Capillary tube mat

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Capillary tube mat

A capillary tube mat is a flat composite of thin tubes ( capillaries ) with a distributor tube and a collector tube. The main areas of application are cooling ceilings and underfloor heating .



The construction of the capillary tube mat is modeled on the networks of fine veins created by nature, which not only supply the organism with nutrients but also serve to regulate the body's heat under the skin (surface) of living beings. The function of heat regulation has given the inspiration to lay capillary tube mats in the areas surrounding rooms just below the surface, to let warm or cool water flow through them and in this way to control the temperature of the rooms. Since, similar to the veins under the skin of the body, there is always flow through many capillary tubes in parallel, the heat exchange with the environment is very intensive and at the same time energetically effective. A room that is tempered using capillary tube mats as a surface heat exchanger requires flow temperatures for heating or cooling that are only a few degrees away from the desired room temperature. At the same time, due to the large number of parallel running capillary tubes, the drive energy to maintain the flow is comparatively low compared to "single-tube systems" that are laid in a meander (typical laying of underfloor heating pipes). Due to the small distance between the capillary tubes and the surface of the room, the system reacts very quickly. Due to the large number of capillary tubes, the temperature of the heating or cooling medium is released very evenly and quickly to the environment. These two properties - very good heat transfer and low pressure loss - are advantageous in terms of energy saving. In a broader version of the terms used in technology, the capillary tube mat is a surface heat exchanger and can be used to transfer heat between two media.


The typical capillary tube mat has capillary tubes with an outside diameter of less than 5 mm. This makes the construction very flexible and underlines the property of the "mat". The individual capillary tubes are arranged in register at a distance of 10 to a maximum of 50 mm. Capillary tube mats are mostly made of plastic. They are usually made from polypropylene , which is often used in construction for pipelines and in ventilation and air conditioning technology. This material and the small dimensions justify the flexibility of the register and thus the properties of the mat. The use of plastic in the manufacture of capillary tube mats instead of copper or steel as in other cooling ceiling tubes has a significant cost-reducing effect. Since the capillary tubes are very thin-walled, the poorer thermal conductivity of the plastic compared to metals does not have a disadvantageous effect on the heat transfer. Polypropylene is very resistant to many chemicals (DIN 8078) and therefore very durable. Polypropylene is very easy to recycle. Polypropylene is open to oxygen diffusion. This property requires that the capillary tube mats are only ever operated in corrosion-protected tube systems. This measure ensures the safe functioning of the systems and is sufficient protection against corrosion damage ( corrosion and corrosion protection ). The capillary tube mats are manufactured using standard plastic processing techniques such as extrusion, thermal plastic welding and injection molding.


The invention of the capillary tube mat goes back to 1981, when the Berlin graduate engineer. Donald Herbst has applied for his first patent ( DE 31 24 048, filing date 15.06.1981, "Pipeline mesh for hot water surface heating of floors or walls" ) for this technology. From his many years of activity in the service of capillary tube mat technology, a large number of complementary inventions / patents followed, whereby the manufacturing processes and the applications of capillary tube mats were continuously developed. In the early years, the capillary tube mats were brought onto the market under the “KaRo” brand. On the occasion of the International Building Exhibition in Berlin in 1984, the design by architects von Gerkan, Marg and Partners for an energy-saving house won. Here, capillary tube mats were used for the first time in a complex system in a 1,200 m² residential building. Extensive scientific work by Prof. Dr. Mathias Fraaß (since 1991) and later by Prof. Dr. Bernd Glück (since 1994) created the necessary fundamentals for the theory in the applications of capillary tube mats. Today capillary tube mats are installed worldwide. The annual production volume is estimated at more than 400,000 m² (2010).

Importance and application

Capillary tube mats are mainly used in cooling ceilings. Every design of a cooling ceiling can be activated by capillary tube mats. In addition to the plaster cooling ceilings with capillary tube mats, which require less than 15 mm plaster layer, the capillary tube mats are also installed in metal coffered ceilings and in suspended plasterboard ceilings. The transferred heating and cooling capacities are between 65 and 90 W / m² for the different versions with a temperature difference of 10 K between the mean medium temperature and the room temperature. Capillary tube mats hanging freely in the room achieve cooling capacities of well over 100 W / m².

Capillary tube mats are also used in thermal component activation BTA. In contrast to conventional concrete core activation BKT, in thermal component activation the capillary tubes are about 5 mm below the ceiling surface. This arrangement ensures a quick reaction and a high transmission capacity of up to 90 W / m² (with a temperature difference of 10 K, see above) and also uses the concrete mass as thermal storage. With capillary tube mats, very thin heating surfaces can be built as underfloor heating or wall heating . A layer thickness of less than 15 mm is possible. Capillary tube mats are also used as compact collectors for utilizing geothermal energy in heat pump systems. The extraction area can be reduced by using the capillary tube mats. In the processing and manufacturing industry, capillary tube mats are already used to control the temperature of acid baths, among other things.

Major projects

  • Olympic Village Vancouver, Canada
  • Twin Towers Vienna, Austria
  • Uniqa Tower Vienna, Austria
  • Allianz Treptower Berlin, Germany
  • Hôpital de Lagny, Marne la Vallée, France
  • Jin Mao Palace, Beijing, China

Performance determination

Since the capillary tube mats can be used in a variety of ways, different methods are required to determine performance. So z. B. DIN EN 14240 for cooling ceilings (measurement in a test room). However, there are no test standards for many areas of application for capillary tube mats, for example for geothermal collectors, cooling shafts, storage tanks with PCM components, etc. For this purpose, simulation methods have become very important. These can also be used economically in the development of components, as previous trend calculations with regard to the services to be expected can sometimes greatly reduce the development effort. Numerous simulation models can be downloaded free of charge. Other general studies are also available free of charge.


  • Mathias Fraaß: Investigations into capillary tube ceiling cooling systems. Part 1. Can the bar theory be used for the calculation of cooling ceilings? In: Heating, ventilation / air conditioning building technology. HLH 44 (1993) No. 10, pp. 603-610
  • Mathias Fraaß, Donald Herbst: Theoretical investigations on capillary tube ceiling cooling systems. Part 2. Do the characteristic values ​​determined on the test stand apply in practice? In: Heating, ventilation / air conditioning building technology. HLH 44 (1993) No. 11, pp. 673-677
  • Mathias Fraaß: The approach procedure from ribs. In: Gesundheit-Ingenieur-Haustechnik-Bauphysik-Umwelttechnik 118 (1997) Issue 3, pp. 142–147
  • Mathias Fraaß: Numerical performance determination of thermally active components using the boundary element method (BEM) . In: Gesundheit-Ingenieur-Haustechnik-Bauphysik-Umwelttechnik 125 (2004) Issue 2, pp. 70–79
  • Mathias Fraaß: A contribution to the theory of the thermally activated component. Dissertation TU Berlin, March 2001

Individual evidence

  1. Olympic Village Vancouver, Canada [1]
  2. Uniqa Tower Vienna, Austria [2]
  3. [3] Bernd Glück: "Innovative heat transfer and heat storage" PTJ research complex LowEx (heating and cooling with ceiling, wall, floor, solar absorber, storage disks, cooling shafts, small cooling towers, etc.)
  4. [4] Bernd Glück: "Heat storage with and without PCM" ROM environmental foundation
  5. [5] Bernd Glück: "Geothermal Collector"
  6. [6] Bernd Glück: "Thermal component activation" ROM environmental foundation
  7. [7] Bernd Glück: "Basics - Capillary Tube Mats"