Hydraulic calculation of heating networks. Hydraulic calculations

To carry out hydraulic calculations of pipelines transporting any energy carrier, the following must be previously determined and specified:

• diagram of the pipeline system indicating the materials from which they are made; the state of their inner surface (equivalent roughness);
• the maximum values ​​of pressure and temperature of the energy carrier that they can withstand without destruction;
• location of the energy source and each consumer;
• geometric lengths of each pipeline section, as well as the number and types of local resistances installed on the section;
• estimated (maximum) needs of each consumer for the transported energy carrier;
• coolant parameters required by each consumer;
• tabular or graphical materials to determine the dependence of the physical properties of the coolant (density, viscosity, etc.) on changes in its parameters when moving through the pipeline.

The task of hydraulic calculations includes:

• determination of the diameters of all sections of the pipeline that ensure delivery to each consumer of the required estimated amount of coolant (energy carrier);
• determination of pressure losses of the energy carrier when passing through the corresponding section of the pipeline system.
• determination of the energy carrier pressure in each section of the pipeline being calculated.

The drop in pressure Δр у, Pa, or pressure Δh у = Δр у /ρg, m, of an energy carrier when moving through a section of a pipeline transporting an energy carrier in the form of a compressible (steam) or incompressible (water) liquid is caused by the expenditure of energy to overcome the friction forces between layers of liquid and the walls of the pipeline (the so-called linear pressure drop Δр с.л. or pressure Δh с.л.) and the energy consumption for vortex formation when the flow passes through the elements of the pipeline section, causing a change in its direction and speed (the so-called pressure drop Δр с.л. or pressure Δh sea level in local resistances located on the pipe section). The values ​​of total pressure and head losses in the area are obtained by summing

Δр у = Δр у.л + Δр у.м or Δh у = Δh у.л + Δh у.м.

Linear pressure drop –

Δр у.л = R l ×l у, Pa,

and the pressure -

Δh y.l = i l y, m,

where l y is the length of the pipeline section, m; R l – specific pressure drop over one meter of section length, Pa/m; i – hydraulic slope, i.e. pressure loss per meter of pipeline length (dimensionless value).

The specific linear pressure drop R l, Pa/m, as well as the hydraulic slope i, are determined by the Darcy–Weisbach equation:

where λ is the coefficient of hydraulic friction; θ – energy carrier velocity averaged over the pipe cross-section, m/s; ρ – energy carrier density, kg/m3; d in – internal diameter of the pipeline, m; G – mass flow of energy carrier, kg/s; g – free fall acceleration, m/s 2 .

From (3.76) and (3.77) follow the formulas for calculating the internal diameter of pipes

as well as dependencies for calculating mass flow G, kg/s:

The value of the hydraulic friction coefficient l depends on the flow regime (characterized by the value of the Reynolds number - Re) and on the state of the inner surface of the pipe wall (which is characterized by the ratio of the size of the protrusions of the equivalent wall roughness D to the inner diameter of the pipe). Data on the values ​​of equivalent absolute roughness D of pipes made of various materials are given in Table 3.8. To calculate l in hydraulic calculations of heating network pipelines, it is advisable to use the formulas given in Table 3.9.

The loss of pressure or head when the flow passes through a local resistance placed on the pipeline is determined by the expressions

Table 3.12.

Values ​​of local resistance coefficients heating network elements

	Meaning []	Characteristics of local resistance	Meaning []
Bends smooth at an angle of 90° at: R db = 1 R db = 3 R d b = 4 R d b > 4 Bent with folds at an angle of 90° at: R d / d b = 3 R gn /d in = 4 Welded at an angle of 90°: single-seam double-seam three-seam Welded single-seam at an angle: 60° 40° 30°	1.0 0.5 0.3 0.1¸0.2 0,8 0,5 0,6 0,5 0,7 0,3 0,2	Tees When dividing flows: for direct passage for a branch When merging flows: for direct passage for counter flows Fittings: gate valves normal valves through valves with an oblique spindle check valves rotary check valves lifting water separator sludge compensator gland compensator wavy	1,0 1,5 1.2¸1.8 3.0 0.5* 4¸8 6.5¸7 8¸12 4¸10 0.2¸0.3 2.5
*The resistance coefficient of a normal valve when it is partially closed is determined by the expression ζ=((1.17-n)/[(0.67-0.57n)n-1) 2, where n = valve opening fraction. Open: n = 1, ζ= 0.5; closed: n = 0, ζ= ∞; open 50%: n = 0.5, ζ = 6.2; 10% open: n = 0.1. ζ= 270.

The above dependencies and tabular data are applicable for hydraulic calculations of pipeline systems with a variety of energy carriers. Below we outline the hydraulic calculation methodology using the example of a branched two-pipe closed water heating network (Fig. 3.17, a), consisting of 4 consumers and 7 sections of the heating network in a two-pipe design.

When designing a heating network, the diameters of the supply and return pipes at each section must be the same and designed to pass the maximum design flow rate of network water G di, kg/s to each i-th consumer.

With high-quality regulation of heat supply in both open and closed heat supply systems, the flow rate G di, kg/s:

G v.r.i – calculated water flow for the ventilation system of the i-th consumer:

• in closed heat supply systems with parallel connection of water heaters

The value of the coefficient k z, which takes into account the share of the average water consumption for hot water supply that passes through a section of the heating network, in calculating its pipe diameter for this section should be taken:

a) with high-quality regulation of heat supply according to the heating load:

• in open systems with a heat flow of up to 100 MW - k z = 0.8, and with a heat flow of 100 MW or more - k z = 1.0
• in closed systems with a heat flow of up to 100 MW - k z = 1.2, and with a heat flow of 100 MW or more - k z = 1.0;

b) with high-quality regulation of heat supply according to the combined load of heating and hot water supply - k h = 0.

Estimated amount of steam required by the i-th consumer to provide process load Q t.p.i, kW:

G t.r.i =Q t.r.i /;

(3.92)

where x is the proportion of returned condensate.

The values ​​of τ 1or, τ 2or, τ 2vr, τ " 1 , τ " 2g, t g, t x, t pr, t s are given in Section. 2.

Using Fig. 3.17, determine the number and location of all consumers, the lengths of all sections, types and quantities of local resistances of each section of the network.

Using expressions (3.86)¸(3.91), the estimated costs for all consumers G d1, G d2, G d3, G d4 are determined. Using Table 3.8, take the value of the equivalent roughness of steel pipes D e = 0.0005 m.

Since an incompressible liquid (network water) moves through the network, the temperature value of which does not actually change when water moves along the length of the pipe, and the determination of the diameters of the heating network is carried out in a mode when the temperature of the network water is τ 1 "°C, then the value is taken for all sections water density ρ = 975 kg/m 3, and the value of its kinematic viscosity ν = 0.416×10 -8 m 2 /s.

Considering that the speed of water movement in pipes is within 0.5-3.5 m/s, and the diameters of pipes used in heating networks are within 0.1-1.4 m, then simple calculations show that in thermal networks under design conditions in any section Re > 568d v/Δ e.

Therefore, formulas (3.76)¸(3.81) are transformed into forms that are more convenient for calculations:

The procedure for hydraulic calculation of two-pipe branched water networks

Calculation of the main highway

1. Since the diameters of the supply and return pipes in each section are the same, only the diameters of the supply line are determined. 2. Select as the main highway a sequence of sections from the energy source to the most distant consumer. In Fig. 3.17 this is consumer 1 and sections l 1 +l 5 + l 6. 3. For all sections of the main line, the numerical value of the specific linear pressure drop R l.e. is accepted (from technical and economic considerations). , Pa/m. 4. Using (3.94), the diameter d in1, m, of the last section of the highway l 1 is determined. Using the data in Table 2.35, round the resulting value towards the nearest standard diameter d in.1.st, m. 5. Using (3.93), the value of the real specific linear pressure drop in section 1 is clarified when the flow flows through a diameter of standard size R l.1 .d. If the system is closed, then the return pipe will have the same diameter, flow rate, values ​​R l1d and Δр l1 = R l1 ×l 1. 6. Using the diagram in Fig. 3.17 and data in table. 3.12, determine the loss in local resistance on the supply pipe of section 1 Δр m1п according to formula (3.82) (one valve ζ к = 6; one valve ζ с = 0.5; one stuffing box compensator ζ ск = 0.2; one tee distributing to passage ζ tr = 1; one mud trap ζ gr = 7) and their share a 1 =Δр m1п /Δр l1. 7. Calculate the total pressure loss in section 1 Δр 1d =R l1d l 1 (1+a 1). 8. The remaining sections of the main highway are calculated in a similar manner.

Fig.3.17. Branched heating network diagrams

a – two-pipe water; b – single-pipe steam; 1–4 – heat consumers; – valve; – normal valve; – compensator; P – the same flexible U-shaped; I– network pump; II– make-up pump; III– water heater; IV– make-up regulator; V– steam boiler

Branch calculation

1. From the diagram in Fig. 3.17 it is obvious that the total pressure losses in the branch section 2 coincide with the total losses in the main line section 1, which is located after the branch connection points. Hence, since R l2 =Δр 2 /l 1 (1+a 2), then they are given by the value a 2 and substituting Δр 1д =Δр 2, determine R l2 =Δр 1д /l 2 (1+a 2) 2. By (3.94) determine the diameter d in2 and round it towards the nearest larger diameter d in.2.st.b. Next, the calculation is carried out according to the above method for calculating the section of the main highway in order to determine R p2o, Δр m2п, а 2, Δр 2д.

When calculating open two-pipe water networks, some changes are made to this methodology:

1) The diameters of both the supply and return pipes of a section of an open two-pipe water network are selected according to a single calculated flow rate

G di = √[(G o.p.i +G v.p.i) 2 +(G o.p.i +G g.p.i)G g.av.i _0.5G g.av.i ]

and rounded to the same standard values ​​d c.sg.i. However, in real conditions, flows through them differ by the value G g.av.i. Therefore, starting from point 6 of the calculation of the main line, differences arise from the calculation of a closed heat supply system.

2) Clarify according to (3.93) the value of the specific linear pressure drop in section 1 separately for the supply

R l1d n =13.62*10 -6 (G o.p.1 +G v.r.1 +G g.av.1) 2 /d v.st1 5.25 ; Δp l1 n =R l1d n *l 1 ;

and return lines

R l1d o =13.62*10 -6 (G o.p.1 +G v.r.1 +G g.av.1) 2 /d v.st1 5.25 ; Δp l1 o =R l1d o *l 1 .

3) Separately take into account the sum of local resistance coefficients for the supply pipe Σζ n

And for the return pipe Σζ o , as well as the magnitude of pressure losses in their local resistances:

Δp m.1.n =0.8106Σζ n (G o.p.1 +G v.r.1 +G g.sr.1) 2 /ρd v.st1 4 ; a 1n =Δp m.1.n /Δp l1 n ;

Δp m.1.o =0.8106Σζ o (G o.p.1 +G v.r.1 +G g.sr.1) 2 /ρd v.st1 4 ; a 1o =Δp m.1.o /Δp l1 o .

4) The total pressure loss in the section is calculated in total across the supply and return pipes

ΣΔp 1d =l 1; and so on in all other sections of the main highway.

Calculation of branches in an open heat supply system

1. Set by the value a 2 and calculate the specific linear pressure drop on the branches R l2 =ΣΔp 1d /2]l 2 (1+a 2)]. 2. Determine the same diameters of the supply and return pipes d b2 of section 2 according to G d2 and R l2 using (3.94), and round each of them towards the nearest larger standard d b2.st. Naturally, d in 2.st.n =d in 2.st.o. 3. Since the real flow rates through the supply and return pipes of the section differ, the values ​​of the specific pressure drop in section 2 are calculated using (3.93) separately for the supply and return pipes.

When performing a hydraulic calculation of branched steam pipelines, in addition to the initial data required for calculating water heating networks, additional parameters of the steam p i, MPa, and t i, °C must be specified, escaping from the heat source, as well as the values ​​p i and t i required by each consumer .

The method of hydraulic calculation of steam pipelines coincides with the above-mentioned method of hydraulic calculation of the supply pipeline of a closed heat supply system and differs from it only in the following points:

4. The direction of the main line is selected towards the consumer for which the smallest specific linear pressure drop is required. For this purpose, in the direction of each consumer, calculate the value of the specific linear pressure drop R l =10 6 (p and -p i)/Σl i-i, Pa/m; where Σl and-i is the sum of the lengths of the network sections through which steam is supplied to the i-th consumer from the heat source, m. In the direction where R li is the smallest of all compared R li, it is assigned the designation R l.ek. For example, in the steam pipeline diagram in Fig. 3.17, l g.m =l 6 +l 7 +l 4 is taken as the main one. 5. The density of steam when moving through a steam pipeline changes significantly, and for each section of the steam pipeline the value of the average steam density ρ avg.i kg/m 3 must be calculated. For this purpose, for each section of the main line, the average vapor pressure p av.i along its length is preliminarily calculated. In relation to the single-pipe steam pipeline diagram shown in Fig. 3.17b, this is done as follows:

p av.6 =p and -(R l.ek *0.5l 6)10 -6 ; p av.7 =p and -(R l.ek *(l 6 +0.5l 7)10 -6 ;

p av.4 =p and -(R l.ek *(l 6 +l 7 +0.5l 4)10 -6 .

Then, for the same sections, the average value of the steam temperature in the section is preliminarily calculated - t av.i , °C:

t av.6 =t av.i -δt m.n 0.5l 6; t av.7 =t av.i -δt m.n (l 6 +0.5l 7); t av.4 =t av.i -δt m.n (l 6 +l 7 +0.5l 4);

Where δt m.n is the experimental value of the temperature drop of superheated steam when moving through a thermally insulated steam pipeline. Typically δt m.n = 0.02°C/m.

When saturated steam moves, its temperature t av.i s is determined by pressure. Based on the found values ​​of p avg.i and t avg.i, the average steam density ρ avg.i, kg/m 3 is determined.

6.According to the data in Table 3.8, take the value of the equivalent roughness of the steam pipelines D = 0.0002 m. 7. Having made appropriate adjustments to the values ​​of D and ρ av.i in (3.93) - (3.95), the hydraulic calculation of the steam pipeline is carried out according to the method for calculating closed water heating networks.

The presented hydraulic calculation methodology makes it possible to determine the diameters of all sections of water or steam heating networks and the pressure drop on each of them, but for water heating networks it will not answer the question: what is the true value of coolant pressure that will be observed in each specific section of the supply and return pipes? The answer can only be obtained after constructing and analyzing the piezometric graph of the heating network.

Piezometric graph is a graph on which the lengths of sections of the main main line and branches of the heating network are plotted on the abscissa scale, and on the ordinate axis the following are plotted: the terrain along which the heating network is laid, the heights of buildings connected to the heating network, as well as the magnitude of the coolant pressure in each section of the supply and return heat pipes.

The methodology for constructing a piezometric graph is presented in relation to the heating network diagram presented in Fig. 3.17, a, and the graph itself is presented in Fig. 3.18.

Fig.3.18. Piezometric graph

Taking as the origin of coordinates the ordinate axis (mark 0) the level of location of the heat supply source, and the abscissa axis (mark 0) the exit point of the heating network main line, plot the lengths of the sections of the main main line along it sequentially: l 6, l 5, l 1, and from the points of the corresponding branches - their lengths l 2, l 7, l 3 and l 4. A line of the terrain along which each section is located is drawn, and at the end of each branch and the main highway the height of the relief is designated accordingly: z 1, z 2, z 3, z 4, m. The heights of buildings in meters, designated 1H, are set off from the relief marks. 2H, 3H, 4H, m.

Then they begin to plot the pressure graph.

The appropriate pressure range in the return pipes of the main line and branches from them is determined from the following considerations:

• the maximum level of pressure (pressure) of coolants moving through return pipelines should not destroy the elements of consumer systems connected to them. With dependent connection of heating systems, the weakest element is the heating devices, which can withstand a pressure of no more than 60 m of water column. Consequently, the maximum pressure in the return pipes cannot be higher than 60 m;
• the minimum level of pressure in the return line with a dependent connection scheme for heating systems cannot be lower than the geometric height of the building plus 5 m of water column in order to ensure circulation of the coolant through the heating devices of the upper floor.
• The maximum level of pressure in the supply pipes is limited by the strength of the pipelines used. In practice this amounts to 160 or 250 m of water column;
• The minimum level of pressure (pressure) of the coolant in the supply pipe must ensure that it does not boil at the highest temperature τ 1.o.p. The maximum value of the temperatures used is τ 1.o.p = 150°C, therefore the pressure in the supply pipe should not be lower than 55 m of water column.

Taking into account the selected areas, select the pressure value at the end of the return pipe of the main line at point O max (below the upper limit and above the lower limit). From the pressure at point O min - h o,max, subtract Δp 1d /ρg=Δh 1d and find the pressure in the return pipe at point a " - h a ". By connecting them with a straight line, we obtain pressure graphs in the section l 1 ". By subtracting the value Δh 5 from the pressure at point a ", we find the pressure in the return pipe at point at " - h in " and, connecting a " and b ", we obtain a pressure graph at section l 5 ". Next, subtracting from the pressure at point b " Δh 7d, we get the pressure at point c ", and adding to the pressure at point b " Δh 7d, we get the pressure at point d ". Continuing similarly, we get a complete picture of the pressure graph in return pipes.

In a closed heating system, the pressure graph in the supply line is a mirror image of the graph in reverse, but in an area limited by 160¸55 m of water. Art.

As can be seen from Fig. 3.18, due to differences in terrain and differences in the building heights, the buildings being served cannot always be connected to the network according to the standard scheme, namely:

A). For the consumer, 1 pressure in the return line (point O max) ensures water circulation through the upper floors and at the same time does not destroy heating devices. However, the difference in pressure h n min and h o max is less than 10 m and does not ensure the operation of elevators. Therefore, consumer connection 1 is dependent, but with a mixing pump.

b). For consumer 2, the upper elevation of the building, together with the relief elevation z 2, is greater than 60 m, therefore, if circulation in the heating network is disrupted, the hydrostatic pressure from this building can destroy the devices on the lower floors of neighboring buildings. Connecting consumer 2 according to an independent circuit will prevent possible destruction of the devices.

V). For consumer 3, the height of the building and geodetic mark z 3 is less than 60 meters, but higher than the pressure in the return line at the connection point. For normal circulation through the upper floors of the building, a pressure valve is installed on the return riser.

Consumer 4 has everything provided, and the building is connected according to a normal dependent scheme with the elevator.

From the construction of pressure lines in the supply and return lines of the heating network, it is easy to determine the coolant pressures at the entrance to the heat supply source - h c " and at the exit from it - h c ", however, a certain part of the pressure - Δh ist - is necessary to overcome the resistance of water heaters III and internal source pipelines. Therefore, for coolant circulation, the pressure developed by the network pump must be

ΔH с.н =h с h с " +Δh source.

In the event of a planned or emergency stop of the circulation of network water, the pressure level in all sections of the heating network will be equalized. To avoid emptying of heating systems (if it is very low) or destruction of heating devices (if it is too large), on the bypass line of the network pump between valves 1 and 2 installed on it, by adjusting the degree of their opening, create the required level of static pressure - h st. The specified value of this pressure is supplied to the flow regulator IV, which will provide the required level of replenishment of the heating network with water from the make-up pump II to maintain h st constant. When network pump I stops operating, this constant static pressure will be established and maintained throughout the entire network.

Page 1

Hydraulic calculation is the most important element in the design of heating networks.

The task of hydraulic calculation includes:

1. Determination of pipeline diameters,

2. Determination of pressure drop in the network,

3. Establishment of pressure values ​​at various points in the network,

4. Linking pressures at various points of the system in static and dynamic modes of its operation,

5. Establishment of the necessary characteristics of circulation, booster and make-up pumps, their quantity and placement.

6. Determination of methods for connecting subscriber inputs to the heating network.

7. Selection of automatic control circuits and devices.

8. Identification of rational operating modes.

Hydraulic calculations are carried out in the following order:

1) in the graphic part of the project, draw a general plan of the city area on a scale of 1:10000, in accordance with the assignment, indicate the location of the heat source (IT);

2) show a diagram of the heating network from IT to each microdistrict;

3) for the hydraulic calculation of the heating network along the pipeline route, the main design line is selected, as a rule, from the heat source to the most remote heating unit;

4) the design diagram indicates the numbers of sections, their lengths, determined according to the general plan, taking into account the accepted scale, and the estimated water consumption;

5) based on the coolant flow rate and, focusing on the specific pressure loss of up to 80 Pa/m, the diameters of pipelines in sections of the main line are assigned;

6) using the tables, determine the specific pressure loss and coolant velocity (preliminary hydraulic calculation);

7) calculate the branches based on the available pressure difference; in this case, the specific pressure loss should not exceed 300 Pa/m, the coolant speed should not exceed 3.5 m/s;

8) draw a pipeline diagram, arrange shut-off valves, fixed supports, compensators and other equipment; the distances between fixed supports for sections of different diameters are determined based on the data in Table 2;

9) based on local resistances, determine equivalent lengths for each section and calculate the reduced length using the formula:

10) calculate the pressure loss in sections from the expression

,

Where α is a coefficient that takes into account the share of pressure losses due to local resistances;

∆ptr – pressure drop due to friction in a section of the heating network.

The final hydraulic calculation differs from the preliminary one in that the pressure drop across local resistances is taken into account more accurately, i.e. after placing compensators and shut-off valves. Stuffing box expansion joints are used for d ≤ 250 mm; for smaller diameters, U-shaped expansion joints are used.

Hydraulic calculations are performed for the supply pipeline; The diameter of the return pipeline and the pressure drop in it are taken to be the same as in the supply pipeline (clause 8.5).

According to paragraph 8.6, the smallest internal diameter of pipes should be at least 32 mm in heating networks, and at least 25 mm for hot water circulation pipelines.

Preliminary hydraulic calculations begin with the last section from the heat source and are summarized in Table 1.

Table 6 – Preliminary hydraulic calculation

Plot number							lpr=lx (1+α), m	∆Р=Rхlр, Pa
HIGHWAY
DESIGN BRANCH
								∑∆Rotv =

Hello! The main purpose of hydraulic calculation at the design stage is to determine the diameters of pipelines based on specified coolant flow rates and available pressure drops in the network, or in individual sections of the heating network. During the operation of networks, one has to solve the inverse problem - to determine the coolant flow rate in sections of the network or the pressure at individual points when hydraulic conditions change. Without hydraulic calculations, it is impossible to construct a piezometric graph of a heating network. This calculation is also necessary for selecting the connection diagram for the internal heat supply system directly at the consumer and selecting network and make-up pumps.

As is known, hydraulic losses in the network consist of two components: hydraulic linear friction losses and pressure losses in local resistances. By local resistances we mean valves, turns, compensators, etc.

That is, ∆P = ∆Pl + ∆Pplace,

Linear friction losses are determined from the formula:

where λ is the coefficient of hydraulic friction; l – pipeline length, m; d – internal diameter of the pipeline, m; ρ – coolant density, kg/m³; w² — coolant movement speed, m/s.

In this formula, the coefficient of hydraulic friction is determined by the formula of A.D. Altshul:

where Re is the Reynolds number, ke/d is the equivalent pipe roughness. These are reference values. Losses in local resistances are determined by the formula:

where ξ is the total coefficient of local resistance. It must be calculated manually using tables with values ​​of local resistance coefficients. In the calculation attached to the article in Excel format, I added a table with local resistance coefficients.

To perform a hydraulic calculation, you will definitely need a heating network diagram, something like this:

In fact, the scheme, of course, should be more expanded and detailed. I provided this diagram only as an example. From the heating network diagram we need the following data: pipeline length l, flow rate G, and pipeline diameter d.

How to perform hydraulic calculation? The entire heating network that needs to be calculated is divided into so-called design sections. A design section is a section of the network where the flow rate does not change. First, hydraulic calculations are carried out section by section in the direction of the main line, which connects the heat source with the most distant heat consumer. Then the secondary directions and branches of the heating network are calculated. My hydraulic calculation of the heating network section can be downloaded here:

This, of course, is the calculation of only one branch of the heating network (hydraulic calculation of a long-distance heating network is quite a labor-intensive task), but it is enough to understand what hydraulic calculation is, and even for an untrained person to start calculating hydraulics.

I will be glad to receive comments on the article.

HYDRAULIC CALCULATION OF HEAT NETWORKS

The task of hydraulic calculation includes:

Determination of pipeline diameter;

Determination of pressure drop (pressure);

Determination of pressures (pressures) at various points in the network;

Linking all network points in static and dynamic modes in order to ensure permissible pressures and required pressures in the network and subscriber systems.

Based on the results of hydraulic calculations, the following problems can be solved.

1. Determination of capital costs, metal (pipes) consumption and the main volume of work on laying a heating network.

2. Determination of the characteristics of circulation and make-up pumps.

3. Determination of operating conditions of the heating network and selection of subscriber connection schemes.

4. Selection of automation for the heating network and subscribers.

5. Development of operating modes.

a. Schemes and configurations of heating networks.

The layout of the heating network is determined by the location of heat sources in relation to the area of ​​consumption, the nature of the heat load and the type of coolant.

The specific length of steam networks per unit of design heat load is small, since steam consumers - usually industrial consumers - are located at a short distance from the heat source.

A more difficult task is the choice of a water heating network scheme due to its large length and large number of subscribers. Water vehicles are less durable than steam vehicles due to greater corrosion, and are more sensitive to accidents due to the high density of water.

Fig.6.1. Single-line communication network of a two-pipe heating network

Water networks are divided into main and distribution networks. The coolant is supplied through main networks from heat sources to areas of consumption. Through distribution networks, water is supplied to GTP and MTP and to subscribers. Subscribers very rarely connect directly to backbone networks. At the points where distribution networks are connected to the main ones, sectioning chambers with valves are installed. Sectional valves on main networks are usually installed every 2-3 km. Thanks to the installation of sectional valves, water losses during vehicle accidents are reduced. Distribution and main vehicles with a diameter of less than 700 mm are usually made dead-end. In the event of an emergency, a break in the heat supply to buildings for up to 24 hours is acceptable for most of the country. If a break in heat supply is unacceptable, it is necessary to provide for duplication or loopback of the heating system.

Fig.6.2. Ring heating network from three thermal power plants Fig. 6.3. Radial heat network

When supplying heat to large cities from several thermal power plants, it is advisable to provide for mutual interlocking of thermal power plants by connecting their mains with interlocking connections. In this case, a ring heat network with several power sources is obtained. Such a scheme has higher reliability and ensures the transmission of redundant water flows in the event of an accident on any part of the network. When the diameters of the mains extending from the heat source are 700 mm or less, a radial heating network diagram is usually used with a gradual decrease in the pipe diameter as the distance from the source increases and the connected load decreases. This network is the cheapest, but in the event of an accident, the heat supply to subscribers is stopped.

b. Basic calculation dependencies

Fig.6.1. Scheme of fluid movement in a pipe

The fluid velocity in pipelines is low, so the kinetic energy of the flow can be neglected. Expression H=p/r g is called the piezometric head, and the sum of the height Z and the piezometric head is called the total head.

H 0 =Z + p/rg = Z + H.(6.1)

The pressure drop in a pipe is the sum of linear pressure losses and pressure losses due to local hydraulic resistances.

D p=D p l + D p m. (6.2)

In pipelines D p l = R l L, Where R l – specific pressure drop, i.e. pressure drop per unit length of pipe, determined by the d'Arcy formula.

. (6.3)

The hydraulic resistance coefficient l depends on the fluid flow regime and the absolute equivalent roughness of the pipe walls k e. The following values ​​can be taken in calculations k e– in steam lines k e=0.2 mm; in water networks k e=0.5 mm; in condensate pipelines and hot water supply systems k e=1 mm.

With laminar flow of liquid in a pipe ( Re < 2300)

In the transition region 2300< Re < 4000

. (6.5)

At

. (6.6)

Usually in heating networks Re > Re pr, therefore (6.3) can be reduced to the form

, Where . (6.7)

Pressure loss at local resistances is determined by the formula

. (6.8)

Values ​​of the coefficient of local hydraulic resistance x are given in reference books. When performing hydraulic calculations, it is possible to take into account pressure losses due to local resistances across an equivalent length.

Then where a=l eq/l– share of local pressure losses.

a. Hydraulic calculation procedure

Typically, during hydraulic calculations, the coolant flow rate and the total pressure drop in the area are specified. You need to find the diameter of the pipeline. The calculation consists of two stages - preliminary and verification.

Advance paynemt.

2. Set the fraction of local pressure drops a=0.3...0.6.

3. Evaluate specific pressure loss

. If the pressure drop in the area is unknown, then they are set by the value R l < 20...30 Па/м.

4. Calculate the diameter of the pipeline from the operating conditions in turbulent mode. For water heating networks, the density is taken equal to 975 kg/m 3.

From (6.7) we find

, (6.9)

Where r– average density of water in a given area. Based on the found diameter value, a pipe with the closest internal diameter is selected according to GOST. When choosing a pipe, indicate either d y And d, or d n And d.

2. Verification calculation.

For end sections, the driving mode should be checked. If it turns out that the movement mode is transitional, then, if possible, you need to reduce the diameter of the pipe. If this is not possible, then calculations must be made using transition regime formulas.

1. Values ​​are being clarified R l;

2. The types of local resistances and their equivalent lengths are specified. Valves are installed at the outlet and inlet of the collector, at the points of connection of distribution networks to the main ones, branches to the consumer and at consumers. If the length of the branch is less than 25 m, then it is allowed to install the valve only at the consumer. Sectional valves are installed every 1 – 3 km. In addition to valves, other local resistances are possible - turns, changes in cross-section, tees, flow merging and branching, etc.

To determine the number of temperature compensators, the lengths of the sections are divided by the allowable distance between the fixed supports. The result is rounded to the nearest whole number. If there are turns in the area, they can be used to self-compensate for temperature extensions. In this case, the number of compensators is reduced by the number of turns.

5. The pressure loss in the area is determined. For closed systems Dp uch =2R l (l+l e).

For open systems, preliminary calculations are based on the equivalent flow rate

During verification calculations, specific linear pressure losses are calculated separately for the supply and return pipelines for actual flow rates.

, .

At the end of the hydraulic calculation, a piezometric graph is constructed.

a. Piezometric graph of a heating network

The piezometric graph shows the terrain, the height of attached buildings, and the pressure in the network on a scale. Using this graph, it is easy to determine the pressure and available pressure at any point in the network and subscriber systems.

Level 1 - 1 is taken as the horizontal plane of pressure reference. Line P1 - P4 is a graph of supply line pressures. Line O1 – O4 – return line pressure graph. Н о1 – total pressure on the return collector of the source; Nsn – pressure of the network pump; Nst – full pressure of the make-up pump, or full static pressure in the heating network; Nk – total pressure in t.K at the discharge pipe of the network pump; DHt – pressure loss in the heat treatment plant; Нп1 – total pressure on the supply manifold, Нп1= Нк - DHт. Available supply water pressure at the CHP collector N1=Np1-No1. The pressure at any point in the network i is denoted as Нпi, Hoi is the total pressure in the forward and return pipelines. If the geodetic height at point i is Zi, then the piezometric pressure at this point is Нпi – Zi, Hoi – Zi in the forward and return pipelines, respectively. The available pressure at point i is the difference between the piezometric pressures in the forward and return pipelines – Нпi – Hoi. The available pressure in the vehicle at the connection point of subscriber D is H4 = Np4 – Ho4.

Fig.6.2. Scheme (a) and piezometric graph (b) of a two-pipe heating network

There is a loss of pressure in the supply line in section 1 - 4 . There is a pressure loss in the return line in section 1 - 4 . When the mains pump is operating, the pressure Hst of the feed pump is regulated by the pressure regulator to No1. When the network pump stops, a static pressure Nst is established in the network, developed by the make-up pump. When hydraulically calculating a steam pipeline, the profile of the steam pipeline may not be taken into account due to the low steam density. Pressure losses from subscribers, for example depends on the subscriber connection scheme. With elevator mixing D N e= 10...15 m, with elevator-free input – D nb e =2...5 m, in the presence of surface heaters D N n=5...10 m, with pump mixing D N ns= 2…4 m.

Requirements for pressure conditions in the heating network:

b. at any point in the system the pressure should not exceed the maximum permissible value. The pipelines of the heat supply system are designed for 16 ata, the pipelines of local systems are designed for a pressure of 6-7 ata;

c. To avoid air leaks at any point in the system, the pressure must be at least 1.5 atm. In addition, this condition is necessary to prevent pump cavitation;

d. at any point in the system, the pressure must be no less than the saturation pressure at a given temperature in order to avoid boiling of water;

6.5. Features of hydraulic calculation of steam pipelines.

The diameter of the steam line is calculated based on either the permissible pressure loss or the permissible steam velocity. The vapor density in the calculated area is preset.

Calculation based on permissible pressure loss.

Evaluate , a= 0.3...0.6. Using (6.9), the pipe diameter is calculated.

They are set by the steam velocity in the pipe. From the equation for steam flow – G=wrF find the diameter of the pipe.

According to GOST, a pipe with the closest internal diameter is selected. Specific linear losses and types of local resistances are specified, and equivalent lengths are calculated. The pressure at the end of the pipeline is determined. Heat losses in the design area are calculated based on normalized heat losses.

Qpot=q l l, Where q l– heat loss per unit length for a given temperature difference between steam and the environment, taking into account heat loss on supports, valves, etc. If q l determined without taking into account heat losses on supports, valves, etc., then

Qpot=q l (tav – to)(1+b), Where tsr- average steam temperature at the site, to– ambient temperature, depending on the installation method. For above-ground installation to = tno, for underground channelless installation to = tgr(soil temperature at laying depth), when laying in through and semi-through channels to=40…50 0 C. When laying in non-passable channels to= 5 0 C. Based on the found heat losses, the change in the enthalpy of steam in the section and the value of the enthalpy of steam at the end of the section are determined.

Diuch=Qpot/D, ik=in - Diuch.

Based on the found values ​​of steam pressure and enthalpy at the beginning and end of the section, a new value of the average steam density is determined rср = (rn + rc)/2. If the new density value differs from the previously specified value by more than 3%, then the verification calculation is repeated with clarification simultaneously and RL.

a. Features of calculating condensate pipelines

When calculating the condensate pipeline, it is necessary to take into account the possible formation of steam when the pressure drops below the saturation pressure (secondary steam), steam condensation due to heat losses, and passing steam after the steam traps. The amount of passing steam is determined by the characteristics of the steam trap. The amount of condensed steam is determined by heat loss and heat of vaporization. The amount of secondary steam is determined by the average parameters in the design area.

If the condensate is close to the saturation state, then the calculation should be carried out as for a steam pipeline. When transporting supercooled condensate, the calculation is performed in the same way as for water networks.

b. Network pressure mode and choice of subscriber input scheme.

1. For normal operation of heat consumers, the pressure in the return line must be sufficient to fill the system, Ho > DHms.

2. The pressure in the return line must be below the permissible value, po > padd.

3. The actual available pressure at the subscriber input must be no less than the calculated one, DHab DHcalc.

4. The pressure in the supply line must be sufficient to fill the local system, Hp – DHab > Hms.

5. In static mode, i.e. When turning off the circulation pumps, there should be no emptying of the local system.

6. Static pressure should not exceed the permissible value.

Static pressure is the pressure that is established after the circulation pumps are turned off. The level of static pressure (pressure) must be indicated on the piezometric graph. The value of this pressure (pressure) is set based on the pressure limit for heating devices and should not exceed 6 ati (60 m). With a calm terrain, the level of static pressure can be the same for all consumers. With large fluctuations in the terrain there may be two, but not more than three, static levels.

Fig.6.3. Graph of static pressures of the heating system

Figure 6.3 shows a graph of static pressures and a diagram of the heat supply system. The heights of buildings A, B and C are the same and equal to 35 m. If we draw a static pressure line 5 meters above building C, then buildings B and A will find themselves in a pressure zone of 60 and 80 m. The following solutions are possible.

7. Heating installations in buildings A are connected according to an independent circuit, and in buildings B and C - according to a dependent one. In this case, a common static zone is established for all buildings. Water-water heaters will be under a pressure of 80 m, which is acceptable from a strength point of view. Static pressure line – S - S.

8. Heating installations of building C are connected according to an independent circuit. In this case, the total static head can be selected according to the strength conditions of the installations of buildings A and B - 60 m. This level is indicated by the line M - M.

9. The heating installations of all buildings are connected according to a dependent scheme, but the heat supply zone is divided into two parts - one at the M-M level for buildings A and B, the other at the S-S level for building C. For this, a check valve is installed between buildings B and C 7 on the direct line and the feed pump of the upper zone 8 and the pressure regulator 10 on the return line. The maintenance of the given static pressure in zone C is carried out by the feed pump of the upper zone 8 and the feed regulator 9. The maintenance of the given static pressure in the lower zone is carried out by pump 2 and regulator 6.

In the hydrodynamic mode of operation of the network, the above requirements must also be met at any point in the network at any water temperature.

Fig.6.4. Plotting a graph of hydrodynamic pressures of a heat supply system

10. Construction of lines of maximum and minimum piezometric pressures.

The lines of permissible pressures follow the terrain, because It is accepted that pipelines are laid in accordance with the terrain. The reference is from the pipe axis. If the equipment has significant dimensions in height, then the minimum pressure is counted from the top point, and the maximum from the bottom.

1.1. Pmax line – line of maximum permissible pressures in the supply line.

For peak water heating boilers, the maximum permissible pressure is counted from the bottom point of the boiler (it is assumed that it is at ground level), and the minimum permissible pressure is measured from the upper boiler manifold. The permissible pressure for steel hot water boilers is 2.5 MPa. Taking into account losses, it is assumed that Hmax = 220 m at the boiler outlet. The maximum permissible pressure in the supply line is limited by the strength of the pipeline (рmax = 1.6 MPa). Therefore, at the entrance to the supply line Hmax = 160 m.

a. Omax line – line of maximum permissible pressures in the return line.

According to the strength conditions of water-water heaters, the maximum pressure should not be higher than 1.2 MPa. Therefore, the maximum pressure value is 140 m. The pressure value for heating installations cannot exceed 60 m.

The minimum permissible piezometric pressure is determined by the boiling temperature, which exceeds the design temperature at the outlet of the boiler by 30 0 C.

b. Pmin line – line of the minimum permissible pressure in a straight line

The minimum permissible pressure at the outlet of the boiler is determined from the condition of non-boiling at the top point - for a temperature of 180 0 C. It is set to 107 m. From the condition of non-boiling water at a temperature of 150 0 C, the minimum pressure should be 40 m.

1.4. Omin line – line of the minimum permissible pressure in the return line. Based on the condition of inadmissibility of air leaks and cavitation of pumps, a minimum pressure of 5 m was adopted.

Under no circumstances can the actual pressure lines in the forward and return lines go beyond the limits of the maximum and minimum pressure lines.

The piezometric graph gives a complete picture of the operating pressures in static and hydrodynamic modes. In accordance with this information, one or another method of connecting subscribers is selected.

Fig.6.5. Piezometric graph

Building 1. The available pressure is more than 15 m, the piezometric pressure is less than 60 m. The heating installation can be connected in a dependent circuit with the elevator unit.

Building 2. In this case, you can also use a dependent scheme, but since the pressure in the return line is less than the height of the building at the connection point, you need to install a pressure regulator “upstream”. The pressure drop across the regulator must be greater than the difference between the installation height and the piezometric pressure in the return line.

Building 3. The static pressure in this place is more than 60 m. It is best to use an independent scheme.

Building 4. The available pressure in this place is less than 10 m. Therefore, the elevator will not work. A pump needs to be installed. Its pressure must be equal to the pressure loss in the system.

Building 5. It is necessary to use an independent scheme - the static pressure in this place is more than 60 m.

6.8. Hydraulic mode of heating networks

Pressure loss in the network is proportional to the square of the flow rate

Using the formula for calculating pressure loss, we find S.

.

Network pressure losses are defined as , where .

When determining the resistance of the entire network, the following rules apply.

1. When connecting network elements in series, their resistances are summed up S.

S S=S si.

11. When connecting network elements in parallel, their conductivities are summed up.

. .

One of the tasks of the hydraulic calculation of a vehicle is to determine the water flow for each subscriber and in the network as a whole. Usually known: network diagram, resistance of sections and subscribers, available pressure at the collector of a thermal power plant or boiler house.

Rice. 6.6. Heat network diagram

Let's denote S I – S V – resistance of sections of the highway; S 1 – S 5 – subscriber resistances together with branches; V– total water flow in the network, m 3 /s; Vm– water flow through the subscriber installation m; SI-5– resistance of network elements from section I to branch 5; SI-5=S I+ S 1-5, where S 1-5 – total resistance of subscribers 1-5 with corresponding branches.

We find the water flow through installation 1 from the equation

, from here .

For subscriber installation 2

. We will find the difference in costs from the equation

, Where . From here

.

For setting 3 we get

Resistance of the heating network with all branches from subscriber 3 to the last subscriber 5 inclusive; , - resistance of section III of the main line.

For some m th consumer from n relative water flow is found by the formula

. Using this formula, you can find the water flow through any subscriber installation if the total flow in the network and the resistance of network sections are known.

12. The relative water flow through a subscriber installation depends on the resistance of the network and subscriber installations and does not depend on the absolute value of water flow.

13. If connected to the network n subscribers, then the ratio of water consumption through installations d And m, Where d < m, depends only on the resistance of the system, starting from the node d to the end of the network, and does not depend on the network resistance to the node d.

If the resistance changes in any section of the network, then for all subscribers located between this section and the end point of the network, the water consumption will change proportionally. In this part of the network, it is enough to determine the degree of change in consumption for only one subscriber. When the resistance of any network element changes, the flow rate both in the network and for all consumers will change, which leads to misadjustment. Misalignments in the network are corresponding and proportional. With a corresponding misadjustment, the sign of the change in costs coincides. With proportional deregulation, the degree of change in flow rates coincides.

Rice. 6.7. Change in network pressure when one of the consumers is disconnected

If subscriber X is disconnected from the heating network, the total resistance of the network will increase (parallel connection). Water consumption in the network will decrease, pressure losses between the station and subscriber X will decrease. Therefore, the pressure graph (dotted line) will be straighter. The available pressure at point X will increase, so the flow in the network from subscriber X to the end point of the network will increase. For all subscribers from point X to the end point, the degree of change in flow rate will be the same - proportional deregulation.

For subscribers between the station and point X, the degree of change in consumption will be different. The minimum degree of change in consumption will be for the first subscriber directly at the station - f=1. As you move away from the station f > 1 and increasing. If the available pressure at the station changes, then the total water consumption in the network, as well as the water consumption of all subscribers, will change in proportion to the square root of the available pressure at the station.

6.9. Network resistance.

Total network conductivity

, from here

.

Similarly

And

. The network resistance is calculated from the most distant subscriber.

a. Switching on pumping substations.

Pumping substations can be installed on the supply, return pipelines,

as well as on the jumper between them. The construction of substations is caused by unfavorable terrain, long transmission range, the need to increase transmission capacity, etc.

A). Installation of the pump on the supply or return lines.

Fig.6.8. Installing the pump on a flow or sequential line (sequential operation)

When installing a pumping substation (PS) on the supply or return lines, water consumption for consumers located between the station and the PP decreases, and for consumers after the PP they increase. In the calculations, the pump is taken into account as some hydraulic resistance. The calculation of the hydraulic mode of the network with OP is carried out by the method of successive approximations.

Set by a negative value of the hydraulic resistance of the pump

Calculate resistance in the network, water consumption in the network and at consumers

The water flow and pump pressure and its resistance are specified by (*).

Fig.6.10. Summary characteristics of series and parallel connected pumps

When pumps are connected in parallel, the total characteristic is obtained by summing the abscissas of the characteristics. When the pumps are switched on in series, the total characteristic is obtained by summing the ordinates of the characteristics. The degree of change in supply when pumps are connected in parallel depends on the type of network characteristic. The lower the network resistance, the more effective the parallel connection and vice versa.

Fig.6.11. Parallel connection of pumps

When pumps are turned on in series, the total water supply is always greater than the water supply of each pump individually. The higher the network resistance, the more effective the sequential activation of pumps.

b). Installation of the pump on the jumper between the flow and return lines.

When installing the pump on a jumper, the temperature conditions before and after the oil pump are not the same.

To construct the total characteristics of two pumps, the characteristics of pump A are first transferred to node 2, where pump B is installed (see Fig. 6.12). In the given characteristic of pump A2 - 2 pressures at any flow rate are equal to the difference between the actual pressure of this pump and the pressure loss in network C for the same flow rate.

. After bringing the characteristics of pumps A and B to the same common unit, they are added according to the rule for adding pumps operating in parallel. When one pump B is operating, the pressure in node 2 is equal to the water flow rate. When connecting the second pump A, the pressure in node 2 increases to , and the total water flow increases to V>. However, the direct flow of pump B is reduced to .

Fig.6.12. Construction of the hydraulic characteristics of a system with two pumps in different units

a. Network operation with two power supplies

If the vehicle is powered by several heat sources, then meeting points of water flows from different sources appear in the main lines. The position of these points depends on the resistance of the vehicle, the distribution of load along the main line, and the available pressures on the collectors of the thermal power plant. The total water flow in such networks is usually specified.

Fig.6.13. Diagram of a vehicle powered from two sources

The watershed point is located as follows. They are set by arbitrary values ​​of water flow in sections of the main line based on Kirchhoff’s 1st law. The pressure residuals are determined based on Kirchhoff's 2nd law. If, with a pre-selected flow distribution, the watershed is selected in t.K, then the second Kirchhoff equation will be written in the form

, .

According to Kirchhoff's 2nd law, the pressure loss discrepancy is determined Dp. To make the pressure mismatch equal to zero, you need to introduce a flow correction into the calculation - the link flow. To do this, it is assumed in the equation Dp=0 and instead V introduce V+dV or V-dV. We get

. Sign Dp equal to the sign dV. Next, the flow distribution in network sections is clarified. To find the watershed point, two adjacent consumers are checked.

Fig.6.14. Determining the position of the watershed point

A). The watershed point is between consumers m And m+1. In this case . Here is the pressure drop across the consumer m when powered from station A. is the pressure drop across the consumer m+1 when powered from station B.

Let the watershed point be between consumers 1 and 2. Then

; . If these two pressure drops are equal, then the watershed point is between consumers 1 and 2. If not, then the next pair of consumers is checked, etc. If equality of available pressures is not found for any pair of consumers, this means that the watershed point is located at one of the consumers.

a. Ring network.

A ring network can be considered as a network with two power sources with equal pressures of the network pumps. The position of the watershed point in the supply and return lines coincides if the resistances of the supply and return lines are the same and there are no booster pumps. Otherwise, the positions of the watershed point in the supply and return lines must be determined separately. Installing a booster pump leads to a displacement of the watershed point only in the line on which it is installed.

Fig.6.15. Graph of pressure in a ring network

In this case HA = NV.

b. Connection of pumping substations in a network with two power sources

To stabilize the pressure regime in the presence of a booster pump at one of the stations, the pressure at the inlet manifold is maintained constant. This station is called fixed, other stations are called free. When installing a booster pump, the pressure in the inlet manifold of a free station changes by the amount .

a. Hydraulic mode of open heating systems

The main feature of the hydraulic mode of open heat supply systems is that in the presence of water intake, the water flow in the return line is less than in the supply. In practice, this difference is equal to water withdrawal.

Fig.6.18. Piezometric graph of an open system

The piezometric graph of the supply line remains constant during any water withdrawal from the return line, since the flow rate in the supply line is maintained constant using flow regulators at the subscriber inputs. With an increase in water withdrawal, the flow rate in the return line decreases and the piezometric graph of the return line becomes flatter. When the water withdrawal is equal to the flow rate in the supply line, the flow rate in the return line is zero and the piezometric graph of the return line becomes horizontal. With the same diameters of the forward and reverse lines and the absence of water withdrawal, the pressure graphs in the forward and reverse lines are symmetrical. In the absence of water supply for hot water supply, water consumption is equal to the calculated heating consumption - V.

From equation (***) we can find f.

1. When DHW water is drawn from the supply line, the flow through the heating system drops. When parsing from the return line, it increases. At b=0.4 water flow through the heating system is equal to the calculated one.

2. The degree of change in water flow through the heating system -

3. The degree of change in water flow through the heating system is greater, the lower the system resistance.

An increase in water withdrawal for DHW can lead to a situation where all the water after the heating system goes to the DHW tap. In this case, the water flow in the return pipeline will be zero.

From (***): , where (****)

When hydraulically calculating heating networks, the total flow rate of main hot water for heating, air conditioning, ventilation and domestic hot water is determined. Based on this calculation, the necessary parameters of pumping equipment, heat exchangers and pipe diameters of the main network are determined.

A little about theory and tasks

The main task of the hydraulic calculation of heating networks is the selection of geometric parameters of the pipe and standard sizes of control elements to ensure:

• qualitative and quantitative distribution of coolant to individual heating devices;
• thermal-hydraulic reliability and economic feasibility of a closed thermal system;
• optimization of investment and operating costs of the heat supply organization.

Hydraulic calculation creates the prerequisites for heating and hot water devices to achieve the required power at a given temperature difference. For example, with a T-graph of 150-70 o C, it will be equal to 80 o C. This is achieved by creating the required water pressure or coolant pressure at each heating point.

This mandatory condition for the operation of a heating system is implemented through proper configuration of network equipment in accordance with design conditions, installation of equipment based on the results of hydraulic calculations of heating networks.

Network hydraulic stages:

1. Pre-launch calculation.
2. Operational regulation.

The initial hydraulics of the network is performed:

• using calculations;
• measuring method.

In the Russian Federation, the calculation method is predominant; it determines all the parameters of the elements of the heat supply system in a single design area (house, block, city). Without this, the network will be misregulated, and the coolant will not be supplied to the upper floors of multi-story buildings. That is why the beginning of the construction of any heating supply facility, even the smallest one, begins with a hydraulic calculation of heating networks.

Drawing up a diagram of heating networks

Before hydraulic calculations, a preliminary pipeline diagram is performed indicating the length L in meters and D of utility water pipelines in mm and the estimated volumes of network water for the design sections of the diagram. Pressure losses in heat supply systems are divided into linear, which arise due to the carrier rubbing against the pipe walls, and losses in areas caused by local structural resistance due to the presence of tees, bends, compensators, turns and other devices.

Calculation example: hydraulic calculation of heating networks:

1. First, a larger calculation is performed in order to determine the maximum network indicators that can fully provide residents with heating services.
2. Upon completion, qualitative and quantitative indicators of the main and intra-block networks are established, including the final pressure and temperature of the medium at the input nodes of heat consumers, taking into account heat losses.
3. Perform a test hydraulic calculation of the heating and hot water supply network.
4. They establish the actual costs in sections of the circuit and at the inputs to residential buildings, the amount of heat received by subscribers when calculating the temperature of the coolant in the supply water pipe of heating systems and the available pressure in the outlet manifold, justification for hydrothermal regimes, and the predicted temperature inside residential premises.
5. Determine the required heat supply temperature at the outlet.
6. Set the maximum size T of heated water at the outlet of a boiler room or other heat source, obtained on the basis of a hydraulic calculation of the heating network. It must ensure sanitary standards indoors.

Applications of the normative method

Hydraulics of networks is carried out on the basis of tables of maximum hourly heat loads and a heat supply diagram for a city or region, indicating the sources, location of the main, intra-block and intra-house engineering systems, indicating the boundaries of the balance sheet ownership of the network owners. Hydraulic calculation of heating network pipelines for each section up to the above diagram is carried out separately.

This calculation method is used not only for heating networks, but also for all pipelines transporting liquid media, including gas condensate and other chemical liquid media. For pipeline heat supply systems, changes must be made taking into account the kinematic viscosity and density of the media. This is due to the fact that these characteristics influence the specific pressure loss in the pipes, and the flow rate is related to the density of the transit medium.

Parameters of hydraulic calculation of water heating network

Heat consumption Q and the amount of coolant G for areas are indicated in the table of maximum hourly heat consumption indicators for the winter and summer seasons separately and corresponds to the amount of heat consumption for the quarters included in the scheme.

An example of a hydraulic calculation of a heating network is presented below.

Since calculations depend on many indicators, they are performed using numerous tables, diagrams, graphs, nomograms, the final value of heat consumption Q for intra-house heating systems is obtained by interpolation.

The amount of liquid circulating in the heating network m 3 / hour, when calculating the hydraulic mode of the heating network, is determined by the formula:

G = (D2 / 4) x V,

• G - carrier consumption, m 3 /hour;
• D - pipeline diameter, mm;
• V - flow velocity, m/s.

Linear pressure drops in 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, vents, bends and others that create resistance to the transit environment.

The reasons for the drop in pressure in 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 Methodology and Process Steps

According to the method of hydraulic calculation of heating networks, it is carried out in two stages:

1. Construction of a diagram of heating networks on which sections are numbered, first in the area of ​​the central main line - a longer and more voluminous network line in terms of load from the connection point to a more distant consumption facility.
2. Calculation of pressure losses of each pipe section, diagrams. 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 is the costs established according to the scheme. In this case, reference data on specific pressure losses in networks are used.

1. The number of compensators according to the scheme.
2. Resistances on actually installed heating network elements.

Pressure losses are calculated using formulas and nomograms. Then, having this data for the entire network, they calculate the hydromechanical regime of individual sections from the point of flow splitting up to the end subscriber.

Calculations are linked to the choice of branch pipe diameters. Inconsistency no more than 10%. Excess pressure in the heating network is extinguished at elevator units, throttle nozzles or automatic regulators at in-house control points.

Given the available pressure of the main heating network and branches, first set the approximate resistivity Rm, Pa/m.

The calculations use tables, nomograms for heating networks and other reference literature, which is mandatory for all stages; it is easy to find on the Internet and in specialized literature.

The algorithm for the calculation scheme is established by regulatory and technical documentation, state and sanitary standards and is carried out in strict accordance with the established procedure.

The article provides an example of a hydraulic calculation of a heating network. The procedure is performed in the following sequence:

1. On the approved city and district, nodal points of calculation, heat source, routing of engineering systems are marked, indicating all branches and connected consumer facilities.
2. The boundaries of the balance sheet affiliation of consumer networks are clarified.
3. Assign numbers to the site according to the scheme, starting numbering from the source to the final consumer.

The numbering system should clearly separate the types of networks: intra-block main lines, inter-house ones from the thermal well to the boundaries of the balance sheet, while the section is established as a section of the network, enclosed by two branches.

The diagram shows all the parameters of the hydraulic calculation of the main heating network from the central heating substation:

• Q - GJ/hour;
• G m 3 /hour;
• D - mm;
• V - m/s;
• L is the length of the section, m.

This heating network is designed for a heat supply system using coolant in the form of steam.

The differences between this scheme and the previous one are caused by temperature indicators and environmental pressure. Structurally, these networks are characterized by a shorter length; in large cities they usually include only main lines, i.e. from the source to the central heating point. They are not used as intra-district and intra-house networks, except at small industrial sites.

The schematic diagram is carried out in the same order as with water coolant. At the sections, all network parameters are indicated for each branch; data is taken from a summary table of maximum hourly heat consumption, with step-by-step summation of consumption indicators from the end consumer to the source.

The geometric dimensions of pipelines are established based on the results of hydraulic calculations, which are performed in accordance with state norms and regulations, 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 high, and a smaller diameter of the steam line will be required. The diameter is selected according to special tables, based on the parameters of the coolant. The data is then entered into pivot tables.

Coolant for condensate network

The calculation for such a heating network differs significantly from the previous ones, since condensate simultaneously exists in two states - in steam and in water. This ratio changes as it moves towards the consumer, i.e. the steam becomes more and more wet and eventually turns completely into a liquid. Therefore, calculations for pipes for each of these media are different and are taken into account by other standards, in particular SNiP 2.04.02-84.

The procedure for calculating condensate pipelines:

1. The internal equivalent roughness of pipes is determined from the tables.
2. Indicators of pressure loss in pipes in the network section, from the coolant outlet from the heating pumps to the consumer, are taken according to SNiP 2.04.02-84.
3. The calculation of these networks does not take into account the heat consumption Q, but only the steam consumption.

The design 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; sections of the network after the network pumps, due to air leaks, quickly corrode from excess oxygen, after which low-quality condensate with iron oxides is formed, which causes metal corrosion. Therefore, it is recommended to install stainless steel pipelines in this area. Although the final choice will be made after completion of the feasibility study of the heating network.

Energy losses due to valves, fittings and bends are caused by localized flow disturbances. Energy loss occurs along a finite 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 is often the case that the resulting losses will be negligible in relation to the total pressure loss in the pipe.

Pipeline losses are measured using actual experimental data and then analyzed to determine a local loss factor that can be used to calculate fitting losses as it varies with the rate of fluid flow through the device.

Pipe Flow Software products make it easy to determine fitting losses and other losses in pressure drop calculations because they come pre-loaded with a valve database that contains many standard factors for various sized valves and fittings. Within a piping system, a pump is often used to add additional pressure to overcome losses due to friction and other resistance.

The pump performance is determined by the curve. The head produced by the pump varies depending on the flow rate, finding the operating point on the pump performance curve is not always an easy task.

Using the Pipe Flow Expert hydraulic design software, it is quite easy to find the exact operating point on the pump curve, ensuring that flows and pressures are balanced throughout the system, to make accurate piping design decisions.

Online calculations are made in order to select the optimal diameter that provides the best operating parameters, low pressure losses and high speeds of fluid movement, which will ensure good technical and economic indicators of heating networks as a whole.

It minimizes effort and provides higher accuracy. It includes all the necessary reference tables and nomograms. Thus, losses per meter of pipes are assumed to be 81 - 251 Pa/m (8.1 - 25.1 mm water column), which depends on the material of the pipes. The water speed in the system depends on the diameter of the installed pipes and is selected in a specific range. The highest water speed for heating networks is 1.5 m/s. The calculation suggests boundary values ​​of water speed in pipelines with an internal diameter:

1. 15.0 mm - 0.3 m/s;
2. 20.0 mm - 0.65 m/s;
3. 25.0 mm - 0.8 m/s;
4. 32.0 mm - 1.0 m/s.
5. For other diameters no more than 1.5 m/s.
6. For pipelines of fire protection systems, medium speeds of up to 5.0 m/s are allowed.

GIS Zulu is a geoinformation program for hydraulic calculation of heating networks. The company specializes in research into GIS applications that require visualization of 3D geodata in vectorial and raster versions, topological study and their relationship with semantic databases. Zulu allows you to create different plans and working diagrams, including heat 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 implemented in an extended module version. The network is easily and quickly entered into the GIS using the mouse or using these coordinates. After which a calculation scheme is immediately created. Afterwards, the circuit parameters are set and the start of the process is confirmed. Calculations are used for dead-end and ring heating networks, including network pumping units and throttling devices, powered from one or many sources. Heating calculations can be carried out taking into account leaks from distribution networks and heat losses in heating pipes.

In order to install a special program on a PC, download “Hydraulic calculation of heating networks 3.5.2” on the Internet via torrent.

Structure of definition stages:

1. Definition of commutation.
2. Verification hydromechanical calculation of the heating network.
3. Adjustment thermal-hydraulic calculation of main and intra-quarter pipes.
4. Design choice of heating network equipment.
5. Calculation of the piezometric graph.

Microsoft Excel for hydraulic calculations in heating networks is the most accessible tool for users. Its comprehensive spreadsheet editor can solve many computing 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 pipe diameter based on a given conditional indicator and reverse calculation;
• establishing a correction factor for the size of the specific pressure loss based on the data and the equivalent roughness of the pipe material;
• calculating the density of a medium from its temperature.

Of course, the use of Microsoft Excel for hydraulic calculations in heating networks does not make it possible to completely simplify the calculation process, which initially creates relatively large labor costs.

Software for hydromechanical calculations of networks or the GRTS package is a computer application that performs hydromechanical calculations of multi-pipe networks, including a dead-end configuration. The GRTS platform contains formula language functionality that allows you to establish the necessary calculation characteristics and select formulas for the accuracy of their determination. Due to the use of this functionality, the calculator has the opportunity to independently find the computing technology and set the required complexity.

There are two modifications of the GRTS application: 1.0 and 1.1. Upon completion, the user will receive the following results:

• calculation, in which the calculation methodology is carefully described;
• report in tabular form;
• transfer of computational databases to Microsoft Excel;
• piezometric graph;
• coolant temperature graph.

The GRTS 1.1 application is considered the most modern modification and supports the latest standards:

1. Calculation of pipe diameters based on given pressures at the end points of the thermal diagram.
2. The help platform has been modernized. Team "?" Opens the help area of ​​the application on the monitor screen.

Hydraulic calculation of heating networks

An example calculation is presented below.

The minimum basic parameters required to design a piping system include:

1. Characteristics and physical properties of liquid.
2. The required mass flow (or volume) of the transit medium to be transported.
3. Pressure, temperature at the starting point.
4. Pressure, temperature and altitude at the end point.
5. Distance between two points and equivalent length (pressure loss) installed by valves and fittings.

These basic parameters are necessary for the design of a piping system. Assuming steady flow, there are a number of equations based on the general energy equation that can be used to design a piping system.

Variables associated with liquid, steam or two-phase condensate flow 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 faced by an engineer can be solved by standard Bernoulli flow equations.

The basic equation developed to represent steady fluid flow is Bernoulli's equation, which assumes that total mechanical energy is conserved for steady, incompressible, inviscid isothermal flow without heat transfer. These constraint conditions may indeed be representative of many physical systems.

The head losses associated with valves and fittings can also be calculated by taking into account the equivalent "lengths" of pipe sections for each valve and fitting. In other words, the calculated head loss caused by the fluid passing through the valve is expressed as an additional 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 design pipe segment.

To summarize, we can say that the goal of the hydraulic calculation of the heating network at the end point is the fair distribution of thermal loads between subscribers of thermal systems. A simple principle applies here: each radiator, as needed, that is, a larger radiator, which is designed to provide a larger volume of heating to the room, should receive a larger coolant flow. This principle can be ensured by correctly performed network calculations.