Thermal properties of building components and materials

Buildings in their own modify the climate and their main function is to provide comfortable living conditions for their inhabitants. It also maintains its indoor climate relatively constant for this purpose. The choice of building materials is of prime importance along with other factors regarding the thermal performance of the building . The choice of material is also responsible for reduction of the energy loads required to maintain comfortable levels with in the closed environment. While dealing with the thermal performance of building, understanding of thermal properties of the material is must. The solar radiation as a greatest source of thermal phenomena should be dealt before going through the material and their thermal properties . Material as such are responsible for absorption, storage and distribution of heat . This can be understanding the different modes of heat transfer.

Three fundamental modes of heat transfer 

• By direct interaction with neighboring particles (collisions): this is conduction

• By mixing different parts of a fluid with different temperature: this is convection

• By absorption or emission of electromagnetic radiation: this is radiation

The steady state

• From a thermal point of view every material is constantly seeking equilibrium between the heat absorbed on a part or over all of its surface and the heat losses at it’s periphery.
• For each level of thermal equilibrium, there is a corresponding level of heat and temperature of equilibrium. This state of static condition or of thermal equilibrium is called the steady state.
• For the purpose of simplification in the analysis, the assumption of steady state condition is made .
• The results thus may be taken as reliable if the fluctuations in the conditions do not exceed ± 3º C.
• If the fluctuation in temperature exceeds this tolerable limit, there is a need of establishing the heating or cooling installation.

 

Thermal insulation: thermal resistance and thermal capacity

Insulation may be defined as materials or features of construction provided to minimize the flow of heat between the spaces separated. Insulation as such reduces heat flow

Functions of insulation

• Conserve energy used for heating and cooling.

• Reduce temperature fluctuations and increase comfort with in the enclosed space.

• Protect buildings and other structures from thermal damage, freezing damage, frost heaving, and damage for condensation of water vapor.

• Control surface temperatures of building components for economy in operation, comfort of occupants, or safety.

• Prevent water vapor condensation on cold surfaces.

• Reduce water vapor transmission, properly seen as the separate but related topic of moisture control.

• A significant contribution of most types of insulation is also in reducing airborne sound transmitted through walls, partitions, floors and ceilings.

Insulation and human thermal comfort 

Insulation is the measure to achieve human thermal comfort. Wherever the occupants feel discomfort in a space inside building in functioning their activities, the question of controlling heat flow comes in the front . The insulation of the surface is the ultimate solution for this.

Thermal comfort

The daily life cycle of human being comprises state of activities, fatigue and recovery. It is essential that the mind and the body recover through recreation, rest and sleep to counter balance the mental and physical fatigue resulting from the activities of the day . The cycle can be and is often impeded by unfavorable climatic conditions and the resulting stress on the body and mind causes discomfort, loss of efficiency and may eventually lead to a break down of health . The effect of climate on human is therefore a factor of considerable importance.

 

Thermal factors

The factor affecting comfort may be divided into followings:

• Personal variables

1. Human activities 

2. Clothing

• Environmental factors

1. Air temperature 

2. Wind

3. Humidity

4. Solar radiation

The fluctuation on these factors cause discomfort to the human being. They must be simultaneously considered to predict the comfort range.