Available pressures and pressure losses in systems. Hydraulic calculation of a water heating system
Q[KW] = Q[Gcal]*1160;Converting load from Gcal to kW
G[m3/hour] = Q[KW]*0.86/ ΔT; where ΔT– temperature difference between supply and return.
Example:
Supply temperature from heating networks T1 – 110˚ WITH
Supply temperature from heating networks T2 – 70˚ WITH
Heating circuit flow G = (0.45*1160)*0.86/(110-70) = 11.22 m3/hour
But for a heated circuit with temperature chart 95/70, the flow rate will be completely different: = (0.45*1160)*0.86/(95-70) = 17.95 m3/hour.
From this we can conclude: the lower the temperature difference (temperature difference between supply and return), the greater the coolant flow required.
Selection of circulation pumps.
When selecting circulation pumps for heating, hot water, ventilation systems, you need to know the characteristics of the system: coolant flow,
which must be ensured and the hydraulic resistance of the system.
Coolant flow:
G[m3/hour] = Q[KW]*0.86/ ΔT; where ΔT– temperature difference between supply and return;
Hydraulic The system resistance should be provided by specialists who calculated the system itself.
For example:
We consider the heating system with a temperature graph of 95˚ C /70˚ With and load 520 kW
G[m3/hour] =520*0.86/25 = 17.89 m3/hour~ 18 m3/hour;
The heating system resistance wasξ = 5 meters ;
In the case of an independent heating system, you need to understand that the resistance of the heat exchanger will be added to this resistance of 5 meters. To do this, you need to look at its calculation. For example, let this value be 3 meters. So, the total resistance of the system is: 5+3 = 8 meters.
Now it’s quite possible to choose circulation pump with flow rate 18m3/hour and a head of 8 meters.
For example this one:
IN in this case, the pump is selected with a large margin, it allows you to ensure the operating pointflow/pressure at the first speed of its operation. If for some reason this pressure is not enough, the pump can be “accelerated” to 13 meters at third speed. The best option a pump version is considered that maintains its operating point at the second speed.
It is also quite possible, instead of an ordinary pump with three or one operating speed, to install a pump with a built-in frequency converter, for example this:
This pump version is, of course, the most preferable, since it allows the most flexible adjustment of the operating point. The only downside is the cost.
It is also necessary to remember that for the circulation of heating systems it is necessary to provide two pumps (main/backup), and for the circulation of the DHW line it is quite possible to install one.
Recharge system. Selection of the charging system pump.
Obviously, a make-up pump is necessary only in the case of using independent systems, in particular heating, where the heating and heated circuit
separated by a heat exchanger. The make-up system itself is necessary to maintain constant pressure in the secondary circuit in case of possible leaks
in the heating system, as well as for filling the system itself. The make-up system itself consists of a pressure switch, a solenoid valve, and an expansion tank.
A make-up pump is installed only when the coolant pressure in the return is not enough to fill the system (the piezometer does not allow it).
Example:
Return coolant pressure from heating networks P2 = 3 atm.
The height of the building taking into account technical requirements. Underground = 40 meters.
3atm. = 30 meters;
Required height = 40 meters + 5 meters (at spout) = 45 meters;
Pressure deficit = 45 meters – 30 meters = 15 meters = 1.5 atm.
The pressure of the feed pump is clear; it should be 1.5 atmospheres.
How to determine consumption? The pump flow rate is assumed to be 20% of the volume of the heating system.
The operating principle of the recharge system is as follows.
A pressure switch (pressure measuring device with a relay output) measures the pressure of the return coolant in the heating system and has
pre-setting. For this concrete example this setting should be approximately 4.2 atmospheres with a hysteresis of 0.3.
When the pressure in the heating system return drops to 4.2 atm, the pressure switch closes its group of contacts. This supplies voltage to the solenoid
valve (opening) and make-up pump (switching on).
Make-up coolant is supplied until the pressure rises to a value of 4.2 atm + 0.3 = 4.5 atmospheres.
Calculation of a control valve for cavitation.
When distributing the available pressure between the elements of a heating point, it is necessary to take into account the possibility of cavitation processes inside the body
valves that will destroy it over time.
The maximum permissible pressure drop across the valve can be determined by the formula:
ΔPmax= z*(P1 − Ps) ; bar
where: z is the cavitation onset coefficient, published in technical catalogs for equipment selection. Each equipment manufacturer has its own, but the average value is usually in the range of 0.45-06.
P1 – pressure in front of the valve, bar
Рs – saturation pressure of water vapor at a given coolant temperature, bar,
Towhichdetermined by the table:
If the calculated pressure difference used to select the valve Kvs is no more
ΔPmax, cavitation will not occur.
Example:
Pressure before valve P1 = 5 bar;
Coolant temperature T1 = 140C;
Valve Z according to catalog = 0.5
According to the table, for a coolant temperature of 140C we determine Рs = 2.69
The maximum permissible pressure drop across the valve will be:
ΔPmax= 0.5*(5 - 2.69) = 1.155 bar
You cannot lose more than this difference on the valve - cavitation will begin.
But if the coolant temperature was lower, for example 115C, which is closer to the actual temperatures of the heating network, the maximum difference
pressure would be greater: ΔPmax= 0.5*(5 – 0.72) = 2.14 bar.
From here we can draw a quite obvious conclusion: the higher the temperature of the coolant, the lower the pressure drop possible across the control valve.
To determine the flow rate. Passing through the pipeline, it is enough to use the formula:
;m/s
G – coolant flow through the valve, m3/hour
d – nominal diameter selected valve, mm
It is necessary to take into account the fact that the flow speed passing through the pipeline section should not exceed 1 m/sec.
The most preferable flow speed is in the range of 0.7 - 0.85 m/s.
The minimum speed should be 0.5 m/s.
Selection criterion DHW systems, as a rule, is determined from technical specifications for connection: the heat generating company very often prescribes
type of DHW system. If the type of system is not specified, a simple rule should be followed: determination by the ratio of building loads
for hot water supply and heating.
If 0.2
Respectively,
If QDHW/Qheating< 0.2 or QDHW/Qheating>1; necessary single-stage DHW system.
The very principle of operation of a two-stage hot water system is based on heat recovery from the return of the heating circuit: return coolant of the heating circuit
passes through the first stage of the hot water supply and heats up cold water from 5C to 41...48C. At the same time, the return coolant of the heating circuit itself cools down to 40C
and when cold it is discharged into the heating network.
The second stage of DHW heats up cold water from 41...48C after the first stage to the required 60...65C.
Advantages of a two-stage DHW system:
1) Due to heat recovery from the heating circuit return, cooled coolant enters the heating network, which sharply reduces the likelihood of overheating
return lines This point is extremely important for heat generating companies, in particular heating networks. Now it is becoming common to carry out calculations of heat exchangers of the first stage of hot water supply at a minimum temperature of 30C, so that even colder coolant is drained into the return of the heating network.
2) The two-stage hot water system allows for more precise control of the temperature of hot water, which is used for analysis by the consumer and temperature fluctuations
at the exit from the system is significantly less. This is achieved due to the fact that the control valve of the second stage of DHW, during its operation, regulates
only a small part of the load, and not the whole thing.
When distributing loads between the first and second stages of DHW, it is very convenient to do the following:
70% load – 1st DHW stage;
30% load – DHW stage 2;
What does it give?
1) Since the second (adjustable) stage is small, in the process of regulating the DHW temperature, temperature fluctuations at the outlet
systems turn out to be insignificant.
2) Thanks to this distribution of the DHW load, in the calculation process we obtain equality of costs and, as a consequence, equality of diameters in the heat exchanger piping.
The consumption for DHW circulation must be at least 30% of the consumption for DHW disassembly by the consumer. This is the minimum number. To increase reliability
system and stability of DHW temperature control, circulation flow can be increased to 40-45%. This is done not only to maintain
hot water temperature, when there is no analysis by the consumer. This is done to compensate for the “drawdown” of DHW at the time of peak DHW withdrawal, since the consumption
circulation will support the system while the heat exchanger volume is filled with cold water for heating.
There are cases of incorrect calculation of the DHW system, when instead of a two-stage system, a single-stage one is designed. After installing such a system,
During the commissioning process, the specialist is faced with extreme instability of the hot water system. Here it is even appropriate to talk about inoperability,
which is expressed by large temperature fluctuations at the outlet of the DHW system with an amplitude of 15-20C from the set setpoint. For example, when the setting
is 60C, then during the regulation process, temperature fluctuations occur in the range from 40 to 80C. In this case, changing the settings
an electronic regulator (PID - components, rod stroke time, etc.) will not give a result, since the DHW hydraulics are fundamentally incorrectly calculated.
There is only one way out: limit the consumption of cold water and maximize the circulation component of the hot water supply. In this case, at the mixing point
a smaller amount of cold water will be mixed with a larger amount of hot (circulation) and the system will work more stable.
Thus, some kind of imitation of a two-stage DHW system is performed due to the circulation of DHW.
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.
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:
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.
General principles of hydraulic calculation of pipelines for water heating systems are described in detail in the section Water heating systems. They are also applicable for calculating heat pipelines of heating networks, but taking into account some of their features. Thus, in the calculations of heat pipelines, the turbulent movement of water is taken (water speed is more than 0.5 m/s, steam speed is more than 20-30 m/s, i.e. quadratic calculation area), values of the equivalent roughness of the inner surface of large-diameter steel pipes, mm, accepted for: steam pipelines - k = 0.2; water network - k = 0.5; condensate pipelines - k = 0.5-1.0.
The estimated coolant costs for individual sections of the heating network are determined as the sum of the costs of individual subscribers, taking into account the connection diagram of the DHW heaters. In addition, it is necessary to know the optimal specific pressure drops in pipelines, which are previously determined by technical and economic calculations. They are usually taken equal to 0.3-0.6 kPa (3-6 kgf/m2) for main heating networks and up to 2 kPa (20 kgf/m2) for branches.
When performing hydraulic calculations, the following tasks are solved: 1) determining the diameters of pipelines; 2) determination of pressure-pressure drop; 3) determination of current pressures at various points in the network; 4) determination of permissible pressures in pipelines under various operating modes and conditions of the heating network.
When carrying out hydraulic calculations, diagrams and a geodetic profile of the heating main are used, indicating the location of heat supply sources, heat consumers and design loads. To speed up and simplify calculations, instead of tables, logarithmic nomograms of hydraulic calculations are used (Fig. 1), and in recent years, computer calculation and graphic programs are used.
Picture 1.
PIEZOMETRIC GRAPH
When designing and in operational practice, piezometric graphs are widely used to take into account the mutual influence of the geodetic profile of the area, the height of subscriber systems, and operating pressures in the heating network. From them it is easy to determine the pressure (pressure) and available pressure at any point in the network and in the subscriber system for the dynamic and static state of the system. Let's consider the construction of a piezometric graph, and we will assume that pressure and pressure, pressure drop and pressure loss are related by the following dependencies: H = p/γ, m (Pa/m); ∆Н = ∆р/ γ, m (Pa/m); and h = R/ γ (Pa), where Н and ∆Н - pressure and pressure loss, m (Pa/m); р and ∆р - pressure and pressure drop, kgf/m 2 (Pa); γ - mass density of the coolant, kg/m3; h and R - specific pressure loss (dimensionless value) and specific pressure drop, kgf/m 2 (Pa/m).
When constructing a piezometric graph in dynamic mode, the axis of the network pumps is taken as the origin of coordinates; taking this point as a conditional zero, they build a terrain profile along the route of the main highway and along characteristic branches (the elevations of which differ from the elevations of the main highway). The heights of the connected buildings are drawn on the profile on a scale, then, having previously assumed a pressure on the suction side of the network pumps collector H sun = 10-15 m, the horizontal line A 2 B 4 is drawn (Fig. 2, a). From point A 2, the lengths of the calculated sections of heat pipelines are plotted along the abscissa axis (with a cumulative total), and along the ordinate axis from the end points of the calculated sections - the pressure loss Σ∆H in these sections. By connecting the upper points of these segments, we obtain a broken line A 2 B 2, which will be the piezometric line of the return line. Each vertical segment from the conditional level A 2 B 4 to the piezometric line A 2 B 2 indicates the pressure loss in the return line from the corresponding point to the circulation pump at the thermal power plant. From point B 2 on a scale, the required available pressure for the subscriber at the end of the line ∆H ab is plotted upward, which is taken to be 15-20 m or more. The resulting segment B 1 B 2 characterizes the pressure at the end of the supply line. From point B 1, the pressure loss in the supply pipeline ∆Н p is postponed upward and a horizontal line B 3 A 1 is drawn.
Figure 2.a - construction of a piezometric graph; b - piezometric graph of a two-pipe heating network
From line A 1 B 3 downward, pressure losses are deposited in the section of the supply line from the heat source to the end of the individual calculated sections, and the piezometric line A 1 B 1 of the supply line is constructed similarly to the previous one.
With closed PZT systems and equal pipe diameters of the supply and return lines, the piezometric line A 1 B 1 is a mirror image of line A 2 B 2. From point A, the pressure loss in the boiler room of the thermal power plant or in the boiler room circuit ∆Н b (10-20 m) is postponed upward. The pressure in the supply manifold will be N n, in the return manifold - N sun, and the pressure of the network pumps will be N s.n.
It is important to note that when connecting local systems directly, the return pipeline of the heating network is hydraulically connected to the local system, and the pressure in the return pipeline is entirely transferred to the local system and vice versa.
During the initial construction of the piezometric graph, the pressure at the suction manifold of the network pumps N vs was taken arbitrarily. Moving the piezometric graph parallel to itself up or down allows you to accept any pressure on the suction side of network pumps and, accordingly, in local systems.
When choosing the position of the piezometric graph, it is necessary to proceed from the following conditions:
1. The pressure (pressure) at any point in the return line should not be higher than the permissible operating pressure in local systems, for new heating systems (with convectors) the operating pressure is 0.1 MPa (10 m of water column), for systems with cast iron radiators 0.5-0.6 MPa (50-60 m water column).
2. The pressure in the return pipeline must ensure that the upper lines and devices of local heating systems are filled with water.
3. The pressure in the return line, in order to avoid the formation of a vacuum, should not be lower than 0.05-0.1 MPa (5-10 m of water column).
4. The pressure on the suction side of the network pump should not be lower than 0.05 MPa (5 m water column).
5. The pressure at any point in the supply pipeline must be higher than the boiling pressure at the maximum (design) temperature of the coolant.
6. The available pressure at the end point of the network must be equal to or greater than the calculated pressure loss at the subscriber input for the calculated coolant flow.
7. In summer, the pressure in the supply and return lines takes on more than the static pressure in the DHW system.
Static state of the central heating system. When the network pumps stop and water circulation in the central heating system stops, it goes from a dynamic state to a static one. In this case, the pressures in the supply and return lines of the heating network will be equalized, the piezometric lines will merge into one - the static pressure line, and on the graph it will take an intermediate position, determined by the pressure of the make-up device of the MDH source.
The pressure of the make-up device is set by the station personnel either by the highest point of the pipeline of the local system directly connected to the heating network, or by the vapor pressure of superheated water at the highest point of the pipeline. So, for example, at the design temperature of the coolant T 1 = 150 °C, the pressure at the highest point of the pipeline with superheated water will be equal to 0.38 MPa (38 m of water column), and at T 1 = 130 °C - 0.18 MPa (18 m water column).
However, in all cases, the static pressure in low-lying subscriber systems should not exceed the permissible operating pressure of 0.5-0.6 MPa (5-6 atm). If it is exceeded, these systems should be transferred to an independent connection scheme. Reducing the static pressure in heating networks can be achieved by automatically disconnecting high buildings from the network.
In emergency cases, in the event of a complete loss of power supply to the station (stopping the network and make-up pumps), circulation and make-up will stop, while the pressures in both lines of the heating network will be equalized along the line of static pressure, which will begin to slowly, gradually decrease due to the leakage of network water through leaks and cooling it in pipelines. In this case, boiling of superheated water in pipelines is possible with the formation of vapor locks. Resuming water circulation in such cases can lead to severe water hammer in the pipelines with possible damage to fittings, heating devices, etc. To avoid this phenomenon, water circulation in the central heating system should begin only after the pressure in the pipelines has been restored by replenishing the heating network at a level not lower than the static one.
To ensure reliable operation of heating networks and local systems, it is necessary to limit possible pressure fluctuations in the heating network to acceptable limits. To maintain the required level of pressure in the heating network and local systems, at one point of the heating network (and in difficult terrain conditions - at several points), a constant pressure is artificially maintained under all operating modes of the network and during static conditions using a make-up device.
The points at which the pressure is maintained constant are called the neutral points of the system. As a rule, pressure is secured on the return line. In this case, the neutral point is located at the intersection of the reverse piezometer with the static pressure line (point NT in Fig. 2, b), maintaining constant pressure at the neutral point and replenishing coolant leakage is carried out by make-up pumps of the thermal power plant or RTS, KTS through an automated make-up device. Automatic regulators are installed on the make-up line, operating on the principle of “after” and “before” regulators (Fig. 3).
Figure 3. 1 - network pump; 2 - make-up pump; 3 - heating water; 4 - make-up regulator valve
The pressures of the network pumps N s.n are taken equal to the sum of the hydraulic pressure losses (at the maximum - design water flow): in the supply and return pipelines of the heating network, in the subscriber's system (including inputs to the building), in the boiler installation of the thermal power plant, its peak boilers or in boiler room Heat sources must have at least two network and two make-up pumps, of which one is a reserve pump.
The amount of recharge for closed heat supply systems is assumed to be 0.25% of the volume of water in the pipelines of heating networks and in subscriber systems connected to the heating network, h.
In schemes with direct water withdrawal, the amount of recharge is taken to be equal to the sum of the calculated water consumption for hot water supply and the amount of leakage in the amount of 0.25% of the system capacity. The capacity of heating systems is determined by the actual diameters and lengths of pipelines or by aggregated standards, m 3 / MW:
The disunity that has developed on the basis of ownership in the organization of operation and management of urban heat supply systems has the most negative impact on both the technical level of their functioning and their economic efficiency. It was noted above that the operation of each specific heat supply system is carried out by several organizations (sometimes “subsidiaries” of the main one). However, the specificity of district heating systems, primarily heating networks, is determined by the tight connection of the technological processes of their functioning, and uniform hydraulic and thermal regimes. The hydraulic mode of the heat supply system, which is the determining factor in the functioning of the system, is extremely unstable by its nature, which makes heat supply systems difficult to control compared to other urban engineering systems (electricity, gas, water supply).
None of the links in the district heating systems (heat source, main and distribution networks, heating points) can independently provide the required technological modes of operation of the system as a whole, and, consequently, the end result - reliable and high-quality heat supply to consumers. Ideal in this sense is an organizational structure in which heat supply sources and heating networks are under the jurisdiction of one enterprise structure.
“Specification of indicators of the quantity and quality of communal resources in the modern realities of 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 Engineering Systems Department
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.
A review of the current rules and regulations for the technical operation of the housing stock in the field of housing and communal services showed that currently construction, sanitary norms and regulations, 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 dated May 23, 2006 No. 307, and other current regulatory documents consider and establish parameters and modes only at the source (central heating station, boiler room, 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 in determining the guilty party for the failure to provide services to the population or the provision of services of inadequate 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 inspections of the quality of supplied utility 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 establish the 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 a central heating system (CH):
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 temperature of the return network water should not exceed the temperature specified by the temperature schedule 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):
The temperature of hot water in the DHW supply pipeline for closed systems is within 55-65 °C, for open heat supply systems 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, the sanitary fixtures of residential premises, in accordance with the regulatory legal acts of the Russian Federation, must have the following values:
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 control devices for the heating point and/or pumping station), while the maximum permissible pressure difference must be no more than 0.10 MPa (1 kgf/cm 2).
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, the effective 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 in the required quantity and standard quality to the boundaries of the operational responsibility of the resource supply and managing housing organization (at the entrance of utilities into 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 for the technical operation of municipal heating systems.
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)
The task of hydraulic calculation includes:
Determination of pipeline diameter;
Determination of pressure drop (pressure);
Determination of pressures (pressures) at various points in the network;
Linking all network points in static and dynamic modes in order to ensure permissible pressures and required pressures in the network and subscriber systems.
Based on the results of hydraulic calculations, the following problems can be solved.
1. Determination of capital costs, metal (pipes) consumption and the main volume of work on laying a heating network.
2. Determination of the characteristics of circulation and make-up pumps.
3. Determination of operating conditions of the heating network and selection of subscriber connection schemes.
4. Selection of automation for the heating network and subscribers.
5. Development of operating modes.
a. Schemes and configurations of heating networks.
The layout of the heating network is determined by the location of heat sources in relation to the area of consumption, the nature of the heat load and the type of coolant.
The specific length of steam networks per unit of design heat load is small, since steam consumers - usually industrial consumers - are located at a short distance from the heat source.
A more difficult task is the choice of a water heating network scheme due to its large length and large number of subscribers. Water vehicles are less durable than steam vehicles due to greater corrosion, and are more sensitive to accidents due to the high density of water.
Fig.6.1. Single-line communication network of a two-pipe heating network
Water networks are divided into main and distribution networks. The coolant is supplied through main networks from heat sources to areas of consumption. Through distribution networks, water is supplied to GTP and MTP and to subscribers. Subscribers very rarely connect directly to backbone networks. Sectioning chambers with valves are installed at the nodes connecting distribution networks to main ones. Sectional valves on main networks are usually installed every 2-3 km. Thanks to the installation of sectional valves, water losses during vehicle accidents are reduced. Distribution and main vehicles with a diameter of less than 700 mm are usually made dead-end. In the event of an emergency, a break in the heat supply to buildings for up to 24 hours is acceptable for most of the country. If a break in heat supply is unacceptable, it is necessary to provide for duplication or loopback of the heating system.
Fig.6.2. Ring heating network from three thermal power plants Fig.6.3. Radial heat network
When supplying heat to large cities from several thermal power plants, it is advisable to provide for mutual interlocking of thermal power plants by connecting their mains with interlocking connections. In this case, a ring heat network with several power sources is obtained. Such a scheme has higher reliability and ensures the transmission of redundant water flows in the event of an accident on any part of the network. When the diameters of the mains extending from the heat source are 700 mm or less, a radial heating network diagram is usually used with a gradual decrease in the pipe diameter as the distance from the source increases and the connected load decreases. This network is the cheapest, but in the event of an accident, the heat supply to subscribers is stopped.
b. Basic calculation dependencies