There are two main types of thermal energy sources (coolants - steam and hot water): boiler houses and thermal power plants.

If a thermal power plant is a source of both thermal and electrical energy, then the boiler house produces only heat.

A boiler room is a set of devices consisting of boilers, auxiliary equipment and systems for storing, preparing and transporting fuel; preparation, storage and transport of water; ash and slag removal, as well as facilities for cleaning flue gases and water.

The main element of any source of thermal energy is a boiler unit that serves to generate steam or hot water. A boiler installation is a combination of a boiler and auxiliary equipment. A boiler is a structurally integrated complex of devices for producing steam or heating water under pressure using thermal energy from fuel combustion. Boilers are divided into steam, water-heating and steam-water-heating.

Steam boilers are divided into energy boilers and industrial heat power boilers.

Energy boilers are part of thermal power plants and are used to produce superheated water steam at various pressures and temperatures. Industrial heat power boilers are used to generate saturated or superheated steam of low and medium parameters. This steam is used either as technological steam in the production processes of the enterprise, or to prepare hot water for the needs of heating, ventilation, air conditioning and hot water supply (DHW).

Hot water boilers can be installed both at thermal power plants and in boiler houses. The water heated in them is used for the same needs.

Steam boilers are classified according to a number of characteristics: design, heating surface layout, performance, steam parameters, type of fuel used, method of supply and combustion of fuel, flue gas pressure.

Widespread steam boilers are vertical water tube boilers of the DKVR type, designed to produce saturated steam at a pressure of 1.4 MPa. Their steam capacity is 4; 6.5; 10; 20 t/h when working on solid fuel and increases by 1.3... 1.5 times when working on fuel oil and gas. Currently, to replace the DKVR, a new series of boilers with a capacity of 2.5 to 25 tons of saturated or superheated steam per hour are being produced, types KE (for layer combustion of solid fuel) and DE (for operating on fuel oil and gas).

In industrial heat power engineering, U-shaped steam boilers of types GM50-14/250, GM50-1, BK375-39/440 are also used. Boilers of the GM type can operate on gas or fuel oil, and BKZ - also on solid fuel.

Steam boilers vary in design, type, performance, steam parameters and type of fuel used.

Boilers of small (up to 25 t/h) and medium (160...220 t/h) productivity with steam pressure up to 4 MPa are used in industrial and heating boiler houses to produce thermal energy in the form of steam, which is used for technological and heating - domestic needs .

Boilers with a capacity of up to 220 t/h have natural circulation without intermediate steam overheating and are used in industrial heat and power plants and thermal power plants.

Hot water boilers are designed to prepare coolant in the form of hot water for technological and domestic use (heating, ventilation, air conditioning and hot water supply).

Hot water boilers can be cast iron sectional or steel water tube.

Cast iron sectional water heating boilers, for example, types KCh-1, “Universal”, “Bratsk”, “Energia”, etc. differ in the size and configuration of the cast iron sections; the power of these types of boilers is 0.12... 1 MW.

Steel hot water boilers are marked TVG, PTVM and KV. These boilers supply water with temperatures up to 150°C and pressure 1.1...1.5 MPa, thermal conductivity from 30 to 180 Gcal/h (35...209 MW).

PTVM type boilers operate on gas and fuel oil. Boilers of the KB type are unified, designed to operate on solid, gaseous and liquid fuels. Depending on the type and method of fuel combustion, KB boilers are divided into KVTS (layer mechanized furnaces), KVTK (chamber furnace for burning pulverized fuel), KVGM (for burning gas and fuel oil).

Combined heat and power plants (CHPs) are stations for the combined production of electrical and thermal energy. Superheated steam from the boiler is supplied to the steam turbine blades mounted on the rotor. Under the influence of steam energy, the turbine rotor rotates. This rotor is rigidly connected by means of a coupling to the rotor of the electric generator, during the rotation of which electricity is generated. The steam, which has partially given up its energy in the turbine, is supplied to consumers either for technological use or for heating water supplied to consumers.

Thermal power plants use heating turbines with intermediate heat extraction of steam and turbines with back pressure.

The thermal diagram of a thermal power plant with turbine backpressure is shown in Fig. 5, where: 1 - steam boiler, 2 - steam turbine, 3. electric generator, 4 - heat consumer, 5 - condensate pump, 6 - deaerator, 7 - feed pump.

The thermal diagram of a thermal power plant with heating turbines is shown in Fig. 6, where 1, 2, 3, 4 correspond to the designations in Fig. 5, 5 - network pump, 6 - condenser, 7 - condensate pump, 8 - deaerator, 9 - feed pump.

Figure 5. Figure 6.

A thermal power plant with back-pressure turbines is characterized by the fact that the production of electricity here is strictly linked to the supply of thermal energy; the operation of such a station is advisable only if there are large consumers of heat with a constant consumption throughout the year, for example, enterprises in the chemical or oil refining industries.

CHP plants with heating turbines do not have this drawback and can operate equally efficiently in a wide range of heat loads. The thermal circuit contains a condenser, and steam for heating water is released from the intermediate stages of the turbine. The amount of steam and its parameters are regulated; such extractions are called heating extractions, in contrast to extractions used for regenerative heating of feedwater.

Heating boiler houses are used to supply heat to cities and towns. They are:

a) individual (house) or group for individual buildings or a group of buildings. The heating capacity of such boiler houses is 0.5...4 MW, the type of boiler is hot-water cast iron sectional, the coolant temperature is 95...115°C, the efficiency of coal is 60-70%, gas and fuel oil is 80-85%;

b) quarterly for heat supply of a block or microdistrict. Heating capacity - 5...50 MW, type of boilers - steel steam boilers type DKVR or DE and water heating types KVTS, KVGM, TVG, coolant temperature 13O...15O°C, efficiency on coal - 80-85%, on gas and fuel oil - 85-92%;

c) district heating for one or more residential areas. Heating capacity - 70...500 MW, type of boilers - steel water heating types PTVM, KVTK, KVGM, coolant temperature 150...200°C, efficiency on coal - 80-88%, on gas and fuel oil - 88-94% ; or steam type DKVR, DE, GM-50.

If a boiler room, in addition to the needs of heating and hot water supply (DHW) I, produces steam, then such a boiler room is called industrial heating. If a boiler house provides thermal energy in the form of steam and hot water only to the needs of the enterprise, then such a boiler house is called industrial. Boiler rooms can also have only hot water boilers (water boiler room), only steam boilers (steam boiler room) and steam and hot water boilers (steam and hot water boiler room). An example of a heating boiler room with steam boilers is shown in the simplified diagram in Fig. 7.

Figure 7.

Here 1 - feed pump, 2 - steam boiler, 3-steam reduction unit (RU), 4 - steam transport for the technological needs of the enterprise, 5 - heating network feed pipeline, 6 - network pump, 7 - heat exchangers for heating network water, 8 - heating network, 9 - deaerator.

A heating network is a system of tightly and tightly interconnected sections of steel pipes (heat pipeline), through which heat is transported using a coolant (steam or, more often, hot water) from sources (CHP or boiler houses) to heat consumers.

Heating mains can be underground or above ground. Overground installation of heating networks is used in cases of high groundwater levels, densely built areas where heating mains are laid, very rough terrain, the presence of multi-track railways, in the territories of industrial enterprises in the presence of existing energy or process pipelines on overpasses or high supports.

The diameters of heating network pipelines range from 50 mm (distribution networks) to 1400 mm (main networks).

About 10% of heating networks are laid above ground. The remaining 90% of heating networks are laid underground. About 4% are laid in through channels and tunnels (semi-through channels). About 80% of heating networks are laid in non-passable channels. About 6% of heating networks are laid without ducts. This is the cheapest installation, but, firstly, it is the most susceptible to damage and, secondly, it requires high repair costs, especially when installed in the acidic wet soils of the North-West.

Thermal energy is used in the process of heating, ventilation, air conditioning, hot water supply, and steam supply.

Heating, ventilation, and air conditioning serve to create comfortable living and working conditions for people. The volume of thermal energy consumption for these purposes is determined by the season and depends primarily on the outside air temperature. Seasonal consumers are characterized by a relatively constant daily heat consumption and significant fluctuations between the seasons.

Hot water supply - domestic and technological - year-round. It is characterized by a relatively constant flow rate throughout the year and independence from the outside temperature.

Steam supply is used in technological processes of blowing, steaming, and steam drying.

Heating can be local or centralized. The simplest type of local heating is a wood heating stove, which is a brickwork with a firebox and a flue system for removing combustion products. The heat released during the combustion process heats the masonry, which in turn releases heat to the room.

Local heating can be carried out using gas heating devices that are small in size and weight and are highly efficient.

Apartment water heating systems are also used. The heat source is a water heating device using solid, liquid or gaseous fuel. The water is heated in the apparatus, supplied to heating devices and, having cooled, returned to the source.

In local heating systems, air can be used as a coolant. Air heating devices are called fire-air or gas-air units. In the rooms, air is supplied by fans through an air duct system.

Local heating with electric devices, produced in the form of portable devices of various designs, has become widespread. In some cases, stationary electric heating devices with secondary coolants (air, water) are used.

At enterprises, local heating is practically not used in production premises, but it can be used in administrative and domestic premises (mainly electrical appliances).

A heating system with one common (central) heat source is called centralized. This is a heating system for an individual building, a group of buildings, one or several blocks, and even a small city (for example, for heating and hot water supply in the city of Sosnovy Bor, Leningrad Region, one heat source is used - the Leningrad Nuclear Power Plant).

The systems also differ in the type of heat transfer to the room air: convective, radiant; type of heating devices: radiator, converter, panel.

In Fig. Figure 8 shows a two-pipe central water heating system, in which water enters the heating devices through hot risers and is discharged through cold risers. In this case, the water temperature is the same in all devices, regardless of their location.

Designations Fig. 8: 1 - boiler room, 2 - main riser, 3 - heating devices, 4 - expansion tank, 5 - hot line, 6 - hot riser, 7 - cold riser, 8 - return line.

Figure 8.

A one-pipe central heating system (Fig. 9) differs from a two-pipe system in that water enters and is discharged from the heating devices through the same riser. The design of a single-pipe system can be flow-through (Fig. 9, a), with axial closing sections (Fig. 9, b), with mixed closing sections (Fig. 9, c). The designations are the same as in Fig. 8.

Figure 9.

In flow-through systems, water sequentially passes through all devices of the riser; in systems with axial closing sections, water partially passes through the devices, partially through closing sections common to two devices on the same floor; in systems with mixed closing sections, water branches off through two closing sections.

In single-pipe systems, the water temperature decreases in the direction of its movement, that is, the devices on the upper floors are hotter than the devices on the lower floors. In these systems, the metal consumption for risers is somewhat less, but the installation of closing sections is required.

Heating devices installed in heated rooms are made of cast iron and steel and have various structural forms from smooth pipes, bent or welded into blocks (registers), to radiators, finned pipes and heating panels.

Water for hot water supply must be of the same quality as drinking water, as it is used for hygienic purposes. The water temperature should be within 55...60°C.

There are local and central hot water supply. Local hot water supply is carried out using autonomous and periodic water heating devices with a device for distributing and dispensing hot water. Water heaters operate on solid fuel (coal, wood), gas and can be electric. According to the principle of operation, water heaters are divided into capacitive and instantaneous.

The central hot water supply system is used for facilities with a thermal power of over 60 kW. The system is part of the internal water supply system and is a network of pipelines that distribute hot water between consumers.

Figure 10.

In Fig. Figure 10 shows a central hot water supply system with recirculation, where 1 - first stage water heater, 2 - second stage water heater, 3 - supply line, 4 - water risers, 5 - circulation risers, 6 - shut-off valves, 7 - circulation line, 8 - pump .

Circulation risers prevent the water in the risers from cooling down when there is no water supply. The heat source is water heaters (boilers) located in the building’s heat input or in a group heating point.

Ventilation serves to introduce clean air into the room and remove polluted air in order to ensure the required sanitary and hygienic conditions. The air supplied to the room is called supply air, and the air removed is called exhaust air.

Ventilation can be natural or forced. Natural ventilation occurs under the influence of the difference in densities of cold and warm air; its circulation occurs either through special channels or through open vents, transoms and windows. With natural ventilation, the pressure is low and the air exchange is correspondingly low.

Forced ventilation is carried out using fans that supply air and remove it from the room with high efficiency.

Depending on the type of air flow organization, ventilation can be general and local. The general exchange system ensures air exchange throughout the entire volume of the room, and the local exchange system ensures air exchange in certain parts of the room (workplaces).

A ventilation system that only removes air from a room is called an exhaust ventilation system, while a ventilation system that only supplies air into a room is called a supply ventilation system.

In residential buildings, as a rule, a general natural exhaust ventilation system is used. Outdoor air enters the premises by infiltration (through leaks in the enclosures), and contaminated indoor air is removed through the building's exhaust ducts. Thermal energy losses from the entry of cold outside air are replenished by the heating system and amount to 5...10% of the heating load in winter.

In public and industrial buildings, supply and exhaust forced ventilation is usually installed, and the consumption of thermal energy is taken into account separately.

Air conditioning is the process of imparting specified properties to it regardless of external meteorological conditions. This is ensured by special devices - air conditioners, which clean the air from dust, heat it, humidify or dry it, cool it, move it, distribute it and automatically adjust the air parameters.

Air conditioning systems for industrial premises at instrument-making, radio-electronic, food, and textile enterprises, where high demands are placed on the air environment, have become widespread.

The main task of an air conditioner is thermal and humidity treatment of air: in winter the air should be heated and humidified, in summer it should be cooled and dried.

The air is heated in heaters, cooled in surface or contact coolers, similar in design to air heaters, but cold water or coolant (ammonia, freon) circulates in the cooling pipes.

Air dehumidification occurs as a result of contact with the surface of the cooler, the temperature of which is below the dew point of the air - condensation forms on this surface.

For air irrigation, water supply nozzles or wetted surfaces with labyrinth passages are used.

Topic 4. Consumers of thermal energy.

Heating systems

Efficiency of implementation of autonomous

The critical situation with the provision of energy resources, the increase in prices for their purchase to the world level requires immediate measures for the active implementation of energy and resource-saving technologies at the level of state policy.

One of the directions to solve this problem is the decentralization of heat supply through the introduction of autonomous heat supply systems (ATS), the effectiveness of which has been confirmed by many years of experience in their operation in many European countries.

HAT is usually understood as a heating and hot water supply system with a heat source located on the heated object (on the roof or in the attic space), or in close proximity to it.

A significant economic effect from the introduction of SAT before centralized heat supply is achieved due to the following factors:

No capital costs for the construction of a boiler house building and the purchase of expensive engineering equipment;

Absence of significant capital costs for the construction, operation and elimination of emergency situations of many kilometers of heating mains, the service life of which does not exceed 10-12 years instead of the standard 25 years;

No heat loss and energy consumption for transporting coolant through heating networks;

Lack of numerous personnel to service boiler heating networks and structures on them.

Ukraine is the first of the post-Soviet states to develop new standards for “rooftop” boiler installations. In 1993 in ᴦ. Bila Tserkva was installed on a 9-storey residential building, the first “rooftop” boiler house in Ukraine. An analysis of the operation of the boiler room over 10 years showed that equipping a house with an autonomous source will ensure high-quality heating of the house, while saving up to 35% of gas, 75% of electricity, 50% of operating costs compared to the current centralized heat supply.

Questions for self-control:

1. What is commonly called a heat supply system?

2. What challenges does the heat supply industry face?

3. Name the sources of thermal energy.

4. How are heat supply systems classified based on the source of heat supply.

5. Conduct a comparative description of various heat supply sources.

Topic questions:

1. Heat consumers.

2. Classification of heat consumers.

3. Uneven consumption of thermal energy.

About 40% of all fuel produced in the country is spent on heating buildings. In residential and public buildings, thermal energy is spent to provide comfortable living conditions for people in premises that correspond to the modern level of development of heat supply technology, as well as for communal and sanitary purposes. In industrial buildings, thermal energy is, in addition, required by technology to ensure the required thermal conditions in the manufacture of certain types of products and a number of production operations.

Taking into account the dependence of the type of heat consumption, all consumers are divided into household and technological. These include consumers of thermal energy for the purposes of heating and ventilation of buildings, as well as for heating water for sanitary, hygienic and domestic purposes. Engineering devices that distribute thermal energy in buildings are heating, ventilation, air conditioning and hot water supply systems and heating equipment, which is extremely important in product production technology.

Heating system provides a given thermal regime in the premises during the cold season by compensating for heat loss through the external building envelope.

Ventilation system creates the required air purity in the working area of industrial buildings, the necessary air and thermal conditions in public buildings through the appropriate organization of air exchange in the premises.

Air conditioning system air is used to create a microclimate in rooms that satisfies increased sanitary and hygienic or technological requirements by ensuring strictly specified temperature, humidity, mobility and cleanliness of air in the work area.

Hot water system designed for heating and transporting water to water collection points for domestic or industrial needs.

Technological heating equipment is a consumer of thermal energy in the form of heated water or water vapor and includes both special heat pipes and heat exchangers, and sometimes electric boilers.

Each device provides one type of heat consumption and has its own operating mode, which is determined by the consumption of thermal energy during a given period of time, for example, one hour of a work shift, day, month, season or year.

Based on the consumption of thermal energy per hour, all consumers are divided into evenly consuming (heating, ventilation) and unevenly consuming (water heating, technological needs).

Based on the duration of continuous use of thermal energy during a certain period of the year, all consumers are combined into two main groups: with seasonal consumption (heating, ventilation) and with annual consumption (water heating, technological needs). The operating mode of seasonal consumers depends on climatic conditions (outside temperature tn and air humidity, wind speed and direction) and is characterized by uneven heat consumption both during the heating season and during each month. For annual consumers, with a relatively constant heat consumption throughout the season, month and week, the operating mode changes sharply not only by hour of the day, but also by day of the week.

The combined action of consumers with different operating modes imposes certain requirements on the type, quantity and potential of the coolant circulating in the external heat pipes. The choice of a rational option for a facility’s heat supply scheme is made based on the total heat load of individual engineering devices of all buildings and process consumers. The heat load, or the need for thermal energy, is usually calculated in characteristic time periods: hour, day, month, season or year, and the calculated heat consumption is hourly.

Based on the calculated flow rate, the type of heat energy source, the power of heat treatment equipment and the pipeline diameters are selected. Taking into account the dependence on changes in heat demand during the day, month, season and year, appropriate modes for the supply of thermal energy are developed - operational modes of heat supply devices. At the same time, the concentration of heat consumers, the distance of consumers from heat sources, the geometric height of buildings and the terrain are taken into account.

Monthly, seasonal and annual heat energy consumption is used in technical and economic calculations when comparing options for heat supply systems. Thermal energy consumption for heating, ventilation and hot water supply is taken according to standard or individual designs of the relevant buildings and structures. Thermal energy consumption for production processes is taken into account according to the technological projects of these industries. In the absence of projects, the calculated heat consumption is determined separately for each consumer. The estimated thermal energy consumption of a building in a block or city includes consumption for heating, ventilation, hot water supply and technological needs.

Taking into account the dependence of the requirements for the reliability and quality of heat supply, as well as the type and parameters of the coolant, centralized heat supply systems are divided into:

a) by type of transported coolant - steam, water and mixed;

b) according to the number of heat pipelines laid in parallel - one-, two-, three- and multi-pipe;

c) on the use of coolant in hot water supply systems and technological consumers - closed (closed) and open (open).

Water two- and four-pipe systems are used for heat supply to residential and public buildings. Two-pipe systems can be either closed or open, usually with local heating substations. Four-pipe systems, as a rule, are closed, and up to the central heating substation, heating networks are made with two pipes, after the central heating substation to the building - with four pipes. The operating mode of two-pipe heating networks is established from the condition of providing thermal energy to all consumers. In four-pipe networks, heating systems are connected to two mains (supply and return), and hot water supply systems are connected to two (supply and circulation).

For heat supply to industrial enterprises, systems of all types are used: steam single- and multi-pipe, water, usually three-pipe, in which the first pipeline is a supply for heating and ventilation, the second is a supply with a constant temperature of the coolant throughout the year for hot water supply and industrial needs, and the third is the reverse general.

In a closed heat supply system, the hot water supply system and other consumers are connected to heating networks through heat exchangers in which tap water (or air) supplied to the water supply is heated.
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The coolant in this system releases part of the thermal energy and is completely returned to the source.

In an open heating system, water intended for hot water supply and technological needs is taken directly from the heating network. However, this system uses not only the thermal energy of the coolant, but also the coolant itself. Part of the coolant not used by consumers (in heating and ventilation systems) is returned to the boiler room.

Single-pipe systems, both water and steam, are open only. In them, the coolant is completely used by the consumer, consistently satisfying all heating needs. At maximum water temperature or steam pressure, the coolant releases part of the heat in heating and ventilation systems and, in addition, is used for hot water supply and technological needs. Single-pipe systems require less capital investment for the construction of heating networks. With an increase in the potential of the coolant, for example, at a steam pressure of more than 1.1 MPa and a water temperature of up to 180 - 200 0 C, their efficiency increases.

For heat supply to cities and residential villages, water two-pipe (open and closed) heat supply systems are most widespread.

In open systems, the connection points of hot water supply systems to heating networks are significantly simplified, the automation scheme is simplified, and most importantly, long-term operational reliability of the pipelines of the hot water supply system is ensured. The supply of water that has undergone softening and degassing in the boiler room prevents corrosion of the inner surface of the pipe walls. The disadvantages of this system include the possible increased color of the water, especially when connecting radiator heating systems to heating networks using a dependent circuit, as well as in the case of repair of thermal inputs.

In closed systems, tap water heated in heat exchangers and entering the hot water supply system, as a rule, is not subjected to chemical treatment; complex and expensive equipment that requires highly qualified maintenance and takes up a lot of space is extremely important. For this reason, hot water supply system pipelines are susceptible to corrosion due to the presence of oxygen and carbon dioxide in tap water. Fistulas often appear in them, and in water heaters, scale is deposited on the walls of the pipes through which tap water flows, sharply reducing efficiency and leading to their rapid failure. When supplying water to a facility from artesian wells, when the water has a higher content of hardness salts compared to water from open reservoirs, descaling of water heaters is required every four to six months.

Questions for self-control:

1. How are heat consumers classified?

2. Name the heat consumers.

3. What is the unevenness of thermal energy consumption?

4. How the choice of heat supply scheme option is selected.

Bibliography:

1. I.I. Pavlov, M.N. Fedorov ʼʼBoiler installations and heating networksʼʼ, p. 150-165, 179-190.

2. Yu.D. Sibikin “Heating, ventilation and air conditioning”, M, 2004, p.
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8

Topic 4. Consumers of thermal energy. - concept and types. Classification and features of the category "Topic 4. Heat energy consumers." 2017, 2018.

Electricity losses

Electricity consumers are everywhere. It is produced in relatively few places close to sources of fuel and hydro resources. Electricity cannot be conserved on a large scale. It must be consumed immediately upon receipt. Therefore, there is a need to transmit electricity over long distances.

Energy transfer is associated with noticeable losses. The fact is that electric current heats the wires of power lines. In accordance with the Joule-Lenz law, the energy spent on heating the line wires is determined by the formula:, where R is the line resistance. If the line length is very long, energy transmission may become economically unprofitable. It is practically very difficult to significantly reduce line resistance. Therefore, you have to reduce the current.

Since current power is proportional to the product of current and voltage, to maintain the transmitted power, it is necessary to increase the voltage in the transmission line. The longer the transmission line, the more beneficial it is to use a higher voltage. Meanwhile, alternating current generators are built for voltages not exceeding 16-20 kV. Higher voltages would require complex special measures to be taken to insulate the windings and other parts of the generator.

That's why step-up transformers are installed at large power plants. The transformer increases the voltage in the line by the same amount as it decreases the current.

To directly use electricity in the electric drive motors of machine tools, in the lighting network and for other purposes, the voltage at the ends of the line must be reduced. This is achieved using step-down transformers.

Typically, a decrease in voltage and, accordingly, an increase in current strength occurs in several stages. At each stage, the voltage becomes less and less, and the territory covered by the electrical network becomes wider.

When the voltage is very high, a corona discharge begins between the wires, leading to energy loss. The permissible amplitude of the alternating voltage must be such that, for a given cross-wire area, energy losses due to corona discharge are insignificant.

Electric power stations in a number of regions of the country are connected by high-voltage transmission lines, forming a common electrical network to which consumers are connected. This combination, called an energy system, makes it possible to smooth out the “peak” loads of energy consumption in the morning and evening hours. The power system ensures uninterrupted supply of energy to consumers regardless of their location.

ELECTRICAL POWER SYSTEMS AND ELECTRICAL NETWORKS.

The electrical part of the power plant includes a variety of main and auxiliary equipment. The main equipment intended for the production and distribution of electricity includes:

Synchronous generators that generate electricity (for TPP-turbine generators);
Busbars designed to receive electricity from generators and distribute it to consumers;
Communication devices - switches designed to turn on and off circuits in normal and emergency conditions, and disconnectors designed to remove voltage from de-energized parts of electrical installations and to create a visible circuit break;
Electrical receivers for own needs (pumps, fans, emergency electric lighting, etc.)

Auxiliary equipment designed to perform measurement, alarm, protection and automation functions, etc.

The energy system (energy system) consists of power plants, electrical networks and electricity consumers, interconnected and connected by a common mode in the continuous process of production, distribution and consumption of electrical and thermal energy under the general control of this mode.

An electric power (electric) system is a set of electrical parts of power plants, electrical networks and electricity consumers, connected by the commonality of the regime and the continuity of the process of production, distribution and consumption of electricity. The electrical system is part of the energy system, with the exception of heating networks and heat consumers. An electrical network is a set of electrical installations for the distribution of electrical energy, consisting of substations, switchgears, overhead and cable power lines. The electrical network distributes electricity from power plants to consumers. Power line (overhead or cable) is an electrical installation designed to transmit electricity.

In our country, standard rated (phase-to-phase) voltages of three-phase current with a frequency of 50 Hz in the range of 6-750 kV, as well as voltages of 0.66; 0.38 kV are used. For generators, rated voltages of 3-21 kV are used.

The transmission of electricity from power plants via power lines is carried out at voltages of 110-750 kV, i.e. significantly exceeding the voltage of generators. Electrical substations are used to transform

electricity of one voltage into electricity of another voltage. An electrical substation is an electrical installation designed to convert and distribute electrical energy. Substations consist of transformers, busbars and switching devices, as well as auxiliary equipment: relay protection and automation devices, measuring instruments. Substations are designed to connect generators and consumers with power lines.

Classification of electrical networks can be carried out according to the type of current, rated voltage, functions performed, the nature of the consumer, the configuration of the network diagram, etc.

According to the type of current, AC and DC networks differ; by voltage: ultra-high voltage( ,high voltage ,low voltage (<1кВ).

According to the configuration, network circuits are divided into closed and open.

According to the functions performed, system-forming, supply and distribution networks are distinguished. System-forming networks with a voltage of 330-1150 kV carry out the functions of forming unified energy systems, including powerful power plants, ensuring their functioning as a single control object and at the same time transmitting electricity from powerful power plants. They also carry out system connections, i.e. connections between power systems of very long length. The mode of backbone networks is controlled by the unified dispatch control manager (UDC). The UDU includes several regional energy systems - regional energy departments (REU).

Supply networks are designed to transmit electricity from substations of the system-forming network and partly from buses of 110-220 kV power plants to power centers (CP) of distribution networks - district substations. The power supply networks are usually closed. As a rule, the voltage of these networks is 110-220 kV, but as load density, station power and the length of electrical networks increase, the voltage sometimes reaches 330-550 kV.

A district substation usually has a higher voltage of 110-220 kV and a lower voltage of 6-35 kV. Transformers are installed at this substation to regulate the voltage on the low-voltage buses under load.

The distribution network is designed to transmit electricity over short distances from low-voltage buses of district substations to industrial, urban, and rural consumers. Such distribution networks are usually open-loop. There are distribution networks of high () and low (voltage). In turn, according to the nature of the consumer, distribution networks are divided into networks for industrial, urban and agricultural purposes. The predominant distribution in distribution networks has a voltage of 10 kV, 6 kV networks are used when enterprises have a significant load of electric motors with a rated voltage 6 kV. Voltage 35 kV is widely used to create 6 and 10 kV power centers mainly in rural areas.

To supply power to large industrial enterprises and large cities, deep high-voltage input is carried out, i.e. construction of substations with primary voltage 110-500 kV near load centers. The internal power supply networks of large cities are 110 kV networks, in some cases these include deep inputs 220/10 kV. Agricultural networks are currently operated at a voltage of 0.4-110 kV.

Overhead power lines (OVL) are designed to transmit electricity over a distance via wires. The main structural elements of overhead lines are wires (used to transmit electricity), cables (used to protect overhead lines from lightning surges), supports (support wires and cables at a certain height), insulators (insulate support wires), linear fittings (with its help, wires are secured on insulators, and insulators on supports).

Length of power lines in Belarus (1996): 750 kV-418 km, 330 kV-3951 km, 220 kV-2279 km, 110 kV-16034 km.

The most common wires are aluminum, steel-aluminum, and aluminum alloys. Power cables consist of one or more conductive wires, separated from each other and from the ground by insulation. Current-carrying conductors are made of aluminum, single-wire (cross-section up to 16) or multi-wire. Cable with copper conductors is used in explosive areas.

The insulation is made of special cable paper impregnated with mineral oil, applied in the form of tapes to the conductors, and can also be rubber or polyethylene. Protective sheaths placed over the insulation to protect it from moisture and air are made of lead, aluminum or polyvinyl chloride. To protect against mechanical damage, armor made of steel tapes or wires is provided. Between the shell and the armor there are internal and external protective covers.

The internal protective cover (cushion under the armor) is a jute layer made of impregnated cotton yarn or cable sulphate paper. The outer protective cover is made of jute coated with an anti-corrosion compound.

A significant part of electricity consumption is made up of losses in networks (7-9%).

ENERGY ECONOMY OF INDUSTRIAL ENTERPRISES AND ENERGY SAVING POTENTIAL.

In industry, more than 2/3 of the energy saving potential is in the sphere of consumption by the most energy-intensive industries - chemical and petrochemical, fuel, building materials, forestry, woodworking and pulp and paper, food and light industry.

Significant reserves for saving fuel and energy resources in these industries are due to the imperfection of technological processes and equipment, energy supply schemes, insufficient implementation of new energy-saving and waste-free technologies, the level of recycling of secondary energy resources, low unit power of technological lines and units, the use of uneconomical lighting equipment, unregulated electric drives, inefficient loading of energy equipment, low level of equipment for metering, monitoring and regulation of technological and energy processes, shortcomings inherent in the design and construction of enterprises and individual industries, low level of operation of equipment, buildings and structures.

Mechanical engineering and metallurgy. Approximately a third of all boiler and furnace fuel used in mechanical engineering goes to the needs of foundry, forging and thermal production. About half of all consumed heat and about a third of all electricity are used for technological needs. Over a third of all electricity goes into mechanical processing. The main consumers of energy resources in mechanical engineering are open-hearth furnaces, cupola furnaces, smelting furnaces, draft machines (fans and smoke exhausters), heating furnaces, dryers, rolling mills, galvanic equipment, welding units, and press facilities.

The reasons for the low efficiency of fuel and energy use in the mechanical engineering industries are the low technical level of furnace facilities, high metal consumption of products, large waste of metal during its processing, insignificant level of waste heat recovery, irrational structure of the energy carriers used, significant losses in thermal and electrical networks.

More than half of the energy saving reserves can be realized in the process of metal smelting and foundry production. The rest of the savings are associated with the improvement of metalworking processes, including through an increase in the level of its automation, and the increased use of less energy-intensive plastics and other structural materials compared to metal.

The largest consumers of fuel in the industry are blast furnace and rolling production, the most energy-intensive are ferroalloy, mining, rolling, electric furnace and oxygen production, and the most heat-intensive is coke production.

Use of effective lining and heat-insulating materials in furnaces, dryers and heat pipelines;
The use of thyristor frequency converters in the processes of induction heating of metal in forging and thermal production;
Introduction of energy-saving paint and varnish materials (with a lower drying temperature, water-based, with a high solids residue);
Reducing energy consumption in metalworking (replacing hot stamping processes with extrusion and cold stamping);
The use of rolling gears instead of manufacturing them on gear hobbing machines;
Expanding the use of powder metallurgy methods;
The use of CNC machines (computer numerical control), the development of robotics and flexible production structures;
Reducing the energy intensity of casting by reducing scrap.

Chemical and petrochemical industry. In these industries, there are a variety of technological processes that consume or produce large amounts of heat. Coal, oil and gas are used both as fuel and as raw materials.

The main areas of energy saving in these industries are:

Application of highly efficient combustion processes in technological furnaces and apparatus (installation of recuperators for heating water);
The use of submerged gas burners to replace steam heating of non-flammable liquids;
Introduction of a new technology for waste-free, environmentally friendly production of caprolactam with the production of thermal energy in the form of steam and combustible gases (PA "Azot");
Increasing the efficiency of rectification processes (optimizing the technological process using heat pumps, increasing the activity and selectivity of catalysts);
Improving and enlarging the unit capacity of units in the production of chemical fibers;
Reducing losses of fuel and raw materials in low-temperature processes;
Repurposing ammonia production to less energy-intensive methanol production (PO Azot).

A major reserve for saving energy resources in the petrochemical industry is the utilization of secondary energy resources, including the introduction of waste heat boilers for the production of steam and hot water in order to recover the heat of high-potential gas emissions.

Among industrial productions, the production of mineral fertilizers is one of the more energy-intensive. Energy costs account for approximately a third of the cost of certain types of products in this industry. Increasing energy efficiency is associated with the need to develop fundamentally new types of equipment for the production of mineral fertilizers, based on the use of modern physical, physico-chemical and physicomechanical influences (acoustic, vibration, electromagnetic) on technological processes, including heat and mass transfer devices, filters for mixing devices , granulators, etc.

Production of building materials.

The production of building materials is based on fire processes associated with the consumption of significant quantities of fuel oil, natural gas and coke, i.e. the most valuable fuels. At the same time, the efficiency of these fuels in the industry does not exceed 40%.

The largest amount of energy resources within the building materials industry is consumed in the production of cement. The most energy-intensive process in cement production is clinker annealing (clinker is a mixture of limestone and clay, raw materials for cement production, burned before sintering). With the so-called wet production method, the specific energy consumption for clinker annealing is approximately 1.5 times higher than with the dry method . Therefore, an important area of energy saving is the use of a dry method for producing cement from waterlogged raw materials.

In the production of concrete, energy-saving ones are the production and introduction of concrete hardening accelerator additives for the transition to low-energy-intensive technology for the production of precast reinforced concrete, as well as the use of heat generators for heat and humidity treatment of reinforced concrete in pit chambers; in brick production - the introduction of the method of evacuated autoclaves in brick factories, the introduction of kilns of panel structures in an all-metal casing for the production of clay bricks.

It is necessary to organize the production of building and insulating materials and structures that reduce heat loss through building envelopes, and to develop and implement a system of measures to use the potential of local fuels for firing wall ceramics.

In the glass industry, the thermal efficiency of fiery glass melting furnaces (the main fuel consumers) does not exceed 20-25%. The greatest energy losses occur through the enclosing structures of the furnaces (30-40%) and with exhaust gases (30-40%). The main tasks in the field of energy saving in the glass industry are to increase the efficiency of glass furnaces, replace scarce types of organic fuel and utilize secondary thermal resources.

In the forestry and woodworking industries, the main areas of energy saving are:

Introduction of economical units for drying wood chips in the production of particle boards;
Development and implementation of new cost-effective methods for the production of paper products, including the production of non-woven materials and paper with synthetic fiber;
Increasing the production of furniture using less energy-intensive methods using new types of facing materials instead of lamination;
Manufacturing of parts from chipboards;
Utilization of the heat of ventilation emissions and low-grade heat of steam-air mixtures;
Development and implementation of equipment for the production and use of generator gas from wood waste to produce heat and electricity;
Conversion of drying chambers PAP-32 from electricity to the production of wood waste.

The main directions of energy saving in light industry:

Improving technological processes for firing porcelain;
Introduction of heat exchangers that use the heat of the drying agent of heat-using equipment at light industry enterprises.

In agriculture, about half of energy savings can be achieved as a result of the introduction of energy-saving machines, technological processes and equipment.

The predominant share of the energy saving potential comes from eliminating direct waste and increasing the efficiency of agricultural machinery, reducing the consumption of fuel and energy resources by livestock farms and greenhouses by improving the thermophysical characteristics of building envelopes, recycling low-potential energy resources, optimizing energy balances in combination with the use of non-traditional sources (biogas, etc.) , reducing fuel consumption for grain drying, using economical fluidized bed boilers instead of electric boilers, using waste (straw, etc.) instead of traditional fuels.

The main directions of energy saving in agriculture, along with the creation of new equipment, are as follows:

Improving the technology of drying grain and feed, methods of using mineral and organic fertilizers;
Development and implementation of systems for using crop and livestock waste for energy purposes, as well as for the production of fertilizers and feed additives;
Using the heat from ventilation emissions from livestock buildings to heat water and heat rooms for young animals (using plate recuperators);
Ensuring optimal temperature conditions and sectioning the heating system of livestock buildings;
The use of heat pumps in heat and cold supply systems and devices for smooth regulation of the operation of ventilation systems, the introduction of modern instrumentation and automation equipment, the installation of energy metering and control devices, as well as the construction of biogas plants.

In the food industry, sugar production is one of the most energy-intensive. The main savings in energy resources in sugar production can be achieved as a result of improving technological schemes and the targeted introduction of energy-saving equipment, the use of low-grade heat from secondary vapors of evaporation and vacuum crystallization plants and condensates in thermal schemes.

Alcohol production is also energy-intensive. To reduce heat consumption, it is necessary to introduce enzymatic hydrolysis when preparing starch containing raw materials for fermentation.

The essence of energy saving policy in the period under review is to ensure the maximum possible satisfaction of the need for fuel and energy resources through their savings in industry, agriculture, the public sector and more efficient use in the electric power industry.

The main reasons for the ineffective use of fuel and energy resources in Belarus are due to the lack of a comprehensive technical, economic, regulatory and legal energy saving policy, deficiencies in design, construction and operation, and the lack of a technical base for the production of the necessary equipment, instruments, apparatus, automation and control systems.

The potential for energy saving in the electric power industry is formed through the widespread development of heating systems based on gas turbine units and combined cycle gas turbine units, the modernization and reconstruction of existing energy facilities, the improvement of technological schemes and optimization of equipment operating modes, increasing the efficiency of fuel combustion processes and their automation, and the introduction of automated control systems.

In the public utility sector, it is formed by improving the thermophysical characteristics of the enclosing structures of buildings and structures, modernizing and increasing the level of operation of small boiler houses, using more economical lighting devices, adjustable electric drives, widespread introduction of control and regulation metering devices, improving the maintenance of buildings and structures, increasing efficiency electric transport, efficiency of gas stoves, quality of thermal insulation, etc.

MAIN CONSUMERS OF THERMAL ENERGY

The main consumers of thermal energy are industrial enterprises and housing and communal services. Most industrial consumers require thermal energy in the form of steam (saturated or superheated) or hot water. For example, for power units that are driven by steam engines or turbines (steam hammers and presses, forging machines, turbopumps, turbocompressors, etc.), steam is required at a pressure of 0.8-3.5 MPa and superheated to 250-450 .

Technological apparatus and devices (various types of heaters, dryers, evaporators, chemical reactors) mainly require saturated or slightly superheated steam with a pressure of 0.3-0.8 MPa and water with a temperature of 150.

In housing and communal services, the main consumers of heat are heating and ventilation systems of residential and public buildings, hot water supply and air conditioning systems. In residential and public buildings, the surface temperature of heating devices, in accordance with the requirements of sanitary and hygienic standards, should not exceed 95, and the temperature of the water in hot water supply taps should not be lower than 50-60 in accordance with comfort requirements and not higher than 70 in accordance with safety standards. In this regard, in heating, ventilation and hot water supply systems, hot water is used as a coolant.

Heat supply systems.

A heat supply system is a complex of devices for the generation, transport and use of heat.

The supply of heat to consumers (heating systems, ventilation, hot water supply and technological processes) consists of three interrelated processes: the transfer of heat to the coolant, the transport of the coolant and the use of the thermal potential of the coolant. Heat supply systems are classified according to the following main characteristics: power, type of heat source and type of coolant. In terms of power, heat supply systems are characterized by the range of heat transfer and the number of consumers. They can be local or centralized. Local heat supply systems are systems in which three main units are combined and located in the same or adjacent rooms. In this case, the receipt of heat and its transfer to the indoor air are combined in one device and located in heated rooms (furnaces). Centralized systems in which heat is supplied from one heat source to many rooms.

Based on the type of heat source, centralized heating systems are divided into district heating and district heating. In a district heating system, the source of heat is the district boiler house, district heating plant, or combined heat and power plant.

The coolant receives heat in the district boiler house (or CHP) and through external pipelines, which are called heating networks, enters the heating and ventilation systems of industrial, public and residential buildings. In heating devices located inside buildings, the coolant releases part of the heat accumulated in it and is discharged through special pipelines back to the heat source.

Coolant is a medium that transfers heat from a heat source to heating devices of heating, ventilation and hot water supply systems.

Based on the type of coolant, heating systems are divided into 2 groups - water and steam. In water heating systems the coolant is water, in steam systems it is steam. In Belarus, water heating systems are used for cities and residential areas. Steam is used at industrial sites for technological purposes.

Water heating systems can be one-pipe or two-pipe (in some cases multi-pipe). The most common is a two-pipe heat supply system (hot water is supplied to the consumer through one pipe, and cooled water is returned to the thermal power plant or boiler room through the other, return pipe). There are open and closed systems heat supply. In an open system, “direct water withdrawal” is carried out, i.e. hot water from the supply network is disassembled by consumers for household, sanitary and hygienic needs. When hot water is fully utilized, a single-pipe system can be used. A closed system is characterized by almost complete return of network water to the thermal power plant (or district boiler house). The place where heat consumers connect to the heating network is called the customer input.

The requirements for coolants in centralized heating systems are sanitary and hygienic (the coolant should not worsen sanitary conditions in enclosed spaces - the average surface temperature of heating devices cannot exceed 70-80), technical and economic (so that the cost of transport pipelines is minimal, the mass of heating devices is small and ensured minimum fuel consumption for heating the premises) and operational requirements (the ability to centrally adjust the heat transfer of consumption systems in connection with variable outdoor temperatures).

Coolant parameters - temperature and pressure. Instead of pressure in operating practice, pressure N is used. Pressure and pressure are related by the relationship

where H is head, m; P - pressure, Pa; - density of the coolant, kg/; g - acceleration of gravity, m/ in centralized heat supply systems from a boiler house or thermal power plant, as well as in heating systems of industrial buildings.

Heating network

In Belarus, the length of heating networks (1996) is: main 794 km, distribution 1341 km.

The main elements of heating networks are a pipeline consisting of steel pipes connected to each other by welding, an insulating structure designed to protect the pipeline from external corrosion and heat loss, and a supporting structure that takes the weight of the pipeline and the forces arising during its operation.

The most critical elements are pipes, which must be sufficiently strong and sealed at maximum pressures and temperatures of the coolant, have a low coefficient of thermal deformation, low internal surface roughness, high thermal resistance of the walls, which helps retain heat, and constant material properties under prolonged exposure to high temperatures and pressures. .

Thermal insulation is applied to pipelines to reduce heat loss during coolant transportation. Heat losses are reduced by 10-15 times when laid above ground, and by 3-5 times when laid underground compared to uninsulated pipelines. Thermal insulation must have sufficient mechanical strength, durability, resistance to moisture (hydrophobicity), not create conditions for corrosion, and at the same time be cheap. It is represented by the following designs: segmental, wrapping, stuffing, cast and mastic. The choice of insulating structure depends on the method of laying the heat pipe.

Segmental insulation is made from previously manufactured molded segments of various shapes, which are applied to the pipeline, tied with wire, and covered on the outside with asbestos-cement plaster. Segments are made of foam concrete, mineral wool, gas glass, etc. Wrapping insulation is made of mineral felt, asbestos thermal insulation cord, aluminum foil and asbestos sheet materials. The pipes are coated with these materials in one or several layers and secured with bandages made of strip metal. Wrapping insulating materials are used mainly for insulating fittings, expansion joints, and flange connections. Printed insulation is used in the form of covers, shells, meshes filled with powdery, bulk and fibrous materials. Mineral wool, foam concrete chips, etc. are used for packing. Cast insulation is used when laying pipelines in non-passing channels and channelless laying.

Channel pipelines are constructed from precast concrete elements. The main advantage of passage channels is the possibility of access to the pipeline, its inspection and repair without opening the soil. Passage channels (collectors) are constructed when there are a large number of pipelines. Equipped with other underground communications - electrical cables, water supply, gas pipelines, telephone cables, ventilation, low voltage electric lighting.

Semi-through channels are used when laying a small number of pipes (2-4) in places where, due to operating conditions, opening the soil is unacceptable, and when laying pipelines of large diameters (800-1400 mm.)

Non-passable channels are made from standardized reinforced concrete elements. They are a trough-shaped tray with a ceiling made of prefabricated reinforced concrete slabs. The outer surface of the walls is covered with roofing felt on bitumen mastic. Insulation - anti-corrosion protective layer, thermal insulation layer (mineral wool or foam glass), protective mechanical coating in the form of metal mesh or wire. On top is a layer of asbestos cement plaster.

Literature:

Isachenko V.P., Osipova V.A., Sukomel A.S. Heat transfer. M.: energoizdat, 1981.
Thermal equipment and heat supply of industrial enterprises/Ed. B.N. Golubkova. M.: Energy, 1979.
Heating equipment and heating networks. G.A. Arsenyev et al. M.: Energoatomizdat, 1988.
Andryushenko A.I., Aminov R.Z., Khlebalin Yu.M. Heating plants and their use. M.: Higher. school, 1983.

Question 1. Classification of heat consumers. Heat load graphs.

BASICS OF GENERAL CHEMISTRY (theory and test materials)

Editor Asylbekova B.A.

Signed for publication 01/24/2002 Format 60x90/16 Price negotiable

Volume 5.7 ed. l. Circulation 300 copies. Order 2511

Printing and duplicating workshop of KarSTU, Karaganda, b. Mira, 56

Question 1. Classification of heat consumers. Heat load graphs.

Classification of heat consumers. (8, p.51..55)

Thermal consumption is the use of thermal energy for a variety of household and industrial purposes (heating, ventilation, air conditioning, showers, baths, laundries, various technological heat-using installations, etc.).

When designing and operating heat supply systems, it is necessary to take into account:

Type of coolant (water or steam);

Coolant parameters (temperature and pressure);

Maximum hourly heat consumption;

Change in heat consumption during the day (daily schedule);

Annual heat consumption;

Changes in heat consumption throughout the year (annual schedule);

The nature of the use of coolant by consumers (direct intake from the heating network or only heat extraction).

Heat consumers place different demands on the heat supply system. Despite this, heat supply must be reliable, economical and qualitatively satisfy all heat consumers.

The operating mode of technological systems is subject to changes, which can be both natural and random, long-term or short-term, but they must occur with minimal energy resources, without harming the reliability of operation of equipment and related systems.

Neglecting this factor usually leads to miscalculations when choosing equipment for power supply sources and unreasonable excessive consumption of fuel to provide the required load.

In order to assess the actual need of an enterprise or its divisions for thermal energy resources, it is necessary to analyze heat consumption schedules during certain periods of operation - during the day, week, month, year.

Characteristics of the uniformity of heat loads throughout the year are the number of hours of use of the maximum heat load, h/year, and the coefficient K, which is the ratio of the average daily load to the maximum daily load for the year.

According to these characteristics, industrial enterprises are divided into three groups: first t=4000 - 5000 hours/year, K=0.57 - 0.68; second t=5000 - 6000 hours/year, K=0.6 - 0.76; third t 6000 h/year, K 0.76.

The first group includes enterprises, for example, light industry and mechanical engineering, in the structure of thermal energy costs of which more than 40% are loaded by heating, ventilation and hot water supply systems. Accordingly, heat costs for the technology are less than 60%. The third group includes enterprises with a prevailing share of heat load costs for technological needs - more than 90%. Heat consumption by consumers of other categories is very small - less than 10% (Table 8).

Table 8

Heat consumers can be divided into two groups:

1) seasonal heat consumers;

2) year-round heat consumers.

Seasonal heat consumers are:

Heating;

Ventilation (with air heating in air heaters);

Air conditioning (obtaining air of a certain quality: cleanliness, temperature and humidity).

Year-round consumers use heat throughout the year. This group includes:

Technological heat consumers;

Hot water supply for municipal consumers.

Changes in seasonal load depend mainly on climatic conditions (outside air temperature, wind speed and direction, solar radiation, air humidity, etc.). Seasonal load has a relatively constant daily schedule and a variable annual load schedule (Fig. 11).

The technological load schedule depends on the profile and operating mode of production enterprises, and the hot water supply load schedule depends on the improvement of buildings, the composition and working hours of the main groups of the population, the operating mode of public utilities - bathhouses, laundries. It has an almost constant annual and sharply variable daily schedule. Daily schedules on Saturdays and Sundays usually differ from daily schedules on other days of the week.

Most heat supply systems have a varied heat load (heating, ventilation, hot water supply, process consumers). Its magnitude and nature depend on many factors, including climatic factors and, mainly, the outside air temperature.

The graph (Fig. 12) shows the dependence of heat consumption for heating, ventilation, hot water supply and technological needs on the outside air temperature, i.e. heat costs.

The ordinate axis shows the relative values of heat consumption in fractions of a unit (the maximum total heat consumption is taken as a unit, i.e., where , , , are the maximum calculated heat consumption for heating, ventilation, hot water supply and technological needs, respectively).

The abscissa axis is the outside air temperature.

Let's build four graphs of different thermal loads. Heat consumption per technological needs And hot water supply is not a function of outside temperature. The schedule will be uneven throughout the day and during the week, but smoothes out over the course of the year and becomes uniform.

As a rule, it is 24 hours a day. At a constant outside temperature, the heating load of residential buildings is almost constant. For industrial enterprises, it has an inconsistent daily and weekly schedule, i.e. In order to save money, the heat supply is artificially reduced at night and on weekends. The maximum heating consumption corresponds to the calculated outside air temperature for heating and is the calculated value of the heating load. The minimum heat consumption for heating corresponds to the calculated outside temperature at the beginning and end of the heating season

Characteristic temperatures for the graph ventilation load the following:

The design outdoor air temperature for ventilation corresponds to the design ventilation load (recirculation heating is used). When the heat consumption for ventilation is constant and ventilation units operate with recirculation, i.e. with the mixing of air taken from the premises with the outside air. Air recirculation is permissible for rooms where the air does not contain pathogenic microorganisms, toxic gases, vapors and dust. Air is mixed in front of the heating unit and in an amount that ensures its constant temperature. As the outside temperature decreases, the admixture increases and the outside air supply decreases. The temperature of the water entering the heaters remains constant. Thus, when the outside air temperature is lower, the heat consumption for ventilation remains equal to the calculated one due to a reduction in the air exchange rate. To regulate the frequency of air exchange in the interval ventilation units must be equipped with automatic regulators.

Ventilation start temperature. The minimum heat consumption for ventilation corresponds to the calculated outside temperature of the beginning and end of the heating period of industrial buildings.

The total heat consumption for heating, ventilation, hot water supply and technological needs in the region is the sum of the expenses of individual subscribers. The heating load is predominant. The graph of the total heat consumption has the form shown in Fig. 12. It has three break points:

a) the moment the heating is turned on;

b) the moment the ventilation is turned on;

c) moment of change in ventilation load.

The nature of the total load graph depends on the ratio of loads of individual consumer groups.

Main heating task is to maintain conditions of thermal comfort (conditions favorable for life and activity).

According to SNiP, permissible (optimal) meteorological conditions in the area of residential and public buildings:

Air temperature 18-22 o C (22-24 o C)

Relative humidity 65% (45-30)

Air movement speed no more than 0.3 m/s (0.1-0.15)

To do this, it is necessary to maintain a balance between the heat losses of the building and the heat gain, which can be expressed as the following equality ( heat balance):

where - total heat losses, - heat influx through the heating system, - internal heat sources.

Includes:

Losses due to heat transfer through external enclosures;

Infiltration losses due to the entry of cold air into the premises through leaks in external fences, , where is the infiltration coefficient ( = 0.03-0.06 - residential, public buildings, = 0.25-0.30 - industrial buildings);

Heat for heating cold objects (materials), ()

Includes:

From solar radiation (lanterns, windows);

From communications and technological equipment;

From electrical equipment and electrical lighting fixtures;

From heated material and products;

During technological processes (condensation);

From combustion products, furnace surfaces;

From people.

There are two calculation methods .

1) For small buildings(premises):

where is the heat transfer coefficient, is the surface area of individual external fences, is the difference in air temperatures from the inside and outside of these fences.

Calculation of heat consumption is the basis for determining the power of heat supply systems during their design, as well as for optimizing heat loads during their operation. The maximum heat consumption is determined at full load of process consumers and hot water supply, taking into account the heat consumption for heating and ventilation in the coldest period of the year. Based on the maximum heat consumption, the power of the industrial heating boiler house of the enterprise or the flow of coolants from centralized heat sources is selected.

Heat consumption for technological needs is given in the design documentation of the enterprise or workshop. Detailed calculations of heat consumption for individual technological processes are carried out using special methods and regulatory materials. In the absence of design data to determine the capacity of the boiler house and the entire heat supply system, the consumption of heat and coolants is calculated using aggregated specific indicators and standards or by analogy with other enterprises. Approximate norms of heat consumption by various consumers, taking into account losses to the environment, are presented in table. 19.2.

Table 19.2

Approximate norms of heat consumption for technological needs per one dense m 3 (sq. m 3) of product

Notes :

1. The difference in heat consumption for drying lumber and veneer is explained by the amount of heat loss in different types of dryers.
2. Heat consumption for pressing depends on the density of the finished slabs. Larger values should be taken for slabs of higher density.
3. Heat for heating the pool is consumed during half the heating season. Large values of heat consumption should be taken for regions with low winter temperatures.

The given standards are not permanent. They are gradually decreasing as a result of the use of energy-saving technologies.

Calculation of the maximum thermal power, MW, of technological consumers, with the exception of pool heating, can be carried out according to the following dependence:

Thermal power, MW, for heating water in a sawmill pool can be calculated using the formula

In formulas (19.1) and (19.2): q npi , q 6 - norms of heat consumption by technological consumers and the sawmill pool per unit of production, MJ/pl. m 3 (see Table 19.2); P™- - annual production by thermal consumer, sq. m 3; - annual volume of logs processed in the pool, MJ/pl.m, sweat - the duration of the heating season is determined according to climatological data for a given region, days; z np - operating time of the heat consumer per year, h/year.

Heat consumption for heating and ventilation buildings depend on the outside temperature and other climatic conditions (solar radiation, wind speed, air humidity), as well as on the design, industrial purpose and volume of the building. Consumers of thermal energy for heating and ventilation, for which heat consumption is required only at relatively low outside temperatures, are called seasonal.

The maximum (calculated) thermal heating power of an individual building, kW, for each building is determined as

thermal power of ventilation with air heating

Where q 0T j And q B i - specific heating and ventilation characteristics of buildings, depending on the purpose of the building and its volume, W/(m 3 K); V t - volume of the building according to external measurements, m 3; t p o - outside air temperature for heating calculations, °C, ; Грв - outside air temperature for ventilation calculations, °С, ; Гвн - indoor temperature according to Sanitary Norms and Rules (SNiP 41-01-2003, updated edition, valid since 2013) is accepted: for industrial premises - 16 °C, administrative and residential - 18 °C.

The total maximum thermal power is determined:

For heating system

For ventilation system

Average heat consumption for heating and ventilation, and (2 in p, kW, for the heating period are determined by the formulas:

Where t c p o - average outside air temperature during the heating period, °C.

Average heat consumption for hot water supply during the heating period Q B P B , kW, determined by the formula

Where from to= 4.19 - specific heat capacity of water, kJDkg-K); T - number of residents or employees in the enterprise; a = 100 - rate of hot water consumption for residential buildings per inhabitant, kg/person-day); b= 20 - water consumption rate for public buildings, kg/person/day); / g = 65 °C - hot water temperature; t x = 5 °C is the temperature of cold water.

The value (9 g avg, kW, can be approximately estimated using the formula

The estimated heat consumption for hot water supply of residential and public buildings Q rB, kW, is calculated using the formula

Where To - coefficient of hourly unevenness of heat consumption during the day (To = 2,04-2,4).

In summer, the heat load of hot water supply decreases due to an increase in the temperature of cold water, the average heat consumption (? g s in l, kW, is determined by the formula

where / x l is the temperature of tap water in summer (15 °C); (3 - coefficient that takes into account the reduction in hot water consumption in summer compared to winter (taken equal to 0.8 for residential and public buildings, for industrial enterprises (3 = 1).