THERMAL INSULATION OF BUILDINGS | PURPOSE | PRINCIPLES | MATERIALS | METHODS

THERMAL INSULATION OF BUILDINGS

Temperature difference exists between the outset and inside of a building and at different units of a building. Heat is transferred from a warm to a cool place. The transfer of heat may take place by conduction, convection or radiation. Heat transfer mainly happens due to conduction through solid building materials. This heat transfer depends on the conductivity of the intervening materials, the temperature difference between two surfaces, the thickness of the material, the area of exposed material and the time through which the heat flow takes place.

Convection and radiation also play their role in the process of heat transfer through the building materials. Convection may take place through large areas and the thickness of the building material by currents of air transmit. Similarly, polished surfaces on the exposed side of a building may retard the inward flow of heat and prevent heat penetration (Sharma, 1988).

 Is it a good idea to use thermal insulation in buildings?

PURPOSE OF THERMAL INSULATION

1. The main purpose of thermal insulation is to conserve a constant heat or temperature inside a building.

2. Thermal insulation provides comfortable living and working indoor conditions. That is, to keep the room cool in summer and warm in winter.

3. In order to reduce the demand of heating in winter and refrigeration in summer.

4. In order to prevent the condensation of moisture on interior walls, ceilings, windows, etc.

5. In order to reduce the risk of water-freezing in case of pipes and heat loss in case of the hot water system.

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CAUSES FOR HEAT TRANSFER

Following are the factors which contribute to the transfer of heat:

1. Value of thermal insulation of the exterior shell (e.g., external walls, roofs, etc.).

2. Difference in temperature between the outside and the inside. If the difference is greater; greater shall be the loss of heat.

3. Surface area of the building is exposed at the external face. Evidently, for a greater area, the heat transfer shall be more.

4. Surface areas of external windows and doors. For example, the heat transfer of a glazed window is about three times more than a typical wall construction.

5. Rate of air movement through any cavities in the enclosing structure. For example, air spaces through the roof or below a suspended floor may cause considerable heat transference.

 

PRINCIPLES OF THERMAL INSULATION

Based on the causes identified for heat transfer, the following general principles govern the thermal insulation:

1. Materials of low thermal conductivity have to be adopted. That is the material used should have adequate heat insulation value.

2. As the thermal resistance of a material is directly varies with the thickness and so the material to be provided should have adequate thickness.

3. Provision of open spaces like cavity walls provides excellent means of thermal insulation.

4. External exposure of windows, ventilators and doors play a major role and hence the orientation of the building and positioning of doors and windows play a vital role.

5. To some extent thermal insulation can be achieved by providing sunshades, increasing the height of parapet walls, etc., which can reduce the heat transfer.

 

HEAT INSULATION MATERIALS

Good insulating material should possess the properties such as adequate fire-resistant, termite resistant, moisture-resistant, adequate strength and stability and long life.

Some of the insulating materials which are in use are:

1. Blanket insulation

2. Bats insulting materials

3. Block or slab insulation

4. Cement concrete products

5. Insulating boards

6. Loose fills

7. Reflecting sheet materials

 

1. Blanket Insulation

Blanket insulators are flexible fibrous materials supplied in rolls or otherwise. They are made out of mineral wool, processed wood fibre, cotton and animal hair. They are available in thickness varying from 1 to 8 cm which can be spread directly on the surface of walls and ceilings.

 

2. Bat Insulating Materials

These materials are similar to the above type but are smaller in size and greater in thickness. Commonly available thicknesses are 5, 7 and 9 cm. For framing purposes, they are made in smaller sizes also.

 

3. Block or Slab Insulators

Block or slab insulators are small rigid small units of 2.5 cm thickness and sizes 60 cm × 120 cm are available. These boards are made out of cork boards, cellular glass blocks, rubber blocks, mineral wood slabs or wood fibreboards together with cement. These small units may be fixed on the walls and roofs for lining purposes.

 

4. Cement Concrete Products

Cement concrete products in general have less insulation value. However, use of cement concrete with lightweight aggregates such as blast furnace slag, burnt clay aggregate, vermiculate, etc., the resistance can be improved.

5. Insulating Boards

These are the boards that are prepared by reducing wood cane or other materials to pulp and then re-assembling fibres into boards. In order to keep the fibres in the desired position, adhesives are used. These boards, available in different sizes and thicknesses, are used for the interior lining of walls and thicknesses, are used for the interior lining of walls and roofs and for partitions.

 

6. Loose Fills

These are fibrous materials like rock wool, slag wool, glass wool, cellulose or wood fibre wool. They are loosely placed into the required space for heat insulation purposes.

 

7. Reflecting Sheet Materials

These materials primarily depend on their surface characteristics for their heat resistant properties. They are used usually along with the air spaces so that the reflecting insulating surface is exposed. These reflective insulations consist of sheet or gypsum boards, steel sheet reflecting materials, aluminium foils, etc.

 

METHODS OF THERMAL INSULATION

Based on the causes of heat transfer, the areas to be concentrated for heat insulation accordingly the methods to be adopted are:

1. Thermal Insulation of roofs

2. Thermal Insulation of exposed walls

3. Thermal Insulation of external windows, and doors

 

1. Thermal Insulation of Roofs

The insulation can be done on the outside or inside of a roof. Generally, it is better to put thermal insulation above the slab. Following methods may be adopted:

(i) Heat insulating materials may be installed over the roof but below a waterproof course. If it is an internal application of the material, it may be fixed by adhesives or otherwise on the underside of the roofs.

(ii) False ceiling may be provided inside by insulating material with certain air gaps.

(iii) On the top of the roof reflecting insulating material may be laid.

(iv) Air spaces may be provided on the top of the flat roof by using asbestos sheets over the bricks.

(v) Spraying water regularly on the top of the roof may reduce the heat flow.

(vi) White-washing of roof before onset of each summer also prevents heat transfer.

(vii) Providing adequate shading on the exposed roof the surface also reduces the heat flow.

 

2. Thermal Insulation of Exposed Walls

(i) Increase in thickness of walls to some extent forms a thermal insulator. But it is expensive.

(ii) Providing cavity walls effectively acts as a thermal insulator.

(iii) Heat insulating materials may be used along with other building materials during the construction of walls.

(iv) Heat insulators explained earlier may be installed or fixed on the inside and outside of the exposed wall in order to reduce the thermal transmittance.

(v) For partition walls air spacing may be created by fixing sheathing of hard boards or battens on either side of the wall.

(vi) Exposed surfaces may be white-washed or light colour distemper may be used on the exposed surface.

 

3. Thermal Insulations of External Windows and Doors

Heat is considerably transmitted through windows and doors which are exposed. This can be reduced by adopting the following method:

 

The incidence of solar heat on exposed doors and windows have to be reduced. This can be done by use of external shading such as louvered shutters, sun breakers, chajjas, etc. Internal shading such as curtains in heavy folds and venition blinds may be used. In the glazed windows, the heat reduction may be achieved by the insulating glass or double glass with air space may be used.

SOURCE: BUILDING CONSTRUCTION MATERIALS AND TECHNIQUES | P. PURUSHOTHAMA RAJ

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