Today we will look at how to make a hydraulic calculation of a heating system. Indeed, to this day the practice of designing heating systems on a whim is spreading. This is a fundamentally wrong approach: without preliminary calculation We raise the bar for material consumption, provoke abnormal operating conditions and lose the opportunity to achieve maximum efficiency.

Goals and objectives of hydraulic calculations

From an engineering point of view, a liquid heating system seems to be a rather complex complex, including devices for generating heat, transporting it and releasing it in heated rooms. Ideal operating mode hydraulic system heating is considered to be one in which the coolant absorbs maximum heat from the source and transfers it to the room atmosphere without loss during movement. Of course, such a task seems completely unattainable, but a more thoughtful approach allows us to predict the behavior of the system under various conditions and get as close as possible to the benchmark indicators. This is the main goal of designing heating systems, the most important part of which is rightfully considered hydraulic calculation.

The practical goals of hydraulic calculation are:

1. Understand at what speed and in what volume the coolant moves in each node of the system.
2. Determine what impact a change in the operating mode of each device has on the entire complex as a whole.
3. Determine what performance and performance characteristics of individual components and devices will be sufficient for the heating system to perform its functions without significantly increasing the cost and providing an unreasonably high margin of reliability.
4. Ultimately, to ensure a strictly dosed distribution of thermal energy across various heating zones and to ensure that this distribution will be maintained with high constancy.

One can say more: without at least basic calculations it is impossible to achieve acceptable operating stability and long-term use of equipment. Modeling the operation of a hydraulic system, in fact, is the basis on which all further design development is built.

Types of heating systems

Engineering calculation tasks of this kind are complicated by the high diversity of heating systems, both in terms of scale and configuration. There are several types of heating junctions, each of which has its own laws:

1. Two-pipe dead-end system a is the most common version of the device, well suited for organizing both central and individual heating circuits.

Transition from thermotechnical calculation to hydraulic is carried out by introducing the concept of mass flow, that is, a certain mass of coolant supplied to each section of the heating circuit. The mass flow is the ratio of the required thermal power to the product of the specific heat capacity of the coolant and the temperature difference in the supply and return pipelines. Thus, in the sketch heating system mark the key points for which the nominal mass flow is indicated. For convenience, the volumetric flow is determined in parallel, taking into account the density of the coolant used.

G = Q / (c (t 2 - t 1))

• Q - required thermal power, W
• c is the specific heat capacity of the coolant, for water assumed to be 4200 J/(kg °C)
• ΔT = (t 2 - t 1) - temperature difference between supply and return, °C

The logic here is simple: to deliver required quantity heat to the radiator, you must first determine the volume or mass of coolant with a given heat capacity passing through the pipeline per unit of time. To do this, it is necessary to determine the speed of movement of the coolant in the circuit, which is equal to the ratio of the volumetric flow to the cross-sectional area of ​​the internal passage of the pipe. If the speed is calculated relative to the mass flow, the coolant density value must be added to the denominator:

V = G / (ρ f)

• V - coolant movement speed, m/s
• G—coolant flow, kg/s
• ρ is the density of the coolant; for water it can be taken as 1000 kg/m3
• f is the cross-sectional area of ​​the pipe, found by the formula π-·r 2, where r is the internal diameter of the pipe divided by two

Flow and velocity data are necessary to determine the nominal diameter of the interchange pipes, as well as the flow and pressure circulation pumps. Devices forced circulation must create excess pressure to overcome the hydrodynamic resistance of pipes and shut-off and control valves. The greatest difficulty is presented by the hydraulic calculation of systems with natural (gravitational) circulation, for which the required excess pressure is calculated based on the speed and degree of volumetric expansion of the heated coolant.

Head and pressure losses

Calculation of parameters using the relationships described above would be sufficient for ideal models. IN real life both the volumetric flow and the coolant velocity will always differ from the calculated ones at different points in the system. The reason for this is hydrodynamic resistance to the movement of the coolant. This is due to a number of factors:

1. The forces of friction of the coolant against the walls of the pipes.
2. Local flow resistance formed by fittings, taps, filters, thermostatic valves and other fittings.
3. The presence of branches of connecting and branch types.
4. Turbulent turbulence at turns, contractions, expansions, etc.

The task of finding the pressure drop and velocity at different areas systems are rightfully considered the most complex; they lie in the field of calculations of hydrodynamic media. Thus, the friction forces of the fluid about internal surfaces pipes are described by a logarithmic function that takes into account the roughness of the material and kinematic viscosity. With the calculations of turbulent vortices, everything is even more complicated: the slightest change in the profile and shape of the channel makes each individual situation unique. To facilitate calculations, two reference coefficients are introduced:

1. Kvs- characterizing the throughput of pipes, radiators, separators and other sections close to linear.
2. K ms- determining local resistance in various fittings.

These coefficients are indicated by manufacturers of pipes, valves, taps, and filters for each individual product. Using the coefficients is quite easy: to determine the pressure loss, Kms is multiplied by the ratio of the square of the coolant velocity to the double value of the acceleration of gravity:

Δh ms = K ms (V 2 /2g) or Δp ms = K ms (ρV 2 /2)

• Δh ms — pressure loss at local resistances, m
• Δp ms — pressure loss at local resistances, Pa
• K ms - coefficient local resistance
• g - free fall acceleration, 9.8 m/s 2
• ρ - coolant density, for water 1000 kg/m 3

The pressure loss in linear sections is the ratio bandwidth channel to a known throughput coefficient, and the result of division must be raised to the second power:

P = (G/Kvs) 2

• P—pressure loss, bar
• G - actual coolant flow, m 3 / hour
• Kvs - throughput, m 3 / hour

Pre-balancing the system

The most important final goal of the hydraulic calculation of the heating system is to calculate the throughput values ​​at which a strictly dosed amount of coolant with a certain temperature is supplied to each part of each heating circuit, which ensures normalized heat release on the heating devices. This task seems difficult only at first glance. In reality, balancing is accomplished by control valves that limit the flow. For each valve model, both the Kvs coefficient for the fully open state and a graph of the change in the Kv coefficient for different degrees of opening of the control rod are indicated. By changing the capacity of valves, which are usually installed at connection points heating devices, it is possible to achieve the desired distribution of the coolant, and therefore the amount of heat transferred by it.

There is, however, a small nuance: when the capacity changes at one point in the system, not only the actual flow rate in the area in question changes. Due to a decrease or increase in flow, the balance in all other circuits changes to some extent. If we take, for example, two radiators with different thermal power, connected in parallel with a counter-movement of the coolant, then with an increase in the throughput of the device that is the first in the circuit, the second one will receive less coolant due to an increase in the difference in hydrodynamic resistance. On the contrary, if the flow decreases due to the control valve, all other radiators further down the chain will automatically receive a larger volume of coolant and will need additional calibration. Each type of wiring has its own balancing principles.

Software systems for calculations

Obviously, performing manual calculations is justified only for small heating systems with a maximum of one or two circuits with 4-5 radiators in each. More complex systems Heating systems with a thermal power of over 30 kW require an integrated approach when calculating hydraulics, which expands the range of tools used far beyond the limits of a pencil and a sheet of paper.

Today there is a fairly large amount of software provided by the largest manufacturers of heating equipment, such as Valtec, Danfoss or Herz. Such software systems use the same methodology that was described in our review to calculate the behavior of hydraulics. First, it is modeled in a visual editor exact copy the designed heating system, for which data on thermal power, type of coolant, length and height of pipeline differences, used fittings, radiators and underfloor heating coils are indicated. The program library contains wide range hydraulic devices and fittings, for each product the manufacturer has determined the operating parameters and basic coefficients in advance. If desired, you can add third-party device samples if the required list of characteristics is known for them.

At the end of the work, the program makes it possible to determine the appropriate nominal diameter of pipes and select sufficient flow and pressure of circulation pumps. The calculation is completed by balancing the system, while during the simulation of hydraulic operation, the dependencies and impact of changes in the throughput of one node of the system on all others are taken into account. Practice shows that mastering and using even paid software products turns out to be cheaper than if the calculations were entrusted to contract specialists.

Regulatory and methodological documents are provided that regulate the design of surface drainage and treatment systems (rain, melt, water-washing) waste water from residential areas and enterprise sites, as well as comments on the provisions of SP 32.13330.2012 “Sewerage. External networks and structures" and "Recommendations for calculating systems for collecting, draining and purifying surface runoff from residential areas and enterprise sites and determining the conditions for its release into water bodies" (JSC "NII VODGEO"). The specified documents allow for the diversion for treatment of the most contaminated part of surface runoff in an amount of at least 70% of the annual volume of runoff for residential areas and enterprise sites close to them in terms of pollution, and the entire volume of runoff from the sites of enterprises, the territory of which may be polluted with specific substances with toxic properties or significant content organic matter. The generally accepted practice of designing engineering structures of separate and combined sewage systems that allow short-term discharge of part of the wastewater during intense (rain) rains of rare frequency through separation chambers (storm discharges) into a water body is considered. Situations related to refusals of the territorial departments of the State Expertise and Rosrybolovstvo to approve the implementation of activities on planned capital construction projects on the basis of Article 60 of the Water Code of the Russian Federation, which prohibits the discharge into water bodies of wastewater that has not been subjected to sanitary treatment and neutralization, are considered.

Keywords

List of cited literature

1. Danilov O. L., Kostyuchenko P. A. Practical guide on the selection and development of energy saving projects. – M., JSC Tekhnopromstroy, 2006. pp. 407–420.
2. Recommendations for calculating systems for the collection, disposal and purification of surface runoff from residential areas, enterprise sites and determining the conditions for its release into water bodies. Addendum to SP 32.13330.2012 “Sewerage. External networks and structures" (updated edition of SNiP 2.04.03-85). – M., JSC “NII VODGEO”, 2014. 89 p.
3. Vereshchagina L. M., Menshutin Yu. A., Shvetsov V. N. On the regulatory framework for the design of systems for the disposal and treatment of surface wastewater: IX scientific and technical conference “Yakovlev Readings”. – M., MGSU, 2014. pp. 166–170.
4. Molokov M.V., Shifrin V.N. Treatment of surface runoff from the territories of cities and industrial sites. – M.: Stroyizdat, 1977. 104 p.
5. Alekseev M.I., Kurganov A.M. Organization of drainage of surface (rain and melt) runoff from urbanized areas. – M.: Publishing house ASV; St. Petersburg, St. Petersburg State University of Civil Engineering, 2000. 352 p.

After collecting the initial data, determining the heat losses of the house and the power of the radiators, all that remains is to perform a hydraulic calculation of the heating system. Done correctly, it is a guarantee of correct, silent, stable and reliable operation heating systems. Moreover, it is a way to avoid unnecessary investment and energy costs.

Calculations and work that need to be done in advance

Hydraulic calculation– the most time-consuming and complex design stage.

• Firstly, the balance of heated rooms and premises is determined.
• Secondly, it is necessary to select the type of heat exchangers or heating devices, as well as arrange them on the house plan.
• Thirdly, calculating the heating of a private house assumes that a choice has already been made regarding the configuration of the system, types of pipelines and fittings (control and shut-off).
• Fourthly, a drawing of the heating system must be made. It is best if it is an axonometric diagram. It should indicate the numbers, length of the calculation sections and thermal loads.
• Fifth, the main circulation ring is installed. This is a closed loop, including successive sections of pipeline directed to the instrument riser (when considering single pipe system) or to the most distant heating device (if there is a two-pipe system) and back to the heat source.

Heating calculation in wooden house performed according to the same scheme as in a brick or any other country cottage.

Calculation procedure

Hydraulic calculation of the heating system involves solving the following problems:

• determination of pipeline diameters at various sections (economically feasible and recommended coolant flow rates are taken into account);
• calculation of hydraulic pressure losses in different areas;
• hydraulic linkage of all branches of the system (hydraulic instrumentation and others). It involves the use of control valves, which allows for dynamic balancing under non-stationary hydraulic and thermal operating conditions of the heating system;
• coolant flow and pressure loss calculation.

Are there free calculation programs?

To simplify the calculation of the heating system of a private house, you can use special programs. Of course, there are not as many of them as graphic editors, but there is still a choice. Some are distributed free of charge, others in demo versions. In any case, it will be possible to make the necessary calculations once or twice without any material investments.

Oventrop CO software

The free software "Oventrop CO" is designed to perform hydraulic calculations for heating a country house.

Oventrop CO was created to provide graphical assistance during the heating design phase. It allows you to perform hydraulic calculations for both single-pipe and two-pipe system. Working in it is simple and convenient: there are ready-made blocks, error control is provided, and a huge catalog of materials

Based on preliminary settings and selection of heating devices, pipelines and fittings, new systems can be designed. In addition, it is possible to adjust existing scheme. It is carried out by selecting the power of existing equipment in accordance with the needs of heated rooms and premises.

Both of these options can be combined in this program, allowing you to adjust existing fragments and design new ones. For any calculation option, Oventrop CO selects the valve settings. In terms of performing hydraulic calculations, this program has wide capabilities: from selecting pipeline diameters to analyzing water flow in equipment. All results (tables, diagrams, drawings) can be printed or transferred to the Windows environment.

Software "Instal-Therm HCR"

The "Instal-Therm HCR" program allows you to calculate radiator and surface heating systems.

It comes with the InstalSystem TECE kit, which includes three more programs: Instal-San T (for designing cold and hot water supply), Instal-Heat&Energy (for calculating heat losses) and Instal-Scan (for scanning drawings).

The “Instal-Therm HCR” program is equipped with expanded catalogs of materials (pipes, water consumers, fittings, radiators, thermal insulation and shut-off and control valves). The calculation results are presented in the form of specifications for the materials and products offered by the program. The only drawback of the trial version is that it cannot be printed.

Computing capabilities of "Instal-Therm HCR": - selection by diameter of pipes and fittings, as well as tees, fittings, distributors, bushings and pipeline thermal insulation; - determination of the lifting height of pumps located in the mixers of the system or on the site; - hydraulic and thermal calculations of heating surfaces, automatic determination optimal temperature input (power); - selection of radiators taking into account cooling in the pipelines of the working agent.

The trial version is free to use, but it has a number of limitations. Firstly, as with most shareware programs, the results cannot be printed, nor can they be exported. Secondly, only three projects can be created in each application of the package. True, you can change them as much as you like. Thirdly, the created project is saved in a modified format. Files with this extension will not be read by any other trial or even standard version.

Software "HERZ C.O."

The program "HERZ C.O." is freely distributed. With its help, you can make a hydraulic calculation of both one-pipe and two-pipe heating systems. An important difference from others is the ability to perform calculations in new or reconstructed buildings, where a glycol mixture acts as a coolant. This software has a certificate of conformity from CSPS LLC.

"HERZ C.O." provides the user with the following options: selection of pipes by diameter, settings of pressure difference regulators (branching, base of drains); analysis of water flow and determination of pressure losses in equipment; calculation of hydraulic resistance of circulation rings; taking into account the necessary authorities of thermostatic valves; decrease in circulation rings overpressure by selecting valve settings. For user convenience, graphical data entry is organized. The calculation results are displayed in the form of diagrams and floor plans.

Schematic representation of the calculation results in HERZ C.O. much more convenient than specifications for materials and products, in the form of which the results of calculations in other programs are displayed

The program has developed contextual help that provides information about individual commands or entered indicators. Multi-window mode allows you to simultaneously view several types of data and results. Working with the plotter and printer is extremely simple; before printing, you can preview the output pages.

Program "HERZ C.O." equipped with a convenient function automatic search and diagnosis of errors in tables and diagrams, as well as quick access to catalog data of fittings, heating devices and pipes

Modern control systems with constantly changing thermal conditions require equipment to monitor changes and regulate them.

It is very difficult to make a choice of control valves without knowing the market situation. Therefore, in order to make heating calculations for the area of ​​the entire house, it is better to use a software application with a large library of materials and products. Not only the operation of the system itself, but also the amount of capital investment that will be required for its organization depends on the correctness of the data obtained.

Introduction
1. Scope of application
2. Normative references
3. Basic terms and definitions
4. General provisions
5. Qualitative characteristics surface runoff from residential areas and enterprise sites
5.1. Selection of priority indicators of surface runoff pollution when designing treatment facilities
5.2. Determination of calculated concentrations of pollutants when surface runoff is diverted for treatment and released into water bodies
6. Systems and structures for draining surface runoff from residential areas and enterprise sites
6.1. Systems and schemes for the disposal of surface wastewater
6.2. Determination of the estimated flow rates of rain, melt and drainage water in rainwater sewer collectors
6.3. Determination of the estimated wastewater flow rates of a semi-separate sewer system
6.4. Regulation of wastewater flows in the storm drainage network
6.5. Surface runoff pumping
7. Estimated volumes of surface wastewater from residential areas and enterprise sites
7.1. Determination of average annual volumes of surface wastewater
7.2. Determination of the estimated volumes of rainwater discharged for treatment
7.3. Determination of estimated daily volumes melt water diverted for treatment
8. Determination of the design capacity of surface runoff treatment facilities
8.1. Estimated productivity of storage-type treatment facilities
8.2. Estimated productivity of flow-type treatment facilities
9. Conditions for the removal of surface runoff from residential areas and enterprise sites
9.1. General provisions
9.2. Determination of permissible discharge standards (VAT) of substances and microorganisms when releasing surface wastewater into water bodies
10. Surface runoff treatment facilities
10.1. General provisions
10.2. Selecting the type of treatment facility based on the principle of water flow regulation
10.3. Basic technological principles
10.4. Cleaning surface runoff from large mechanical impurities and debris
10.5. Separation and regulation of flow into wastewater treatment plants
10.6. Purification of wastewater from heavy mineral impurities (sand collection)
10.7. Accumulation and preliminary clarification of wastewater using static settling method
10.8. Reagent treatment of surface runoff
10.9. Surface runoff treatment using reagent sedimentation
10.10. Treatment of surface runoff using reagent flotation
10.11. Purification of surface runoff using contact filtration
10.12. Additional purification of surface runoff by filtration
10.13. Adsorption
10.14. Biological treatment
10.15. Ozonation
10.16. Ion exchange
10.17. Baromembrane processes
10.18. Disinfection of surface runoff
10.19. Waste management technological processes surface wastewater treatment
10.20. Basic requirements for control and automation of technological processes for surface wastewater treatment
References
Appendix A. Terms and Definitions
Appendix B. Meaning of rain intensity values
Appendix B. Parameter values ​​for determining the estimated flow rates in rainwater sewer collectors
Appendix D. Territory zoning map Russian Federation along the melt runoff layer
Appendix E. Map of zoning of the territory of the Russian Federation according to coefficient C
Appendix E. Methodology for calculating the volume of a reservoir for regulating surface runoff in a storm drainage network
Appendix G. Methodology for calculating productivity pumping stations for pumping surface runoff
Appendix I. Methodology for determining the value of the maximum daily rainfall layer for residential areas and enterprises of the first group
Appendix K. Methodology for calculating the maximum daily precipitation layer with a given probability of exceedance
Appendix L. Normalized deviations from the mean value of the ordinates of the logarithmically normal distribution curve Ф at different meanings security and asymmetry coefficient
Appendix M. Normalized deviations of the ordinates of the binomial distribution curve Ф for different values ​​of security and asymmetry coefficient
Appendix H. Average daily precipitation layers Hsr, coefficients of variation and asymmetry for various territorial regions of the Russian Federation
Appendix P. Methodology and example of calculating the daily volume of melt water discharged for treatment