Thermal insulation reduces heat loss from buildings. This property is highlighted in Sandwich Panels.
According to the Energy Conservation Building Code we have the following definitions:
Conduction: Conduction is heat transfer through a solid medium due to temperature gradient. The heat flow direction is in accordance with these cond laws of thermodynamics –from a region of higher temperature to that of lower temperature. The conductivity is the property of material.
Thermal Resistance: Thermal Resistance is proportional to the thickness of material of construction and inversely proportional to its conductivity. This, a lower value of conductivity, means less heat flow and greater thickness of material. Together these parameters form the 'Thermal Resistance' to the process ofheat conduction.
Description of Surface Resistance
The total thermal resistance RT of a plane element consisting of thermally homogeneous layers perpendicular to the heat flow is calculated by the following formula:
RT :Rsi + Rt + Rse
Where Rt is the thermal resistance of the component in the wall/roof.
Rt : R1 + R2+ …+ Rn
For the calculation of the thermal transmittance under ordinary building conditions, the seasonal mean values of the exterior surface thermal resistance (Rse) and the interior surface thermal resistance (Rsi) can be obtained from the table below. These values are the result of empirical studies and merely represent magnitudes of order.
They consider both convection and radiation influences.
|Direction of Heat Flow||Direction of Heat Flow|
A building element is usually composed of a number of different materials. When materials are placed in series, their thermal resistances are added so that the same area will conduct less energy for a given temperature difference. Formation of air film at the surface of wall or roof, due to convection movements of air, also provides resistance to the heat flow, similar to the construction material. The total resistance of the wall or the roof includes all the resistances of the individual materials that it is made of, as well as, both the internal and external air-film resistance.
R1, R2, …,Rn are the thermal resistances of each layer.
Thermal Resistance is also depicted as reciprocal of Thermal Conductance (U): R =1/U
Solar Heat Gain Coefficient:
Conduction heat flow through the fenestration (e.g. glass windows) is similar to the process discussed for walls and roofs. However, regardless of outside temperature, heat gain through the fenestration is also dependent on direct and indirect solar radiation. The ability to control this heat gain is characterized in terms of SHGC. SHGC is the ratio of the solar heat gain that passes through the fenestration to the total incident solar radiation that falls on the fenestration. The solar heat gain includes directly transmitted solar heat and absorbed solar radiation, which is then re-radiated, convected, or conducted into the interior space. SHGC indicates how well the glazing/glass and fenestration products insulate heat caused by sun falling directly on the glass.
In hot climates, SHGC is more important than the U-factor of the glazing. A lower SHGC means that lesser heat can pass through the glazing. The SHGC is based on the properties of the glazing material, whether the window has single, double, or triple glazing, and the window operation (either operable or fixed). Glazing units with a low SHGC will help reduce the air conditioning energy use during the cooling season.
The total R Value would be as follows:
R1 R Value of the 230 mm thick brick wall = 0.284 K m2/W
R2 R Value of the 50 mm Air Gap = 0.18 K m2/W
R3 R value of 4mm thick Sandwich Panels = 0.0103 K m2/W
Rt R value = R1 + R2 + R3
= 0.284 + 0.18 + 0.0103 K m2/W
= 0.4743 K m2/W
RT = Rsi + Rse+ Rt
= 0.1 + 0.04 + 0.4743
= 0.643 K m2/W
U value = 1/ RT
= 1.552 W/K m2
Vertical Fenestration U Value and SHGC Requirements:
The SHGC requirement is based on Wall to Window Ratio(WWR)
|Climate||Max. U Factor||WWR<=40% Max SHGC||40%<=WWR<=60%Max SHGC|
|Hot & Dry||3.30||0.25||0.20|
|Warm & Humid||3.30||0.25||0.20|
According to the table above which is according to Energy Conservation Building Codes, Sandwich Panels can be used in any climate in India.