Repair and construction

Aerodynamic calculation of the chimney of the boiler room. Calculation of height and diameter

September 15, 2019

The chimney is an integral part of a single system, which includes a heat generating installation, air ducts and flues. The chimney ensures dispersion of harmful emissions in the atmosphere, contained in flue gases. Aerodynamic calculation of boiler room smoke pipe parameters must be carried out for that, so that the system performs its functions effectively and does not pose a threat to human health.

The selection of the pipe for the boiler room and its installation are made only in accordance with the results of preliminary calculations, for which special formulas or computer programs are used

How to calculate boiler room smoke pipe parameters using computer programs

Conducting an aerodynamic calculation of a smoke pipe for an industrial boiler room is a very complex and difficult process. Currently, similar calculations are carried out using various computer programs, which take into account many operating conditions of the equipment. The calculation is aimed at that, so that at the maximum load of the boiler room, the emission of the combustion residues of processed fuel goes unhindered through the pipe for further utilization in the atmospheric space. With the help of computer calculation, it is possible to reliably determine the minimum throughput of smoke pipes. Errors during such calculations are extremely undesirable, as they can turn into a dangerous accumulation of gases.

Calculation of the chimney using a computer program involves entering the declared indicators into the system, which are related:

  • to boiler capacity;
  • the gas formation temperature at the outlet specified in the passport. If this data is missing, it is customary to use the value c 200? WITH;
  • temperature outside. To turn on the heating, it can be reached +8? WITH, hot water supply — +20? WITH;
  • Efficiency of boilers of this type. In the absence of these data, contained in the equipment passport, the calculation is carried out with the value, equal 0,92;
  • coefficient of excess air mass for oppression. If no data is provided, then use the indicator 1,4;
  • type of fuel;
  • length of chimneys, coming from boiler equipment;
  • material, used to make a smoke pipe;
  • room temperature;
  • in the form of a chimney;
  • chimney dimensions, etc. d.

The type of pipe and its dimensions depend on the type of heating boiler and its power

After entering all the data, the computer program calculates the natural draft (Self-propelled). If it turns out, that large losses occur, then you need to make changes to the design, related to its form, diameter, height.

Indicators for practical aerodynamic calculation of the chimney

Chimneys of boiler houses and private houses with a solid fuel boiler (fireplaces) require a careful calculation taking into account a number of indicators:

  • climatic features of this area;
  • terrain and soil type, on which the building is erected;
  • regional seismic activity;
  • wind speed and precipitation rates, as well as critical values;
  • type of furnace masonry;
  • dynamic oscillations of the equipment;
  • material, from which a chimney will be built, and its temperature expansion;
  • type of fuel, its heat output;
  • technical characteristics, inherent boiler;
  • outlet gas temperature.

Operating with such data, can be calculated:

  • the height of the building;
  • optimal diameter;
  • permissible mass, which can have a rising chimney and, so, choose material, which is suitable for arranging the structure.

The results of the calculations will allow you to determine the diameter of the future chimney, its height and mass

Correctly calculated height and passability, selection of form and materials will contribute to natural traction, providing good heat transfer. The correct calculation is facilitated by the involvement of professional specialists. Manifestation of carelessness will turn into structural errors, as a result of which:

  • internal surfaces will be subject to excessive soot and ash deposition;
  • the internal cross-section will gradually decrease, which will lead to a weakening of the thrust and the penetration of carbonaceous gas formations into the interior;
  • the possibility of ignition of accumulated resins and deformation of the pipe will increase, caused by temperature changes;
  • fire hazard will increase.

Chimney for a boiler room: design and types (types)

It is impossible to calculate the height of the chimney of the boiler room and its other parameters without taking into account the features of its design, which consists:

  • foundation and support;
  • gas outlet barrel;
  • thermal insulation;
  • anti-corrosion protection;
  • device, that introduces gas ducts.

Bricks are used to build the chimney, ceramic, galvanized or stainless pipes

Flue gas, cool in a cleaning device - scrubber, to 60? WITH, undergoes purification in the absorber and is released into the atmosphere.

They can be used to build chimneys:

  • brick. Brick construction, installed ??professional bakers, practically does not accumulate soot. It has sufficient fire safety, mechanical strength and heat capacity. Given the destruction of bricks by reactions, occurring upon contact with sulfur oxides, which settle on the walls, with water, the use of brick structures decreased dramatically;
  • steel. Allows you to model the pipe configuration. It will last for about ten years, provided that fuel with a low sulfur content is used;
  • ceramics. Resistant to condensation, differs in fire resistance. But constructions, burdened with metal rods, characterized by excessive massiveness, which makes installation difficult;
  • polymers. They are used for installation on gas columns and in a boiler room with a temperature of no more 250? WITH.

Depending on the features of the supporting structure, smoke pipes can be:

  • self-supporting, made of sandwich tubes. They are easily mounted on roofs with fixing inside the structure and, if necessary, are transported, but have significant limitations in application - in terms of temperature (350 ° C), snow and wind load, level of chemical aggressiveness of combustion products;
  • columns. It is possible to install a multi-barrel steel structure with a diameter, which reaches three meters when connected to several boilers;
  • (Close) facade. The design is considered the most economical, as it does not require a powerful foundation and the use of load-bearing elements, and the use of modules ensures ease of replacement;
  • farm. They are applied, usually, in areas with increased seismic activity;
  • masts. The use of steel braces provides additional stability to the support tower of three or four masts with attached chimneys.

High pipes are subject to wind load, so you need to take care of additional fastening

How to calculate the height of the chimney

The correctness of the calculation of the height of the chimney affects the efficiency of the heating unit, speaking in the achievement of the necessary amount of natural thrust. According to regulations, which is specified by SNiP, the height cannot be less than five meters. Neglecting this indication leads to a drop in the level of natural draft and inefficient operation of the heating system. Installing a pipe that is too high, we will also reduce the natural draft, because the smoke, which passes through an excessively elongated canal, will cool down and move with decreasing speed. Incorrect calculations lead to air vortices and problems, associated with the zone of wind support. Even a fire in a furnace can be extinguished by strong gusts of wind.

Calculation, produced during the construction of industrial construction facilities, very complex and related to the introduction of a large number of different indicators. Determining the height of the chimney for a private construction site, it is advisable to follow the following recommendations:

  • the length must be at least five meters per segment, connecting the base and the highest point. With such a length, sufficient fire safety is ensured;
  • chimney, which is installed on a flat roof, should rise above its surface no less, than half a meter;
  • when erecting a chimney on a sloping roof, a pipe, located at a distance of less than one and a half meters from the grasshopper, is installed above it by half a meter. In this case, additional strengthening of the structure with stretchers to increase stability is mandatory, otherwise, it may be damaged by strong gusts of wind. At a distance of up to three meters from the ridge, the pipe is installed at the same height as it. If the distance exceeds three meters, then the angle between the horizontal line of the roof ridge and the virtual line, conducted between the ridge and the upper section of the chimney, must make 10 ?;
  • the distance between the pipe and tall trees and buildings should be more than two meters;
  • if the roofing material is combustible, then the height of the chimney should be increased by half a meter;
  • on a multi-level roof with height differences, calculations are based on the height of the ridge;
  • when the boiler room is located in the house extension, the pipe head must rise above the zone of wind support, located in space, to the given held at an angle v 45? a line from the top of the house to the surface of the ground.

If the roofing material does not have fire-resistant properties, the length of the outer part of the chimney should be increased

Documentation, which is added to the heating equipment, contains parameter values, affecting the selection of the height of the chimney.

Calculations are connected with the use of a formula:

Hmin = vA * Mi * F / (Inheritance * Sfi * vV * T)

This formula assumes the use of such parameters: A is the coefficient, which characterizes the regional meteorological situation; Mi are the masses of gas formations, passing through the chimney per unit of time; F — particle settling velocities, formed during combustion; Spdki and Sfi are indicators, reflecting the concentration level of substances, which contains flue gas; V — volume of gas; T is the difference in air temperature values ​​when entering the pipe and when leaving it.

How to calculate the diameter of the chimney

Determination of the required diameter of the smoke pipe is carried out for that, to calculate the thrust. If you know the power of the heating unit, you can rely on the recommendations, according to which:

  • if the power is lower 3,5 kw, then a chimney with a section of 0.14x0.14 m will be enough;
  • with a power of four to five kW, a section of 0.14x0.2 m will be optimal;
  • with a power of five to seven kW — 0.14x0.27 m.

Calculation of the chimney section requires the following data:

  • amount of fuel, consumed in one hour (information is contained in the equipment passport). This parameter is considered basic;
  • gas temperature indicators, that enters the pipe (as well as passport data, order 150-200 ° C);
  • chimney height;
  • speed of gas movement in the pipe, is usually taken for 2 m / With;
  • indicator of natural thrust, accepted, as a general rule, for 4Pa.

It is easy to calculate, by multiplying the height of the chimney by the difference in density of atmospheric air and combustion products.

You can use the following formula:

d2 = 4V /? W, In which:

d2 is the desired value of the cross-sectional area; V is the gas volume; W is the speed of gas movement in the pipe.

The formula for calculating the diameter:

S = m /? W, In which:

S is the cross-sectional area; m is the value consumed during an hour of fuel; ? — gas density in the chimney. Usually, simplifying calculations, it is taken as equal to air density; w is the velocity of gases in the chimney. In cases, when the value of the diameter of the chimney must be determined with high accuracy, it is better to seek the help of specialists, who have the necessary qualifications. To arrange a chimney for a private home, it will be enough to follow the recommendations of the most general nature.

Carrying out the aerodynamic calculation of the chimney, carried out quite competently, allows you to count on many years of successful functioning of the heating system. Having achieved good natural traction and high throughput, you can not worry, that the chimney will be clogged with soot and require repair. Competent calculations will determine the operation of the boiler equipment in full compliance with the requirements of environmental standards. A combination of two factors will be achieved, which provide existence, which corresponds to the norms of modern civilization — a comfortable temperature in heated rooms and the absence of harm to the environment and human health.