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.
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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