Hydraulic calculation of the heating system is an example calculation. Types of heating boilers. What determines this calculation
What is the hydraulic calculation of the heating system? What quantities need to be counted? Finally, the main thing: how to calculate them, not having exact values of hydraulic resistance of all sections, heating devices and elements of the stop valves? Let's understand.
What we expect
For any heating system, the most important parameter is its heat output.
It is determined by:
- The temperature of the coolant.
- Thermal capacity of heating appliances.
Note: in the documentation, the last parameter is indicated for a fixed temperature delta between the coolant temperature and air in a heated room of 70 ° C.
Reducing the delta of temperatures by half will result in a twofold decrease in thermal power.
Methods for calculating the thermal power, we still leave behind the scenes: they are devoted enough thematic materials.
However, in order to ensure the transfer of heat from the route or boiler to the radiators, two more parameters are important:
- The internal section of the pipeline, tied to its diameter.
- The flow rate in this pipeline.
In an autonomous heating system with forced circulation it is important to know a couple more values:
- Hydraulic resistance of the circuit. Calculation of the hydraulic resistance of the heating system will determine the requirements for the pressure created by the circulation pump.
- The flow of the heat carrier through the circuit, determined by the capacity at the corresponding head.
Problems
As they say in Odessa, "they are."
In order to calculate the total hydraulic resistance of the circuit, it is necessary to take into account:
- Resistance of straight pipe sections. It is determined by their material, internal diameter, flow velocity and degree of wall roughness.
- Resistance of each rotation and diameter transition.
- Resistance of each element of the stop valve.
- Resistance of all heaters.
- Resistance of the boiler heat exchanger.
Collecting all the necessary data will clearly become a problem even in the simplest scheme.
What to do?
Formulas
Fortunately, for offline heating system Hydraulic calculation of heating can be performed with acceptable accuracy and without deepening into the jungle.
Flow rate
On the lower side, it is limited by the increase in the temperature difference between the feed and the return flow, and at the same time the increased probability of ejection. A fast flow will force air from the jumpers to the automatic air vent; A slow one can not cope with this task.
On the other hand, too fast flow will inevitably generate hydraulic noise. Elements of stop valves and rotations of bottling will become a source of irritating hum.
For heating, the range of acceptable flow rate is taken from 0.6 to 1.5 m / s; while the calculation of other parameters is usually performed for a value of 1 m / s.
Diameter
It is easiest to select it with the known thermal power from the table.
| Inside diameter of pipe, mm | Heat flow, W at Dt = 20С | ||
| Speed 0,6 m / s | Speed 0,8 m / s | Speed 1 m / s | |
| 8 | 2453 | 3270 | 4088 |
| 10 | 3832 | 5109 | 6387 |
| 12 | 5518 | 7358 | 9197 |
| 15 | 8622 | 11496 | 14370 |
| 20 | 15328 | 20438 | 25547 |
| 25 | 23950 | 31934 | 39917 |
| 32 | 39240 | 52320 | 65401 |
| 40 | 61313 | 81751 | 102188 |
| 50 | 95802 | 127735 | 168669 |
Head
In a simplified version, it is calculated by the formula H = (R * I * Z) / 10000.
In it:
- H - the desired value of the pressure in meters.
- I - loss of pressure in the pipe, Pa / m. For a straight pipe section of the design diameter, it assumes a value in the range of 100-150.
- Z - additional compensation factor, which depends on the presence of additional equipment in the circuit.
In the photo there is a mixing unit for heating.
If there are several elements in the system, the corresponding coefficients are multiplied. So, for a system with ball valves, and a thermostat controlling the flowability of filling, Z = 1.3 * 1.7 = 2.21.
Performance
The manual for calculating the pump's own performance is also not difficult.
Performance is calculated by the formula G = Q / (1,163 * Dt), in which:
- G - productivity in m3 / hour.
- Q is the thermal power of the circuit in kilowatts.
- Dt is the temperature difference between the supply and return pipelines.
Example
Let's give an example of the hydraulic calculation of a heating system for the following conditions:
- Delta temperatures between feeder and return pipeline is equal to the standard 20 degrees.
- Thermal power boiler - 16 kW.
- The total length of the single-tube Leningrad tower is 50 meters. The heating devices are connected in parallel to the filling. Thermostats that break the filling, and there are no secondary circuits with mixers.
So, let's get started.
The minimum internal diameter according to the above table is 20 millimeters with a flow velocity of at least 0.8 m / s.
It is useful: modern circulation pumps often have stepped or, more conveniently, smooth adjustment of productivity.
In the latter case, the price of the device is slightly higher.
The optimal head for our case will be (50 * 150 + 1.3) / 10000 = 0.975 m. Actually, in most cases the parameter does not need a calculation. Differential heating system apartment building, providing it with circulation - only 2 meters; this is the minimum value of the pressure of the absolute majority of pumps with a wet rotor.
The productivity is calculated as G = 16 / (1,163 * 20) = 0,69 m3 / hour.
Conclusion
We hope that the above calculations will help the reader to calculate the parameters of his own heating system without climbing into the jungle of complex formulas and reference data. As always, the attached video will offer additional information. Good luck!
For the efficient operation of the heating system, it is necessary to fulfill several conditions - to correctly select the components and make the calculation. From the correct calculation of the parameters of the system depends on its efficiency and uniform heat distribution. How to make a hydraulic calculation of heating systems - examples, the programs will help to carry out these calculations.
Purpose of hydraulic calculation of heating
When any heat supply system is operating, a hydraulic resistance inevitably arises when the coolant moves. To account for this parameter, a hydraulic calculation of the two-pipe heating system is necessary. Its essence lies in the correct choice of system components taking into account their performance.
In fact, the hydraulic calculation of water heating systems is a complex procedure, during which all subtleties and nuances are taken into account. At the first stage it is necessary to determine the required heating power, choose optimal scheme distribution of pipelines, as well as thermal operation. On the basis of these data, a hydraulic calculation of the heating system in Excel or a specialized program is done. The result of the calculations should be the following parameters of water heat supply:
- Optimal diameter of the pipeline. Based on this, one can know their throughput, heat losses. Taking into account the choice of the material of manufacture, the resistance of the water to the inner surface of the main line will be known;
- Loss of pressure and pressure in certain parts of the system. An example of a hydraulic calculation of a heating system will allow you to think in advance of the mechanisms for their compensation;
- Water flow rate;
- Required capacity of pumping equipment. Actual for closed systems with forced circulation.
At first glance, the hydraulic resistance of the heating system is difficult. However, it is enough to delve into the essence of calculations and then you can do them yourself.
For the heat supply of a small house or apartment, it is also recommended to perform a calculation of the hydraulic resistance of the heating system.
Procedure for calculating hydraulic parameters of heating
At the first stage of calculating the parameters of the heating system, a preliminary diagram should be drawn up, indicating the location of all components. This determines the total length of the mains, calculates the number of radiators, the volume of water, as well as the characteristics of the heating appliances.
How to make a hydraulic calculation of heating, without the experience of such calculations? It should be remembered that for autonomous heat supply it is important to choose the correct diameter of the pipes. It is from the implementation of this stage that we must begin the calculations.
It is best to make a heating scheme on an already prepared house plan. This will allow you to correctly calculate the consumption of material and determine its quantity for the arrangement of the system.
Determination of the optimal diameter of pipes
The simplest hydraulic calculation of a heating system involves only calculating the cross-section of pipelines. Often, when designing small systems, they do without it. For this, the following parameters of pipe diameters are taken, depending on the type of heat supply:
- Open circuit with gravitational circulation. Pipes from 30 to 40 mm in diameter. Such a larger cross-section is necessary to reduce losses due to water friction against the internal surface of the mains;
- Closed system with forced circulation. Cross-section of pipelines varies from 8 to 24 mm. The smaller it is, the greater the pressure in the system and, correspondingly, the total volume of the coolant will decrease. But at the same time, hydraulic losses will increase.
If there is a specialized program for hydraulic calculation of the heating system - it is enough to fill in the data on technical characteristics boiler and transfer the heating circuit. The software kit will determine the optimum pipe diameter.
The received data can be checked independently. The procedure for performing hydraulic calculation of a two-pipe heating system manually when calculating the diameter of pipelines consists in calculating the following parameters:
- V - speed of water movement. It should be in the range from 0.3 to 0.6 m / s. Determine the performance of pumping equipment;
- Q - heat flow. This ratio of the amount of heat passing in a certain time interval is 1 second;
- G - water flow. Measured in kg / hour. Directly depends on the diameter of the pipeline.
In the future, to perform the hydraulic calculation of water heating systems, you need to know the total volume of the heated room - m³. Suppose that this value for one room is 50 m³. Knowing the power of the heating boiler (24 kW), we calculate the total heat flux:
Q = 50/24 = 2.083 kW
Then, to select the optimal diameter of the pipes, you need to use the data in the table, compiled during the hydraulic calculation of the heating system in Excel.
In this case, the optimal internal diameter of the pipe in a particular section of the system is 10 mm.
In the future, to perform an example of hydraulic calculation of the heating system, you can find out the approximate flow of water, which will whistle from the diameter of the pipe.
Manufacturers of polymer pipes indicate the outer diameter. Therefore, in order to correctly calculate the hydraulic resistance of the heating system, two wall thicknesses should be taken away.
Accounting for local resistances in the highway
An equally important step is the calculation of the hydraulic resistance of the heating system on each section of the highway. For this purpose, the whole heat supply scheme is conditionally divided into several zones. It is best to make calculations for each room in the house.
As initial data for entering into the program for hydraulic calculation of the heating system, the following quantities will be needed:
- The length of the pipe in the section, m.
- The diameter of the main. The order of calculations is described above;
- Required flow rate. Also depends on the pipe diameter and power circulating pump;
- Reference data, characteristic for each type of fabrication material - coefficient of friction (λ), friction loss (ΔР);
- The density of water at a temperature of + 80 ° C is 971.8 kg / m³.
In carrying out this work, it must be remembered that the smaller the selected area of heating, the more accurate will be the data of the general parameters of the system. As it will be difficult to make a hydraulic calculation of heat supply from the first time - it is recommended to perform a series of calculations for a certain interval of the pipeline. It is desirable that it had as few possible additional devices as possible - radiators, shut-off valves, etc.
To check the hydraulic calculation of a two-pipe heating system, it is necessary to execute it in several different programs or additionally manually by yourself.
Overview of programs for hydraulic calculations
In fact, any hydraulic calculation of water heating systems is a complex engineering task. To solve it, a number of software complexes have been developed that simplify the implementation of this procedure.
You can try to make a hydraulic calculation of the heating system in the Excel shell, using already ready-made formulas. However, the following problems may occur:
- The big error. In most cases, one-pipe or two-pipe schemes are taken as an example of a hydraulic calculation of a heating system. Finding such calculations for the collector is problematic;
- To properly take into account the hydraulic resistance of the pipeline, reference data is required that are not in the form. They need to be looked for and introduced in addition.
Oventrop CO
The most simple and clear program for the hydraulic calculation of the heat supply system. An intuitive interface and flexible configuration help you quickly understand the nuances of data entry. Small problems can arise during the initial configuration of the complex. It will be necessary to enter all the parameters of the system, starting from the material of the pipe making and ending with the location of the heating elements.
HERZ C.O.
It is characterized by the flexibility of the settings, the ability to do a simplified hydraulic calculation of heating for both the new heat supply system and for retrofitting the old one. It differs from analogues with a convenient graphical interface.
Instal-Therm HCR
The software package is designed for professional hydraulic resistance of the heat supply system. The free version has many limitations. The scope of application is the design of heating in large public and industrial buildings.
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 circulating 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 + 1kVB). 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.
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 conservation - 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, temperature controllers);
- 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.
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 the characteristics of the circulation pump, such as capacity 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 of the heating system, the type of pipeline (single-pipe or two-pipe), valves for locking and regulating (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.
