Thermal insulation is defined as the set of materials and installation techniques that are applied to one element or to a hot space to minimize the transmission of heat to other adjacent elements. There are many situations in which it is convenient to reduce the heat flow in a certain direction. The most common case is the insulation of buildings to minimize heat losses in winter and gains in summer, although there are many others such as the insulation of cold rooms or hot or cold liquid distribution pipes. The use of thermal insulation is especially relevant when lining the ducts of a double-flow ventilation system. During the summer, and once the heat is extracted from the air that enters through the impulsion ducts, these must be properly insulated so that the air that circulates through them remains cold until it reaches the impulse nozzles. The thermal insulation of the ducts fulfills the same function in winter, but at this season of the year, it prevents the heat from the air introduced into the home through the exchanger from being transmitted to the environment and the insufflated air being kept at 19ºC until reaching drive ports.
Types of thermal insulation
Insulating materials are all characterized by their low thermal conductivity. In a very simplified way, they can be classified into three types of materials:
Fibrous: they are made up of filaments with small or low-quality particles. They are placed as filler in openings or as blankets in the form of boards or blankets. They have a very high porosity of around 90%. They are used depending on the temperature: fiberglass for temperatures up to 200ºC, mineral wool up to 700ºC and alumina or silica fibers between 700 and 1700ºC.
Cellular: they are materials that are formed into closed or open cells, generally forming rigid or flexible boards, although they can also be formed in situ by spraying or irrigation. Its advantages are: its low density, low heating capacity and acceptable compressive strength. The most used are polyurethane and expanded polyethylene.
Granular: they are small particles of agglomerated inorganic materials such as perlite and vermiculite.
Properties of thermal insulators
When choosing an insulating material, it must be taken into account that its main property is conductivity, but density, chemical stability, structural rigidity or degradation are also important.
Conductivity: expressed in W / (m.k), it refers to the dry insulating material since it is a property that varies with humidity and temperature.
Permeability: expressed in gr / (m.s.Pa)
Bulk density: expressed in Kgr / m3
Heat capacity: it is used to assess the behavior of the insulation over a period of time
Mechanical properties: compressive strength, flexural strength, and coefficient of thermal expansion
Water absorption: can be expressed in of volume of water per volume of material. It is very important because it can alter other values such as conductivity, density and heat capacity.
