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Transcript of Thermal Insulations
Thermal Insulations
Prof. Dr. Saiful HuqueInstitute of Renewable Energy
University of Dhaka 19-11-2013
What is thermal Insulation
Thermal insulation are material or
combination of materials that help retard the flow of heat energy by conductive, convective or radiation mode of heat
Types of thermal insulation
They can be of several typesFibrousParticulateFilmBlockAnd composites of these materials
Application of thermal insulation
Conserve energy by reducing heat loss and gain of structure and ducts Control surface temperature of structure for comfortPrevent vapor condensation on surfaces having temperature below the point temperature of the surrounding atmosphere
Application of thermal insulation
Reduce temperature fluctuation within an enclosure when required heating or cooling is not available
Reduce temperature variations within a conditioned space for increased personal Comfort
Thermal insulation can serve extra
Add structural strength to wall ceiling or floor
Provide support to surface finish
Impede water vapor transmission and air Infiltration
Reduce noise and vibration
Limiting material of thermal insulation
The own survival temperature is considered as second selection criteria after primary criteriaLike consideration of low thermal conductivity
Based on origin thermal insulation material can be
categorized into three categories1
inorganic or fibrous or cellularlike glass wool, rock wool, slag
wool, calcium silicate bonded perlite, Vermicular or ceramic products
Category of thermal insulation
2 Organic fibrous material like cellulose, cotton,
animal hair, wood pulp, cane or synthetic fibers and organic cellular materials such as cork, foamed rubber, polystyrene, polyurethane and other polymers
Category of thermal insulation
3
Metallic or metallic organic reflective membrane.
These surfaces must face an air, gas filled or evacuated space to be effective.
Properties of Insulating materialsPhysical properties:Loose fill insulationInsulating cementFlexible and semi rigid insulationRigid materialReflective materialFoam-in-place insulation Accessory materials
Properties of Insulating materials
Thermal properties:Thermal resistance and insulationThermal conductivityThe R-value:Conductance of a material C = k/L where k and
L are thermal conductivity and thickness of insulating material.
Properties of Insulating materials
The R value of the insulation is defined as R = 1/C = L/k it means for obtaining a higher R-
value of insulation, either more thickness of insulating material or a material of low conductance should be used.
Names like R11, R-12 represent ratio of thickness and thermal conductivity in BTU system of units
Properties of Insulating materials
Mechanical properties:Some insulation materials have sufficient structural strength to act as load bearing members. Mechanical properties vary with basic composition such as density, composition, cell size, fiber diameter and orientation, type and amount of binder and temperature
Properties of Insulating materials
Health and safety:Most thermal insulations have good resistance to potential risk to health, such as fire, vermin, rot, objectionable odors and vapors.Potential risks from insulation material can be
put into two categories :Risk related to storage, handling and installationRisks that can occur after installation e.g. Aging
Properties of Insulating materials
Health and safety:Potential health effects range from temporary Irritation to serious changes in body functions.
Manufactures recommendations and government codes must be concerned beforeusing insulating materials.
Properties of Insulating materials
Acoustics:Some thermal insulation materials can also serve purpose of acoustic control.Acoustic efficiency depends upon physical structure of the material. Materials with open porous surfaces have sound absorption capability. Sound absorption insulation material are installed on interior surfaces.
Factors Affecting Thermal Performance Of Insulation Materials
Physical ParametersEnvironmental parametersSurface conductanceAir Cavities For Insulation
Insulation practices
Selection of insulation in buildings is based upon thermal properties of materials, space availability, compatibility of materials withadjacent materials and interior and exterior climatic conditions.Insulation practices differ from the type of basicconstruction
Insulating materials
Wood Frame
Steel Frame
Concrete block
Fire brick
Insulation can reduce operating cost and size of the cooling system significantly
Thank you