In building physics, insulation technology includes all measures for thermal insulation, cold insulation (as a special form of thermal insulation) and soundproofing.
The main reasons for insulating buildings are: to avoid energy losses and structural damage, to guarantee building hygiene standards and the safety of people and property, and to protect the physical and mental health of people.
In addition, insulation technology for industrial plants plays an important role in increasing the effectiveness of plants, reducing costs, protecting plants and extending their service life.
Physical approach to explanation
Vacuum is the best insulating medium because heat conduction and convection as well as sound transmission are impossible. As in the thermos flask, the heat radiation can be greatly reduced by mirroring. Nevertheless, the gap is usually filled with gas, mostly air, because maintaining the vacuum and, above all, controlling the enormous forces that the pressure difference exerts on the walls are often problematic.
In a larger cell, still air is only possible if all cell walls have the same temperature. As soon as one wall has a higher temperature than the other, the enclosed air is set in motion by natural convection : it then heats up on the warm surface, the density drops, the air rises. It cools down on the cold surface and falls down. This creates a flow circuit from the warm to the cold side and back - the convection .
Also to be considered is the heat transport that occurs through the conduction of heat in the cell walls themselves. All insulation materials are based on the principle that the air cells are so small that hardly any convection can develop due to the frictional forces on the walls, but hardly any radiation due to the minimal temperature differences between the walls . In addition, the cell walls must be made of a material that does not conduct heat well and that keeps the prevailing temperatures constant. The most important prerequisite for a good insulation effect is therefore that the heat protection material is evenly interspersed with as many microscopic air pores as possible and the pore walls themselves are made of a poorly thermally conductive material.
The calculation of the insulation capacity of a fabric
The thermal conductivity is a material property and is used for calculation of the heat flow through a material because of the heat conduction using this material. The unit of thermal conductivity is W / ( m · K ).
Main areas of insulation technology
The thermal insulation of external components in both residential and commercial construction has a major impact on the energy demand and consumption of buildings and systems. An important goal is to save energy both in the manufacture of building materials and in the manufacture and use of buildings and industrial facilities.
The aim of cold insulation is to maintain the lowest possible temperature, e.g. B. to avoid condensation or to minimize system performance losses. Preferred insulation materials are foamed plastics such as styrofoam and foamed neoprene rubber. New innovative products based on polyethylene show considerable technical and building material values in this area.
Ever higher production rates and shorter delivery times require economical production processes. The consequences are u. a. High-speed and therefore noise-generating machines. This sound level is often disruptive or even unreasonable for the employees of a company or the neighborhood surrounding the systems. In addition to design changes to the machines, sound insulation offers a way of reducing the sound level.
The history of insulation technology in pipeline and heating construction
Plastic heat protection compounds
In the 1920s, plastic heat protection compounds were widespread. B. made of kieselguhr , magnesia or "Depegee" dust and mixed with a binder and water to a pulp and then applied in layers to the object to be insulated. For this purpose, the container or pipeline was preheated and heated until the insulation material was set and the water was expelled from the insulation material. At that time, insulation technology was faced with a number of problems. It could not be avoided that a certain amount of residual moisture remained in the mass, and even 1% moisture content reduced the insulation effect by approx. 10%. The water filled the fine pores and prevented their lasting insulating effect. The insulating bricks and molded parts on the market at the time had to be applied to the heat transfer medium with wet insulating compound as a binder, grouted with the wet compound and then wiped off on the outside - therefore moisture remained in the insulation.
In addition, the types of insulation did not have a low thermal conductivity and such high volume weights that the supporting structures of the pipes and containers had to be designed more heavily. The materials adhering rigidly to the surfaces and the different expansion coefficients also caused cracks, which led to the insulation material crumbling.
Dry plug insulation in the sheet metal jacket
Due to the disadvantages of the plastic heat protection masses, the dry plug insulation in the sheet metal jacket was developed by the Bohle Group at the end of the 1920s . A sheet metal jacket made of leaded or galvanized sheet iron was laid around the pipeline on spacers and the cavity was "stuffed" with the insulation material through a filling slot and then closed with a lid. As the filler, powdery "Depegee" -Gichtstaub, a served sediment the stack gases in the blast furnace process ; later purified slag wool, a fiber material made from blown blast furnace slag, was used.
This new method brought decisive advantages:
- the stable sheet metal jacket protected the high-quality insulation material from external mechanical damage
- Due to the meter-by-meter overlapping of the seams and the fact that the round seams were not connected to each other, the outer sheet metal jacket was able to take part in the thermal expansion of the heat carrier; the stretching was absorbed in the circumferential seams
- Loose and, above all, dry materials could be used as insulating materials, which adapted to the thermal expansion and had a low thermal conductivity and a lower density
- the insulation could be installed on the cold object and did not need to dry out for days or even weeks: it applied its full insulation effect right from the first hour
- the service life was four to five times longer than the old insulation method, and even reached the service life of the system itself.
The disadvantage of this method was the high acquisition costs for the sheet metal jacket and high labor intensity for assembly.
Mineral wool sheet metal mat insulation
Mineral wool sheet metal mat insulation was developed in the early 1930s. First, a system of thin sheet metal clips that protruded through the insulation layer was soldered to the inside of the precisely fitted sheet metal jacket. As corrosion protection , the inside was given a rich bitumen coating, in which mineral or glass wool was padded with the prescribed thickness and the necessary density while it was still wet . A close-meshed wire netting formed the end to the inside, around which the protruding clips were bent. The result was a uniform, ready-to-assemble component. The process was roughly comparable to the previous dry-lock insulation, but much more economical.
Wire mesh quilted mats for insulation
In the 1950s, mats quilted with wire mesh were used for insulation: The insulation material was separated from the sheet metal jacket again and you had an insulation body that was manufactured with a guaranteed even tamping density, which was much faster and easier to assemble. Before attaching the jacket, joints and other cavities could even be filled. In addition, the conditions for dismantling and reassembly improved, as the insulation material was connected to the wire mesh through the quilting. The only handicap was that the quilting threads could burn over 100 ° C on the hot object. The problem was eliminated by using asbestos or glass thread, later replaced by thin, galvanized wire. Modern insulation technology is practically a further development of this principle, which was based on the processing of loose, dry mineral fiber materials behind a protective sheet metal jacket and is now widespread all over the world.
Insulation today with polyurethane foam
Polyurethane foams are produced by polymerizing polyisocyanates with polyols in the presence of catalysts . Monofluorotrichloromethane (e.g. Frigen R11) is used as the propellant. During the chemical reaction of the polyol with the isocyanate, heat is released which heats the liquid propellant gas above the boiling point and thus causes it to evaporate. The plastic, which is still soft, surrounds the gas bubbles, and the foam structure thus created hardens after the reaction has ended. During this time, pressure is created, which forces the foam, which is still flowable, into every smallest cavity. Due to its adhesiveness during the reaction time, the foam bonds intimately with the outer layers surrounding it, such as. B. Sheet metal jacket and object surface. The set foam forms a structure from a large number of tiny, more or less elastic cells with an absolutely uniform structure. The proportion of closed cells is up to 95%. The density can be varied by changing the recipe of the mixture depending on the requirements.
A distinction is made between pouring and spraying methods in the types of process. With the pouring method, filler holes are cut in the formwork material (usually sheet metal jackets) at suitable points. Then the material is poured into the cavity in the liquid state as a compact jet by hand with the machine. It is also possible to use the so-called overlay method, where the material is applied in layers. Here, the already solidified foam structure connects exactly and seamlessly with the subsequently applied layer. With the spray method, also known as spray insulation , the foam is created so quickly after the mixture has been sprayed that vertical surfaces as well as surfaces overhead can be foamed without the fear of the foam running off or dripping off. It is precisely this advantage of the polyurethane foam that makes it an ideal insulation material in addition to its excellent insulation values and compressive strength. The Forschungsinstitut für Wärmeschutz eV, Munich, measured the thermal conductivity of the cast foam (in-situ foam, which was officially taken from the point of use) in 1984 with the following test result: At a bulk density of 46 kg / m³ the following values were obtained:
|Average temperature in ° C||Thermal conductivity in W / (m K)|
These figures are proof of the excellent thermal insulation properties of the polyurethane foam.
Energy savings through insulation technology
Appropriate insulation and thus the rational use of energy is particularly worth mentioning in connection with the greenhouse effect ( CO 2 emissions). In private households, almost 80% of the energy used is used for space heating. The potential for savings in terms of CO 2 generation is 70–90%. Many industrial processes take place at several hundred degrees Celsius. If the thermal conductivity of the building materials used is reduced by professional, modern insulation, energy losses can be reduced by up to 70%, as the "Pro Klimaschutz" initiative has found - lower energy consumption means lower CO 2 emissions.
Against the background of steadily rising energy costs, an investment in modern insulation technology should also be considered. It is interesting to look at the consumer prices of the common energy sources over the past ten years. The fuel oil price is € / l increased according to the Federal Ministry of Economics and the Environment from 2001 to 2011 from 38.45 to 81.62 100 € / 100 l (↑ 212%). The price of natural gas increased in this period of 4.84 ct / kWh to 6.66 ct / kWh (↑ 138%). The electricity price rose from 15.44 ct / kWh to 25.08 ct / kWh (↑ 162%). The numbers show how much energy prices have risen in recent years. Companies and private households can therefore save money by using modern, high-quality insulation and at the same time protect the environment.
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