Today the most common types of «warm floors» are water and electric based. They each have advantages and disadvantages. In an electric floor, the main advantage is that it will not leak under any circumstances. But, like any appliance, with the electric cable in the «warm floor» there is a theoretical possibility of a short circuit. The systems of water «warm floor» are completely safe, electrically, but theoretically the pipes for the «warm floor» can be mechanically damaged and leak.
Under-floor heating provides more comfortable conditions than that of any other system — the warm flows are evenly distributed throughout the room (see Figure 99) and the temperature decreases evenly with height in the room, and these factors create comfortable conditions. The ideal temperature distribution in a room for people is a regime in which a person’s feet are slightly warmer than the head (floor temperature is between 22 and 25 C, and air temperature at head level is between 19 and 20 C). With floor heating, almost 70% of warmth is transferred in the form of heat radiation, which is not conducive to raising dust into the air. If the room air temperature is 20 degrees, the graph below shows that with floor heating a difference of temperatures between floor and ceiling is 1–2 degrees. With radiator heating the temperature difference is 6 — 8 degrees, but the colder air is at floor level and the warmer air at the ceiling. This is the reason for the strong air convection which contributes to taking dust from the floor and raising it. With floor heating, the reverse is true. The natural motion of air is limited and therefore there is not raising of dust and besides, there will be considerably less external air blowing into the room.
The contours of «warm floors» are made of copper and metal-plastic pipes in undetachable fitting connections. The ability of metal-plastic pipes to bend allows easy and simple installation of the heating contour. The low roughness coefficient, absence of corrosion, and lack of encrustation of the cross-section prevent large head loss, which is especially important for long heating contours. The floor heating system can be installed as a primary one or in a combination with other heating systems.
For the installation of the floor heating system, the following layout of schemes can be chosen (see Figure 100): spiral — the angles of the pipe turnings are 90 degrees, facilitating installation; «loops» or «snake» — «snake» is used when the distance between pipes allows them to be bent 180 degrees, pear-shaped «loops» are used in the cases when the distance between rows prevents bending at 180 degrees; a double spiral is used in large areas or when zoned heating of high capacity is needed, for example in front of the entrance door.
Due to the limited minimum bending radius of pipes, the first layout method is recommended when the distance between the rows of pipes is 225–300 mm. In the places where there is a need for a higher capacity of heating, under windows or in front of the entrance doors, more heating pipes need to be laid and in the places which have furniture, it is better not to have any pipes. Therefore the types of contours and the distance between pipes are combined — near the windows the pipes are close together and under the main area of the floor they are more widely spaced. When a more dense pipe layout is needed, then the 180 degree turns should be pear shaped in order to avoid flattening the pipes.
When calculating the density of the pipe layout, it is necessary to consider the temperature in each room, making a more dense layout in lower temperature zones. If you have a large number of pipes which are put close to each other, for example in corridors or near the collector, you should insulate some of them, especially the suuply ones, in order not to have a local surface overheating. In order for the bare foot not to notice the change of temperature zone, the distance between the pipes of the heating contour should not be more than 350 mm. In determining the quantity of heat, it is necessary to consider that the most comfortable temperature on the floor’s surface is 26–31 C. The floor temperature on the zones bordering windows or doors can be up to 35 C; in bathrooms and swimming pools, 33 C.
Typically in the heating contour a loss of pressure is permitted up to 0,2 bar. Therefore the total length of the contour pipes should not be more than 100 m and not more than 15–20 m² of floor should be heated by one contour. For heating large areas, several contours are used, putting them side by side, but connecting to different outlets of the collectors.