Designing cable heating
The main differences in electric underfloor heating are the heating elements, which consist of cables or cable sections. Consider varieties and calculation methods.
Resistive heating cable is a heating element of one or two-core cable in a protective shield, with a constant resistance, which is laid over the area of the floor.
The cable has a standard length, and therefore the resistance and generated heat. The length of the cable must not be changed, this will change the current and cause malfunction.
Specific wattage and length
This is the wattage of one square meter of Lenovo wire.m of underfloor heating. Under this figure is selected the length of electric heating cable.
For example, the power of the cable system for proper heating should be about 100-150 W/m2; if the floor heating is to be used as the main heating, you need 150-200 W/m2. If we need to heat 10 m2, we need a cable with a capacity of 10100 = 1000 watts.
It will already depend on its cross section. The thicker the wire, the greater its power, and the greater will be the pitch of the installation. A thinner wire has to be installed in shorter lengths to meet the watt density selected, so the cable consumption will be higher.
For ease of calculation and laying electric TP are sold in the form of mats, rolled up in a roll. The cable in them is laid in a snake with a certain pitch and fixed. The width of such a “mat” cannot be changed; as a rule, it is equal to 50 cm. It turns out that the specific power is given by the manufacturer, for example 130 W/m2. The customer only needs to choose the appropriate heating element area from those available on the market.
How to do the calculation of the length of the pipe and the power of the floor heating without a calculator?
To create the optimum comfort conditions in each room, it is necessary to determine the “need” for heat. It is calculated in kilowatts. Thus calculation of water heating floors is carried out on the area without a calculator and complex calculations. Take into account that:
- 1m3 volume of space needs 40 watts of heat;
- Each window in the room adds 100 watts, and the door 200 watts (entrance);
- the first and last floors increase the heat consumption of underfloor heating by 1.2-1.4 (compensation factors).
By simple calculations, experts have calculated that in the laying of pipes with a pitch of 25 cm every 1 m2 of the system generates 82 watts of heat. Now knowing how much pipe you need for 1m2 of underfloor heating, you can vary the size of the step to achieve optimal conditions. That is, when the distance between the coils is 15 cm get 101 watts, 10 cm. respectively, 117 watts. To make it easier for you to calculate the heat output of the underfloor heating per square meter when using non-standard steps, we provide a table of dependencies.
How to calculate the pipe spacing of 16 and 20 mm for underfloor heating
Systems for underfloor heating are installed in cottages, private homes. They have replaced the bulky radiators. In order for the heating to work effectively, you need to take into account a number of features of the installation, to correctly calculate the distance between the pipes of the underfloor heating. If the project is not designed properly, the heat will not spread evenly around the premises, heating will work in idle mode.
Spacing of underfloor heating pipes
Builders use four common piping layouts, each better suited for use in a differently shaped room. Their “pattern” to a large extent determines the maximum length of the floor heating circuit. This:
- “Serpentine”. Consecutive laying, where hot and cold lines go one after another. Suitable for elongated rooms with separation into zones of different temperatures.
- “Double serpentine.”. Used in rectangular rooms, but without zoning. Provides uniform heating of the area.
- “Corner serpentine”. Consistent system for rooms with equal wall lengths and low heat zone.
- “Snail”. Twin laying system, suitable for approximate square shaped rooms without cold areas.
The chosen installation option has an impact on the maximum length of the water floor, because it changes the number of pipe loops and the bend radius, which also “eats” a certain percentage of the material.
Construction and materials of underfloor heating
Fig. 1. The design of “wet” underfloor heating (example): 1. floor foundation (floor slab); 2. vapor barrier; 3. heat insulation layer (polystyrene foam); 4. cement-sand or concrete screed; 5. glue layer; 6. finish floor covering; 7. damper tape; 8. wire mesh; 9. floor heating pipes.
Fig. 2. Construction of “dry” warm floor (example): 1. buckling on the joists; 2. vapor barrier; 3. layer of insulation (polystyrene foam); 4. joists; 5. floor; 6. base bars; 7. heat spreading plate; 8. floor heating pipes; 9. GFB layer; 10. floorboard; 11. skirting.
The maximum length of the floor heating pipe for each circuit is calculated separately. To get the required value you will need the following formula:
Values are specified in meters and mean the following:
- W. width of the room.
- E. room length.
- Shu. “pitch of laying” (distance between loops).
- K is the distance from the collector to the connection point to the circuits.
The resulting length of the floor heating loop is additionally increased by 5%, which includes a small margin for leveling errors, changes in the bending radius of the pipe and connection to fittings.
As an example of calculating the maximum pipe length for underfloor heating for 1 circuit, let’s take a room of 18 m2 with sides of 6 and 3 m. The distance to the collector is 4 m and the laying pitch is 20 cm, we get the following:
5 % are added to the result, which is 4.94 m and the recommended length of the water floor heating loop is increased to 103.74 m, which is rounded to 104 m.
The efficiency of the heating system depends on the properly laid contour To maintain a given temperature regime in the room, it is necessary to correctly calculate the length of loops used to circulate the coolant.
First it is necessary to collect the initial data, on the basis of which the calculation will be made, and which consist of the following indicators and characteristics:
- the temperature that should be above the floor covering;
- Layout of loops with heat carrier;
- the distance between the pipes;
- the maximum possible length of the pipe;
- the possibility of using several different lengths of circuits;
- Connection of several loops to one manifold and one pump and the possible number of loops in this connection.
Based on the data listed above, you can perform the correct calculation of the length of the floor heating circuit and thereby ensure a comfortable temperature regime in the room with minimal energy costs.
Current pipe types for underfloor heating.
Underfloor heating is well-proven, not only in mild, but also in cold climates. Pipes for warm water floor heating can be applied instead of usual batteries or used together with them.
Example of floor layout
Today, a wide range of pipes for underfloor heating is available for sale. The following factors should be considered when purchasing them:
- Timing and operating characteristics.
- Thermal conductivity.
- Chemical resistance.
- Difficulty and peculiarities of installation.
- Manufacturer’s reputation.
On the choice of pipe, affects the price range, quality and the ability to use certain varieties of materials. A pipe for a warm water floor, and expendable material (made of black metal). after a few years, will fail. In the case of a leak, you will have to change the entire structure.
For underfloor heating pipes are chosen exclusively for heating. Diameter usually from 16 mm to 18 mm. They should be purchased from well-known manufacturers
Pay attention to the originality and availability of certificates
In the manufacture of different materials are used:
SlimFix low profile underfloor heating installation by Continal Underfloor
Regardless of all kinds of developments and the emergence of other raw materials, copper will still be universal and in demand as a pipe material. They have a fairly large heat output, resistance to corrosion. These products can withstand both low (-100 ° C) and high (250 ° C) temperatures well. Observing all the requirements of the manufacturer in operation, they are able to last quite a long time (up to 50 years). This makes up for their high cost.
Stainless steel pipes also have a practically unlimited service life. However, rubber seals, fail within 30 years. Corrugated pipes made of stainless steel, have a high cost.
Metal plastic. is a reliable and inexpensive material. Products made of it will be a good alternative to both copper and non-rusting pipes. This material has the following properties:
Metal plastic pipes are made by bonding multiple layers:
Polymer material, is the outer and inner, absolutely smooth protective layer. Aluminum. acts as a coolant. The service life of the pipe depends on the condition of the adhesive layer. When it breaks down, fluid leaks where the layers separate from each other. Metal plastic pipes, checked by heating them to 90. 100 ° C. If the structure does not change at the cut, then the pipe is made according to standard.
Another budget-friendly material is polypropylene. Products made of this material are subject to little corrosion. They are not sensitive to negative influences in contact with cement mortars. Their service life is up to half a century.
One of the most common materials is so-called cross-linked polyethylene. The reason for this is its good flexibility. Even products with a relatively large diameter of up to 20 mm can easily be installed in relatively small spaces. Marked as PE RT and PEX.
How the pipe length is calculated
Traditionally 5 m of pipe are assumed to be sufficient for heating one m² of floor (see chart above). table above). The nominal distance in this case will be 200 mm. Based on this ratio, you can calculate the nominal length of the entire pipeline: multiply the total area of the room by 5 and round up.
For corner rooms with one window it is better to increase this length by 20% (by 1.2), with two windows. by 30% (1.3). For northern regions of the Russian Federation, multiply the resulting length by another 20% (by 1.2).
For example, for a corner room of 20 m² with two windows and in a cold region of Russia, the length of the pipeline will be:
This calculation uses the total area of the room without deducting the area of large pieces of furniture. This is done because the air above the sofas (and even cabinets) must also be heated, some of the heat is spent on heating the furniture itself. If you calculate with a smaller area, it will be cool in the room, and in a small room full of furniture can be simply cold.
When buying, you need to add a small margin for bends and inaccuracies (6%, or a factor of 1.06) and double the distance from the collector to the room.
Determining the maximum length of a single circuit
The maximum length of one circuit under no circumstances should not exceed 100 m. otherwise the pump simply does not press the coolant into the circuit. And a hundred-meter circuit is better to divide into two. heating will improve, and in case of excessive heating you can always adjust the heating of each circuit with a three-way valve in the manifold node.