Calculation of heating excel. How to make a hydraulic calculation of the heating system. Purpose and progress of the calculation

Recently, an autonomous heating system has become more and more in demand. Most apartment owners refuse centralized heating, considering the individual system to be more reliable and of high quality. At the same time, quite often the main reason for choosing an autonomous heating system is its availability and efficiency. Of course, initially you will have to spend money on the purchase of the necessary equipment and installation of the system. However, all costs pay off quite quickly, since in the future the maintenance of such a system is much cheaper than the monthly payment for centralized heating. Of course, the cost-effectiveness of an autonomous system is only achieved if it has been properly selected and installed. In this regard, the hydraulic calculation of the heating system, which must be carried out in advance, is of great importance.

What is it for?

First of all, it should be understood that the old program for monitoring the functioning of the heating system differs significantly from the modern one precisely because of the different implementation of the hydraulic regime. In addition, modern heating systems are distinguished by the use of better materials and installation technologies - which is also reflected in their cost and efficiency. Moreover, a modern system allows you to control at all stages and notices even a slight temperature fluctuation.

A simple conclusion can be drawn: the use of a better, modernized modern system can significantly reduce the level of energy consumption, which, in turn, leads to an increase in the efficiency of the system. However, you should not mount the heating system yourself, since this process requires special knowledge and skills. In particular, problems often arise due to an incorrectly installed frame and refusal to carry out a hydraulic calculation of the heating system. What is important to consider when installing the system:

only in the case of a correctly performed installation, a uniform supply of coolant to all elements of the system will be carried out. And this indicator is a guarantee of balance between the regularly changing air temperature outside and inside the room.
minimizing the cost of operating the system (especially the fuel one) leads to the fact that the hydraulic resistance of the heating system is significantly reduced.
the larger the diameter of the pipes used, the higher the cost of the heating system will be.
the system must be not only reliable and well-established. An important factor is its noiselessness.

What information do we get after the hydraulic calculation of heating is made:

pipe diameter applicable in various parts of the system for its most efficient operation;
hydraulic stability of the heating system in different segments of the heating system;
type of hydraulic piping connection. In some cases, a special frame is used to achieve maximum balance of individual processes.
flow rate and pressure of the coolant during circulation in the heating system.

Of course, calculating the hydraulic resistance of a heating system is a rather costly process. However, it should be borne in mind that the correctness of its implementation makes it possible to obtain the most accurate information necessary to create a high-quality heating system. Therefore, it is most correct to involve a specialist, and not an attempt to make this calculation on your own.

Before the hydraulic calculation of the heating system is carried out online, the following data should be obtained:

balance of heat indicators in all rooms that will need to be heated;
the most suitable type of heating devices, draw their detailed location on the preliminary plan of the heating system;
determination of the type and diameter used for the installation of the pipe system;
development of a plan for the locking and guiding frames. In addition, it is important to think over to the smallest detail the location of all elements in the system - from heat generators to valves, pressure stabilizers and sensors for controlling the temperature level of the coolant;
creation of the most detailed plan of the system, which will indicate all its elements, as well as the length and load of the segments;
determine the location of the closed loop.

Example of calculation of heating hydraulics

Let us give an example of a hydraulic calculation of a heating system. Let's take a separate section of the pipeline, where stable heat loss is observed. The pipe diameter does not change.

This site should be determined based on data on the heat balance of the room in which it is located. It is important to remember that the numbering of sections starts from the heat source. We mark the connecting nodes present on the supply section of the highway in capital letters.

If there are nodes on the highway, they should be marked with a small stroke. We use Arabic numerals to determine the nodal points that are present in the branches of the branch. With a horizontal heating system, each of the points corresponds to the floor number of the building. In the case of a vertical system, the value of the point corresponds to the value of the riser. The nodes where the flow is collected should also be marked with strokes. It should be noted that the numbers must necessarily consist of two digits. The first of them means the beginning of the section, and the second, respectively, the end.

In the case of a vertical system, the numbering of the risers should be carried out in Arabic numerals, while following clockwise.

To determine the length of all sections of the pipeline, a pre-compiled detailed plan should be used. When creating it, an accuracy of 0.1 m should be adhered to. At the same time, the heat flow of the area in which the calculations take place is equal to the heat load given off by the coolant in this segment of the system.

Indicators of hydraulic calculation of the calculated circulation circuit, taking into account pressure losses due to local resistances in the sections

Use of programs

In the process of modeling a new building, the most rational is the use of a special program that determines the thermal and hydraulic characteristics of the future heating system as accurately as possible. Or you can use excel. The program provides the following information:

required diameter of the pipeline;
size of heating devices;
type of regulation of balancing valves;
adjustment level of control valves;
level of pre-regulation of thermostatic valves;
adjustment of pressure fluctuation sensors in the system.

Of course, it will be extremely difficult for an uninitiated user to independently calculate and hydraulically test the heating system. The most correct option is to contact a specialist who has sufficient experience in this field. In the case when there is no opportunity to involve a professional, you should carefully read the methodological literature, which describes the process of hydraulic calculation in as much detail as possible.

Heating based on the circulation of hot water is the most common option for arranging a private house. For the competent development of the system, it is necessary to have preliminary results of the analysis, the so-called hydraulic calculation of the heating system, linking the pressure in all sections of the network with pipe diameters.

The presented article describes in detail the calculation technique. To better understand the algorithm of actions, we examined the calculation procedure using a specific example.

Adhering to the described sequence, it will be possible to determine the optimal diameter of the line, the number of heaters, the boiler power and other system parameters necessary for arranging an efficient individual heat supply.

The determining factor in the technological development of heating systems has become the usual savings on energy. The desire to save money makes us take a more careful approach to the design, choice of materials, methods of installation and operation of heating for a home.

Therefore, if you decide to create a unique and, first of all, economical heating system for your apartment or house, then we recommend that you familiarize yourself with the calculation and design rules.

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As a result of the hydraulic calculation, we obtain several important characteristics of the hydraulic system, which provide answers to the following questions:

what should be the power of the heating source;
what is the flow rate and speed of the coolant;
what is the diameter of the main line of the heat pipeline;
what are the possible losses of heat and the mass of the coolant itself.

Another important aspect of hydraulic calculation is the procedure for balancing (linking) all parts (branches) of the system during extreme thermal conditions with the help of control devices.

There are several main types of heating products: cast iron and aluminum multi-section, steel panel, bimetallic radiators and covectors. But the most common are aluminum multi-section radiators.

The design zone of the pipeline line is a section with a constant diameter of the line itself, as well as an unchanging hot water consumption, which is determined by the formula for the heat balance of rooms. The enumeration of design zones starts from the pump or heat source.

Initial conditions of the example

For a more concrete explanation of all the details of the hydraulic miscalculation, let's take a specific example of an ordinary dwelling. We have a classic 2-room apartment in a panel house with a total area of 65.54 m 2 , which includes two rooms, a kitchen, a separate toilet and bathroom, a double corridor, a double balcony.

After commissioning, we received the following information regarding the readiness of the apartment. The described apartment includes walls made of monolithic reinforced concrete structures treated with putty and soil, windows made of a profile with two chamber glasses, tyrso-pressed interior doors, and ceramic tiles on the bathroom floor.

A typical panel 9-storey building with four entrances. There are 3 apartments on each floor: one 2-room apartment and two 3-room apartments. The apartment is located on the fifth floor

In addition, the presented housing is already equipped with copper wiring, distributors and a separate shield, gas stove, bathroom, washbasin, toilet bowl, heated towel rail, sink.

And most importantly, there are already aluminum heating radiators in the living rooms, bathroom and kitchen. The question regarding pipes and the boiler remains open.

How data is collected

The hydraulic calculation of the system is mostly based on calculations related to the calculation of heating for the area of the room.

Therefore, you need to have the following information:

the area of each individual room;
dimensions of window and door connectors (internal doors practically do not affect heat loss);
climatic conditions, features of the region.

We will proceed from the following data. Common room area - 18.83 m 2, bedroom - 14.86 m 2, kitchen - 10.46 m 2, balcony - 7.83 m 2 (total), corridor - 9.72 m 2 (total), bathroom - 3.60 m 2, toilet - 1.5 m 2. Entrance doors - 2.20 m 2, window showcase of the common room - 8.1 m 2, bedroom window - 1.96 m 2, kitchen window - 1.96 m 2.

The height of the walls of the apartment is 2 meters 70 cm. The external walls are made of B7 class concrete plus internal plaster, 300 mm thick. Internal walls and partitions - load-bearing 120 mm, ordinary - 80 mm. The floor and, accordingly, the ceiling are made of concrete floor slabs of class B15, thickness 200 mm.

Performing a hydraulic calculation of the heating system means choosing the diameters of individual sections of the network (taking into account the available circulation pressure) in such a way that the calculated flow rate of the coolant passes through them. The calculation is carried out by selecting the diameter according to the existing range of pipes.

For low-rise buildings, a two-pipe heating system is most often used, for high-rise buildings - a single-pipe heating system. To calculate such a system, the following initial data must be available:

1. The temperature difference of the coolant common to the system (i.e. the difference in water temperature in the supply and return lines).

2. The amount of heat that must be supplied to each room to provide the required air parameters.

3. Axonometric diagram of the heating system with heating devices and control valves applied to it.

Hydraulic Calculation Sequence

1. The main circulation ring of the heating system is selected (the most unfavorably located hydraulically). In dead-end two-pipe systems, this is a ring passing through the lower device of the most remote and loaded riser, in single-pipe systems - through the most remote and loaded riser.

For example, in a two-pipe heating system with an upper wiring, the main circulation ring will pass from the heat point through the main riser, the supply line, through the most remote riser, the lower floor heater, the return line to the heat point.

In systems with associated water movement, the ring passing through the middle most loaded riser is taken as the main one.

2. The main circulation ring is divided into sections (the section is characterized by a constant water flow and the same diameter). The diagram shows the section numbers, their lengths and thermal loads. The heat load of the main sections is determined by summing the heat loads served by these sections. Two values are used to select the pipe diameter:

a) a given water flow;

b) approximate specific pressure losses due to friction in the calculated circulation ring R Wed .

For calculation R cp it is necessary to know the length of the main circulation ring and the calculated circulation pressure.

3. The calculated circulation pressure is determined by the formula

Where - pressure created by the pump, Pa. The practice of designing a heating system has shown that it is most advisable to take a pump pressure equal to

, (5.2)

Where
- the sum of the lengths of sections of the main circulation ring;

- natural pressure that occurs when water is cooled in appliances, Pa, can be defined as

, (5.3)

Where - distance from the center of the pump (elevator) to the center of the device of the lower floor, m.

Coefficient value  can be determined from Table 5.1.

Table 5.1 - Meaning  depending on the calculated water temperature in the heating system

( ), 0 C	, kg / (m 3 K)

- natural pressure resulting from the cooling of water in pipelines.

In pumping systems with lower wiring, the value
can be neglected.

The specific friction pressure losses are determined

, (5.4)

where k=0.65 determines the proportion of pressure losses due to friction.

5. Water consumption at the site is determined by the formula

(5.5)

(t g - t o) - the temperature difference of the coolant.

6. By magnitude
And
standard pipe sizes are selected.

6. For the selected diameters of pipelines and estimated water flow rates, the speed of the coolant is determined v and the actual specific friction pressure losses are established R f .

When selecting diameters in areas with low coolant flow rates, there may be large discrepancies between
And
. underestimated losses
in these areas are compensated by an overestimation of the values
in other areas.

7. Friction pressure losses are determined in the calculated section, Pa:

. (5.6)

The results of the calculation are entered in Table 5.2.

8. Pressure losses in local resistances are determined using either the formula:

, (5.7)

Where
- the sum of the coefficients of local resistance in the calculated area.

Meaning ξ at each site are summarized in the table. 5.3.

Table 5.3 - Coefficients of local resistance

9. Determine the total pressure loss in each section

. (5.8)

10. Determine the total pressure loss due to friction and in local resistances in the main circulation ring

. (5.9)

11. Compare Δp With Δp R. The total pressure loss along the ring must be less than the value Δp R on

The reserve of available pressure is necessary for hydraulic resistance not taken into account in the calculation.

If the conditions are not met, then it is necessary to change the pipe diameters in some sections of the ring.

12. After calculating the main circulation ring, the remaining rings are linked. In each new ring, only additional non-common sections are calculated, connected in parallel with sections of the main ring.

The discrepancy of pressure losses in parallel connected sections is allowed up to 15% for dead-end water movement and up to 5% for associated water movement.

Table 5.2 - Results of hydraulic calculation for the heating system

, W

On the piping diagram

By preliminary calculation

By final settlement

Lot number

Coolant consumption G, kg/h

Section length l, m

Diameter d, mm

Speed v, m/s

Specific friction pressure loss R, Pa/m

Friction pressure loss Δp tr, Pa

The sum of the coefficients of local resistance ∑ξ

Pressure loss in local resistances Z

d, mm

v, m/s

R, Pa/m

Δp tr, Pa

Z, Pa

Rl+ Z, Pa

It should be noted that the engineering calculations of water supply and heating systems cannot be called simple, but it is impossible to do without them, only a very experienced practitioner can draw a heating system “by eye” and accurately select pipe diameters. This is if the scheme is quite simple and is designed to heat a small house with a height of 1 or 2 floors. And when it comes to complex two-pipe systems, you still have to calculate them. This article is for those who decide to independently calculate the heating system of a private house. We will present the methodology somewhat simplified, but in such a way as to obtain the most accurate results.

Purpose and progress of the calculation

Of course, you can turn to specialists for the results or use an online calculator, which is enough on any Internet resources. But the first costs money, and the second can give an incorrect result and it still needs to be checked.

So it's better to be patient and get down to business yourself. It must be understood that the practical goal of hydraulic calculation is the selection of the flow sections of pipes and the determination of the pressure drop in the entire system in order to choose the right circulation pump.

Note. When giving recommendations on how to perform calculations, it is assumed that heat engineering calculations have already been made, and radiators have been selected according to their power. If not, then you will have to go the old way: take the heat output of each radiator by the quadrature of the room, but then the accuracy of the calculation will decrease.

The general calculation scheme looks like this:

preparation of an axonometric diagram: when the calculation of heating devices has already been completed, then their power is known, it must be applied to the drawing near each radiator;
determination of coolant flow and pipeline diameters;
calculation of system resistance and selection of a circulation pump;
calculation of the volume of water in the system and the capacity of the expansion tank.

Any hydraulic calculation of a heating system begins with a diagram drawn in 3 dimensions for clarity (axonometry). All known data is applied to it, as an example, let's take the section of the system shown in the drawing:

Determination of coolant flow and pipe diameters

First, each heating branch must be divided into sections, starting from the very end. The breakdown is done by water consumption, and it varies from radiator to radiator. This means that after each battery a new section begins, this is shown in the example that is presented above. We start from the 1st section and find the mass flow rate of the coolant in it, focusing on the power of the last heater:

G = 860q/∆t, Where:

G is the coolant flow rate, kg/h;
q is the thermal power of the radiator in the area, kW;
Δt is the temperature difference in the supply and return pipelines, usually take 20 ºС.

For the first section, the calculation of the coolant looks like this:

860 x 2 / 20 = 86 kg/h.

The result obtained must be immediately applied to the diagram, but for further calculations we will need it in other units - liters per second. To make a transfer, you need to use the formula:

GV = G /3600ρ, Where:

GV – water volume flow, l/s;
ρ is the density of water, at a temperature of 60 ºС it is equal to 0.983 kg / liter.

We have: 86 / 3600 x 0.983 = 0.024 l / s. The need to convert units is explained by the need to use special ready-made tables to determine the diameter of a pipe in a private house. They are freely available and are called "Shevelev Tables for Hydraulic Calculations". You can download them by clicking on the link: http://dwg.ru/dnl/11875

In these tables, the values of the diameters of steel and plastic pipes are published, depending on the flow rate and speed of the coolant. If you turn to page 31, then in table 1 for steel pipes, the first column shows the flow rates in l / s. In order not to make a complete calculation of pipes for the heating system of a frequent house, you just need to select the diameter according to the flow rate, as shown in the figure below:

Note. In the left column under the diameter, the speed of water movement is immediately indicated. For heating systems, its value should lie in the range of 0.2-0.5 m / s.

So, for our example, the internal size of the passage should be 10 mm. But since such pipes are not used in heating, we safely accept the DN15 (15 mm) pipeline. We put it on the diagram and go to the second section. Since the next radiator has the same capacity, there is no need to apply the formulas, we take the previous water flow and multiply it by 2 and get 0.048 l / s. Again we turn to the table and find the nearest suitable value in it. At the same time, do not forget to monitor the speed of the water flow v (m / s) so that it does not exceed the specified limits (in the figures it is marked in the left column with a red circle):

Important. For heating systems with natural circulation, the speed of the coolant should be 0.1-0.2 m / s.

As you can see in the figure, section No. 2 is also laid with a DN15 pipe. Further, according to the first formula, we find the flow rate in section No. 3:

860 x 1.5 / 20 = 65 kg / h and convert it to other units:

65 / 3600 x 0.983 = 0.018 l / s.

Adding it to the sum of the costs of the two previous sections, we get: 0.048 + 0.018 = 0.066 l / s and again refer to the table. Since in our example we do not calculate the gravitational system, but the pressure system, then the DN15 pipe is suitable for the speed of the coolant this time too:

Going in this way, we calculate all the sections and apply all the data to our axonometric diagram:

Calculation of the circulation pump

The selection and calculation of the pump is to find out the pressure loss of the coolant flowing through the entire pipeline network. The result will be a figure showing how much pressure the circulation pump should develop in order to “push” water through the system. This pressure is calculated by the formula:

P = Rl + Z, Where:

P - pressure loss in the pipeline network, Pa;
R is specific friction resistance, Pa/m;
l is the length of the pipe in one section, m;
Z is the pressure loss in local resistances, Pa.

Note. Two - and one-pipe heating systems are calculated the same way, along the length of the pipe in all branches, and in the first case - the direct and return lines.

This calculation is quite cumbersome and complicated, while the value of Rl for each section can be easily found using the same Shevelev tables. In the example, the blue circle marks the values of 1000i in each section, it only needs to be recalculated along the length of the pipe. Let's take the first section from the example, its length is 5 m. Then the friction resistance will be:

Rl \u003d 26.6 / 1000 x 5 \u003d 0.13 bar.

We also calculate all sections of the associated heating system, and then summarize the results. It remains to find out the value of Z, the pressure drop in local resistances. For the boiler and radiators, these figures are indicated in the product passport. For all other resistances, we advise taking 20% of the total friction loss Rl and summing up all these indicators. We multiply the resulting value by a safety factor of 1.3, this will be the required pump pressure.

You should be aware that the performance of the pump is not the capacity of the heating system, but the total water consumption for all branches and risers. An example of its calculation is presented in the previous section, but for the selection of a pumping unit, it is also necessary to provide for a margin of at least 20%.

Expansion tank calculation

To calculate an expansion tank for a closed heating system, it is necessary to find out how much the volume of liquid increases when it is heated from room temperature +20 ºС to working temperature, which is in the range of 50-80 ºС. This task is also not easy, but it can be solved in another way.

It is considered quite correct to take the volume of the tank in the amount of a tenth of the total amount of water in the system, including radiators and the water jacket of the boiler. Therefore, we open the equipment passports again and find in them the capacity of 1 section of the battery and the boiler tank.

Further, the calculation of the volume of the coolant in the heating system is carried out according to a simple scheme: the cross-sectional area of \u200b\u200bthe pipe of each diameter is calculated and multiplied by its length. The obtained values are summed up, passport data are added to them, and then a tenth is taken from the result. That is, if there is 150 liters of water in the entire system, then the capacity of the expansion tank should be 15 liters.

Conclusion

Many, after reading this article, may abandon the intention to consider hydraulics on their own due to the sheer complexity of the process. The recommendation for them is to contact a practitioner. Those who have shown a desire and have already calculated the heat output of heating for a building will certainly cope with this task. But the finished scheme with the results is still worth showing to an experienced installer for verification.

Comfort in a country house largely depends on the reliable operation of the heating system. Heat transfer during radiator heating, the "warm floor" and "warm plinth" systems is ensured by the movement of the coolant through the pipes. Therefore, the correct selection of circulation pumps, shut-off and control valves, fittings and the determination of the optimal diameter of pipelines is preceded by a hydraulic calculation of the heating system.

This calculation requires professional knowledge, so we are in this part of the training course "Heating systems: selection, installation", with the help of a REHAU specialist, we will tell you:

What nuances should be known before performing a hydraulic calculation.
What is the difference between heating systems with dead-end and passing movement of the coolant.
What are the goals of hydraulic calculation.
How the material of the pipes and the way they are connected affects the hydraulic calculation.
How special software allows you to speed up and simplify the process of hydraulic calculation.

Nuances to be aware of before performing a hydraulic calculation

Sergey Bulkin

With the help of these programs, you can make a hydraulic calculation, determine the control characteristics of shut-off and control valves, and automatically draw up an order specification. Depending on the type of programs, the calculation is carried out in the AutoCAD environment or in its own graphics editor.

We add that now in the design of industrial and civil facilities there has been a trend towards the use of BIM technologies (building information modeling). In this case, all designers work in a single information space. To do this, a "cloud" model of the building is created. Thanks to this, any inconsistencies are identified at the design stage, and the necessary changes are made to the project in a timely manner. This allows you to accurately plan all construction work, avoid delaying the completion of the facility and thereby reduce the estimate.