Contents

• 1. Introduction
• 2. History
• 3. The list of references

1. Introduction

Since the intensive development of district heating in Russia and the CIS countries, the time used a lot of concepts, which were based on the definition of radius of a heat supply. We will mention only three of them, the most common: the optimal radius of a heat supply; the optimal radius of the heat; the radius of reliable heat supply.

Since the introduction of the law "On heat supply" has another definition: the effective heating radius is the maximum distance from het consuming installation to the nearest source of heat energy in the heating system which, if exceeded, connection het consuming installation to the heat supply system is impractical, owing to the increase of total expenditure in the heating system.

2. History

For the First time in 1935 for the analysis of efficiency of district heating of S. F. Kopienam were applied two simplex: specific material characteristic of µ and the specific length λ heat network in the area of the heat source. In the first case, the specific material characteristics of thermal network representing the relationship of the material characteristics of the heat network, forming a zone of a heat source, connected to this heat network heat load. In the second case, the ratio of the length of the route of the heat network to connected to this heat network heat load (as the magazine "news of heat supply" is a specialized periodical, we will get rid of the obvious definitions. - Approx. ed.).

Where M is the material characteristics of the heat network, m²; Q^p is the total heat load in the range of a heat source (heat power) that is attached to the heat network to this source, Gcal/h; L - the total length of pipelines of thermal networks, forming the area of operation of the source of heat.

The Relationship between the specific material characteristic of µ and the specific length of heating λ can be set by using the average diameter of the heat network in the area of the heat source d_CP):

These two parameters is quite informative, because it reflects the basic rule of building a district heating system - specific material characteristics is always less than where the high density heat load. And if you take into account that the very material feature is the equivalent of cost and connected heat load - analogue effects, then the less specific material characteristics, the more productive the process of district heating. This analogy was used by our predecessors.

Pretty interesting to watch changes in specific material features of life in the process (development) of the heating system (Fig. 1). It will change in time fully reflects the process phases of construction of main heating networks, the gradual build-up of internal networks and the increase of the heat load, fully reflecting the changing pace of development. Only at the end of the 40-year period (in this example) the heating system becomes a kind of acceptable with specific material characteristics.

Of the two heating systems are always more efficient one that has a smaller specific material characteristics (Fig. 2). It is a relative material characteristic allows us currently to build a consistent method of comparison of centralized heat supply systems.

Or in other words: it is meaningless to compare the heating system with different relative material characteristics, they first need to lead to a comparable mind.

It is Worth also to mention that the relative material characteristic enables the assessment and heat energy losses during its transmission through heat networks. Simplified the asymptotes can be considered, for example, as follows. Imagine a heating system that is attached to a heat load equal to 1 Gcal/h, length of heat network is 10 km with a diameter of 1000 mm. relative material characteristics of such a heat network is 10 thousand m²/Gcal/h. Normative thermal energy losses during its transmission through such a network (designed after 2004) will be approximately 3000 Gcal for the heating period, and the total amount of useful heat of about 3600 Gcal. From this it follows that only normative losses during its transmission through such a heat network will be 83% of the useful released. It is not difficult to calculate what are the normative heat loss of the heat network length of 100 m and a diameter of 100 mm with an attached heat load of 1 Gcal/h. This, of course, does not asymptote, but from a practical point of view close to the asymptotes of the magnitude.

A relative material characteristic of calorific nets µ - is an integral indicator of the effectiveness of the heat network installed in the area of the heat source. And the basis of calculation of this indicator is the hypothesis about the uniformity of the heat flux in the range (ie the same density of thermal load).

To account For uneven heat load distributed in the area of the (already functioning or planned), E. P. Shubin was in 1951 offered another figure, based on consideration of thermal loads as concentrated at the points of their accession to the heat network. This figure was named E. P. Shubin turnover of heat.

Justifying the introduction of this indicator, the author took that from the point of view of the transport of thermal energy each point heat load is characterized by two quantities:

• The calculated heat load Q_pⁱ;
• distance from the heat source to the point of its accession, adopted on the route of the heat network (for the distance vector from point to point) l_i.

The Product of these values Z_i= Q_i^p L_i (Gcal/h) is called the moment of the heat load relative to the source of heat. The greater the magnitude of this moment, so, obviously, more needs to be and the material characteristics of a heat pipe connecting the heat source with the point of application of thermal load, material characteristic and grows depending on the growth time is not directly proportional to, and in accordance with the known power law Z_i >Q_i ^0.38. For thermal networks with the number of subscribers is greater than one the characteristic is the magnitude of the sum of the moments of the heat load of Z_T (Gcal m/h):

This value is called the theoretical turnover of heat for a given location of the subscribers relative to the source of heat.

since the calculation of this turnover value of I, are measured along the vector connecting the heat source with the attachment point of the i-th subscriber, the theoretical value of circulation does not depend on the alignment selected and the configuration of the heat network. However, it reflects the degree of heat transit, which is inevitable given the location of the subscribers relative to the source of heat.

When the magnitude of the circulation of heat with other transport coefficients are expressed generally in the following proportions:

Where R_cp - ratio of turnover to the total heat calculated heat load of all subscribers, describing an average distance of subscribers from the source of heat or the distance from the source to the center of gravity of the heat load of all subscribers.

An explanation of the procedures for the calculation of the average radius of a heat supply will consider on the basis of utilitarian radial thermal network (Fig. 3). Radial thermal network formed on the basis of the heat source 1, located in the industrial area 2.

Thermal energy transported by the heat network with the conclusions in three areas. One area is the industrial district, with areas of industrial enterprises 4. The other two directions are formed on the basis of heat supply in the residential part of the city 3 city blocks 5, 6. The thermal network consists of transit of part 7 of the trunk part 8, part 9 distribution and internal parts (not shown in the diagram) attached to the Central thermal points 10.

Depending on the pace of building the residential and industrial parts of the city the construction of heat networks could be implemented by a queue. Such other schemes of heat supply of any city determined in the General schemes of heat supply, which is closely linked with the General development plan of the city (the industrial center).

E. P. Shubin was introduced one specific indicator: the turnover of the specific heat per unit length of heating networks Z_cp (Gcal/h), it was also simple:

By definition, the specific heat turnover - the ratio of turnover to heat the total length of all vectors connecting points of connection of subscribers with the power supply system.

All the above values describe the heating system without a specifically selected route of the heat network and determine only the position of the heat source relative to the planned (or existing subscribers). Assuming that you are choosing the route of the heat network and its configuration, you can also specify the calculation of the turnover of heat, taking as lengths connecting the heat source with a specific user, a distance along the track. As this distance is always greater than the vector, then the circulation of heat over a particular track Z_c is always greater theoretical turnover of heat Z_T. Dimensionless ratio of these two values the speed of heat is called the coefficient of configurations thermal networks χ

The Value of this ratio is always greater than unity. This value characterizes the excessive heat in transit heat networks associated with the choice of route. The higher the value of the coefficient of thermal network configuration χ, so to a certain extent, more material characteristics of the heat network compared to the theoretically required minimum. Thus, this factor, to some extent, characterizes the correctness of the choice of route to radial heat network without redundancy, and shows how economical the designer (taking into account all possible constraints on the geological and urban requirements) chose the route.

Handling of project data (primarily for the heating schemes) showed that the values of the coefficient configuration χ for real projects a small non-redundant networks is in the range of 1.25+2,3, and values of about 1.2+1,25 is already close to optimal, i.e. corresponding to the minimum value of the specific material characteristics of the heat network. On the other hand (except required reserves), the values of χ=1,4+1,5 indicate excessive heat in transit networks and oversized material characteristics.

For the urban heating networks of medium and small scale quantities of heat momentum Z_c in the range of 10⁴+ 4.10⁵ m Gcal/h, to major, such as Moscow, to 810⁶ m Gcal/h.

The radius of a heat supply (or the ratio of turnover to the total heat calculated heat load of all subscribers) is structured within the following ranges:

1. Township and district heating networks - up to 250 m;
2. Network quarterly distribution from 250 to 1000 m;
3. Network backbone without significant amounts of transit) - from 1000 to 2500 m.
4. Network transit (tubes pins) from 2.5 to 5 km.

Attempt to determine an analytical expression for the optimum, the marginal economic and radius of heat transfer was first made in the "Norms for design of heat networks", published in 1938, In the section of this document entitled "Technical and economic assessment of thermal networks" (the author of the method of E. I. Sokolov) are the main analytical ratios and requirements to determine the optimal range of thermal networks. So it was prescribed during thermal zoning of large cities to determine the number and location of large thermal power stations and boiler plants: "consider the optimal range of thermal networks in which unit costs for production and transport of heat from one heat are minimal."

3. The list of references

1. Magazine "news of heat supply"
2. Problems of heat supply depressed areas, D. G. Zakirov, V. P. Sorokin, V. V. Ovechkin
3. Methodical instructions by definition of heat losses in water and steam heating networks.
4. Log the "Diagnostics and reliability of power equipment"
5. Article V. P. Papushkin Crisis "district heating Schemes" or rise of "Energy planning"
6. Article I. P. Pollner " improving the efficiency of operation of urban heating systems