Underfloor heating

The underfloor heating belongs to the surface heating.

History

First floor heating systems have already been used by the Romans ( hypocaust ), later, around 700 AD, also by the Koreans, the underfloor heating " ondol ".

The big breakthrough of the underfloor heating has occurred rapidly since the 1970s. An important reason is the comfort. So it will give you around a heated floor to go even in the winter in the house barefoot. Another advantage is the architectural freedom of interior design. Add to this the hygienic aspects of underfloor heating. Dust dispersion does not take place. The uniform surface heat the growth of dust mites and mold growth is prevented.

Hot water heaters

In or under the heating screed pipes are laid out mostly made of plastic or rare copper. As plastics are various materials used. The plastic most often used is the crosslinked, oxygen-tight (otherwise the risk of corrosion in the boiler ), polyethylene (PE- X). The transfer takes place either modular, meandering or bifilar ( snail-shaped ). The modular installation is given by way of priority, because with this installation method, a uniform distribution of heat in the heated space is achieved. The modular transfer also takes place in the concrete core activation. Finally, there are routing types with Kunststoffkapillarrohrmatten, the parallel arranged PP tubes ( dimensions 4.3 mm × eg 0.8 mm) are preferably incorporated in the direct sense. The small pipe distances from 15 to 30 cm cause a very low, practically not perceptible to the floor surface temperature ripple. The application in the concrete core activation leads to a very homogeneous temperature distribution component, whereby the heat storage capacity over large distances tube rises sharply. The underfloor heating is again (very common cement screed or anhydrite screed, due to the better heat transfer in liquid screed ) divided into wet and dry systems systems ( dry screed plates). In the wet system, the pipes are installed in the floor.

In the wet system, there are various options for to fix the pipe in screed:

• The tubes are mounted on carrier mats of steel with brackets
• The tubes are secured with clamps on a carrier insulation (due to damage to the protective layer for insulation and the insulation actually not allowed)
• The pipes are threaded between a steel honeycomb panel
• The tubes ( fitted with a velcro strip ) to be coated with nonwoven backing mats aufgeklettet

Drying Systems

In the dry system, the pipes are located under the floor covering. The fixing occurs there on the carrier insulation equipped with grooves and heat conducting strips. The heat deflectors are used for better heat distribution. The drying system is suitable for low floor constructions and is used in the old building or in building modernization. Dry systems can also be performed with directly placed topsoils (screed bricks, tiles, floating parquet and laminate) and thus lead to a further reduction of the flow temperature and a faster set-up and Abheizphase.

Another variant of the dry systems consists of dry screed plates with a pre- milling, which fixes the heating pipes. Thus, this system combines the previously separate components - dry screed plates and underfloor heating - earlier systems together. The minimal assembly time is of great benefit architects who have in public institutions, such as schools and kindergartens, only the holiday periods for installation are available. In addition, this simplified system also be installed by a private citizen, so that the client only needs a heating engineer for pipe connections.

Newer floor heating systems are increasingly designed for building renovation, without interfering with the existing floor structures. This very low installation heights arise from about 8 mm. A special balancing mass is the basis for the flooring.

Hot water distribution

In both systems for heat distribution, a heating circuit is required. All heating circuits are connected to the flow and return to a respective heating circuit. At the heating circuit each individual heating circuit can be adjusted hydraulically by means of a valve. Can be made ​​optically visible through integrated in the heating circuit flow meter to the volume flow. Hydraulic balancing is necessary because the individual components of the underfloor heating (eg heating manifold, pipe circuits, etc.) produce different high flow resistances. A uniform heat distribution is possible only with the same high throughputs in all heating circuits. Maybe the project is targeted for uneven distribution of heat to compensate for the increased cooling in rooms with large outdoor wall surfaces compared to inland areas. As an underfloor heating as opposed to radiators, the flow temperature is much reacts slower often derived from an external temperature sensor. The control unit outputs an electrical signal to the servomotor, then the four-way valve further opens or closes. For higher-quality equipment, the power supply can with thermostat ( room controllers ), the temperature sensor can be mounted in the heating region (eg living room), be regulated. The heating power is in well-insulated residential buildings about 50 to 100 W / m². In addition, the floor heating can be connected directly to the existing heating circuit (depending on the flow resistance of the floor heating used ) up to a certain area. The control is then performed via a RTL - valve (return temperature limiter, German: return temperature ), which is mounted in the return of floor heating.

There are numerous types of installation of the pipes possible. In order to achieve a largely uniform heat distribution in the room, pipes should be laid with opposite hot-water flow direction. This is achieved by the forward and return runs are in each case arranged next to one another.

Electric Heaters

In addition to hot water heating systems also bound electrically powered heaters are used. Here, resistance cables or films with incorporated under heat conductors, installed in or on the floor. They are suitable for all types of installation that are common even in hot water systems. Due to the low height they are particularly recommended for direct installation under floor coverings. Heating cable with a diameter of 3 mm can be laid in the bed of adhesive tiles and films even under laminate. For underfloor heating (not full heating), there are mats of about 2 mm height. For bathing, showering and other wet rooms cables must be used with a grounded shield to guarantee safety against electrical accidents. The applicable standards for electric radiant heaters are DIN EN 60335-1 and DIN EN 60335-2-96.

Applications in commercial and municipal buildings

In addition to the underfloor heating systems used in residential construction here come industrial space heaters or heaters sprung floor ( gymnasiums ) are used. Air heaters heat the air in the room, but escapes when you open the hall doors immediately. It takes a long time and is associated with high energy consumption to increase the indoor temperature. At a bottom temperature of, e.g., 10 ° C and an air temperature of 20 ° C is calculated arithmetically a perceived temperature of only 15 ° C. Therefore, it is recommended for an acceptable thermal environment temperature, a floor heating. Underfloor heating is the heating of a Hall of radiant heat. This is their users even during the open hall doors available. After closure of the hall doors of the users feel this comfortable radiant heat in no time.

Cooling of hot water systems

Floor heating systems are also used for floor cooling. In conjunction eg with heat pumps and geothermal offers itself, this variant. The surface temperature of the finished floor should not be below 20 ° C and 29-35 ° C - Do not exceed (see section boundary conditions) - depending on location. Furthermore, the dew point should be monitored with a corresponding moisture sensor and control the flow temperature accordingly. The inlet temperature of the cold water is usually 16 ° C, with a spread of 2 to 3 ° C.

Disadvantages of underfloor heating

In addition to depending on the circumstances high -defaulting installation or repair costs are further problems, firstly, that only a slow adjustment of the room temperature is possible, on the other hand is a combination of underfloor heating with a carpeted floor is not recommended, as this inhibits too strong heat exchange. There are also special carpets to buy, which are suitable for underfloor heating systems on the market.

Traditionally difficult is the restoration of underfloor heating, as certain types of plastic pipes used can clog over time. Meanwhile, there are also a method which allows the restoration from the inside without the costly removal and replacement of the heating pipes. Modern floor heating pipes are diffusion-tight, thus no oxygen through the tube entering the heating system. This in turn prevents corrosion on steel parts in the heating system and correspondingly low the so-called blowdown is in -floor heating system. Another protection against sludge formation can be a system separation from the old heating system using plate heat exchanger.

Boundary conditions

For underfloor heating, the following standard applies:

• DIN EN 1264 ( formerly DIN 4725 ).

Other standards that have an interface for underfloor heating:

• Energy Saving Ordinance: Energy Saving Ordinance
• DIN 18560: Concrete Standard
• DIN 1055: Traffic loads
• DIN 18202: Tolerances in building construction
• DIN 4109: Noise protection in buildings

The flow temperature of the heating water is set to 35 ° C (for older systems to 55 ° C) with a spread of 5 ° C (the difference between flow and return temperature). The surface temperatures of the finished floor must not exceed 29 ° C in the occupied zone, 33 ° C in the bath and 35 ° C in the marginal zones. ( The temperatures have been determined in long-term studies. Here, the human physiology was considered and it was found that these temperatures has been classified by the majority of the people to be safe. Therefore they have been included in the relevant DIN standards and now in the European standard for floor heating. thus a uniform standard for the underfloor heating was found. Maybe even the "bad" properties of the floor heating is known, swollen feet, varicose veins, etc. It was then partially operates with surface temperatures above these limits. )

The thermal resistance of the floor covering shall not exceed 0.15 m² K / W. Most carpet flooring are marked with the symbol underfloor heating and approved it.

At the edges of the screed edge insulation strips are to be placed. They should allow the expansion of the screed and also ensure the sound insulation. For larger areas expansion joints are also provided. The rule here is the screed DIN 18560th

The leadership of the tubes is determined by the pipe spacing, which is determined from a calculation. The deviation from the calculated pipe spacing must not be exceeded in a given tolerance, because this creates the danger of too great a ripple in the screed. The ripple is the difference in temperature between the pipes.

Calculation

The calculation of the floor heating is based on the DIN EN 1264 part 2 and 3

An important parameter is the base characteristic. There, the connection between the central floor, and over-temperature, the heat flow density is described.

Example:

Here you can clearly see that any increase in the internal temperature results in a lower heat flux.

From the heat flux density, we can also calculate the heat transfer coefficient.

Is to calculate the heat flow density in the design case are the so -called logarithmic Heizmittelübertemperatur needed.

Now, the heat flux can be calculated

The manufacturer of floor heating systems provide to their systems performance charts for various floor coverings and tube spacings, from which the heat flux can be determined graphically in W/m2 based on the Heizmittelübertemperatur above.

Furthermore, there exists for wet systems, a generally applicable calculation method based on the algorithm of FAX, which is applicable for all pipe dimensions and pipe spacing. The calculation method is verified on the DIN EN 1264-2. The method, described in detail in presented has been extended in dry systems and wet systems with dynamic operation with incorporation of materials with phase change effects ( so-called PCM).