Schematic diagrams of open and closed heat supply systems. Heat supply closed and open heat supply systems - heat supply using hot water coolant or steam for heating, ventilation, hot water supply systems
Topic 6 Heat supply systems
Classification of heat supply systems.
Thermal schemes of heat sources.
Water systems.
Steam systems.
Air systems.
The choice of heat carrier and heat supply system.
Classification of heat supply systems (ST)
Heat supply system (ST) is a set of heat sources, devices for heat transport (heat networks) and heat consumers.
The heat supply system (ST) consists of the following functional parts:
Source of heat energy production (boiler house, CHPP);
Transporting devices of thermal energy to the premises (heat networks);
Heat-consuming devices that transfer thermal energy to the consumer (heating radiators, heaters).
Heat supply systems (ST) are divided into:
1. At the place of heat generation at:
centralized and decentralized.
In decentralized systems the source of heat and heat sinks of consumers are combined in one unit or are close to each other, therefore, special devices for heat transport (heating network) are not required.
In a centralized system The source and consumers of heat supply are significantly removed from each other, so heat is transferred through heating networks.
Systems decentralized heat supplies are divided into individual and local .
ATindividual systems, the heat supply of each room is provided from a separate own source (stove or apartment heating).
ATlocal systems, heating of all premises of the building is provided from a separate common source (house boiler).
centralized heat supply can be divided into:
- for group - heat supply from one source of a group of buildings;
- regional - heat supply from one source of the district of the city;
- urban - heat supply from one source to several districts of the city or even the city as a whole;
- intercity - heat supply from one source of several cities.
2. according to the type of transported coolant :
steam, water, gas, air;
3. According to the number of pipelines for transferring the coolant to:
- one-, two- and multi-pipe;
4. according to the method of connecting hot water supply systems to heating networks:
-closed(water for hot water supply is taken from the water supply and heated in a heat exchanger network water);
- open(water for hot water supply is taken directly from the heating network).
5. by type of heat consumer for:
- communal - household and technological.
6. according to the schemes for connecting heating installations to:
-dependent(the coolant heated in the heat generator and transported through heating networks enters directly into the heat-consuming devices);
-independent(the coolant circulating through the heating networks in the heat exchanger heats the coolant circulating in the heating system.
Figure 6.1 - Schemes of heat supply systems
When choosing the type of coolant, it is necessary to take into account its sanitary and hygienic, technical, economic and operational indicators.
gasesare formed during the combustion of fuel, they have a high temperature and enthalpy, however, the transportation of gases complicates the heating system and leads to significant heat losses. From a sanitary and hygienic point of view, when using gases, it is difficult to ensure acceptable temperatures heating elements. However, being mixed in a certain proportion with cold air, gases in the form of a now gas-air mixture can be used in various technological installations.
Air- easily movable coolant, used in air heating systems, allows you to quite simply regulate the constant temperature in the room. However, due to the low heat capacity (about 4 times less than water), the mass of air heating the room must be significant, which leads to a significant increase in the dimensions of the channels (pipelines, ducts) for its movement, an increase in hydraulic resistance and electricity consumption for transportation. So air heating at industrial enterprises, it is carried out either combined with ventilation systems, or by installing special heating installations in workshops ( air curtains etc.).
Steamduring condensation in heating devices (pipes, registers, panels, etc.) it gives off a significant amount of heat due to the high specific heat of conversion. Therefore, the mass of steam at a given thermal load is reduced compared to other coolants. However, when using steam, the temperature of the outer surface of the heating devices will be above 100°C, which leads to the sublimation of the dust settled on these surfaces, to the release of harmful substances in the premises and the appearance of unpleasant odors. In addition, steam systems are sources of noise; the diameters of the steam pipelines are quite significant due to the large specific volume of steam.
WaterIt has a high heat capacity and density, which makes it possible to transfer large amounts of heat over long distances with low heat losses and small pipeline diameters. The surface temperature of water heating devices meets sanitary and hygienic requirements. However, the movement of water is associated with at great expense energy.
This is a system whose coolant is isolated and works exclusively for its intended purpose. It does not directly participate in the water supply, but only indirectly, it is not taken from the network by consumers. Let's just say that the "transfer" of heat for heating systems and for hot supply passes through heat exchangers. To do this, heat exchangers (heaters), pumps of various specializations, mixers, control equipment, etc. are installed in the heating units of buildings.
The list may vary depending on the type and capacity of the item. Central and individual heat points can have a different degree of automation, systems can be multi-stage and include several points on the way from the CHP to consumers. As a standard, with closed heat supply, the heat point has two circuits that ensure the transfer of heat to the heating system and the water supply system. Each circuit is equipped with a heat exchanger of the corresponding type, plate, multi-pass, etc. individually determines the project.
The liquid or antifreeze that transfers heat from the heat-preparation plant to secondary networks has a constant volume and can only be replenished by the feed system in case of losses. The heat carrier of the main line must undergo water treatment to give it the necessary properties that ensure harmlessness for network pipelines and heat exchange, both for heat points and for heat preparation facilities.
Coolant efficiency
The cycle passed by the heat carrier is a little more complicated than in an open mechanism. The cooled coolant, through the return line, enters the heating heaters or boiler rooms, where it receives the temperature from the hot process steam of turbines, condensate or is heated in the boiler. Losses, if any, are made up by the make-up liquid, thanks to the regulator. The device always maintains the set pressure, keeping its static value. If heat is received from CHP, the heat carrier is heated by steam having a temperature of 120° - 140°C.
The temperature is pressure dependent and sampling is usually done from medium pressure cylinders. Often there is only one heat extraction at the plant. The removed steam has a pressure of 0.12 - 0.25 MPa, which is increased (with controlled extraction) during seasonal cooling or steam consumption for aeration. When it gets cold, the liquid can be heated up by the peak boiler. An aerator can be connected to one of the turbine outlets, and chemically treated, treated water enters the feed tank. The heat removed for consumers, obtained from steam condensates and steam, is regulated qualitatively, that is, with a constant volume of the carrier, only the temperature is regulated.
Through the network pipeline, the coolant enters the heating unit, where the heating circuits form the required temperature. The water supply circuit does this with the help of a circulation line and a pump, having received water heated by a heat exchanger and mixing it with tap water and cooling water in pipes. The heating one has its own control valves, which make it possible to qualitatively influence the heat extraction. The closed system assumes independent regulation of heat extraction.
However, such a scheme does not have sufficient flexibility and must have a productive pipeline. In order to reduce investments in the heating network, a coupled regulation is organized, in which the water supply flow regulator determines the balance in the direction of one of the circuits. As a result, the heating demand is compensated from the heating circuit.
The disadvantage of such balancing is a somewhat floating temperature of heated rooms. The standards allow temperature fluctuations within 1 - 1.5 ° C, which usually occurs until the maximum consumption for water exceeds 0.6 of the calculated one for heating. As in an open heat supply system, it is possible to use a combined quality control of heat supply. When the flow rate of the coolant and the heat transfer networks themselves are calculated for the load of the heating and ventilation system, increasing the temperature of the carrier to compensate for the need for hot supply. In such a case, the thermal inertia of buildings acts as heat accumulators, leveling out temperature fluctuations caused by uneven heat extraction from the connected system.
Advantages
Unfortunately, in the post-Soviet space, heat supply to the vast majority of consumers is still organized according to the old, open scheme. A closed scheme promises a significant gain in many ways. That is why the transition to closed heating, on a national scale, can bring serious economic benefits. For example, in Russia, at the state level, the transition to a more economical option has become part of an energy-saving program for the future.
Rejection old scheme will bring a reduction in heat loss, due to the possibility of precise adjustment of consumption. Each heat point has the ability to finely regulate heat consumption by subscribers.
Heating equipment operating in the isolated mode of a closed system is much less affected by the factors introduced by an open network. The consequence of this is an extended life of boilers, heat-preparation installations and intermediate communications.
It does not require increased resistance to high pressure throughout the heat-conducting lines, this significantly reduces the accident rate of pipelines due to pressure bursts. In turn, this reduces heat loss due to leaks. As a result, savings, stability and quality of heat and hot water compensate for the shortcomings of the system. And they also exist. Procedures cannot be carried out centrally. Each individual closed circuit requires its own maintenance. Be it turbines, subscriber circuits or an intermediate line.
Each heat station is a separate unit for water treatment. Most likely, when upgrading the circuit from open to closed, in most cases it will be necessary to increase the area required for installing ITP equipment, as well as reorganize the power supply. In addition, the consumption of cold water for supplying the building increases significantly, since it is it that is used for heating in heat exchangers and further to the consumer, with independent connection of hot water. This will invariably entail the reconstruction of the water supply, for the sake of switching to closed circuit hot.
The global introduction of independent connection of hot equipment to heating networks will entail a significant increase in the load on external cold water supply networks, since consumers will have to be fed with increased volumes required for hot water supply, which are now provided through heating networks. For many localities, this will become a serious obstacle to modernization. Additional equipment with pumping units in hot supply and circulation installations, in the heating mechanisms of buildings will cause an additional load on the electrical networks and it is also impossible to do without their reconstruction.
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 district heating systems connected to CHPs, two methods of hot water supply (DHW) to consumers are used: preparing water of the required quality and heating it at the CHP, followed by hot water dissipation by consumers directly from the heating network (c) and heating of tap drinking water before being supplied to consumers by the network water in surface heat exchangers of local heating points ().
Historically, these two methods of hot water supply are used equally in domestic heating systems: for example, Moscow has the world's largest closed heat supply system, and the world's largest open system. Each of these two heating systems has its own advantages and disadvantages. The discussion about which of these two systems is better began with the polemics of the patriarchs of district heating, professors S.F. Kopiev and E.Ya. Sokolov in the 40-50s. last century and continues to this day. The procedure for choosing heat supply systems for new design has long been regulated by imperfect recommendations, in which one of the most important factors in choosing the type of system was chemical composition impurities in the source water of the city water supply.
Closed heat supply 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 combined generation of electric and thermal energy through the use of low-grade heat sources to heat large amounts of make-up water for the heating network at CHPPs.
One example of the rational use of low-potential heat can serve in St. Petersburg with a flow rate of feed water from the heating network of several thousand tons per hour. Heating of the source water in front of the make-up water vacuum deaerators at this CHPP is carried out only by the exhaust steam of three T-250-240 turbines in built-in condenser bundles, and the heating of water used as a heating agent in vacuum deaerators is carried out by steam from highly economical heating extractions of one of the turbines in accordance with with a solution. Thus, the use of open heat supply systems is currently particularly relevant due to the ever-increasing requirements for energy efficiency in all sectors of the domestic economy.
Over the years, however, there have been calls to eliminate the existing open heating systems due to some disadvantage, for example, due to the more complex hydraulic regime of these systems or under the pretext of improving the quality of hot water. Especially often the question of the elimination of open systems has been raised recently. These appeals come from "specialists" and managers who have a poor idea of the basics of the operation of CHPPs and heating systems in general. I was especially struck by the recent release of the Federal Law “On Amendments to Certain Legislative Acts of the Russian Federation in connection with the adoption,” in which its unknown authors wrote: “From January 1, 2013, the connection of objects capital construction consumers to centralized open systems of heat supply (hot water supply) for the needs of hot water supply, carried out by selecting a 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 the needs of hot water supply, carried out by taking the coolant for the needs of hot water supply, is not allowed.
The law was adopted ostensibly in connection with 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 this law, I did not find there 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 nothing is done lightly in the modern era of wild capitalism (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 facilities 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 practical implementation similar innovations. So, only at one, already mentioned, Yuzhnaya CHPP, the refusal to prepare make-up water for an open heat supply system would lead to an annual overrun of more than 100 thousand tons of fuel equivalent.
One of the main arguments of the supporters of closed systems is the allegedly 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 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 and 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 DHW heaters, there are huge overflows of non-deaerated tap water into the heating network, leading to intense internal corrosion of heating network pipelines. In a number of cases, the flow of non-deaerated water into the heating network makes the high-quality deaeration of small amounts of make-up water at the CHPP practically useless. It is for this reason, as shown by the results of the VTI conducted in the early 90s. large-scale survey of domestic heating systems, the intensity of internal corrosion in open and closed systems is approximately the same. Moreover, when the pressure of the heating network water exceeds the pressure of the heated tap water, unregulated flows of network water that do not meet drinking water quality standards occur in hot water pipelines supplied to consumers, i.e. sanitary and hygienic requirements for hot water supply are not met. These flows are, in essence, 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 heat networks. In closed systems, a significant part of these losses are accounted for by the flow of network water through leaks in heaters to local DHW systems. In this regard, one can hardly speak of increased sanitary and epidemiological safety of such systems.
In open systems, where potable water is used as source water for making 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 disadvantages are practically eliminated.
In connection with the above arguments, paragraphs. 3.1.3 SanPiN, which states that from the sanitary and epidemiological standpoint the most reliable systems centralized hot water supply connected to closed heating systems.
Arguments about the instability of the hydraulic regimes of open systems are becoming less relevant at the present time. The presence of a large fleet of modern automatic control devices and their wide distribution in heat supply systems makes it possible to reliably compensate for the influence of variable water flow rates in network highways.
An attempt was 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 heating 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 CHP turbines to prepare a large amount of make-up water for the heating system. 2. Maintaining the high quality of network water in the entire heat supply system and in local heating and hot water systems of consumers due to the possibility of highly efficient centralized anti-scale and anti-corrosion treatment of make-up water at the CHPP. 3. Low cost of local heating points of consumers. disadvantages 1. A more complex hydraulic mode of the system due to the difference in network water flow rates in the supply and return lines (the disadvantage is overcome by using modern devices for automatic mode control). 2. The high cost of equipment for the preparation of a large amount of make-up water for the heating system at the CHPP. |
Advantages
1. Stable hydraulic mode of the system due to approximately the same consumption of network water in the supply and return lines. 2. Low cost installation for the preparation of a small amount of make-up water for a heating network at a CHP plant. disadvantages 1. Reduced energy efficiency of the system due to limited possibilities of using low-grade heat sources at CHP. 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 in case of unregulated overflows 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 DHW systems. |
For decades of production and scientific work I have heard many times in various government offices proposals, and even demands for the transfer of existing open systems to closed ones. Fortunately, so far, it seems, in none of the cities of the country, no one has gotten around to implementing these requirements. I have no doubt that the above provisions of the law on the prohibition of 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 the source water in the water supply sources of specific cities.
It should also be noted that a necessary condition for the energy efficient operation of heating systems with open water intake is the use of vacuum deaeration make-up water of the heating system. It is the use of low-potential heat sources, incl. exhaust steam of turbines for heating coolants in front of vacuum deaerators of make-up water allows you to maximize the effect of heating at thermal power plants.
Experts have proved that the competent use of vacuum deaerators in open heat supply systems ensures high quality of anti-corrosion treatment of make-up water, a significant increase in the thermal efficiency of CHPPs, and the elimination of losses of heating steam condensate, which is typical for atmospheric deaerators, reduction of capital costs for deaeration plants, as well as complete environmental safety of hot water supply in open heating systems.
It seems to me that the provisions on the gradual ban on open heating 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 heating systems. Today we should not deny everything positive that has been achieved in the domestic thermal power industry and heat supply. I believe that the initiative in this matter should be taken by NP "Russian Heat Supply", which has recently been the most authoritative organization for coordinating technical policy in the field of heat supply.
findings
1. Open heat supply systems, in contrast to closed systems, make it possible to maximize the effect of combined generation of electric and thermal energy through the use of low-grade heat sources to heat large amounts of make-up water for the heating network at CHPPs. The use of open heat supply systems is currently particularly relevant due to the ever-increasing requirements for energy efficiency in all sectors of the domestic economy.
2. In open heat supply systems, the high quality of network water is maintained throughout the entire heat supply system and in local heating and hot water systems of consumers due to the possibility of highly efficient centralized anti-scale and anti-corrosion treatment of make-up water at CHPPs.
3. Open heat supply systems are more reliable than closed systems in sanitary and epidemiological terms due to the exclusion of ingress into local DHW systems of network water that does not meet the drinking water quality criteria through leaks in DHW heaters.
Literature
2. Patent No. 1366656 (USSR). IPC F01K17/02. Thermal power plant / V.I. Sharapov//Discoveries. Inventions. 1988. No. 2.
3. Federal Law of the Russian Federation of November 23, 2009 No. 261-FZ “On Energy Saving and Energy Efficiency Improvement and on Amendments to Certain Legislative Acts of the Russian Federation”.
4. Federal Law No. 417-FZ dated December 7, 2011 “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 No. 416-FZ of 07.12.2011 “On Water Supply and Sanitation”.
6. Sharapov V.I. On the prevention of internal corrosion of the heating system in closed heat supply systems. Teploenergetika. 1998. No. 4. S. 16-19.
7. Sanitary and epidemiological rules and regulations SanPiN 2.1.4.1074-01. Drinking water and water supply of populated areas. Drinking water. Hygienic requirements for water quality of centralized drinking water supply systems. Quality control. // M.: Ministry of Health of Russia. 2002.
10. Sharapov V.I. Actual problems of using vacuum deaerators in open heat supply systems. Teploenergetika. 1994. No. 8. S. 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. Izvestiya vuzov. 2000. No. 5-6. pp. 3-8.
Energy saving in heat supply systems
Completed by: students of group T-23
Salazhenkov M.Yu.
Krasnov D.
Introduction
Today, the energy saving policy is a priority direction in the development of energy and heat supply systems. In fact, every state enterprise draws up, approves and implements plans for energy saving and energy efficiency improvement of enterprises, workshops, etc.
The country's heating 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 complexes 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 household (heating, ventilation, hot water supply) and technological needs of consumers.
In most cases, heat supply is the creation of a comfortable indoor environment - at home, at work or in a public place. Heat supply also includes heating of tap water and water in swimming pools, heating of greenhouses, etc.
The distance over which heat is transported in modern district heating systems reaches several tens of kilometers. The development of heat supply systems is characterized by an increase in the power of the heat source and unit capacities of the installed equipment. Thermal power of modern thermal power plants reaches 2-4 Tkal/h, regional boiler houses 300-500 Gkal/h. In some heat supply systems, several heat sources work together for common heat networks, which increases the reliability, flexibility and efficiency of heat supply.
The water heated in the boiler room can circulate directly to 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. The 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. The temperature difference can also be achieved by using a three-way valve that mixes 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 for the main type of heat load - heating or for a combination of two types of load - heating and hot water supply. It consists in changing the temperature of the heat carrier supplied from the heat supply source to the heat 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 supplemented by local quantitative regulation in heating points; the latter is most common in hot water applications and is usually carried out automatically. In steam heating 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 heat energy production (boiler house, thermal power plant, solar collector, devices for the utilization of industrial heat waste, installations for the use of heat from geothermal sources);
2) transporting devices of thermal energy to the premises (heating networks);
3) heat-consuming devices that transfer thermal energy to the consumer (heating radiators, heaters).
1.2 Classification of heating systems
According to the place of heat generation, heat supply systems are divided into:
1) centralized (the source of heat energy production works for the heat supply of a group of buildings and is connected by transport devices with heat consumption devices);
2) local (the consumer and the source of heat supply are located in the same room or in close proximity).
The main advantages of district heating over local heating are a significant reduction in fuel consumption and operating costs (for example, by automating boiler plants and increasing their efficiency); the possibility of using low-grade fuel; reducing the degree of air pollution and improving the sanitary condition of populated areas. In local heating systems, heat sources are furnaces, hot water boilers, water heaters (including solar), etc.
According to the type of heat carrier, heat supply systems are divided into:
1) water (with temperature up to 150 °C);
2) steam (pressure 7-16 atm).
Water serves mainly to cover domestic, and steam - technological loads. The choice of temperature and pressure in heat supply systems is determined by the requirements of consumers and economic considerations. With an increase in the distance of heat transportation, an economically justified increase in the parameters of the coolant increases.
According to the method of connecting the heating system to the heat supply system, the latter are divided into:
1) dependent (the heat carrier heated in the heat generator and transported through heat networks enters directly into heat-consuming devices);
2) independent (the heat carrier circulating through the heating networks heats the heat carrier circulating in the heating system in the heat exchanger). (Fig.1)
In independent systems, consumer installations are hydraulically isolated from the heating network. Such systems are mainly used in large cities - in order to increase the reliability of heat supply, as well as in cases where the pressure regime in the heat network is unacceptable for heat-consuming installations due to their strength or when the static pressure created by the latter is unacceptable for the heat network ( such are, for example, the heating systems of high-rise buildings).
Figure 1 - Schematic diagrams of 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 heat supply system:
1) closed;
2) open.
In closed systems, hot water supply is supplied with water from the water supply, heated to the required temperature by water from the heating network in heat exchangers installed in heating points. In open systems, water is supplied directly from the heating network (direct water intake). Water leakage due to leaks in the system, as well as its consumption for water intake, are compensated by additional supply of an appropriate amount of water to the heating network. To prevent corrosion and scale formation on the inner surface of the pipeline, the water supplied to the heating network undergoes water treatment and deaeration. In open systems, the water must also meet the requirements for drinking water. The choice of system is determined mainly by the presence of a sufficient amount of water of drinking quality, its corrosive and scale-forming properties. Both types of systems have become widespread in Ukraine.
According to the number of pipelines used to transfer the coolant, heat supply systems are distinguished:
single-pipe;
two-pipe;
multipipe.
Single-pipe systems are used in cases where the coolant is completely used by consumers and is not returned back (for example, in steam systems without condensate return and in open water systems, where all the water coming from the source is taken apart for hot water supply to consumers).
In two-pipe systems, the heat carrier is fully or partially returned to the heat source, where it is heated and replenished.
Multi-pipe systems suit, if necessary, the allocation of certain types of heat load (for example, hot water supply), which simplifies the regulation of heat supply, operation mode and methods of connecting consumers to heating networks. In Russia, two-pipe heat supply systems are predominantly used.
1.3 Types of heat consumers
The heat consumers of the heat supply system are:
1) heat-using sanitary systems of buildings (systems of heating, ventilation, air conditioning, hot water supply);
2) technological installations.
The use of hot water for space heating is quite common. At the same time, a variety of methods for 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 floor heating, when the heating circuits are located under the floor. The floor heating circuit is usually connected to the heating radiator circuit.
Ventilation - a fan coil unit that supplies hot air to a room, usually used in public buildings. Often a combination of heating devices is used, for example, radiators for heating and underfloor heating or radiators for heating and ventilation.
Hot tap water has become part of everyday life and daily needs. Therefore, a hot water installation must be reliable, hygienic and economical.
According to the mode of heat consumption during 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 - 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 ratio 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 plant between multiple buildings. There is a very wide range of sources that serve to generate heat, including the burning of oil and natural gas or the use of geothermal waters. The use of heat from low temperature sources, such as geothermal heat, is possible with the use of heat exchangers and heat pumps. The possibility of using non-utilized heat from industrial enterprises, surplus heat from waste processing, industrial processes and sewerage, target heating plants or thermal power plants in district heating, allows for the optimal choice of heat source in terms of energy efficiency. This way you optimize costs and protect the environment.
Hot water from the boiler house is fed to a heat exchanger that separates the production site from the distribution pipelines of the district heating network. The heat is then distributed to the final consumers and fed through the substations to the respective buildings. Each of these substations usually includes one heat exchanger for space heating and hot water.
There are several reasons for installing heat exchangers to separate a heating plant from a district heating network. Where significant pressure and temperature differences exist that could cause serious damage to equipment and property, a heat exchanger can protect sensitive heating and ventilation equipment from the ingress of contaminated or corrosive media. Another important reason for separating the boiler house, distribution network and end users is to clearly define the functions of each component of the system.
In a combined heat and power plant (CHP), heat and electricity are produced simultaneously, with heat being the by-product. Heat is usually 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%. The efficiency will be 35–40% higher than in the case of separate production of heat and electricity.
In CHP plants, fuel combustion heats water, which turns into steam at high pressure and high temperature. The steam drives a turbine connected to a generator that produces electricity. After the turbine, the steam is condensed in a heat exchanger. The heat released during this process is then fed into the district heating pipes and distributed to the final consumers.
For the end consumer, district heating means uninterrupted energy supply. A district heating system is more convenient and efficient than small individual home heating systems. Modern fuel combustion and emission treatment technologies reduce negative impact on the environment.
In apartment buildings or other buildings heated by district heating, 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 the safety of the internal system by separating end users from the distribution network. This is necessary because of the significant difference in temperature and pressure values. 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 the hot water system. It is particularly advantageous in combined heat and power plant applications where a low return water temperature is 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 - Scheme of connecting heat exchangers
Parallel connection of a DHW heat exchanger (Fig.2, B) is less complicated than a two-stage connection and can be applied to any size plant that does not need a low return water temperature. Such a 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 heaters in accordance with SP 41-101-95.
Most district heating systems place high demands on the installed equipment. The equipment must be reliable and flexible, providing the necessary safety. 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 district heating system is in a deplorable state:
technical equipment and the level of technological solutions in the construction of heat 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 pipelines, thermal insulation, shut-off and control valves, construction and laying of heat pipelines are significantly inferior to foreign counterparts, which leads to large losses of thermal energy in networks;
poor conditions for thermal and waterproofing of heat pipelines and channels of heat networks contributed to an increase in the damage of underground heat pipelines, which led to serious problems in replacing the equipment of heat networks;
domestic equipment of large CHPPs corresponds to the average foreign level of the 1980s, and at present, steam turbine CHPPs are characterized by a high accident rate, since almost half of the installed capacity of the turbines has reached the design resource;
operating coal-fired CHP plants do not have flue gas purification systems from NOx and SOx, and the efficiency of trapping particulate matter often does not reach the required values;
The competitiveness of DH at the present stage can only be ensured by the introduction of specially new technical solutions, both in terms of the structure of systems, and in terms of schemes, equipment of energy sources and heating networks.
2.2 Efficiency of district heating systems
One of the most important conditions for the normal operation of the heat supply system is the creation of a hydraulic regime that provides pressure in the heat network sufficient to create network water flows in heat-consuming installations in accordance with a given heat load. The normal operation of heat consumption systems is the essence of providing consumers with thermal energy of the appropriate quality, and for the energy supply organization it consists in maintaining the parameters of the heat supply mode at the level regulated by the Rules for Technical Operation (PTE) of power plants and networks of the Russian Federation, PTE of thermal power plants. The hydraulic regime is determined by the characteristics of the main elements of the heat supply system.
During operation in the existing district heating system, due to a change in the nature of the heat load, the connection of new heat consumers, an increase in the roughness of pipelines, adjustments of the calculated temperature for heating, changes in the temperature schedule for the release of heat energy (TE) from the TE source, as a rule, uneven heat supply occurs consumers, overestimating network water costs and reducing pipeline throughput.
In addition to this, as a rule, there are problems in the heating systems. Such as misregulation of heat consumption modes, understaffing elevator nodes, unauthorized violation by consumers of connection schemes (established by projects, specifications and contracts). These problems of heat consumption systems are manifested, first of all, in the misregulation of the entire system, which is characterized by increased coolant flow rates. As a result, insufficient (due to increased pressure losses) available pressures of the coolant at the inlets, which in turn leads to the desire of subscribers to provide the necessary drop by draining the network water from the return pipelines to create at least a minimum circulation in the heating appliances (violations of connection schemes and etc.), which leads to an additional increase in flow and, consequently, to additional pressure losses, and to the emergence of new subscribers with reduced pressure drops, etc. There is a "chain reaction" in the direction of a total misalignment 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 when the water treatment capacity is exhausted, forced replenishment with raw water (consequence - 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 should be pointed out that in the heat supply system there is always an interrelation of steady-state thermal and hydraulic regimes. A change in the flow distribution (including its absolute value) always changes the heat exchange condition, both directly in heating installations and in heat consumption systems. The result of abnormal operation of the heat supply system is, as a rule, a high temperature of the 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 operational characteristics designed to analyze the state of the equipment of thermal networks and the modes of operation of the heat supply system, as well as to assess the effectiveness of measures taken by organizations operating thermal networks in order to increase the level operation of the heating system. As a rule, in the case of misalignment of the heat supply system, the actual value of this temperature differs significantly from its normative, calculated value for this heat supply system.
Thus, when the heat supply system is misaligned, 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, almost in all intervals of the heating season, it is 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 the connected heat load) characterizes the quality level of thermal energy consumption, is underestimated in comparison with the required values.
It should be noted one more aspect related to the increase relative to the calculated value of network water consumption for the thermal regime of heat consumption systems (heating, ventilation). For direct analysis, it is advisable to use the dependence that determines, in the event of a deviation of the actual parameters and structural elements of the heat supply system from the calculated ones, the ratio of the actual heat energy consumption in heat consumption systems to its calculated value.
where Q is the consumption of thermal energy in heat consumption systems;
g - consumption of network water;
tp and tо - temperature in the supply and return pipelines.
This dependence (*) is shown in Fig.3. The ordinate shows the ratio of the actual consumption of thermal energy to its calculated value, the abscissa shows the ratio of the actual consumption of network water to its calculated value.
Figure 3 - Graph of the dependence of the consumption of thermal energy by systems
heat consumption from the consumption of network water.
As general trends, it is necessary to point out that, firstly, an increase in network water consumption by n times does not cause an increase in thermal energy consumption corresponding to this number, that is, the heat consumption coefficient lags behind the network water consumption coefficient. Secondly, with a decrease in the consumption of network water, the supply of heat to the local heat consumption system decreases the faster, the lower the actual consumption of network water compared to the calculated one.
Thus, heating and ventilation systems react very poorly to excessive consumption of network water. Thus, an increase in the consumption of network water for these systems by 50% relative to the calculated value causes an increase in heat consumption by only 10%.
The point in Fig. 3 with coordinates (1; 1) displays the calculated, actually achievable mode of operation of the heat supply system after commissioning. Under the actually achievable mode of operation is meant such a mode, which is characterized by the existing position of the structural elements of the heat supply system, heat losses by buildings and structures and determined by the total consumption of network water at the outlets of the heat source, necessary to provide a given heat load with the existing heat supply schedule.
It should also be noted that the increased consumption of network water, due to the limited capacity of heat networks, leads to a decrease in the available pressures at the consumer inlets necessary for the normal operation of heat-consuming equipment. It should be noted that the pressure loss in the heating network is determined by a quadratic dependence on the network water flow:
That is, with an increase in the actual consumption of network water GF by 2 times relative to the calculated value GP, the pressure losses in the heating network increase by 4 times, which can lead to unacceptably small available pressures at the thermal nodes of consumers and, consequently, to insufficient heat supply to these consumers, which can cause unauthorized discharge of network water to create circulation (unauthorized violation by consumers of connection schemes, etc.)
Further development of such a heat supply system along the path of increasing the flow rate of the coolant, firstly, will require the replacement of the head sections of the heat pipelines, the additional installation of network pumping units, an increase in the productivity of water treatment, etc., and secondly, it leads to an even greater increase in additional costs - the cost of compensation for electricity, make-up water, heat losses.
Thus, it seems technically and economically more justified 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 consumption (circulation and make-up) in heat consumption systems and , respectively, in the entire heating system.
Thus, the main measure that can be proposed to optimize such a heat supply system is the adjustment of the hydraulic and thermal regime of the heat supply system. The technical essence of this measure is to establish the 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 consumption for each heat consumption system. This is achieved by installing appropriate throttling devices (autoregulators, throttle washers, elevator nozzles), the calculation of which is 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 measures, it is also necessary to carry out work to optimize the hydraulic mode of the heat supply system.
Regime adjustment covers the main links of the district heating system: a water-heating installation of a heat source, central heating points (if any), a heat network, control and distribution points (if any), individual heating points and local heat consumption systems.
Commissioning begins with an inspection of the district heating system. The collection and analysis of initial data on the actual operating modes of the system of transport and distribution of heat energy, information on the technical condition of heat networks, the degree of equipment of the heat source, heat networks and subscribers with commercial and technological measuring instruments is carried out. The applied modes of heat energy supply are analyzed, possible defects in the design and installation are identified, information is selected to analyze the characteristics of the system. The analysis of operational (statistical) information (sheets of registration of coolant parameters, modes of supply and consumption of energy, actual hydraulic and thermal modes of heating networks) is carried out at various values of the outdoor temperature in the base periods, obtained from the readings of standard measuring instruments, and an analysis of reports of specialized organizations is carried out .
At the same time, a design scheme for heat 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 operation of the heat supply system.
It should be pointed out that there is a fairly common approach, which consists in minimizing the financial costs associated with the development of measures to adjust and optimize the heat supply system, namely, the costs are limited to the acquisition of a specialized software package.
The "pitfall" in this approach is the reliability of the original data. The mathematical model of the 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 DH systems
Recently, there have been criticisms of district heating based on cogeneration - the joint generation of heat and electricity. As the main disadvantages, there are large heat losses in pipelines during heat transport, a decrease in the quality of heat supply due to non-compliance with the temperature schedule and the required pressure from 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 with lower cost and no need to lay heat pipelines. But at the same time, as a rule, it is not taken into account that the connection of the heat load to the boiler room makes it impossible to generate cheap electricity for heat consumption. Therefore, this part of the ungenerated electricity should be replaced by its production by the condensation cycle, the efficiency of which is 2-2.5 times lower than that of the heating cycle. Consequently, the cost of electricity consumed by the building, the heat supply of which is carried out from the boiler house, should be higher than that of the building connected to the heating system of heat supply, 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, suggested that home boiler houses complement district heating, acting as peak heat sources, where the lacking capacity of networks does not allow for high-quality supply consumer heat. At the same time, heat supply is preserved and the quality of heat supply is improved, but this decision reeks of stagnation and hopelessness. It is necessary that the district heating supply fully performs its functions. Indeed, 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 capacity of the networks is insufficient, then it is necessary to shift the networks or cut off this load from the networks so that it does not violate the quality of heat supply to other consumers.
Great success in district heating has been achieved by Denmark, which, despite the low concentration of heat load per 1 m2 of surface area, is ahead of us in terms of district heating coverage per capita. Denmark is holding a special public policy by preference for connecting new heat consumers to district heating. In Western Germany, for example in Mannheim, district heating based on district heating is developing rapidly. In the Eastern lands, where, focusing on our country, heat supply was also widely used, despite the rejection of panel housing construction, central heating in residential areas that turned out to be inefficient in a market economy and the Western way of life, the area of centralized heat supply based on heat supply 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 positions in the field of district heating, and for this it is necessary to modernize the district heating system in order to increase its attractiveness and efficiency.
All the advantages of joint generation of heat and electricity were attributed to electricity, district heating was financed according to the residual principle - sometimes the CHP had already been built, but the heating networks had not yet been brought up. As a result, low-quality heat pipelines with poor insulation and inefficient drainage were created, heat consumers were connected to heat networks without automatic load control, at best, using hydraulic regulators for stabilizing the coolant flow of very poor quality.
This forced the supply of heat from the source according to the method of central quality control (by changing the temperature of the heat carrier depending on outdoor 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 mode and the impossibility of joint operation of several heat sources on a single network for mutual redundancy. The absence or inefficiency of the operation of control devices at the points of connection of consumers to heating networks also caused an overrun of the volume of the coolant. This led to an increase in the return water temperature to such an extent that there was a danger of failure of the station circulating pumps and this forced the reduction of heat supply at the source, violating the temperature schedule even in conditions of sufficient power.
Unlike us, in Denmark, for example, all the benefits of district heating in the first 12 years are given to the side of thermal energy, and then they are divided in half with electrical energy. As a result, Denmark was the first country where prefabricated insulated pipes for channelless laying with a sealed cover layer and an automatic leak detection system, which dramatically reduced heat loss during its transportation. In Denmark, for the first time, silent, supportless "wet-running" circulation pumps, heat metering devices and effective systems for auto-regulating the heat load were invented, which made it possible to build automated individual heating points (ITP) directly in the buildings of consumers with automatic control of the supply and metering of heat in places of its use.
Total automation of all heat consumers made it possible: to abandon the qualitative method of central regulation at the heat source, which causes undesirable temperature fluctuations in the pipelines of the heating network; reduce the maximum water temperature parameters to 110-1200C; ensure the possibility of operation of several heat sources, including waste incinerators, on a single network with the most efficient use of each.
The temperature of the water in the supply pipeline of heating networks varies depending on the level of the established outdoor temperature in three steps: 120-100-80°C or 100-85-70°C (there is a tendency to an even greater decrease in this temperature). And inside each stage, depending on the change in load or the deviation of 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 the set value, then the subsequent heat generating and pumping stations are switched on installation. 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 steps are used, which is apparently caused by the boundaries of property ownership. Thus, the following connection scheme was demonstrated: to the main networks with design parameters of 125 ° C, which are administered by the energy producer, through a heat exchanger, after which the temperature of the water in the supply pipeline drops to 120 ° C, distribution networks are connected, which are in municipal ownership.
The level of maintenance of this temperature is set by an electronic regulator that acts on a valve installed on the return pipeline of the primary circuit. In the secondary circuit, the coolant is circulated by pumps. Connection to these distributing networks of local heating and hot water supply systems of individual buildings is carried out through independent heat exchangers installed in the basements of these buildings with a full range of heat control and metering devices. Moreover, the regulation of the temperature of the water circulating in the local heating system is carried out according to the schedule, depending on the change in the temperature of the outside air. Under design conditions, the maximum water temperature reaches 95°C, recently there has been a tendency to decrease it to 75-70°C, the maximum return water temperature is 70 and 50°C, respectively.
The connection of heating points of individual buildings is carried out according to standard schemes with parallel connection of a hot water storage tank or according to a two-stage scheme using the potential of the heat carrier from the return pipeline after the heating water heater using high-speed hot water heat exchangers, while it is possible to use a hot water pressure storage tank with a pump for tank charging. In the heating circuit, pressurized membrane tanks are used to collect water when it expands from heating; in our case, atmospheric expansion tanks installed at the top of the system are more used.
To stabilize the operation of the control valves at the inlet to the heating point, a hydraulic regulator for the constancy of the pressure difference is usually installed. And in order to bring the heating systems with pump circulation to the 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, according to the pressure loss measured on it, to set the correct flow rate of the circulating coolant.
In Denmark, they do not pay much attention to the increase in the calculated flow rate of the heat carrier at the heating point when turning on the heating of water for domestic needs. In Germany, it is forbidden by law to take into account the load on hot water supply when selecting heat power, and when automating heating points, it is accepted that when the hot water heater is turned on and when the storage tank is filled, the pumps that circulate in the heating system are turned off, i.e., the heat supply to the heating.
In our country, great importance is also attached to preventing an increase in the power of the heat source and the estimated flow rate of the heat carrier circulating in the heating network during the hours of the 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 load ratio of hot water supply and heating, due to the large absolute consumption of household water and the higher population density.
Therefore, when automating the heat points of consumers, the limitation of the maximum water flow from the heating network is used when the specified value is exceeded, determined based on the average hourly load of the hot water supply. When heating residential areas, this is done by closing the valve of the heat supply regulator for heating during the hours of the maximum water consumption. By setting the heating controller to some overestimation of the maintained heat carrier temperature curve, the underheating in the heating system that occurs when the maximum watershed is passed is compensated during drawdown periods below the average (within the specified water flow from the heating network - coupled 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 inlet to the central heating substation or ITP. The differential pressure regulator at the inlet cannot serve as a flow limiter, since it provides a given differential pressure in conditions of full opening of the valves of the heating and hot water supply regulators installed in parallel.
In order to increase the efficiency of the joint generation of heat and electricity and equalize the maximum energy consumption in Denmark, heat accumulators, which are installed at the source, are widely used. The lower part of the accumulator is connected to the return pipeline of the heating network, the upper part is connected to the supply pipeline through a movable diffuser. With a reduction in circulation in the distribution heating networks, the tank is charged. With an increase in circulation, the 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 CHP plants with backpressure turbines, in which the ratio of generated electrical and thermal energy is fixed.
If the design temperature of the water circulating in the heat networks is below 100°C, then atmospheric storage tanks are used; at a higher design temperature, pressure is created in the tanks to ensure that hot water does not boil.
However, the installation of thermostats together with heat flow meters for 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 to 15% and there is a significant residual heat transfer of devices in the closed position of the thermostat, which reduces the efficiency of auto-regulation. Therefore, an alternative to such systems, especially in low-cost municipal construction, are façade automatic heating control systems - for extended buildings and central ones with temperature graph correction based on the deviation of air temperature in the prefabricated exhaust ventilation ducts from apartment kitchens - for point buildings or buildings with a complex configuration.
However, it must be borne in mind that when reconstructing existing residential buildings, it is necessary to enter each apartment with welding to install thermostats. At the same time, when organizing façade autoregulation, it is enough to cut jumpers between façade branches of sectional heating systems in the basement and in the attic, and for 9-story non-attic 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 indicates the importance of the reconstruction of existing buildings in order to reduce the cost of heat for heating. However, it is impossible to automate all buildings at once, and in conditions where several buildings are automated, real savings are not achieved, since the heat carrier saved at automated facilities is redistributed among non-automated ones. The above once again confirms that it is necessary to build the PDC at the existing heat networks at a faster pace, since it is much easier to automate all the buildings that are fed from one PDC than from the CHP, and other already created PDCs will not let an excess amount of 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 re-laying a large number of networks is necessary). But in the conditions of the existing system of district heating from CHP, this should have a local character. The possibility of using heat pumps, transferring part of the load to CCGTs and GTUs is not ruled out, but given the current conjuncture of prices for fuel and energy carriers, this is not always profitable.
Heat supply of residential buildings and microdistricts in our country, as a rule, is carried out through group heating points (CHP), after which individual buildings are supplied through independent pipelines with hot water for heating and domestic needs tap water, heated in heat exchangers installed in the CHP. Sometimes up to 8 heat pipelines leave the central heating center (with a 2-zone hot water supply system and a significant ventilation load), and although galvanized hot water 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, in connection with the privatization of housing and service enterprises, as well as with the increase in the cost of energy carriers, the transition from group heating points to individual (ITP) located in a heated building is relevant. This makes it possible to use a more efficient system of façade automatic heating control for long buildings or a central system with correction for the internal air temperature in point buildings, it allows to abandon hot water distribution networks, reducing heat losses during transportation and electricity consumption for domestic hot water pumping. Moreover, it is expedient to do this not only in new construction, but also in the reconstruction of existing buildings. There is such experience in the Eastern lands of Germany, where central heating stations were built in the same way as we did, but now they are left only as pumping water pumping stations (if necessary), and heat exchange equipment, together with circulation pumps, control and accounting units, are transferred to the ITP of buildings . Intra-quarter networks are not laid, hot water pipelines are left in the ground, and heating pipelines, as more durable ones, are used to supply superheated water to buildings.
In order to improve the manageability of heating networks, to which a large number of IHS will be connected, and to ensure the possibility of redundancy in automatic mode, it is necessary to return to the device of control and distribution points (CDP) at the points of connection of distribution networks to the main ones. Each KRP is connected to the main on both sides of the sectional valves and serves consumers with a thermal load of 50-100 MW. Switching electric valves at the inlet, pressure regulators, circulating-mixing pumps, a temperature regulator, a safety valve, heat and coolant consumption meters, control and telemechanics devices are installed in the KRP.
The automation circuit of the KRP ensures that the pressure is maintained at a constant minimum level in the return line; maintaining a constant predetermined pressure drop in the distribution network; reduction and maintenance of water temperature in the supply pipeline of the distribution network according to a given schedule. As a result, in the backup mode, it is possible to supply a reduced amount of circulating water with an increased temperature through the mains from the CHPP without disturbing the temperature and hydraulic regimes in the distribution networks.
KRP should be located in ground pavilions, they can be blocked with water pumping stations (this will allow in most cases to refuse to install high-pressure, and therefore noisier pumps in buildings), and can serve as the boundary of the balance sheet ownership of the heat-releasing organization and the heat-distributing one (the next boundary between the heat-distributing and the wall of the building will be the heat-using organization). Moreover, the KRP should be under the jurisdiction of the heat-producing organization, since they serve to control and reserve the main networks and provide the ability to operate several heat sources for these networks, taking into account the maintenance of the coolant parameters specified by the heat-distributing organization at the outlet of the KRP.
The correct use of the heat carrier on the part of the heat consumer is ensured by the use of effective control automation systems. Now there are a large number of computer systems that can perform any complexity of control tasks, but technological tasks and circuit solutions for connecting heat consumption systems remain decisive.
Recently, they began to build water heating systems with thermostats, which carry out individual automatic control of the heat transfer of heating devices according to 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 appliance as a share 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 rate of the coolant through the nozzle, regardless of the change in the flow rate of water circulating in the heating system. As a result, in 2-pipe heating systems, in which thermostats, when closed, lead to a reduction in the flow rate of the coolant circulating in the system, when connected to an elevator, the water temperature in the supply pipe will increase, and then in the opposite direction, which will lead to an increase in heat transfer from the unregulated part of the system (risers) and to underutilization of the coolant.
In a single-pipe heating system with permanent closing sections, when the thermostats are closed, hot water is discharged into the riser without cooling, which also leads to an increase in the water temperature in the return pipeline and, due to the constant mixing ratio in the elevator, to an increase in the water temperature 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 control the temperature of the water in the supply pipeline according to the schedule, depending on changes in the outside air temperature. Such regulation is possible by changing the circuit design 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 it through a heat exchanger with pump circulation and a control valve on network water in front of the heat exchanger. [
3 DECENTRALIZED HEATING
3.1 Development prospects decentralized heat supply
Previously decisions made on the closure of small boiler houses (under the pretext of their low efficiency, technical and environmental danger) today turned into over-centralization of heat supply, when hot water passes from the CHPP to the consumer, a path of 25-30 km, when the heat source is turned off due to non-payments or an emergency situation leads to freezing cities with millions of people.
Most of the industrialized countries went the other way: they improved the heat generating equipment by increasing the level of its safety and automation, the efficiency of gas burners, sanitary and hygienic, environmental, ergonomic and aesthetic indicators; created a comprehensive energy accounting system for all consumers; brought the regulatory and technical base in line with the requirements of expediency and convenience of the consumer; optimized the level of heat supply centralization; 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, maximum proximity of the heat source to the consumer, 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 plant 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 an apartment building is equipped with an autonomous system for providing heat and hot water, are a heating boiler, heating appliances, air supply and combustion products removal systems. The wiring is carried out using a steel pipe or modern heat-conducting systems - plastic or metal-plastic.
Traditional for our country, the system of centralized heat supply through CHP and main heat pipelines known and has a number of advantages. But in the context of the transition to new economic mechanisms, the well-known economic instability and the weakness of interregional, interdepartmental ties, many of the advantages of the district heating 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 heat pipelines has now increased to 200 registered damage per year per 100 km of heat networks. According to an emergency assessment, at least 15% of heating networks require urgent replacement. In addition to this, over the past 10 years, as a result of underfunding, the main fund of the industry has practically not been updated. As a result, heat energy losses during production, transportation and consumption reached 70%, which led to poor quality heat supply at high cost.
Organizational structure interaction between consumers and heat supply companies 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 has found itself suggests that in the near future a large-scale crisis situation in the field of heat supply will arise, the resolution of which will require enormous financial investments.
pressing question– reasonable decentralization of heat supply, apartment heat supply. Decentralization of heat supply (DT) is the most radical, efficient and cheap way to eliminate many shortcomings. Reasonable use of diesel fuel in combination with energy-saving measures in the construction and reconstruction of buildings will provide greater energy savings 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 heat supply is an autonomous supply of heat and hot water to an individual house or a separate apartment in high-rise building. The main elements of such autonomous systems are: heat generators - heating devices, pipelines for heating and hot water supply, systems for supplying fuel, air and smoke removal.
The objective prerequisites for the introduction of autonomous (decentralized) heat supply systems are:
the absence in some cases of free capacities at centralized sources;
densification of the development of urban areas with housing objects;
in addition, a significant part of the development falls on areas with undeveloped engineering infrastructure;
lower capital investment and the possibility of phased coverage of thermal loads;
ability to maintain comfortable conditions in your own apartment own will, which in turn is more attractive compared to apartments with district heating, the temperature of which depends on the directive decision on the start and end heating period;
appearance on the market of a large number of various modifications of domestic and imported (foreign) heat generators of low power.
Today, modular boiler plants have been developed and are being mass-produced, designed to organize autonomous diesel fuel. The block-modular principle of construction provides the possibility of simple construction of a boiler house of the required power. The absence of the need to lay heating mains and build a boiler house reduces the cost of communications and can significantly increase the pace of new construction. In addition, this makes it possible to use such boiler houses for the prompt provision of heat supply in emergency and emergency situations during the heating season.
Block boiler rooms are a fully functionally finished product, equipped with all necessary automation and safety devices. The level of automation ensures the smooth operation of all equipment without the constant presence of an operator.
Automation monitors the object'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 the event of emergency situations, gas leaks, the security system automatically stops the gas supply and prevents the possibility of accidents.
Many enterprises, having oriented themselves to today's conditions and having calculated the economic benefits, are moving away from centralized heat supply, from remote and energy-intensive boiler houses.
The advantages of decentralized heat supply are:
no need for land allotments for heating networks and boiler houses;
reduction of heat losses due to the absence of external heating networks, reduction of network water losses, reduction of water treatment costs;
a significant reduction in the cost of repair and maintenance of equipment;
full automation of consumption modes.
If we take into account the lack of autonomous heating from small boiler houses and relatively low chimneys and, in connection with this, environmental damage, then a significant reduction in gas consumption associated with the dismantling of the old boiler house also reduces emissions by 7 times!
With all the advantages, decentralized heat supply also has negative aspects. In small boiler houses, including "roof" ones, the height of the chimneys, as a rule, is much lower than in large ones, because of the dispersion conditions deteriorate sharply. In addition, small boiler houses are located, as a rule, near the residential area.
Implementation of programs for decentralization of heat sources makes it possible to halve the need for natural gas and several times reduce the cost of heat supply to end consumers. The principles of energy saving, incorporated in the current system of heat supply of Ukrainian cities, stimulate the emergence of new technologies and approaches that can fully solve this problem, and economic efficiency DT makes this area very attractive for investment.
The use of an apartment heating system for multi-storey residential buildings makes it possible to completely eliminate heat losses in heating networks and during distribution between consumers, and significantly reduce losses at the source. It will allow organizing individual accounting and regulation of heat consumption depending on economic opportunities and physiological needs. Apartment heating will lead to a reduction in one-time capital investments and operating costs, and also saves energy and raw materials for the generation of thermal energy and, as a result, leads to a decrease in the burden on the environmental situation.
The apartment heating system is an economically, energetically, environmentally efficient 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 the use of a particular heat supply system, taking into account many factors.
Thus, the analysis of the components of losses in autonomous heat supply allows:
1) for the existing housing stock, increase the coefficient of energy efficiency of heat supply to 0.67 versus 0.3 for district heating;
2) for new construction, only by increasing the thermal resistance of enclosing structures, increase the coefficient of energy efficiency of heat supply to 0.77 versus 0.45 for centralized heat supply;
3) when using the entire range of energy-saving technologies, increase the coefficient to 0.85 against 0.66 with district heating.
3.2 Energy efficient solutions for diesel fuel
With autonomous heat supply, new technical and technological solutions can be used to completely eliminate or significantly reduce all unproductive losses in the chain of generation, transportation, distribution and consumption of heat, and not just by building a mini-boiler house, but by the possibility of using new energy-saving and effective technologies, such as:
1) transition to fundamentally new system quantitative regulation of generation and supply of heat at the source;
2) effective use of frequency-controlled electric drive on all pumping units;
3) reducing the length of circulating heating networks and reducing their diameter;
4) refusal to build central heating points;
5) transition to a fundamentally new scheme of individual heat points with quantitative and qualitative regulation depending on the current outdoor temperature using multi-speed mixing pumps and three-way regulator valves;
6) installation of a "floating" hydraulic mode of the heating network and a complete rejection of hydraulic balancing of consumers connected to the network;
7) installation of regulating thermostats on apartment heating appliances;
8) apartment-by-apartment wiring of heating systems with the installation of individual heat consumption meters;
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 of the modes of the amount of generated and consumed heat in time.
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 cost of the construction part is reduced (no foundations are required for the equipment). The installed power of the source can be chosen almost equal to the consumed one, while it is possible to ignore the load of hot water supply, since during the maximum hours it is compensated by the storage capacity of the consumer's building. Today it is a reserve. Simplifies and reduces the cost of the control scheme. Heat losses are excluded due to the mismatch between the modes of production and consumption, the correspondence of which is established automatically. In practice, only the losses associated with the efficiency of the boiler remain. Thus, at the source it is possible to reduce losses by more than 3 times.
2 Heating networks - the length is reduced, the diameters are reduced, the network becomes more maintainable. A constant temperature regime increases the corrosion resistance of the pipe material. The amount of circulating water decreases, its losses with leaks. There is no need to build a complex water treatment scheme. There is no need to maintain a guaranteed differential pressure before entering the consumer, and in this regard, it is not necessary to take measures for the hydraulic balancing of the heating network, since these parameters are set automatically. Experts imagine what it is difficult problem- annually make hydraulic calculations and perform work on hydraulic balancing of an extensive heat network. Thus, losses in heat networks are reduced by almost an order of magnitude, and in the case of a roof-top boiler house for one consumer, these losses do not exist at all.
3 Distribution CHP systems and ITP. Required
SOURCES OF HEAT
§ 1.1. Classification of heat supply systems
Depending on the location of the heat source in relation to consumers, heat supply systems are divided into two types:
1) centralized;
2) decentralized.
1) The process of district heating consists of three operations: preparation, transport and use of the heat carrier.
The heat carrier is prepared in special heat treatment plants at CHPPs, as well as in city, district, group (quarterly) or industrial boiler houses. The coolant is transported through heating networks, and is used in consumer heat sinks.
In district heating systems, the heat source and heat sinks of consumers are located separately, often at a considerable distance, so heat is transferred from the source to consumers through heating networks.
Depending on the degree of centralization, district heating systems can be divided into the following four groups:
- group - heat supply of a group of buildings;
- district - heat supply of several groups of buildings (district);
- urban - heat supply of several districts;
- intercity - heat supply of several cities.
According to the type of heat carrier, district heating systems are divided into water and steam. Water is used to satisfy the seasonal load and the load of hot water supply (DHW); steam - for industrial process load.
2) B decentralized systems heat source and heat sinks of consumers are combined in one unit or placed so close that heat transfer from the source to heat sinks can be carried out without an intermediate link - a heat network.
Decentralized heat supply systems are divided into individual and local. AT individual systems heat supply for each room (section of the workshop, room, apartment) is provided from a separate source. These systems include stove and apartment heating. In local systems, heat is supplied to each building from a separate heat source, usually from a local boiler house.
2. Non-traditional and renewable energy sources. Characteristic.
Chapter 1. Characteristics of renewable energy sources and the main aspects of their use in Russia1.1 Renewable energy sources
These are types of energy that are continuously renewable in the Earth's biosphere. These include the energy of the sun, wind, water (including wastewater), excluding the use of this energy at pumped-storage electric power stations. The energy of tides, waves of water bodies, including reservoirs, rivers, seas, oceans. Geothermal energy using natural underground heat carriers. Low-potential thermal energy of the earth, air, water using special heat carriers. Biomass includes plants specially grown for energy production, including trees, as well as production and consumption wastes, with the exception of wastes obtained in the process of using hydrocarbon raw materials and fuels. As well as biogas; gas emitted by production and consumption wastes in landfills of such wastes; gas from coal mines.
Theoretically, energy is also possible, based on the use of the energy of waves, sea currents, and the thermal gradient of the oceans (HPPs with an installed capacity of more than 25 MW). But so far it hasn't caught on.
The ability of energy sources to be renewed does not mean that a perpetual motion machine has been invented. Renewable energy sources (RES) use the energy of the sun, heat, the earth's interior, and the rotation of the Earth. If the sun goes out, the Earth will cool down, and RES will not function.
1.2 Advantages of renewable energy sources in comparison with traditional ones
Traditional energy is based on the use of fossil fuels, the reserves of which are limited. It depends on the amount of deliveries and the level of prices for it, market conditions.
Renewable energy is based on a variety of natural resources, which makes it possible to conserve non-renewable sources and use them in other sectors of the economy, as well as preserve clean energy for future generations.
Independence of RES from fuel ensures the energy security of the country and the stability of electricity prices
RES are environmentally friendly: there are practically no wastes, emissions of pollutants into the atmosphere or water bodies during their operation. There are no environmental costs associated with the extraction, processing and transportation of fossil fuels.
In most cases, RES power plants are easily automated and can operate without direct human intervention.
Renewable energy technologies implement the latest achievements of many scientific areas and industries: meteorology, aerodynamics, electric power industry, thermal power engineering, generator and turbine construction, microelectronics, power electronics, nanotechnology, materials science, etc. The development of science-intensive technologies allows creating additional jobs by saving and expansion of the scientific, industrial and operational infrastructure of the power industry, as well as the export of science-intensive equipment.
1.3 Most common renewable energy sources
Both in Russia and in the world, this is hydropower. About 20% of the world's electricity generation comes from hydroelectric power plants.
The global wind energy industry is actively developing: the total capacity of wind turbines doubles every four years, amounting to more than 150,000 MW. In many countries, wind energy has a strong position. For example, in Denmark, more than 20% of electricity is generated by wind energy.
The share of solar energy is relatively small (about 0.1% of global electricity production), but has a positive growth trend.
Geothermal energy is of great local importance. In particular, in Iceland, such power plants generate about 25% of electricity.
Tidal energy has not yet received significant development and is represented by several pilot projects.
1.4 The state of renewable energy in Russia
This type of energy is represented in Russia mainly by large hydroelectric power plants, which provide about 19% of the country's electricity production. Other types of RES in Russia are still poorly visible, although in some regions, for example, in Kamchatka and the Kuril Islands, they are of significant importance in local energy systems. The total capacity of small hydroelectric power plants is about 250 MW, geothermal power plants - about 80 MW. Wind power is positioned by several pilot projects with a total capacity of less than 13 MW.
Ticket number 5
1. Characteristics of steam systems. Advantages and disadvantages.
steam system- a system with steam heating of buildings, where water vapor is used as a heat carrier. A feature is the combined heat transfer of the working fluid (steam), which not only reduces its temperature, but also condenses on the inner walls of the heating devices.
Heat source in the steam heating system can serve as a heating steam boiler. Heating devices are heating radiators, convectors, ribbed or smooth pipes. The condensate formed in the heaters returns to the heat source by gravity (in closed systems) or is pumped (in open systems). The vapor pressure in the system can be below atmospheric (vacuum steam systems) or above atmospheric (up to 6 atm.). The steam temperature should not exceed 130 °C. Changing the temperature in the premises is carried out by regulating the flow of steam, and if this is not possible, by periodically stopping the supply of steam. Currently steam heating can be used both for centralized and autonomous heat supply in industrial premises, in stairwells and lobbies, in heating points and pedestrian crossings. It is advisable to use such systems in enterprises where steam is used in one way or another for production needs.
Steam systems are divided into:
Vacuum-steam (absolute pressure<0,1МПа (менее 1 кгс/см²));
Low pressure (overpressure> 0.07 MPa (more than 0.7 kgf / cm²)):
Open (communicating with the atmosphere);
Closed (not communicating with the atmosphere);
By the method of returning condensate to the system boiler:
Closed (with direct return of condensate to the boiler);
Open circuit (with condensate return to the condenser tank and its subsequent pumping from the tank to the boiler);
According to the scheme of connecting pipes with system devices:
Single-pipe;
Single-pipe.
Advantages:
Small size and lower cost of heating devices;
· Low inertia and fast heating of the system;
· No heat loss in heat exchangers.
Disadvantages:
High temperature on the surface of heating devices;
Impossibility of smooth regulation of room temperature;
Noise when filling the system with steam;
· Difficulties in installing taps in a running system.
2. Fittings of thermal networks. Classification. Features of use.
According to their functional purpose, valves are divided into shut-off, control, safety, throttling and instrumentation.
Pipe fittings installed on pipelines of ITP, central heating substation, main pipelines, risers and connections to heating devices, piping centrifugal pumps and heaters
The fittings are characterized by three main parameters: nominal diameter Dy, working pressure and temperature of the transported medium.
Shut-off valves are designed to shut off the coolant flow. It includes gate valves, taps, gates, valves, rotary, gates.
Shut-off valves in heating networks are installed:
At all pipeline outlets of heating networks from heat sources;
For sectioning highways;
On branch pipelines;
For draining water and venting air, etc.
In housing and communal services, cast-iron gate valves of the 30ch6bk type for pressure Py = 1 MPa (10 kgf / cm²) and ambient temperatures up to 90 ° C, as well as gate valves of the 30ch6bk type for pressure Py = 1 MPa and ambient temperatures up to 225 ° C . These valves are available in diameters: 50, 80, 100, 125, 200, 250, 300, 350 and 400 mm.
Control valves are used to control the parameters of the coolant: flow, pressure, temperature. Control valves include control valves, pressure regulators, temperature regulators, control valves.
Safety valves are designed to protect heat pipelines and equipment from unacceptable pressure increase by automatically releasing excess heat carrier.
Ticket 6
1. Water heating systems. Advantages and disadvantages of heating systems.
Water heating systems are classified according to various criteria.
According to the location of the basic elements of the system, they are divided into central and local. Local are based on the work of autonomous boiler houses. The central ones use a single thermal center (CHP, boiler house) for heating many buildings.
As a coolant in water systems, not only water can be used, but also antifreeze liquids (antifreezes - mixtures of propylene glycol, ethylene glycol or glycerin with water). According to the temperature of the coolant, all systems can be divided into low-temperature (water is heated up to 70°C, no more), medium-temperature (70-100°C) and high-temperature (more than 100°C). The maximum media temperature is 150°C.
According to the nature of the movement of the coolant, heating systems are divided into gravitational and pumping. Natural (or gravitational) circulation is used quite rarely - primarily in buildings where noise and vibration are unacceptable. Installation of such a system involves the mandatory installation of an expansion tank, which is located in the upper part of the building. The use of structures with natural circulation greatly limits the planning possibilities.
Centralized pumping (forced regulation) systems are by far the most popular form of hot water heating. The coolant moves not due to the circulation pressure, but due to the movement created by the pumps. In this case, the pump is not necessarily located in the building itself, it can be located in the district heating point.
According to the method of connection to external networks, the systems are divided into three types:
Independent (closed). The boilers have been replaced with water heat exchangers, the systems use high pressure or a special circulation pump. Such systems allow for some time to maintain circulation in the event of external accidents.
Dependent (open). They use mixing water from the supply and discharge lines. For this, a pump or water jet elevator is used. In the first case, it is also possible to maintain the circulation of the coolant during accidents.
Direct-flow - the most simple systems used for heating several neighboring buildings of one small boiler house. The disadvantage of such solutions is the impossibility of high-quality local control and the direct dependence of the heating mode on the carrier temperature in the supply channel.
According to the method of delivery of the coolant to the heating radiators, the systems are divided into one- and two-pipe systems. A single-pipe scheme is a sequential passage of water throughout the network. The consequence is the loss of heat as you move away from the source and the impossibility of creating a uniform temperature in all rooms and apartments.
Single-pipe heating systems are cheaper and more hydraulically stable (at low temperatures). Their disadvantage is the impossibility of individual control of heat transfer. Single-pipe systems have been used in construction since the 1940s, for this reason most buildings in our country are equipped with them. Even today, such systems can be used in those public buildings where separate accounting and regulation of heat supply is not required.
A two-pipe system involves the creation of a single line that supplies heat to each individual room. As a rule, the supply and return risers are installed in the stairwells of houses. To account for heat supply, either apartment meters or an apartment-house system (a common meter for the house and local hot water meters) can be used. In multi-storey buildings with a two-pipe apartment heating scheme, it is possible to regulate the thermal regime in each apartment without causing “damage” to neighbors. It should be noted that due to the fact that low operating pressures are used in two-pipe systems, inexpensive thin-walled radiators can be used for heating.
The choice of the way in which the heat supply of buildings will be carried out depends on the technical characteristics (the ability to connect to a centralized heating system) and on the personal preferences of the owner. Each system has its own advantages and disadvantages.
For example, district heating systems are widespread, and due to their wide application, the installation and laying of pipelines are well developed. It is also worth noting the competitiveness of such networks due to the low cost of thermal energy.
But centralized heating networks also have such disadvantages as a high probability of malfunctions and accidents in the system, as well as a rather significant time that it takes to eliminate them. To this we can add the cooling of the coolant, which is delivered to remote consumers.
Autonomous heating networks can operate from various power sources. Therefore, when one of them is turned off, the quality of heat supply remains at the same level. Such systems ensure the supply of heat to the building even in emergency circumstances, when the premises are disconnected from the power grid and the water supply stops. The disadvantage of an autonomous heating network can be considered the need to store fuel reserves, which is not always convenient, especially in the city, as well as dependence on energy sources.
In addition to providing heat to a building, cooling also plays an important role in the functioning of buildings. In commercial premises (warehouses, shops, etc.), refrigeration is a prerequisite for normal operation. In private buildings, air conditioning and refrigeration is relevant in the summer. Therefore, when compiling project documentation construction, the design of heating and cooling systems must be approached with due attention and professionalism.
2. Protection of hot water systems from corrosion
Water supplied to hot water supply must meet the requirements of GOST. Water should be colorless, odorless and tasteless. Corrosion protection on subscriber inputs is used only for hot water installations. In open heat supply systems for hot water supply, network water that has undergone deaeration and chemical water treatment is used. This water does not need additional treatment at thermal points. In closed heating systems, hot water installations are filled with tap water. The use of this water without degassing and softening is unacceptable, since when heated to 60 ° C, electrochemical corrosion processes are activated, and at the temperature of hot water, the decomposition of temporary hardness salts into carbonates that precipitate and into free carbon dioxide begins. The accumulation of sludge in stagnant sections of pipelines causes pitting corrosion. There are cases when pitting corrosion for 2-3 years completely disabled the hot water supply system.
The method of treatment depends on the content of dissolved oxygen and the carbonate hardness of tap water, therefore, a distinction is made between anti-corrosion and anti-scale water treatment. Soft tap water with a carbonate hardness of 2 mg-eq/l does not produce scale and sludge. When using soft water, there is no need to protect the hot water supply system from sludge. But soft waters are characterized by a high content of dissolved gases and a low concentration of hydrogen ions, so soft water is the most corrosive. Tap water of medium hardness, when heated, forms a thin layer of scale on the inner surface of the pipes, which somewhat increases the thermal resistance of the heaters, but quite satisfactorily protects the metal from corrosion. Water with increased hardness of 4-6 mg-eq/l gives a thick coating of sludge, which completely eliminates corrosion. Hot water installations supplied with such water must be protected against sludge. Water with high hardness (more than 6 mg-eq/l) is not recommended for use due to weak “saponification” according to quality standards. Thus, in closed heat supply systems, hot water installations using soft water need protection against corrosion, and with increased rigidity, from sludge. But since, with hot water supply, low heating of water does not cause decomposition of salts of constant hardness, simpler methods are applicable for its treatment than for make-up water at a thermal power plant or in boiler houses. Protection of hot water supply systems from corrosion is carried out by using anti-corrosion installations at the central heating station or by increasing the anti-corrosion resistance of hot water supply systems.
Ticket number 8
1. Appointment and general characteristics deaeration process
The process of removing corrosive gases dissolved in water (oxygen, free carbon dioxide, ammonia, nitrogen, etc.), which, being released in the steam generator and heating network pipelines, cause metal corrosion, which reduces the reliability of their operation. Corrosion products contribute to the violation of circulation, which leads to burnout of the pipes of the boiler. The rate of corrosion is proportional to the concentration of gases in water. The most common thermal deaeration of water is based on the use of Henry's law - the law of the solubility of gases in a liquid, according to which the mass amount of gas dissolved in a unit volume of water is directly proportional to the partial pressure under isothermal conditions. The solubility of gases decreases with increasing temperature and is equal to zero for any pressure at the boiling point. During thermal deaeration, the processes of release of free carbon dioxide and decomposition of sodium bicarbonate are interconnected. The process of decomposition of sodium bicarbonate is most intense with an increase in temperature, a longer stay of water in the deaerator, and the removal of free carbon dioxide from the water. For the efficiency of the process, it is necessary to ensure the continuous removal of free carbon dioxide from deaerated water to the steam space and the supply of steam free from dissolved CO2, as well as to intensify the removal of released gases, including carbon dioxide, from the deaerator. 2. Pump selection
Main parameters circulation pump are the head (H), measured in meters of water column, and the flow (Q), or productivity, measured in m3 / h. The maximum head is the greatest hydraulic resistance of the system that the pump is able to overcome. In this case, its supply is equal to zero. The maximum flow is the largest amount of coolant that the pump can pump in 1 hour with the hydraulic resistance of the system tending to zero. The dependence of pressure on the performance of the system is called the pump characteristic. Single-speed pumps have one characteristic, two- and three-speed pumps have two and three, respectively. Variable speed pumps have many characteristics.
The selection of the pump is carried out, taking into account, first of all, the required volume of the coolant that will be pumped over the hydraulic resistance of the system. The flow rate of the coolant in the system is calculated based on the heat loss of the heating circuit and the required temperature difference between the direct and return lines. Heat losses, in turn, depend on many factors (thermal conductivity of building envelope materials, ambient temperature, orientation of the building relative to cardinal points, etc.) and are determined by calculation. Knowing the heat loss, calculate the required coolant flow rate according to the formula Q = 0.86 Pn / (tpr.t - trev.t), where Q is the coolant flow rate, m3 / h; Pn - the power of the heating circuit necessary to cover the heat losses, kW; tpr.t - temperature of the supply (direct) pipeline; tareb.t - temperature of the return pipeline. For heating systems, the temperature difference (tpr.t - torr.t) is usually 15-20°C, for a floor heating system - 8-10°C.
After determining the required flow rate of the coolant, the hydraulic resistance of the heating circuit is determined. The hydraulic resistance of the elements of the system (boiler, pipelines, shut-off and thermostatic valves) is usually taken from the corresponding tables.
Having calculated the mass flow rate of the coolant and the hydraulic resistance of the system, the parameters of the so-called operating point are obtained. After that, using manufacturers' catalogs, a pump is found whose operating curve lies not lower than the operating point of the system. For three-speed pumps, the selection is carried out, focusing on the second speed curve, so that there is a margin during operation. To obtain the maximum efficiency of the device, it is necessary that the operating point is in the middle of the pump characteristic. It should be noted that in order to avoid the occurrence of hydraulic noise in pipelines, the coolant flow rate should not exceed 2 m/s. When using antifreeze, which has a lower viscosity, as a coolant, a pump is purchased with a power reserve of 20%.
Ticket number 9
1. HEAT CARRIERS AND THEIR PARAMETERS. HEAT OUTPUT CONTROL
4.1. In district heating systems for heating, ventilation and hot water supply of residential, public and industrial buildings as a heat carrier, as a rule, water should be taken. The possibility of using water as a heat carrier for technological processes should also be checked.
The use of steam for enterprises as a single coolant for technological processes, heating, ventilation and hot water supply is allowed with a feasibility study.
Paragraph 4.2 shall be deleted.
4.3. The water temperature in hot water supply systems should be taken in accordance with SNiP 2.04.01-85.
Paragraph 4.4 shall be deleted.
4.5. Regulation of heat supply is provided: central - at the source of heat, group - in the control units or in the central heating point, individual in the ITP.
For water heating networks, as a rule, a qualitative regulation of heat supply according to the heating load or according to the combined heating and hot water supply load should be taken according to the schedule of water temperature changes depending on the outside air temperature.
When justified, regulation of heat supply is allowed - quantitative, as well as qualitative
quantitative.
4.6. With central quality regulation in heat supply systems with a predominant (more than 65%)
housing and communal load should be regulated by the combined load of heating and
hot water supply, and when the heat load of the housing and communal sector is less than 65% of the total
heat load and the share of the average load of hot water supply is less than 15% of the calculated heating load - regulation according to the heating load.
In both cases, the central quality control of heat supply is limited by the lowest water temperatures in the supply pipeline, necessary to heat the water entering the hot heat supply systems of consumers:
for closed heat supply systems - not less than 70 °С;
for open heat supply systems - at least 60 °C.
Note. With central quality regulation by combined
load of heating and hot water supply break point of the temperature graph
water in the supply and return pipelines should be taken at a temperature
outside air, corresponding to the break point of the control curve according to
heating load.
4.7. For separate water heating networks from one heat source to enterprises and residential areas
it is allowed to provide different schedules of water temperatures:
for enterprises - by heating load;
for residential areas - according to the combined load of heating and hot water supply.
4.8. When calculating temperature graphs, the following are accepted: the beginning and end of the heating period at a temperature
outside air 8 °C; the average design temperature of the internal air of heated buildings for residential areas is 18 °С, for buildings of enterprises - 16 °С.
4.9. In buildings for public and industrial purposes, for which a reduction is provided
air temperature at night and after hours, it is necessary to ensure the regulation of the temperature or flow of the heat carrier in the heat points. 2 Purpose and design of the expansion tank
According to its physicochemical characteristics, water (coolant) is a practically incompressible liquid. It follows from this that when you try to compress water (reduce its volume), it leads to a sharp increase in pressure.
It is also known that in the required temperature range from 200 to 900C, water expands when heated. Taken together, the two properties of water described above lead to the fact that in the heating system, water must be provided with the possibility of changing (increasing) its volume.
There are two ways to ensure this possibility: to use an "open" heating system with an open expansion tank at the highest point of the heating system or in a "closed" system to use expansion tank membrane type.
In an open heating system, the function of balancing the expansion of water when the “spring” is heated is performed by a column of water up to the expansion tank, which is installed at the top of the heating system. In a closed-type heating system, the role of the same "spring" in a membrane expansion tank is performed by a compressed air cylinder.
An increase in the volume of water in the system during heating leads to an influx of water from the heating system into the expansion tank and is accompanied by compression of the compressed air cylinder in the expansion tank of the membrane type and an increase in pressure in it. As a result, water has the ability to expand, as in the case of an open heating system, but in one case it does not directly contact air.
There are a number of reasons why the use of a membrane expansion tank is preferable to an open one:
1. The membrane tank can be placed in the boiler room and there is no need to install the pipe to the top point, where, moreover, there is a risk of freezing the tank in winter.
2. In a closed heating system, there is no contact between water and air, which excludes the possibility of oxygen dissolving in water (which provides the boiler and radiators in the heating system with an additional service life).
3. It is possible to provide additional (excessive) pressure even in the upper part of the heating system, as a result of which the risk of air bubbles in radiators located at high points is reduced.
4. In recent years, attic spaces have become increasingly popular: they are often used as living quarters and there is simply nowhere to place an open-type expansion tank.
5. This option is simply significantly cheaper when you consider materials, finishes and work.
Ticket number 11
Heat pipe designs
Rational designs of heat pipelines, firstly, should allow the construction of heat networks by industrial methods and be economical both in terms of the consumption of building materials and the cost of funds; secondly, they must have considerable durability, ensure minimal heat losses in networks, and not require large material and labor costs for maintenance during operation.
The existing designs of heat pipelines largely meet the above requirements. However, each of these designs of heat pipelines has its own specific features that determine the scope of its application. Therefore, it is important right choice of one or another design in the design of heating networks, depending on local conditions.
The most successful designs should be considered underground laying of heat pipelines:
a) in common collectors from precast concrete blocks together with other underground networks;
b) in prefabricated reinforced concrete channels (impassable and semi-passage);
c) in reinforced concrete shells;
d) in reinforced concrete shells made of centrifuged pipes or half-cylinders with mineral wool thermal insulation;
e) in asbestos-cement shells.
These structures are used in the construction of urban heating networks and are successfully operated.
When choosing designs for laying heat pipes, it is necessary to take into account:
a) hydrogeological conditions of the route;
b) conditions for the location of the route in the urban area;
c) construction conditions;
d) operating conditions.
The hydrogeological conditions of the route are of the most significant importance for the choice of the design of heat pipelines, and therefore they must be carefully studied.
In the presence of sufficiently dense dry soils, there is an opportunity for a large selection of heat pipeline designs. In this case, the final choice depends on the location of the route in the city, as well as on the conditions of construction and operation.
Unfavorable hydrogeological conditions (the presence of a high level of groundwater, soils with weak bearing capacity etc.) severely limit the choice of designs for heating networks. With a high level of groundwater, the most acceptable solution for the underground construction of heat pipelines is the laying of the latter in channels with associated drainage with suspended thermal insulation of pipes. The use of channels with waterproofing is effective only for channels through which the waterproofing can be done with sufficient quality.
Drainage can be additionally organized in the passage channels, which guarantees heat pipelines from flooding with groundwater. When designing associated drainage, it is necessary to ensure the reliable discharge of drainage water into urban drains or water bodies.
When designing heat networks in conditions of temporary flooding by groundwater (flood waters), the type of laying heat pipelines in semi-through channels without drainage and waterproofing can be adopted. In this case, measures should be taken to protect thermal insulation and pipes from moisture: coating pipes with borulin, installing a waterproof asbestos-cement peel over thermal insulation, etc.
When designing a heat network in wet soils on the territory of industrial enterprises, the best solution is the above-ground laying of heat pipelines.
The location of the route in the urban area largely affects the choice of the type of heating pipelines.
When the route is located under the main city passages, the laying of heat pipelines in shells and impassable channels is unacceptable, since during the repair of the heating network it is necessary to open the road pavement over a significant length of the route. Therefore, under the main passages, heat pipelines should be laid in semi-through and through channels, allowing inspection and repair of the heating network without opening.
It is most expedient when designing heat networks to combine them with other underground utilities in a common city collector.
TYPES OF GASING PIPELINES.
Crossing of rivers, railways and highways by heat pipelines. The simplest method of crossing river barriers is to lay heat pipelines along building structure railway or road bridges. However, there are often no bridges across rivers in the area where heat pipelines are laid, and the construction of special bridges for heat pipelines with a long span is expensive. Possible options for solving this problem are the construction of overhead passages or the construction of an underwater siphon.
Heat pipelines that transfer heat energy from a heat source to consumers, IB, depending on local conditions, are laid in various ways. (Distinguish between underground and air ways pipeline laying. In cities, underground [laying is usually used. With any method of laying heat pipelines, the main task is to ensure reliable and durable operation of the structure with minimum cost materials and means.
The next type of impassable channels are gaskets, IB of which there is no air gap between the outer surface of the thermal insulation and the channel wall. Such gaskets were made of reinforced concrete half-cylinders, "forming a rigid shell, IB which was a pipe wrapped with a layer of mineral wool. This type of heating pipeline laying was used for supply networks, but due to design imperfections (iMHOroHiOBHocTb) mineral wool was moistened and pipes due to poor corrosion protection due to external corrosion quickly failed.
2. Characteristics of shell-and-tube heat exchangers. The principle of choice. Shell and tube heat exchangers are among the most common devices. They are used for heat transfer and thermochemical processes between various liquids, vapors and gases - both without change, and with a change in their state of aggregation.
Shell and tube heat exchangers appeared at the beginning of the 20th century due to the need of thermal plants for large surface heat exchangers, such as condensers and water heaters, operating at relatively high pressure. Shell and tube heat exchangers are used as condensers, heaters and evaporators. At present, their design, as a result of special developments, taking into account operating experience, has become much more advanced. In the same years, the widespread industrial use of shell-and-tube heat exchangers in the oil industry began. For operation in difficult conditions heaters and mass coolers, evaporators and condensers were required for various fractions of crude oil and associated organic liquids. Heat exchangers often had to work with contaminated liquids at high temperatures and pressures, and therefore they had to be designed so that they could be easily repaired and cleaned.
The casing (body) of a shell-and-tube heat exchanger is a pipe welded from one or more steel sheets. Shells differ mainly in the way they are connected to the tube sheet and covers. The wall thickness of the casing is determined by the pressure of the working medium and the diameter of the casing, but is assumed to be at least 4 mm. Flanges are welded to the cylindrical edges of the casing for connection with covers or bottoms. Apparatus supports are attached to the outer surface of the casing.
Ticket number 12
1.PIPELINE SUPPORTS
Pipeline supports are an integral part of pipelines for various purposes: technological pipelines of industrial enterprises, thermal power plants and nuclear power plants, oil and gas pipelines, pipelines of engineering networks of housing and communal services, for completing pipeline systems in shipbuilding. A support is a part of a pipeline intended for its installation or fastening. In addition to the installation and fastening of pipelines, supports are used to relieve various loads on the pipeline (axial, transverse, etc.). They are usually installed as close as possible to the loads: shutoff valves, details of the pipeline. Pipeline supports cover the entire range of diameters from 25 to 1400 depending on the diameter of the pipeline. It is also worth noting that the material of the pipeline supports must match the material of the pipe, i.e. if the pipe is from st.20, then the pipeline support must be from st.20. The main material specified in the working drawings - carbon steel - is used for the manufacture of supports used in areas with an estimated outdoor temperature of up to minus 30˚С. In the case of the use of fixed supports in areas with outdoor temperatures down to minus 40 ° C, the material used for manufacturing is low-alloy steel: 17GS-12, 17G1S-12, 14G2-12 according to GOST 19281-89, the dimensions of the supports and their parts remain unchanged . For areas with an estimated outdoor temperature of up to minus 60˚С, steel 09G2S-14 is used in accordance with GOST 19281-89. Supports for pipelines are a necessary part of the heat transfer system. It serves to distribute the load from the pipeline to the ground. Supports for pipelines are divided into:
1. Movable (sliding, roller, ball, spring, frontal guides) and fixed (welded, clamp, thrust).
The sliding (movable) support assumes the weight of the pipeline system, ensuring unhindered vibrations of the pipeline when temperature conditions change.
2. The fixed support is fixed in certain places of the pipeline, perceiving the loads that occur at these points when temperature conditions change.
The production of pipeline supports is now normalized and unified by machine building standards. Their use is necessary for all design, installation and construction organizations. The OSTs spell out all the dimensions of the details of the supports for pipelines, the permissible loads on metal supports, including the friction force of the sliding supports. Supports must withstand the loads laid down in state standards and regulatory documentation. After removing the loads from the parts, tears should not appear on them.
2. DESIGN AND OPERATING PRINCIPLE A plate heat exchanger is an apparatus, the heat exchange surface of which is formed from thin stamped plates with a corrugated surface. Working media move in slot channels between adjacent plates. Channels for heating and heated coolants alternate with each other. The corrugated surface of the plates enhances the turbulence of the flow of working media and increases the heat transfer coefficient. Each plate on the front side has a rubber contour gasket that limits the channel for the flow of the working medium and covers two corner holes through which the flow of the working medium passes into the interplate channel and exits it, and the oncoming coolant passes through the other two holes. Gaskets of a collapsible plate heat exchanger are mounted on the plate in such a way that after assembly and compression of the plates, two systems of sealed interplate channels are formed in the apparatus, isolated from each other. Both systems of interplate channels are connected to their manifolds and further to fittings for inlet and outlet of working media located on the pressure plates. The plates are assembled in a package in such a way that each subsequent plate is rotated by 180° relative to the adjacent ones, which creates a grid of intersection of the corrugation tops and supports the plates under the action of different pressures in the media. Plate heat exchangers can be single-pass and multi-pass. In multi-pass devices, two of the four fittings are located on a movable pressure plate, and in the plate package there are special rotary plates with non-punched corner holes to direct the flows along the passages. The plates are assembled in a package on a frame, which consists of two plates (fixed and movable) connected by rods. Plate material - steel 09G2S. The material of the plates is stainless steel 12X18H10T. Gasket material - thermal rubber of various grades (depending on the properties of the coolant and operating parameters). When choosing a plate heat exchanger at the first stage, it is necessary to correctly formulate the problem of heat transfer, which is solved using a plate heat exchanger. When choosing a heat exchanger, it is advisable to consider all possible cases of load on the heat exchanger (for example: taking into account seasonal fluctuations) and select a heat exchanger according to the most loaded modes. With a high flow rate of heat carriers, it is possible to install several plate heat exchangers in parallel, which improves maintainability thermal node. The size of the heat exchanger, the number of plates and the layout of the plates can be selected in the following ways:
1. Fill out the questionnaire in the prescribed form and send it to the manufacturer's specialists or dealers.
2. Select a heat exchanger using simplified tables for selecting heat exchangers according to power and purpose (for heating or hot water).
3. Using a computer program for selecting heat exchangers, which can be obtained from the manufacturer's specialists or dealers.
When choosing a heat exchanger, it is necessary to foresee the possibility of increasing the capacity of the apparatus (increasing the number of plates) and inform the manufacturer about this. The pressure loss in the TPR can be either greater or less than the resistance in a shell-and-tube heat exchanger. The resistance of the TPR depends on the number of plates, on the number of strokes, on the consumption of coolants. When filling out the questionnaire, you can specify the required resistance range. The common belief that the TPR resistance is always greater than the resistance of a shell and tube heat exchanger is incorrect - it all depends on the specific conditions.
Ticket number 13
1. Thermal insulation. Classification and scope
Today in the building materials market technical thermal insulation occupies one of the key positions. Not only the level of heat loss, but also energy efficiency, sound protection, as well as the degree of waterproofing and vapor barrier of the object depend on how reliable the thermal insulation of the room will be. There are a large number of thermal insulation materials that differ from each other in purpose, structure and characteristics. In order to understand which material is optimal in a particular case, consider their classification.
Thermal insulation according to the mode of action
preventive thermal insulation - thermal insulation that reduces heat loss as a result of reduced thermal conductivity
reflective thermal insulation - thermal insulation that reduces heat loss by reducing infrared radiation
Thermal insulation according to purpose
1. Technical insulation is used to isolate utilities
"cold" application - the temperature of the medium in the system is less than the ambient air temperature
"hot" application - the temperature of the carrier in the system is higher than the ambient air temperature
2. Building thermal insulation is used to insulate building envelopes.
Thermal insulation materials according to the nature of the source material
1. Organic thermal insulation materials
Thermal insulation materials of this group are obtained from materials of organic origin: peat, wood, agricultural waste, etc. Almost all organic heat-insulating materials have low moisture resistance and are prone to biological decomposition, with the exception of gas-filled plastics: foam plastic, extruded polystyrene foam, honeycomb plastic, foam plastic and others.
2. Inorganic thermal insulation materials
Heat-insulating materials of this type are made by processing melts of metallurgical slags or melts of rocks. Inorganic heaters include mineral wool, foam glass, expanded perlite, cellular and lightweight concrete, fiberglass, and so on.
3. Mixed thermal insulation materials
A group of heaters based on mixtures of asbestos, asbestos, as well as mineral binders and perlite, vermiculite, intended for installation.
General classification of thermal insulation materials
Thermal insulation in appearance and shape is divided into
rolled and corded - bundles, mats, cords
piece - blocks, bricks, segments, slabs, cylinders
Loose, loose - perlite sand, cotton wool
Thermal insulation materials by type of feedstock
organic
inorganic
mixed
Thermal insulation materials according to the structure are
cellular - foam plastics, foam glass
granular - vermiculite, perlite;
Fibrous - fiberglass, mineral wool
According to their rigidity, thermal insulation materials are classified as soft, semi-rigid, rigid, increased rigidity, and solid.
According to thermal conductivity, thermal insulation materials are divided into:
class A - low thermal conductivity
class B - average thermal conductivity
class B - increased thermal conductivity
Thermal insulation is also classified according to the degree of flammability, here, in turn, the materials are divided into combustible, fireproof, flammable, slow-burning.
The main parameters of thermal insulation materials
1. Thermal conductivity of the insulation
Thermal conductivity - the ability of a material to conduct heat, is the main technical characteristic of all types of thermal insulation. The thermal conductivity of heaters is affected by the dimensions, type, overall density material and location of voids. The thermal conductivity is directly affected by the humidity and temperature of the material. The thermal resistance of enclosing structures directly depends on thermal conductivity.
2. Vapor permeability of thermal insulation material
Vapor permeability - the ability to diffuse water vapor, is one of the most significant factors that affect the resistance of the building envelope. To avoid the accumulation of excess moisture in the layers of the building envelope, it is necessary that the vapor permeability increases from a warm wall to a cold one.
3. Fire resistance
Thermal insulation materials must withstand high temperatures without structural damage, ignition, etc.
4. Breathability
The lower the air permeability characteristic, the higher the thermal insulation properties of the material.
5. Water absorption
Water absorption - the ability of heat-insulating materials to absorb moisture in direct contact with water and retain it in the cells.
6. Compressive strength of thermal insulation material
Compressive strength is the load value (kPa) causing a change in the thickness of the product by 10%.
7. Material density
Density - the ratio of volume to mass of dry material, which is determined at a certain load.
8. Compressibility of the material
Compressibility - change in the thickness of the product under pressure
2. Schematic diagram and principle of operation of a hot water boiler
The operation of a heating boiler room using hot water boilers is carried out as follows. Water from the return line of heating networks with a small pressure enters the suction of the network pump. Water is also supplied there from the make-up pump, which compensates for water leaks in heating networks. Hot water is also supplied to the pump suction, the heat of which is partially used in heat exchangers and for heating, respectively, chemically purified and raw water.
In order to ensure that the water temperature in front of the boiler, specified from the conditions for preventing corrosion, is fed into the pipeline after the mains pump using recirculation pump the required amount of hot water coming out of the boiler. The line through which hot water is supplied is called recirculation. In all operating modes of the heating network, except for the maximum winter one, part of the water from the return line after the network pump, bypassing the boiler, is fed through the bypass line to the supply line, where it, mixed with hot water from the boiler, provides the specified design temperature in the supply line of thermal networks. Water intended for replenishing leaks in heating networks is preliminarily supplied by a raw water pump to the raw water heater, where it is heated to a temperature of 18–20 ºC and then sent to chemical water treatment. Chemically purified water is heated in heat exchangers and deaerated in a deaerator. Water for feeding heating networks from the deaerated water tank is taken by the make-up pump and supplied to the return line. AT boiler houses that use hot water boilers, vacuum deaerators are often installed. But they require careful supervision during operation, so they prefer to install atmospheric deaerators.
Ticket number 14
1. Purpose and general characteristics of calibration and hydraulic calculations of heat networks.
1. Calibration hydraulic calculation of heat networks for non-heating
period is made in order to determine the pressure loss in pipelines from
source of heat supply to each of the consumers of thermal energy at
coolant flow rate in the non-heating period of operation, reduced
compared with the flow rate of the coolant in the heating period. According to the results
verification hydraulic calculation is developed optimal
operational mode of operation of heating networks and is produced
selection of equipment installed at the source of heat supply, for
operation during the non-heating period.
2. The following data are used as initial information for the verification hydraulic calculation of the heat network for the non-heating period:
Calculated values of the coolant flow for each of the systems
heat consumption (hot water supply) connected to the heating network;
Design scheme heating network with indication of hydraulic characteristics
pipelines (lengths of calculated sections, diameter of pipelines on each
settlement area, characteristics of local resistances).
4.3. The design scheme of the heat network, as a rule, is drawn up for
heating period and containing all the calculated characteristics
pipelines, must be adjusted when used for
verification hydraulic calculation for the non-heating period in part of the list
buildings with hot water supply.
2. The principle of operation of a steam boiler with a description of the scheme.
On fig. 1.1 shows a diagram of a boiler plant with steam boilers. The installation consists of a steam boiler 4, which has two drums - upper and lower. The drums are interconnected by three bundles of pipes forming the heating surface of the boiler. When the boiler is operating, the lower drum is filled with water, the upper drum is filled with water in the lower part, and saturated steam in the upper part. In the lower part of the boiler there is a furnace 2 with a mechanical grate for burning solid fuel. When burning liquid or gaseous fuel instead of a grate, nozzles or burners are installed through which fuel, together with air, is supplied to the furnace. The boiler is limited by brick walls - brickwork.
Rice. 1.1. Scheme of a steam boiler plant
The working process in the boiler room proceeds as follows. Fuel from the fuel storage is fed by a conveyor to the bunker, from where it enters the grate of the furnace, where it burns. As a result of fuel combustion, flue gases are formed - hot products of combustion. Flue gases from the furnace enter the boiler gas ducts, formed by lining and special partitions installed in pipe bundles. When moving, the gases wash the bundles of pipes of the boiler and superheater 3, pass through the economizer 5 and the air heater 6, where they are also cooled due to the transfer of heat to the water entering the boiler and the air supplied to the furnace. Then, the significantly cooled flue gases are removed by means of a smoke exhauster 5 through the chimney 7 into the atmosphere. Flue gases from the boiler can also be discharged without a smoke exhauster under the action of natural draft created by chimney. Water from the source of water supply through the supply pipeline is supplied by pump 1 to the water economizer, from where, after heating, it enters the upper drum of the boiler. The filling of the boiler drum with water is controlled by the water-indicating glass installed on the drum. From the upper drum of the boiler, water descends through pipes into the lower drum, from where it rises again through the left bundle of pipes into the upper drum. In this case, the water evaporates, and the resulting steam is collected in the upper part of the upper drum. Then the steam enters the superheater 3, where it is completely dried due to the heat of the flue gases, and its temperature rises. From the superheater, steam enters the main steam pipeline and from there to the consumer, and on after use, it condenses and returns as hot water (condensate) back to the boiler room. Losses of condensate at the consumer are replenished with water from the water supply system or from other sources of water supply. Before entering the boiler, water is subjected to appropriate treatment. The air necessary for fuel combustion is taken, as a rule, from the top of the boiler room and is supplied by fan 9 to the air heater, where it is heated and then sent to the furnace. In boiler rooms of low power, air heaters are usually absent, and cold air is supplied to the furnace either by a fan or due to rarefaction in the furnace created by a chimney. Boiler plants are equipped with water treatment devices (not shown in the diagram), instrumentation and appropriate automation equipment, which ensures their uninterrupted and reliable operation.