Advantages and disadvantages of centralized and decentralized heat supply systems Davronov Ismat Zokir ugli Tashkent State Technical University, 2nd stage master

Advantages and disadvantages of centralized and decentralized heat supply systems
Davronov Ismat Zokir ugli
Tashkent State Technical University, 2nd stage master
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Abstract. The main direction of energy development in our country is industry, energy supply to agriculture, cities and towns is centralization. This direction is to increase labor productivity technical and economic issues of the country capacity building and energy security helps to solve. Electricity in industry, agriculture, transport within energy carriers with use and transmission over long distances is particularly important.
Key words: energy development, industry, energy supply, heat generating equipment, gas furnaces, environment and etc.

Most industrialized countries have taken a different approach: they have improved the level of safety and automation of heat generating equipment, increasing the efficiency of gas furnaces, sanitary, environmental, ergonomic and aesthetic performance; a comprehensive energy metering system has been established for all consumers; adjusted the regulatory and technical framework to the requirements of expediency and convenience of the consumer; the degree of centralization of heat supply is optimized; switched to the common adoption method, alternative sources of thermal energy. The result of this work has been the realization of energy savings in all sectors of the economy, including utilities. Consistent growth of the share of decentralized heat supply, maximum proximity of the heat source to the consumer and measurement of all types of energy sources by the consumer will not only create more favorable conditions for the consumer, but also save real gas fuel provides.

In general, the decisive situation of the industry includes the emergence of a large-scale crisis in the heat supply sector in the near future, the solution of which will require large financial investments. Rational decentralization of heat supply for home heating is a matter of time. Decentralized heat supply (DT) is the most radical, efficient, and inexpensive way to overcome many shortcomings. The judicious use of diesel fuel in the construction and reconstruction of buildings, combined with energy saving measures, will allow Russia to save a lot of energy. For a quarter of a century, quarterly and regional boilers have not been built in the most developed countries. In the current difficult environment, the only way out is to create and develop a DT system using autonomous heat sources. Depending on the heat supply of the apartment, it is the supply of heat and hot water to a private house or a separate apartment in a multi-storey house. The main elements of such autonomous systems are: heat generators - heating devices, heating and hot water pipes, fuel, air and smoke exhaust systems. Today, modular boilers designed for the organization of autonomous diesel fuel are developed and mass-produced. The principle of block-modular construction provides the ability to easily build a boiler with the required capacity. The absence of the need to lay a heating main and build a boiler house reduces communication costs and significantly increases the pace of new construction. In addition, these heating boilers allow the use of such boilers to provide a rapid supply of heat in emergencies and emergencies.
Central heating supply is characterized by the presence of a broadband subscriber heating network supplied with multi-sector (factories, enterprises, buildings, apartments, residential buildings, etc.) electricity. The connected scheme of the heating system - the central heating system is designed to work on very hot water. Its price is much lower than the cost of an independent circuit, with the exception of elements such as a heat exchanger, expansion tank and make-up pump, whose functions are performed centrally at the heat station. Overheated water from the main external heating system is mixed with water from the domestic heating system (t \ u003d 70-750S) and as a result water is delivered to the heating devices at the desired temperature. In this regard, the internal heating devices of the house are usually equipped with mixing plants (elevators). Disadvantages of the interconnection scheme associated with mixing Risk of hydrostatic pressure rise through the direct return heat pipe, which is dangerous for the integrity of the heating devices and fittings of the system. Decentralized hot water supply (DHW) and heat supply have so far been used only in the absence of a central heating supply or in cases where the possibility of centralized hot water supply is limited. Modern innovative technologies allow the use of decentralized hot water systems in the construction and reconstruction of multi-storey buildings. Local heat supply has many advantages. First, the quality of life of St. Petersburgers will improve: heating can be turned on in any season, regardless of the average daily temperature outside the window, hygienically clean water flow from the faucet, the possibility of erosion and burns and system malfunctions are reduced. In addition, the system ensures optimal heat distribution, eliminates heat loss as much as possible, and also allows for a reasonable consideration of resource consumption. The source of local hot water treatment in residential and public buildings is gas or electric water heaters or water heaters that use solid or gas fuel.
The advantages of decentralized heating systems help to increase the reliability of heat supply, as they are not connected to hot networks in our country more than 20 thousand km, and most of the pipes due to normative life (25 years), which leads to accidents. In addition, the construction of an extended heat main is associated with a capital cost of capital and a large weight loss. Hot pumps on the principle of action refer to heat transformers, in which the change in heat potential is carried out as a result of work. Today, energy saving policy is a priority in the development of energy and heat supply systems. In fact, every state-owned enterprise develops, approves, and implements energy saving and energy efficiency plans for enterprises, workshops, and so on. The country’s heating system is no exception. It is very large and cumbersome, consumes a lot of energy, and at the same time there are no large losses of heat and energy. Let’s take a look at what a heat supply system is, where the biggest losses occur, and what sets of energy-saving measures can be applied to increase the “efficiency” of that system.
Heat supply - heat supply of residential, public and industrial buildings (structures) to meet the domestic (heating, ventilation, hot water supply) and technological needs of consumers. In many cases, heat supply is to create a comfortable indoor environment - at home, at work or in a public place. Heat supply also includes tap water and water heating in swimming pools, heating of greenhouses and more. In modern central heating systems, the distance of heat transfer reaches several tens of kilometers. The development of heat supply systems is characterized by an increase in heat source capacity and unit capacity of installed equipment. The heat capacity of modern thermal power plants is 2-4 tcal / h, in regional boilers - 300-500 Gcal/h. In some heat supply systems, multiple heat sources work together for common heat networks, which increases the reliability, flexibility, and efficiency of the heat supply.
The water heated in the boiler room can be converted directly into a heating system. The hot water is heated in a heat exchanger (DHW) of the hot water supply system to a lower temperature, approximately 50-60 ° C. Temperature return water can be an important factor in protecting the boiler. The heat exchanger not only transfers heat from one phase to another, but also effectively copes with the pressure difference that exists between the first and second cycles. The desired floor heating temperature (30 ° C) can be obtained by adjusting the circulation temperature of hot water. The temperature difference can also be achieved by using a three-way valve that mixes the hot water in the system with the return water. In heat supply systems (daily, seasonal) the regulation of heat supply is carried out both at the heat source and at the devices consuming heat. Central quality control of heat supply in water heating systems is usually carried out for the main type of heat load - heating or a combination of two types of load - for heating and hot water supply. It consists of changing the temperature of the heat carrier delivered from the heat supply source to the heating network according to the accepted temperature schedule (i.e. the dependence of the required water temperature in the network on the outside air temperature). The central quality regulation is supplemented by local quantitative regulation at heating points; the latter is most common in hot water applications and is usually done automatically. In steam heating systems, mainly local quantitative regulation is carried out; the steam pressure at the heat supply source is kept constant, the steam flow is regulated by the consumers.
Central heating is an environmentally friendly and reliable method of heat supply. Central heating systems distribute hot water or, in some cases, steam from a central boiler between several buildings. There is a very wide range of sources that serve to generate heat, including burning oil and natural gas or using geothermal water. The use of heat from low temperature sources, such as geothermal heat, is possible using heat exchangers and heat pumps. The possibility of using unused heat from industrial enterprises, waste recycling, industrial processes and sewage, excess heat from target thermal power plants or thermal power plants allows for optimal selection of heat source in terms of energy efficiency. In this way, you optimize costs and protect the environment. Hot water from the boiler is supplied to the heat exchanger, which separates the production area from the distribution pipes of the central heating network. The heat is then distributed to the final consumers and transferred to the respective buildings through substations. Each of these substations typically includes a single heat exchanger for space heating and hot water. There are several reasons to install heat exchangers to separate the heating device from the central heating network. When there are significant pressure and temperature differences that can cause serious damage to equipment and property, the heat exchanger can provide sensitive heating and heat protection. ventilation equipment from the ingress of contaminated or corrosive environment. Another important reason for separating the boiler, the distribution network, and the end users is to clearly define the functions of each component of the system.
Another very important function of heat exchangers in a central heating system is to ensure safety. the internal system by separating the end consumers from the distribution network. This is necessary due to the significant difference in temperature and pressure values. In the event of an accident, the risk of flooding can also be minimized. A two-stage circuit is often found to connect heat exchangers at central heating points. This connection means maximum heat utilization and low return water temperature when using a hot water system. This is especially useful in combined applications of heating and power plants where low return water temperatures are required. This type of Substance can provide heat to up to 500, and sometimes more, homes. When operating in an existing district heating supply system, changes in the nature of the heat load, connection of new heat consumers, increase in the roughness of pipes, adjustment of the calculated temperature for heating, change of the temperature table for heating. the removal of thermal energy (TE) from a TE source, as a rule, leads to uneven heat supply to consumers, increases water costs in the network and reduces pipe permeability.
In addition, as a rule, there are problems with heating systems. Improper regulation of heat consumption regimes, elevator nodes such as lack of staff, unauthorized violation of connection schemes by consumers (installed by projects, specifications and contracts). These problems of heat consumption systems are manifested primarily in the misregulation of the entire system, which is characterized by an increase in the flow of cooling water. As a result, there is insufficient cooling water pressure at the inlet points (due to pressure loss), which in turn leads to the desire of subscribers to provide the required reduction by draining the network water from the return pipes to create at least a minimum level will bring. circulating heating devices inside (violation of connection schemes, etc.), which leads to an additional increase in flow and, consequently, to the emergence of new subscribers, which leads to additional pressure losses and pressure drops, and so on. There is a “chain reaction” in the completely wrong direction of the system. All this has a negative impact on the entire heat supply system and the activities of the energy supply organization: non-compliance with the temperature schedule; increase in filling of the heat supply system and forced filling with raw water when the water treatment capacity is exhausted (consequence - internal corrosion, premature failure of pipes and equipment); mandatory increase in heat supply to reduce the number of complaints from the population; increase in operating costs in the system of transportation and distribution of thermal energy.
It should be noted that there is always a correlation of stable thermal and hydraulic regimes in the heat supply system. A change in the flow distribution (including its absolute value) always changes the state of heat exchange directly in both heating devices and heat consumption systems. The result of abnormal operation of the heating system is, as a rule, a high temperature of the return network water. It should be noted that the temperature of the mains water returning at the heat source is one of the main operational characteristics designed to analyze the condition of the heating network equipment and the operating modes of the heat supply system. Evaluate the effectiveness of measures taken by organizations using heating networks to improve the performance of the heating system. As a rule, in case of improper placement of the heat supply system, the actual value of this temperature is significantly different from its normative, calculated value for this heat supply system. Thus, when the heat supply system is faulty, the temperature of the mains water turns out to be one of the main indicators of the mode of supply and consumption of thermal energy in the heat supply system: almost in the supply pipe. at all intervals of the heating season it is characterized by low performance; the temperature of the returning mains water, however, is characterized by increasing values; the temperature difference in the supply and return pipes, i.e. this indicator (along with the specific consumption connected to the heat load of the mains water) characterizes the level of quality of heat energy consumption, underestimated relative to the required values. It should be noted another aspect related to the growth of heat consumption systems (heating, ventilation) relative to the calculated value of network water consumption for the heating mode. It is recommended to use a dependency that determines the actual parameters and deviation cases for direct analysis. heat supply systems from structural elements, the ratio of the actual consumption of thermal energy in heat consumption systems to its calculated value.
All the advantages of co-production of heat and electricity belonged to electricity, centralized heating was financed on the principle of residual - sometimes CHP is already built, but heating networks have not yet risen. As a result, low-quality heat pipes with poor thermal insulation and inefficient drainage were installed, and work was done to connect heat consumers to the heating network. automatic regulation load, at best, using hydraulic regulators to stabilize very low quality cooling water flow. This forced the delivery of heat from the source according to the central quality control method (by changing the temperature of the heat carrier). according to a single table for all consumers with constant circulation in outdoor temperature networks), significant overconsumption of heat due to differences in the operating mode of consumers and the impossibility of using several heat sources in a single network for mutual backup led to. The lack or inefficiency of control devices at the points of connection of consumers to the heating networks has led to an excessive increase in the volume of cooling water. This led to an increase in the return water temperature to such an extent that there was a risk of the station circulating pumps failing and forcing this to reduce the heat supply to the source, disrupting the temperature schedule even under adequate power conditions.
Against this background, the position of decentralized heating supply is becoming increasingly reliable, which includes apartment heating and hot water supply systems, as well as residential buildings, including multi-storey buildings with a roof or an attached autonomous boiler. need The use of decentralization allows the heat supply system to better adapt to the conditions of heat consumption of a particular facility it serves, and the absence of external distribution networks virtually excludes non-production heat losses during transportation of the heat carrier does. Interest in autonomous heat sources (and systems) has increased in recent years. This is largely due to the country's financial situation and investment and credit policy, as the construction of a centralized heat supply system requires a one-time large capital investment; heating network and internal systems buildings, and on an irreversible basis with or without an unknown tin term. With decentralization, it is possible not only to reduce capital investment due to the lack of heating networks, but also to shift costs to the cost of housing (i.e., to the consumer). It is this factor that has recently led to an increase in interest in decentralized heating systems for new housing projects. The organization of autonomous heat supply allows the reconstruction of facilities in urban areas of old and dense buildings in the absence of idle capacity in centralized systems. Modern decentralization (including condensing boilers) based on the latest generation high-efficiency heat generators, using energy-saving automatic control systems, allows to fully meet the needs of the most demanding consumer.
An important advantage of decentralized systems is the possibility of local regulation of apartment heating and hot water systems. However, the heat source and the operation of the entire complex auxiliary equipment by non-professional staff (residents) does not always allow the heating system of apartments to take full advantage of this advantage. It should also be borne in mind that in any case it is necessary to establish or engage a repair and maintenance organization to service the heat supply sources.