Express analysis of a water heating system in Excel. Hydraulic calculation of the heating system of a private house

IN apartment buildings most of the regions Russian state As a rule, central heating is used, but recently autonomous heating systems have begun to gain popularity. For both the first and second cases, a hydraulic calculation of the heating system is required.

Hydraulic calculation

The practical goal of calculating the hydraulics of a heating system is to ensure that the flow rate in the circuit elements matches the actual flow rate. The volume of coolant entering the heating devices must form a certain temperature regime inside a private house, taking into account the external temperatures and those set by the customer for each room, according to its functional purpose.

To correctly carry out hydraulic heating calculations, you will need to study the basic terminology in order to better understand the processes occurring within the system. For example, an increase in the speed of a heated working fluid can provoke a parallel increase in hydraulic resistance in pipelines. The resistance of the heating system is measured in meters of water column.

The main mistakes in installing home heating. Home heating systems.

Most classic heat supply schemes consist of the following mandatory elements:

1. 1. heat generator;
2. 2. main pipeline;
3. 3. heating elements (registers or radiators);
4. 4. hydraulic valves (shut-off and control).

Using adjusting fittings, alignment is carried out heating system. Each element has its own individual technical specifications, which is used for hydraulic calculations of the heating system. Online calculator or excel spreadsheet with formulas and calculation algorithms will be able to greatly simplify this task. These programs are provided absolutely free of charge and will not affect the project budget in any way.

How to perform hydraulic tests of heating systems

Pipe diameter

To calculate the hydraulics of a heating system, you will need information on thermal calculations and an axonometric diagram. To select the cross-section of pipes, those that are expedient from an economic point of view are used. final heat calculation data:

To determine the internal diameter of each section, use a table. Previously, each heating branch is divided into segments starting from the very end point. The breakdown is based on coolant flow, which varies from one heating element to another. A new segment starts after each heating device.

In the first segment, the value of the mass flow rate of the coolant is determined, starting from the power indicator of the last battery: G = 860q / ∆t, where q is the power of the heating element (kW).

The coolant in the first section is calculated as follows: 860 x 2 / 20 = 86 kg/h. The results obtained are directly plotted on the axonometric diagram, however, in order to continue further calculations, the resulting final value will need to be converted into other units of measurement - liters per second.

To perform the conversion, use the formula: GV = G / 3600 x ρ, where GV is the capacitive liquid consumption (l/sec), ρ is the coolant density indicator (at a temperature of 60 ºC it is 0.983 kg/liter). It turns out: 86 ÷ 3600 x 0.983 = 0.024 l/sec. The need to convert the measure physical quantity is justified by using tabular values, with the help of which the cross-section of the pipeline is determined.

Hydraulic calculation of water supply systems in Revit (Revit+liNear Analyze Potable Water)

Definition of resistance

Engineers are often faced with calculations of heat supply systems large objects. Such systems require a large number of heating devices and hundreds of linear meters of pipes. You can calculate the hydraulic resistance of a heating system using equations or special automated programs.

To determine the relative heat loss for adhesion in the line, the following approximate equation is used: R = 510 4 v 1.9 / d 1.32 (Pa/m). Application given equation justified for speeds of no more than 1.25 m/s.

If the consumption value is known hot water, then an approximate equation is used to find the cross-section inside the pipe: d = 0.75 √G (mm). After receiving the result, you will need to refer to a special table to obtain the cross-section of the nominal diameter.

The most tedious and labor-intensive calculation will be the calculation of local resistance in the connecting parts of the pipeline, control valves, gate valves and heating devices.

There are two classes of heating pumps: with wet and dry type rotors. For a private household heating system with a short pipeline length, a pump is best suited wet type. Using a rotor rotating in the middle of the housing, circulation of working fluid accelerates. Thanks to the liquid medium in which the rotor is placed, the mechanism is lubricated and cooled. When installing a pump of this type, it is necessary to control the horizontalness of the shaft.

Dry type pumps are used in long-distance systems. The electric motor and the working part are separated by o-rings, which must be changed once every three years. The coolant does not come into contact with the rotor. The advantages of pumps of this type include high productivity - approximately 80%. Disadvantages include: high level noise and monitoring the absence of dust in the engine.

The main purpose of the circulation pump is to create a coolant pressure capable of coping with the hydraulic resistance that occurs in certain sections of the pipeline, and to ensure the required performance by transporting the heat in the system necessary to warm up the home.

Calculation of a single-pipe heating system

Therefore, choosing circulation pump, it is necessary to calculate the heat energy needs of the room, and also find out the value of the total hydraulic resistance of the heating system. Without knowing this data, it will be extremely difficult to select the appropriate pump.

The productive power of an electric pump can be calculated manually using the equation: Q = 0.86 x P / Δt, where Q is the required efficiency (m3 / hour), P is the required heat flow (kW), Δt is the temperature difference between the supply and return circuits, with the help of which the volume of thermal energy given off by a section of the heat supply system is determined.

An electric pump with a power controller is selected based on performance, having previously set the regulator to the middle position. This manipulation will allow you to adjust the power up or down in case of an erroneous action. The speeds in the circulation pump can be switched either manually or automatically. Depending on the length of the pipeline, they are used different types heating pumps.

Comfort in a country house largely depends on reliable operation heating systems. Heat transfer with radiator heating, “warm floor” and “warm baseboard” systems is ensured by the movement of the coolant through the pipes. That's why correct selection 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 specialist from REHAU, we will tell you:

• What nuances should you be aware of before performing a hydraulic calculation?
• What is the difference between heating systems with dead-end and associated movement of coolant?
• What are the goals of hydraulic calculations?
• How the material of the pipes and the method of their connection affects the hydraulic calculation.
• How special software can speed up and simplify the hydraulic calculation process.

Nuances that you need to know before performing a hydraulic calculation

Sergei Bulkin

Using these programs, you can make hydraulic calculations, determine the adjustment characteristics of shut-off and control valves, and automatically create a custom specification. Depending on the type of program, calculations are carried out in the AutoCAD environment or in your own graphic editor.

Let us add that now, when designing industrial and civil facilities, there is a tendency to use BIM technologies(building information modeling). In this case, all designers work in a single information space. For this purpose, 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 delays in the completion of the project and thereby reduce the estimate.

Perform a hydraulic calculation of the heating system - this means selecting the diameters of individual sections of the network (taking into account the available circulation pressure) so that the calculated coolant flow 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 is most often used. 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 ensure the required air parameters.

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

Sequence of hydraulic calculations

1. Select the main circulation ring of the heating system (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 overhead wiring, the main circulation ring will pass from the heating point through the main riser, the supply line, through the most distant riser, the lower floor heating device, the return line to the heating point.

In systems with associated movement of water, the main ring is taken to be the ring passing through the middle, most loaded riser.

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

a) specified water flow;

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

For calculation R cp It is necessary to know the length of the main circulation ring and the design 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 cooling water in devices, Pa, can be defined as

, (5.3)

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

Coefficient value  can be determined from Table 5.1.

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

- natural pressure resulting from cooling water in pipelines.

In pumping systems with bottom wiring of size
can be neglected.

Specific pressure losses due to friction are determined

, (5.4)

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

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

(5.5)

(t g - t o) – coolant temperature difference.

6. By size
And
standard pipe sizes are selected.

6. For selected pipeline diameters and calculated water flow rates, the coolant movement speed is determined v and the actual specific pressure loss due to friction is 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 overestimation of values
in other areas.

7. Pressure loss due to friction in the calculated area is determined, Pa:

. (5.6)

The calculation results 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 local resistance coefficients in the design area.

Meaning ξ at each site are tabulated. 5.3.

Table 5.3 - Local resistance coefficients

9. Determine the total pressure loss in each section

. (5.8)

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

. (5.9)

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

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

If the conditions are not met, then it is necessary to change the diameters of the pipes 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 connected in parallel to sections of the main ring are calculated.

The discrepancy between pressure losses in parallel connected sections is allowed up to 15% with dead-end water movement and up to 5% with passing water.

Table 5.2 - Results of hydraulic calculations for the heating system

Good day everyone! Today I will describe how to do a hydraulic calculation of a heating system and what it is all about. Let's start with the last question.

What is hydraulic calculation and why is it needed?

Hydraulic calculation (hereinafter referred to as GR) is a mathematical algorithm, as a result of which we will obtain the required diameter of pipes in a given system (meaning the internal diameter). In addition, it will be clear which one we need to use - the pressure and flow rate of the pump are determined. All this will make it possible to make the heating system economically optimal. It is produced on the basis of the laws of hydraulics - a special branch of physics devoted to motion and equilibrium in liquids.

Theory of hydraulic calculation of a heating system.

Theoretically, GR heating is based on the following equation:

This equality is valid for a specific site. This equation is deciphered as follows:

• ΔP—linear pressure loss.
• R is the specific pressure loss in the pipe.
• l is the length of the pipes.
• z—pressure loss in outlets, .

It is clear from the formula that the pressure loss is greater, the longer it is and the more branches or other elements it contains that reduce the passage or change the direction of fluid flow. Let's figure out what R and z are equal to. To do this, consider another equation showing pressure loss from friction against pipe walls:

This is the Darcy-Weisbach equation. Let's decipher it:

• λ is a coefficient depending on the nature of the pipe movement.
• d is the internal diameter of the pipe.
• ρ is the density of the liquid.

From this equation it is established important dependency— pressure loss due to friction is lower, the larger the internal diameter of the pipes and the lower the speed of fluid movement. Moreover, the dependence on speed is quadratic. Losses in bends, tees and shut-off valves are determined using another formula:

ΔP reinforcement = ξ*(v²ρ/2)

• ξ is the coefficient of local resistance (hereinafter referred to as KMR).
• v is the speed of fluid movement.
• ρ is the density of the liquid.

This equation also shows that the pressure drop increases with increasing fluid velocity. Also, it is worth saying that if used it will also play important role its density - the higher it is, the heavier the circulation pump. Therefore, when switching to “anti-freeze”, you may have to replace the circulation pump.

From all of the above we derive the following equality:

ΔP =ΔP friction +ΔP reinforcement =((λ/d) (v²ρ/2)) + (ξ(v²ρ/2)) = ((λ/α) l(v²ρ/2)) + (ξ*(v²ρ/2)) = R l + z;

From here we obtain the following equalities for R and z:

R = (λ/α)*(v²ρ/2) Pa/m;

z = ξ*(v²ρ/2) Pa;

Now let's figure out how to calculate hydraulic resistance using these formulas.

How is the hydraulic resistance of a heating system calculated in practice?

Engineers often have to calculate heating systems for large facilities. In them a large number of heating devices and many hundreds of meters of pipes, but you still need to count. After all, without GR it will not be possible to choose the right circulation pump. In addition, the GR allows you to determine even before installation whether all this will work.

To make life easier for designers, various numerical and software methods determination of hydraulic resistance. Let's start from manual to automatic.

Approximate formulas for calculating hydraulic resistance.

To determine specific friction losses in a pipeline, the following approximate formula is used:

R=5 10 4 v 1.9 /d 1.32 Pa/m;

Here, an almost quadratic dependence on the speed of fluid movement in the pipeline is preserved. This formula is valid for speeds of 0.1-1.25 m/s.

If you know the coolant flow rate, then there is an approximate formula for determining the internal diameter of the pipes:

d = 0.75√G mm;

Having received the result, you must use the following table to obtain the nominal diameter:

The most labor-intensive will be the calculation of local resistance in fittings, shut-off valves and heating devices. Earlier I mentioned the local resistance coefficients ξ; their selection is made using reference tables. If with corners and shut-off valves everything is clear, then choosing a CCM for tees turns into a whole adventure. To make it clear what I'm talking about, let's look at the following picture:

The picture shows that we have as many as 4 types of tees, each of which will have its own local resistance CMS. The difficulty here will be making the right choice direction of coolant flow. For those who really need it, I will give here a table with formulas from the book by O.D. Samarin “Hydraulic calculations of engineering systems”:

These formulas can be transferred to MathCAD or any other program and calculate the CMR with an error of up to 10%. The formulas are applicable for coolant speeds from 0.1 to 1.25 m/s and for pipes with a nominal diameter of up to 50 mm. Such formulas are quite suitable for heating cottages and private houses. Now let's look at some software solutions.

Programs for calculating hydraulic resistance in heating systems.

Now on the Internet you can find many different programs for calculating heating, paid and free. It is clear that paid programs have more powerful functionality than free ones and allow you to solve a wider range of problems. It makes sense for professional design engineers to purchase such programs. For an average person who wants to independently calculate the heating system in his home, free programs will be sufficient. Below is a list of the most common software products:

• Valtec.PRG - demon paid program for calculating heating and water supply. It is possible to calculate heated floors and even heated walls
• HERZ is a whole family of programs. With their help, you can calculate both single-pipe and two-pipe heating systems. The program has a convenient graphical presentation and the ability to break down into floor plans. It is possible to calculate heat losses
• Potok is a domestic development, which is a comprehensive CAD system that can design utility networks of any complexity. Unlike the previous ones, Stream is a paid program. Therefore, the average person is unlikely to use it. It is intended for professionals.

There are several other solutions. Mainly from pipe and fittings manufacturers. Manufacturers customize calculation programs for their materials and thereby, to some extent, force people to buy their materials. This is a marketing ploy and there is nothing wrong with it.

Summary of the article.

Calculating the hydraulic resistance of a heating system is not the easiest thing to do and requires experience. Mistakes here can be very costly. Some branches and risers may not work. There will simply be no circulation through them. For this reason, it is better for people with education and experience in such work to do this. The installers themselves almost never do the calculations. They tend to make the same decisions everywhere that worked for them before. But what worked for another person will not necessarily work for you. For this reason, I strongly recommend contacting an engineer and making a full-fledged project. That's all for now, I'm waiting for your questions in the comments.