fiberglass-reinforced plastic (FRP), or wood

 Each has its own advantages and

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Distributing Heat for Liquid

Systems

 Heat is distributed by radiant slab

heaters, a central air-forced system, or by using hot water baseboards or

radiators

 Solar heated water moves through the

pipes and heats the floor

 This then radiates the room

 Radiant slab heaters are the best for

liquid systems

 Hot water baseboards and radiators

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Air Systems with Storage

 Air systems uses air as the

working fluid for collecting heat

 Air systems are composed of

collectors, rock bin storage fans, ductwork, and controls

 Operates in three modes:

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Delivering Heat to Home by the

Air System

 For storing heat, an air system delivers hot

air from the collectors to the storage bin

 The air enters an empty mixing space at the

top of the bin

 It passes down through the bin where the

rocks absorb most of the heat

 When storing heat, the top of the bin is

usually 60°C and 21.1°C

 If the air in the bin is too cool then the back

system kicks in

 The air delivers warm air from the rock bin to

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Solar Concentrating

Collectors

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Introduction

 For energy intensive applications,

the flat-plate collectors cannot provide sufficient energy.

 Thus concentrating collectors are

used.

 These collectors have more

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Types of concentrating

collectors

 Parabolic trough system

 Parabolic dish

 Power tower

 Stationary concentrating

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Working principles of

concentrating collectors

• _{Unlike solar (photovoltaic) cells, which use}

light to produce electricity, concentrating

solar power systems generate electricity with heat.

• _{Concentrating solar collectors use mirrors and}

lenses to concentrate and focus sunlight onto a thermal receiver, similar to a boiler tube.

• _{The receiver absorbs and converts sunlight}

into heat. The heat is then transported to a steam generator or engine where it is

converted into electricity.

• _{A concentrating solar power system that}

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Parabolic Trough System

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Axis tracking of the parabolic

trough

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Parabolic Dish System

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Power Tower System

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Stationary concentrating

collectors

 Stationary concentrating

collectors use compound

parabolic reflectors and flat reflectors for directing solar energy to an accompanying

absorber or aperture through a wide acceptance angle.

 The wide acceptance angle for

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Major Advantages of

using Passive or Active Solar Energy for

Heating Buildings

 ƒ ƒ Energy is free

 ƒ ƒ Net energy is moderate(active) to high

(passive)

 ƒ ƒ No CO₂ emissions

 ƒ ƒ Very low air + water pollution

 ƒ ƒ Very low land disturbance (built into roof

or window)

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Major disadvantages of

using Passive or Active Solar

Energy for

Heating Buildings

 ƒ Need access to sun 60% of time

 ƒ ƒ Blockage of sun access by other

structures

 ƒ ƒ Need heat storage system

 ƒ ƒ High cost (active)

 ƒ ƒ Active system needs maintenance and

repair