- Describe FOUR (4) effects of heat on building.
Buildings, like the human body, tend to have a heat exchange process with the environment. As heat flow from a hot body to a cold body, the increase in heat in the external or internal environment of the building directly affects the materials which are used in the composition of the building. The four effects of heat on the building are:
- Increase in heat will increase the thermal loading to the building. Usually office buildings are more vulnerable to increase in thermal loading and hence they have more cooling needs as compare to the residential buildings.
- The rate of deterioration of building materials increases with the increase in the rate of heat particularly the heat absorbs by the building from Sunlight.
- During the cycle of heating and cooling the shrinkage and expansion of building materials happen.
- Heat rate also directly effects the organic materials like elastomeric products, sealants and gaskets. The deterioration of these organic materials happen due to increase in heat rate.(“High Temperature Gaskets, High Temp Gasket Material | Stockwell Elastomerics,” n.d.)
R-value determines the extent of resistance faced by the heat to flow through the body. This resistance depends upon the thickness of the body. R-value is used in calculating the heat transfer in Insulation. The higher R-value of a material means that the given material is a good insulator and vice versa. R-value is actually the ratio of the temperature difference across an insulator and the amount of heat transfer per unit time per unit area through it.(“R-values of Insulation and Other Building Materials—Archtoolbox.com,” n.d.)
U-value determines the heat flow through a structure divided by the temperature difference across the structure. It is the reciprocal of the R-value of the material. So U-value can be calculated by calculating the reciprocal of the sum of the thermal resistances of each material used in the composition of the building. Like R-value, U-value also determines the quality of the insulating material the lower the U-value the higher the quality of the insulator.(“What is a U-value? | Insulation | Kingspan | Great Britain,” n.d.)
U = 1/(R 1 +R 2 + R 3 + … + R)
- Thermal Capacity:
Thermal Capacity is determined as the amount of heat required to increase the temperature by 1 degree centigrade of 1 square meter of area. It is basically the ability of a material to absorb, store and release heat. Dense materials like Brick, Concrete, etc. tend to have a higher thermal capacity as compare to the less dense materials like wood, plastic, etc. Thermal capacity is crucial when heat flow is multidirectional and when there is an extreme swing in temperature within 24 hours. (“Thermal Capacity—An overview | ScienceDirect Topics,” n.d.)
“In this formula: Q is the heat absorbed or released by a material (J);
m is the mass of a material (g);
C is the specific heat of a material [J/(g∙K)];
T2 –T1 is the temperature difference before and after heating or cooling (K).
- how hollow spaces (cavities) help to improve thermal performance of buildings?
Cavities also serve as insulators or heat resistors and help in maintaining the building temperature. Heat transfer occurs through either Conduction, Convection, and Radiation. The transfer of heat by conduction is inversely proportional to the depth of airspace. The amount of heat transfer during convection is determined by the depth and height of airspace meanwhile during radiation heat transfer is dependent upon the reflectivity of the internal surfaces. As heat transfer is greatly dependent upon surface temperature so if the airspace is left between two surfaces (layers), the air trapped between these two layers being a poor conductor of heat will resist the heat transfer and thus improve the thermal performance of the buildings. (“Cavities and Air Spaces,” n.d.)