“Keep your head cold and your feet warm” is a folk wisdom to keep you he althy. This proverb is put into practice by underfloor heating - one of the most technologically advanced types of space heating. But in order for the system to fulfill its duties, it is necessary to calculate the warm water floor, taking into account the operating conditions.
What is a warm water floor
This type of space heating became widely used in Europe in the 80s of the last century. It was then that the mass production of polypropylene pipes began, which served as an impetus for the installation of such systems.
Warm water floor is a structure of pipes connected together inside a concrete screed. The water circulating inside evenly warms the floor, and he? in turn heats the room air. The water temperature is 26-40°C, which creates a comfortable temperature.
This heating works from boilers of any kind. But more often used gas. Temperature inThe system is controlled by sensors installed in the room, as well as thermal mixing valves.
Pros and cons
The basis is pipes made of polypropylene, metal-plastic, copper, corrugated stainless steel. Steel pipes are rarely used due to the complexity of installation and the high cost of the material. This type of heating has the following advantages:
- The room warms up evenly throughout, and not locally, as when using radiators.
- Heating from the very bottom creates an air temperature that is the same at any height.
- Small amount of heat allows you to use different types of flooring.
- During the hot season, the water system can be used to remove excess heat from the room.
However, you need to take into account the fact that the water floor in its design is more complicated and more expensive than radiator heating. You also need to understand that it will not work to install the system in an apartment building, because the consumer is forbidden to connect personal heating equipment to the engineering systems of the house.
Based on the above, we can conclude that this heating is suitable for private homes. But before you mount it, you need to make a calculation of a warm water floor.
Initial data
The starting point for calculating a pipe for a warm water floor is the determination of the heat loss of a house per unit of time. The house consists of many elements, each of which has its own heat transfer. To find out how much heat a building loses, you need to add up the heat losses of walls, floors, ceilings, windowsand doorways. To the resulting number must be added the losses associated with the ventilation of the room. This is another 10 to 40%. The calculation is made for the coldest time of the year.
Building materials have different heat transfer. Therefore, the main task is to determine how much heat goes outside through each square meter of the building. Knowing the heat loss, you can choose the power of the boiler and calculate the length of the warm water floor. In addition, the thermal conductivity of the concrete screed and flooring is taken into account, which will retain heat.
Summing up, you need to list the parameters that are taken into account in the design:
- Floor temperature. It must be heated up to +30 °C. This temperature should not be confused with the coolant temperature, which is naturally higher.
- The part of the floor adjacent to the outer walls should be heated to +35 °C to compensate for heat dissipation through walls and windows.
- In all places with high humidity (bathrooms, rooms for drying clothes), the floor temperature should be at least +33 °C.
- Pipe laying configuration. This takes into account the mounting distances between the branches.
- Materials from which the house is built.
- Floor covering. The higher its thermal conductivity, the more quickly the floor and the room will heat up. The most optimal materials are tiles, porcelain stoneware, marble slabs. Materials made from wood, as well as from its waste, do not transfer heat well.
Heat floor construction
The warm floor has a complex structure. In construction, it is called a pie because of the largenumber of layers. It consists of:
- Bearing base. It can be a subfloor or a concrete floor slab.
- Waterproofing from a layer of polyethylene film, limited along the contour by a damper tape.
- Heat-insulating layer. It does not allow heat to escape under the floor.
- Pipes serving as a conductor of coolant.
- Concrete screed.
- Floor covering.
Varieties of pipe laying
Before starting the design, a warm water floor is calculated. The length of the pipe is the main characteristic that needs to be established. It depends on the required thermal power and on the material of the pipes, which have a different coefficient of thermal conductivity. The higher it is, the shorter the pipe can be used. The highest coefficient for copper pipe. However, it is rarely used due to its high cost. The water circuit, depending on its length, is performed in several ways:
- Snail. The pipe in double addition is laid in a spiral starting from the center of the room to the periphery. The distance between adjacent branches is taken equal to 100 mm. This method is good because in a room of any size the floor has the same temperature.
- Snake. The pipe is laid out in parallel branches, successively filling the area of the room. This type of laying is simpler, but it has a drawback: the floor temperature changes depending on the distance from the coolant source. In a large room, the difference can be up to 10°C due to the gradual cooling of the water.
The location of the water circuit is first drawn on paper with markings. Then, according to the scheme, the required pipe length is found.
Calculation of the length of the pipe of a warm water floor
To calculate the length of the thermal circuit, 3 parameters are needed: room area, laying step, pipe bending coefficient. The formula for the calculation will look like this:
L=S/N x 1, 1, where L is the length of the circuit, S is the area of the room, N is the distance between the turns.
From the distribution manifold to the return line, the circuit is laid in a single cut. The thicker the pipe, the higher the heat transfer. Sizes from 16 to 25 mm are used. Concrete screed is made no more than 60 mm. If you do more, then the heat will be absorbed by the concrete pad.
What temperature should the coolant have
The temperature of the water in the circuit depends on the temperature of the water jacket of the boiler. For the normal operation of a solid fuel boiler, it is required that the carrier temperature does not fall below 55 °C. Therefore, the calculation of the power of a warm water floor is based on this figure. This temperature is enough to warm the room up to 25-27 °C.
The amount of water passing through the system depends on the thickness of the pipe as well as the power of the pump. On average, this is 2 l / min per 10 sq. m.
The room temperature is reduced by reducing the capacity of the supply manifold.
Heat power calculation
Calculation of a warm water floorproduced to determine the required heat output. The materials of the building and the configuration of the rooms are taken into account. The dependence of power on the heat loss of the house is expressed in the formula:
Mp=Q x 1, 2, where Q is the total heat loss of the room in watts. Coefficient 1, 2 indicates that there should be a power margin when designing the circuit.
To determine the heat loss, the materials from which the ceilings, windows, doorways are made, as well as their area, are taken into account. The thermal conductivity of materials is taken from the tables.
Floor heat loss is not taken into account. The area of wall ceilings is measured on the outside, taking into account the corners. The heat loss of each part of the room is calculated as follows:
Q=1/R x (t in - t n) x S x (1+ ∑β), where:
- R - thermal resistance of the material from which the ceiling is made. It is obtained by multiplying the tabular value of the resistance coefficient by the thickness: R=δ / λ;
- t in - the desired indoor temperature, t n - the minimum temperature in the region;
- S - overlap area, calculated by multiplying the width by the length. ∑β - the sum of heat losses associated with the location of the building relative to the cardinal points. You can also add wind direction losses to this category.
Calculation example
Specific option makes it clearer how formulas are applied. Take for example a wooden room with a total wall area of 80 square meters. m. The maximum temperature in winter is -35 ° C,room temperature +25 °C. Let's perform the calculation for warm water floors, the installation of which is planned in the northwestern part of the house:
- Find the thermal resistance (R) of the wall slabs. The value of λ is taken from tabular data. For wood, it equals 0.14 m² x C° / W. Divide by 0.2m wall thickness to get 0.7m² x C°/W.
- Find the total heat loss of the walls of the room. Q=1 / 0.7 x (25 - (-35)) x 80 x (1 + 0, 1)=7542 W.
R for the ceiling is calculated based on the thermal resistance of the ceiling insulation. The area is taken equal to the floor area. In addition, there is a similar heat loss for windows and doorways. The sum of all found values will be the total heat loss of the room. The resulting figure must be increased by 1.2 times. This product will be the required power of underfloor heating.
If the design of the water circuit does not provide the desired heat transfer, then in this case additional heaters are installed to compensate for the missing power.
Computer calculation
To avoid studying thermal conductivity tables, you can calculate a warm water floor in the V altec program. It is free and does not require registration. In addition to heating, it can calculate data on water supply, sewerage, hydraulics. And also calculate the aerodynamics of the chimney.
In addition to computer programs on the Internet, there are online calculators that, given the size of the room, draw up a laying schemepipes for underfloor heating, and also make the calculation of underfloor heating by area.
Another kind of calculator determines the cost of underfloor heating based on the heated area, pipe pitch, materials used. Such a program is more suitable for budgeting.
