In the hydraulic calculation of heating networks, the total flow rate of the main hot water for heating, air conditioning, ventilation and hot water is established. Based on this calculation, the necessary parameters of pumping equipment, heat exchangers and pipe diameters of the main network are determined.
A bit about theory and problems
The main task of the hydraulic calculation of heating networks is the choice of the geometric parameters of the pipe and the standard sizes of the controls to ensure:
- qualitative and quantitative distribution of the coolant to individual heating devices;
- heat-hydraulic reliability and economic feasibility of a closed thermal system;
- optimization of investment and operating costs of the heat supplying organization.
Hydraulic calculation of heating networks creates the prerequisites for heating and domestic hot water appliances to achieve the required power at a given temperature difference. For example, with a T-graph of 150-70 , it will be equal to 80 . This is achieved by creating the required water pressure at each heating point or the heat carrier pressure.
Such a prerequisite for the operation of the heating system is implemented by correctly setting up network equipment in accordance with the design conditions, installing equipment based on the results of hydraulic calculation of heating networks.
Hydraulics stages of the network:
- Pre-launch calculation.
- Operational regulation.
The initial hydraulics of the network are:
- using calculations;
- in a measuring way.
In the Russian Federation, the calculation method is predominant, it defines all the parameters of the elements of the heat supply system in a single settlement area (house, quarter, city). Without this, the network will be deregulated, and the coolant will not be supplied to the upper floors of multi-storey buildings. That is why the beginning of the construction of any heat supply facility, even the smallest one, begins with the hydraulic calculation of heating networks.
Mapping of heating networks
Before calculating the hydraulics, a preliminary line diagram is performed indicating the length L in meters and D of the engineering pipelines in mm and the estimated volumes of network water for the project sections of the scheme. Pressure losses in heat supply systems are divided into linear ones, arising due to carrier loss on the pipe walls, and losses in sections caused by local structural resistances due to the presence of tees, bends, compensators, turns and other devices.
Calculation example hydraulic calculation of heating networks:
- First, an integrated calculation is performed in order to determine the maximum network performance that can fully provide residents with heating services.
- Upon completion, qualitative and quantitative indicators of the main and intra-quarter networks are established, including the total pressure and temperature of the carrier at the input nodes of the heat consumers, taking into account heat losses.
- Perform verification hydraulic calculation of the heating network and hot water supply.
- They determine the actual costs at the circuit sections and at the entrances to residential buildings, the amount of heat received by the subscribers when calculating the temperature of the coolant in the supply pipe of the heating systems and the available pressure in the outlet manifold, the rationale for the thermal conditions, and the predicted temperature inside the living quarters.
- Determine the required temperature of the heat supply at the outlet.
- Set the maximum size T of heated water at the outlet of the boiler room or other heat source, obtained on the basis of hydraulic calculation of the heating system. It should provide sanitary standards indoors.
Normative Method Applications
Hydraulics of networks is carried out on the basis of tables of maximum hourly heat loads and heat supply schemes of a city or district with an indication of the sources, location of main, intra-quarter and intra-house engineering systems, with the designation of the boundaries of the balance of ownership of the network owners. Hydraulic calculation of pipelines of heating networks of each section to the above scheme is performed separately.
This calculation procedure is used not only for heating networks, but also for all pipelines transporting liquid media, including gas condensate and other chemical liquid media. For piped heating systems, changes should be made taking into account the kinematic viscosity and carrier density. This is due to the fact that these characteristics affect the rate of specific pressure loss in the pipes, and the flow rate is associated with the density of the transit medium.
Parameters of hydraulic calculation of water heating network
The heat consumption Q and the amount of coolant G for the sections are indicated in the table of maximum indicators of hourly heat consumption for winter and summer seasons separately and corresponds to the sum of heat consumption for the quarters included in the scheme.
An example of the design of the hydraulic calculation of the heating network is presented below.
Since the calculations depend on many indicators, they are performed using numerous tables, charts, graphs, nomograms, the final value of the heat consumption Q for house heating systems is obtained by interpolation.
The amount of fluid circulating in the heating network m 3 / h, when calculating the hydraulic mode of the heating network is determined by the formula:
G = (D2 / 4) x V,
Where:
- G is the flow rate of the carrier, m 3 / hour;
- D is the diameter of the pipeline, mm;
- V is the flow velocity, m / s.
Linear pressure drops during the hydraulic calculation of heating networks are taken from special tables. When installing heating systems, dozens and hundreds of auxiliary elements are installed in them: valves, fittings, air vents, bends and others, which create resistance to the transit medium.
The reasons for the pressure drop in the pipelines also include the internal state of the pipe materials and the presence of salt deposits on them. The coefficient values used in technical calculations are given in the tables.
Standard procedure and process steps
According to the method of hydraulic calculation of heat networks, it is carried out in two stages:
- Construction of a heating network scheme on which the sections are numbered, first in the area of the central highway - a longer and more voluminous load line of the network from the connection point to the more distant consumption object.
- Calculation of pressure losses of each pipe section, circuit. It is carried out using tables and nomograms, which are indicated by the requirements of state norms and standards.
The first to carry out calculations for the main highway for the costs established by the scheme. At the same time, reference data on the specific pressure losses in the networks are used.
Next, calculating the diameters of the pipes, calculate:
- The number of compensators according to the scheme.
- Resistance to actually installed elements of the heating system.
Pressure losses are calculated by formulas and nomograms. Then, having these data throughout the network, the hydromechanical regime of individual sections from the place of fragmentation of the flow up to the end user is calculated.
The calculations are linked to the choice of branch pipe diameters. Discrepancy is not more than 10%. Excessive pressure in the heating system is extinguished at elevator units, throttle nozzles or auto-regulators in intra-house executive points.
With the available available pressure of the main heating network and branches, first establish the approximate resistivity Rm, Pa / m.
The calculations use tables, nomograms for hydraulic calculation of pipelines of heating networks and other reference literature, which is mandatory for all stages, it is easy to find on the Internet and special literature.
Hot water transport
The algorithm of the calculation scheme is established by normative and technical documentation, state and sanitary standards and is carried out in strict accordance with the established procedure.
The article provides an example of calculating the hydraulic calculation of the heating system. The procedure is performed in the following sequence:
- On the approved heat supply scheme of the city and the district, the nodal points of calculation, the heat source, the trace of the engineering systems with the indication of all branches, connected consumers' facilities are marked.
- Clarify the boundaries of the balance sheet of consumer networks.
- Assign numbers to the site according to the scheme, starting numbering from the source to the end user.
The numbering system should clearly subdivide the types of networks: main intra-quarter, inter-house from the heat well to the borders of the balance sheet, while the section is set as a network segment, enclosed by two branches.
The diagram indicates all the parameters of the hydraulic calculation of the main heating network from the central heating system:
- Q - GJ / hour;
- G m 3 / hour;
- D - mm;
- V - m / s;
- L is the length of the plot, m
The calculation of the diameter is established by the formula.
Steam heating networks
This heating network is designed for a heat supply system using a heat carrier in the form of steam.
Differences of this scheme from the previous one are caused by temperature indicators and medium pressure. Structurally, these networks are distinguished by a shorter length; in large cities, they usually include only backbone networks, i.e., from the source to the central heating point. They are not used as intra-district and intra-house networks, except on small industrial sites.
The circuit diagram is performed in the same order as with a water coolant. In the sections, all network parameters for each branch are indicated, data are taken from the summary table of the maximum hourly heat consumption, with a phased summation of the flow rates from the end consumer to the source.
The geometric dimensions of the pipelines are set according to the results of the hydraulic calculation, which is carried out in accordance with state norms and rules, and in particular SNiP. The determining value is the pressure loss of the gas condensate medium from the heat supply source to the consumer. With a greater pressure loss and a smaller distance between them, the speed of movement will be large, and the diameter of the steam pipe will need a smaller one. The choice of diameter is carried out according to special tables, based on the parameters of the coolant. After that, the data is entered into pivot tables.
Coolant for condensate network
The calculation for such a heating network is significantly different from the previous ones, since the condensate is simultaneously in two states - in steam and in water. This ratio changes as it moves toward the consumer, that is, the steam becomes more and more moist and ultimately completely turns into liquid. Therefore, the calculations for the pipes of each of these media have differences and are already taken into account by other standards, in particular SNiP 2.04.02-84.
The procedure for calculating condensate pipelines:
- The tables establish the internal equivalent roughness of the pipes.
- Indicators of pressure loss in the pipes on the network section, from the coolant outlet from the heat supply pumps to the consumer, are accepted according to SNiP 2.04.02-84.
- The calculation of these networks does not take into account the heat consumption Q, but only the steam consumption.
The structural features of this type of network significantly affect the quality of measurements, since the pipelines for this type of coolant are made of black steel, the network sections after network pumps quickly corrode from oxygen excess due to air leaks, after which low-quality condensate forms with iron oxides, which causes metal corrosion. Therefore, it is recommended to install stainless steel pipelines in this section. Although the final choice will be made after the completion of the feasibility study of the heating network.
Design Programs
Energy losses due to valves, fittings and bends are caused by localized flow disturbances. Energy loss occurs over the final and not necessarily short section of the pipeline, however, for hydraulic calculations it is generally accepted that the entire volume of this loss is taken into account at the location of the device. For piping systems with relatively long pipes, it often happens that the resulting loss will be negligible with respect to the total pressure loss in the pipe.
Losses of pipelines are measured using real experimental data and then analyzed to determine the local loss factor, which can be used to calculate fitting losses, since it changes the rate of fluid passage through this device.
Pipe Flow Software products make it easy to determine fitting losses and other losses when calculating differential pressure, because they come with a pre-loaded valve database that contains many standard factors for valves and fittings of various sizes. A pump is often used inside the piping system, which adds extra pressure to overcome friction and other resistance losses.
Pump performance is determined by the curve. The head created by the pump varies depending on the flow rate; finding the operating point on the pump performance curve is not always an easy task.
If you use the program for the hydraulic calculation of Pipe Flow Expert heating networks, it is quite easy to find the exact operating point on the pump curve, with the guarantee that the flows and pressure will be balanced throughout the system to make an accurate decision on the choice of piping design.
The calculation is carried out online in order to select the optimal diameter that provides the best operating parameters, low pressure loss and high speed media, which will provide good technical and economic indicators of heating networks in general.
It minimizes effort and provides higher accuracy. It includes all the necessary lookup tables and nomograms. So, losses per meter of pipes are accepted in the amount of 81 - 251 Pa / m (8.1 - 25.1 mm water column), which depends on the material of the pipes. The water velocity in the system depends on the diameter of the installed pipes and is selected in a specific range. The highest water velocity for heating networks is 1.5 m / s. The calculation proposes the boundary values of the water velocity in pipelines with an inner diameter:
- 15.0 mm - 0.3 m / s;
- 20.0 mm - 0.65 m / s;
- 25.0 mm - 0.8 m / s;
- 32.0 mm - 1.0 m / s.
- For other diameters no more than 1.5 m / s.
- For pipelines of fire-fighting systems, a medium velocity of up to 5.0 m / s is permitted.
Instrumental Geographic Information System
GIS Zulu - geographic information program for hydraulic calculation of heating networks. The company specializes in researching GIS applications that need 3D-rasterized visualization in vector and raster versions, topological studies and their relationship with semantic databases. Zulu allows you to create different plans and work schemes, including heating and steam networks using topology, can work with rasters and acquire data from different databases, such as BDE or ADO.
The calculations are carried out in close integration with the geographic information system; they are executed as an extended module. The network is elementarily and vividly introduced into the GIS with the mouse or by given coordinates. After that, a settlement scheme is immediately created. After that, the parameters of the circuits are set, and the beginning of the process is confirmed. Calculations are applied to dead-end and ring heating networks, including network pumping units and throttling devices powered from one or many sources. Calculation of heating can be performed taking into account leaks from distribution networks and heat losses in heating pipes.
In order to install a special program on a PC, download on the Internet via torrent "Hydraulic calculation of heating networks 3.5.2".
The structure of the stages of determination:
- Definition of switching.
- Verification hydromechanical calculation of the heating system.
- Adjustment thermohydraulic calculation of main and intra-quarter pipes.
- Design selection of heating equipment.
- Calculation of the piezometric graph.
Microsoft Excel Developer Tool
Microsoft Excel for hydraulic calculation in heating networks is the most accessible tool for users. Its comprehensive spreadsheet editor can solve many computational problems. However, when performing calculations of thermal systems, special requirements must be met. These can be listed:
- finding the previous section in the direction of movement of the medium;
- calculation of the diameter of the pipe according to this conditional indicator and the inverse calculation;
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There are two modifications to the GRTS application: 1.0 and 1.1. At the end, the user will receive the following results:
- calculation, in which the calculation methodology is carefully painted;
- report in tabular form;
- transfer of computing databases to Microsoft Excel;
- piezometric graph;
- graph of coolant temperature.
The GRTS 1.1 application is considered the most modern modification and supports the latest standards:
- Calculation of pipe diameters according to these pressures at the end points of the thermal circuit.
- Help platform has been upgraded. Command "?" opens the application help area on the monitor screen.
Hydraulic calculation of heating networks
An example of the calculation is presented below.
The minimum basic parameters required to design a piping system include:
- Characteristics and physical properties of the fluid.
- The required mass flow rate (or volume) of the transit medium to be transported.
- Pressure, temperature at the starting point.
- Pressure, temperature and altitude at the end point.
- The distance between two points and the equivalent length (pressure loss) established by valves and fittings.
These basic parameters are necessary for designing a piping system. Assuming a stationary flow, there are a number of equations based on a general energy equation that can be used to design a piping system.
Variables associated with a liquid, steam, or two-phase condensate stream affect the calculation result. This leads to the derivation and development of equations applicable to a particular fluid. Although piping systems and their design can become complex, the vast majority of design problems an engineer faces can be solved with standard Bernoulli flow equations.
The basic equation developed to represent the stationary fluid flow is the Bernoulli equation, which assumes that the total mechanical energy is conserved for a stable, incompressible, inviscid isothermal flow without heat transfer. These restrictive conditions can indeed be representative of many physical systems.
Pressure losses associated with valves and fittings can also be calculated by taking into account the equivalent “lengths” of pipe lengths for each valve and fitting. In other words, the estimated pressure loss caused by the fluid passing through the valve is expressed as the extra pipe length that is added to the actual pipe length when calculating the pressure drop.
All equivalent lengths caused by valves and fittings in the pipe segment will be added together to calculate the pressure drop for the calculated pipe segment.
Summing up, we can say that the goal of hydraulic calculation of the heat network at the end point is the equitable distribution of heat loads between subscribers of thermal systems. Here a simple principle applies: for each radiator - as necessary, that is, a larger radiator, which is designed to provide a larger volume of heating the room, should receive a larger flow of coolant. This principle can be ensured by a correctly performed network calculation.