Heating cable as a warm floor

The heating system " warm floor" has long proved its effectiveness and comfort, therefore it is widely used in all world. The question is what source of energy is used to produce heat. While there is a modern difference in energy prices, it is cheaper for a person to burn hard fuel or hydrocarbons, heat the water received by heat, and then pump it through the pipes of the warm floor. But it is much more convenient to use the heating cable as warm floor, rather than the complex system of pipelines, manifolds and pumps. The dominance of hydrocarbons in the energy market will not be permanent, and the electrical energy more convenient for transmission and use will inevitably be used for heating more and more.

theoretical educational program heating cable

As you knowfrom the school course of physics, an electric current is nothing more than a directed movement of charged particles under the influence of an electric field. If any substance has such free charged particles that can move, then it is called a conductor, and if is not, then a dielectric. Those substances that can change the number of particles depending on some external factors are called semiconductors. In the usual metals, the charge is transferred by electrons, in electrolytes - cations and anions, and in gases, the electron s and ones.

Any conductor does not pass the stream of charged particles unhindered, but renders it certain resistance, which is physically explained by the fact that that particles collide with the conductor atoms, "loosen" them, losing their energy , and as a result energy electriccurrent is partially converted into the internal energy of the conductor, that is expressed in its heating.

The ability of the conductor to resist the flow of electric current is quite logical was called resistance.

As can be seen from the formula, the resistance depends on the resistivity, which refers to the reference data( it is invariant for a particular material), the length of the conductor and its cross-sectional area. The resistivities of different conductors can be seen in the table.

Obviously, for transmission of electrical energy, materials having the lowest resistivity - should be used then the percentage of losses will be low. These are aluminum, copper and steel of large cross-section for the manufacture of cables, wires, power lines. In electronics are used: silver, gold, tin, platinum.

If the conductors are to be used for heating, the properties harmful to the transfer of energy loss are very useful for obtaining heat, therefore materials with a high specific resistivity are chosen: tungsten, nichrome, galvanized steel, various alloys that the heater manufacturer can keep secret.

To assess the amount of thermal energy that a conductor can emit when an electric current flows through it, the Joule-Lenz law is applied, the was discovered in the 19th century.

According to this law, the amount of heat Q is equal to work A, and it directly depends on the square of the current strength - I, the resistance - R, and the time interval Δt.

From the of the schematic, is seen that in the closed circuit the current flows as measured by the ammeter, with it will be the same on each in its section. In the water tank there is a heating element R, whose resistance is greater than other conductors so that they can simply be neglected. According to of the Law of Joule-Lenz, at resistance R, will be allocated amount of heat, it will start to heat the water in the tank, while in other sections of the circuit heat will not be released. The rheostat can change the current in the circuit, and accordingly the amount of heat released will change.

It is the operation of this law that we see on the example of electric kettles, irons, boilers where the resistance of their thermoelectric heaters is TAN , much more than electrical wiring. Therefore, they allocate more heat. The heating cable is the same heater, only having a long length, so the heat is not generated locally but over the entire length of the cable. The heat generated by the cable is transferred to the for building structures, including the floor covering. Heating cables can be laid in the material of the screed, in tile glue, in special assemblies of metal. Leading power cables with low resistance are called "cold" or mounting ends.

Classification of heating cables

It would seem, which is easier? We need to take a material that has a high resistivity, make a cable out of it, calculate the heat it generates and everything is ready. But in fact this is far from the case, heating cables must meet the set of certain requirements, which will be discussed below.

The cable heating systems( CSR) can use completely different in design, materials used, the specific power of the cable, depending on the purpose:

• Room heating. First of all, the system " warm floor" is used, but still apply and warm walls and even warm ceiling. Usually electric warm floors make for comfort or additional heating in the makeweight of the main system. As the main source of heat, their use is not recommended because of unprofitable and in most cases unacceptable, since no power supply organization will issue a permit for the allocated capacity.

• Heating of the roof and drains is most effective by means of heating cables, as they save from expensive repair of the roof, and also exclude t equalism from falling icicles.

• Heating of the porch, stairs, ramps, entrance to the garage, space under the gateway to the entrance to the territory of the house. In winter, the benefits of comfort and safety with the change CSR in these places are palpable.

• Heating pipelines in private homes. It is always necessary to lay the pipes below the freezing depth of the ground, but it happens that in places of exit, passage through the foundation, even thermal insulation does not help to protect the pipes from freezing. Heating cables are the best salvation.

Resistive heating cable

The very name of this type of cable means that it is a resistive load - is a kind of elongated conductor with a constant resistance that is greater than the resistance of "cold cables": power and installation. Heating occurs by conductive copper or special alloy, heating conductors, prisoners in isolation. On top of the insulation the is necessarily applied a shield of copper braid or a foil sheath together with a drainage vein.

The screen performs very important functions:

• The screen reduces electromagnetic radiation, which is typical of any conductors with a current, especially variables.
• The screen is connected to the ground( PE conductor) , which is part of the potential equalization system( EMS).If the happens insulation breakdown, then the ki leakage will close on the screen, and go to the ground, which will protect the person from electric shock. In addition, this will trigger tripping of circuit breakers and residual current devices( RCDs).

Resistive cables in their design are:

• Single-core resistive cable - one conductor is used for heating. This is the most inexpensive type of heating cables required by t for a thorough installation, since the beginning and the end of this cable must converge at one point and be connected to special regulating devices - thermostats.
• A two-core heating cable in the central part has two cores, enclosed by in the screen. In this case, either the veins can be heating, or one of the heating wires, and the other conductor or its is called a return wire. At the end of the two-core cable section, there is a special end clutch that connects two heating conductors and an insulating cable. Advantages of a two-wire cable are obvious - for its packing it simply needs to be laid in a snake scheme, without need to return back to the thermostat. The level of electromagnetic radiation in a two-wire cable is much less than the of a single-core , since currents flow in counter currents in the heating conductors. Obviously, such cables are more expensive.

Resistive cables are sold ready-made sections that have a fixed length, which can not be changed categorically. Why? The fact is that the most important characteristic of any heating cable is the specific power allocated by one running meter of cable. It should be in the range of 10-20 W / and and in no case is more, since this will cause the to overheat the cable and break it. For example, when the resistive cable is shortened by half, the resistance is reduced by half, that according to the law of the Joule Lenz leads the to a twofold increase in the amount of heat, and the cable material is not calculated for this.

mounting kit The length of the section is selected based on the of the calculations. Manufacturers produce kits with a section length of 10 to 110 meters, so it is always possible to select the required cable with the required specific power. There are resistive cables on reels, from which the can cut any length, but it is the prerogative of specialists capable of making the necessary calculations.

Advantages of a resistive heating cable:

• Reasonable cost.
• Constancy of characteristics.
• The absence of starting currents does not require the use of special circuit breakers of type C.

The disadvantages of a resistive cable are:

• If there is an illiterate installation, there is a risk of local overheating that the will cause the to malfunction the cable.
• Unable to reduce the length of the heating cable without changing the characteristics.
• The cable needs to provide the required heat transfer parameters.

Resistance zone( sectional) cable

The evolution of the development of resistive heating cables has become invention zone( sectional) cable in which two low resistance conductors, of prisoners pass through the center in isolation. Pove px pr ovodnikov wound spiral of wire with high resistance. Through the , the defined ( usually 1 meter) , this wire is connected alternately to one and then to another central conductor. Obviously, in this case each section( zone) will be an independent heating element, like a parallel connection of resistors.

Advantages of zone cable:

• The same specific cable power over the entire length.
• Stability characteristics.
• When starting, does not consume large currents.

Disadvantages of Area Resistive Cable:

• Danger of local overheating.
• The need for to provide heat dissipation.
• Higher price compared to conventional resistive cables.

Heating mats

To facilitate the laying process of the warm floor, the manufacturer make special heating mats where the cable with the required step is attached to the polymer network. Such mats are very convenient to lay on a flat base before laying ceramic tiles. They can be mounted directly into the layer of tile glue, this is their main advantage. True, we must carefully monitor that there are no air cavities that will cause local overheating.

. In rooms with complex geometry, there can be difficulties in laying mats. This is their main drawback.

Self-regulating heating cable

A flagship among all heating cables is a self-regulating heating cable, which can change the heating temperature, and hence the heat release, depending on the ambient temperature.

A special polymer matrix with semiconductor properties is pressed between the two conductors. When the temperature is lowered, the matrix contracts, but in it many heat-conducting paths with high resistance are formed. The current that flows causes the matrix and cable to heat up. As the temperature rises, the polymer expands and the number of current paths decreases and, eventually, the moment when the currents become negligibly small, which leads to the termination of heating the cable. Each section of the cable works autonomously.

There is a layer of heat-resistant insulation on top of the semiconductor polymer, then a copper or steel shield and another one layer of insulation. Each cable has its dependence of running( specific) power on temperature and is selected based on operating conditions and purpose.

The advantages of self-regulating cables:

• The energy savings that occurs over account heating are not enough warm plots.
• Independence of the specific power from the cable length.
• This cable "forgives" installation errors. Even the cable overlap of the non- will cause the to overheat and malfunction.

Disadvantages of self-regulating cables:

• These cables have high starting currents, especially if there are long cold areas. This calls for the installation of Class C protective circuit breakers, which allow ten times the current jumps in comparison with the rated current.
• The polymer semiconductor matrix has a limited lifespan.
• High on such cables often makes their use a dubious benefit.

Heating cable as warm floor

When planning the arrangement of the electrical of a warm floor in the premises, you first need to decide what function it will perform.

Heating cable for warm flooring direct action

Warm flooring of direct action is usually located in a thin layer of screed just before the floor covering, for example in a layer of tile adhesive. The main task of such floors is a quick warming up of the floor surface to a comfortable temperature of 24-27 ° C.For this purpose, mats with a thin cable are ideal, as well as a resistive single-core or a two-core heating cable. You can see the required characteristics in the table.

The required installed power is achieved by the cable laying step, so that one square meter is packed with the same cable that will provide the required power. Depending on the area of ​​the room, the total length of the heating cable is calculated. The method of calculating for warm floor is given in a separate article on this topic.

In warm direct-acting floors, thermal insulation may not be used, or be of minimum thickness, since the task is to heat the surface rather than the main heating. When heating wooden floors, a heater is used between the lags, as well as a special metal mesh that distributes heat and a foil shield reflecting heat towards the floor covering.

Heating cable for heat accumulating warm floors

warm floors require mandatory thermal insulation, as they heat a concrete screed of considerable thickness: from 5 to 15 cm, which will accumulate heat. Such floors are better heated during reduced electricity tariffs, and at other times the heat will be gradually supplied to the premises. A thick layer of insulation will significantly reduce the heat leakage down.

Such floors are better to do in those rooms where the coatings with high thermal resistance will be laid: a parquet board, a laminate, a carpet. Then the transfer of heat will occur very gently, which will only increase comfort. Such a floor heating system can act as a basic heating.

The cable of the warm floor is laid in the middle layer of the screed, for a more even distribution of thermal energy. From the table, is seen that the cable for such a system should be used with a higher specific power in combination with a metal grid that will help distribute heat and be the reinforcing element of the screed. Given that the cable will be hidden in the thick layer of the screed that will provide heat dissipation, it is best to use a two-wire resistive cable with a specific power of 20 W / m for warm accumulating floors. A self-regulating cable can also be used, but its price is 3-5 times higher than the resistive one.

The use of such heating systems is limited for two reasons:

• The cost of heating with electric energy is still high compared to gas heating.
• The allocated for an apartment or a house of power can simply not suffice for heating accumulating of warm floors.

General requirements for heating cables warm floor

Temporary technical requirements from 2003 regulate the order of for the application of heating cables. Their this voluminous document will do the most important excerpts.

• For personal use, it is recommended to use CSR only for comfort and addition to the basic heating system.
• In warm floors of direct action and for heating of floors from a tree the cable should not have a nominal power more than 2 kilowatts.
• In thermo-accumulating floors and when heating external stairways and ramps, the maximum rated power of the cable is 4 kilowatts.
• The iron rule should be observed: one room - one cable. Exceptions are the premises of more than 25 square meters.m.
• The heating cable must not be moved to other rooms.
• The heating cable must not be laid under stationary furniture.
• Mounting strips and other accessories always come with the heating cables. It is them that should be used, no initiative is welcomed.

• The cable must be snake-shaped and must be observed rules :
  • Touch, intersect, twist and loop on the cable is not allowed.
  • From the boundaries of the stacking zone to the of the edges of the cable must be an distance, which is not less than the stacking step.
  • From metal structures and wiring elements, the cable must have a distance of at least 50 mm, from wooden structures - 30 mm, and from elements of other heating systems - not less than 500 mm.
  • The laying step should always be more than 6 - 10 outer diameters.
  • The distance between the sections of the laid cable must be greater than or equal to the stacking step.
  • All hot part of the cable must be in a homogeneous material.
  • For the cable inside the screed, the step is not more than 20 cm, and in direct action floors - 10 cm.
• All cables must be connected via a temperature controller with a temperature sensor. Direct connection to the network is allowed only in exceptional cases for self-regulating cables.

• The thermostat should be located 0.5-1.5 meters above the floor level.
• The floor temperature sensor should be located at a distance of at least 0.5 meters from the walls, connected only by a copper wire, placed in a corrugated plastic or metal tube.
• All connections of the heating and supply cables must be carried out on thermostats, in junction boxes and electrical panels using terminals. No twists are allowed.
• Power cables must be protected by circuit breakers of the appropriate ratings, and for protection of people it is mandatory to use an RCD with a differential current of no more than 30 mA .

• circuit-breaker. The installation of the CSR must only be carried out by qualified personnel having the appropriate approval.

Conclusion

• The heating cable is recommended for use with warm floors. The most preferred method of use is a direct heating system or a "thin floor".
• Among all the variety of heating cables, it is best to use a two-wire resistive cable in terms of price-quality ratio.
• The selection of the required cable with the required specific power, its length and stacking step is obtained as a result of the calculations of the .
• It is not allowed to change the length of the resistive cable section( except for the zone cable).

Video: Underfloor heating cable test

Video: Installation of a warm floor cable Devi

Video: Installation of heating mats