Hello! In order to build a piezometric graph, or as I call it, a pressure graph, you must:
1. Diagram of the heating network, with branches in sections. The diagram must indicate the diameters of the pipelines, their length, section numbers and other data.
2. Profile of the highway (conventionally take the ground level).
3. Hydraulic calculation of the heating network. This is generally key point. I wrote about the hydraulic calculation of the heating network in this.
4. Height of buildings along the heating main.
5. Pressure of the end user of the heating network.
In the last, fifth point, the pressure at the end user is taken, as a rule, equal to the required available pressure in front of the elevator (for a schedule of 150/70 °C - at least 15 m.w.s., for a schedule of 130/70 °C - at least 12 m.v.st.). The required pressure is multiplied by a factor of 1.5. If there is a possibility and prospect of further construction of buildings, then the required pressure is at least 20 m.w.s.
If you have all the above initial data, then you can begin drawing up a piezometric graph. Piezometric graph(Fig. 1) consists of the following elements:
1. Supply pressure line
2. Return pressure line
3. Static pressure line
This is where the results come in handy hydraulic calculation heating network, since slopes in the supply line and return line characterize the pressure drop in the heating network. And the greater the digital values of the pressure drop, the steeper the line of the pressure graph (piezometric graph).
The line that closes the supply and return at the end consumer displays the required required pressure and is taken from the source data.
The line that closes the supply and return lines at the beginning of the heating network (from the heat source) means the total pressure drop in the supply and return and end input (pressure at the outlet from the heat source).
The return pressure line of the piezometric graph should be quite high, this indicates that the local heat supply systems of buildings are full. Also, it should not intersect buildings on the graph. This is a condition for uninterrupted heat supply. But at the same time, the minimum pressure line of the piezometric graph in the return must be such that the cast iron heating radiators are not damaged. More on this below in the text.
The fulfillment of all these conditions is very dependent on the terrain and the height of buildings along the heating main. In view of this, the starting point of the pressure line often has to be found by selection.
If the terrain profile is sufficiently calm, then the construction of the piezometric graph begins from a neutral point. We take the neutral point at the suction pipe of the network pump so that the return line of the heating network is located at 3-5 m.w. higher than the highest building.
What requirements for pressure regimes in the heating network should be followed when constructing a piezometric graph? Let's consider two pressure regimes in the heating network. Namely, dynamic - mode when network pumps are running. And static mode - when the network pumps are turned off. In dynamic mode, the following requirements must be met.
For return line:
1. The return pressure must be higher than the static pressure in local heating systems, which means the return line must be located on the graph above any of the buildings, and with a margin of 3 - 5 m.v.st.
2. The maximum pressure should not exceed 60 m.w.st. This is necessary so that cast iron heating radiators do not collapse.
3. The minimum pressure must be at least 5 m.w.st. This is necessary to ensure that air does not leak into the heat supply pipeline and that there is no interruption in circulation in internal systems heat supply and corrosion.
For supply pipe:
The minimum pressure is taken from the condition of non-boiling of the coolant in the heating network:
at t1 = 130 °C - 18 m.w.st.
at t1 = 140 °C - 27 m.w.st.
at t1 = 150 °C - 39 century.
Let us now consider the statistical mode. This is the mode for the static pressure line. As you know, static pressure is created using a make-up pump. This pressure ensures that internal heating systems are filled even when stopped. network pumps. Consequently, during the inter-heating period in the heating network and local internal heating systems there must be a pressure higher than static in order to prevent air from entering and corrosion of pipelines.
This means that the minimum pressure must be no less than the height of the tall building. Plus a pressure reserve of 3 - 5 m.v.st. The maximum pressure is assumed to be 60 m.v.st. If the pressure is higher, then there is a possibility of destruction of the heating radiators. This is especially true for cast iron radiators.
When installing a heating system, several pressure gauges are cut into the pipeline. Using these measuring instruments, they control working pressure in the heating system. If deviations from the standardized values are recorded, measures are taken to eliminate the reasons that caused changes in the operation of the system. A drop in pressure level of 0.02 MPa is considered critical. Under no circumstances should pressure drops in the heating system be ignored, as this will negatively affect the efficiency of heating the room and the operation of the heating system. installed equipment and its service life. In preparation for the new heating season, tests are carried out during which excess pressure is created in the system to identify “weak” areas and repair them in advance. A system tested in this way allows you to be sure that all its elements are able to withstand hydraulic shocks that occur in the heating network.
What pressure value is considered normal?
The pressure in an autonomously operating heating system of a private house should be 1.5-2 atmospheres. In houses connected to a centralized heating network, this value depends on the number of floors of the building. In low-rise buildings, the pressure in the heating system is in the range of 2-4 atmospheres. In nine-story buildings this indicator equal to 5-7 atmospheres. For heating systems of high-rise buildings, the optimal pressure value is considered to be 7-10 atmospheres. In the heating main running underground from the thermal power plant to the points of heat consumption, the coolant is supplied under a pressure of 12 atm.
To reduce pressure hot water on the lower floors apartment buildings use pressure regulators. Increase pressure by upper floors allows pumping equipment.
A manual balancing valve (regulator), equipped with needle-type measuring nipples, allows you to control the pressure drop in the heating system
Influence of coolant temperature
After installation is complete heating equipment in a private house they begin to pump coolant into the system. At the same time, the minimum possible pressure is created in the network, equal to 1.5 atm. This value will increase as the coolant heats up, since it expands in accordance with the laws of physics. By changing the temperature of the coolant, you can adjust the pressure in the heating network.
You can automate the control of operating pressure in the heating system by installing expansion tanks that prevent an excessive increase in pressure. These devices come into operation when a pressure level of 2 atm is reached. Excess heated coolant is removed by expansion tanks, thereby maintaining the pressure at the required level. It may happen that the capacity of the expansion tank is not enough to collect excess water. At the same time, the pressure in the system approaches the critical level, which is at the level of 3 atm. Saves the situation safety valve, which allows you to keep the heating system intact by freeing it from excess coolant volume.
Points for inserting pressure gauges into the heating system: before and after the boiler, circulation pump, regulator, filters, mud traps, as well as at the exit of heating networks from the boiler room and at their entrance to houses
Reasons for the increase and decrease in pressure in the system
One of the most common causes of pressure drop in a heating system is a coolant leak. The “weak” links most often become the joints of individual parts. Although pipes can burst if they are already very worn out or defective. The presence of a leak in the pipeline is indicated by a drop in the level of static pressure measured with the circulation pumps turned off.
If the static pressure is normal, then the fault must be looked for in the pumps themselves. To make it easier to find the location of the leak, you need to turn off one by one various areas, monitoring the pressure level. Having identified the damaged area, it is cut off from the system, repaired, sealing all connections and replacing parts with visible defects.
Elimination of visible coolant leaks after they are detected during an inspection of the heating system circuit of a private house or apartment
If the coolant pressure drops and the leak cannot be found, then specialists are called. Using professional equipment, experienced craftsmen air is pumped into the system, previously freed from water, and also cut off from the boiler and. The whistling air escaping through microcracks and loose connections makes it easy to detect leaks. If pressure losses in the heating system are not confirmed, then proceed to checking the serviceability of the boiler equipment.
Use of professional equipment when searching for hidden leaks. Scanner detection excess moisture allows you to accurately determine a crack in a pipe
The reasons leading to a decrease in pressure in the system due to a malfunction of boiler equipment include:
- accumulation of scale in the heat exchanger (typical for areas with hard tap water);
- the appearance of microcracks in the heat exchanger caused by physical wear and tear of equipment, preventive flushing, and manufacturing defects;
- destruction of the bithermal heat exchanger that occurred during;
- camera damage expansion tank heating boiler.
In each case the problem is solved differently. Water hardness is reduced using special additives. The damaged heat exchanger is sealed or replaced. The tank built into the boiler is plugged, replacing it external device with suitable parameters. must be carried out by a suitably qualified engineer.
Reasons for the increase in pressure in the system:
- the movement of the coolant along the circuit is stopped (check the heating regulator);
- constant replenishment of the system, occurring due to human fault or as a result of automation failure;
- shutting off the tap or valve in the direction of the coolant flow;
- education ;
- clogged filter or sump.
Once you start the heating system, you should not wait for the pressure level to immediately normalize. Over the course of several days, air will escape from the coolant pumped into the system through automatic air vents or taps installed on radiators. It is possible to restore the coolant pressure by additionally pumping it into the system. If this process drags on for several weeks, then the reason for the pressure drop lies in the incorrectly calculated volume of the expansion tank or the presence of leaks.
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Heat supply design of a large multi-storey building is a complex mechanism that can function effectively provided that many parameters of the elements included in it are observed. One of them is the working pressure in the heating system. Not only the quality of heat transferred to the air, but also the reliable and safe operation of heating equipment depends on this value.
Pressure in the heating system multi-storey buildings must meet certain requirements and standards established and prescribed in SNiPs. If there are deviations from the required values, serious problems may arise, including the inability to operate the heating system.
Why is there pressure in the system?
Many consumers are interested in why there is pressure in the heating system and what depends on it. The fact is that it has a direct impact on the efficiency and quality of heating the premises of the house. Thanks to the working pressure it is possible to achieve best performance heat supply system due to the guaranteed flow of coolant into pipelines and radiators in each apartment of a multi-story building.Types of working pressure in heating structures
The pressure in the heating design of a multi-story building is of several types:- Static pressure heating system is an indicator of the force with which the volume of liquid, depending on the height, acts on pipelines and radiators. In this case, when carrying out calculations, the pressure level on the surface of the liquid is zero.
- Dynamic pressure occurs during movement coolant liquid through pipes. It affects the pipeline and radiators from the inside.
- The permissible (maximum) operating pressure in the heating system is a parameter for the normal and trouble-free functioning of the heat supply structure.
Normal pressure indicators
In all domestic multi-storey buildings, built both several decades ago and in new buildings, the heating system operates according to closed schemes using forced movement of the coolant. Operating conditions are considered ideal when the heating system operates under a pressure of 8-9.5 atmospheres. But in old houses, a loss of pressure may be observed in the heat supply structure, and accordingly the pressure indicators may drop to 5 -5.5 atmospheres. Read also: "".When choosing pipes and radiators to replace them in an apartment located in multi-storey building, initial indicators should be taken into account. Otherwise, the heating equipment will work unstably and even complete destruction of the heating supply circuit, which costs a lot of money, is possible.
What pressure should be in the heating system of a multi-storey building is dictated by standards and other regulatory documents.
As a rule, it is impossible to achieve the required parameters according to GOST, since performance indicators are influenced by various factors:
- Equipment power required for supplying coolant. The pressure parameters in the heating system of a high-rise building are determined at heating stations, where the coolant is heated for supply through pipes to the radiators.
- Equipment condition. Both dynamic and static pressure in the heat supply structure are directly affected by the level of wear of boiler room elements such as heat generators and pumps. The distance from the house to the heating station is of no small importance.
- Diameter of pipelines in the apartment. If, when carrying out repairs with their own hands, the apartment owners installed pipes larger diameter than in the inlet pipeline, a decrease in pressure parameters will occur.
- Location separate apartment in a high-rise building. Of course, the required pressure value is determined in accordance with the norms and requirements, but in practice a lot depends on what floor the apartment is on and its distance from the common riser. Even when living rooms are located close to the riser, the pressure of the coolant in corner rooms is always lower, since there is often an extreme point of the pipelines.
- Degree of wear of pipes and batteries. When the elements of the heating system located in the apartment have served for decades, some reduction in equipment parameters and performance cannot be avoided. When such problems occur, it is advisable to initially replace worn pipes and radiators and then emergency situations will be avoided.
Test pressure
Residents of apartment buildings know how utility services, together with specialists from energy companies, check the coolant pressure in the heating system. Usually they are before heating season coolant is supplied to pipes and batteries under pressure, the value of which approaches critical levels.They use pressure when testing the heating system in order to test the performance of all elements of the heat supply structure in extreme conditions and find out how efficiently heat will be transferred from the boiler room to a multi-story building.
When served test pressure heating systems often its elements come in emergency condition and require repairs, as worn-out pipes begin to leak and holes form in the radiators. Timely replacement of outdated heating equipment in the apartment will help to avoid such troubles.
During testing, parameters are monitored using special devices installed in the lowest (usually a basement) and highest ( attic space) points of the high-rise building. All measurements taken are subsequently analyzed by specialists. If there are deviations, it is necessary to detect problems and correct them immediately.
Checking the tightness of the heating system
To ensure effective and reliable operation heating systems, not only check the coolant pressure, but also test the equipment for leaks. How this happens can be seen in the photo. As a result, you can monitor the presence of leaks and prevent equipment breakdown at the most crucial moment.The tightness test is carried out in two stages:
- test using cold water. Pipelines and batteries in a multi-story building are filled with coolant without heating it, and pressure readings are measured. Moreover, its value during the first 30 minutes cannot be less than the standard 0.06 MPa. After 2 hours, losses cannot be more than 0.02 MPa. In the absence of gusts, the heating system of the high-rise building will continue to function without problems;
- test using hot coolant. Heating system tested before starting heating season. Water is supplied under a certain compression, its value should be the highest for the equipment.
Testing is carried out before starting the heating equipment, otherwise the cost of an error can be too expensive, and, as is known, it is quite difficult to eliminate an accident at sub-zero temperatures.
The pressure parameters in the heat supply scheme of a multi-storey building determine how comfortable you can live in each room. Unlike own home ownership with autonomous system heating in a high-rise building, apartment owners do not have the opportunity to independently adjust the parameters heating structure, including temperature and coolant supply.
But the tenants multi-storey buildings if desired, they can install such measuring instruments like pressure gauges in the basement and in case of the slightest deviation in pressure from the norm, report it to the relevant utility services. If, after all the steps taken, consumers are still unhappy with the temperature in the apartment, perhaps they should consider organizing alternative heating.
As a rule, the pressure in the pipelines of domestic multi-story buildings does not exceed the maximum standards, but still, installing an individual pressure gauge will not be superfluous.
The pressure in the heating system should be normal - 1.5 - 2.0 atmospheres for private houses with a height of up to 2 floors. If the pressure differs from the specified limits, the system must be “treated”.
In this article we will analyze the nuances of the heating system and boiler room equipment. Let's decide what pressure needs to be maintained, how to set it, what it depends on... Probably the given material will help readers in matters related to the performance of the heating system and the use of equipment.
What pressure should be in the heating system
In low-rise private houses, the operating pressure of the heating system is about 2 atmospheres. More often 1.5 – 2.0 atmospheres. The maximum pressure rise is allowed up to 3 atmospheres, and above that the emergency valve must be activated.
IN high-rise buildings normal pressure ranges from 5 to 10 atm. More often – 5 – 8 atm. The maximum that heating radiators in high-rise apartments are designed for is 12 atm.
The same pressure - 12 atm - can also be found in the main pipes of heating networks.
IN high-rise buildings Hydraulic gearboxes are installed on heating risers to reduce pressure.
Why does blood pressure rise?
According to the laws of physics, when a liquid or gas is heated, its volume increases. Therefore, if the liquid is in a closed heating system, then its pressure will increase with increasing temperature.
A liquid cannot be significantly compressed like a gas. If the space is closed, then a large pressure surge may occur and the shell will rupture.
In the “wrong” heating system closed type This is what happens - the weakest link, for example, the boiler heat exchanger, is destroyed, and the liquid finds its way out.
IN open systems ah heating - with gravity movement of liquid (in which the expansion tank is open), the pressure does not increase during heating. It is set there by the height of the water column - usually on 1 - 2 floors - respectively, up to 1 atm. The “excess” liquid simply goes into the tank or runs down the drain.
But in closed systems other special equipment is used.
How to normalize the situation
To avoid a dangerous increase in pressure when heating the coolant, in closed systems(With forced circulation liquids) include the required elements:
- Expansion tank- a closed vessel partially filled with air, which is capable of significantly compressing when pressure increases, freeing up volume for an “incompressible” liquid.
- A safety valve is a device that opens the release of liquid from the system if the pressure in it has reached the set maximum pressure - usually 3 atm.
- A pressure gauge is a device that measures and indicates the pressure of a liquid or gas. Its readings are also used when filling, pumping up the system, monitoring operation...
The same equipment should be installed on the hot water supply system in private houses, which includes an indirect heating boiler.
- safety valve, air vent, pressure gauge.
IN wall-mounted boilers These devices are built-in.
What is the volume of the expansion tank?
It is unacceptable to use an expansion tank of a smaller volume than 1/10 of the entire heating system.
However, for professional calculation of the volume of the expansion tank there is special technique. But at the household level it is decided this way - no less than 1:10 of the coolant poured into the heating system. Then the expansion tank can compensate for the increase in liquid volume from its heating without problems.
How to find out how much coolant is in the system?
All that remains is to arm yourself with geometric formulas and reference data on the equipment used. But in practice, when creating heating with your own hands, without a project, the volume is simply calculated in buckets during the initial filling. After which they purchase a suitable expansion tank.
Why does the pressure in the heating system decrease?
The pressure in the heating system constantly decreases from the initial set value. This decrease can be very small and not noticeable on instruments (pressure gauges). Or it may drop significantly.
A large decrease in pressure can occur for two reasons:
- After filling the liquid, there is air in the heating system. It will gradually be released through automatic air vents (must be present). The decrease in pressure must be compensated by adding new coolant.
- There is a leak in the heating system and the coolant is leaving. But there may also be an air leak from a closed expansion tank.
It is not allowed to automatically refill the heating system with water when the pressure decreases. If there is a leak, the water in the system will be constantly renewed, which will lead to significant sediment and failure of the entire system.
How to find a leak in a heating system
Typically, coolant leaks occur at joints due to poor-quality installation. It is enough to carefully inspect the system and pay attention to drips and red marks (sediment from the water). Repair based on “diagnosis”.
But sometimes it is difficult to detect visually. Then they search by ear - the system is drained and filled with air under pressure. A characteristic whistle will indicate where the “hole” is located.
You can also use special equipment - an excess humidity scanner.
We must not forget about the boiler. The presence of a leak in the heat exchanger, through small cracks, is not a rare occurrence. It will not be possible to detect it “on the fly” - the coolant immediately evaporates and leaves along with the gases. Checked with the boiler stopped.
It is not advisable to locate the junction points in places inaccessible for inspection and repair.
Check out - .
How to set the pressure in the heating system
The initial pressure in the heating system is set by pumping the expansion tank with air when the coolant is cold.
The expansion tank is filled with air until a pressure of 1.3 - 1.5 atm is created.
Accordingly, when heated, if the volume of the tank is selected correctly, the pressure can reach – 2.0 atm.
The expansion tank is equipped with a regular air valve, just like on a car, and can be inflated by a car pump or compressor.
The piezometer is based on hydraulic calculation data on pressure losses in sections of the heating network; it gives a clear picture of the pressures in the heating network and in subscriber installations ( rice. 6.1). The graph shows the terrain, the heights of connected local systems (buildings), and the magnitude of pressures (pressures) on a certain scale. In this case, it is conventionally accepted that the marks for laying pipes of the heating network, pumps and heating devices on the ground floor of buildings coincide with the ground surface level. The conditional zero level line (CNL) can be drawn at any height, but in practice it is more convenient to take the mark of the lowest point of the heating supply system as zero.
There are total, available and piezometric pressures. Total heads are counted from the total LPU. They do not reflect the actual pressure in the pipelines, because... do not take into account the dependence of pressures on geodetic marks of the system. But with their help it is convenient to plot a graph and determine (from the graph) piezometric and available pressures.
Piezometric pressures are measured from the pipeline axis at a given point. They take into account the geodetic elevations of the system points (equal to the difference between the total pressure and the geodetic elevation) and therefore reflect the actual pressures in the system.
The available pressure is the difference between the supply and return pressures at a given point in the system. It can be determined by the difference in both total and piezometric pressures.
The mode, in the presence of water circulation in the system, is called dynamic, and in the absence of circulation (with network pumps turned off) - static.
In static mode, the pressures in the supply and return are the same, and on the piezometer this mode is expressed by a horizontal line.
Natural static pressure is established by the pressure at the highest point of the heating system. When the water temperature is less than 100 o C the static pressure line will pass at the mark highest level water in the system.
Artificial static pressure provided by special make-up pumps (at the source) can be maintained at any given level.
Rice. 6.1. Piezometric graph of a heating network section: OK – location
imposed pressure at point A; MK – full pressure in supply to
point A; MO – total pressure in the return at point A; NK – piezo-
metric delivery head at point A; NO – piezometric
high pressure in the return at point A
Constant static pressure is maintained by make-up pumps. The piezometer configuration does not depend on the terrain. Piezometric lines always have a slope along the flow of water, and the magnitude of the slope depends on R l, and therefore on consumption.
For normal and reliable operation of the heat supply system, the pressure in it must be maintained within certain limits.
Rice. 6.2.
Not a single large heat supply system can be correctly designed and subsequently be operated normally without considering the pressure regimes in all its links - at the source, the heating network and subscriber installations.
Excessively high pressure will lead to accident damage equipment. At the same time, low pressures can cause air to leak into the system, “exposing” the upper points of the system to water, and disrupting circulation. For water temperatures above 100 o C due to insufficient pressure, water may boil, accompanied by hydraulic shocks.
The pressure regime in the heat supply system must satisfy the following requirements:
1. Excess pressure (above atmospheric) must be maintained at all points of the system to protect the system from air leaks. The minimum value is 5 m.v.st.
To comply with this requirement, the return piezometer must pass above the mark of the heating network pipeline and local systems. The piezometer at the return customer inputs must be higher than the local heating systems, i.e.:
(rice. 6.3).
Rice. 6.3.
This condition must be checked under conditions with the lowest pressures in the return of the heating network.
In open heat supply systems, this mode will occur with maximum water withdrawal from the return.
In addition, for open heating systems, the required pressure at the point of water intake must be ensured. In a hot water supply system, the pressure of the heating network must overcome the geometric height of the hot water supply system and the pressure loss in the pipes, plus there must be free pressure on the water outlet from the tap.
Hot water system:
2. The suction pressure of network pumps must be no lower than 5 -10 m.v.st ( Figure 6.4).
Rice. 6.4.
3. Pressures should not exceed those permissible for the strength of the equipment: N max< N add. N additional depends on the type of pipes, fittings and equipment used. For heating systems with cast iron radiators – 60 m.v.st.; with steel radiators – 100 m.v.st.; with convectors – 160 m.w.st., hot water heaters (local) – 100 m.v.st.; (network) – 140 m.v.st.; hot water boilers – 250 m.v.st.; heating network pipelines – 160 m.v.st.
In some cases, at thermal power plants the piezometer is located above the permissible pressure for network heaters. In this case, the thermal power plant provides 2 groups of pumps connected in series ( rice. 6.5).
Rice. 6.5.
Pump CH1 creates the pressure in the system necessary to compensate for hydraulic losses in the network water heater. The CH2 pump creates the pressure necessary to compensate for hydraulic losses in the hot water boiler, heating network and subscriber installations.
The most vulnerable link in the entire heat supply system in terms of permissible pressure is the local heating system installations. The supply pressure is throttled at the inlet by a washer or elevator. Therefore, the pressure in the heating system is determined by the value of the return pressure: ( rice. 6.6).
4. The pressure must ensure that the water does not boil. When the water temperature is more than 100 o C The non-boiling of water in the heating network and subscriber installations operating on superheated water must be ensured. For this, the pressure must be greater than the pressure of saturated water vapor at a given water temperature:
; .
Rice. 6.6.
At T = 150 o S R n > 5 ata; at T = 130 o S R n > 2.8 ata; at T = 105 o S R n > 1.25 ata. In the heating network T > 100 o C typical only for submission: N p> N n.
In the heating surface pipes of hot water boilers, the water temperature may be higher than the temperature of the water leaving the boiler. Therefore, to prevent local boiling of water in boilers, the required pressure in them is higher than for heating networks. The required minimum pressure in boilers is determined by the saturation temperature exceeding design temperature by 30 o C: T us = T 1p + 30 o C. The pressure at the inlet to the boiler must be greater than the outlet pressure by the amount of hydraulic losses.
5. Available pressures at customer inputs must be no less than the calculated pressure losses in local systems ( Fig.6.7): 
; for elevator connection of the heating system: .
At sequential connection Hot water boilers must additionally take into account their resistance, which is usually taken to be 6 - 8 m.v.st.
6. The static pressure in the system is selected from the condition of filling the entire system by 5 m.v.st.
Rice. 6.7. Rice. 6.8.