Hydraulic calculation of heating networks. Operation of heating networks Calculation of natural circulation pressure

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

Level 1 – 1 is taken as the horizontal plane of pressure reference (see Fig. 6.5). Line P1 – P4 – graph of supply line pressures. Line O1 – O4 – return line pressure graph. N o1 – total pressure on the return collector of the source; Nсн – pressure of the network pump; N st – full pressure of the make-up pump, or full static pressure in the heating network; N to– total pressure in t.K at the discharge pipe of the network pump; D H t – pressure loss in the heat treatment plant; N p1 – total pressure on the supply manifold, N n1 = N k–D H t. Available supply water pressure at the CHP collector N 1 =N p1 - N o1. Pressure at any point in the network i denoted as N p i, H oi – total pressures in the forward and return pipelines. If the geodetic height at a point i There is Z i , then the piezometric pressure at this point is N p i – Z i , H o i – Z i in the forward and return pipelines, respectively. Available head at point i is the difference in piezometric pressures in the forward and return pipelines – N p i – H oi. The available pressure in the heating network at the connection point of subscriber D is N 4 = N p4 – N o4.

Fig.6.5. Scheme (a) and piezometric graph (b) of a two-pipe heating network

There is a loss of pressure in the supply line in section 1 - 4 . There is a pressure loss in the return line in section 1 - 4 . When the mains pump is operating, the pressure N The speed of the charging pump is regulated by a pressure regulator to N o1. When the network pump stops, a static pressure is established in the network N st, developed by the make-up pump.

When hydraulically calculating a steam pipeline, the profile of the steam pipeline may not be taken into account due to the low steam density. Pressure losses from subscribers, for example , depends on the subscriber connection scheme. With elevator mixing D N e = 10...15 m, with elevator-free input – D n BE =2...5 m, in the presence of surface heaters D N n =5...10 m, with pump mixing D N ns = 2…4 m.

Requirements for pressure conditions in the heating network:

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

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;

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

Warning There is not enough pressure at the source Delta=X m. Where Delta is the required pressure.

WORST CONSUMER: ID=XX.

Figure 283. Message about the worst consumer




This message is displayed when there is a lack of available pressure at the consumer, where DeltaH− the value of the pressure that is not enough, m, a ID (XX)− individual number of the consumer for whom the pressure shortage is maximum.



Figure 284. Message about insufficient pressure




Double-click the left mouse button on the message about the worst consumer: the corresponding consumer will blink on the screen.

This error can be caused by several reasons:

1. Incorrect data. If the amount of pressure shortage goes beyond the actual values ​​for a given network, then there is an error when entering the initial data or an error when plotting the network diagram on the map. You should check whether the following data has been entered correctly:

   

   Hydraulic network mode.

   If there are no errors when entering the initial data, but a lack of pressure exists and is of real significance for a given network, then in this situation the determination of the cause of the shortage and the method for eliminating it is carried out by the specialist working with this heating network.

ID=ХХ "Name of consumer" Emptying the heating system (H, m)

This message is displayed when there is insufficient pressure in the return pipeline to prevent emptying of the heating system of the upper floors of the building; the total pressure in the return pipeline must be at least the sum of the geodetic mark, the height of the building plus 5 meters to fill the system. The head reserve for filling the system can be changed in the calculation settings ().

XX− individual number of the consumer whose heating system is being emptied, N- pressure, in meters of which is not enough;

ID=ХХ "Name of consumer" Pressure in the return pipeline is higher than the geodetic mark by N, m

This message is issued when the pressure in the return pipeline is higher than permissible according to the strength conditions of cast iron radiators (more than 60 m. water column), where XX- individual consumer number and N- pressure value in the return pipeline exceeding the geodetic mark.

The maximum pressure in the return pipeline can be set independently in calculation settings. ;

ID=XX "Name of consumer" Elevator nozzle cannot be selected. Set the maximum

This message may appear when there is a large heating load or when an incorrect connection diagram is selected that does not correspond to the design parameters. XX- individual number of the consumer for whom the elevator nozzle cannot be selected;

ID=XX "Name of consumer" Elevator nozzle cannot be selected. Set the minimum

This message may appear when there are very small heating loads or when an incorrect connection diagram is selected that does not correspond to the design parameters. XX− individual number of the consumer for whom the elevator nozzle cannot be selected.

Warning Z618: ID=XX "XX" The number of washers on the supply pipe to CO is more than 3 (YY)

This message means that, as a result of the calculation, the number of washers required to adjust the system is more than 3 pieces.

Since the default minimum diameter of the washer is 3 mm (indicated in the calculation settings “Setting up the calculation of pressure losses”), and the consumption of the consumer’s heating system ID=XX is very small, the calculation results in determining the total number of washers and the diameter of the last washer (in consumer database).

That is, a message like: The number of washers on the supply pipeline for CO is more than 3 (17) warns that to set up this consumer, you should install 16 washers with a diameter of 3 mm and 1 washer, the diameter of which is determined in the consumer database.

Warning Z642: ID=XX The elevator at the central heating station is not working

This message is displayed as a result of a verification calculation and means that the elevator unit is not functioning.

The available pressure drop to create water circulation, Pa, is determined by the formula

where DPn is the pressure created by the circulation pump or elevator, Pa;

ДПе - natural circulation pressure in the calculation ring due to cooling of water in pipes and heating devices, Pa;

In pumping systems, it is allowed not to take into account DP if it is less than 10% of DP.

Available pressure drop at the entrance to the building DPr = 150 kPa.

Calculation of natural circulation pressure

The natural circulation pressure that arises in the design ring of a vertical single-pipe system with bottom distribution, adjustable with closing sections, Pa, is determined by the formula

where is the average increase in water density when its temperature decreases by 1? C, kg/(m3?? C);

Vertical distance from heating center to cooling center

heating device, m;

Water flow in the riser, kg/h, is determined by the formula

Calculation of pump circulation pressure

The value, Pa, is selected in accordance with the available pressure difference at the inlet and the mixing coefficient U according to the nomogram.

Available pressure difference at the inlet =150 kPa;

Coolant parameters:

In the heating network f1=150?C; f2=70?C;

In the heating system t1=95?C; t2=70?C;

We determine the mixing coefficient using the formula

µ= f1 - t1 / t1 - t2 =150-95/95-70=2.2; (2.4)

Hydraulic calculation of water heating systems using the method of specific pressure loss due to friction

Calculation of the main circulation ring

1) Hydraulic calculation of the main circulation ring is carried out through riser 15 of a vertical single-pipe water heating system with bottom wiring and dead-end movement of the coolant.

2) We divide the main central circulation system into calculation sections.

3) To pre-select the diameter of the pipes, an auxiliary value is determined - the average value of the specific pressure loss from friction, Pa, per 1 meter of pipe according to the formula

where is the available pressure in the adopted heating system, Pa;

Total length of the main circulation ring, m;

Correction factor taking into account the share of local pressure losses in the system;

For a heating system with pump circulation, the share of loss due to local resistance is b=0.35, and due to friction b=0.65.

4) Determine the coolant flow rate in each section, kg/h, using the formula

Parameters of the coolant in the supply and return pipelines of the heating system, ?C;

Specific mass heat capacity of water equal to 4.187 kJ/(kg??С);

Coefficient for taking into account additional heat flow when rounding above the calculated value;

Coefficient of accounting for additional heat losses by heating devices near external fences;

6) We determine the coefficients of local resistance in the design areas (and write their sum in Table 1) by .

Table 1

7) At each section of the main circulation ring, we determine the pressure loss due to local resistance Z, depending on the sum of the local resistance coefficients Uo and the water speed in the section.

8) We check the reserve of available pressure drop in the main circulation ring according to the formula

where is the total pressure loss in the main circulation ring, Pa;

With a dead-end coolant flow pattern, the discrepancy between pressure losses in the circulation rings should not exceed 15%.

We summarize the hydraulic calculation of the main circulation ring in Table 1 (Appendix A). As a result, we obtain the pressure loss discrepancy

Calculation of a small circulation ring

We perform a hydraulic calculation of the secondary circulation ring through riser 8 of a single-pipe water heating system

1) We calculate the natural circulation pressure due to the cooling of water in the heating devices of riser 8 using formula (2.2)

2) Determine the water flow in riser 8 using formula (2.3)

3) We determine the available pressure drop for the circulation ring through the secondary riser, which should be equal to the known pressure losses in the main circulation circuit sections, adjusted for the difference in natural circulation pressure in the secondary and main rings:

15128.7+(802-1068)=14862.7 Pa

4) Find the average value of linear pressure loss using formula (2.5)

5) Based on the value, Pa/m, of the coolant flow rate in the area, kg/h, and based on the maximum permissible speeds of coolant movement, we determine the preliminary diameter of the pipes dу, mm; actual specific pressure loss R, Pa/m; actual coolant speed V, m/s, according to .

6) We determine the coefficients of local resistance in the design areas (and write their sum in Table 2) by .

7) In the section of the small circulation ring, we determine the pressure loss due to local resistance Z, depending on the sum of the local resistance coefficients Uo and the water speed in the section.

8) We summarize the hydraulic calculation of the small circulation ring in Table 2 (Appendix B). We check the hydraulic connection between the main and small hydraulic rings according to the formula

9) Determine the required pressure loss in the throttle washer using the formula

10) Determine the diameter of the throttle washer using the formula

At the site it is required to install a throttle washer with an internal passage diameter of DN=5mm

The operating pressure in the heating system is the most important parameter on which the functioning of the entire network depends. Deviations in one direction or another from the values ​​​​provided by the project not only reduce the efficiency of the heating circuit, but also significantly affect the operation of the equipment, and in special cases can even cause it to fail.

Of course, a certain pressure drop in the heating system is determined by the principle of its design, namely the difference in pressure in the supply and return pipelines. But if there are larger spikes, immediate action should be taken.

1. Static pressure. This component depends on the height of the column of water or other coolant in the pipe or container. Static pressure exists even if the working medium is at rest.
2. Dynamic pressure. It is a force that acts on the internal surfaces of the system when water or other medium moves.

The concept of maximum operating pressure is distinguished. This is the maximum permissible value, exceeding which can lead to the destruction of individual network elements.

What pressure in the system should be considered optimal?

Table of maximum pressure in the heating system.

When designing heating, the coolant pressure in the system is calculated based on the number of floors of the building, the total length of the pipelines and the number of radiators. As a rule, for private houses and cottages, the optimal values ​​of medium pressure in the heating circuit are in the range from 1.5 to 2 atm.

For apartment buildings up to five floors high, connected to a central heating system, the pressure in the network is maintained at 2-4 atm. For nine- and ten-story buildings, a pressure of 5-7 atm is considered normal, and in taller buildings - 7-10 atm. The maximum pressure is recorded in the heating mains through which the coolant is transported from boiler houses to consumers. Here it reaches 12 atm.

For consumers located at different heights and at different distances from the boiler room, the pressure in the network must be adjusted. To reduce it, pressure regulators are used, and to increase it, pumping stations are used. However, it should be taken into account that a faulty regulator can cause an increase in pressure in certain areas of the system. In some cases, when the temperature drops, these devices can completely shut off the shut-off valves on the supply pipeline coming from the boiler plant.

To avoid such situations, the regulator settings are adjusted so that complete shutoff of the valves is impossible.

Autonomous heating systems

Expansion tank in an autonomous heating system.

In the absence of a centralized heating supply, autonomous heating systems are installed in houses, in which the coolant is heated by an individual low-power boiler. If the system communicates with the atmosphere through an expansion tank and the coolant circulates in it due to natural convection, it is called open. If there is no communication with the atmosphere, and the working medium circulates thanks to the pump, the system is called closed. As already mentioned, for the normal functioning of such systems, the water pressure in them should be approximately 1.5-2 atm. This low figure is due to the relatively short length of pipelines, as well as a small number of instruments and fittings, which results in relatively low hydraulic resistance. In addition, due to the low height of such houses, the static pressure in the lower sections of the circuit rarely exceeds 0.5 atm.

At the stage of launching the autonomous system, it is filled with cold coolant, maintaining a minimum pressure in closed heating systems of 1.5 atm. There is no need to sound the alarm if, some time after filling, the pressure in the circuit drops. Pressure losses in this case are caused by the release of air from the water, which dissolved in it when the pipelines were filled. The circuit should be de-aired and completely filled with coolant, bringing its pressure to 1.5 atm.

After heating the coolant in the heating system, its pressure will increase slightly, reaching the calculated operating values.

Precautionary measures

A device for measuring pressure.

Since when designing autonomous heating systems, in order to save money, a small safety margin is included, even a low pressure surge of up to 3 atm can cause depressurization of individual elements or their connections. In order to smooth out pressure drops due to unstable pump operation or changes in coolant temperature, an expansion tank is installed in a closed heating system. Unlike a similar device in an open type system, it does not communicate with the atmosphere. One or more of its walls are made of elastic material, due to which the tank acts as a damper during pressure surges or water hammer.

The presence of an expansion tank does not always guarantee that pressure is maintained within optimal limits. In some cases it may exceed the maximum permissible values:

• if the expansion tank capacity is incorrectly selected;
• in case of malfunction of the circulation pump;
• when the coolant overheats, which is a consequence of malfunctions in the operation of the boiler automation;
• due to incomplete opening of shut-off valves after repairs or maintenance work;
• due to the appearance of an air lock (this phenomenon can provoke both an increase in pressure and a drop);
• when the throughput of the dirt filter decreases due to its excessive clogging.

Therefore, in order to avoid emergency situations when installing closed-type heating systems, it is mandatory to install a safety valve that will release excess coolant if the permissible pressure is exceeded.

What to do if the pressure in the heating system drops

Pressure in the expansion tank.

When operating autonomous heating systems, the most common emergency situations are those in which the pressure gradually or sharply decreases. They can be caused by two reasons:

• depressurization of system elements or their connections;
• problems with the boiler.

In the first case, the location of the leak should be located and its tightness restored. You can do this in two ways:

1. Visual inspection. This method is used in cases where the heating circuit is laid in an open manner (not to be confused with an open-type system), that is, all its pipelines, fittings and devices are visible. First of all, carefully inspect the floor under the pipes and radiators, trying to detect puddles of water or traces of them. In addition, the location of the leak can be identified by traces of corrosion: characteristic rusty streaks form on radiators or at the joints of system elements when the seal is broken.
2. Using special equipment. If a visual inspection of the radiators does not yield anything, and the pipes are laid in a hidden way and cannot be inspected, you should seek the help of specialists. They have special equipment that will help detect leaks and fix them if the home owner is unable to do this themselves. Localizing the depressurization point is quite simple: water is drained from the heating circuit (for such cases, a drain valve is installed at the lowest point of the circuit during the installation stage), then air is pumped into it using a compressor. The location of the leak is determined by the characteristic sound that leaking air makes. Before starting the compressor, the boiler and radiators should be insulated using shut-off valves.

If the problem area is one of the joints, it is additionally sealed with tow or FUM tape and then tightened. The burst pipeline is cut out and a new one is welded in its place. Units that cannot be repaired are simply replaced.

If the tightness of pipelines and other elements is beyond doubt, and the pressure in a closed heating system still drops, you should look for the reasons for this phenomenon in the boiler. You should not carry out diagnostics yourself; this is a job for a specialist with the appropriate education. Most often the following defects are found in the boiler:

Installation of a heating system with a pressure gauge.

• the appearance of microcracks in the heat exchanger due to water hammer;
• manufacturing defects;
• failure of the make-up valve.

A very common reason why the pressure in the system drops is the incorrect selection of the expansion tank capacity.

Although the previous section stated that this may cause increased pressure, there is no contradiction here. When the pressure in the heating system increases, the safety valve is activated. In this case, the coolant is discharged and its volume in the circuit decreases. As a result, the pressure will decrease over time.

Pressure control

For visual monitoring of pressure in the heating network, dial pressure gauges with a Bredan tube are most often used. Unlike digital instruments, such pressure gauges do not require an electrical power connection. Automated systems use electrical contact sensors. A three-way valve must be installed at the outlet to the control and measuring device. It allows you to isolate the pressure gauge from the network during maintenance or repair, and is also used to remove an air lock or reset the device to zero.

Instructions and rules governing the operation of heating systems, both autonomous and centralized, recommend installing pressure gauges at the following points:

1. Before the boiler installation (or boiler) and at the exit from it. At this point the pressure in the boiler is determined.
2. Before and after the circulation pump.
3. At the entrance of the heating main into a building or structure.
4. Before and after the pressure regulator.
5. At the inlet and outlet of the coarse filter (mud filter) to control its level of contamination.

All control and measuring instruments must undergo regular verification to confirm the accuracy of the measurements they perform.

In water heat supply systems, the provision of heat to consumers is carried out by appropriately distributing the estimated costs of network water between them. To implement such distribution, it is necessary to develop a hydraulic mode of the heat supply system.

The purpose of developing the hydraulic mode of the heating supply system is to ensure optimal permissible pressures in all elements of the heating supply system and the necessary available pressures at the nodes of the heating network, at group and local heating points, sufficient to supply consumers with the calculated water flow rates. The available pressure is the difference in water pressure in the supply and return pipelines.

To ensure reliable operation of the heat supply system, the following conditions apply:

Not exceeding permissible pressures: in heat supply sources and heating networks: 1.6-2.5 mPa - for steam-water network heaters of the PSV type, for steel hot water boilers, steel pipes and fittings; in subscriber installations: 1.0 mPa - for sectional water-water heaters; 0.8-1.0 mPa - for steel convectors; 0.6 mPa - for cast iron radiators; 0.8 mPa - for air heaters;

Ensuring excess pressure in all elements of the heat supply system to prevent pump cavitation and protect the heat supply system from air leaks. The minimum value of excess pressure is assumed to be 0.05 MPa. For this reason, the piezometric line of the return pipeline in all modes must be located above the point of the tallest building by at least 5 m of water. Art.;

At all points of the heating system, a pressure must be maintained that exceeds the pressure of saturated water vapor at the maximum water temperature, ensuring that the water does not boil. As a rule, the danger of water boiling most often occurs in the supply pipelines of the heating network. The minimum pressure in the supply pipelines is taken according to the calculated temperature of the supply water, table 7.1.

Table 7.1

The non-boiling line must be drawn on the graph parallel to the terrain at a height corresponding to the excess pressure at the maximum temperature of the coolant.

It is convenient to depict the hydraulic mode graphically in the form of a piezometric graph. The piezometric graph is plotted for two hydraulic modes: hydrostatic and hydrodynamic.

The purpose of developing a hydrostatic mode is to ensure the necessary water pressure in the heating system, within acceptable limits. The lower pressure limit should ensure that consumer systems are filled with water and create the necessary minimum pressure to protect the heating system from air leaks. The hydrostatic mode is developed with charging pumps running and no circulation.

The hydrodynamic mode is developed on the basis of data from the hydraulic calculation of heating networks and is ensured by the simultaneous operation of make-up and network pumps.

The development of a hydraulic mode comes down to constructing a piezometric graph that meets all the requirements for the hydraulic mode. Hydraulic modes of water heating networks (piezometric graphs) should be developed for heating and non-heating periods. The piezometric graph allows you to: determine the pressures in the supply and return pipelines; available pressure at any point in the heating network, taking into account the terrain; select consumer connection schemes based on available pressure and building heights; select auto regulators, elevator nozzles, throttling devices for local heat consumer systems; select network and make-up pumps.

Construction of a piezometric graph(Fig. 7.1) is done as follows:

a) scales are selected along the abscissa and ordinate axes and the terrain and the height of the building blocks are plotted. Piezometric graphs are constructed for main and distribution heating networks. For main heating networks the following scales can be adopted: horizontal M g 1:10000; vertical M in 1:1000; for distribution heating networks: M g 1:1000, M v 1:500; The zero mark of the ordinate axis (pressure axis) is usually taken to be the mark of the lowest point of the heating main or the mark of the network pumps.

b) the value of the static pressure is determined to ensure the filling of consumer systems and the creation of minimal excess pressure. This is the height of the highest building plus 3-5 m.water column.

After plotting the terrain and building heights, the static head of the system is determined

H c t = [N building + (3¸5)], m (7.1)

Where N rear- height of the highest building, m.

The static head H st is parallel to the x-axis, and it should not exceed the maximum operating pressure for local systems. The maximum operating pressure is: for heating systems with steel heating devices and for air heaters - 80 meters; for heating systems with cast iron radiators - 60 meters; for independent connection schemes with surface heat exchangers - 100 meters;

c) Then the dynamic mode is constructed. The suction pressure of network pumps H sun is arbitrarily selected, which should not exceed the static pressure and provides the necessary supply pressure at the inlet to prevent cavitation. The cavitation reserve, depending on the size of the pump, is 5-10 m.water column;

d) from the conditional pressure line at the suction of the network pumps, the pressure losses in the return pipeline DН return of the main heating network (line A-B) are successively plotted using the results of hydraulic calculations. The amount of pressure in the return line must comply with the requirements specified above when constructing the static pressure line;

e) the required available pressure is set aside at the last subscriber DN ab, based on the operating conditions of the elevator, heater, mixer and distribution heating networks (line B-C). The amount of available pressure at the connection point of distribution networks is assumed to be at least 40 m;

f) starting from the last pipeline node, pressure losses are deposited in the supply pipeline of the main line DH under (line C-D). The pressure at all points of the supply pipeline, based on the condition of its mechanical strength, should not exceed 160 m;

g) pressure losses in the heat source DН it are postponed (line D-E) and the pressure at the outlet of the network pumps is obtained. In the absence of data, the pressure loss in the communications of a thermal power plant can be assumed to be 25 - 30 m, and for a district boiler house 8-16 m.

The pressure of the network pumps is determined

The pressure of the charging pumps is determined by the pressure of the static mode.

As a result of this construction, the initial form of a piezometric graph is obtained, which allows one to estimate pressures at all points of the heat supply system (Fig. 7.1).

If they do not meet the requirements, change the position and shape of the piezometric graph:

a) if the return pipeline pressure line crosses the height of the building or is less than 3¸5 m from it, then the piezometric graph should be raised so that the pressure in the return pipeline ensures filling of the system;

b) if the maximum pressure in the return pipeline exceeds the permissible pressure in heating devices, and it cannot be reduced by shifting the piezometric graph down, then it should be reduced by installing booster pumps in the return pipeline;

c) if the non-boiling line intersects the pressure line in the supply pipeline, then boiling of water is possible beyond the intersection point. Therefore, the water pressure in this part of the heating network should be increased by moving the piezometric graph upward, if possible, or by installing a booster pump on the supply pipeline;

d) if the maximum pressure in the equipment of the heat treatment plant of the heat source exceeds the permissible value, then booster pumps are installed on the supply pipeline.

Division of the heating network into static zones. The piezometric graph is developed for two modes. Firstly, for static mode, when there is no water circulation in the heating system. It is assumed that the system is filled with water at a temperature of 100°C, thereby eliminating the need to maintain excess pressure in the heat pipes to avoid boiling of the coolant. Secondly, for hydrodynamic mode - in the presence of coolant circulation in the system.

The development of the schedule begins with the static mode. The location of the full static pressure line on the graph should ensure the connection of all subscribers to the heating network according to a dependent scheme. To do this, the static pressure should not exceed what is permissible based on the strength of subscriber installations and should ensure that local systems are filled with water. The presence of a common static zone for the entire heating system simplifies its operation and increases its reliability. If there is a significant difference in geodetic elevations of the earth, establishing a common static zone is impossible for the following reasons.

The lowest position of the static pressure level is determined from the conditions of filling local systems with water and ensuring that at the highest points of the systems of the tallest buildings located in the area of ​​​​the highest geodetic marks, an excess pressure of at least 0.05 MPa. This pressure turns out to be unacceptably high for buildings located in that part of the area that has the lowest geodetic elevations. Under such conditions, it becomes necessary to divide the heat supply system into two static zones. One zone is for part of the area with low geodetic marks, the other - with high ones.

In Fig. Figure 7.2 shows a piezometric graph and a schematic diagram of the heat supply system for an area that has a significant difference in geodetic ground level marks (40m). The part of the area adjacent to the heat supply source has zero geodetic marks; in the peripheral part of the area the marks are 40 m. The height of the buildings is 30 and 45m. To be able to fill building heating systems with water III and IV, located at the 40 m mark and creating an excess pressure of 5 m at the upper points of the systems, the level of the total static pressure should be located at the 75 m mark (line 5 2 - S 2). In this case, the static head will be equal to 35m. However, a head of 75m is unacceptable for buildings I And II, located at the zero mark. For them, the permissible highest position of the level of total static pressure corresponds to 60 m. Thus, under the conditions under consideration, it is impossible to establish a common static zone for the entire heat supply system.

A possible solution is to divide the heat supply system into two zones with different levels of total static heads - the lower one with a level of 50 m (line S t-Si) and the upper one with a level of 75m (line S 2 -S 2). With this solution, all consumers can be connected to the heat supply system according to a dependent scheme, since the static pressures in the lower and upper zones are within acceptable limits.

So that when water circulation in the system stops, the static pressure levels are established in accordance with the accepted two zones, a separating device is placed at the point of their connection (Fig. 7.2 6 ). This device protects the heating network from increased pressure when the circulation pumps stop, automatically cutting it into two hydraulically independent zones: upper and lower.

When the circulation pumps are stopped, the pressure drop in the return pipeline of the upper zone is prevented by the pressure regulator “towards itself” RDDS (10), which maintains a constant specified pressure RDDS at the point of impulse selection. When the pressure drops, it closes. The pressure drop in the supply line is prevented by the non-return valve (11) installed on it, which also closes. Thus, the RDDS and the check valve cut the heating network into two zones. To feed the upper zone, a feed pump (8) is installed, which takes water from the lower zone and supplies it to the upper one. The pressure developed by the pump is equal to the difference between the hydrostatic heads of the upper and lower zones. The lower zone is fed by the make-up pump 2 and the make-up regulator 3.

Figure 7.2. Heating system divided into two static zones

a - piezometric graph;

b - schematic diagram of the heat supply system; S 1 - S 1, - line of total static pressure of the lower zone;

S 2 – S 2, - line of total static pressure of the upper zone;

N p.n1 - pressure developed by the feed pump of the lower zone; N p.n2 - pressure developed by the top zone make-up pump; N RDDS - pressure to which the RDDS (10) and RD2 (9) regulators are set; ΔН RDDS - pressure activated on the RDDS regulator valve in hydrodynamic mode; I-IV- subscribers; 1-make-up water tank; 2.3 - feed pump and feed regulator for the lower zone; 4 - pre-switched pump; 5 - main steam-water heaters; 6- network pump; 7 - peak hot water boiler; 8 , 9 - make-up pump and top zone make-up regulator; 10 - pressure regulator “towards you” RDDS; 11- check valve

The RDDS regulator is set to the pressure Nrdds (Fig. 7.2a). The make-up regulator RD2 is set to the same pressure.

In hydrodynamic mode, the RDDS regulator maintains the pressure at the same level. At the beginning of the network, a make-up pump with a regulator maintains the pressure of H O1. The difference in these pressures is spent on overcoming the hydraulic resistance in the return pipeline between the separating device and the circulation pump of the heat source, the rest of the pressure is activated in the throttle substation on the RDDS valve. In Fig. 8.9, and this part of the pressure is shown by the value ΔН RDDS. The throttle substation in hydrodynamic mode makes it possible to maintain the pressure in the return line of the upper zone not lower than the accepted level of static pressure S 2 - S 2.

Piezometric lines corresponding to the hydrodynamic regime are shown in Fig. 7.2a. The highest pressure in the return pipeline at consumer IV is 90-40 = 50m, which is acceptable. The pressure in the return line of the lower zone is also within acceptable limits.

In the supply pipeline, the maximum pressure after the heat source is 160 m, which does not exceed what is permissible based on the strength of the pipes. The minimum piezometric pressure in the supply pipeline is 110 m, which ensures that the coolant does not boil over, since at a design temperature of 150 ° C the minimum permissible pressure is 40 m.

The piezometric graph developed for static and hydrodynamic modes provides the ability to connect all subscribers according to a dependent circuit.

Another possible solution to the hydrostatic mode of the heating system shown in Fig. 7.2 is the connection of some subscribers according to an independent scheme. There may be two options here. First option- set the general level of static pressure at 50 m (line S 1 - S 1), and connect the buildings located at the upper geodetic marks according to an independent scheme. In this case, the static pressure in water-water heating heaters of buildings in the upper zone on the side of the heating coolant will be 50-40 = 10 m, and on the side of the heated coolant will be determined by the height of the buildings. The second option is to set the general level of static pressure at 75 m (line S 2 - S 2) with the connection of the buildings of the upper zone according to a dependent scheme, and the buildings of the lower zone - according to an independent one. In this case, the static pressure in water-water heaters on the side of the heating coolant will be equal to 75 m, i.e. less than the permissible value (100 m).

Main 1, 2; 3;

add. 4, 7, 8.