The available pressure drop to create water circulation, Pa, is determined by the formula
where DPn is the pressure created circulation pump or elevator, Pa;
DPE - 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
Natural circulation pressure arising in the design ring of the vertical single pipe system with lower wiring, adjustable with closing sections, Pa, 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 The main circulation ring is carried out through riser 15 of a vertical single-pipe water heating system with lower 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
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1 plot Gate valve d=25 1 piece Bend 90° d=25 1 piece |
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2nd section Tee for passage d=25 1 piece |
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Section 3 Tee for passage d=25 1 piece Bend 90° d=25 4pcs |
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Section 4 Tee for passage d=20 1 piece |
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5th section Tee for passage d=20 1 piece Bend 90° d=20 1 piece |
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6th section Tee for passage d=20 1 piece Bend 90° d=20 4pcs |
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Section 7 Tee for passage d=15 1 piece Bend 90° d=15 4pcs |
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8th section Tee for passage d=15 1 piece |
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Section 9 Tee for passage d=10 1 piece Bend 90° d=10 1 piece |
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10th section Tee for passage d=10 4pcs Bend 90° d=10 11pcs Crane KTR d=10 3 pcs Radiator RSV 3 pcs |
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11th section Tee for passage d=10 1 piece Bend 90° d=10 1 piece |
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Section 12 Tee for passage d=15 1 piece |
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Section 13 Tee for passage d=15 1 piece Bend 90° d=15 4pcs |
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Section 14 Tee for passage d=20 1 piece Bend 90° d=20 4pcs |
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15th section Tee for passage d=20 1 piece Bend 90° d=20 1 piece |
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16th section Tee for passage d=20 1 piece |
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17th section Tee for passage d=25 1 piece Bend 90° d=25 4pcs |
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Section 18 Tee for passage d=25 1 piece |
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19th section Gate valve d=25 1 piece Bend 90° d=25 1 piece |
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 coefficients local resistance Uo and water speed in the area.
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 losses pressure 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
Read also:
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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 flows. 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;
Security overpressure 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 maximum temperature water, 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 regime is developed based on the data hydraulic calculation heating networks and is provided simultaneous work 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, throttle devices for local systems heat consumers; 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 network pumps, pressure losses in the return pipeline DН return of the main heating line are successively deposited ( line A-B) using the results of hydraulic calculations. The amount of pressure in the return line must meet 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;
e) starting from the last pipeline node, pressure losses are deposited in the supply pipeline of the main line DN under ( line C-D). Pressure at all points of the supply pipeline based on its conditions mechanical strength should not exceed 160 m;
g) pressure losses are delayed in the heat source DН it ( 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 pressure line of the return pipeline 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 high points systems of the tallest buildings located in the area of the highest geodetic elevations, 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. 7.2 shows the piezometric graph and circuit diagram heat supply systems for an area with 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 45 m. 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 full static pressure - to the lower one with a level of 50m (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 high blood 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 set pressure RDDS at the point where the pulse is taken. 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 - make-up pump and lower zone make-up regulator; 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. Minimum piezometric head 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.
To others possible solution 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.
“Specification of quantity and quality indicators utility resources V modern realities Housing and communal services"
SPECIFICATION OF INDICATORS OF QUANTITY AND QUALITY OF COMMUNAL RESOURCES IN MODERN REALITIES OF HUSING AND UTILITIES
V.U. Kharitonsky, Head of Department engineering systems
A. M. Filippov, Deputy Head of the Engineering Systems Department,
State Housing Inspectorate of Moscow
Documents regulating the indicators of the quantity and quality of communal resources supplied to household consumers at the border of responsibility of the resource supply and housing organizations have not been developed to date. Specialists from the Moscow Housing Inspectorate, in addition to the existing requirements, propose to specify the values of the parameters of heat and water supply systems at the entrance to the building, in order to maintain the quality of public services in residential apartment buildings.
Review of current rules and regulations for technical operation housing stock in the field of housing and communal services showed that currently construction, sanitary standards and rules, GOST R 51617 -2000* “Housing and communal services”, “Rules for the provision of utility services to citizens”, approved by Decree of the Government of the Russian Federation of May 23, 2006 No. 307, and other valid regulations consider and set parameters and modes only at the source (central heating station, boiler house, water pumping station) that produces communal resources (cold, hot water and thermal energy), and directly in the resident’s apartment, where utilities are provided. However, they do not take into account the modern realities of the division of housing and communal services into residential buildings and public utility facilities and the established boundaries of responsibility of the resource supply and housing organizations, which are the subject of endless disputes when determining the guilty party for the failure to provide services to the population or provide services poor quality. Thus, today there is no document regulating the indicators of quantity and quality at the entrance to the house, at the border of responsibility of the resource supply and housing organizations.
However, an analysis of quality checks of supplied communal resources and services carried out by the Moscow Housing Inspectorate showed that the provisions of federal regulatory legal acts in the field of housing and communal services can be detailed and specified in relation to apartment buildings, which will allow establishing mutual responsibility of resource supply and housing management organizations. It should be noted that the quality and quantity of communal resources supplied to the boundary of the operational responsibility of the resource supplying and managing housing organization, and public services to residents, is determined and assessed based on the readings, first of all, of common house metering devices installed at the inputs
heat and water supply systems to residential buildings, and an automated system for monitoring and accounting for energy consumption.
Thus, the Moscow Housing Inspectorate, based on the interests of residents and many years of practice, in addition to the requirements of regulatory documents and in development of the provisions of SNiP and SanPin in relation to operating conditions, as well as in order to maintain the quality of utility services provided to the population in residential apartment buildings, proposed regulating when introducing heat and water supply systems into the house (at the metering and control unit), the following standard values of parameters and modes recorded by general house metering devices and an automated control and accounting system for energy consumption:
1) for the system central heating(CO):
The deviation of the average daily temperature of the network water entering the heating systems must be within ±3% of the established temperature schedule. The average daily return water temperature should not exceed the set value temperature chart temperature by more than 5%;
The network water pressure in the return pipeline of the central heating system must be no less than 0.05 MPa (0.5 kgf/cm2) higher than the static pressure (for the system), but not higher than permissible (for pipelines, heating devices, fittings and other equipment ). If necessary, it is allowed to install pressure regulators on the return pipelines in the ITP of heating systems of residential buildings directly connected to the main heating networks;
The network water pressure in the supply pipeline of central heating systems must be higher than the required water pressure in the return pipelines by the amount of available pressure (to ensure coolant circulation in the system);
The available pressure (pressure difference between the supply and return pipelines) of the coolant at the entrance of the central heating network into the building must be maintained by heat supply organizations within the limits:
a) with dependent connection (with elevator units) - in accordance with the design, but not less than 0.08 MPa (0.8 kgf/cm 2);
b) with independent connection - in accordance with the design, but not less than 0.03 MPa (0.3 kgf/cm2) more than the hydraulic resistance of the in-house central heating system.
2) For hot water supply system (DHW):
Temperature hot water in the DHW supply pipeline for closed systems within 55-65 °C, for open systems heat supply within 60-75 °C;
Temperature in the DHW circulation pipeline (for closed and open systems) 46-55 °C;
The arithmetic mean value of the hot water temperature in the supply and circulation pipelines at the inlet of the DHW system in all cases must be at least 50 °C;
The available pressure (pressure difference between the supply and circulation pipelines) at the calculated circulation flow rate of the hot water supply system must be no lower than 0.03-0.06 MPa (0.3-0.6 kgf/cm2);
The water pressure in the supply pipeline of the hot water supply system must be higher than the water pressure in the circulation pipeline by the amount of available pressure (to ensure the circulation of hot water in the system);
The water pressure in the circulation pipeline of hot water supply systems must be no less than 0.05 MPa (0.5 kgf/cm2) higher than the static pressure (for the system), but not exceed the static pressure (for the highest located and high-rise building) more than by 0.20 MPa (2 kgf/cm2).
With these parameters in apartments near sanitary fixtures of residential premises, in accordance with regulatory legal acts Russian Federation, the following values must be provided:
Hot water temperature is not lower than 50 °C (optimal - 55 °C);
The minimum free pressure for sanitary fixtures in residential premises on the upper floors is 0.02-0.05 MPa (0.2-0.5 kgf/cm 2);
The maximum free pressure in hot water supply systems at sanitary fixtures on the upper floors should not exceed 0.20 MPa (2 kgf/cm2);
The maximum free pressure in water supply systems at sanitary fixtures on the lower floors should not exceed 0.45 MPa (4.5 kgf/cm2).
3) For a cold water supply system (CWS):
The water pressure in the supply pipeline of the cold water system must be at least 0.05 MPa (0.5 kgf/cm 2) higher than the static pressure (for the system), but not exceed the static pressure (for the highest located and high-rise building) by more than 0.20 MPa (2 kgf/cm2).
With this parameter in apartments, in accordance with regulatory legal acts of the Russian Federation, the following values must be provided:
a) the minimum free pressure for sanitary fixtures in residential premises on the upper floors is 0.02-0.05 MPa (0.2-0.5 kgf/cm 2);
b) the minimum pressure in front of the gas water heater on the upper floors is not less than 0.10 MPa (1 kgf/cm2);
c) the maximum free pressure in water supply systems at sanitary fixtures on the lower floors should not exceed 0.45 MPa (4.5 kgf/cm2).
4) For all systems:
The static pressure at the inlet to the heat and water supply systems must ensure that the pipelines of the central heating, cold water and hot water supply systems are filled with water, while the static water pressure should not be higher than permissible for this system.
The water pressure values in the DHW and cold water systems at the entrance of pipelines into the house must be at the same level (achieved by setting automatic devices regulation of a heating point and/or pumping station), while the maximum permissible pressure difference should be no more than 0.10 MPa (1 kgf/cm2).
These parameters at the entrance to buildings must be ensured by resource supplying organizations by implementing measures for automatic regulation, optimization, uniform distribution of thermal energy, cold and hot water between consumers, and for return pipelines of systems - also by housing management organizations through inspections, identification and elimination of violations or re-equipment and adjustment of building engineering systems. The specified measures should be carried out when preparing heating points, pumping stations and intra-block networks for seasonal operation, as well as in cases of violations of the specified parameters (indicators of the quantity and quality of utility resources supplied to the boundary of operational responsibility).
If the specified parameter values and modes are not observed, the resource supplying organization is obliged to immediately take all necessary measures to restore them. In addition, in case of violation of the specified values of the parameters of the supplied utility resources and the quality of the provided utility services, it is necessary to recalculate the payment for the provided utility services with a violation of their quality.
Thus, compliance with these indicators will ensure comfortable living for citizens, efficient functioning of engineering systems, networks, residential buildings and public utility facilities that provide heat and water supply to the housing stock, as well as the supply of utility resources to required quantity and standard quality on the boundaries of the operational responsibility of the resource supply and management housing organization (at the input engineering communications to the house).
Literature
1. Rules for the technical operation of thermal power plants.
2. MDK 3-02.2001. Rules for the technical operation of public water supply and sewerage systems and structures.
3. MDK 4-02.2001. Standard instructions on technical operation of thermal systems of municipal heating supply.
4. MDK 2-03.2003. Rules and regulations for the technical operation of housing stock.
5. Rules for the provision of public services to citizens.
6. ZhNM-2004/01. Regulations for the preparation for winter operation of heat and water supply systems of residential buildings, equipment, networks and structures of fuel, energy and public utilities in Moscow.
7. GOST R 51617 -2000*. Housing and communal services. General technical conditions.
8. SNiP 2.04.01 -85 (2000). Internal water supply and sewerage of buildings.
9. SNiP 2.04.05 -91 (2000). Heating, ventilation and air conditioning.
10. Methodology for checking violations of the quantity and quality of services provided to the population by accounting for heat energy consumption, cold and hot water consumption in Moscow.
(Energy Saving Magazine No. 4, 2007)
Based on the results of calculating water supply networks for various water consumption modes, the parameters of the water tower and pumping units are determined to ensure the operability of the system, as well as free pressures in all network nodes.
To determine the pressure at supply points (at the water tower, at the pumping station), it is necessary to know the required pressures of water consumers. As mentioned above, the minimum free pressure in the water supply network of a settlement with maximum domestic and drinking water supply at the entrance to the building above the ground surface in a one-story building should be at least 10 m (0.1 MPa), with a higher number of storeys it is necessary to add 4 to each floor m.
During the hours of lowest water consumption, the pressure for each floor, starting from the second, is allowed to be 3 m. For individual multi-storey buildings, as well as groups of buildings located in elevated areas, local pumping installations are provided. The free pressure at the water dispensers must be at least 10 m (0.1 MPa),
IN external network In industrial water pipelines, free pressure is taken according to the technical characteristics of the equipment. The free pressure in the consumer's drinking water supply network should not exceed 60 m, otherwise for individual areas or buildings it is necessary to install pressure regulators or zoning the water supply system. When operating a water supply system, a free pressure of no less than the standard must be ensured at all points in the network.
Free heads at any point in the network are determined as the difference between the elevations of the piezometric lines and the ground surface. Piezometric marks for all design cases (for domestic and drinking water consumption, in case of fire, etc.) are calculated based on the provision of standard free pressure at the dictating point. When determining piezometric marks, they are set by the position of the dictating point, i.e., the point with a minimum free pressure.
Typically, the dictating point is located in the most unfavorable conditions both in terms of geodetic elevations (high geodetic elevations) and in terms of distance from the power source (i.e., the sum of the pressure losses from the power source to the dictating point will be the greatest). At the dictating point they are set by a pressure equal to the normative one. If at any point in the network the pressure is less than the standard one, then the position of the dictating point is set incorrectly. In this case, they find the point with the lowest free pressure, take it as the dictating one, and repeat the calculation of the pressure in the network.
The calculation of the water supply system for operation during a fire is carried out on the assumption that it occurs at the highest points and remotest from power sources in the territory served by the water supply. According to the method of fire extinguishing, water pipelines are of high and low pressure.
As a rule, when designing water supply systems, low pressure fire water supply should be adopted, with the exception of small settlements(less than 5 thousand people). Fire-fighting water supply system high pressure must be economically justified,
In low-pressure water supply systems, the pressure is increased only while the fire is being extinguished. The necessary increase in pressure is created by mobile fire pumps, which are transported to the site of the fire and take water from the water supply network through street hydrants.
According to SNiP, the pressure at any point in the low-pressure fire-fighting water supply network at ground level during fire fighting must be at least 10 m. Such pressure is necessary to prevent the possibility of vacuum formation in the network when water is drawn from fire pumps, which, in turn, can cause penetration into network through leaky soil water joints.
In addition, a certain supply of pressure in the network is required for the operation of fire truck pumps in order to overcome significant resistance in the suction lines.
A high-pressure fire extinguishing system (usually adopted at industrial facilities) provides for the supply of water to the fire site as required by fire regulations and increasing the pressure in the water supply network to a value sufficient to create fire jets directly from the hydrants. The free pressure in this case should ensure a compact jet height of at least 10 m at full fire water flow and the location of the fire nozzle barrel at the level of the highest point of the tallest building and water supply through fire hoses 120 m long:
Nsv = N building + 10 + ∑h ≈ N building + 28 (m)
where H building is the height of the building, m; h - pressure loss in the hose and barrel of the fire nozzle, m.
In high-pressure water supply systems, stationary fire pumps are equipped with automatic equipment that ensures that the pumps start no later than 5 minutes after a signal about a fire is given. The network pipes must be selected taking into account the increase in pressure during a fire. The maximum free pressure in the combined water supply network should not exceed 60 m of water column (0.6 MPa), and during the hour of a fire - 90 m (0.9 MPa).
When there are significant differences in the geodetic elevations of the object supplied with water, a large length of water supply networks, as well as when there is a large difference in the values of free pressure required by individual consumers (for example, in microdistricts with different number of storeys), zoning of the water supply network is arranged. It may be due to both technical and economic considerations.
The division into zones is carried out based on the following conditions: at the highest point of the network the necessary free pressure must be provided, and at its lowest (or initial) point the pressure must not exceed 60 m (0.6 MPa).
According to the types of zoning, water supply systems come with parallel and sequential zoning. Parallel zoning of water supply systems is used for large ranges of geodetic elevations within the city area. To do this, lower (I) and upper (II) zones are formed, which are supplied with water by pumping stations of zones I and II, respectively, with water supplied at different pressures through separate water pipelines. Zoning is carried out in such a way that at the lower boundary of each zone the pressure does not exceed the permissible limit.
Water supply scheme with parallel zoning
1 - pumping station of the second lift with two groups of pumps; 2—pumps of the II (upper) zone; 3 — pumps of the I (lower) zone; 4 - pressure-regulating tanks
Working pressure in the heating system - the most important parameter, on which the functioning of the entire network depends. Deviations in one direction or another from the values specified in the design 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.
- 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.
- Dynamic pressure. Represents the force that acts on internal surfaces systems 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 optimal values The medium pressure in the heating circuit is in the range from 1.5 to 2 atm.
For apartment buildings up to five floors high, connected to a central heating system, the network pressure 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 on different heights and at different distances from the boiler room, the pressure in the network has to be adjusted. To reduce it, pressure regulators are used, to increase it - pumping stations. 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 similar 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.
With absence district heating In houses, autonomous heating systems are installed, 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 systems In heating systems, in order to save money, a small safety margin is laid down; even a small 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, in closed system heating system, install an expansion tank. Unlike a similar device in the system open type, it has no communication 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.
Availability expansion tank does not always guarantee maintaining pressure 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 boiler automation;
- due to incomplete opening shut-off valves after repair or maintenance work;
- due to the appearance 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 heating systems closed type 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 are the following: emergency situations, in which the pressure decreases smoothly or sharply. 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:
- Visual inspection. This method is used in cases where the heating circuit is laid open method(not to be confused with an open type system), that is, all its pipelines, fittings and instruments 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.
- 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 examined, 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 problem area is one of the connections; 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 in previous section it was said that this could cause an increase in pressure, there is no contradiction here. When the pressure in the heating system increases, it triggers safety valve. 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 connection electrical supply. IN automated systems use electrical contact sensors. At the outlet to the control and measuring device it is necessary to install three way valve. 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:
- Before the boiler installation (or boiler) and at the exit from it. At this point the pressure in the boiler is determined.
- Before and after the circulation pump.
- At the entrance of the heating main into a building or structure.
- Before and after the pressure regulator.
- At the inlet and outlet of the coarse filter (sludge 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.
