Distribution and transportation of heat carrier between consumers takes place through a special heat network. It is one of the main elements of the entire structure of engineering communications. The reliability and quality of transmission directly depend on how it works. Pipelines of heat networks are not the only elements of this structure. In addition to them, it also includes various structures. These include, in particular, throttle and pumping stations, heating points.
Structure
Heat network, based on a centralized supply scheme, is divided into two levels in its structure: main and quarterly (micro-district). The first one consists of elements connecting heat sources with local (district) points of its distribution among end consumers. In most cases, they are a looped system of pipes (diameter 500–1400 mm) and engineering structures. These elements are located throughout the city, which ensures the reliability of transmission and the ability to meet the demand for consumption. Thanks to the separation, the operation of heating networks is greatly facilitated. So, various schemes are createdcontrols that increase the reliability of work and increase the quality of supply. Design and laying of heating networks of the main type are carried out taking into account possible failures in the operation of any underwater element. In this regard, backup links are created. They are connected to heat sources. With this approach, a unified management system is created. It is able to uninterruptedly provide the declared indicators of thermal and hydraulic modes. At the same time, work is carried out even if one of its elements (supplying source, one of the branches of the main line) fails. The distribution of the coolant under such conditions is better, losses due to transmission are reduced, and fuel savings are observed.
Management
The rules of heat networks provide for the presence of special elements with the help of which the structure is controlled. These include, in particular, locking mechanisms - valves. With their help, the general heating network is divided into separate sections. The impact on the valves allows you to turn on (turn off) small sections of the highway, as well as pumping and throttle stations located on them. Most modern devices are equipped with an electric drive. They are placed on average every 1-3 km of the highway. The general management of networks includes the control of the mode of operation and the state of structural elements, the prevention of possible malfunctions. To protect against water hammer, a special relief device is installed at local points.
Quarter heating network. Features
These structures are branched dead-end systems. They are connected to heating points. Management occurs both in manual and offline modes. Such a structure has a diameter of up to 400 mm; therefore, interruptions in the supply of thermal energy to consumers as a result of a breakdown in such a network are considered acceptable. However, as a result of the general design of supply schemes, only a small part of end-users suffers in the event of a malfunction. Repair of heating networks in this case does not take much time. The points through which the media enters the system are automated. This allows you to save on the consumption of thermal energy.
Connecting to the backbone
Distribution networks are connected to the general system using mixers or pumps (mixing-circular), less often through water heaters. The use of the latter makes the system more flexible and reliable. This is possible due to the separation of the hydraulic regimes of the main and distribution systems. The carrier entering the general networks from different sources may have different temperatures, exceeding that which is already in the pipeline. Supply systems equipped with pumps exclude hydraulic isolation of lines from distribution circuits. As a result, the management of the corresponding emergency mode becomes more complicated. In this case, it becomes possible to independently maintain with the help of a pump in the distribution networks of circular andtemperature conditions, which will differ from the main ones.
Two-level view of the system
The scheme of the large structure of the heat network has a two-level view. At the top is the ring highway. Branches depart from it to the heating points of the regions. The connection uses the ordinary method. In case of failure of the section of the main line to which the heating point is connected, end consumers are deprived of thermal energy. Users are connected to the district point using local systems - this is the lower level.
Serving reservation
The coolant is supplied to the main network from the thermal power plant and the district boiler house. In this case, it is possible to carry out the process of reserving the supply in case of a breakdown of one of the media heating points. This is done by installing a connecting jumper on the supply and return lines. The combination of these elements forms a single ring heating network. The designed diameter of the conductive elements of the systems is calculated in such a way as to ensure the throughput of the required carrier even in emergency situations. Under conditions of stable, uninterrupted operation, the coolant moves through all the heat pipelines of the network. In this case, the use of jumpers loses its meaning. For a more efficient use of jumpers and a reduction in the cost of heating the coolant, the "unloaded reserve" method is used. In this case, there is a complete overlap of the jumpers. The jumpers are switched on only in case of failure of the thermal elements.network.
Heat pipelines of networks
The movement of the carrier is carried out along these elements, in the form of which water appears. Heat pipelines are installed by above-ground and underground methods. In the first case, the gasket has a number of significant advantages: increased service life, easy monitoring of the system status, and easier access for troubleshooting. However, the installation of an above-ground heat pipeline in modern cities is practically impossible due to architectural restrictions. Under these conditions, most systems are underground. To install such pipelines, special channels break out.
Using the system
Before the working launch, thermal tests of heating networks are carried out. The installed elements are filled with hot water of different temperatures. The fluid is subsequently drained repeatedly during its service life. As a result of all internal influences, the walls of the pipe change, the way out of this situation is the installation of compensators in the pipelines. The two ends of the section are fixedly fixed on the supports. A compensator is installed in the middle. Additionally, pipelines are fixedly fixed near heat exchangers, pumps. This is done to relieve the load exerted by thermal deformation. Supports are placed in channels or special chambers. In the channels, the pipeline is laid on movable supports. In order to constantly monitor the state of the systems, special underground chambers are being built. They accommodate various valves, drain valves, air cocks andcompensators. In some cases (for example, with a water pipe diameter of more than 500 mm), ground pavilions are erected above the chambers to test heating networks and more comfortable maintenance. Placement of points and pumping stations takes place in specially equipped buildings.
Choosing the optimal option for heating networks
Currently, there are a huge number of schemes of heating networks and ways to lay them. Therefore, several options are considered at the design stage. Comparing all possible conditions, technical and economic calculations are made, the least expensive option with the best characteristics is selected. According to these calculations, the diameter of the elements used, the insulating materials and their thickness, the power of the installed pumps are determined. In addition, the costs for the construction and maintenance of the heat pipeline, for heat losses during transmission from the source to the consumer are kept.
Russian heating systems
Most of the currently operated heating networks in Russia were built back in the USSR, after the collapse of which funding for the relocation and renewal of existing heat pipelines was sharply reduced. Scheduled checks of the state of systems and their regular replacements have ceased, control by the state has also begun to weaken.
The overall situation with heating networks in the country began to deteriorate sharply. In conditions of significant savings, the requirements for the quality of elements began to decrease,used in the relocation of existing systems. Savings led to a reduction in the cost of work, which affected their final quality. The systems built in these years had a low service life and required re-replacement after 5-7 years. All this led to a sharp increase in the number of malfunctions, which led to an increase in the capacity of emergency services. Heat losses during the transfer of the carrier are estimated at 20-50% of the total output during the heating period and from 30 to 70% - in the summer. These figures are several times higher than the norms adopted in the developed countries of Europe.
