Energy Conservation is “buzz” words of our times. There are many forms of energy conservation and
this handbook is only concerned with the methods of conserving energy by means of thermal
To change the temperature of an object, energy is required in the form of heat generation to increase
temperature, or heat extraction to reduce temperature. Once the heat generation or heat extraction is
terminated a reverse flow of heat occurs to revert the temperature back to ambient. To maintain a given
temperature considerable continuous energy is required. Insulation will reduce this energy loss.
Heat may be transferred in three mechanisms: conduction, convection and radiation. Thermal
conduction is the molecular transport of heat under the effect of a temperature gradient. Convection
mechanism of heat occurs in liquids and gases, whereby flow processes transfer heat. Free convection
is flow caused by differences in density as a result of temperature differences. Forced convection is
flow caused by external influences (wind, ventilators, etc.) Thermal radiation mechanism occurs when
thermal energy is emitted similar to light radiation.
Heat transfers through insulation material occur by means of conduction, while heat loss to or heat gain
from atmosphere occurs by means of convection and radiation.
Heat passes through the raw materials through conductivity and the rate of its formation,
the thermal conductivity (expressed in W/mK) of the material in question and the temperature drive.
In general the greater the density of a material, the greater the thermal conductivity, for example,
metals has a high density and a high thermal conductivity.
Thermal insulation materials fall into the latter category. Thermal insulation materials may be natural
substances or man-made.
If the insulation density is low, the air or gas gaps are relatively large, best insulation for low to medium temperatures where compression and/or vibration is not a factor.
However, when compared with high temperatures, the dimensions of air and gas voids must be reduced to minimize the convection within the voids and this is achieved by increasing the density of the insulation. Density can be increased to a certain point when the solid content of the insulation is as follows.
the heat bridge of the solids overcomes the insulating effect of the voids. It follows therefore, that by
encasing a container of heat with thermal insulation material the reverse heat flow will be retarded with
resultant reducing energy loss and cost.
The word “retarded” is important because no matter how much insulation is applied, the reverse flow of
heat to ambient can never be stopped. The primary reasons for insulation are many and varied, the
main ones being:
• To conserve energy
• To reduce heat loss or gain
• To maintain a temperature condition
• To maintain the effective operation of equipment or chemical reaction
• To assist in maintaining a product at a constant temperature
• To prevent condensation
• To create a comfortable environmental condition
• To protect personnel
The type and thickness of insulation depend on the foregoing primary reasons together with the
parameters of the specific conditions.
Economic thickness is the thickness of insulation, which will result in minimum total cost of energy
losses plus the cost of the erected insulation. The calculation of economic thickness is complex and in
some cases is overruled by the other listed primary reasons, which can make the calculation
The exception is when retro fitting of insulation is envisaged. Retro fitting is the application of
additional insulation to existing insulation to further reduce heat loss or gain in order to reduce the cost
of energy losses.
The amount of economic thickness must be prepared by the person and is usually not the function of this system.
insulation contractor. It includes salient factors such as:
• Cost of the energy losses, which include capital cost of installed equipment to generate/extract
• Expected price movement in the cost of fuel
• Capital cost of installed insulation
• Payback period that the user requires for capital investments
• Various other accounting factors