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|See also the Thermal insulation category.|
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At the simplest, thermal insulation is any material used to reduce the transfer of heat. By keeping heat in or out as desired, energy use is reduced.
Typical materials used as thermal insulation in walls and roofs of buildings include glass fiber batting, rigid foam panels, spray foam which solidifies in place, loose fill cellulose.
Some considerations that must be considered when selecting insulation include cost, durability, environmental friendliness, flammability, toxicity (e.g. formaldehyde gas from some formulations of spray foam).
Thermal insulation is also commonly used in applications where temperatures significantly higher or lower than the ambient temperature are desired, such as refrigeration or solar collectors. Thermal insulation is crucial in these applications because the significant potential difference between the heat-controlled environment and the ambient difference mean there is a high tendency for the heat to transfer to attempt to reach equilibrium. Because of this, thermal insulation must be used to ensure that the temperature difference is maintained while reducing heat transfer between the two mediums.
Certain types of insulating walls also act as good thermal mass, storing heat or coolness - e.g. stone or earth construction. In this context, thermal masses are useful because they can prevent heat from leaving (or entering) a room, while ensuring that even when heat does begin transfer, the thermal mass can continue to regulate temperature. Thermal masses are sometimes problematic because they can act as a heat sink, meaning that a lot of the energy intended to heat a room might end up heating the thermal mass instead, potentially causing the heating process to be more energy intensive, especially if a fast result is desired. Thermal masses can retain and give off heat for a long time if they have a high specific heat capacity.
Types of Insulation
Thermal insulation can be implemented in three different ways: it can be designed to prevent convection, to prevent conduction, or to prevent radiation (or any combination thereof).
Conduction can be prevented with the use of materials that don't conduct heat very well. Conductivity is an intrinsic property of different types of material. For example, metals tend to have high conductivity, while styrofoam generally has low conductivity. Modern day houses are most commonly equipped with insulation materials (like fiber glass or foam) that reduce heat loss to the environment.
Convection, the other hand, doesn't transfer through solid objects, it is transferred through bodies of fluid (like air). If there is a cold room and a warm room next to each other with small gaps between the connecting door, heat will travel via convection between these rooms. This transfer can be reduced by closing, or filling, the physical gaps.
Radiation transfers through light (electromagnetic waves). Radiation heat loss can be reduced by using reflective or opaque materials.
- Insulation Fact Sheet, US Department of Energy.
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