Disadvantage of the radial scheme of heating networks. Power supply systems and sources (3 sem.). head valves distributor

To transport heat from the heat supply source to consumers, external heating network. They are one of the most labor-intensive and expensive elements of the heat supply system. Networks consist of steel pipes, connected by welding, thermal insulation, shut-off valves, compensators(thermal extenders), drainage And air venting devices, movable And fixed supports. The complex of building structures includes service chambers And underground canal system.

Heating networks are distinguished by the number of heat pipelines transmitting coolant in one direction (one-, two-, three- and four-pipe). Single-pipe The main line is used to supply water without returning it to the boiler room or thermal power plant and steam without returning condensate. This solution is possible when using water from the heating network itself for hot water supply, technological needs or long-distance heat supply from thermal power plants, as well as when using thermal waters.

In heat supply to small populated areas it is used two-pipe open heat supply system, when the heat network consists of supply and return heat pipes. Part of the water circulating in the open network is collected by subscribers for hot water supply.

In water and steam two-pipe closed systems, water circulating in heating networks or steam is used only as a coolant. The connection of a two-pipe heat supply system for heating and ventilation needs with a single-pipe hot water supply system leads to three-pipe. If the hot water supply system has two pipes, the second pipe is auxiliary to create circulation, eliminating the cooling of water with low water consumption. Then the entire heat supply system together with the two-pipe heating system is called four-pipe. Three-pipe or four-pipe can be used in cases where it is more rational to allocate hot water supply to a third pipe. In hot water supply systems of residential buildings, hospitals, hotels, etc., it is desirable to provide for water circulation.

The layout of the heating network is determined by the location of the thermal power plant or village boiler house among the heat consumers. Networks are running radial dead-end.

For settlements of agricultural enterprises, built up with two- and three-story houses located in groups (Fig. 1), forming parallel building fronts or closed contours, can be used ring monopipe heating network. Ring systems can be arranged

Rice. 1. Configuration of heating networks: A - radial network; B- radial network with jumpers; 1 - boiler room; 2 - heating network; 3 - jumper

both from group boiler houses and from a two-pipe heating boiler main.

Single-pipe ring systems have the same general principles actions as single-pipe internal heating systems. The coolant in the network sequentially passes through each connected building and in the latter approaches the temperature of the return water. Regulation of heat transfer in heated buildings is achieved by installing devices with different heating surfaces.

Single-pipe networks are laid parallel to the building front of the connected buildings at a distance of 3 to 5 m from the building line. The number of buildings connected to the heating network is determined from the condition of not exceeding the permissible pressure for heating devices.

Heat network pipelines are laid in impassable channels And ductless(underground installation), as well as on free-standing supports (ground installation). The latter is used on the territory of production sites, thermal power plants or when passing through undeveloped areas. Its use is limited to architectural considerations.

The main type of underground installation of heating networks is installation in non-passable channels.

In Fig. Figure 2 shows the design of a non-passable channel with concrete walls. With this design, the main costs (50-58%) fall on the construction part, thermal insulation of pipes, i.e. on auxiliary installation structures. Channels are laid at a depth of 0.7-1 m from the ground surface to the top of the floor slab. To avoid drainage devices, the heating network must be laid above the groundwater level. If this cannot be avoided, waterproofing the channel from two layers of roofing material on klebemass or laying with the smallest depth (up to 0.5 m). However, waterproofing the channels of heating networks does not provide reliable protection from groundwater, since in practical conditions it is difficult to carry out such insulation efficiently. Therefore, at present, when laying heating networks below the groundwater level, accompanying reservoir drainage is arranged.

Drainage pipes with a sand-gravel (crushed stone) filter are laid along the canal, usually on the side of the largest influx of groundwater. Sandy soil is laid under the canal and along its side walls, which facilitates the drainage of groundwater. In some cases, drainage pipes

placed under the channel (Fig. 2), and inspection wells are arranged inside compensatory niches. Installing drainage under a canal is much cheaper, especially in rocky and quicksand soils, since in this case no additional widening of the trenches is required.

The use of porous concrete pipes reduces the cost and speeds up the construction of drainage, since the labor-intensive work on installing filters is reduced.

When constructing a heating main channel in fine-grained sandy and sandy loam soils, a sand-gravel or sand filter with a layer of 150 can be installed mm under the canal.

The depth of heat pipelines is determined, as a rule, by the profile of the earth, the marks of the inputs, the length of the network and the laying of other underground communications. Water and gas pipelines are usually laid at the level of heating pipelines.

At intersections, it is allowed to install local bends in the water supply or gas pipelines, laying them above or below the heating pipelines.

To significantly reduce the cost of laying networks, ductless pipe laying in thermal insulating shells is used. In this case, the thermal insulation of the pipes is in direct contact with the ground. The material for constructing the heat-insulating shell must be hydrophobic, durable, cheap and neutral with respect to the metal of the pipes. It is desirable that it have dielectric properties. For this purpose, designs for channelless pipe laying in piece products made of cellular ceramics and in polyceramic shells are being mastered.

In places where the heating main branches to consumers, brick underground chamber-wells with shut-off and other fittings. The height of the chambers is assumed to be at least 1.8 m. The entrance to the chamber is through a cast-iron hatch; the depth is assumed to be 0.4-0.5 m. For cameras located inside residential buildings, they are allowed to be elevated above the ground to a height of no more than 400 mm.

To compensate for thermal elongation of pipelines due to changes in coolant temperature in straight sections of the heating main, flexible U-shaped compensators, and on broken sections the angles of rotation of the route are used (natural compensation). Compensators are placed in special brick niches provided along the length of the heating main. The distance between compensators is established by calculation or taken according to nomograms depending on the temperature of the coolant.

Pipes in the channels are laid on support concrete pads. The movement of pipes as their length changes ensures that the chambers are laid from the ground surface to the top of the coating.

The distance between the support pads depends on the diameters of the pipes being laid. For pipes with a diameter of no more than 250 mm distances accepted 2-8 m.

Thermal energy in the form of hot water or steam is transported from the heat source (CHP or large boiler house) to heat consumers through special pipelines called heating networks.

Heat network- one of the most labor-intensive elements of centralized heating systems. It represents heat pipelines - complex structures consisting of steel pipes connected by welding, thermal insulation, thermal expansion compensators, shut-off and control valves, building structures, movable and fixed supports, chambers, drainage and air release devices.

Based on the number of heat pipes laid in parallel, heat networks can be single-pipe, double-pipe and multi-pipe.

Single pipe networks most economical and simple. In them, network water after heating and ventilation systems must be completely used for hot water supply. Single-pipe heating networks are progressive in terms of significantly accelerating the pace of construction of heating networks. IN three-pipe networks two pipes are used as supply pipes to supply coolant with different thermal potentials, and the third pipe is used as a common return pipe. IN four-pipe networks one pair of heat pipes serves the heating and ventilation systems, and the other - the hot water supply system and technological needs.

Currently the most widespread two-pipe heating networks, consisting of supply and return heat pipelines for water networks and a steam pipeline with a condensate pipeline for steam networks. Due to the high storage capacity of water, which allows for long-distance heat supply, as well as greater efficiency and the possibility of central regulation of heat supply to consumers, water networks are more widely used than steam networks.

Water heating networks According to the method of preparing water for hot water supply, they are divided into closed and open. IN closed networks For hot water supply, tap water is used, heated by network water in water heaters. In this case, the network water is returned to the thermal power plant or to the boiler house. In open networks, water for hot water supply is collected by consumers directly from the heating network and, after use, is not returned to the network.

Heating networks are divided into main, laid in the main directions of populated areas, distribution- inside a block, microdistrict and branches to individual buildings.

Radial networks(Fig. 1a) are constructed with a gradual decrease in the diameters of heat pipes in the direction from the heat source. Such networks are the simplest and most economical in terms of initial costs. Their main drawback is the lack of redundancy. In order to avoid interruptions in heat supply (in the event of an accident on the main line of the radial network, the heat supply to consumers connected in the emergency area is stopped), reservation of heat supply to consumers must be provided by installing jumpers between the heating networks of adjacent areas and collaboration heat sources (if there are several of them). The range of water networks in many cities reaches a significant value (15–20 km).

Rice. 1. Heat network diagrams: dead-end(A) and ring (b)

1- radial main heat pipeline; 2 - heat consumers; 3 - jumpers; 4 - district (quarter) boiler houses; 5 - sectioning chambers; 6 - ring highway; 7 - central heating points; 8 - industrial enterprises

By installing jumpers, the heating network turns into a radial-ring network, and a partial transition to ring networks occurs. For enterprises where interruptions in heat supply are not allowed, duplication or ring circuits (with two-way heat supply) are provided for heating networks. Although ringing networks significantly increases their cost, in large heat supply systems the reliability of heat supply is significantly increased, the possibility of redundancy is created, and the quality of civil defense is also improved.

Steam networks They are arranged mainly with two pipes. Condensate is returned through a separate pipe - a condensate pipeline. Steam from a thermal power plant travels through a steam pipeline at a speed of 40–60 m/s or more to the point of consumption. In cases where steam is used in heat exchangers, its condensate is collected in condensate tanks, from where it is returned to the thermal power plant by pumps through a condensate pipeline.

Rice. 2. Laying heat pipes on masts

Rice. 3. Passage channel made of prefabricated reinforced concrete blocks

The direction of the route of heating networks in cities and other populated areas should be provided for in areas of the most dense heat load, taking into account existing underground and above-ground structures, data on the composition of soils and the level of groundwater, in the technical strips allocated for engineering networks parallel to the red lines of streets, roads, outside the roadway and green space. You should strive for the shortest route length, and therefore, less work on laying.

Rice. 4. Non-pass channels of the KL (a), KLp (b) and KLS (c) brands

Based on the method of installation, heating networks are divided into underground and above-ground (air). Aboveground laying of pipes (on free-standing masts or trestles, on brackets embedded in the walls of a building) is used in the territories of industrial enterprises, when constructing heating networks outside the city, when crossing ravines, etc. Overground laying of heating networks is recommended mainly at high groundwater standing. The predominant method of laying pipelines for heating networks is underground installation: in passage channels and collectors together with other communications; in semi-passing and non-passing canals; ductless (in protective shells of various shapes and with backfill thermal insulation).

The most advanced, but also more expensive method is the laying of heat pipes in passage channels, which are used when there are several heat pipes of large diameters. When the air temperature in the ducts is more than 50 °C, natural or mechanical ventilation is provided.

Exhaust shafts on the route are placed approximately every 100 m. Supply shafts are located between exhaust shafts and, if possible, combined with emergency hatches. In sections of heating networks with a large number of pipelines and high temperatures of coolants, mechanical ventilation is installed. When the air temperature in the channels is below 40 ° C, they are periodically ventilated by opening hatches and entrances. During repair work, a mechanical mobile ventilation unit can be used. In large cities, so-called urban collectors are built, in which heat pipelines, water supply, electrical and telephone cables are laid.

Semi-bore channels consist of L-shaped wall blocks, reinforced concrete bottoms and floors. They are built under passages with heavy street traffic, under railway tracks, at the intersection of buildings, where it is difficult to open heating pipes for repairs. Their height usually does not exceed 1600 mm, the width of the passage between the pipes is 400–500 mm. In the practice of centralized heating, the most widely used impassable channels.

Rice. 5. Structural elements of heating networks

a - heating network chamber; 1- stuffing box compensators; 2 - pressure gauges; 3 - fixed support; 4 - channel; b - placement of niches along the route of heat pipelines: N - fixed support; P - movable support; c - placement of the compensator in a niche: 1 - supply pipeline; 2 - return pipeline; 3 - wall; G - stuffing box compensator; 1 - pipe; 2 - ground book; 3 - cord packing; 4 - ring sealing; 6 - frame; 6 - counter axle; 7 - safety ring; 8- bolt: 9 - washer; 10 - screw; d - fixed shield support; 1 - reinforced concrete slab-shield; 2 - welded stops; 3-channel; 4 - concrete preparation: 5 - pipelines; 6 - drainage hole; e- roller movable support: 1 - roller; 2 - guides; 3 - metal lining

Rice. 6. Channelless installation of heat pipes in monolithic shells made of reinforced foam concrete

1- reinforced foam concrete shell; 2 - sand bedding; 3 - concrete preparation; 4 - soil

Three types of standard channels have been developed: a KL channel, consisting of trays and reinforced concrete floor slabs; a channel of the KLp brand, consisting of a bottom slab and a tray; and a channel of the KLS brand, consisting of two trays laid one on top of the other and connected with cement mortar using I-beams. Along the route of the underground heat pipeline, special chambers and wells are installed for installing fittings, measuring instruments, stuffing box expansion joints, etc., as well as niches for U-shaped expansion joints. The underground heating pipeline is laid on sliding supports. The distance between the supports is taken depending on the diameter of the pipes, and the supports of the supply and return pipelines are installed staggered.

Heating networks in general, especially main ones, are a serious and responsible structure. Their cost, compared to the costs of constructing a thermal power plant, is a significant part.

Ductless method of laying heat pipes- the cheapest. Its use makes it possible to reduce the construction cost of heating networks by 30–40%, significantly reduce labor costs and the consumption of building materials. Heat pipe blocks are manufactured at the factory. Installation of heat pipes on the route involves only laying the blocks in a trench using a truck crane and welding the joints. The depth of heating networks from the surface of the earth or road surface to the top of the channel or collector slab is taken, m: with a road surface - 0.5, without a road surface - 0.7, to the top of the channelless laying shell - 0.7, to the top of the chamber slab - 0.3.

Currently, over 80% of heating networks are laid in non-passage channels, about 10% are above-ground, 4% are in through channels and tunnels, and about 6% are channelless. The average service life of underground duct heating pipelines is half the standard and does not exceed an average of 10–12 years, and ductless ones with bitumen-based insulation are no more than 6–8 years. The main cause of damage is external corrosion, which occurs due to the absence or poor-quality application of anti-corrosion coatings, unsatisfactory quality or condition of the coating layers, allowing excessive moisture in the insulation, as well as due to flooding of channels due to structural leaks. Both in our country and abroad, a constant search is being carried out, and in recent years especially intensively, in the direction of increasing the durability of heat pipelines, the reliability of their operation and reducing the costs of their construction.

A heating network is a set of pipelines and devices that provide

transporting heat from the heat supply source to consumers using a coolant (hot water or steam).

Structurally, the heating network includes pipelines with thermal insulation and compensators, devices for laying and securing pipelines, as well as shut-off or control valves.

The choice of coolant is determined by an analysis of its positive and negative properties. The main advantages of a water heating system: high storage capacity of water; possibility of transportation over long distances; compared to steam, less heat loss during transportation; the ability to regulate the thermal load by changing the temperature or hydraulic mode. The main disadvantage of water systems is the high energy consumption to move the coolant in the system. In addition, the use of water as a coolant necessitates its special preparation. During preparation, carbonate hardness, oxygen content, iron content and pH are standardized. Water heating networks are usually used to satisfy heating and ventilation loads, hot water supply loads and low-potential process loads (temperatures below 100 0 C).

The advantages of steam as a coolant are the following: low energy losses when moving in channels; intense heat transfer during condensation in thermal appliances; In high potential process loads, steam can be used at high temperatures and pressures. Disadvantage: the operation of steam heating systems requires special safety measures.

The layout of the heating network is determined by the following factors: the location of the heat supply source in relation to the area of ​​heat consumption, the nature of the heat load of consumers, the type of coolant and the principle of its use.

Heat networks are divided into:

Trunk lines laid along the main directions of heat consumption facilities;

Distribution, which are located between the main heating networks and branch nodes;

Branches of heating networks to individual consumers (buildings).

Heat network diagrams are usually used as radial ones, Fig. 5.1. From the thermal power plant or boiler house 4, the coolant is supplied through radial lines 1 to heat consumer 2. In order to provide backup heat to consumers, the radial lines are connected by jumpers 3.

The radius of action of water heating networks reaches

12 km. For small lengths of pipelines, which is typical for rural heating networks, a radial scheme is used with a constant decrease in the diameter of the pipes as they move away from the heat supply source.

Laying of heating networks can be above-ground (air) and underground.

Aboveground pipe laying (on

free-standing masts or overpasses, on concrete blocks and is used in the territories of enterprises, when constructing heating networks outside the city limits when crossing ravines, etc.

In rural settlements, ground laying can be on low supports and supports of medium height. This method is applicable at temperatures warm

carrier no more than 115 0 C. Underground installation is the most common. There are channel and non-channel installations. In Fig. Figure 5.2 shows a channel gasket. When laying in a channel, the insulating structure of the pipelines is unloaded from the external loads of the backfill. For channelless installation (see Fig. 5.3), pipelines 2 are laid on supports 3 (gravel

or sand cushions, wooden blocks, etc.).

Backfill 1, which is used: gravel, coarse sand, milled peat, expanded clay, etc., serves as protection against external damage and at the same time reduces heat loss. When laying in a channel, the temperature of the coolant can reach 180 °C. For heating networks, steel pipes with a diameter of 25 to 400 mm are most often used. In order to prevent the destruction of metal pipes due to temperature deformation, compensators are installed along the length of the entire pipeline at certain distances.

Various designs of compensators are shown in Fig. 5.4.

Rice. 5.4. Compensators:

a – U-shaped; b– lyre-shaped; V– stuffing box; G– lens

Type compensators A (U-shaped) and b (lyre-shaped) are called radial. In them, the change in pipe length is compensated by the deformation of the material in bends. In stuffing box expansion joints V It is possible for the pipe to slip within the pipe. In such compensators there is a need for a reliable seal design. Compensator G - lens type selects a change in length due to the springing action of the lenses. Great prospects for reinforced compensators. A bellows is a thin-walled corrugated shell that allows it to absorb various movements in the axial, transverse and angular directions, reduce vibration levels and compensate for misalignment.

Pipes are laid on special supports of two types: free and fixed. Free supports ensure the movement of pipes during temperature deformations. Fixed supports fix the position of pipes in certain areas. The distance between the fixed supports depends on the diameter of the pipe, for example, with D = 100 mm L = 65 m; at D = 200 mm L = 95 m. Between the fixed supports under the pipes with compensators, 2...3 movable supports are installed.

Currently, instead of metal pipes, which require serious protection against corrosion, plastic pipes have begun to be widely used. The industry of many countries produces a wide range of pipes made of polymer materials (polypropylene, polyolephen); metal-plastic pipes; pipes made by winding threads from graphite, basalt, glass.

On main and distribution heating networks, pipes with thermal insulation applied in an industrial manner are laid. For thermal insulation of plastic pipes, it is preferable to use polymerizing materials: polyurethane foam, polystyrene foam, etc. For metal pipes, bitumen-perlite or phenolic-polymer plastic insulation is used.

5.2. Heating points

A heating point is a complex of devices located in a separate room, consisting of heat exchangers and elements of heating equipment.

Heating points provide connections of heat-consuming objects to the heating network. The main task of the TP is:

– transformation of thermal energy;

– distribution of coolant among heat consumption systems;

– control and regulation of coolant parameters;

– accounting for coolant and heat costs;

– shutdown of heat consumption systems;

– protection of heat consumption systems from emergency increases in coolant parameters.

Heating points are divided according to the presence of heating networks after them into: central heating points (CHP) and individual heating points (ITP). Two or more heat consumption facilities are connected to the central heating station. ITP connects the heating network to one object or part of it. According to their location, heating points can be free-standing, attached to buildings and structures, or built into buildings and structures.

In Fig. Figure 5.5 shows a typical diagram of ITP systems that provide heating and hot water supply to a separate facility.

Two pipes are connected from the heating network to the shut-off valves of the heating point: supply (high-temperature coolant enters) and

return (cooled coolant is removed). Parameters of the coolant in the supply pipeline: for water (pressure up to 2.5 MPa, temperature - not higher than 200 0 C), for steam (p t 0 C). At least two heat exchangers of a recuperative type (shell-and-tube or plate) are installed inside the heating point. One ensures the transformation of heat into the heating system of the facility, the other into the hot water supply system. In both systems, devices for monitoring and regulating parameters and coolant supply are installed in front of the heat exchangers, which allows for automatic recording of consumed heat. For the heating system, the water in the heat exchanger is heated to a maximum of 95 0 C and pumped through the heating devices by a circulation pump. Circulation pumps (one working, the other standby) are installed on the return pipeline. For hot water supply

The water pumped through the heat exchanger by a circulation pump is heated to 60 0 C and supplied to the consumer. The water flow is compensated into the heat exchanger from the cold water supply system. To account for the heat expended on heating water and its consumption, appropriate sensors and recording devices are installed.

Commercial risk (risk of reduction in service volumes) is minimized the right choice marketing strategy and promotions, continuous monitoring of customer needs, implementation of a flexible assortment policy. It should be noted that during the financial and economic assessment of the project, a cautious assessment of the volume of services was taken.

Profitability risk (failure to achieve the planned level of project profitability) minimized due to a flexible tariff policy, choosing prices for services at the average market level, and cost control.

Political risks to a certain extent can be limited through contacts with city authorities and legal support for the project during its implementation.

HYDRAULIC CALCULATION

TASKS OF HYDRAULIC CALCULATION

Hydraulic calculation tasks:

1) determination of pipeline diameters;

2) determination of pressure drop (pressure);

3) determination of pressures (pressures) at various points in the network;

4) linking all points of the system in static and dynamic modes in order to ensure permissible pressures and required pressures in the network and subscriber systems.

In some cases, the task of determining bandwidth pipelines with a known diameter and a given pressure loss.

The results of hydraulic calculations are used for:

1) determining capital investments, metal (pipes) consumption and the main volume of work on the construction of a heating network;

2) establishing the characteristics of circulation and make-up pumps, the number of pumps and their placement;

3) clarifying the operating conditions of heat sources, the heating network and subscriber systems and selecting schemes for connecting heat-consuming installations to the heating network;

5) development of operating modes for heat supply systems.

The initial data for carrying out a hydraulic calculation must be the design and profile of the heating network, the location of heat sources and consumers and the design loads.

DIAGRAMS AND CONFIGURATIONS OF HEATING NETWORKS

The heating network is the connecting and transport link of the heat supply system.

She must have the following qualities:

1. reliability; they must maintain the ability to continuously supply coolant to the consumer in the required quantity throughout the year, with the exception of a short break for preventative maintenance in the summer;

2. controllability – i.e. ensure the required operating mode, the possibility of joint operation of heat supply sources and mutual redundancy of mains.

The required operating mode is the fast and accurate distribution of coolant to heating points under normal conditions, in critical situations, as well as when heat sources work together to save fuel.

The heating network diagram is determined:

Placement of heat sources (CHP or boiler houses) in relation to the area of ​​heat consumption;

The nature of the heat load of consumers in the area;

Type of coolant.

The basic principles that should be followed when choosing a heating network diagram are the reliability and efficiency of heat supply. When choosing the configuration of heating networks, you should strive to obtain the most simple solutions and the shortest length of heat pipes.

Increasing network reliability is carried out using the following methods:

Increasing the reliability of individual elements included in the system;

Using a “gentle” operating mode of the system as a whole or its most damaged elements by maintaining the water temperature in the supply lines at 100°C and above, and in the return lines at 50°C and below;

Reservations, i.e. the introduction of additional elements into the system that can completely or partially replace failed elements.

According to the degree of reliability, all consumers are divided into two categories:

I – medical institutions with hospitals, industrial enterprises with constant heat consumption for technological needs, groups of urban consumers with a thermal power of 30 MW. A break in the heat supply is allowed only for the switching period, i.e. no more than 2 hours;

II – all other consumers.

Steam as a coolant is used mainly for process loads of industrial enterprises. The main load of steam networks is usually concentrated in a relatively small number of nodes, which are the workshops of industrial enterprises. Therefore, the specific length of steam networks per unit of design heat load is small. When, due to the nature of the technological process, short-term (up to 24 hours) interruptions in the steam supply are permissible, the most economical and at the same time quite reliable solution is to lay a single-pipe steam pipeline with a condensate pipeline.

It must be borne in mind that duplication of networks leads to a significant increase in their cost and consumption of materials, primarily steel pipelines. When laying, instead of one pipeline designed for 100% load, two parallel ones designed for 50% load, the surface area of ​​the pipelines increases by 56%. Accordingly, metal consumption and the initial cost of the network increase.

A more difficult task is the choice of a water heating network scheme, because their load is less concentrated.

Water networks are less durable than steam networks due to:

Greater susceptibility to external corrosion of steel pipelines of underground water networks compared to steam pipelines;

Sensitivity to accidents due to the higher density of the coolant (especially in large systems with dependent connection of heating installations to the heating network).

When choosing a water heating network scheme Special attention pay attention to issues of reliability and redundancy of heat supply systems.

Water heating networks are divided into main And distribution.

Main lines usually include heat pipelines that connect heat sources with areas of heat consumption, as well as with each other.

The operating mode of main heating networks should ensure the greatest efficiency in the generation and transport of heat due to the joint operation of thermal power plants and boiler houses.

The operating mode of distribution networks should provide the greatest savings in heat when using it by adjusting the parameters and flow of coolant in accordance with the required consumption mode, simplifying the layout of heating points, reducing the design pressure for their equipment and reducing the number of heat supply regulators for heating.

The coolant comes from the main networks to the distribution networks and is supplied through the distribution networks through group heating points or local heating points to the heat consuming installations of subscribers. Direct connection of heat consumers to main networks is allowed only when connecting large industrial enterprises.

Main heating networks are divided into sections 1-3 km long using valves. When a pipeline opens (ruptures), the location of the failure or accident is localized by sectional valves. Thanks to this, losses of network water are reduced and the duration of repairs is reduced due to a decrease in the time required to drain water from the pipeline before repairs and to fill the pipeline section with network water after repairs.

The distance between the sectional valves is selected from the condition that the time required for repairs is less than the time during which the internal temperature in the heated rooms, when the heating is completely turned off at the design outside temperature for heating, does not fall below the minimum limit value, which is usually taken as 12- 14 °C in accordance with the heat supply agreement. The time required to carry out repairs increases with the diameter of the pipeline, as well as the distance between the sectional valves.

Fig.1. Schematic diagram of a two-pipe heating network with two mains: 1 – CHP collector; 2 – backbone network; 3 – distribution network; 4 – sectioning chamber; 5 – sectional valve; 6 – pump; 7 – blocking connection.

The distance between sectional valves should be smaller for larger pipeline diameters and at lower design outside temperatures for heating.

The condition for repairing a large-diameter heat pipeline during the period of permissible decrease in internal temperature in heated buildings is difficult to fulfill, since the repair time increases significantly with increasing diameter.

In this case, it is necessary to provide for system backup of heat supply in the event of failure of a section of the heating network, if the above condition regarding repair time is not met. One of the redundancy methods is to block adjacent highways.

Sectional valves are placed at the junction points of distribution networks to main heating networks.

In these nodal chambers, in addition to sectional valves, there are also head valves of distribution networks, valves on blocking lines between adjacent mains or between mains and backup heat supply sources, for example, district boiler houses.

There is no need to section steam lines, since the mass of steam required to fill long steam lines is small. Sectional valves must be equipped with an electric or hydraulic drive and have a telemechanical connection with the central control center. Distribution networks must be connected to the main line on both sides of sectional valves so that uninterrupted heat supply to subscribers can be ensured in case of accidents on any sectioned section of the main line.

Interlocking connections between highways can be made using single pipes.

In buildings of a special category that do not allow interruptions in heat supply, the possibility of backup heat supply from gas or electric heaters or from local boiler houses should be provided in case of emergency interruption of centralized heating supply.

According to SNiP 2.04.07-86, it is allowed to reduce the heat supply in emergency conditions to 70% of the total design consumption (maximum hourly for heating and ventilation and average hourly for hot water supply). For enterprises in which interruptions in the heat supply are not allowed, duplicate or ring circuits of heating networks should be provided. Estimated emergency heat consumption must be taken in accordance with the operating mode of enterprises.

The radius of the heating network (Fig. 1) is 15 km. To the final heat consumption area, network water is transmitted through two two-pipe transit mains 10 km long. The diameter of the lines at the exit from the thermal power plant is 1200 mm. As water is distributed into associated branches, the diameters of the main lines decrease. In the final area of ​​heat consumption, network water is introduced through four mains with a diameter of 700 mm, and then distributed through eight mains with a diameter of 500 mm. Interlocking connections between main lines, as well as redundant pumping substations, are installed only on lines with a diameter of 800 mm or more.

This solution is acceptable in the case when, with the accepted distance between sectional valves (2 km in the diagram), the time required to repair a pipeline with a diameter of 700 mm is less than the time during which the internal temperature of heated buildings when the heating is turned off at an external temperature of 1 will decrease from 18 up to 12 °C (not lower).

Interlocking connections and sectioning valves are distributed in such a way that in the event of an accident on any section of the main line with a diameter of 800 mm or more, heat supply is provided to all subscribers connected to the heating network. Heat supply to subscribers is disrupted only in case of accidents on lines with a diameter of 700 mm or less.

In this case, the heat supply to subscribers located behind the accident site (along the heat flow) is stopped.

When supplying heat to large cities from several thermal power plants, it is advisable to provide for mutual interlocking of thermal power plants by connecting their mains with interlocking connections. In this case, a combined ring heat network with several power sources can be created (Fig. 2). In some cases, the heat networks of thermal power plants and large district or industrial boiler houses can be combined into the same system.

The integration of main heating networks of several heat sources, along with heat supply redundancy, makes it possible to reduce the total boiler reserve at a thermal power plant and increase the degree of use of the most economical equipment in the system due to optimal load distribution between heat sources.

Blocking connections between large-diameter mains must have sufficient capacity to ensure the transmission of redundant water flows. If necessary, pumping substations are built to increase the capacity of blocking connections.

Regardless of the blocking connections between the mains, it is advisable in cities with a developed hot water supply load to provide jumpers of a relatively small diameter between adjacent heat distribution networks to reserve the hot water supply load.

When the diameters of the mains emanating from the heat source are 700 mm or less, a radial (radial) heating network diagram is usually used with a gradual decrease in diameter as the distance from the station increases and the connected heat load decreases (Fig. 3). Such a network is the cheapest in terms of initial costs, requires the least metal consumption for construction and is easy to operate. However, in the event of an accident on the main line of the radial network, the heat supply to subscribers connected to the site of the accident is stopped. For example, in the event of an accident at point “a” on radial highway 1, the power supply to all consumers located along the route from the thermal power plant after point a is cut off. If an accident occurs on the main line near the station, the heat supply to all consumers connected to the main line is stopped. This solution is acceptable if the repair time for pipelines with a diameter of at least 700 mm satisfies the above condition.

For more reliable heat supply, heating networks should be constructed according to the block principle. The block should be a distribution network with a range of 500-800 m. Each block should provide heat supply to a residential neighborhood of approximately 10 thousand apartments or a thermal power of 30-50 MW. The unit must be directly connected to the source collector, or have a two-way heat supply from heat mains.

On the heat map of the area, the locations of the GTP are tentatively outlined;

After placing the GTP, possible routes of highways and jumpers between them are outlined;

The location of distribution networks is planned.

Distribution networks are designed as dead-end networks; sectional valves are not designed.

Distribution networks are allowed to be laid in the basements of buildings

On the importance of the thermal point in common system There is no need to say much about heat supply. Thermal circuits of thermal units are involved both in the network and in the internal consumption system.

The concept of a heating point

The efficiency of use and the level of heat supply to the consumer directly depends on the correct functioning of the equipment.

In fact, a heating point represents a legal boundary, which in itself presupposes equipping it with a set of control and measuring equipment. Thanks to this internal filling, determining the mutual responsibilities of the parties becomes more accessible. But before you understand this, you need to understand how thermal diagrams of thermal units function and why read them.

How to determine the diagram of a thermal unit

When determining the layout and equipment of a heating point, they rely on specifications local heat consumption system, external network branch, operating mode of systems and their sources.

In this section, you will become familiar with the coolant flow graphs - the thermal diagram of the heating unit.

A detailed examination will allow you to understand how the connection to the common collector is made, the pressure within the network and relative to the coolant, the indicators of which directly depend on the heat consumption.

Important! If a heating unit is connected not to the collector, but to the heating network, the coolant flow of one branch inevitably affects the flow of the other.

Analysis of the circuit in detail

The figure shows two types of connections: a - in case of connecting consumers directly to the collector; b - when connecting to a branch of the heating network.

The drawing reflects graphical changes in coolant flow rates when the following circumstances occur:

A - when connecting heating systems and to heat source collectors separately.

B - when connecting the same systems to an external one. It is interesting that the connection in this case is characterized by high pressure loss in the system.

Considering the first option, it should be noted that the total coolant flow rates increase synchronously with the flow rate for hot water supply (in modes I, II, III), while in the second, although there is an increase in the flow rate of the heating unit, along with it Heating consumption figures are automatically reduced.

Based on the described features of the thermal circuit of the thermal unit, we can conclude that as a result of the total flow rate of the coolant considered in the first option, when applied in practice, it is about 80% of the flow rate when using the second prototype of the circuit.

Place of the diagram in design

When designing a diagram of a thermal heating unit in a residential neighborhood, provided that the heat supply system is closed, pay special attention to the choice of the connection diagram of hot water supply heaters to the network. The selected project will determine the estimated coolant flow rates, functions and control modes, etc.

The choice of the thermal heating unit circuit is primarily determined by the established thermal regime of the network. If the network operates according to the heating schedule, then the selection of the drawing is made based on the technical and economic calculation. In this case, parallel and mixed circuits of thermal heating units are compared.

Features of heating point equipment

In order for the home’s heating network to function properly, the following is additionally installed at heating points:

• gate valves;
• special filters that capture dirt particles;
• control and statistical instruments: thermostats, pressure gauges, flow meters;
• auxiliary or reserve pumps.

Diagram legends and how to read them

The picture above shows circuit diagram thermal unit with detailed description all constituent elements.

Item number	Symbol
	Three way valve
	Gate valve
	Plug tap
	Sump
	Check Valve
	Throttle washer
	V-shaped fitting for thermometer
	Thermometer
	Pressure gauge
	Elevator
	Heat meter
	Water flow regulator
	Sub-steam regulator
	Valves in the system
	Stroke line

The designations on the diagrams of thermal units help to understand the functioning of the unit by studying the diagram.

Engineers, based on the drawings, can guess where a breakdown occurs in the network when problems are observed, and quickly fix it. Diagrams of thermal units will also be useful if you are designing a new house. Such calculations are necessarily included in the package project documentation, because without them it is impossible to install the system and wiring throughout the house.

Information about what a thermal system drawing is and how to use it in practice will be useful to anyone who has encountered heating or water heating devices at least once in their life.

We hope that the material presented in the article will help you understand the basic concepts and understand how to identify the main nodes and designation points of the fundamental elements on the diagram.