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CONSTRUCTION TECHNIQUE V

3RD YEAR VSEM.

ASST. PROF. ASHWIN MUKUL

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Thermal Insulation of Building

• Law of Heat Transfer:• Heat flows from the higher level to lower level.• In building the heat transfer takes place form the

hotter area to the cooler zones.• Heat flows as per the capacity of the building

materials or units like floors, walls, roofs, doors, windows.

• The property is measured in “thermal transmittance”

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Cont…..

• In summer the heat transfer is from the out side to inside and in winters the process is reversed.

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Thermal Insulation and its advantage.

• Thermal insulation is retention of temp. with in the buildings irrespective of the change in temp.outside the building.

• It maintains the comfort conditions during summer the thermal insulation should not allow the heat to transfer from out side – and during winters the heat should not leave the building thus giving comfort for the users.

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Advantage of the thermal insulation or merits of the heat proof…….

• Thermal insulation in building results in living and working indoor- conditions because it keeps the room cool in summer and warmer in winter.

• Due to the Thermal insulation, the demand of heating in winter and cooling in summer is considerably reduced.

• This results in lot of fuel saving and maintenance cost.• The use of thermal insulation material further reduces

the risk of water freezing in case of pipes and heat loss of hot water system.

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Heat transfer takes place in following ways…..

Conduction: Transmission of heat through material. The amount of heat transfer by conduction depends on

1) Temp. difference 2) Thickness of solid medium 3) Area of exposure 4) Time for which the heat flow takes place 5) Conductivity of the material

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Cont…

• Convection: Heat is transmitted by convection in fluids and gases, due to circulation. Air movement causes the heat insulation, and excessive air change should be avoided.

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• Radiation: Heat is transfer by radiation (through space) in the form of radiant energy .When the radiation strikes on object, some of the energy is absorbed and transformed into heat and some of the energy one of the ways of reducing heat absorption from radiation is to introduce a suitable reflecting surface.

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General Principle of Thermal Insulations

1. The materials used in the construction should have a high degree of heat resistance per unit of thickness i.e. the materials should have adequate heat insulation value and low heat conductivity.

2. The thermal resistance of the material directly varies with its thickness and hence depending upon the insulation desired, the material of an adequate heat insulation values and adequate thickness should be used.

3. The provision of air space in materials for walls roof ,ceiling etc. offers very good insulation against heat transmission. The presence of air spaces in materials incenses thermal insulation, where as the presence of the moisture decreases the this value.

4. The thermal insulation of the building in general and of doors and windows in particular depends on its orientation w.r.t movement of sun. The building should be so located that there is min transfer of solar heat during the day in summer and the is max transfer of solar heat during the day in winter.

5. Thermal insulation to some extent can be achieved by adopting general measures such as –use of sun shading devices like sun breakers, etc., increasing the height of ceiling (about 1 to 1.3 m abv. The occupants’ height), increase the height of the parapet walls when the altitude angle of the sun is low etc.

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Prevention of heat transfer in summer from exterior to interior.

1. Thermal insulation of external shell like floors, roofs ext. wall to be adequate.

2. Lesser temp. diff. between outside and inside.

3. Lesser overexposed area of external part of the building.

4. The area of door and window exposed outside should be minimum. As the heat transfer is 3 time that of the walls, so the orientation should be w.r.t sun movement.

5. The air space, cracks, openings, etc. should not exit in roof, walls as heat transfer will take place through air infiltration.

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Prevention of heat transfer in winter from interior to exterior.

1. The air flow which displaces the hot air inside the building with the outside cold air , which usually takes place through doors, windows , ventilation, etc. should be controlled.

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Thermal Insulation material are in the following form:-

1.Slab or block insulation:Blocks or board 2.5mmthk., 60cm x 120cm in area.

2. Blanket Insulation: These are flexible fibrous rolls made from mineral wool, cotton, animal hair, etc available in thk.

Of 12mm to 80mm.

3.Bat insulating materialThese are similar to blanket insulations except that these are small in size of grater thickness- they

are also spared on surface of the wall and ceiling.

4. Insulating Boards. These are used for the interior lining of walls , also for the partition walls, structural insulation board is manuf. Making pulp of the wood, cane or other material and then pressing them in form of boards by adding suitable adhesive.

5. Reflective sheet material: Reflective sheet materials have high reflective and low emissivity , thus offering high heat resistance.

Solar energy striking reflective surface gets reflected and amount of heat which may get transmitted is greatly reduced. This may consist of gypsum board steel sheet reflective materials, alum. Foils , sheet alu. Reflective material.

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The choice of insulating material depends upon:

1)Cost of the material

2) Area to be covered

3) Standard of insulation required and

4) Coat of heating or cooling.

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Insulating material should have the following properties :

1. It should have high thermal resistance

2. It should be reasonably fire proof

3. It should be insect proof

4. It should be durable

5. It should be non- absorbent of moisture

6. It should be cheaper

7. It should be readily available

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Methods of Heat Insulation or thermal Insulation:

Heat enters in to building through: roofs, terraces, walls, windows, doors, opening etc:

I. Method of heat insulating the roofs:i. In case of installing the heat resisting material it can be placed above

but below the waterproof course.

ii. In case of internal application the material may be fixed with adhesive , on the underside of roofs with in the rooms.

iii. The false ceiling of insulating materials may be as shown in fig. as false ceiling

Rcc slab.

Suspenders False ceiling

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Cont..

iv. Shining or reflective insulation material may be installed or laid on the top of the roof.

v. Flat roof may be kept cool by flooded water either by storing or spraying .

vi. White washing of the roof before each summer also helps in heat insulation.

vii. Suitable shading device on the exposed surface also reduce the surface temp.

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II. Method of heat insulating the exposed wallsi. The thickness of the walls may be increased depending upon the extent of insulation derived

ii. Hollow walls or cavity wall construction may be adopted

iii. For partition walls, air space may be adopted by fixing the sheathing of hard boards or battens on either

side of the wall.

iv. White wash or distemper of light colour may be applied on the exposed surface of the wall to incense

thermal insulating value.

v. The wall may be constructed out of suitable heat insulating material, provide structure requirements are

met like cement concrete , fiber class sand stone, granite, timber and other which should have high thermal

resistivity and low thermal conductivity.

vi. The heat insulating materials of different types as shown in fig, can be installed on the inside of the exposed

wall and inside/outside of ceiling I order to reduce the thermal transmittance to the required limits.

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Heat insulation with different methods and materials.

4cm thk.

5cm thk.

50mm thk, air gap

Rcc slb Cement Plaster

Foam Plaster

Brick tiles

Brick wall Brick walls

Foam Plastic

10cm thk.

115mm thk,

230mm thk,

Cement Plaster

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Method of insulation of exposed windows, doors, ventilators

• Reduction of incidence of solar heat: by use of external shading, such as louvered shutters, sun breakers, chajjas or weather shed, by adopting internal shading such as curtain in heavy folds, venetian blinds, etc.

• Reduction of heat transmission:

Where glazed door and windows are provided ,the reduction of heat transmission may be achieved by insulating glass or double glaze with air gap in between or by any other suitable means.

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