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Hydraulic calculation is the most important element in the design of heat networks.
The task of hydraulic calculation includes:
1. Determination of pipeline diameters,
2. Determination of the pressure drop in the network,
3. Establishing the magnitude of pressure (pressure) at various points in the network,
4. Coordination of 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 number and location.
6. Determination of methods for connecting subscriber inputs to the heating network.
7. Selection of schemes and devices for automatic control.
8. Identification of rational modes of operation.
Hydraulic calculation is carried out in the following order:
1) in the graphic part of the project, a general plan of the city district is drawn on a scale of 1: 10000, in accordance with the task, the location of the heat source (IT) is applied;
2) show the scheme of the heat network from IT to each microdistrict;
3) for the hydraulic calculation of the heat network on the pipeline route, the main design line is selected, as a rule, from the heat source to the most remote heat unit;
4) on the calculation scheme indicate the numbers of sections, their lengths, determined according to the general plan, taking into account the accepted scale, and the estimated water flow;
5) on the basis of coolant flow rates and, focusing on a specific pressure loss of up to 80 Pa / m, designate the diameters of pipelines in sections of the main;
6) according to the tables, the specific pressure loss and the coolant velocity are determined (preliminary hydraulic calculation);
7) calculate the branches according to the available pressure drop; in this case, the specific pressure loss should not exceed 300 Pa / m, the coolant velocity - 3.5 m / s;
8) draw a diagram of pipelines, arrange shut-off valves, fixed supports, compensators and other equipment; distances between fixed supports for sections of different diameters are determined based on the data in table 2;
9) based on local resistances, determine the equivalent lengths for each section and calculate the reduced length using the formula:
10) calculate the pressure loss in the sections from the expression
,
Where α is a coefficient that takes into account the proportion of pressure losses at local resistances;
∆ptr is the pressure drop due to friction in the section of the heating network.
The final hydraulic calculation differs from the preliminary one in that the pressure drop due to local resistances is taken into account more accurately, i.e. after the arrangement of compensators and shut-off fittings. Gland expansion joints are used for d ≤ 250 mm, for smaller diameters - U-shaped expansion joints.
Hydraulic calculation is 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 taken in heating networks at least 32 mm, and for hot water circulation pipelines - at least 25 mm.
The preliminary hydraulic calculation starts from the last section from the heat source and is summarized in Table 1.
Table 6 - Preliminary hydraulic calculation
|
plot number |
lpr=lx (1+α), m |
∆Р=Rхlpr, Pa | |||||||
|
HIGHWAY |
|||||||||
|
SETTLEMENT BRANCH |
|||||||||
|
∑∆Rotv = | |||||||||
The task of hydraulic calculation includes:
Determining the diameter of pipelines;
Determination of pressure drop (pressure);
Determination of pressures (heads) at various points in the network;
Coordination of all network points in static and dynamic modes in order to ensure acceptable pressures and required pressures in the network and subscriber systems.
According to the results of hydraulic calculation, the following tasks can be solved.
1. Determination of capital costs, consumption of metal (pipes) and the main scope of work for laying a heating network.
2. Determination of the characteristics of circulation and make-up pumps.
3. Determination of the operating conditions of the heating network and the choice of schemes for connecting subscribers.
4. The choice of automation for the heating network and subscribers.
5. Development of operating modes.
a. Schemes and configurations of thermal networks.
The scheme of the heat network is determined by the placement of heat sources in relation to the area of consumption, the nature of the heat load and the type of heat carrier.
The specific length of steam networks per unit of calculated heat load is small, since steam consumers - as a rule, industrial consumers - are located at a short distance from the heat source.
A more difficult task is the choice of the scheme of water heating networks due to the large length, a large number of subscribers. Water vehicles are less durable than steam ones due to greater corrosion, more sensitive to accidents due to the high density of water.
Fig.6.1. Single-line communication network of a two-pipe heat network
Water networks are divided into main and distribution networks. Through the main networks, the coolant is supplied from heat sources to the areas of consumption. Through distribution networks, water is supplied to the GTP and MTP and to subscribers. Subscribers rarely connect directly to backbone networks. Sectioning chambers with valves are installed at the distribution network connection points to the main ones. Sectional valves on main networks are usually installed after 2-3 km. Thanks to the installation of sectional valves, water losses during vehicle accidents are reduced. Distribution and main TS with a diameter of less than 700 mm are usually made dead-end. In case of accidents, for most of the country's territory, a break in the heat supply of buildings up to 24 hours is allowed. If a break in heat supply is unacceptable, it is necessary to provide for duplication or loopback of the TS.
Fig.6.2. Ring heating network from three CHPPs Fig.6.3. Radial heating network
When supplying large cities with heat from several CHPs, it is advisable to provide for mutual blocking of CHPs by connecting their mains with blocking connections. In this case, a ring heating network with several power sources is obtained. Such a scheme has a higher reliability, provides the transfer of reserving water flows in case of an accident in any section of the network. With diameters of lines extending from the heat source of 700 mm or less, a radial scheme of the heat network is usually used with a gradual decrease in the diameter of the pipe as it moves away from the source and the connected load decreases. Such a network is the cheapest, but in the event of an accident, heat supply to subscribers is stopped.
b. Main calculated dependencies
Fig.6.1. Scheme of the movement of fluid 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 \u003d Z + p/rg = Z + H.(6.1)
The pressure drop in the 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 is the specific pressure drop, i.e. pressure drop per unit length of the pipe, determined by the formula d "Arcy.
. (6.3)
The coefficient of hydraulic resistance l depends on the fluid flow regime and the absolute equivalent roughness of the pipe walls to e. can be taken into account the following values to e- in steam lines to e=0.2 mm; in water networks to e=0.5 mm; in condensate pipelines and hot water systems to e=1 mm.
For laminar fluid flow in a pipe ( Re < 2300)
In the transition region 2300< Re < 4000
. (6.5)
At 
. (6.6)
Usually in heating networks Re > Re pr, so (6.3) can be reduced to the form
, Where 
. (6.7)
Pressure losses at local resistances are determined by the formula
. (6.8)
Values of the coefficient of local hydraulic resistance x are given in reference books. In hydraulic calculations, pressure losses due to local resistances through the equivalent length can be taken into account.
Then where a=l equiv /l is the proportion of local pressure losses.
a. Hydraulic calculation procedure
Usually, in a hydraulic calculation, the flow rate of the coolant and the total pressure drop in the section are set. It is required to find the diameter of the pipeline. The calculation consists of two stages - preliminary and verification.
Advance paynemt.
2. Specified by the proportion of local pressure drops a=0.3...0.6.
3. Estimate the specific pressure loss
. If the pressure drop in the area is unknown, then they are given 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 assumed to be 975 kg / m 3.
From (6.7) we find
, (6.9)
Where r- the average density of water in this area. According to the diameter value found, a pipe with the nearest inner diameter is selected according to GOST. When choosing a pipe, indicate either d 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 transient, then, if possible, it is necessary to reduce the diameter of the pipe. If this is not possible, then it is necessary to carry out the calculation according to the formulas of the transient mode.
1. Values are specified R l;
2. Types of local resistances and their equivalent lengths are specified. Gate 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 branch length is less than 25 m, then it is allowed to install the valve only at the consumer. Sectional valves are installed after 1 - 3 km. In addition to gate valves, other local resistances are also possible - turns, changes in section, tees, merging and branching of the flow, 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 section, then they can be used for self-compensation of temperature elongations. 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 \u003d 2R l (l + l e).
For open systems, preliminary calculation is carried out according to the equivalent flow rate
In the verification calculation, the 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 built.
a. Piezometric graph of the heat network
On the piezometric graph, the relief of the terrain, the height of the attached buildings, and the pressure in the network are plotted 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.
The level 1 - 1 is taken as the horizontal reference plane for the pressures. Line P1 - P4 - the graph of the pressures of the supply line. Line O1 - O4 - graph of the pressure of the return line. H o1 - full pressure on the return collector of the source; Hsn - pressure of the network pump; Нst is the total head of the make-up pump, or the total static head in the heating network; Hk - total pressure in t.K on the discharge pipe of the network pump; DHt is the pressure loss in the heat-preparation plant; Np1 - full pressure on the supply manifold, Np1 \u003d Hk - DHt. The available pressure of network water on the collector of the CHPP is H1=Np1-No1. The pressure at any point in the network i is denoted as Нпi, Hoi - total pressure in the forward and reverse pipelines. If the geodetic height at point i is Zi, then the piezometric head at this point is Hpi - Zi, Hoi - Zi in the straight line 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 TS at the subscriber's connection point D is H4 = Hp4 - No4.
Fig.6.2. Scheme (a) and piezometric graph (b) of a two-pipe heating network
There is a pressure loss in the supply line in section 1 - 4. There is a pressure loss in the return line in section 1 - 4 
. During the operation of the network pump, the pressure Hst of the feed pump is regulated by the pressure regulator up to No1. When the network pump stops, a static head Hst is established in the network, developed by the make-up pump. In the hydraulic calculation of the steam pipeline, the profile of the steam pipeline can be ignored due to the low steam density. Pressure loss at subscribers, for example 
depends on the connection scheme of the subscriber. With elevator mixing D H e = 10 ... 15 m, with elevatorless input - D nb e = 2 ... 5 m, in the presence of surface heaters D H n=5…10 m, with pump mixing D H ns= 2…4 m.
Requirements for the pressure regime in the heating network:
b. at any point in the system, the pressure must not exceed the maximum allowable value. Pipelines of the heat supply system are designed for 16 atm, pipelines of local systems - for pressure of 6-7 atm;
c. in order 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 not be less than the saturation pressure at a given temperature in order to prevent water from boiling;
6.5. Features of the hydraulic calculation of steam pipelines.
The diameter of the steam line is calculated based on either the allowable pressure loss or the allowable steam velocity. The steam density in the calculated section is preliminarily set.
Calculation of admissible pressure losses.
Appreciate 
, a= 0.3...0.6. According to (6.9), the pipe diameter is calculated.
Set by the speed of steam in the pipe. From the equation for steam flow - G=wrF find the pipe diameter.
According to GOST, a pipe with the nearest inner diameter is selected. Specific linear losses and types of local resistances are specified, equivalent lengths are calculated. The pressure at the end of the pipeline is determined. Heat losses are calculated in the design area according to 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 losses on supports, valves, etc. If q l determined without taking into account heat losses on supports, valves, etc., then
Qpot \u003d q l (tav - to) (1 + b), Where tav- average steam temperature in the area, to- ambient temperature, depending on the laying method. For ground laying to = tno, for underground channelless laying to = tgr(soil temperature at the laying depth), when laying in through and semi-through channels to= 40 ... 50 0 С. When laying in impassable channels to= 5 0 C. Based on the heat losses found, 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 rav = (rн + rk)/2. If the new density value differs from the previously specified one by more than 3%, then the verification calculation is repeated with clarification at the same time and Rl.
a. Features of the calculation of condensate pipelines
When calculating the condensate pipeline, it is necessary to take into account the possible vaporization 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 the heat loss and the heat of vaporization. The amount of secondary steam is determined by the average parameters in the design area.
If the condensate is close to saturation, then the calculation should be carried out as for a steam pipeline. When transporting supercooled condensate, the calculation is carried out 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 > pperm.
3. The actual available pressure at the subscriber's input must not be 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 must be no emptying of the local system.
6. Static pressure must not exceed the allowable.
Static pressure is the pressure that is set after the circulation pumps are switched off. The level of static pressure (pressure) must be indicated on the piezometric graph. The value of this pressure (pressure) is set on the basis of the pressure limit for heating appliances and should not exceed 6 atm (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 pressure and a diagram of the heat supply system. The height of buildings A, B and C is the same and equal to 35 m. If you draw a line of static pressure 5 meters above building C, then buildings B and A will be in a pressure zone of 60 and 80 m. The following solutions are possible.
7. Heating installations of buildings A are connected according to an independent scheme, 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 pressure of 80 m, which is acceptable in terms of strength. Line of static pressure - S - S.
8. Heating installations of building C are connected according to an independent scheme. 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 M-M level for buildings A and B, the other on S-S level for building C. To do this, between buildings B and C, a check valve 7 is installed on the direct line and a make-up pump of the upper zone 8 and a pressure regulator 10 on the return line. The specified static head in zone C is maintained by the boost pump of the upper zone 8 and the boost regulator 9. The preset static head in the lower zone is maintained by pump 2 and regulator 6.
In the hydrodynamic mode of the network, the above requirements must also be observed 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 heads.
The lines of permissible pressures follow the terrain, because it is assumed that pipelines are laid in accordance with the relief. Reading - from the axis of the pipe. If the equipment has significant dimensions in height, then the minimum pressure is counted from the upper point, and the maximum - from the lower one.
1.1. The Pmax line is the line of the maximum allowable pressure in the supply line.
For peak hot water boilers, the maximum allowable head is measured from the lower point of the boiler (it is assumed that it is at ground level), and the minimum allowable head is measured from the upper collector of the boiler. Permissible pressure for steel boilers 2.5 MPa. Taking into account the losses, Hmax=220 m is assumed at the outlet of the boiler. The maximum allowable 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. The Omax line is the line of the maximum allowable pressure in the return line.
According to the strength condition of water-to-water heaters, the maximum pressure should not exceed 1.2 MPa. Therefore, the maximum head value is 140 m. The head value for heating installations cannot exceed 60 m.
The minimum allowable piezometric head is determined by the boiling temperature, which is 30 0 C higher than the calculated temperature at the outlet of the boiler.
b. Pmin line - the line of the minimum allowable head in a straight line
The minimum allowable pressure at the outlet of the boiler is determined from the condition of non-boiling at the upper 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 head should be 40 m.
1.4. The Omin line is the line of the minimum allowable head in the return line. From the condition of inadmissibility of air leaks and cavitation of pumps, a minimum head of 5 m was adopted.
The actual pressure lines in the forward and reverse lines under no circumstances can go beyond the lines of maximum and minimum pressures.
The piezometric graph gives a complete picture of the acting heads 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, piezometric - less than 60 m. It is possible to connect the heating installation according to a dependent scheme with an elevator unit.
Building 2. In this case, you can also apply the dependent scheme, but since the pressure in the return line is less than the height of the building in the connection point, it is necessary to install a pressure regulator "to yourself". The differential pressure across the regulator must be greater than the difference between the installation height and the piezometric head in the return line.
Building 3. The static head 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. You need to install a pump. Its pressure must be equal to the pressure loss in the system.
Building 5. It is necessary to use an independent scheme - the static head in this place is more than 60 m.
6.8. Hydraulic mode of heating networks
The pressure loss in the network is proportional to the square of the flow
Using the formula for calculating pressure losses, we find S.
.
The head loss in the network is defined as , where 
.
When determining the resistance of the entire network, the following rules apply.
1. When the network elements are connected in series, their resistances are summed up S.
S S=S si.
11. When the network elements are connected in parallel, their conductivities are summed up.
. 
.
One of the tasks of the hydraulic calculation of the TS is to determine the water consumption for each subscriber and in the network as a whole. Usually known: network diagram, resistance of sections and subscribers, available pressure on the collector of a CHP or boiler house.
Rice. 6.6. Heat network diagram
Denote S I- S V - resistance sections of the highway; S 1 – S 5 - resistance of subscribers together with branches; V- total water consumption in the network, m 3 / s; Vm– water consumption through a 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 - the total resistance of subscribers 1-5 with the corresponding branches.
The water flow through installation 1 is found from the equation
, hence 
.
For indoor installation 2
. We 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 highway.
For some m-th consumer from n the 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 the network sections are known.
12. The relative water flow through the subscriber installation depends on the resistance of the network and subscriber installations and does not depend on the absolute value of the 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 resistance of the network to the node d.
If resistance changes on any section of the network, then all subscribers located between this section and the end point of the network will change the water flow proportionally. In this part of the network, it is sufficient to determine the degree of change in the consumption of only one subscriber. When the resistance of any element of the network changes, the flow rate will change both in the network and for all consumers, which leads to misalignment. Misregulations in the network are corresponding and proportional. With a corresponding misadjustment, the sign of the change in costs coincides. With proportional misalignment, the degree of change in costs coincides.
Rice. 6.7. Change in network pressure when one of the consumers is turned off
If subscriber X is disconnected from the heating network, then the total resistance of the network will increase (parallel connection). The water flow in the network will decrease, the pressure loss between the station and the subscriber X will decrease. Therefore, the pressure graph (dotted line) will go more smoothly. 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 will be the same - proportional misalignment.
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 at the first subscriber directly at the station - f=1. As you move away from the station f > 1 and increases. 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
, hence
.
Similarly
And
. The calculation of the network resistance is carried out from the most remote subscriber.
a. Inclusion of pumping substations.
Pumping substations can be installed on the supply, return pipelines,
and also on the jumper between them. The construction of substations is caused by unfavorable terrain, long transmission distance, the need to increase the bandwidth, etc.
A). Installation of a pump on the supply or return lines.
Fig.6.8. Installing a pump in a supply or series line (serial operation)
When installing a pumping substation (NP) on the supply or return lines, the water consumption for consumers located between the station and the NP decreases, and for consumers after the NP they increase. In the calculations, the pump is taken into account as some hydraulic resistance. The calculation of the hydraulic regime of the network with NP is carried out by the method of successive approximations.
Set by the 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 rate and the pump pressure and its resistance are specified by (*).
Fig.6.10. Total characteristics of series and parallel connected pumps
When the pumps are connected in parallel, the total characteristic is obtained by summing the abscissas of the characteristics. When the pumps are connected in series, the total characteristic is obtained by summing the ordinates of the characteristics. The degree of change in supply when the pumps are connected in parallel depends on the type of network characteristic. The lower the resistance of the network, the more efficient the parallel connection and vice versa.
Fig.6.11. Parallel connection of pumps
When the pumps are connected in series, the total water supply is always greater than the water supply by each of the pumps individually. The greater the resistance of the network, the more efficient the series connection of the pumps.
b). Installation of the pump on the jumper between the supply and return lines.
When installing the pump on the jumper temperature regime before and after NP is not the same.
To build the total characteristic of two pumps, the characteristic of pump A is first transferred to node 2, where pump B is installed (see Fig. 6.12). On the given characteristic of the pump A2 - 2, the pressures at any flow rate are equal to the difference between the actual pressure of this pump and the head loss in the network C for the same flow rate.
. After bringing the characteristics of pumps A and B to the same common node, they are added according to the rule of addition of pumps operating in parallel. When one pump B is operating, the pressure in node 2 is equal to , water flow. When the second pump A is connected, the pressure in node 2 increases to , and the total water flow increases to V>. However, the direct supply of pump B is reduced to .
Fig.6.12. Building a hydraulic characteristic of a system with two pumps in different nodes
a. Network operation with two power supplies
If the vehicle is powered by several heat sources, then in the main lines there are points of meeting of water flows from different sources. The position of these points depends on the resistance of the vehicle, the distribution of the load along the main, and the available pressures on the collectors of the CHP. The total water consumption in such networks is usually given.
Fig.6.13. Scheme of a vehicle powered by two sources
The watershed point is found as follows. They are set by arbitrary values of water flow in sections of the highway based on the 1st Kirchhoff law. The head residuals are determined on the basis of the 2nd Kirchhoff 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 - pressure drop at the consumer m + 1 when powered from station B. or .
2. According to the equation (*), the second is calculated.
3. Calculate the resistance of the network and the flow rates of water supplied from stations A and B.
4. Calculate the consumption of water at the consumer - and.
5. The condition is checked
, 
.
a. Ring network.
The ring network can be considered as a network with two power supplies with equal heads of network pumps. The position of the watershed point in the supply and return lines is the same 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. The installation of a booster pump leads to a displacement of the watershed point only in the line on which it is installed.
Fig.6.15. Diagram of pressure in the ring network
In this case ON = HB.
b. Switching on pumping substations in a network with two power supplies
To stabilize the pressure regime in the presence of a booster pump at one of the stations, the pressure on the inlet manifold is maintained constant. This station is called fixed, the other stations are called free. When a booster pump is installed, the pressure in the inlet manifold of a free station changes by .
a. Hydraulic mode of open heat supply 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 line. In practice, this difference is equal to the water intake.
Fig.6.18. Piezometric plot of an open system
The piezometric curve of the supply line remains constant for any withdrawal from the return line, since the flow in the supply line is kept constant by means of flow regulators on the subscriber inlets. With an increase in water intake, the flow in the return line decreases and the piezometric curve of the return line becomes flatter. When the draw-off is equal to the flow in the flow, the flow in the return is zero and the piezometric curve of the return line becomes horizontal. With the same diameters of the direct and return lines and the absence of water intake, the head graphs in the direct and return lines are symmetrical. In the absence of water intake for hot water supply, the water consumption is equal to the estimated heating consumption - V.
From equation (***) one can find f.
1. When DHW is drawn from the supply line, the flow through the heating system drops. When parsing from the reverse line, it grows. 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 the greater, the lower the resistance of the system.
An increase in the DHW drawdown can lead to a situation where all the water after the heating system will go to the DHW drawdown. In this case, the water flow in the return pipeline will be equal to zero.
From (***): 
, where (****)
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Introduction
Initial data
Settlement part
8.1 Selection of network pumps
8.3 Selection of booster pumps
8.4 CHP steam turbine selection
9.3 Calculation of a section with a U-shaped compensator
heating network equipment mounting
Introduction
Heat supply is one of the main subsystems of heat power engineering.
The main purpose of any heat supply system is to provide consumers with the necessary amount of heat of the required quality.
Water heating systems are used in two types: closed and open. In closed systems, network water circulating in the heating network is used only as a heat carrier, but is not taken from the network.
For the heat supply of cities, in most cases, two-pipe water systems are used, in which the heat network consists of two pipelines: supply and return. Through the supply pipeline, hot water is supplied from the station to the subscribers, through the return pipeline, the cooled water is returned to the station.
The predominant use of two-pipe systems in cities is explained by the fact that these systems, compared with multi-pipe systems, require lower initial investments and are cheaper to operate. Two-pipe systems are applicable in cases where all consumers of the area require heat of approximately the same potential.
The number of parallel pipelines in a closed system must be at least two, since after the heat is released in subscriber units, the coolant must be returned to the station.
Despite the significant diversity of the heat load, it can be divided into two groups according to the nature of the flow in time: seasonal and year-round. The change in seasonal load depends mainly on climatic conditions: outdoor temperature, wind direction and speed, solar radiation, air humidity, etc. The year-round load includes process load and hot water supply.
One of the primary tasks in the design and development of the operation mode of district heating systems is to determine the values and nature of thermal loads, which we will do in this calculation.
Initial data
General plan number 2
CHP number 5
Type of system closed
Population density, person/ha 340
Heat carrier parameters:
Thermal insulation material IPS-T
Construction area Kirov
1. Determination of hourly and annual heat consumption
The areas of the residential and industrial zones are determined according to the master plan.
Determining the number of inhabitants:
Where R- population density, persons/ha; F- area of blocks under construction, ha (according to the master plan).
Total living area of the quarter:
Where f- norm total area residential building per person (9 - 12).
Accept f=10.
The calculation results are shown in Table 1.
Table 1.
|
quarter number |
Quarter area, ha |
Number of people living |
Residential area of the quarter |
|
The necessary data for calculating heat flows for heating, ventilation and hot water are taken from Table 2.
table 2
Maximum heat flow, W, for heating residential and public buildings:
where - an aggregated indicator of the maximum heat flow for heating residential buildings per 1 total area, - is taken from table 3; - coefficient taking into account the heat flow for heating public buildings.
Table 3
the aggregated indicator of the maximum heat flow for heating residential buildings per 1 total area is accepted for buildings after 1985, with a height of 5 or more floors. .
Maximum heat flux, W, for ventilation of public buildings:
where =0.6 - coefficient taking into account the heat flow to the ventilation of public buildings.
Average heat flux, W, for hot water supply of residential and public buildings:
where is an aggregated indicator of the average heat flow for hot water supply per person; A- the rate of water consumption for hot water supply at a temperature per person per day living in a building with hot water supply, we accept A=110; b- the rate of water consumption for hot water supply consumed in public buildings, at a temperature, we accept b\u003d 25 l / day. for one person; - temperature of cold (tap) water in heating period, accept; With- specific heat capacity of water, we take With=4,187 .
Maximum heat flow, W, for hot water supply of residential and public buildings:
When determining the estimated heat consumption for the city district, it is taken into account that during the transportation of the coolant, heat losses occur in environment, which are taken equal to 5% of the heat load, so the total heat consumption for heating, ventilation and hot water supply:
The calculation results are shown in Table 4.
Table 4
|
quarter number |
Heat consumption, kW |
|||||
|
Total, taking into account losses: |
During the summer period, which in heat supply is conditionally determined by the period with outside temperatures, only DHW works out of 3 heat loads.
The average hourly heat consumption for hot water supply in the summer will be:
where is the average temperature hot water, is accepted; - coefficient taking into account the change in water consumption for hot water supply during the non-heating period, because Kirov is not a resort city, then we accept = 0.8; - cold temperature tap water during the heating period, we accept; - the temperature of cold tap water in the non-heating period, we accept.
where is the average temperature of heated rooms, we accept; - outdoor air temperature for designing a heating system, is taken from table 2.
The total water consumption for heating, ventilation and hot water at a temperature t=+8 :
Average heat flow for heating and ventilation during the heating period:
where is the average outdoor temperature for the heating period, .
Annual heat consumption for heating, ventilation and hot water supply of residential and public buildings:
where is the duration of the heating period, days; Z- the number of hours of operation of the ventilation systems of public buildings averaged over the heating period during the day, Z=16, by ; - the estimated number of days in the year of operation of the DHW system, is taken = 350 days.
Table 5
According to table 5, a graph of the annual heat load is built. This graph is shown in Figure 1.
2. Calculation and construction of schedules for the regulation of heat supply
According to B water heating networks, central quality control of heat supply should be used by changing the temperature of the heat carrier depending on the outdoor temperature.
2.1 Control of heat output in closed systems
Determine the temperature difference of the heater:
where - the temperature of the water in the supply pipeline of the heating system after the elevator at, is taken; - the temperature of the water in the return pipe after the heating system at, - the calculated temperature of the internal air, is accepted.
Estimated water temperature difference in the heating network:
where is the temperature of the water in the supply pipeline of the heating network at the outdoor temperature, .
Estimated water temperature difference in the local heating system:
Given different values of outdoor air temperature ranging from +8 to, determine the water temperature in the supply and return lines, respectively, and according to the formulas:
The results are shown in table 6.
Table 6
Since heat is simultaneously supplied through heating networks for heating, ventilation and hot water supply, in order to meet the heat load of hot water supply, it is necessary to make adjustments to the heating curve of water temperatures. The temperature of the hot water in the water risers of the DHW system must be at least 55, respectively, the temperature of the heated water at the outlet of the DHW heater must be 60-65. Therefore, the minimum temperature of the network water in the supply line is assumed to be 70 for closed heat supply systems. To do this, the heating curve is cut off at level 70. The outdoor temperature corresponding to the break point of the curve is found by linear interpolation:
The temperature of the water in the return pipeline after the heating system, corresponding to the break point of the temperature graph:
The break point of the graph divides it into 2 parts with different control modes: in the range of outdoor air temperatures from to, central quality control of heat supply is carried out; in the temperature range from +8 to local regulation of all types of thermal loads.
The calculation of the increased temperature graph consists in determining the temperature difference of the network water in the water heaters of the upper and lower stages at various outdoor temperatures and the DHW balance load:
where - the balance coefficient, taking into account the uneven consumption of heat for hot water supply during the day, is accepted.
The total temperature drop of the network water in the water heaters of the upper and lower stages during the entire heating period:
Underheating of tap water to the temperature of the heating water in the lower stage of the water heater: ; because there are storage tanks, then we accept.
The temperature of the heated tap water after the lower (I) stage of the water heater:
Temperature drop of network water in the lower stage of the water heater, corresponding to the break point of the graph:
where is the temperature of hot water entering the DHW system, we accept; - the temperature of cold tap water during the heating period, we accept.
The temperature of the network water in the return line according to the increased schedule, corresponding to the break point of the schedule:
Temperature drop of network water in the upper (II) stage of the water heater, corresponding to the break point of the graph:
The temperature of the network water in the supply line of the heating network for the increased schedule, corresponding to the break point of the schedule:
where is the water temperature in the supply line, corresponding to the break point of the graph, .
At an outside air temperature in the range from to:
Temperature drop of network water in the lower stage of the water heater:
The temperature of the network water in the return line according to the increased schedule:
Temperature drop of network water in the upper (II) stage of the water heater:
The temperature of the network water in the supply line of the heating network for an increased schedule:
The calculation results of these parameters are shown in Table 7. Based on these values, a graph of heat supply control is built.
Table 7
2.2 Ventilation load control
Regulation of heat supply for ventilation can be carried out by changing the flow rate of network water or heated air. Regulation of heat supply for ventilation uses a method of regulation by changing the flow of network water.
Based on the graphs of heat consumption for ventilation Q v = f(t m) and water temperature in the supply line 1 = f(t m) the entire heating period can be divided into three ranges:
I range - from t n = +8 o C up to when the temperature of the network water in the supply line is constant, and the heat consumption for ventilation changes. In this range of outdoor air temperatures, in addition to the central regulation, local quantitative regulation is carried out by changing the flow of network water through the heater.
Water temperature after heater 2, v determined from the equation
where is the temperature of the network water in the supply line at; - water temperature after the heater when we accept.
This equation is solved by the method of successive approximations or graphoanalytically.
Asking
II range - from to, when the temperature of the network water in the supply line and the heat consumption for ventilation increase with decreasing temperature. In this range, the central quality control of heat supply is carried out. According to table 2: .
Range III - from to, when the temperature of the network water in the supply line increases with a decrease in the outside air temperature, and the heat consumption for ventilation remains constant. In this range, in addition to the central quality control, local quantitative control of the ventilation load is applied.
The water temperature after the heaters is determined from the equation:
where is the temperature of the network water in the supply line at the outdoor temperature; - the temperature of the water after the heaters at the outside temperature, is accepted; - the temperature of the network water after the heating installation, at the temperature of the outside air.
Graphically we find:
Asking
Using the obtained values, we build a graph for regulating the ventilation load (dashed lines).
The graph of heat supply regulation is shown in Figure 2.
3. Determination of the calculated coolant flow rates in heat networks
With a qualitative regulation of heat supply, the estimated consumption of network water for heating:
Estimated consumption of network water for ventilation:
Estimated consumption of network water for hot water supply depends on the scheme for connecting water heaters. In this work, a two-stage sequential scheme was used, therefore, the average hourly water consumption for hot water supply:
Maximum water consumption for DHW:
The total estimated consumption of network water in two-pipe heating networks with regulation according to an increased schedule:
Estimated consumption of network water for heating and ventilation and total consumption at outdoor temperature:
Based on the data obtained, a graph of the estimated coolant flow rates in heat networks is built.
The graph of the estimated coolant flow rates is shown in Figure 3.
Network water consumption by quarters of the district, t/h are shown in Table 8.
Table 8
|
quarter number |
Consumption of network water for heating, t/h |
Supply water consumption for ventilation, t/h |
Consumption of network water for hot water supply, t/h |
Total estimated consumption of network water, t/h |
||
|
Hourly average |
Maximum |
|||||
4. The choice of the design of the heating network and the development of the wiring diagram
The design of heating networks begins with the choice of the route and the method of laying them. In cities and other settlements, the route should be provided in the technical lanes allocated for engineering networks, parallel to the red lines of streets, roads and driveways, outside the carriageway and the strip of green spaces, and inside microdistricts and quarters - outside the carriageway. On the territory of quarters and microdistricts, it is allowed to lay heat pipelines along driveways that do not have a major road surface, sidewalks and green areas. The diameters of pipelines laid in quarters or microdistricts, according to safety conditions, should be chosen no more than 500 mm, and their route should not pass in places of possible congestion of the population (sports grounds, squares, courtyards of public buildings, etc.).
When choosing the route of heat pipelines, it is necessary to take into account the efficiency and reliability of the operation of heat networks. It is necessary to strive for the shortest length of heating networks, for a smaller number of thermal chambers, using, if possible, two-way connection of quarters. Water heating network should be taken, as a rule, 2-pipe, supplying the coolant simultaneously for heating, ventilation, hot water supply and technological needs. Schemes of quarterly heating networks are accepted as dead-end, without redundancy.
In settlements for heating networks, as a rule, underground laying is provided. Above-ground laying in the city can be used in areas with difficult soil conditions, when crossing railways general network, rivers, ravines, with a high density of underground structures and in other cases [SNiP 41-02-2003]. The slope of heating networks, regardless of the direction of movement of the coolant and the method of laying, must be at least 0.002.
Underground laying of heat networks can be carried out in channels and without channels. Laying in impassable channels of various designs has now become widespread. The most promising for the construction of heating networks are impassable channels of the KLp and KLs type, which provide free access to pipelines in the production of welding, insulating and other types of work.
In order to improve the reliability of heating networks, it is advisable to arrange a reservation for the supply of heat to consumers due to joint work several sources of heat, as well as the device of blocking jumpers between the mains of heating networks when underground laying.
When choosing a route, one input of heating networks is provided for each quarter. It is allowed to connect adjacent quarters from one thermal chamber. In the course project, unified standard designs of prefabricated reinforced concrete channels are used, the dimensions of which depend on the diameters of the heat pipes.
The choice of pipes and fittings in the design is carried out according to the working pressure and temperature of the coolant. For heating networks, electric-welded steel longitudinal pipes are used in accordance with GOST 10704-91. Pipes are connected by welding. The main types of valves are steel gate valves with manual drive with a diameter of up to 500 mm and electric with a diameter of more than 500 mm.
The wiring diagram is drawn in two lines, and the supply heat pipe is located on the right side in the direction of movement of the coolant from the heat source. In places of branches to quarters or buildings, thermal chambers are provided.
The development of the installation scheme consists in the placement of fixed supports, compensators and shut-off and control valves on the heating network route. In the areas between the nodal chambers, i.e. chambers in branch nodes, fixed supports are placed, the distance between which depends on the diameter of the heat pipe, the type of compensator and the method of laying heat networks. A compensator is provided in the area between two fixed supports.
Fixed supports should be provided:
a) persistent - for all methods of laying pipelines;
b) panel board - for channelless laying and laying in impassable channels when supports are placed outside the chambers;
c) clamp - when laying above-ground and in tunnels (in areas with flexible compensators and self-compensation).
Turns of the heating network route at an angle of 90-130 ° are used for self-compensation of temperature elongations, and in places of turns at an angle of more than 130 °, fixed supports are installed.
Compensation for temperature deformations in heating networks is provided by compensators - stuffing box, bellows, radial, as well as self-compensation - using sections of turns of the heating main. Gland compensators have a large compensating capacity, low metal consumption, but require constant monitoring and maintenance. Thermal chambers should be provided at the locations of stuffing box compensators for underground laying. Gland compensators are produced with D y \u003d 100-1400 mm for nominal pressure up to 2.5 MPa and temperature up to 300C, one-sided and two-sided. It is desirable to use stuffing box compensators on straight sections of pipelines with large diameters. Bellows expansion joints are available for pipelines with diameters from 50 to 1000 mm. They do not require maintenance and can be used for any laying method. However, they have a relatively small compensating capacity (up to 100 mm) and they can be used using guide supports. Radial (mainly U-shaped) compensators have been widely used. Radial compensators can be used for any diameter, they do not require maintenance, however, they are metal-intensive, have a significant axial reaction and greater hydraulic resistance compared to stuffing box and bellows. When solving the issues of compensation for thermal deformations in heating networks, it is first necessary to use the natural angles of the route for self-compensation, and only then apply special compensating devices.
The project provides for unified prefabricated reinforced concrete chambers. For descent into and out of the chamber, at least two hatches, metal ladders or brackets are provided. When the area of the chamber according to the internal measurement is more than 6 m 2, four hatches are installed: The bottom is arranged with a slope of 0.02 towards the pit for collecting and removing water. On all branches of the heat pipes in the chamber, a shut-off valve is installed. The transition to another pipe diameter is carried out within the chamber. The minimum camera height is assumed to be 2 m.
In order to reduce the height of the chamber and deepen the heating networks, the valves can be installed at an angle of 45 ° or horizontally. In the places of installation of sectional valves on the side of the heat source, a jumper is arranged between the supply and return heat pipes with a diameter equal to 0.3 of the heat pipe diameter. Two valves are installed on the jumper, and between them - a drain control valve d= 25 mm. It is allowed to increase the distance between sectional valves up to 1500 m on pipelines d\u003d 400 - 500 mm, provided that the sectioned section is filled with water or drained within 4 hours, for pipelines d 600 mm - up to 3000 m, provided that the area is filled with water or the water is drained for 5 hours, and for overhead laying d 900 mm - up to 5000 m.
When installing large-diameter valves, above-ground pavilions can be arranged instead of thermal chambers. In chambers on branches to individual buildings with a diameter of branches up to 50 mm and a length of up to 30 m, it is allowed not to install shutoff valves. At the same time, shut-off valves should be provided to ensure shutdown of a group of buildings with a total heat load of up to 0.6 MW.
The working scheme of the most loaded branch is shown in Figure 4.
5. Hydraulic calculation of water heating networks
Hydraulic calculation is one of the most important sections of the design and operation of heating networks.
When designing, the hydraulic calculation includes the following tasks:
Determination of pipeline diameters;
Determination of pressure drop (pressure);
Determination of pressures (heads) at various points in the network;
Coordination of all points of the system in static and dynamic modes in order to ensure acceptable pressures and required pressures in the network and subscriber systems.
The results of the hydraulic calculation give the following source material:
To determine capital investments, metal consumption and the main scope of work on the construction of a heating network;
Establishing the characteristics of circulation and make-up pumps, the number of pumps and their location;
Clarification of the operating conditions of heat sources, heat networks and subscriber systems and the choice of schemes for connecting heat-consuming installations to the heat network;
Development of modes of operation of heat supply systems.
First of all, it is necessary to draw a general plan of the city district on Whatman paper, then put on the plan a CHP plant and a heating network with pairwise branches to microdistricts.
In order to save capital costs, the heating network is laid not along each street, but across the street. They find the main line of the heating network and the nearest branch to the CHP for hydraulic calculation. Determine the estimated water consumption in each microdistrict. Determine the optimal specific linear pressure drop in the line no more than 30-80 and the branch no more than 50-300.
5.1 Preliminary hydraulic calculation
The selection of pipe diameters for sections of the main and branch lines in the preliminary hydraulic calculation is made depending on the water flow and specific pressure drops. The pressure loss in local resistances in the preliminary calculation is taken into account by the coefficient of local losses. Preliminary hydraulic calculation starts from the last section to the heat source.
The results of the preliminary calculation are shown in Table 9.
Table 9
Since at all 3 points the discrepancy is greater than the permissible 10%, it is necessary to install throttle washers. Calculation of throttle washers (throttle diaphragm hole diameter):
5.2 Final hydraulic calculation
After the preliminary calculation, the final hydraulic calculation is carried out, in which the head loss in local resistances is determined in a more accurate way based on the equivalent lengths of the actual nodes of local resistances. To do this, a wiring diagram of the main line and branches is drawn in two lines with the application of fixed supports, sectional valves, compensators, transitions, jumpers, thermal chambers.
According to the completed wiring diagram, the local resistance coefficients are determined and entered in table 10.
Table 10
|
plot number |
Conditional pass |
local resistance |
Quantity |
Local resistance coefficient |
Total coefficient of local resistance |
Total for the site |
|
|
Main line |
|||||||
|
gate valve |
|||||||
|
U-shaped compensator |
|||||||
|
Tee per passage |
|||||||
|
gate valve |
|||||||
|
Gland compensator |
|||||||
|
Tee per passage |
|||||||
|
gate valve |
|||||||
|
Gland compensator |
|||||||
|
Tee per passage |
|||||||
|
gate valve |
|||||||
|
Gland compensator |
|||||||
|
Tee per passage |
|||||||
|
Branch welded 2-sutural at an angle 90 |
|||||||
|
Gland compensator |
|||||||
|
Branches |
|||||||
|
gate valve |
|||||||
|
U-shaped compensator |
|||||||
|
Tee per passage |
|||||||
|
gate valve |
|||||||
|
U-shaped compensator |
|||||||
|
Branch tee |
|||||||
|
gate valve |
|||||||
|
U-shaped compensator |
|||||||
|
Tee per passage |
|||||||
|
gate valve |
|||||||
|
U-shaped compensator |
|||||||
|
Branch tee |
|||||||
|
gate valve |
|||||||
|
U-shaped compensator |
|||||||
|
Tee per passage |
|||||||
|
gate valve |
|||||||
|
U-shaped compensator |
|||||||
|
Branch tee |
In the final hydraulic calculation, the pressure drop in sections is determined from the updated equivalent lengths.
Total pressure loss in the pipeline section:
The reduced length of the pipeline, which is calculated by the formula:
The equivalent length of local resistances is found by the formula:
Equivalent length of local resistances at, which is in table 8.2. We accept the coefficient of equivalent roughness
The results of the final hydraulic calculation are summarized in table 11.
Table 11
The head loss discrepancy along the main line (from the branch point) and along the branch line:
The discrepancy is less than 10% (), in sections 5-11 and 3-7, and in section 4-9 the discrepancy exceeds the allowable 10%. Therefore, in section 9, a throttle diaphragm should be installed. Throttle aperture calculation:
6. Development of pressure graphs and selection of schemes for connecting subscribers to heating networks
The distribution of pressure in heat networks is conveniently depicted in the idea of a piezometric graph, which gives a visual representation of the head pressure at any point in the heat network and therefore provides great opportunities to take into account numerous factors (terrain, building height, features of subscriber systems, etc.) when choosing the optimal hydraulic mode.
A piezometric graph is developed for winter and summer design conditions. The design of open heat supply systems is associated with the need to build piezometric graphs for the heating season, taking into account the maximum water intake from the supply and separately from the return pipelines.
Pressure. expressed in linear units is called pressure head. In heat supply systems, piezometric graphs characterize the heads corresponding to excess pressure, and they can be measured with conventional pressure gauges, followed by conversion of the measurement results into meters.
The piezometric graph allows you to: determine the pressure and available pressure at any point in the network; take into account the mutual influence of the terrain, the height of the connected consumers and the pressure loss in the network when developing the hydraulic regime; select consumer connection schemes; pick up network and make-up pumps, automatic regulators.
When constructing a piezometric graph, the following conditions must be met:
1. The pressure in subscriber systems directly connected to the network should not exceed the allowable value both in static and dynamic modes. For radiators of the heating system, the maximum overpressure should not exceed 0.6 MPa (60 m).
2. The maximum head in the supply pipelines is limited by the strength of the pipes and all water heating installations.
3. The pressure in the supply pipelines, through which water with a temperature above 100C moves, must be sufficient to prevent vaporization.
4. To prevent cavitation, the pressure in the suction pipe of the network pump must be at least 5 m.
5. At the points of connection of subscribers, sufficient pressure should be provided to create water circulation in local systems. With elevator mixing at the subscriber input, the available pressure must be at least 10-15 m.
The levels of piezometric lines in both static and dynamic modes should be set taking into account the possibility of connecting the majority of subscriber systems using the cheapest dependent schemes. The static pressure must also not exceed the allowable pressure for all elements of the heating system. When determining the static pressure, the possibility of boiling water in the supply pipes can be ignored.
The piezometric graph is built for the static and dynamic modes of the heat supply system. When constructing it, the mark of the axis of the network pumps is taken as the origin of coordinates, conditionally considering that it coincides with the mark of the earth at the outlet of the heat pipeline from the CHP. On the y-axis, the pressure values are plotted in the supply and return lines of the heating network, the terrain marks and the height of the connected consumers; along the abscissa axis, a terrain profile is built and the length of the calculated sections of the heat pipeline is plotted. The axis of the heating main is conditionally taken to coincide with the surface of the earth.
After constructing the terrain profile and plotting the heights of connected consumers, they begin to develop a pressure graph in the hydrostatic mode, when there is no coolant circulation in the heating network and the pressure in the system is supported by make-up pumps. In this mode, the head graph is a straight line parallel to the x-axis. The construction of the static pressure line is carried out from the condition of filling the heating installations of all consumers with water and creating an excess pressure of 5 m at their upper points.
When implementing the project, one should strive to establish the same static head for the entire heat supply system, when it is impossible to achieve this condition, the heat supply system is divided into several static zones or consumers are connected according to an independent scheme.
After constructing the static head line, they begin to develop pressure graphs in the hydrodynamic mode, when the coolant is circulated in the heating network by network pumps. The construction of a piezometric graph in this mode begins with drawing lines of maximum and minimum piezometric pressures for the supply and return lines of heating networks. The lines of maximum and minimum pressures are applied parallel to the profile of the earth's surface along the length of the route. The lines of the actual pressures of the supply and return heat pipes should not go beyond the lines of the limiting pressure values. When constructing a piezometric graph, it must be taken into account that the required pressure at the suction pipe of the network pump depends on the brand of the pump.
The piezometric graph is shown in Figure 5.
7. Development and construction of a longitudinal profile of heating networks
The longitudinal profile of the heating network section is built on a vertical scale of 1:100 and a horizontal scale of 1:5000 or 1:1000. Construction begins with determining the minimum depth of the thermal chamber along the route, taking into account the overall dimensions of the equipment installed in them. It is necessary to strive for the minimum depth of laying channels or heat pipes. For this purpose, in thermal chambers it is allowed to install valves in a horizontal position or at an angle of 45. The number of conjugation of sections with reverse slopes should be as small as possible. The slope of heat pipelines, regardless of the laying method, must be at least 0.002. When laying heat pipelines along bridge structures when crossing rivers, ravines, slopes may not be provided.
On the longitudinal profile they show: marks of the earth's surface (design - with a solid line, existing - with a dashed line); all intersecting engineering networks and structures with marks of the top of their structure when the designed heating network is located on top and with marks of the bottom of engineering networks and structures when the heating networks are located at the bottom; marks of the bottom of the pipe of the heating network, the bottom and ceiling of the channel; the depth of the heat pipe; slope and length of sections of the heating network; heat pipe diameter and channel type; a detailed plan of the route is given indicating the angles of rotation, branches, fixed supports, compensators, compensatory niches and thermal chambers. When designing longitudinal drainage, the marks of the tray, the diameter and slope of the drainage pipes are indicated.
With the above-ground method of laying on the longitudinal profile, marks are given for the top of the supporting structure and the bottom of the heat pipe. At the lowest points of the heat pipelines, drainage outlets are provided, and at the highest points, air outlets are provided. It is necessary to observe the permissible vertical distances from the heating network structures to utilities.
8. Selection of the main equipment of the heat treatment plant of the CHPP
8.1 selection of network pumps
We find the pressure of network pumps according to the piezometric graph:
Total network resistance:
We choose a pump brand SE-800-100-11, with technical characteristics:
pump resistance.
Number of pumps:
Accept n=2.
We accept 3 pumps for installation: 2 working and 1 reserve.
We construct the characteristics of the pump operation using the equation. The characteristics of the network and the operation of the pump are shown in Figure 6.
Summer mode:
Rice. 6 Characteristics of the heating network and the operation of network pumps
8.2 Selection of make-up pumps
The head of the make-up pumps is equal to the static head. According to the piezometric graph, we determine:
Make-up water consumption, taking into account the emergency mode:
where - specific volumes of network water located in external networks with heating installations and in local systems.
According to the obtained value, we build the network characteristic according to the equation.
We choose a pump brand KM80-50-200 / 2-5, with technical characteristics:
Head in the absence of flow;
pump resistance.
Number of pumps:
Accept n=4.
We accept 5 pumps for installation: 4 working and 1 reserve.
We construct the characteristics of the pump operation using the equation. The characteristics of the network and the operation of the pump are shown in Figure 7.
Rice. 7 Characteristics of the heat network and operation of make-up pumps
8.3 Selection of booster pumps
The pressure of the booster pumps is assumed to be:
The total resistance of the heating network:
According to the obtained value, we build the network characteristic according to the equation.
We choose a pump brand D200-36, with technical characteristics:
Head in the absence of flow;
pump resistance.
Number of pumps:
Accept n=6.
We accept 6 pumps for installation: since the number of working pumps is more than 5, a backup pump is not required.
We construct the characteristics of the pump operation using the equation. The characteristics of the network and the operation of the pump are shown in Figure 8.
Rice. 8 Characteristics of the heating network and the operation of booster pumps
8.4 CHP steam turbine selection
To select CHP steam turbines, it is necessary to know the required total amount of steam from the turbine extractions, which is necessary to heat the water in the main heaters to a temperature. Drink temperature. To do this, we set the value of the heat supply coefficient: (at seasonal heat load for high-pressure CHP).
Estimated heat load of extractions of heating turbines:
To cover the load on heating turbines, we select (according to the nominal load of extractions) the following turbines: T-110 / 120-130-5M, with technical characteristics:
Number of turbines:
accept
We accept 1 T-110/120-130-5M turbine for installation. Turbine T-110/120-130 has two heat extraction steam pressure:
0.05-0.2MPa in the lower heating unit ();
0.06-0.25 MPa in the upper heating selection ().
Steam consumption in extraction: D=480t/h.
The turbine is equipped with two horizontal PSG heaters with a heating surface of each F=1300 .
Corrected heating coefficient:
The temperature of the network water after the heaters of the lower and upper stages, respectively:
where - undercooling in the heaters of the lower and upper stages, respectively.
Supply water temperature at the inlet to the lower stage heater for closed systems:
where is the average temperature of the network water in the return pipeline, we accept; - estimated consumption of make-up water (according to the characteristics of the make-up pump); - make-up water temperature, taken for the winter period.
Distribution of heat load between the heaters of the lower and upper stages:
Mean-logarithmic temperature difference of network water at heaters:
Heat transfer coefficient of heaters:
8.5 Selection of peak boilers
Peak boilers are selected according to the total peak heat load:
Choose hot water boilers KVGM-40, with technical characteristics:
Unit heat output:
Number of peak hot water boilers:
; accept.
We accept 3 KVGM-40 peak hot water boilers for installation: 2 workers, 1 reserve.
9. Mechanical calculation of heat pipes
9.1 Calculation of fixed supports with angle of rotation
Consider, as an example, the section UP2 in accordance with the wiring diagram.
Determine the stress from thermal deformations in a pipeline with a diameter of mm at a fixed support WITH at the calculated coolant temperature of 150C and ambient temperature.
Modulus of longitudinal elasticity of steel MPa,
Linear elongation coefficient: ,
Rotation angle u=90° (v=0),
Permissible bending stress in the pipeline MPa,
Long arm =110m, small arm =80m.
Linear extension of the long arm:
According to the nomograms, we determine the coefficients:
IN=7,15;
For the pipe we find:
Substituting the found values into the formulas for this scheme of the design section, we find the desired values of the forces and compensation stresses at various points:
The stresses on the fixed supports do not exceed the allowable ones.
9.2 Calculation of a straight section
Consider as an example the area between supports H20 and H21 according to the wiring diagram.
Heat pipe diameter mm;
The coefficient of friction on fixed supports is accepted;
The coefficient of friction of the gland packing on the glass is accepted;
The working pressure in this area is determined by the piezometric graph: m;
Distance between fixed supports m; distance between the fixed support and the stuffing box compensator m.
We accept the force of gravity per unit length of the heat pipe with insulation and water:
The resulting force on the fixed support with the valve closed ( A=1):
The resulting force on the fixed support with the valve open ( A=0):
Friction force in stuffing box compensator:
9.3 Calculation of a section with a U-shaped compensator
Consider as an example the area between supports H28 and H29 according to the wiring diagram.
Heat pipe diameter mm;
Section length L=125 m;
Estimated ambient temperature;
coolant temperature;
Permissible compensation voltage for flexible compensators:
Total thermal elongation of the section:
Calculated thermal force at mounting extension of the compensator by 50%:
Compensator dimensions:
According to the nomogram, we determine:
Adjoining shoulder length:
When using hard bends:
bend radius;
Stiffness coefficient;
Voltage correction factor.
The central moment of inertia of the pipeline section:
Estimated axial force:
Maximum tension in the middle part of the compensator back:
The maximum stress in the middle part of the back of the compensator does not exceed the allowable value.
10. Thermal calculation of the heat-insulating structure
In the thermal insulation structures of equipment and pipelines with a temperature of the substances contained in them in the range from 20 to 300 ° C for all laying methods, except for channelless, heat-insulating materials and products with a density of not more than 200 and a thermal conductivity coefficient in a dry state of not more than 0.06 should be used W/(m K).
At thermal calculation required: select the thickness of the main layer of the insulating structure, calculate the heat losses by heat pipes, determine the temperature drop of the coolant along the length of the heat pipe and calculate the temperature fields around the heat pipe.
The thickness of the main layer of the insulating structure is selected on the basis of a technical and economic calculation or according to the norms of heat loss at a given final temperature of the coolant and in accordance with the temperature difference.
For the first section from the CHPP Dy=600 mm., Initially, we take the thickness of the insulation mm;
Thermal insulation layer - fiberglass IPS-T, with a coefficient of thermal conductivity;
Type of coating for protecting the outer surfaces of pipes of heating networks - brizol (m);
The average annual temperature of the heat pipe in the supply heat pipe: , in the reverse: ;
Soils - mixed with temperature at the laying depth. Channel laying depth - h= 0.7 m
Preliminarily we select a non-passing channel KL 210-120, with the parameters:
1) internal dimensions: 18401200mm
2) outer dimensions: 21601400 mm
3) distance from the channel wall to the insulation 110 mm
4) distance between insulating surfaces 200mm
5) distance from the bottom of the channel to the insulation 180 mm
6) distance from ceiling to insulation 100 mm
Normalized heat flux densities:
Plot 5:
Plot 4:
Plot 3:
Plot 2:
Plot 1:
Thermal resistance of heat pipes:
Plot 5:
Plot 4:
Plot 3:
Plot 2:
Plot 1:
The heat transfer coefficient on the surfaces of thermal insulation and the channel is accepted
Equivalent internal and external diameters of the channel:
Thermal resistance of the inner surface of the channel:
We accept the coefficient of thermal conductivity of the channel design. Thermal resistance of the channel walls:
We accept the coefficient of thermal conductivity of the soil. Soil thermal resistance:
Thermal resistance of the cover layer:
Plot 5:
Plot 4:
Plot 3:
Plot 2:
Plot 1:
Thermal resistance on the surface of the cover layer:
Plot 5:
Plot 4:
Plot 3:
Plot 2:
Plot 1:
Thermal resistance of the insulation layer of the supply and return pipelines:
Plot 5:
Plot 4:
Plot 3:
Plot 2:
Plot 1:
Thermal insulation thickness:
Plot 5:
Plot 4:
Plot 3:
Plot 2:
Plot 1:
Conclusion: the heat-insulating material IPS-T provides a normalized heat flux density.
Choice of channels for laying the route:
Plot 1: KL 120x60;
Plot 2: KL 150x90;
Plot 3: KL 210x120;
Plot 4: KLS 120x120;
Plot 5: KLS 120x120.
List of used literature
1. Water heating networks: Ref. Design guide / ed. N.K. Gromov; E.P. Shubina, M.: Energoatomizdat, 1988. 376 p.
2. Gromov N. K. Subscriber devices of water heating networks. M.: Energy, 1979. 248 p.
3. Ionin A. A., Khlybov B. M. et al. Heat supply. M.: Stroyizdat, 1982. 360s.
4. Safonov A. P. Collection of tasks for heating and heating networks. 3rd ed. M.: Energoizdat, 1985. 232 p.
5. Senkov F. V. Regulation of heat supply in closed and open heat supply systems: Tutorial.M.: VZISI, 1979. 88 p.
6. Sokolov E. Ya. Heating and heating networks. 4th ed. M.: Energy, 1975. 376 p.
7. Designer's Handbook. Design of thermal networks / Ed. A. A. Nikolaev. M.: Stroyizdat, 1965. 360 p.
8. Falaleev Yu.P. Design of central heating: Proc. allowance / NGASU. N. Novgorod, 1997, 282 p.
9. SNiP 2.04.01-85. Internal plumbing and sewerage of buildings.
10. SNiP 3.05.03-85. Heating network.
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Hello! The main purpose of hydraulic calculation at the design stage is to determine the diameters of pipelines for given coolant flow rates and available pressure drops in the network, or in separate sections of the heating network. During the operation of networks, one has to solve the inverse problem - to determine the flow rates of the coolant in sections of the network or the pressure at individual points with a change hydraulic modes. Without calculations for hydraulics, it is impossible to build a piezometric graph of the heating network. Also, this calculation is necessary to select the connection scheme for the internal heat supply system directly at the consumer and the selection of network and make-up pumps.
As you know, the hydraulic losses in the network are made up of two components: from the hydraulic linear friction losses and pressure losses in local resistances. By local resistances are meant - 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 is the length of the pipeline, m; d is the internal diameter of the pipeline, m; ρ is the heat carrier density, kg/m³; w² is the speed of the coolant, 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 resistances. It must be calculated manually using tables with local resistance coefficient values. In the Excel calculation attached to the article, I added a table with local resistance coefficients.
To perform a hydraulic calculation, you will definitely need a heat network diagram, something like this:
In fact, the scheme, of course, should be more detailed and detailed. I gave this diagram only as an example. From the heating network scheme, we need such data as: the length l of the pipeline, the flow rate G, and the diameter of the pipeline d.
How to perform a hydraulic calculation? The entire heating network that needs to be calculated is divided into so-called settlement sections. The calculated section is a section of the network where the flow rate does not change. First, hydraulic calculation is carried out in sections in the direction of the main line, which connects the heat source to the most remote heat consumer. Then, secondary directions and branches of the heating network are already 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 a rather laborious task), but it is enough to understand what the calculation of hydraulics is, and even for an unprepared person to start calculating hydraulics.
I will be glad to comments on the article.
Water heating systems are complex hydraulic systems, in which the work of individual links is mutually dependent. One of the important conditions for the operation of such systems is the provision in the heating network in front of central or local heating points of available pressure sufficient to supply water consumption to subscriber installations corresponding to their heat load.
Hydraulic calculation is one of the important sections of the design and operation of a heating network. When designing a heat network, the hydraulic calculation includes the following tasks: determining the diameters of pipelines, determining the pressure drop, determining pressures at various points in the network, linking the entire system under various network operating modes. The results of the hydraulic calculation give the following initial data:
1) To determine the investment, consumption of pipe metal and the main scope of work for the construction of a heating network;
2) Establishing the characteristics of circulation and make-up pumps, the number of pumps and their location;
3) Finding out the working conditions of the conditions of heat sources, heat networks and subscriber systems for choosing schemes for connecting heat-consuming installations to the heat network;
5) Development of modes of operation of heat supply systems.
As initial data for the calculation, the following are usually set: the scheme of the heat network, the parameters of the heat carrier at the inlet to the calculated section, the flow rate of the heat carrier and the length of the network sections. Since a number of quantities are unknown at the beginning of the calculation, the problem has to be solved by the method of successive approximations in two stages: approximate and verification calculations.
Advance paynemt
1. The available pressure loss in the network is determined based on the provision of the necessary static pressure at the subscriber input. The type of piezometric graph is determined.
2. The most distant point of the heating network (calculated main) is selected.
3. The main is divided into sections according to the principle of constancy of the coolant flow rate and the diameter of the pipeline. In some cases, within a section with equal flow, the diameter of the pipeline changes. On the site is the sum of local resistances.
4. The preliminary pressure drop in this area is calculated, it is also the maximum possible pressure drop in the area under consideration.
5. The proportion of local losses of a given section and the specific linear pressure drop are determined. The share of local losses is the ratio of the pressure drop in local resistances to the linear pressure drop of straight sections.
6. The diameter of the pipeline of the calculated section is preliminarily determined.
Check calculation
1. The precalculated pipe diameter is rounded up to the nearest standard pipe size.
2. The linear pressure drop is specified and the equivalent length of local resistances is calculated. The equivalent length of local resistances is a straight pipeline, the linear pressure drop on which is equal to the pressure drop in local resistances.
3. Calculate the true pressure drop in the section, which is the impedance of this section.
4. The pressure loss and the available pressure at the end point of the section between the supply and return lines are determined.
All sections of the heating network are calculated according to this method and are linked to each other .
To carry out a hydraulic calculation, they are usually set by the scheme and profile of the heating network, and then the most remote point is selected, which is characterized by the smallest specific drop in the main. Estimated temperature of network water in the supply and return lines of the heating network: t1=150 °С, t2=70 °С. The calculation scheme of the heat network is shown in fig. 5.1.
Available pressure at the entry point m. Art. Available pressure at all subscriber inputs m. Art. The average specific gravity of water γ \u003d 9496 N / m 2, the length of the calculated main, L (0-11) \u003d 820 m.
We determine the water consumption in the areas in accordance with the design scheme and summarize the results in Table. 5.1.
Table 5.1.
Water consumption by plots
| plot number | 1-2 | 2-3 | 3-4 | 4-5 | 5-6 | 6-7 | 7-8 | 8-9 | 9-10 |
| G,t/h | 65,545 | 60,28 | 47,1175 | 31,3225 | 26,6425 | 18,745 | 9,6775 | 6,1675 | 3,8275 |
| plot number | 10-11 | 1-1.1 | 2-2.1 | 3-3.1 | 3.1-3.2 | 3.1-3.3 | 3.3-3.4 | 3.3-3.5 | 3.5-3.6 |
| G,t/h | 1,755 | 0,585 | 0,585 | 9,945 | 0,585 | 8,19 | 0,585 | 5,5575 | 3,51 |
| plot number | 3.5-3.7 | 4-4.1 | 5-5.1 | 6-6.1 | 7-7.1 | 8-8.1 | 9-9.1 | 10-10.1 | 11-1.1 |
| G,t/h | 1,17 | 0,585 | 0,8775 | 0,585 | 0,8775 | 0,8775 | 0,8775 | 2,6325 | 0,8775 |
Advance paynemt
Available head loss m.Wat. Art. We distribute this pressure loss equally between the supply and return lines of the heating network, since the heating network is made in two pipe design, the same pipe profile 
. water. Art.
Pressure drop in section 1-2, Pa:
δP1-2 = δH*ƴ*L1-2/L1-27=4748
∑Ƹ=∑Ƹrear+∑Ƹ90ᵒ+∑Ƹcomp=2.36
Determine the share of local resistances
0,20
where is the coefficient of roughness equivalent ..
We preliminarily calculate the specific linear pressure drop, Pa / m and the diameter of the section 1-2, m:
Pa/m;
,
where is the coefficient at the equivalent roughness for steel pipes, 
.
Verification calculation
We choose the nearest standard inner diameter, mm according to GOST 8731-87 "Steel pipes".
Dv.1-2 = 0.261 mm.
We determine the specific linear pressure drop, Pa/m:
11.40Pa/m,
where is the coefficient at the roughness equivalent, 
.
We calculate the equivalent length of local resistances, m of the pipeline section in section 1-2
28.68m,
where is a coefficient depending on the absolute equivalent roughness .
Pressure loss in the pipeline section 0-1, Pa:
Loss of pressure in the pipeline section 0-1, m w.c.:
0.13m.
Since the pressure loss in the supply and return lines of the heating network is the same, the available pressure at point 1 can be calculated by the formula:
For the remaining sections of the highway under consideration, calculations are carried out similarly, their results are presented in Table. 5.2.
Table 5.2
Hydraulic calculation of the heat pipeline
| Preliminary | verification | |||||||||||
| № | L,m | δP,Pa | Σξ | A | Rl, Pa/m | d, m | d", m | R", Pa/m | Le, m | δP,Pa | δH", m | ΔH", m |
| 0-1 | 1,34 | 0,46 | 40,69 | 0,29 | 0,313 | 9,40 | 17,05 | 348,14 | 0,04 | 29,93 | ||
| 1-2 | 2,36 | 0,20 | 49,38 | 0,28 | 0,261 | 11,40 | 28,68 | 1238,73 | 0,13 | 29,74 | ||
| 2-3 | 3264,25 | 1,935 | 0,24 | 47,83 | 0,28 | 0,261 | 11,04 | 23,69 | 868,90 | 0,09 | 29,82 | |
| 3-4 | 3857,75 | 2,105 | 0,22 | 48,58 | 0,28 | 0,261 | 11,21 | 25,68 | 1016,91 | 0,11 | 29,79 | |
| 4-5 | 10979,75 | 4,145 | 0,15 | 51,46 | 0,27 | 0,261 | 11,88 | 49,87 | 2789,63 | 0,29 | 29,41 | |
| 5-6 | 3857,75 | 2,105 | 0,22 | 48,58 | 0,28 | 0,261 | 11,21 | 25,68 | 1016,91 | 0,11 | 29,79 | |
| 6-7 | 7418,75 | 3,125 | 0,17 | 50,68 | 0,27 | 0,261 | 11,70 | 37,74 | 1903,62 | 0,20 | 29,60 | |
| 7-8 | 3,38 | 0,17 | 50,93 | 0,27 | 0,261 | 11,76 | 40,77 | 2125,15 | 0,22 | 29,55 | ||
| 8-9 | 2670,75 | 1,765 | 0,27 | 46,79 | 0,28 | 0,261 | 10,80 | 21,72 | 720,73 | 0,08 | 29,85 | |
| 9-10 | 1483,75 | 1,425 | 0,39 | 42,69 | 0,28 | 0,313 | 9,86 | 17,92 | 423,17 | 0,04 | 29,91 | |
| 10-11 | 890,25 | 1,255 | 0,57 | 37,74 | 0,29 | 0,313 | 8,72 | 16,25 | 272,45 | 0,03 | 29,94 |
The branch is calculated as transit sections with a given pressure drop (pressure). When calculating complex branches, first find the design direction as the direction with the minimum specific pressure drop, and then carry out all other operations.
The hydraulic calculation of the heat pipe branch is shown in Table. 5.3.
Table 5.3
Results of hydraulic calculation of branches
| № | L,m | δP,Pa | Σξ | A | Rl, Pa/m | d, m | d", m | R", Pa/m | Le, m | δP,Pa | δH", m | ΔH", m |
| 3-3.1 | 1,34 | 0,458607 | 25,36 | 0,31 | 0,313 | 5,86 | 19,07 | 229,1455 | 0,02 | 29,95 | ||
| 3.1-3.2 | 593,5 | 1,17 | 0,80085 | 27,35 | 0,31 | 0,313 | 6,32 | 16,36 | 166,6545 | 0,02 | 29,96 | |
| 3.1-3.3 | 2077,25 | 1,595 | 1,224859 | 22,87 | 0,32 | 0,313 | 5,29 | 23,27 | 308,2111 | 0,03 | 29,94 | |
| 3.3-3.4 | 593,5 | 1,17 | 0,80085 | 27,35 | 0,31 | 0,313 | 6,32 | 16,36 | 166,6545 | 0,02 | 29,96 | |
| 3.3-3.5 | 890,25 | 1,255 | 0,572688 | 26,32 | 0,31 | 0,313 | 6,08 | 17,71 | 199,023 | 0,02 | 29,96 | |
| 3.5-3.6 | 2,02 | 0,230444 | 19,65 | 0,33 | 0,313 | 4,55 | 30,55 | 411,7142 | 0,04 | 29,91 | ||
| 3.5-3.7 | 1,34 | 0,458607 | 25,36 | 0,31 | 0,313 | 5,86 | 19,07 | 229,1455 | 0,02 | 29,95 | ||
| 4-4.1 | 593,5 | 1,17 | 0,80085 | 27,35 | 0,31 | 0,313 | 6,32 | 16,36 | 166,6545 | 0,02 | 29,96 | |
| 5-5.1 | 890,25 | 1,255 | 0,572688 | 26,32 | 0,31 | 0,313 | 6,08 | 17,71 | 199,023 | 0,02 | 29,96 | |
| 6-6.1 | 593,5 | 1,17 | 0,80085 | 27,35 | 0,31 | 0,313 | 6,32 | 16,36 | 166,6545 | 0,02 | 29,96 | |
| 7-7.1 | 890,25 | 1,255 | 0,572688 | 26,32 | 0,31 | 0,313 | 6,08 | 17,71 | 199,023 | 0,02 | 29,96 | |
| 8-8.1 | 890,25 | 1,255 | 0,572688 | 26,32 | 0,31 | 0,313 | 6,08 | 17,71 | 199,023 | 0,02 | 29,96 | |
| 9-9.1 | 890,25 | 1,255 | 0,572688 | 26,32 | 0,31 | 0,313 | 6,08 | 17,71 | 199,023 | 0,02 | 29,96 | |
| 10-10.1 | 2670,75 | 1,765 | 0,268471 | 21,46 | 0,32 | 0,313 | 4,97 | 26,14 | 353,213 | 0,04 | 29,93 | |
| 11-11.1 | 890,25 | 1,255 | 0,572688 | 26,32 | 0,31 | 0,313 | 6,08 | 17,71 | 199,023 | 0,02 | 29,96 |
The piezometric graph is shown in fig. 5.2.
6. Calculation of insulation thickness
The average annual temperature of the coolant t 1 \u003d 100, t 2 \u003d 56.9
Let's define the internal d w.e and outdoor d AD equivalent channel diameters for internal (0.9 × 0.6 m) and external (1.15 × 0.78 m) dimensions of its cross section:
m
m
Let us determine the thermal resistance of the inner surface of the channel
Let us determine the thermal resistance of the channel wall Rk, assuming the coefficient of thermal conductivity of reinforced concrete λst = 2.04 W/(m deg):
Let us determine at the depth of laying the axis of the pipes h = 1.3 m and the thermal conductivity of the soil λgr = 2.0 W / (m deg), the thermal resistance of the soil
Assuming the temperature of the surface of the thermal insulation is 40 ° C, we determine the average temperatures of the thermal insulation layers of the supply t t.p. and return t t.o. pipelines: 
Let's define also, using adj. , coefficients
thermal conductivity of thermal insulation (Heat-insulating products
polyurethane foam) for feeder λ k1 and vice versa λ k2 pipelines:
λ To 1 = 0,033 + 0,00018 t m.p. = 0.033 + 0.00018 ⋅ 70 = 0.0456 W/(m⋅°С);
λ c2 = 0.033 + 0.00018 t so \u003d 0.033 + 0.00018 ⋅ 48.45 \u003d 0.042 W / (m ⋅ ° C).
Let us determine the thermal resistance of the surface of the heat-insulating layer:
Let's take app. normalized linear densities of heat fluxes for supply ql1 = 45 W/m and return ql2 = 18 W/m pipelines. Let us determine the total thermal resistance for the supply Rtot1 and return Rtot2 pipelines at K1 = 0.9:
Let us determine the coefficients of mutual influence of the temperature fields of the supply ϕ1 and return ϕ2 pipelines:
Let us determine the required thermal resistance of the layers for the supply Rk.p and return Rk.o pipelines, m ⋅ ° С / W:
R k.p = R tot1 - R a.c − (1+ϕ 1)( R p.k + R to + R gr)=
2.37 - 0.1433 - (1 + 0.4) (0.055 + 0.02 + 0.138) = 1.929 m⋅ °C / W;
R k.o = R tot2 - R a.c − (1+ϕ 1)( R p.k + R to + R gr)=
3.27 - 0.1433 - (1 + 2.5) (0.055 + 0.02 + 0.138) = 2.381 m ⋅ ° C / W.
Let's determine the values of B for the supply and return pipelines:
Let us determine the required thicknesses of thermal insulation layers for the supply δk1 and return δk2 pipelines:
We accept the thickness of the main insulation layer for the supply mm, return pipelines mm.
Compensator calculation
Compensators are designed to compensate for thermal elongations and deformations to prevent the destruction of pipelines. Compensators are located between fixed supports.
Calculation of the compensator for the 3rd section.
Taking the coefficient of thermal elongation α=1.25 10⋅ − 2 mm/(m ⋅°C), using the data in Table. 14.2 app. 14 , we determine the maximum length of the section on which one bellows compensator can provide compensation:
Here λ is the amplitude of the axial stroke, mm, λ = 60mm
The required number of compensators n on the calculated area will be
PC
Let's take the same spans between fixed supports
83/2= L f = 41.5m.
Let us determine the actual amplitude of the compensator λ f at the length of the span between the fixed supports L f = 41.5 m .
R s. k, assuming equal spans between fixed supports L= 41.5 m:
R c.k \u003d R w + R p,
Where R– axial reaction arising due to the rigidity of the axial stroke is determined by the formula (1.85)
R = WITH λ λ f = 278 36.31 = 10094.2 N
Where WITHλ – wave stiffness, N/mm, ( WITH λ = 278 N/mm);
R p– axial reaction from internal pressure, H, defined
Let us determine the reaction of the compensator R s. To
R c.k = R f + R p = 10094.2+ 17708 = 27802.2 N.
In the heat supply system, the heat point connecting the heat network with the heat consumer occupies an important place. By means of a heat point (TP), local consumption systems (heating, hot water supply, ventilation) are controlled, it also transforms the coolant parameters (temperature, pressure, maintaining a constant flow rate, heat accounting, etc.). At the same time, the network itself is controlled in the heating point, since it distributes the heat carrier in relation to the heating network and controls its parameters.
We carry out the project of a heating point for a 5-storey building connected on site 6.
The scheme of an individual heat point is given
Selection of mixing pumps
The pump flow is determined in accordance with SP 41-101-95 by the formula:
where is the estimated maximum water consumption for heating from the heating network kg / s;
u- mixing coefficient, determined by the formula:
where is the temperature of the water in the supply pipeline of the heating network at the design outdoor temperature for heating design t n.o, °С;
- also, in the supply pipeline of the heating system, ° С;
- the same, in the return pipeline from the heating system, ° С;
;
The pressure of the mixing pump with such installation schemes is determined depending on the pressure in the heating network, as well as the required pressure in the heating system, and is taken with a margin of 2-3 m.
We choose circulation pumps WiloStratos ECO 30/1-5-BMS. These are standard pumps with a wet rotor and flange connection. The pumps are designed for use in heating systems, industrial circulation systems, water supply and air conditioning systems.
WiloStratos ECO are successfully used in systems where the temperature of the pumped liquid is in a wide range: from -20 to +130°C. A multi-stage (2, 3) speed switch allows the equipment to adapt to the current conditions of the heating system.
We install 2 Wilo pumps of the ECO 30/1-5-BMS brand with a flow of 3 m ^ 3 / h, a head of 6 m. One of the pumps is in reserve.
Selection circulation pump
We select a circulation pump of the GrundfosComfort type. These pumps circulate the water in the DHW system. Thanks to this, hot water flows immediately after the tap is opened. This pump is equipped with a built-in thermostat that automatically maintains the set water temperature in the range from 35 to 65 °C. This is a wet rotor pump, but due to its spherical shape, it is practically impossible to block the impeller due to contamination of the pump by impurities contained in the water. We select the Grundfos UP 15-14 B pump with a flow rate of 0.8 m 3 / hour, a head of 1.2 m, and a power of 25 watts.
Selection of Magnetic Flanged Filters
Magnetic filters are designed to trap persistent mechanical impurities (including ferromagnets) in non-aggressive liquids with temperatures up to 150 °C and a pressure of 1.6 MPa (16 kgf/cm2). They are installed in front of cold and hot water meters. We accept the FMF filter.
The choice of sump
Mud collectors are designed to purify water in heat supply systems from suspended particles of dirt, sand and other impurities.
We install a sump series Du65 Ru25 T34.01 p.4.903-10 on the supply pipeline when entering the heating point.
Selecting a flow and pressure regulator
The regulator is used as a direct action regulator for automation of subscriber inputs of residential buildings. It is selected according to the valve capacity coefficient:
where D R= 0.03 ... 0.05 MPa - pressure drop across the valve, we accept D R= 0.04 MPa.
m 3 / h.
The choice of flow and pressure regulator Danfoss AVP with a nominal diameter, D y - 65 mm, - 2 m 3 / h
Choosing a thermostat
Designed for automatic temperature control in open DHW systems. The regulator is equipped with a blocking device that protects the heating system from emptying during DHW peak hours and in emergency situations.
We choose a DanfossAVT / VG thermostat with a nominal diameter, D y - 65 mm, - 2 m 3 / h.
Check valve selection
check valves are shutoff valves. They prevent backflow of water.
Check valves type 402 from Danfoss are installed on the pipeline after the PP, on the jumper after the pumps, after the circulation pump, on the DHW pipeline.
Relief valve selection
Safety valves are a type pipe fittings, designed to automatically protect the technological system and pipelines from an unacceptable increase in pressure of the working medium by partially dumping it from the protected system. The most common spring safety valves, in which the pressure of the working medium is counteracted by the force of a compressed spring. The direction of supply of the working medium is under the spool. The safety valve is most often connected to the pipeline using a flange, with the cap up.
We choose a safety spring valve without manual undermining 17nzh21nzh (SPPK4) with D y = 65 mm.
Selection of ball valves
On the supply pipeline from the heating network, as well as on the return, on the pipelines to the thermostat and after it, we install Ball Valves, made of carbon steel (ball - stainless steel), welded, with handle, flanged, ( R y = 2.5 MPa) Jip type, Danfoss, s D y = 65 mm. On the circulation pipeline of the DHW line before and after the circulation pump, we install ball valves with D y = 65 mm. Before the flow line of the heating system and after the return line, ball valves with D y = 65 mm and s D y = 65 mm. On the jumper of the mixing pumps we install ball valves with D y = 65 mm.
Selecting a heat meter
Heat meters for closed heat supply systems are designed to measure the total amount of thermal energy and the total volumetric amount of heat carrier. We install the heat calculator Logic 9943-U4 with SONO 2500 CT flowmeter; Dy = 32 mm.
The heat calculator is designed for operation in open and closed systems of water heat supply from 0 to 175 ºС and pressure up to 1.6 MPa. The difference in water temperatures in the supply and return pipelines of the system is from 2 to 175 ºС. The device provides connection of two similar platinum resistance thermocouples and one or two flowmeters. Provides registration of parameter readings in electronic archive. The device generates monthly and daily reports, where all the necessary information about the consumption of thermal energy and coolant is presented in tabular form.
A set of thermocouples KTPTR-01-1-80 platinum is designed to measure the temperature difference in the supply and return pipelines of heat supply systems. It is used as part of heat meters. The principle of operation of the kit is based on a proportional change electrical resistance two thermal converters matched in terms of resistance and temperature coefficient depending on the measured temperature. Temperature measurement range from 0 to 180 о С.
Conclusion
The aim of the work was to develop a heating system for a residential microdistrict. The area consists of thirteen buildings, eleven residential, one kindergarten and one school., the location of the district of Omsk.
The developed heat supply system is closed with central quality regulation with a temperature schedule of 130/70. By the nature of the heat supply, it is two-stage - the buildings are directly connected to the heating network through automated ITPs, there are no central heating stations.
When developing the heating network, the following necessary calculations were performed:
Thermal loads for heating, ventilation and hot water supply of all subscribers are determined. As a method for determining the loads of heating and ventilation, the method of aggregated indicators was used. Based on the type and volume of the building, specific heat losses of the building were set. Design temperatures are taken according to the outside temperature according to SNiP "Construction Climatology". Indoor temperature according to reference data according to SanPiN based on the purpose of the room. The load on hot water supply was determined by the standard consumption of hot water per person according to reference data based on the type of building.
The schedule of the central quality regulation is calculated
The estimated costs of network water (subscribers) are determined
A hydraulic diagram of the heating network has been developed and a hydraulic calculation has been performed, the purpose of which is to determine the diameters of pipelines and the pressure drop in sections of the heating network
The thermal calculation of heat pipelines has been performed, i.e. calculation of insulation to reduce heat loss in the network. The calculation was made according to the method of not exceeding the normalized heat losses. A pre-insulated pipe with polyurethane foam insulation was chosen as the heat conductors. Pipeline laying method channelless
Compensators were selected to compensate for elongation of pipelines due to thermal expansion. Bellows expansion joints are used as compensators.
- a scheme of an individual heating point was developed and the main elements were selected, i.e. pumps, control valves, thermostats, etc.
Bibliographic list
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