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Insulated pipes (called also preinsulated pipes or bonded pipe ) are widely used for
district heating District heating (also known as heat networks) is a system for distributing heat generated in a centralized location through a system of insulated pipes for residential and commercial heating requirements such as space heater, space heating and w ...
and hot water supply. They consist of a steel pipe called "service pipe", a thermal insulation layer and an outer casing. The insulation bonds the service pipe and the casing together. The main purpose of such pipes is to maintain the
temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...
of the fluid inside the service pipes. Insulated pipes are commonly used for transport of hot water from district heating plants to district heating networks and for distribution of hot water inside district heating networks. Thermal insulation material usually used is
polyurethane Polyurethane (; often abbreviated PUR and PU) is a class of polymers composed of organic chemistry, organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane term ...
foam or similar, with a
thermal conductivity The thermal conductivity of a material is a measure of its ability to heat conduction, conduct heat. It is commonly denoted by k, \lambda, or \kappa and is measured in W·m−1·K−1. Heat transfer occurs at a lower rate in materials of low ...
λ50 of about 0.024–0.033 W/(m·K). While polyurethane has outstanding mechanical and thermal properties, the high toxicity of the iisocyanatesrequired for its manufacturing has caused a restriction on their use. This has triggered research on alternative insulating foam fitting the application, which include
polyethylene terephthalate Polyethylene terephthalate (or poly(ethylene terephthalate), PET, PETE, or the obsolete PETP or PET-P), is the most common thermoplastic polymer resin of the polyester family and is used in synthetic fibre, fibres for clothing, packaging, conta ...
(PET) and
polybutylene Polybutylene (polybutene-1, poly(1-butene), PB-1) is a polyolefin or saturated polymer with the chemical formula (CH2CH(Et))n. Not be confused with polybutene, PB-1 is mainly used in piping. Production Polybutylene is produced by polymerisation ...
(PB-1). The outer casing is usually made of
high-density polyethylene High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a thermoplastic polymer produced from the monomer ethylene. It is sometimes called "alkathene" or " polythene" when used for HDPE pipes. With a high strength-to-density rati ...
(HDPE). Preinsulated pipes for district heating are described in European standards EN 253 and EN 15698-1. EN 253 describes "District heating pipes - Bonded single pipe systems for directly buried hot water networks - Factory made pipe assembly of steel service pipe, polyurethane thermal insulation and a casing of polyethylene". EN 15698-1 describes "District heating pipes - Bonded twin pipe systems for directly buried hot water networks - Factory made twin pipe assembly of steel service pipes, polyurethane thermal insulation and one casing of polyethylene". Both standards don't give "short names" or abbreviations for described pipes. According to EN 253:2019 & EN 15698-1:2019, pipes must be produced to work at constant temperature of for 30 years. Thermal conductivity λ50 in unaged condition shall not exceed 0.029 W/(m·K). Both standards describe three insulation thickness levels. Both standards require use of polyurethane foam for thermal insulation and HDPE for casing. Insulated pipelines are usually assembled from pipes of , , or in length, directly buried in
soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...
in depths of commonly .


See also

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Heat conduction Thermal conduction is the diffusion of thermal energy (heat) within one material or between materials in contact. The higher temperature object has molecules with more kinetic energy; collisions between molecules distributes this kinetic energy u ...
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Heat transfer Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, ...
* Heat transfer mechanisms * R-value *
Specific Heat In thermodynamics, the specific heat capacity (symbol ) of a substance is the amount of heat that must be added to one unit of mass of the substance in order to cause an increase of one unit in temperature. It is also referred to as massic heat ...
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Thermal bridge A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...
* Thermal contact conductance *
Thermal diffusivity In thermodynamics, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It is a measure of the rate of heat transfer inside a material and has SI, SI units of m2/s. It is an intensive ...
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Thermal resistance in electronics In heat transfer, thermal engineering, and thermodynamics, thermal conductance and thermal resistance are fundamental concepts that describe the ability of materials or systems to conduct heat and the opposition they offer to the heat current. ...
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Thermocouple A thermocouple, also known as a "thermoelectrical thermometer", is an electrical device consisting of two dissimilar electrical conductors forming an electrical junction. A thermocouple produces a temperature-dependent voltage as a result of the ...


References

{{reflist Energy conservation Heating, ventilation, and air conditioning Piping Residential heating de:Kunststoffmantelverbundrohr