What is the hydraulic calculation of the heating system. Hydraulic calculation of the heating system: components, recommendations and calculations

Electronic assistants facilitate calculations

Thanks to the development of modern technologies and engineering sciences, the effectiveness of most processes in human life related to machinery has significantly increased. Even one of the most complex and unpredictable sections of the communal economy - the heating system - has been thoroughly studied and inscribed in the framework of generally accepted norms and rules. Thanks to numerous studies conducted in the field of water heating, engineers were able to create a single system of information that fits into the hydraulic calculation of the heating system.

Its main purpose is to maximize the efficiency in closed circuits with natural and forced circulation. Among the tasks of calculation can be identified:

Reducing operating costs.
Reducing energy consumption.
Reducing the cost of building a heating system.
Increase of efficiency of heating of all premises.
Ensuring the complete safety of tenants at home.
Noise reduction to natural level.
Prevention of destructive water hammer in confined space.

As a result of a correctly performed calculation, a significant improvement in performance is achieved, regardless of the construction scheme. The correct arrangement of the system will also give you the opportunity to forget about the need for its maintenance for many years.

However, the calculation process is not so simple - in practice it can take quite a long time. In addition, it is considered by specialists the most difficult stage in the design of the hydraulic heating of a private house.

The calculation procedure includes the following steps:

Creating a "heat balance" of the building.
The choice of the scheme and the main elements of the heating system - including with natural or forced circulation.
Transferring the scheme to the axonometric projection.
Isolation of the circulation ring.
Determination of the required diameter of the water pipeline.
Calculation of the hydraulic mechanism of pressure losses in individual sections of circulation.
Execution of the linkage of parallel branches of water heating.
Determination of the fluid flow to ensure the operability of the entire system.

Calculations are carried out for a section with a constant diameter of a hydraulic pipeline, which has a stable capacity of the coolant. Consider the process in more detail, taking as an example the heating scheme two-story house.

Determination of the diameter of pipelines

One of the most important tasks of hydraulic calculation is to obtain data on the pipes required for use. First you have to determine what material is planned to lay the pipeline, and what its diameter should be.

Initially, the value of several indicators is known. Most experts believe that the velocity of the coolant in the system of water heating should be 0.2-0.7 m / s - with natural circulation. At a lower value of this parameter, air bubbles will form in the pipes, and with a higher noise level, there will be an increased risk of a hydraulic shock in a confined space.

The material of the pipes is of great importance when calculating their desired diameter

Optimal option is the installation of metal-plastic pipelines. They have a lower coefficient of hydraulic friction and lower pressure losses (45-280 Pa / m) in systems with natural and forced circulation. However, such an example is ideal. In practice, water-gas pipes with a loss of 60-480 Pa / m are much more often used. Having data on the heat flux, and also taking the temperature difference between the cold and hot stream at 20 degrees (for a single-tube default of 35 degrees), you can determine the diameter of the pipes in the table below.

The calculation of the internal diameter of the heating pipe

It should be taken into account that it is impossible to pursue the minimization of the diameter of water heating indefinitely. When an excessively small value is reached, the velocity of the coolant in them will exceed 1.0-1.2 m / s, which will cause strong noises. Of course, for systems with natural circulation, this figure is almost unattainable, but in them the efficiency of heating can be significantly reduced.

If we consider the example chosen by us, it should be noted that in sufficiently large houses the hydraulic pump is an obligatory component of the system. Taking as the starting point an area of 200 square meters and a flow rate of 0.5 m / s, we determine that it is necessary to stop on pipes with a diameter of 25 mm.

Attention! Table values are given for the variant using water as the heat carrier. The installation of a system with antifreeze will require independent calculations or receiving data from its manufacturer.

Loss of pressure

When drawing up a scheme it is important to take into account all the nuances

Taking into account the pressure loss, which is especially important for circuits with natural circulation, it is necessary first to separate all the circulation rings, which represent the pipeline section leading from the boiler to the heat consumer and back. For single-pipe circuit ring is a separate riser, and for a two-pipe - each heater separately. Total pressure loss throughout hydraulic system are equal to the sum of the losses in each of the rings, which in turn decompose into losses due to friction and due to local resistances.

The first figure is half the product of the water density per square of the speed in meters per second. The second is the ratio of the length to the diameter of the pipeline, multiplied by the coefficient of hydraulic friction and added to the sum of the coefficients of local hydraulic resistances. For the calculation, formulas are used that require knowledge of the pipe roughness coefficients, but there are special tables in which you can obtain the finished number.

But if such a hydraulic calculation is of great complexity, and the manufacturer gives a ready-made figure for the specific pressure loss per meter of pipe, one can use a simplified formula in which the ratio of the coefficient of friction to the diameter of the pipe is replaced by a constant. Such a calculation scheme is most often used for single-pipe heating, when the accuracy of the final indicator is not so important.

In addition, the use of a simplified coefficient is also fully justified when natural circulation coolant. In our example we will add additional data - the length of a conventional steel pipeline is 100 m, the diameter of the pipe is estimated, the local losses are equal to 800, the number of sections is 1, the table resistance is 1.02. In this case, the losses will be equal to 1.02 * 100 * (971.8 * 0.5 2) / 2 + 800 = 13190.5 Pa.

Attention! The sum of local coefficients of hydraulic resistance also includes indicators of all stop valves, heating devices, expansion tanks and compression equipment.

Example - boiler, pump, expansion tank, adjustment valves, radiators, needle valves, bypasses, etc.

Binding of contour rings

Connection to the pipeline

The effect of the laws of physics leads to the fact that at the points of alignment of the rings the magnitude of the pressure loss will always be the same. If you look at the example of the water circuit of our two-story house and assume that there are 20 rings of different diameters located at different distances from the boiler, then everyone will see different pressures and different speeds of water movement. For a system with both natural and forced circulation, this is a significant disadvantage, which will require resolution to ensure maximum efficiency.

Alignment for the system of these indicators, obtained as a result of the above calculation, is performed with the help of manual or automatic control-stop valves. In the field of manual water line fittings best example are products of the company Stromax. And automatic, which is ideal for systems with forced circulation - HERZ. To obtain the maximum result, radiator thermostatic water heating valves are used, which are combined with balancing valves located as close to the rings as possible. In this case, the system will operate in a dynamic mode of automatic adjustment.

Hydraulic calculation is carried out on the basis of an axonometric scheme, to which, based on thermal calculation The thermal load is applied to the heating devices, which are summed up by the risers and individual rings. The purpose of hydraulic calculation is the selection of the diameter of the pipes. Hydraulic calculation can be performed in two ways:
1) For specific linear pressure losses. The calculation is based on the selection of the diameter of the pipes at constant water t-drops in all risers and branches of the sow. With this method, the water flow in each section is calculated, then the frictional pressure loss and the overcoming of local resistances at the site are determined. Total pressure losses in the circulating ring of the system with a series connection of N sections should be taken into account. are equal to the sum of pressure losses in the ring section:; Rl-loss of pressure along the length; z-loss of pressure on local resistance. The hydraulic calculation carried out by this method shows the distribution of resistances and their effect on the motion of the coolant. This calculation is performed with residuals of pressure losses in the sections and after completion of the installation work, mandatory system regulation is required. This method is mainly used for calculation of highways.
2) Hydraulic calculation for resistance and conductivity characteristics. Calculation by this method makes it possible to determine the distribution of the water flow in the circulating rings of the system and to obtain variable drops in the water troughs in the risers and branches, taking into account the permissible water velocity and site design. The diameter of the pipes in this case is selected at each site. The loss of pressure on friction and the overcoming of local resistances is determined jointly. ΔPuch = Sуч * G2уч, where Sуч - the characteristic of hydraulic resistance of a site; Guch-water flow in the area. Based on the conductivity of each section, the pressure loss in the section:, where σ is the conductivity of the section. The characteristic of the hydraulic resistance of the section expresses the pressure loss in the section at a single flow rate of water (1kg / h) and is determined:, where Au is the specific hydrodynamic pressure at the site; λ-co-nt of hydraulic friction; db is the diameter of the pipeline; lach-length of the site; Σξuch is the sum of the local resistance coefficients in the plot. The conductivity σ is related to the char resistance by the dependence: σ = 1 / √S. The resistance characteristic is calculated both for a single section and for several sections connected to each other. When the N sections are successively connected and the water flow rates are the same at all sites, the total resistance of the hydraulic resistance is equal to the sum of the resistances of the reactors: Sobsh =. Hydraulic calculation by this method is used in the presence of an increased water velocity in the s.o. This calculation is less used in design practice, although it allows you to determine the actual values of flow and t-water in all parts of the system.

The hydraulic calculation of the heating system is based on the equation,

ΔР = ΔРл + ΔРм

ΔРл - linear pressure losses, Pa, caused by frictional forces in pipes;

ΔРм - the sum of local pressure losses, Pa, due to the change in the flow structure (velocity, direction, fusion ...) in fittings, locking devices and equipment.

Hydraulic calculation of the system of water heating is carried out different ways. Consider the most common of them.

The first wayhydraulic calculation - by the specific linear loss of pressure,when the diameter of the pipes is selected for equal (or, as they say, constant) water temperature drops in all risers and branches Δtst corresponding to the calculated difference in water temperature in the whole system Δtc

The second wayhydraulic calculation - on the characteristics of resistance anddimosti,when the distribution of water flows in the circulation rings of the system is established and unequal (also use the terms: variable, sliding) water temperature differences in risers and branches.

Hydraulic calculation by the first method reveals a physical picture of the distribution of resistances in the system, but is performed with pressure loss discrepancies in adjacent circulation rings. Consequently, in practice, after the completion of the installation work, commissioning of the system is required in order to avoid a violation of the design distribution of water by the heating devices.

Hydraulic calculation for the second method is applied at an increased water velocity in the system, when it is possible to use the constant values of the coefficients λ, and ζ. As a result of the calculation, the actual flow and water temperatures in the branches, risers and appliances of the heating system are determined.

There are also known methods of hydraulic calculation of heating systems for the given lengths and for dynamic pressures

The reduced lengths of the sections include additional tube lengths, equivalent to loss of pressure losses at sites in local resistances (1pr = 1ych + 1ECB). The method of reduced lengths is used for hydraulic calculations of systems steam heating high pressure and external heat pipes.

In the case of hydraulic calculations for dynamic pressures (pdin = ρw2 / 2), on the contrary, additional CMCs equivalent to pressure losses to linear losses in the sections (Σζpr = Σζуч + Σζeq) are added to the Coefficient of the sections. The method of dynamic pressures is advisable to apply for the calculation of water heating systems with short sections and numerous local resistances.

Perform a hydraulic calculation of the heating system - this means choosing the diameters of individual sections of the network (taking into account the available circulating pressure) so that the calculated flow of the coolant passes through them. The calculation is carried out by selecting the diameter according to the available pipe grade.

For buildings with a small number of storeys, the most commonly used is a two-pipe heating system, for a high-rise one-pipe system. To calculate such a system, the following initial data should be available:

1. The temperature drop of the heat carrier common to the system (i.e., the difference between the 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.

Sequence of performance of hydraulic calculation

1. The main circulating ring of the heating system is selected (most disadvantageously located hydraulically). In dead-end two-pipe systems this ring passes through the lower device of the most remote and loaded riser, into single-tube ones - through the most remote and loaded riser.

For example, in a two-pipe heating system with an overhead wiring, the main circulation ring will pass from the heat point through the main riser that feeds the main, through the outermost riser, the lower floor heater, the return line to the heat point.

In systems with a co-moving water movement, the main one is the ring passing through the middle most loaded riser.

2. The main circulation ring is divided into sections (the section is characterized by a constant flow of water and the same diameter). The diagram shows the number 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) set water flow rate;

b) approximate specific losses of frictional pressure in the design circulating 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 circulating pressure is determined by formula

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

, (5.2)

where

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

- the natural pressure produced by cooling the water in the instruments, Pa, can be defined as

, (5.3)

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

Coefficient value  It can be determined from Table 5.1.

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

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

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

In pumping systems with a lower wiring size

can be neglected.

Specific friction pressure losses are determined

, (5.4)

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

5. The water flow at the site is determined by the formula

(5.5)

(t r - t 0) is the temperature difference of the coolant.

6. In terms of

and

the standard sizes of pipes are selected.

6. For the selected pipeline diameters and design water flow rates, the velocity of the coolant v and the actual specific frictional pressure loss is set R f .

When selecting diameters in areas with low flow rates, there may be large discrepancies between

and

. Low loss

on these sites are compensated by overestimation of the values

at other sites.

7. Determine the pressure loss for friction at the calculated site, Pa:

. (5.6)

The results of the calculation are recorded 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 resistances at the calculated site.

Value ξ on each site is reduced to tab. 5.3.

Table 5.3 - Coefficients of local resistances

9. Determine the total pressure loss in each section

. (5.8)

10. Determine the total loss of frictional pressure and local resistances in the main circulation ring

. (5.9)

11. Compare Δp from Δp r . The total pressure losses along the ring should be less than the value Δp r on

The stock of available pressure is necessary for the hydraulic resistance not calculated 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 circulating ring, the remaining rings are tied together. In each new ring, only additional non-common areas are calculated, in parallel connected to the sections of the main ring.

The discrepancy in pressure losses in parallel connected areas is allowed up to 15% in case of dead-end water movement and up to 5% - at a passing one.

Table 5.2 - Results of hydraulic calculation for the heating system

, W

In the pipeline diagram

By prior calculation

Upon final settlement

Site number

Coolant flow rate G, kg / h

Length of the plot l, m

Diameter d, mm

Speed v, m / s

Specific friction pressure loss R, Pa / m

Loss of pressure on friction Δp tr , Pa

The sum of the coefficients of local resistances ∑ξ

Loss of pressure in local resistances Z

d, mm

v, m / s

R, Pa / m

Δp tr , Pa

Z, Pa

Rl+ Z, Pa

The centralized type gradually gives way to an autonomous heating system. Many people decide to heat the premises on their own, wishing to create the perfect combination of economy, warmth and comfort. That is why the hydraulic calculation of the heating system becomes especially urgent.

At the initial stage, there are financial expenses. However, the newest heating equipment has an innovative approach to the process of regulating heat supply in comparison with the old one, therefore, the invested money quickly pays off. But such harmony can provide only the systems created by all the rules. They will be able to overcome the emerging hydraulic resistance professionally.

What is the calculation for?

Calculations are performed primarily in order to determine such characteristics circulating pump, as productivity and pressure, which will allow the heating system to work with the greatest efficiency.

Of course, any pump will create some kind of circulation in the circuit, even the smallest, but how economical will such a scheme be? It often happens that the boiler works properly and there are enough radiators in the house, but they do not heat because of weak circulation in the system.

In order for the heating circuits to work at full strength, it is necessary that the pump overcomes the hydraulic resistance of the system components to the flow of water in the pipes, as well as the pressure loss. But a pump with more power than needed will also lead to undesirable effects. In addition to increased power consumption, excess pressure will have a negative effect on the longevity of the connections, and an increase in the velocity of the coolant will lead to noise.

Correctly calculated hydraulic resistance and quality control valves are the most effective combination.

Observance of key conditions is ensured by the following factors:

supply should be carried out in sufficient volume for an ideal balance in the room with temperature fluctuations of air outside and in the dwelling;
minimizing operating costs to overcome systemic hydraulic resistance;
reduction of capital costs during heating.

What is included in the calculation?

Before you start the calculations, you should perform a series of graphs

(often a special program is used for this). Hydraulic calculation involves determining the heat balance of the room in which the heating process takes place.

For the calculation of the system, the longest heating circuit is considered, which includes the largest number of devices, fittings, control and shut-off valves and the greatest pressure drop in height. In the calculation involved such quantities:

material of pipelines;
total length of all pipe sections;
diameter of the pipeline;
bends of the pipeline;
resistance fittings, fittings and heating appliances;
bypass presence;
fluidity of the coolant.

To take into account all these parameters there are specialized computer programs, as an example - "NTP Pipeline", "Oventrop CO", HERZ SO. version 3.5. or a number of their analogues, making it easier for specialists to make calculations.

Make the right calculations in terms of overcoming resistance - this is the most time consuming, but neo

a step in the design of water-type heating systems.

Selection of radiators and length of pipeline sections

It is necessary to determine the type of devices for heating and place their location on the floor plan. Next, a decision should be made on the final configuration heating system, type of pipeline (single-tube or two-pipe), fittings for locking and regulation (valves, regulators, valves, pressure, flow and temperature sensors).

Then the number of heat loads and the exact length of the sections for which the calculation is made are indicated on the drawn out diagram. In conclusion, a "circulating ring" is defined. It is a closed loop that includes all consecutive pipeline sections where an increased heat carrier flow is expected from a source that radiates heat to the farthest heating device (for a two-circuit system) or to a branch line (at single-pipe system) and back to the heating mechanism.

Nuances

With hydraulic calculation using a computer, excel is not the only, albeit the simplest. For this type of calculation, specialized programs have been developed, with which it is much easier to work.

In the role of the design pipeline, there is usually a section with a constant consumption of the heat carrier and a constant diameter. So it will be easier to get the correct data. It is determined by the heat balance of the room.

The numbering of sections should be from a heat source. To denote the nodal points on the pipeline that feeds, the letters of the alphabet are used at the branch points. On the trunk lines of the corresponding nodes, they are marked with strokes (an example illustrates this well).

Nodal points on branches of instrumental branches are denoted by Arabic numerals. Each corresponds to the floor number if a horizontal type system is used, or the branch line number with instruments, if it is a vertical system. The number always includes two digits - the beginning and the end of the plot. The length of the pipeline sections is determined according to the plan, which is drawn on a scale. The accuracy is 0.1 m.

With the fact that an autonomous heating system is better than a centralized heat supply, it is unlikely that anyone will argue. Today, many people are trying to warm their homes with their own forces. And the reason in the first place is the desire to create the optimal combination: warmth and comfort. And let first have to incur certain costs. Due to the fact that modern heating systems have a fundamentally different approach to regulating heat supply in comparison with old systems, the invested funds will quickly pay off. But such harmony will be achieved only if the heating is properly created. And in this connection, the hydraulic calculation of the heating system becomes particularly topical.

The difference between the old approach to controlling the heating process and the new one lies in the mechanisms for ensuring the hydraulic regime. Thanks to new solutions, materials and constructions used in heating systems, sophisticated dynamic technologies are created, which make it possible to react very sensitively to changes in the temperature regime. On the one hand, the benefits are obvious: energy saving - optimized capital costs, and on the other, the device of such a system requires special knowledge in the specific application of high-tech control valves and other means in the process of the device of such heating.

Note! Hydraulic calculation and control valves - guarantee the effective operation of modern heating systems.

Hydraulic calculation will help correctly arrange the heating system with minimum energy costs

Observance of these key conditions is provided by such circumstances:

the supply of the coolant to the devices of the heating system must be carried out in sufficient quantity, which will ensure the heat balance of the rooms at a variable outdoor air temperature and set by the consumer inside the room;

minimization of operating costs, primarily energy, aimed at overcoming the hydraulic resistance of the heating system;
minimization of capital investments during the heating device, depending primarily on the diameter of the pipes used;
noiselessness, reliability and stability of the heating system.

What determines such a calculation?

The diameter of the pipeline in the constituent parts of the heating system, taking into account all recommended and economically expedient speeds of the coolant flow.
Hydraulic pressure losses at different parts of the system.
Hydraulic linking of parallel and other branches of the system. In this case, a control armature is used, designed for dynamic balancing in conditions of non-stationary and thermal operating modes.
Loss of pressure of the coolant and its loss in the system.

Note! Hydraulic calculation is the most laborious, complex and important stage in the process of designing water heating.

An example of a scheme for locating the structural elements of a heating system

However, before proceeding directly to the calculations, it is necessary to perform such computational and graphic work:

determine the heat balance of the heated room;
determine the type of heating devices, as well as heat exchange surfaces and indicate on the plans of the premises their placement;
make the final decision regarding the configuration of the system (location of the heat source, instrument branches and trace of the main pipelines), the type of pipeline, shut-off and control valves (valves, valves, valves, pressure and flow regulators, thermostats);
draw a complete scheme of the heating system (preferably axonometric), indicating the number of thermal loads and the length of the calculated areas;
determine the main circulating ring, that is, a closed loop that includes consecutive sections of the pipeline, where the maximum flow of the heat carrier is expected to be at a distance from the heat source to the most remote heating device (2-circuit system) or to the riser (1-pipe system ) and back to the heating equipment.

Features of the calculation part

As a design pipeline, a section with a constant flow of coolant and constant diameter is taken. It is determined on the basis of the heat balance of the room. The numbering of the calculation areas starts from a heat source (heat generator or ITP). To indicate the nodal points on the supply main pipeline, the capital letters of the alphabet are used at the junction points. On prefabricated lines in the corresponding nodes they are marked with a stroke.

The nodal points on the instrument branches at the branch points are denoted by Arabic numerals. Each of them corresponds to the floor number with a horizontal system or the number of the instrument branch-riser - with the vertical one. The nodes for collecting coolant flows also have the notation for these points, but they are performed in the form of a stroke. The number always consists of two digits: the beginning and the end of the plot.

Example of a working scheme in a program when performing a hydraulic calculation

In vertical systems, the numeration of instrument branches is performed in Arabic numerals along the entire perimeter of the building clockwise.

The length of pipeline sections is determined by a plan drawn on a scale. The accuracy is 0.1 m.

The heat flow of the design section is equal to the heat load that the heat transfer medium must convey or transmit.

Performing the hydraulic and thermal calculation of the heating system when designing a new structure is best performed in a special program, for example, HERZ SO. This program itself "knows how" to select:

diameter of the pipeline;
dimensions of heating devices;
adjustment of balancing valves;
adjustment of control valves;
pre-setting of thermostatic valves (if necessary);
adjustment of differential pressure regulators.

Of course, the information given in this article is generalizing and you can not do without reading the special literature. But all the same, we dare to hope that the main accents and peculiarities of the hydraulic calculation of the heating system have been set. Now you need to show some patience and perhaps you will be able to perform the most difficult part of the heating system project of your home on your own.