Calculation of Thermal Resistances of Walls and Thermal Insulations

Calculation of Thermal Resistances of Walls and Thermal Insulations

According to different geographies and climates, different kinds of construction materials are used in buildings. The use of construction materials depends on the advantages of nature and compatibleness o with climate. In very hot climates, thin walls and wide windows are generally used. But in very cold climates, thick walls and relatively small windows are used in buildings. Everybody can guess that these preferences of thickness and design shapes of walls and the windows are made according to the thermal insulation. But, we would like to explain its basic logic of it. 

Thermal insulation illustration(Image Source: Wikimedia).

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What is the Conduction Resistance of Walls? 

We should not think about them as walls. Thermal barriers are generally used in different applications such as insulated pots. These pots are designed to hold substances hot or cold inside them. In insulation design, the total insulation is strictly calculated by engineers. In these calculations, the thermal resistance of the used insulation materials is a very important parameter. 

In the insulation studies, the same approach in electrical resistance circuits is used. If you remember from the basic physics lessons, the total resistance of the circuit is calculated by summing all the serial resistances and summing the inverse resistance for parallel resistance circuits. 

In thermal resistance insulation designs, the same approach is employed. But first, we need to take a look at how the conduction resistance is calculated for materials. 

According to this formula, the thermal conduction resistance of a thermal barrier is calculated with different parameters. 

Here, ‘L’ is the total thickness of the thermal barrier. The unit of the total thickness of the thermal barrier is ‘m’. The second parameter is the ‘k’ which is the thermal conductivity of the material of the thermal barrier. ‘A’ is the total area of the thermal barrier in ‘m^3’. 

Once you put the parameters and variables in that formula, you will have the total thermal resistance of the wall. Each layer of insulation is calculated like this. 

You need to take special care of the thermal conductivity value. If you use the thermal conductivity value as W/m.°C, the obtained unit will be °C/W. But if you use W/m.K, you will obtain K/W. 

If multi-layers of insulation walls are used, all the resistances are calculated with the formula above, and the total thermal resistance is calculated according to the electrical resistance theory. 

Parameters of Thermal Conduction Resistance

Advantages of thermal insulation(Image Source: isowall).

The first parameter is the thickness of the wall. It is very simple that if the total thickness of the wall increases, the thermal resistance increases thus thermal insulation increases. 

The second parameter is thermal conductivity. With the increasing amount of thermal cınductivity, the total thermal resistance decreases. So, total heat transfer increases. 

With the increasing amount of insulated surface area, much more heat energy is dissipated. In insulation design, the area must be lower as much. 

Conclusion

The general logic of the conduction insulation in thermal studies is like that. 

Do not forget to leave your comments and questions below about the thermal conduction insulation in heat transfer mechanisms. 

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