Water heating in an individual residential building it consists of a boiler and radiators connected by pipes. The water is heated in the boiler, moves through pipes to the radiators, gives off heat in the radiators and again enters the boiler.
Central heating is arranged in the same way as autonomous heating. The difference is that a central boiler house or CHP heats many houses.
The terms “closed system” and “open system” are used to characterize autonomous heating and central heating, but differ in meaning:
- In autonomous heating systems, open systems are those that communicate with the atmosphere through an expansion vessel. Systems that have no communication with the atmosphere are called closed.
- In houses with central heating, an open system is called, where hot water to the taps comes directly from heating system. And closed, when the hot water entering the house heats the tap water in the heat exchanger.
Autonomous heating systems
The water that fills the boiler, pipes and radiators expands when heated. The pressure inside rises sharply. If you do not provide for the possibility of removing the additional volume of water, the system will rupture. Compensation for changes in water volumes when temperature changes occurs in expansion vessels. As the temperature rises, excess water moves into the expansion vessel. As the temperature decreases, the system is replenished with water from the expansion vessel.
- Open system permanently connected to the atmosphere through an open expansion vessel. The vessel is made in the form of a rectangular or round tank. The form doesn't matter. It is important that it has sufficient capacity to accommodate the additional volume of water resulting from the thermal expansion of the circulating water. The expansion vessel is located in the highest part of the heating system. The vessel is connected to the heating system by a pipe called a riser. The riser is attached at the bottom of the tank - to the bottom or side wall. A drain pipe is connected to the top of the expansion tank. It is discharged into the sewer or outside the building. A drain pipe is needed in case the tank overflows. It also ensures a constant connection between the tank and the heating system and the atmosphere. If the system is filled with water manually using buckets, the tank is additionally equipped with a lid or hatch. If the tank capacity is selected correctly, the water level in the tank is checked before turning on the heating. The water pressure in an “open system” is equal to atmospheric pressure, and does not change when the temperature of the water that circulates in the system changes. No overpressure safety device is required.
- Closed system isolated from the atmosphere. The expansion vessel is sealed. The shape of the vessel is chosen so that it can withstand highest pressure with minimal wall thickness. Inside the vessel there is a rubber membrane that divides it into two parts. One part is filled with air, the other part is connected to the heating system. The expansion vessel can be installed at any point in the system. As the water temperature increases, the excess enters the expansion vessel. The air or gas in the other half of the membrane is compressed. As the temperature decreases, the pressure in the system decreases, water from the expansion vessel under the action of compressed air is forced out of the expansion vessel into the system. In a closed system, the pressure is higher than in an open system and constantly changes depending on the temperature of the circulating water. In addition, the closed system must be equipped with a safety valve in case of a dangerous increase in pressure and a device for releasing air.
District heating
Water at central heating heated in a central boiler room or thermal power plant. This is where the expansion of water with temperature changes is compensated. Next, hot water is pumped into the heating network by a circulation pump. Houses are connected to the heating network by two pipelines - direct and return. Having entered the house through a direct pipeline, the water is divided in two directions - for heating and for hot water supply.
- Open system. Water goes directly to the taps hot water, and is discharged into the sewer after use. An “open system” is simpler than a closed one, but in central boiler houses and thermal power plants it is necessary to perform additional water treatment - purification and air removal. For residents, this water is more expensive than tap water, and its quality is lower.
- Closed system. Water passes through the boiler, giving off heat for heating tap water, connects to the heating return water and returns to the heating network. Heated tap water flows into hot water taps. A closed system, due to the use of heat exchangers, is more complex than an open one, but tap water is not subject to additional processing, but is only heated.
In open heat supply systems, the water prepared in the boiler unit not only serves as a coolant, but also goes to the needs of hot water supply, i.e., water is drawn directly from the pipelines of the heating network without intermediate heaters. The amount of make-up water in this case is determined by water losses in networks, in the boiler room (2 - 2.5% of network water consumption) and water consumption for hot water supply needs. To equalize the daily schedule of loads on hot water supply, it is planned to install storage tanks, the volume of which is 9 times greater than the average hourly daily water consumption for hot water supply.
A schematic thermal diagram of a heating boiler room with an open two-pipe heat supply system is shown in Fig. 7.9. Thermal and hydrodynamic regimes of water heating boiler units, water treatment water treatment units, recirculation units (line SD) and mixing jumper AB, the creation of a vacuum in the HP vacuum deaerator is similar to those discussed earlier. Heat carried away with evaporation D issue used to heat softened water in the T3 vapor cooler.
From the vacuum deaerator, VDvoda flows by gravity into the deaerated water tank BD, from where it is supplied to the accumulator tank BA by a transfer pump PN. Usually at least two metal tanks are installed, the inner surface of which is protected with an anti-corrosion coating, and the outer surface with thermal insulation. Water is taken from the BA storage tank by the PPN make-up pump and supplied to the heating networks.
Operation of the heating network in winter heating mode. Water from the return pipeline with a pressure of 0.2 - 0.4 MPa is supplied to the suction manifold network pumps SN. Water is also supplied there from make-up pumps along the line KN(lines KL And E.F. closed by valves), as well as chilled water from the heat exchangers for softened water T2 and source water T1 (Fig. 7.9)
Rice. 7.9. Schematic diagram of a heating boiler room with an open two-pipe
heating system
Return network water is pumped by network pumps CH into the hot water boiler unit KA, where it is heated to a temperature of 150 °C, and at the exit from the boiler is divided into three streams: into the heating network , for recycling and for the boiler house’s own needs, which include water consumption:
· on fuel oil farm,
· for heating water to 70 °C in a vacuum deaerator,
· to heat exchanger T2 for heating softened water to 65 °C,
· to heat exchanger T1 for heating source water to 30 °C .
Cooled water from heat exchangers T1 and T2 enters the suction manifold of network pumps SN. The water flow through hot water boiler units is determined for the maximum winter mode and, according to operating conditions, is assumed to be constant under different modes.
The temperature of the water entering the heating and ventilation system of the consumer, ~ 95 °C, regulated using the elevator unit E by mixing direct network water with return water from the heating system.
The average hourly daily consumption of hot water supplied to the consumer is a calculated value, constant and independent of the season. In maximum winter mode, the DHW consumer, directly to the water intake taps, receives return network water from the heating and ventilation system. In other operating modes, during heating season the temperature of the return network water drops below the normalized temperatures for hot water supply, therefore, in the hot water preparation unit S The required amount of direct network water is mixed into the return network water through the RTG temperature regulator.
Part of the water (5 - 10% of the consumer's consumption) passes through heated towel rails, is cooled to a temperature of 40 - 45 ° C and is returned through the circulation line by the circulation pump TsN to the return pipeline of the heating network.
When working during the heating season, it is necessary to take into account that due to high water flow rates through the water treatment unit, make-up water and used heating water supplied to the return pipeline (units) M And N) mix with return network water and significantly change the flow temperature. After calculating the final flow temperature, the coolant flow through the recirculation line and through the mixing jumper is determined.
At the final stage, the correctness of the calculation of the operating modes of the thermal circuit is controlled by checking the correspondence of the values of heat consumption for auxiliary needs accepted and obtained as a result of the calculation and the total thermal power of the boiler house. If the discrepancy differs by more than 2%, the calculation is repeated.
Operation of the thermal circuit in summer mode. The presence of make-up water in storage tanks in quantity and at a temperature corresponding to the purposes of hot water supply allows this water to be supplied directly to the heating network in the summer when there is no heating and ventilation load. Only circulating water from local hot water supply systems, which is directed through the unit, will be returned through the return pipeline to the boiler room E to the BA battery tanks along the line E.F.
Thus, in summer period the water heating boiler unit is disconnected from the heating network on the site NE return pipeline and on site B.L. supply pipeline. Water for hot water supply will be supplied to the supply pipeline of the heating network directly from the BA battery tanks along the line KL make-up pump, which in this case is called “summer” (line KN at the same time closed by a valve).
In the summer, the boiler unit is turned on only for load q sn, and the water flow through the boiler unit consists of heating water flows , entering heat exchangers T1, T2 and the vacuum deaerator VD. Therefore, with a low share of the hot water supply load of the boiler house (0.25 - 0.3), in the summer the number of boiler units is reduced to one.
Doctor of Technical Sciences IN AND. Sharapov, Professor, Head of the Department of Heat and Gas Supply and Ventilation, Ulyanovsk State Technical University
In large centralized heating systems connected to CHP, two methods of hot water supply (DHW) to consumers are used: water preparation required quality and heating it at a thermal power plant with subsequent collection of hot water by consumers directly from the heating network (in) and heating of tap drinking water before supplying consumers with network water in surface heat exchangers of local heating points ().
Historically, in domestic heating systems these two methods of hot water supply are used equally: for example, Moscow has the world's largest closed heat supply system, and the world's largest open system. Each of these two heat supply systems has its own advantages and disadvantages. The discussion about which of these two systems is better began with a polemic between the patriarchs of district heating, Professors S.F. Kopyev and E.Ya. Sokolov in the 40-50s. last century and has not yet ended. The procedure for selecting heat supply systems during a new design was for a long time regulated by imperfect recommendations, in which one of the most important factors when choosing the type of system was chemical composition impurities in the source water of the city water supply.
Closed heating systems have a more stable hydraulic regime due to the relative constancy of water flow in the supply and return lines. Open heat supply systems make it possible to maximize the effect of the combined generation of electrical and thermal energy through the use of low-potential heat sources to heat large quantities of make-up water for the heating network at thermal power plants.
One example of the rational use of low-grade heat is in St. Petersburg, with the heating network make-up water consumption of several thousand tons per hour. Heating of the source water before the vacuum deaerators of the make-up water at this thermal power plant is carried out only by the exhaust steam of three T-250-240 turbines in the built-in condenser banks, and the heating of the water used as a heating agent in the vacuum deaerators is carried out by the steam of highly economical heating extraction from one of the turbines in accordance with solution. Thus, the use of open heat supply systems is currently especially relevant due to the constantly increasing requirements for energy efficiency of all sectors of the domestic economy.
IN different years, however, there have been calls to eliminate existing open systems heating supply due to some shortcoming, for example, due to a more complex hydraulic mode these systems or under the pretext of improving DHW quality. The issue of eliminating open systems has been raised especially often recently. These calls come from “specialists” and managers who have little understanding of the basics of the operation of thermal power plants and heating systems in general. I was especially struck by the recent release of the Federal Law “On Amendments to Certain Legislative Acts” Russian Federation in connection with the adoption, in which its unknown authors wrote: “From January 1, 2013, the connection of capital construction projects of consumers to centralized open heat supply systems (hot water supply) for the needs of hot water supply, carried out by selecting coolant for the needs of hot water supply, is not allowed. From January 1, 2022, the use of centralized open heat supply systems (hot water supply) for hot water supply needs, carried out by selecting coolant for hot water supply needs, is not allowed.”
The law was adopted allegedly due to the need to amend some legislative acts after the release of the Federal Law “On Water Supply and Sanitation”. No matter how much I read into this law, I did not find any requirements to eliminate open heat supply systems (including in Article 24 “Ensuring the quality of hot water”). The authors of the law clearly overdid it. Since in the modern era of wild capitalism nothing is done easily (except in cases of outright stupidity), it can be assumed that the initiators of the cited amendments were guided by their own commercial interests.
Supporters of the elimination of open systems do not even try to at least roughly estimate the scale of fuel losses in the thermal power industry and the scale of costs in urban households during the transition from open heat supply systems to closed systems in half of the country's large cities. And if they could figure it out, they would understand the absurdity and impossibility of the practical implementation of such “innovations.” Thus, at only one, already mentioned, Southern CHPP, refusal to prepare make-up water for an open heating supply system would lead to an annual overconsumption of more than 100 thousand tons of equivalent fuel.
One of the main arguments of supporters of closed systems is the supposedly increased reliability and low corrosion damage due to the tightness of these systems and the low consumption of make-up water, from which an additional amount of dissolved corrosive gases is introduced.
My many years of experience research and commissioning work in closed heat supply systems in a number of cities and the experience of colleagues, in particular, the former head of the chemical service, and then the head of the Department of Water Chemical Problems of the All-Russian Thermal Engineering Institute (VTI) B.S. Fedoseev, shows that the complete tightness of closed systems should be considered a myth: in all closed systems, due to leaks in hot water heaters, there are huge flows of non-deaerated tap water into the heating network, leading to intense internal corrosion of heating network pipelines. In some cases, the flow of non-deaerated water into the heating network makes high-quality deaeration of small quantities of make-up water at thermal power plants practically useless. It is for this reason, as shown by the results of the VTI conducted in the early 90s. large-scale survey domestic systems heat supply, the intensity of internal corrosion in open and closed systems is approximately the same. Moreover, when the pressure of heating network water exceeds the pressure of heated tap water, unregulated flows of network water that does not meet drinking water quality standards occur into the hot water pipelines supplied to consumers, i.e. sanitary and hygienic requirements for hot water supply are not met. These flows are essentially regulated by the current rules of technical operation, paragraphs. 4.12.30 which allows hourly losses of network water for any heat supply systems in the amount of 0.25% of the average annual volume of water in heating networks. In closed systems, a significant part of these losses occurs due to the flow of network water through leaks in heaters into local DHW systems. In this regard, it is hardly possible to talk about increased sanitary and epidemiological safety of such systems.
In open systems, where drinking water is used as the source water for preparing make-up water, and anti-scale and anti-corrosion treatment of make-up water is carried out centrally by qualified personnel and under constant control, such shortcomings are practically eliminated.
In connection with the above arguments, paragraph 1 appears completely unconvincing. 3.1.3 SanPiN, which states that from a sanitary and epidemiological point of view, the most reliable systems centralized hot water supply connected to closed heat supply systems.
Arguments about the instability of the hydraulic regimes of open systems are now becoming less and less relevant. Availability of a large fleet of modern devices automatic regulation and their widespread use in heat supply systems makes it possible to reliably compensate for the influence of variable water flow rates in network mains.
An attempt has been made to compare the advantages and disadvantages of open and closed heat supply systems (see table). From this table it follows that in modern conditions open heat supply systems are more preferable.
| Open systems | Closed systems |
| Advantages
1. High energy efficiency due to the use of low-grade heat sources, incl. exhaust steam from turbines of thermal power plants for the preparation of large quantities of make-up water for the heating network. 2. Maintenance High Quality network water throughout the entire heat supply system and in local heating and domestic hot water systems of consumers thanks to the possibility of highly efficient centralized anti-scale and anti-corrosion treatment of make-up water at thermal power plants. 3. Low cost of local heating points for consumers. Flaws 1. More complex hydraulic mode of the system due to the difference in the flow rates of network water in the supply and return lines (the disadvantage is overcome by the use of modern automatic mode control devices). 2. The high cost of equipment for preparing a large amount of make-up water for the heating system at a thermal power plant. |
Advantages
1. Stable hydraulic mode of the system due to approximately the same flow rate of network water in the supply and return lines. 2. Low cost of installation for preparing a small amount of make-up water for the heating network at a thermal power plant. Flaws 1. Reduced energy efficiency of the system due to limited possibilities for using low-grade heat sources at thermal power plants. 2. The high cost of a large number of local heating points of consumers due to the presence of DHW heaters in them. 3. Flows of non-deaerated tap water into the heating network through leaks in hot water heaters, leading to intense internal corrosion of heating network pipelines. 4. Violations of sanitary and hygienic requirements for hot water supply due to unregulated flows of network water that does not meet drinking water quality standards into hot water pipelines supplied to consumers through leaks in hot water heaters. 5. High intensity of internal corrosion of metal sections of non-deaerated hot water pipelines in local hot water systems. |
Over decades of production and scientific work I have heard many times in various government offices proposals, and even demands, to transfer existing open systems to closed ones. Fortunately, so far it seems that no one in any city in the country has gotten around to implementing these demands. I have no doubt that the above-cited provisions of the law banning open heating systems are stillborn. I am sure that in the foreseeable future the problem of choosing a hot water supply method will be solved primarily based on the energy efficiency of heating systems and taking into account the quality of source water in the water supply sources of specific cities.
It should also be noted that a necessary condition for energy efficient operation of heating systems with open water intake is the use of vacuum deaeration heating network make-up water. It is the use of low-grade heat sources, incl. exhaust steam from turbines for heating coolants in front of vacuum deaerators of make-up water makes it possible to maximize the effect of cogeneration at thermal power plants.
Experts have proven that proper use vacuum deaerators in open heat supply systems provides high quality anti-corrosion treatment of make-up water, a significant increase in the thermal efficiency of thermal power plants, elimination of losses of heating steam condensate, characteristic of atmospheric deaerators, reducing capital costs for deaeration units, as well as complete environmental safety of hot water supply in open heat supply systems.
It seems to me that the provisions on the gradual ban on open heat supply systems, which it is not clear how they got into the law, should be immediately eliminated. We should be proud of the experience of domestic district heating. During the energy crisis of the 70-80s. all of Europe appreciated this experience and used it in the development of their heat supply systems. Today we should not disown everything positive that has been achieved in the domestic heat and power industry and heat supply. I believe that the initiative in this matter should be taken by the Russian Heat Supply NP, which has recently been the most authoritative organization for coordinating technical policy in the field of heat supply.
conclusions
1. Open heat supply systems, in contrast to closed systems, make it possible to maximize the effect of combined generation of electrical and thermal energy through the use of low-grade heat sources to heat large quantities of make-up water for the heating network at thermal power plants. The use of open heat supply systems is currently especially relevant due to the constantly increasing requirements for energy efficiency of all sectors of the domestic economy.
2. In open heat supply systems, the maintenance of high quality network water is ensured throughout the entire heat supply system and in local heating and domestic hot water systems of consumers due to the possibility of highly efficient centralized anti-scale and anti-corrosion treatment of make-up water at thermal power plants.
3. Open heat supply systems are more reliable than closed systems in sanitary and epidemiological terms due to the exclusion of network water that does not meet the drinking water quality criteria from entering local hot water supply systems through leaks in hot water supply heaters.
Literature
2. Patent No. 1366656 (USSR). IPC F01K17/02. Thermal power station/V.I. Sharapov//Discoveries. Inventions. 1988. No. 2.
3. Federal Law of the Russian Federation dated November 23, 2009 No. 261-FZ “On energy saving and increasing energy efficiency and on introducing amendments to certain legislative acts of the Russian Federation.”
4. Federal Law of December 7, 2011 No. 417-FZ “On amendments to certain legislative acts of the Russian Federation in connection with the adoption of the Federal Law “On Water Supply and Sanitation”.
5. Federal Law of December 7, 2011 No. 416-FZ “On Water Supply and Sanitation”.
6. Sharapov V.I. On the prevention of internal corrosion of the heating network in closed heating systems // Thermal power engineering. 1998. No. 4. pp. 16-19.
7. Sanitary and epidemiological rules and regulations SanPiN 2.1.4.1074-01. Drinking water and water supply to populated areas. Drinking water. Hygienic requirements for water quality centralized systems drinking water supply. Quality control. // M.: Ministry of Health of Russia. 2002.
10. Sharapov V.I. Current problems of using vacuum deaerators in open heat supply systems // Thermal power engineering. 1994. No. 8. P. 53-57.
11. Sharapov V.I., Rotov P.V. On ways to overcome the crisis in the operation of heat supply systems // Problems of energy. News from universities. 2000. No. 5-6. pp. 3-8.
In our latitudes it is impossible to do without heating. Too cool autumn and spring, long winter leave no choice - all rooms have to be heated to create comfortable conditions life. At the same time, along with heat, hot water is also supplied to apartments, organizations and enterprises.
To provide heat supply services, in accordance with the law, an appropriate agreement must be concluded between the supplier and the consumer.
Space heating systems are divided into open or closed.
At the same time, heating also happens:
- centralized (when heating is provided by one boiler house for the whole microdistrict);
- local (installed in a separate building or serving a small complex of buildings).
The difference between closed systems and open ones is quite significant. The latter involves supplying heated water to consumers' homes while taking it directly from the heating network.
Open heating system
In this format, boiling water is sent to the water supply directly from the heating pipes, which allows you to completely avoid complete consumption even if its entire volume is taken away. During the Soviet era, the work of approximately half of all heating networks was based on this principle. This popularity was due to the fact that the scheme helped to use energy resources more economically and significantly reduce heating costs in winter period and hot water supply.
However, this method of supplying residential buildings with heat and boiling water has many disadvantages. The thing is that very often heated water, due to its dual purpose, does not meet sanitary and hygienic standards. The coolant can circulate through metal pipes enough long time before it hits the taps. As a result, it often changes its color and becomes bad smell. In addition, employees of sanitary and epidemiological services have repeatedly identified dangerous microorganisms in it.
The need to filter such water before feeding it into the hot water supply system greatly reduces the efficiency and increases the cost of heating. However, until now there is no truly effective way to purify such water. The significant length of pipelines actually makes this procedure useless.
The circulation of water in such a system occurs due to the consideration of thermodynamic processes in the design. The heated liquid rises and leaves the heater due to increased pressure. At the same time, cool water creates a slightly lower pressure at the inlet to the boiler. This is what allows the coolant to move independently through the communications.
Water, like any other liquid, increases in volume when heated. Therefore, in order to prevent excessive load on heating networks, their design must include a special open expansion tank located above the level of the boiler and pipes. Excess coolant is squeezed out there. This gives grounds to call such a system open.
In this case, heating occurs up to 65 degrees Celsius, and then through water taps the water flows directly into consumer homes. This system allows the installation of inexpensive, simple faucets.
Since it is impossible to predict how much hot water will be used, it is always supplied based on the highest consumption.
Heat supply systems operating in a closed circuit - what is it?
The difference between this scheme central heating houses from the previous one is that hot water is used exclusively for heating. Hot water supply is provided through a separate circuit or individual heating devices.
The coolant circulates through vicious circle; Any minor losses that occur are compensated for by automatic pumping when there is a loss of pressure.
Energy saving in heat supply systems
Completed by: students of group T-23
Salazhenkov M.Yu
Krasnov D.
Introduction
Today, energy saving policy is a priority direction in the development of energy and heat supply systems. In fact, at every state enterprise, plans for energy saving and increasing the energy efficiency of enterprises, workshops, etc. are drawn up, approved and implemented.
The country's heat supply system is no exception. It is quite large and cumbersome, consumes colossal amounts of energy and at the same time there are no less colossal losses of heat and energy.
Let's consider what the heat supply system is, where the greatest losses occur, and what sets of energy-saving measures can be applied to increase the “efficiency” of this system.
Heating systems
Heat supply – supply of heat to residential, public and industrial buildings (structures) to meet the domestic (heating, ventilation, hot water supply) and technological needs of consumers.
In most cases, heating is about creating a comfortable indoor environment - at home, at work or in a public place. Heat supply also includes heating tap water and water in swimming pools, heating greenhouses, etc.
The distance over which heat is transported in modern district heating systems reaches several tens of km. The development of heat supply systems is characterized by an increase in the power of the heat source and the unit capacity of installed equipment. Thermal power modern thermal power plants reach 2-4 Tcal/h, district boiler houses 300-500 Gcal/h. In some heat supply systems, several heat sources work together on common heating networks, which increases the reliability, maneuverability and cost-effectiveness of heat supply.
Water heated in the boiler room can circulate directly in the heating system. Hot water is heated in the heat exchanger of the hot water supply system (DHW) to a lower temperature, about 50–60 °C. Return water temperature can be an important factor in boiler protection. The heat exchanger not only transfers heat from one circuit to another, but also effectively copes with the pressure difference that exists between the first and second circuits.
The required floor heating temperature (30 °C) can be obtained by adjusting the temperature of the circulating hot water. Temperature differences can also be achieved when using three way valve mixing hot water with return water in the system.
Regulation of heat supply in heat supply systems (daily, seasonal) is carried out both in the heat source and in heat-consuming installations. In water heating systems, the so-called central quality control of heat supply is usually carried out according to the main type of heat load - heating or a combination of two types of load - heating and hot water supply. It consists of changing the temperature of the coolant supplied from the heat supply source to the heating network in accordance with the accepted temperature schedule (that is, the dependence of the required water temperature in the network on the outside air temperature). Central qualitative regulation is complemented by local quantitative regulation at heating points; the latter is most common for hot water supply and is usually carried out automatically. In steam heat supply systems, local quantitative regulation is mainly carried out; The steam pressure in the heat supply source is maintained constant, the steam flow is regulated by consumers.
1.1 Composition of the heating system
The heat supply system consists of the following functional parts:
1) source of thermal energy production (boiler house, thermal power plant, solar collector, devices for recycling industrial thermal waste, installations for using heat from geothermal sources);
2) transporting devices of thermal energy to premises (heating networks);
3) heat-consuming devices that transmit thermal energy to the consumer (heating radiators, air heaters).
1.2 Classification of heat supply systems
Based on the location of heat generation, heat supply systems are divided into:
1) centralized (the source of thermal energy production works to supply heat to a group of buildings and is connected by transport devices to heat consumption devices);
2) local (the consumer and the heat supply source are in the same room or in close proximity).
The main advantages of centralized heat supply over local heat supply are a significant reduction in fuel consumption and operating costs (for example, due to the automation of boiler plants and increasing their efficiency); possibility of using low-grade fuel; reducing air pollution and improving the sanitary condition of populated areas. In local heat supply systems, heat sources include stoves, hot water boilers, water heaters (including solar), etc.
Based on the type of coolant, heat supply systems are divided into:
1) water (with temperatures up to 150 °C);
2) steam (under pressure 7-16 at).
Water serves mainly to cover municipal and household loads, and steam - technological loads. The choice of temperature and pressure in heat supply systems is determined by consumer requirements and economic considerations. With an increase in the distance of heat transportation, an economically justified increase in coolant parameters increases.
According to the method of connecting the heating system to the heat supply system, the latter are divided into:
1) dependent (coolant heated in a heat generator and transported through heating networks goes directly to heat-consuming devices);
2) independent (the coolant circulating through the heating networks in the heat exchanger heats the coolant circulating in the heating system). (Fig.1)
IN independent systems consumer installations are hydraulically isolated from the heating network. Such systems are used mainly in large cities - in order to increase the reliability of heat supply, as well as in cases where the pressure regime in the heating network is unacceptable for heat-consuming installations due to the conditions of their strength, or when static pressure, created by the latter, is unacceptable for the heating network (such as, for example, heating systems of high-rise buildings).
Picture 1 - Schematic diagrams heat supply systems according to the method of connecting heating systems to them
According to the method of connecting the hot water supply system to the heating system:
1) closed;
2) open.
In closed systems, the hot water supply is supplied with water from the water supply system, heated to the required temperature by water from the heating network in heat exchangers installed at heating points. In open systems, water is supplied directly from the heating network (direct water supply). Water leakage due to leaks in the system, as well as its consumption for water collection, are compensated by additional supply of the corresponding amount of water to the heating network. To prevent corrosion and scale formation on the inner surface of the pipeline, water supplied to the heating network undergoes water treatment and deaeration. In open systems, the water must also meet drinking water requirements. The choice of system is determined mainly by the availability of a sufficient amount of potable water, its corrosive and scale-forming properties. Both types of systems have become widespread in Ukraine.
Based on the number of pipelines used to transfer coolant, heat supply systems are distinguished:
single-pipe;
two-pipe;
multi-pipe.
Single-pipe systems are used in cases where the coolant is completely used by consumers and is not returned (for example, in steam systems without condensate return and in open water systems, where all the water coming from the source is disassembled for hot water supply to consumers).
In two-pipe systems, the coolant is completely or partially returned to the heat source, where it is heated and replenished.
Multi-pipe systems are suitable when it is necessary to allocate certain types of heat load (for example, hot water supply), which simplifies the regulation of heat supply, operating mode and methods of connecting consumers to heating networks. In Russia, two-pipe heat supply systems have become prevalent.
1.3 Types of heat consumers
Heat consumers of the heating supply system are:
1) heat-using sanitary systems of buildings (heating, ventilation, air conditioning, hot water supply systems);
2) technological installations.
Using heated water for space heating is quite common. In this case, a variety of methods of transferring water energy are used to create a comfortable indoor environment. One of the most common is the use of heating radiators.
An alternative to heating radiators is underfloor heating, where the heating circuits are located under the floor. The floor heating circuit is usually connected to the radiator circuit.
Ventilation - a fan coil unit that supplies hot air to a room, usually used in public buildings. A combination is often used heating devices, for example, heating and floor heating radiators or heating and ventilation radiators.
Hot tap water has become part of everyday life and daily needs. Therefore, the hot water installation must be reliable, hygienic and economical.
Based on heat consumption patterns throughout the year, two groups of consumers are distinguished:
1) seasonal, requiring heat only during the cold season (for example, heating systems);
2) year-round, requiring heat all year round (hot water supply systems).
Depending on the ratio and modes of individual types of heat consumption, three characteristic groups of consumers are distinguished:
1) residential buildings (characterized by seasonal heat consumption for heating and ventilation and year-round heat consumption for hot water supply);
2) public buildings(seasonal heat consumption for heating, ventilation and air conditioning);
3) industrial buildings and structures, including agricultural complexes (all types of heat consumption, the quantitative relationship between which is determined by the type of production).
2 District heating
District heating is an environmentally friendly and reliable way to provide heat. District heating systems distribute hot water, or in some cases steam, from a central boiler room among numerous buildings. There is a very wide range of sources used to produce heat, including burning oil and natural gas or using geothermal waters. The use of heat from low-temperature sources, such as geothermal heat, is possible through the use of heat exchangers and heat pumps. The possibility of using non-recovered heat from industrial enterprises, excess heat from waste processing, industrial processes and sewerage, targeted heating plants or thermal power plants in district heating, allows for optimal choice heat source in terms of energy efficiency. This way you optimize costs and protect the environment.
Hot water from the boiler room is supplied to a heat exchanger that separates the production site from the distribution pipes of the district heating network. The heat is then distributed among end users and supplied to the relevant buildings through substations. Each of these substations usually includes one heat exchanger for space heating and hot water supply.
There are several reasons for installing heat exchangers to separate the heating plant and the district heating network. Where there are significant differences in pressure and temperature that can cause serious damage to equipment and property, a heat exchanger can keep sensitive heating and ventilation equipment from being exposed to contaminated or corrosive fluids. Another important reason for separating the boiler plant, distribution network and end users is to clearly define the functions of each system component.
In a combined heat and power plant (CHP), heat and electricity are produced simultaneously, with heat as a by-product. The heat is typically used in district heating systems, leading to increased energy efficiency and cost savings. The degree of use of energy obtained from fuel combustion will be 85–90%. Efficiency will be 35–40% higher than in the case of separate production of heat and electricity.
In a thermal power plant, burning fuel heats up water, which turns into steam. high pressure and high temperature. The steam drives a turbine connected to a generator that produces electricity. After the turbine, the steam condenses in a heat exchanger. The heat generated by this process is then fed into district heating pipes and distributed to end users.
For the end consumer, centralized heat supply means uninterrupted energy supply. District heating system is more convenient and efficient than small ones customized systems heating houses. Modern technologies fuel combustion and emissions reduction are reduced negative impact on the environment.
In apartment buildings or other buildings heated by central heating units, the main requirement is heating, hot water supply, ventilation and underfloor heating for a large number of consumers with minimal energy consumption. Using high-quality equipment in the heating system, you can reduce overall costs.
Another very important task of heat exchangers in district heating is to ensure safety internal system by separating end consumers from the distribution network. This is necessary due to the significant difference in temperature and pressure. In the event of an accident, the risk of flooding can also be minimized.
In central heating points, a two-stage scheme for connecting heat exchangers is often found (Fig. 2, A). This connection means maximum heat utilization and low return water temperature when using a hot water system. It is particularly advantageous in combined heat and power (CHP) applications where low return water temperatures are desired. This type of substation can easily supply heat to up to 500 apartments, and sometimes more.
A) Two-stage connection B) Parallel connection
Figure 2 – Heat exchanger connection diagram
Parallel connection of a DHW heat exchanger (Fig. 2, B) is less complicated than a two-stage connection and can be used for any installation size that does not require low return water temperatures. This connection is usually used for small and medium-sized heating points with a load of up to approximately 120 kW. Connection diagram for hot water supply water heaters in accordance with SP 41-101-95.
Most district heating systems place high demands on installed equipment. The equipment must be reliable and flexible, providing the necessary security. In some systems it must also meet very high hygiene standards. Another important factor in most systems is low operating costs.
However, in our country the centralized heating system is in a deplorable state:
the technical equipment and level of technological solutions in the construction of heating networks correspond to the state of the 1960s, while the radii of heat supply have sharply increased and there has been a transition to new standard sizes of pipe diameters;
the quality of metal of heat pipes, thermal insulation, shut-off and control valves, designs and laying of heat pipes is significantly inferior to foreign analogues, which leads to large losses of thermal energy in networks;
bad conditions thermal and waterproofing of heating pipelines and heating network channels contributed to increased damage to underground heating pipelines, which led to serious problems in replacing heating network equipment;
domestic equipment of large CHPPs corresponds to the average foreign level of the 1980s, and currently steam turbine CHPPs are characterized by a high accident rate, since almost half of the installed turbine capacity has reached its design life;
at existing coal-fired thermal power plants there are no systems for cleaning flue gases from NOx and SOx, and the efficiency of collecting solid particles often does not reach the required values;
competitiveness of the central heating system modern stage can only be ensured by introducing specially new technical solutions, both in the structure of systems and in diagrams and equipment of energy sources and heating networks.
2.2 Efficiency of district heating systems
One of the most important conditions normal operation of the heat supply system is the creation of a hydraulic mode that provides pressure in the heating network sufficient to create network water flows in heat-consuming installations in accordance with the given heat load. The normal operation of heat consumption systems is the provision of consumers with thermal energy of appropriate quality, and for the energy supplying organization it is to maintain the parameters of the heat supply regime at the level regulated by the Rules Technical Operation(PTE) of power plants and networks of the Russian Federation, PTE of thermal power plants. The hydraulic mode is determined by the characteristics of the main elements of the heating system.
During operation in the existing centralized heat supply system, due to changes in the nature of the heat load, the connection of new heat consumers, an increase in the roughness of pipelines, adjustments to the design temperature for heating, changes temperature chart When thermal energy (TE) is released from a TE source, as a rule, there is an uneven supply of heat to consumers, an overestimation of network water costs and a reduction in pipeline capacity.
In addition to this, there are usually problems in heat consumption systems. Such as misregulation of heat consumption modes, understaffing of elevator units, unauthorized violation by consumers of connection schemes (established by projects, technical specifications and contracts). These problems of heat consumption systems manifest themselves, first of all, in the misalignment of the entire system, characterized by increased coolant costs. As a consequence, there are insufficient (due to increased pressure losses) available coolant pressures at the inlets, which in turn leads to the desire of subscribers to provide the necessary drop by draining network water from the return pipelines to create at least minimal circulation in heating devices(violations of connection diagrams, etc.), which leads to an additional increase in flow rate and, consequently, to additional pressure losses, and to the emergence of new subscribers with reduced pressure drops, etc. A “chain reaction” occurs in the direction of total deregulation of the system.
All this has a negative impact on the entire heat supply system and on the activities of the energy supply organization: the inability to comply with the temperature schedule; increased replenishment of the heat supply system, and if the water treatment capacity is exhausted, forced replenishment with raw water (resulting in internal corrosion, premature failure of pipelines and equipment); forced increase in heat supply to reduce the number of complaints from the population; increase in operating costs in the system of transport and distribution of thermal energy.
It is necessary to point out that in a heat supply system there is always a relationship between established thermal and hydraulic regimes. A change in flow distribution (its absolute value inclusive) always changes the condition of heat exchange, both directly in heating installations and in heat consumption systems. The result of abnormal operation of the heating system is, as a rule, heat return network water.
It should be noted that the temperature of the return network water at the source of thermal energy is one of the main operating characteristics intended to analyze the condition of the equipment of heating networks and operating modes of the heat supply system, as well as to assess the effectiveness of measures taken by organizations operating heating networks in order to increase the level operation of the heating system. As a rule, in the event of misadjustment of the heat supply system, actual value of a given temperature differs significantly from its standard value calculated for a given heat supply system.
Thus, when the heat supply system is deregulated, the temperature of the network water, as one of the main indicators of the mode of supply and consumption of thermal energy in the heat supply system, turns out to be: in the supply pipeline in almost all intervals heating season characterized by low values; the temperature of the return network water, despite this, is characterized by increased values; temperature difference in the supply and return pipelines, namely this indicator (along with specific consumption network water to connected thermal load) characterizes the quality level of thermal energy consumption, which is underestimated compared to the required values.
One more aspect should be noted, related to the increase relative to the calculated value of the flow of network water for the thermal regime of heat consumption systems (heating, ventilation). For direct analysis, it is advisable to use the dependence, which determines, in case of deviation of the actual parameters and structural elements of the heat supply system from the calculated ones, the ratio of the actual consumption of thermal energy in heat consumption systems to its calculated value.
where Q is the consumption of thermal energy in heat consumption systems;
g- flow of network water;
tп and to - temperature in the supply and return pipelines.
This dependence (*) is shown in Fig. 3. The ordinate axis shows the ratio of the actual consumption of thermal energy to its calculated value, and the abscissa axis shows the ratio of the actual consumption of network water to its calculated value.
Figure 3 – Graph of the dependence of thermal energy consumption by systems
heat consumption from network water consumption.
As general trends, it is necessary to point out that, firstly, an increase in the consumption of network water by n times does not cause an increase in thermal energy consumption corresponding to this number, that is, the coefficient of heat consumption lags behind the coefficient of consumption of network water. Secondly, when the flow of network water decreases, the heat supply to the local heat consumption system decreases the faster, the lower the actual consumption of network water is compared to the calculated one.
Thus, heating and ventilation systems react very poorly to excessive consumption of network water. Thus, an increase in the flow of network water for these systems relative to the calculated value by 50% causes an increase in heat consumption by only 10%.
The point in Fig. 3 with coordinates (1;1) displays the calculated, actually achievable operating mode of the heat supply system after commissioning activities. By actually achievable operating mode is meant a mode that is characterized by the existing position of the structural elements of the heat supply system, heat losses by buildings and structures, and the determined total flow of network water at the terminals of the thermal energy source necessary to provide a given heat load under the existing schedule of thermal energy supply.
It should also be noted that the increased consumption of network water, due to the limited throughput of heating networks, leads to a decrease in the available pressure values at the consumer inputs necessary for the normal operation of heat-consuming equipment. It should be noted that pressure losses through the heating network are determined by a quadratic dependence on the flow of network water:
That is, with an increase in the actual flow rate of network water GF by 2 times relative to the calculated value GP, pressure losses through the heating network increase 4 times, which can lead to unacceptably low available pressures at the thermal nodes of consumers and, consequently, to insufficient heat supply to these consumers, which may cause unauthorized drainage of network water to create circulation (unauthorized violation by consumers of connection diagrams, etc.)
Further development of such a heat supply system along the path of increasing coolant flow, firstly, will require replacing the head sections of heat pipelines, additional installation of network pumping units, increasing water treatment productivity, etc., and secondly, leads to an even greater increase in additional costs - expenses for compensation for electricity, make-up water, thermal energy losses.
Thus, it seems technically and economically more feasible to develop such a system by improving its quality indicators - increasing the temperature of the coolant, pressure drops, increasing the temperature difference (heat removal), which is impossible without a drastic reduction in coolant costs (circulation and make-up) in heat consumption systems and , respectively, throughout the entire heat supply system.
Thus, the main measure that can be proposed to optimize such a heat supply system is the adjustment of hydraulic and thermal regime heat supply systems. The technical essence of this event is to establish flow distribution in the heat supply system based on the calculated (i.e. corresponding to the connected heat load and the selected temperature schedule) network water flow rates for each heat consumption system. This is achieved by installing appropriate throttling devices (autoregulators, throttle washers, elevator nozzles), the calculation of which is made based on the calculated pressure drop at each input, which is calculated based on the hydraulic and thermal calculation of the entire heat supply system.
It should be noted that the creation of a normal mode of operation of such a heat supply system is not limited only to carrying out adjustment activities; it is also necessary to carry out work to optimize the hydraulic mode of the heat supply system.
Regime adjustment covers the main parts of the centralized heat supply system: water heating installation of the heat source, central heating points(if any), heating network, control and distribution points (if available), individual heating points and local heat consumption systems.
The setup begins with an inspection of the centralized heating system. Collection and analysis of initial data on actual operating modes operation of the thermal energy transport and distribution system, information on technical condition heating networks, the degree of equipment of the heat source, heating networks and subscribers with commercial and technological measuring instruments. The applied heat supply modes are analyzed, possible design and installation defects are identified, and information is selected to analyze the characteristics of the system. An analysis of operational (statistical) information is carried out (records of coolant parameters, energy supply and consumption modes, actual hydraulic and thermal modes of heating networks) when different meanings outdoor air temperature in base periods, obtained from the readings of standard measuring instruments, and an analysis of reports from specialized organizations is also carried out.
In parallel, a design diagram of heating networks is being developed. A mathematical model of the heat supply system is being created on the basis of the ZuluThermo calculation complex, developed by Politerm (St. Petersburg), capable of simulating the actual thermal and hydraulic operating conditions of the heat supply system.
It is necessary to point out that there is a fairly common approach, which consists in minimizing the financial costs associated with the development of measures for setting up and optimizing the heat supply system, namely, costs are limited to the acquisition of a specialized software package.
The pitfall with this approach is the reliability of the source data. A mathematical model of a heat supply system, created on the basis of unreliable initial data on the characteristics of the main elements of the heat supply system, turns out, as a rule, to be inadequate to reality.
2.3 Energy saving in district heating systems
Recently, there have been criticisms about centralized heat supply based on district heating - the joint production of heat and electrical energy. The main disadvantages include large heat losses in pipelines during heat transport, and a decrease in the quality of heat supply due to non-compliance with the temperature schedule and required pressures at consumers. It is proposed to switch to decentralized, autonomous heat supply from automated boiler houses, including those located on the roofs of buildings, justifying this by lower cost and the absence of the need to lay heat pipelines. But at the same time, as a rule, it is not taken into account that connecting the heat load to the boiler house makes it impossible to generate cheap electricity at heat consumption. Therefore, this part of ungenerated electricity must be replaced by its production through the condensation cycle, the efficiency of which is 2-2.5 times lower than that of the cogeneration cycle. Consequently, the cost of electricity consumed by a building, the heat supply of which is provided from the boiler house, should be higher than that of a building connected to a district heating system, and this will cause a sharp increase in operating costs.
S. A. Chistovich at the anniversary conference “75 years of district heating in Russia”, held in Moscow in November 1999, proposed that house boiler houses complement centralized heat supply, acting as peak heat sources, where the lack of network capacity does not allow for high-quality supply heat of consumers. At the same time, district heating is preserved and the quality of heat supply is improved, but this decision reeks of stagnation and hopelessness. It is necessary that the centralized heating supply fully fulfill its functions. After all, district heating has its own powerful peak boiler houses, and it is obvious that one such boiler house will be more economical than hundreds of small ones, and if the network capacity is insufficient, then it is necessary to shift the networks or cut off this load from the networks so that it does not disturb the quality of heat supply to other consumers.
Denmark has achieved great success in district heating; despite the low concentration of heat load per 1 m2 of surface area, it is ahead of us in district heating coverage per capita. In Denmark, a special government policy is being pursued to prefer connecting new heat consumers to centralized heat supply. In Western Germany, for example in the city of Mannheim, district heating based on district heating is developing rapidly. In the Eastern lands, where, focusing on our country, district heating was also widely used, despite the abandonment of panel housing construction, central heating stations in residential neighborhoods, which turned out to be ineffective in a market economy and Western way of life, the area of centralized heating based on district heating continues to develop as the most environmentally friendly and cost-effective.
All of the above indicates that at the new stage we must not lose our leading position in the field of district heating, and for this it is necessary to modernize the centralized heating system in order to increase its attractiveness and efficiency.
All the advantages of the joint production of heat and electrical energy were attributed to the electricity side; centralized heat supply was financed on a residual basis - sometimes a thermal power plant had already been built, but the heating networks had not yet been connected. As a result, low-quality heat pipelines were created with poor insulation and ineffective drainage; heat consumers were connected to heating networks without automatic load control, at best using hydraulic regulators for stabilizing coolant flow of very low quality.
This forced heat supply from the source using the method of central quality control (by changing the temperature of the coolant depending on the outside temperature according to a single schedule for all consumers with constant circulation in the networks), which led to a significant overconsumption of heat by consumers due to differences in their operating modes and the impossibility of joint operation of several heat sources on a single network for mutual redundancy. The absence or ineffectiveness of control devices at the points where consumers are connected to heating networks also caused excessive consumption of the coolant volume. This led to an increase in the temperature of the return water to such an extent that there was a danger of failure of the station circulation pumps and this forced a reduction in heat supply at the source, violating the temperature schedule even under conditions of sufficient power.
Unlike us, in Denmark, for example, all the benefits of district heating in the first 12 years are transferred to the thermal energy side, and then divided in half with electrical energy. As a result, Denmark was the first country to have pre-fabricated insulated pipes for channelless installation with a sealed cover layer and automatic system leak detection, which sharply reduced heat loss during transportation. In Denmark, silent, supportless “wet running” circulation pumps, heat metering devices and effective automatic heat load control systems were invented for the first time, which made it possible to construct automated individual heating points (IHP) directly in consumers’ buildings with automatic regulation of heat supply and metering in places where it is used. use.
Complete automation of all heat consumers made it possible to: abandon the high-quality method of central regulation at the heat source, which causes unwanted temperature fluctuations in the pipelines of the heating network; reduce the maximum water temperature parameters to 110-1200C; to ensure the ability to operate several heat sources, including waste incineration plants, on a single network with the most efficient use of each.
The water temperature in the supply pipeline of heating networks changes depending on the level of the established outside air temperature in three steps: 120-100-80°C or 100-85-70°C (there is a tendency for this temperature to decrease even more). And inside each stage, depending on the change in load or deviation in the outside temperature, the flow rate of the coolant circulating in the heating networks changes according to the signal of the fixed value of the pressure difference between the supply and return pipelines - if the pressure difference drops below a predetermined value, then subsequent heat-generating and pumping units. Heat supply companies guarantee each consumer a specified minimum level of pressure drop in the supply networks.
Consumers are connected through heat exchangers, and, in our opinion, an excessive number of connection stages are used, which is apparently caused by property boundaries. Thus, the following connection scheme was demonstrated: to the main networks with design parameters of 125°C, which are managed by the energy producer, through a heat exchanger, after which the water temperature in the supply pipeline is reduced to 120°C, distribution networks that are in municipal ownership are connected.
The level of maintaining this temperature is set by an electronic regulator acting on a valve installed on the return pipeline of the primary circuit. In the secondary circuit, coolant circulation is carried out by pumps. Connection of local heating and hot water supply systems of individual buildings to these distribution networks is carried out through independent heat exchangers installed in the basements of these buildings with a full set of heat regulation and metering devices. Moreover, the temperature of the water circulating in the local heating system is regulated according to a schedule depending on changes in the outside air temperature. In design conditions Maximum temperature water reaches 95°C, recently there has been a tendency to reduce it to 75-70°C, the maximum return water temperature is 70 and 50°C, respectively.
Connection of heating points of individual buildings is carried out according to standard schemes with parallel connection of a hot water supply tank water heater or by two-stage scheme using the potential of the coolant from the return pipeline after the heating water heater using high-speed hot water heat exchangers, while it is possible to use a pressure hot water storage tank with a pump to charge the tank. In the heating circuit, pressure membrane tanks are used to collect water as it expands from heating; we have greater application have atmospheric expansion tanks installed at the top point of the system.
To stabilize the operation of control valves, a hydraulic constant pressure differential regulator is usually installed at the inlet to the heating point. And to bring heating systems with pump circulation to optimal operating mode and facilitate the distribution of the coolant along the risers of the system - a “partner valve” in the form of a balance valve, which allows you to set the correct flow rate of the circulating coolant based on the pressure loss measured on it.
They don't pay in Denmark special attention to increase the calculated coolant flow to the heating point when water heating is turned on for domestic needs. In Germany, it is legally prohibited to take into account the load on the hot water supply when selecting heat power, and when automating heating points, it is accepted that when the hot water supply water heater is turned on and when the storage tank is filled, the pumps that provide circulation in the heating system are turned off, i.e., the heat supply to the heating system is stopped. heating.
Our country also attaches great importance to preventing an increase in the power of the heat source and the calculated flow rate of the coolant circulating in the heating network during the hours of maximum hot water supply. But the solution adopted in Germany for this purpose cannot be applied in our conditions, since we have a much higher ratio of hot water supply and heating loads, due to the large absolute value of domestic water consumption and higher population density.
Therefore, when automating consumer heating points, a restriction is applied maximum flow water from the heating network when the set value is exceeded, determined based on the average hourly DHW loads. When supplying heat to residential neighborhoods, this is done by closing the valve of the heat supply regulator for heating during hours of maximum water consumption. By setting the heating regulator to slightly overestimate the maintained coolant temperature schedule, the underheating in the heating system that occurs when the maximum watershed is passed is compensated for during periods of water withdrawal below average (within the limits of a given water flow from the heating network - related regulation).
The water flow sensor, which is a signal for limitation, is a water flow meter included in the heat meter kit installed at the heating network input to the central heating substation or ITP. The inlet pressure differential regulator cannot serve as a flow limiter, since it provides a given pressure differential under conditions of full opening of the heating and hot water supply regulator valves installed in parallel.
In order to increase the efficiency of the joint production of thermal and electrical energy and level out the maximum energy consumption, thermal accumulators that are installed at the source have been widely used in Denmark. The lower part of the battery is connected to the return pipeline of the heating network, the upper part is connected to the supply pipeline through a movable diffuser. When the circulation in the heating distribution networks decreases, the tank is charged. As circulation increases, excess coolant flow from the return pipeline enters the tank, and hot water is squeezed out of it. The need for heat accumulators increases in thermal power plants with back-pressure turbines, in which the ratio of generated electrical and thermal energy is fixed.
If the design temperature of water circulating in heating networks is below 100°C, then atmospheric storage tanks are used; at higher temperatures design temperature Pressure is created in the tanks to ensure that hot water does not boil.
However, installing thermostats together with heat flow meters on each heating device leads to an almost double increase in the cost of the heating system, and in a single-pipe scheme, in addition, the required heating surface of the devices increases by up to 15% and there is a significant residual heat transfer of the devices in the closed position of the thermostat, which reduces the efficiency of autoregulation. Therefore, an alternative to such systems, especially in low-cost municipal construction, are façade-by-facade automatic heating control systems - for extended buildings and central ones with correction of the temperature schedule based on the deviation of air temperature in the prefabricated exhaust ventilation ducts from apartment kitchens - for single-point buildings or buildings with a complex configuration.
However, it must be borne in mind that when reconstructing existing residential buildings, in order to install thermostats, it is necessary to enter each apartment with welding. At the same time, when organizing façade-by-facade automatic regulation, it is enough to insert jumpers between the facade branches of sectional heating systems in the basement and attic, and for 9-story attic-free buildings of mass construction of the 60-70s - only in the basement.
It should be noted that new construction per year does not exceed 1-2% of the existing housing stock. This shows how important reconstruction is becoming existing buildings in order to reduce heat costs for heating. However, it is impossible to automate all buildings at once, and in conditions when several buildings are automated, real savings are not achieved, since the coolant saved on automated objects is redistributed among non-automated ones. The above once again confirms that it is necessary to build PSCs on existing heating networks at an accelerated pace, since it is much easier to simultaneously automate all buildings powered by one PSC than from a thermal power plant, and other already created PSCs will not allow excess coolant into their distribution networks.
All of the above does not exclude the possibility of connecting individual buildings to boiler houses with an appropriate feasibility study with an increase in the tariff for consumed electricity (for example, when laying or relaying a large number of networks is necessary). But in the conditions of the existing system of centralized heat supply from thermal power plants, this should be local in nature. The possibility of using heat pumps and transferring part of the load to CCGTs and GTUs cannot be ruled out, but given the current price environment for fuel and energy resources, this is not always cost-effective.
Heat supply to residential buildings and neighborhoods in our country, as a rule, is carried out through group heating points (CHS), after which individual buildings are supplied through independent pipelines with hot water for heating and for domestic needs with tap water heated in heat exchangers installed in the CHS. Sometimes up to 8 heat pipelines leave the central heating station (with a 2-zone hot water supply system and the presence of a significant ventilation load), and although galvanized hot water supply pipelines are used, due to the lack of chemical water treatment they are subject to intense corrosion and after 3-5 years of operation on them fistulas appear.
Currently, due to the privatization of housing and service enterprises, as well as the rising cost of energy resources, the transition from group heating points to individual ones (IHP) located in a heated building is relevant. This makes it possible to use a more efficient façade-by-facade automatic heating control system for extended buildings or a central one with correction for internal air temperature in single-point buildings; it allows one to abandon hot water supply distribution networks, reducing heat losses during transportation and energy consumption for pumping domestic hot water. Moreover, it is advisable to do this not only in new construction, but also during the reconstruction of existing buildings. Such experience exists in the Eastern states of Germany, where, just like ours, central heating stations were built, but now they are left only as pumping water supply stations (if necessary), and heat exchange equipment together with circulation pumps, regulation and accounting units are transferred to the ITP of buildings. Intra-block networks are not laid, hot water supply pipelines are left in the ground, and heating pipelines, as they are more durable, are used to supply superheated water to buildings.
To improve the controllability of heat networks, to which a large number of ITPs will be connected, and to ensure the possibility of automatic backup, one should return to the construction of control and distribution points (CDP) at the points where distribution networks are connected to the main ones. Each distribution point is connected to the main line on both sides of sectional valves and serves consumers with a heat load of 50-100 MW. The control panel is equipped with switching electric gate valves at the inlet, pressure regulators, circulation and mixing pumps, a temperature controller, safety valve, heat and coolant flow metering devices, control and telemechanics devices.
The automation circuit of the control valve ensures that the pressure is maintained at a constant minimum level in the return line; maintaining a constant specified pressure drop in the distribution network; reducing and maintaining the water temperature in the supply pipeline of the distribution network according to a given schedule. As a result, in backup mode, it is possible to supply a reduced amount of circulating water from the thermal power plant through the mains. elevated temperature without disturbing the temperature and hydraulic conditions in distribution networks.
PSCs should be located in ground pavilions, they can be interlocked with water pumping stations (this will, in most cases, eliminate the installation of high-pressure and therefore noisier pumps in buildings), and can serve as the boundary of the balance sheet between the heat-distributing organization and the heat-distributing one (the next boundary between the heat-distributing and the heat-using organizations will be the wall of the building). Moreover, the distribution centers must be under the jurisdiction of the heat distributing organization, since they serve to manage and back up the main networks and provide the ability to operate several heat sources on these networks, taking into account the maintenance of the coolant parameters specified by the heat distribution organization at the exit from the distribution center.
Proper Use coolant on the heat consumer side is ensured by using efficient systems control automation. Nowadays there are a large number of computer systems that can perform control tasks of any complexity, but technological tasks and circuit solutions for connecting heat consumption systems remain decisive.
Recently, they have begun to build water heating systems with thermostats that carry out individual automatic regulation of the heat transfer of heating devices based on the air temperature in the room where the device is installed. Such systems are widely used abroad with the addition of mandatory measurement of the amount of heat used by the device as a proportion of the total heat consumption of the building's heating system.
In our country, in mass construction, such systems began to be used for elevator connection to heating networks. But the elevator is designed in such a way that, with a constant nozzle diameter and the same available pressure, it passes a constant flow of coolant through the nozzle, regardless of changes in the flow of water circulating in the heating system. As a result, in 2-pipe heating systems, in which the thermostats, when closed, lead to a reduction in the flow of coolant circulating in the system, with an elevator connection the water temperature in the supply pipeline will increase, and then in the return pipeline, which will lead to an increase in heat transfer from the unregulated part of the system (risers) and to underutilization of coolant.
In a single-pipe heating system with constantly operating closing sections, when the thermostats are closed, hot water is discharged into the riser without cooling, which also leads to an increase in the temperature of the water in the return pipeline and, due to the constancy of the mixing coefficient in the elevator, to a rise in the temperature of the water in the supply pipeline, and therefore to the same consequences as in a 2-pipe system. Therefore, in such systems it is mandatory to automatically regulate the water temperature in the supply pipeline according to a schedule depending on changes in the outside air temperature. Such regulation is possible by changing the circuit solution for connecting the heating system to the heating network: replacing a conventional elevator with an adjustable one, by using pump mixing with a control valve, or by connecting through a heat exchanger with pump circulation and a control valve on network water in front of the heat exchanger. [
3 DECENTRALIZED HEAT SUPPLY
3.1 Development prospects decentralized heat supply
Previously made decisions to close small boiler houses (under the pretext of their low efficiency, technical and environmental dangers) today have turned into over-centralization of heat supply, when hot water travels 25-30 km from the thermal power plant to the consumer, when the heat source is turned off due to non-payment or emergency situation leads to the freezing of cities with a million people.
Most industrialized countries followed a different path: they improved heat-generating equipment, increasing the level of its safety and automation, the efficiency of gas-burning devices, sanitary, environmental, ergonomic and aesthetic indicators; created a comprehensive system for accounting for energy resources by all consumers; brought the regulatory and technical framework into line with the requirements of expediency and consumer convenience; optimized the level of centralization of heat supply; switched to the widespread introduction of alternative sources of thermal energy. The result of this work was real energy saving in all areas of the economy, including housing and communal services.
A gradual increase in the share of decentralized heat supply, bringing the heat source as close as possible to the consumer, and accounting by the consumer of all types of energy resources will not only create more comfortable conditions for the consumer, but also ensure real savings in gas fuel.
A modern decentralized heat supply system is a complex set of functionally interconnected equipment, including an autonomous heat generating unit and building engineering systems (hot water supply, heating and ventilation systems). The main elements of the apartment heating system, which is a type of decentralized heat supply, in which each apartment in apartment building is equipped with an autonomous system for providing heat and hot water, including a heating boiler, heating appliances, air supply and combustion product removal systems. Wiring is carried out using steel pipe or modern heat-conducting systems - plastic or metal-plastic.
The system of centralized heat supply, traditional for our country, through thermal power plants and main heat pipelines, is well known and has a number of advantages. But in the conditions of transition to new economic mechanisms, known economic instability and weakness of interregional, interdepartmental relations, many of the advantages of the centralized heat supply system turn into disadvantages.
The main one is the length of heating mains. The average percentage of wear is estimated at 60-70%. The specific damage rate of heating pipelines has currently increased to 200 registered damages per year per 100 km of heating networks. According to emergency estimates, at least 15% of heating networks require immediate replacement. In addition to this, over the past 10 years, as a result of underfinancing, the industry's fixed assets have practically not been updated. As a result, heat energy losses during production, transportation and consumption reached 70%, which led to poor quality of heat supply at high costs.
The organizational structure of interaction between consumers and heat supply enterprises does not stimulate the latter to save energy resources. The system of tariffs and subsidies does not reflect the real costs of heat supply.
In general, the critical situation in which the industry finds itself suggests the emergence of a large-scale crisis in the heat supply sector in the near future, the resolution of which will require colossal financial investments.
The pressing issue is reasonable decentralization of heat supply, apartment-by-apartment heat supply. Decentralization of heat supply (DH) is the most radical, effective and cheap way eliminating many shortcomings. The justified use of diesel fuel in combination with energy-saving measures during the construction and reconstruction of buildings will provide great savings in energy resources in Ukraine. In the current difficult conditions, the only way out is the creation and development of a diesel fuel system through the use of autonomous heat sources.
Apartment heating is an autonomous provision of heat and hot water individual house or a separate apartment in a multi-storey building. The main elements of such autonomous systems are: heat generators - heating devices, heating and hot water supply pipelines, fuel supply, air and smoke removal systems.
The objective prerequisites for the implementation of autonomous (decentralized) heat supply systems are:
the absence in some cases of free capacity at centralized sources;
densification of urban areas with housing facilities;
in addition, a significant part of the development is located in areas with undeveloped engineering infrastructure;
lower capital investments and the ability to gradually cover thermal loads;
the ability to maintain comfortable conditions in the apartment at your own request, which in turn is more attractive compared to apartments with centralized heat supply, the temperature in which depends on the directive decision on the beginning and end of the heating period;
the appearance on the market of a large number of different modifications of domestic and imported (foreign) low-power heat generators.
Today, modular boiler units designed for organizing autonomous diesel fuel have been developed and are being mass-produced. The block-modular construction principle makes it possible to easily build a boiler room required power. The absence of the need to lay heating mains and construct a boiler house building reduces the cost of communications and makes it possible to significantly increase the pace of new construction. In addition, this makes it possible to use such boiler houses to quickly provide heat supply in emergency situations during the heating season.
Block boiler rooms are a fully functionally complete product, equipped with all the necessary automation and safety devices. The level of automation ensures uninterrupted operation of all equipment without the constant presence of an operator.
Automation monitors the facility’s need for heat depending on weather conditions and independently regulates the operation of all systems to ensure the specified modes. This achieves better compliance with the thermal schedule and additional fuel savings. In case of emergency situations, gas leaks, the security system automatically stops the gas supply and prevents the possibility of accidents.
Many enterprises, having adjusted to today's conditions and having calculated the economic benefits, are moving away from centralized heating supply and from remote and energy-intensive boiler houses.
The advantages of decentralized heat supply are:
no need for land allocation for heating networks and boiler houses;
reduction of heat losses due to the lack of external heating networks, reduction of network water losses, reduction of water treatment costs;
significant reduction in costs for equipment repair and maintenance;
full automation of consumption modes.
If we take into account the lack of autonomous heating from small boiler houses and relatively low chimneys and the resulting environmental damage, then a significant reduction in gas consumption associated with the dismantling of the old boiler house also reduces emissions by 7 times!
Despite all the advantages, decentralized heat supply also has negative sides. In small boiler houses, including “roof” ones, the height of the chimneys, as a rule, is much lower than in large ones, due to the sharply worsening dispersion conditions. In addition, small boiler houses are usually located near residential areas.
The introduction of programs for the decentralization of heat sources makes it possible to halve the need for natural gas and reduce costs for heat supply to end consumers several times. The principles of energy saving embedded in the current heat supply system of Ukrainian cities stimulate the emergence of new technologies and approaches that can solve this problem fully, and the economic efficiency of diesel fuel makes this area very attractive for investment.
The use of apartment-by-apartment heat supply systems for multi-storey residential buildings makes it possible to completely eliminate heat losses in heating networks and during distribution between consumers, and to significantly reduce losses at the source. Allows you to organize individual accounting and regulation of heat consumption depending on economic capabilities and physiological needs. Apartment heating supply will lead to a reduction in one-time capital investments and operating costs, and also allows saving energy and raw materials for the production of thermal energy and, as a consequence, leads to a reduction in the load on the environmental situation.
Apartment system heat supply is an economically, energetically, environmentally effective solution to the issue of heat supply for multi-storey buildings. And yet, it is necessary to conduct a comprehensive analysis of the effectiveness of using a particular heat supply system, taking into account many factors.
Thus, analysis of the components of losses during autonomous heat supply allows:
1) for the existing housing stock, increase the energy efficiency coefficient of heat supply to 0.67 versus 0.3 for centralized heat supply;
2) for new construction, only by increasing the thermal resistance of enclosing structures, increase the energy efficiency coefficient of heat supply to 0.77 versus 0.45 for centralized heat supply;
3) when using the entire complex of energy-saving technologies, increase the coefficient to 0.85 versus 0.66 with centralized heat supply.
3.2 Energy efficient solutions for diesel fuel
With autonomous heat supply, it is possible to use new technical and technological solutions that make it possible to completely eliminate or significantly reduce all unproductive losses in the chain of heat generation, transportation, distribution and consumption, and not just by building a mini-boiler house, but by using new energy-saving and effective technologies, such as:
1) transition to fundamentally new system quantitative regulation of heat production and supply at the source;
2) effective use of variable frequency electric drives on all pumping units;
3) reducing the length of circulation heating networks and reducing their diameter;
4) refusal to build central heating points;
5) transition to a fundamentally new scheme of individual heating points with quantitative and qualitative regulation depending on the current outside air temperature using multi-speed mixing pumps and three-way regulator valves;
6) installation of a “floating” hydraulic mode of the heating network and complete rejection of hydraulic linkage of consumers connected to the network;
7) installation of control thermostats on apartment heating devices;
8) apartment-by-apartment wiring of heating systems with installation individual meters heat consumption;
9) automatic maintenance of constant pressure on hot water supply devices for consumers.
The implementation of these technologies allows, first of all, to minimize all losses and creates conditions for the coincidence in time of the regimes of the amount of generated and consumed heat.
3.3 Benefits of decentralized heating
If we trace the entire chain: source-transport-distribution-consumer, we can note the following:
1 Heat source - significantly reduced heat dissipation land plot, the construction part becomes cheaper (no foundations are required for the equipment). The installed power of the source can be chosen to be almost equal to the consumed one, while it is possible not to take into account the load of hot water supply, since during peak hours it is compensated by the storage capacity of the consumer’s building. Today it is a reserve. The regulation scheme is simplified and made cheaper. Heat losses are eliminated due to the discrepancy between production and consumption modes, the correspondence of which is established automatically. In practice, only losses associated with the efficiency of the boiler unit remain. Thus, it is possible to reduce losses at the source by more than 3 times.
2 Heating network- the length is reduced, the diameters are reduced, the network becomes more maintainable. Constant temperature conditions increase the corrosion resistance of the pipe material. The amount of circulating water and its losses through leaks are reduced. There is no need to construct a complex water treatment scheme. There is no need to maintain a guaranteed pressure drop before connecting the consumer, and therefore there is no need to take measures for hydraulic linking of the heating network, since these parameters are set automatically. Experts imagine what a difficult problem it is to annually carry out hydraulic calculations and carry out work on hydraulic connection of an extensive heating network. Thus, losses in heating networks are reduced by almost an order of magnitude, and in the case of installing a rooftop boiler room for one consumer, these losses are absent at all.
3 Distribution systems central heating and heating substations. Required
