Calculation of pipes for floor heating: types of pipes, methods and step of installation + calculation of consumption
Despite the complexity of installation, floor heating with a water circuit is considered one of the most cost-effective methods of heating a room. In order for the system to function as efficiently as possible and not to fail, it is necessary to correctly calculate the pipes for a heated floor — determine the length, loop pitch, and contour laying scheme.
From these indicators depends largely on the comfort of using water heating.
Parameters for calculating the thermal circuit
At the design stage, it is necessary to solve a number of issues that determine the design features of the heated floor and the mode of operation. Technical aspects of the organization of the heating branch are largely dependent on its purpose.
In addition to the assignment, to accurately calculate the footage of the water circuit, you will need a number of indicators: the area of coverage, the density of heat flow, the temperature of the heat carrier, the type of floor covering.
Coverage area. When determining the dimensions of the base for laying pipes into account, a space is taken that is not cluttered with large appliances and built-in furniture. It is necessary to think in advance about the layout of objects in the room.
Heat flux density. This is a calculated indicator characterizing the optimal amount of heat energy for heating a room. The value depends on a number of factors: thermal conductivity of walls, floors, glazing area, the presence of insulation and the intensity of air exchange. Based on the heat flux, the step of laying the loop is determined.
Coolant temperature. The maximum rate is 60 ° C. However, the thickness of the screed and the floor covering bring down the temperature - in fact, about 30-35 ° C is observed on the floor surface. The difference between thermal indicators at the inlet and outlet of the circuit should not exceed 5 ° С.
Type of flooring. Finishing affects system performance.The optimal thermal conductivity of tile and porcelain - the surface heats up quickly. A good indicator of the efficiency of the water circuit when using laminate and linoleum without a heat-insulating layer. The lowest thermal conductivity of a wooden coating.
The degree of heat transfer depends on the fill material. The most effective system when using heavy concrete with natural aggregates, for example, sea pebbles of small fraction.
When calculating pipes for underfloor heating, it is necessary to take into account the established norms of the temperature regime of the coating:
- 29 ° С - living room;
- 33 ° С - rooms of high humidity;
- 35 ° С - passage zones and cold belts - sections along the end walls.
An important value for determining the density of laying the water circuit will play the climatic features of the region. When calculating heat losses, it is necessary to take into account the minimum temperature in winter.
As practice shows, to reduce the load will help pre-warming the whole house.It makes sense to first insulate the room, and then proceed to the calculation of heat loss and parameters of the pipe circuit.
Due to the non-standard operating conditions, high requirements are made to the material and size of the water floor coil:
- chemical inertness, resistance to corrosive processes;
- the presence of a completely smooth inner coating, not prone to the formation of lime build-up;
- strength - from the inside on the walls constantly affects the coolant, and outside - the screed; the pipe must withstand pressure up to 10 bar.
It is desirable that the heating branch had a small proportion. Pie water floor already exerts a significant load on the floor, and a heavy pipeline only exacerbates the situation.
Three categories of pipe rolled products meet one or another of the requirements listed above: cross-linked polyethylene, metal-plastic, and copper.
Crosslinked Polyethylene (PEX). The material has a net-rich cellular molecular structure.Modified from ordinary polyethylene is characterized by the presence of both longitudinal and transverse ligaments. Such a structure increases the specific gravity, mechanical strength and chemical resistance.
The water circuit made of PEX pipes has several advantages:
- high elasticity, allowing to lay the coil with a small bend radius;
- safety - when heated, the material does not emit harmful components;
- heat resistance: softening - from 150 ° С, melting - 200 ° С, burning - 400 ° С;
- maintains structure during temperature fluctuations;
- resistance to biological disrupters and chemical reagents.
The pipeline retains its original throughput capacity — no sediment is deposited on the walls. The estimated service life of the PEX circuit is 50 years.
The strength characteristics of PEX pipes depend on the method of crosslinking polyethylene. There are four groups of products:
- PEX-a - peroxide crosslinking. Achieved the most durable and uniform structure with a density of bonds up to 75%.
- PEX-b - silane crosslinking. The technology uses silanides - toxic substances that are not allowed for domestic use. Manufacturers of plumbing products replace it with a safe reagent. To install valid pipes with hygienic certificate. The density of crosslinking is 65-70%.
- PEX-c - radiation method. Polyethylene is irradiated with gamma rays or an electron. As a result, bonds are sealed to 60%. Disadvantages PEX-c: insecurity of use, uneven stitching.
- PEX-d - nitriding. The reaction to create a grid proceeds at the expense of nitrogen radicals. The output is a material with a crosslink density of about 60-70%.
Metal plastic. The leader of the pipe hire for arranging underfloor heating. Structurally, the material includes five layers.
The metal increases the strength of the line, reduces the rate of thermal expansion and acts as an anti-diffusion barrier - it blocks the flow of oxygen to the coolant.
Features of metal pipes:
- good thermal conductivity;
- the ability to retain a given configuration;
- working temperature with preservation of properties - 110 ° C;
- low specific weight;
- noiselessness of movement of the heat carrier;
- safety of use;
- corrosion resistance;
- Duration of operation - up to 50 years.
The lack of composite pipes - the inadmissibility of bending on the axis. With repeated twisting there is a risk of damage to the aluminum layer.
Copper. On the technical and operational characteristics of the yellow metal will be the best choice. However, its demand is limited to high cost.
In addition to the high cost, copper piping has an additional negative - the complexity of installation. To bend the contour, you need a press machine or a pipe bender.
Polypropylene and stainless steel. Sometimes the heating branch is made of polypropylene or stainless corrugated pipes. The first option is affordable, but fairly tough to bend - the minimum radius of the eight diameters of the product.
This means that pipes with a size of 23 mm will have to be placed at a distance of 368 mm from each other - an increased installation pitch will not ensure uniform heating.
Possible ways of laying the contour
In order to determine the flow rate of the pipe for arranging a warm floor, it is necessary to determine the layout of the water circuit.
Snake. The coolant is supplied to the system along the wall, passes through the coil and returns to the distribution manifold. In this case, half of the room is heated with hot water, and the remainder is cooled.
When laying a snake it is impossible to achieve uniformity of heating - the temperature difference can reach 10 ° C. The method is applicable in narrow spaces.
Double snake. Laying allows you to achieve a softer transition of temperatures. Forward and reverse loop runs parallel to each other.
Snail or spiral. It is considered the optimal scheme to ensure uniform heating of the floor covering. Forward and reverse branches are stacked alternately.
On large areas implement a combined scheme. The surface is divided into sectors and each develops a separate circuit leading to a common collector. In the center of the room, the pipeline is laid out by a snail, and along the outer walls - by a snake.
Step-by-step method for calculating pipes
In order not to get confused in calculations, we propose to divide the solution of the issue into several stages. First of all, it is necessary to evaluate the heat loss of the room, determine the laying step, and then calculate the length of the heating circuit.
Principles of construction of the scheme
Starting the calculations and creating a sketch, you should familiarize yourself with the basic rules for the location of the water circuit:
- It is advisable to lay the pipes along the window opening - this will significantly reduce the heat loss of the building.
- The recommended coverage area of one water circuit is 20 square meters. In large premises it is necessary to divide the space into zones and for each to lay a separate heating branch.
- The distance from the wall to the first branch is 25 cm. The permissible pitch of the turns of the pipes in the center of the room is up to 30 cm, at the edges and in cold zones is 10-15 cm.
- Determining the maximum pipe length for underfloor heating should be based on the diameter of the coil.
For a contour with a cross section of 16 mm, a maximum of 90 m is permissible, the restriction for a pipeline 20 mm thick is 120 m. Compliance with the norms will ensure normal hydraulic pressure in the system.
Basic formula with explanations
The calculation of the length of the contour of the heated floor is performed according to the formula:
L = S / n * 1.1 + k
- L is the desired length of the heating line;
- S is the floor area covered;
- n is the laying step;
- 1.1 - the standard factor of ten percent bending margin;
- k - collector distance from the floor - the distance to the wiring of the circuit at the flow and return flow is taken into account.
Decisive importance will cover the area of coverage and step turns.
It should be remembered that the placement of heating pipes is not recommended for large appliances and built-in furniture. The parameters of the designated items must be subtracted from the total area.
To find the optimal distance between the branches, it is necessary to carry out more complex mathematical manipulations, operating with the heat loss of the room.
Thermal calculation: determination of contour pitch
The density of placement of pipes directly affects the amount of heat flow from the heating system. To determine the required load, it is necessary to calculate the heat costs in winter.
The power of the heating system is determined by the formula:
M = 1.2 * Q
- M - circuit performance;
- Q - total heat loss of the room.
The value of Q can be decomposed into its components: energy consumption through the building envelope and the costs caused by the operation of the ventilation system. We will understand how to calculate each of the indicators.
Heat loss through building elements. It is necessary to determine the heat energy consumption for all enclosing structures: walls, ceilings, windows, doors, etc. Calculation formula:
Q1 = (S / R) * Δt
- S is the area of the element;
- R is thermal resistance;
- Δt is the difference between the temperature inside and outside.
When determining Δt, the indicator is used for the coldest time of the year.
Thermal resistance is calculated as follows:
R = A / Ct
- And - layer thickness, m;
- CT - coefficient of thermal conductivity, W / m * K.
For the combined elements of the structure, the resistance of all layers must be summed up.
Ventilation heat loss. For the calculation of the indicator formula is used:
Q2 = (V * K / 3600) * C * P * Δt
- V - volume of the room, cub. m;
- K - air exchange rate;
- C - specific heat capacity of air, J / kg * K;
- P - air density at normal room temperature - 20 ° С.
The air exchange rate of most rooms is equal to one. The exception is at home with internal vapor barrier - to maintain a normal microclimate, the air must be updated twice per hour.
Specific heat capacity is a reference. At standard temperature without pressure, the value is 1005 J / kg * K.
The total amount of heat loss of the room will be: Q = Q1 * 1.1 + Q2. Coefficient 1.1 - an increase in energy consumption by 10% due to the infiltration of air through the cracks, leaks in building structures.
Multiplying the obtained value by 1.2, we obtain the required floor heating power to compensate for heat losses. Using the graph of heat flow versus coolant temperature, you can determine the appropriate pitch and diameter of the pipe.
The data is relevant for warm floors on a sand-cement screed with a thickness of 7 mm, the coating material is ceramic tile. For other conditions, an adjustment of the values is necessary, taking into account the thermal conductivity of the finishing.
For example, when laying carpet, the value of the coolant temperature should be increased by 4-5 ° C. Each additional centimeter of the screed reduces the heat output by 5-8%.
Final contour length selection
Knowing the step of laying the coils and the covered area is easy to determine the flow of pipes. If the value obtained is greater than the allowable value, then it is necessary to equip several contours.
Optimally, if the loops have the same length, then nothing needs to be adjusted and balanced. However, in practice, more often there is a need to break the heating line to different areas.
An example of the calculation of the heating branch
Suppose you want to determine the parameters of the thermal circuit for a house of 60 square meters.
For the calculation will need the following data and characteristics:
- the dimensions of the room: height - 2.7 m, length and width - 10 and 6 m, respectively;
- The house has 5 metal-plastic windows of 2 square meters each. m;
- external walls - aerated concrete, thickness - 50 cm, Kt = 0.20 W / mK;
- additional wall insulation - foamed polystyrene 5 cm, CT = 0.041 W / mK;
- ceiling material - reinforced concrete plate, thickness - 20 cm, CT = 1.69 W / mK;
- attic insulation - expanded polystyrene plates 5 cm thick;
- the dimensions of the entrance door are 0.9 * 2.05 m, thermal insulation is polyurethane foam, a layer is 10 cm, CT = 0.035 W / mK.
Step 1 - calculation of heat losses at home through structural elements.
Thermal resistance of wall materials:
- aerated concrete: R1 = 0.5 / 0.20 = 2.5 square meters * K / W;
- expanded polystyrene: R2 = 0.05 / 0.041 = 1.22 sq.m * K / W.
Thermal resistance of the wall as a whole is: 2.5 + 1.22 = 3.57 square meters. m * K / W. The average temperature in the house is taken as +23 ° C, the minimum outside of 25 ° C with a minus sign. The difference is 48 ° C.
Calculation of the total area of the wall: S1 = 2.7 * 10 * 2 + 2.7 * 6 * 2 = 86.4 sq. M. m. From the resulting figure, it is necessary to take away the size of windows and doors: S2 = 86.4-10-1.85 = 74.55 sq. m. m
Substituting the obtained parameters into the formula, we obtain wall heat loss: Qc = 74.55 / 3.57 * 48 = 1002 W
The final thermal resistance of the ceiling is: 0.2 / 1.69 + 0.05 / 0.041 = 0.118 + 1.22 = 1.338 sq. M. m * K / W.Heat losses will be: Qп = 60 / 1,338 * 48 = 2152 W.
To calculate the leakage of heat through the windows, it is necessary to determine the weighted average value of the thermal resistance of materials: a double-glazed window - 0.5 and a profile - 0.56 square meters. m * K / W, respectively.
Ro = 0.56 * 0.1 + 0.5 * 0.9 = 0.56 m * K / W. Here, 0.1 and 0.9 is the share of each material in the window construction.
Window heat loss: Qо = 10 / 0.56 * 48 = 857 W.
Taking into account the thermal insulation of the door, its thermal resistance will be: Rd = 0.1 / 0.035 = 2.86 square meters. m * K / W. Qd = (0.9 * 2.05) / 2.86 * 48 = 31 W.
Total heat losses through the enclosing elements are equal: 1002 + 2152 + 857 + 31 = 4042 W. The result should be increased by 10%: 4042 * 1.1 = 4446 watts.
Step 2 - pheat input for heating incoming air. Volume of premises: 2.7 * 10 * 6 = 162 cu. m. Accordingly, the ventilation heat losses will be: (162 * 1/3600) * 1005 * 1.19 * 48 = 2583 W.
Step 3- determination of total heat loss. According to the parameters of the room, the thermal costs will be: Q = 4446 + 2583 = 7029 watts.
Step 4 - the required power of the thermal circuit to compensate for heat losses.
N = 1.2 * 7029 = 8435 W.
q = N / S = 8435/60 = 141 W / sq.m.
Step 5 - Defining the Stacking Step. The obtained value is compared with the dependency graph.If the temperature of the heat carrier in the system is 40 ° C, then a circuit with the following parameters will be suitable: pitch - 100 mm, diameter - 20 mm.
If water circulates to 50 ° C, then the interval between branches can be increased to 15 cm and a pipe with a section of 16 mm can be used.
Step 6 - calculation of the contour length. L = 60 / 0.15 * 1.1 = 440 m. Separately, it is necessary to take into account the distance from the collectors to the heating system.
As can be seen from the calculations, for the arrangement of the water floor will have to do at least four heating loops.
Conclusions and useful video on the topic
Visual video reviews will help to make a preliminary calculation of the length and pitch of the thermal circuit.
Selection of the most effective distance between the branches of the floor heating system:
A guide on how to find out the length of the loop of a heated floor:
The method of calculation can not be called simple. At the same time, there are many factors that affect the parameters of the circuit. If the water floor is planned to be used as the only source of heat, then this work is better to be entrusted to professionals - errors at the planning stage can be costly.