Heat supply to the microdistrict

Contents

PART 1. EXPLANATORY PART

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1. Source Data

2. Introduction

3. Heat Flux Determination Method

4. Selection of heat supply system and heat transfer agents

5. Control of heat release

6. Heat networks

7. Hydraulic calculation of heat networks

8. Hydraulic mode of thermal network operation

9. Thermal Network Building Structures

List of literature used

PART 2. DESIGN PART

1. Definition of heat flows

2. Plot Heat Flow

3. Hydraulic calculation of heat networks

4. Selection of mains and makeup pumps

5. Selection of water jet pump (elevator)

6. Calculation of U-shaped compensator K

7. Calculation of SR self-compensation angle

Application

Application

Application

Application

Application

Application

Application

List of literature used

Explanatory part

1. source data

1. The projected microdistrict is located in Astrakhan

2. Design temperature of external air for design of heating of tno = - 22 wasps.

3. Design temperature of external air for design of ventilation of tnv = - 8 wasps.

4. Heat source: boiler room.

5. Heat supply system: closed four-tube.

6. Design parameters of coolant:,.

7. Type of gasket: underground.

2. Introduction

Heat supply means a system for providing heat to buildings and structures. Reliable operation of heat supply systems is of great economic importance, since the co-building of comfortable conditions for working and living people and optimal conditions for various technological processes largely depends on it.

Heat supply systems are divided into centralized, decentralized and, as a type of decentralized, local systems.

In centralized systems, heat generation is carried out in separate sources (CHP or boiler houses), and coolant is supplied to heat consumption systems through special pipelines called heat networks. At the same time, thermal networks have significant lengths and diameters, are equipped with thermal points, pumping stations, automation and a control system.

A heat supply system having no developed heat networks, in which the heat source is located directly near the objects consuming heat, is called decentralized.

And finally, if the thermal unit provides heat supply to one small building, the system will be called local.

In modern cities, heat supply to various consumers is carried out mainly from centralized systems. However, recently, in many cities of Russia, heat supply of newly built facilities based on autonomous sources has become increasingly important. The greatest effect is the use of autonomous heat sources during the construction of objects, carried out in the order of compaction of the existing construction site. The cost of heat generated in them can be several times lower than in centralized systems.

In this project, a centralized heating system of the microdistrict with heat generation in the boiler room was designed and designed.

3. Heat Flux Determination Method

The development of the heat supply project begins with the determination of heat flows for heating, ventilation and hot water supply. Heat flows are calculated in various ways depending on specific conditions: the design stage, scale and degree of detail of the image on the gene plan.

Since the plot plan has separate buildings and their purposes and characteristics are indicated, then the calculation is carried out according to the specific thermal characteristics of the buildings according to the corresponding formulas. The heat flows determined by these formulas are calculated, that is, maximum, because they are calculated at the calculated external temperature.

The heating consumption for ventilation in residential buildings does not exceed 510% of the heating consumption, so for residential buildings it is not calculated, but only for public buildings.

4. Selection of heat supply system and

heat carriers

The selection of the heat supply system should be made on the basis of technical and economic calculations taking into account the quality of the source water, the degree of its availability and the maintenance of the required quality of hot water for consumers.

In small cities or villages, if there is a boiler house designed to heat the housing and communal sector with a range of such a boiler house up to 1.2 km, the construction of 4-covered pipe heating networks is economically justified, which is provided for by this project. At the same time, water for hot water supply is prepared in a heat source and supplied to subscribers through independent pipelines. The central heat point is obtained in such a case, as it were, blocked with the heat source.

As heat carrier in district heat supply systems for heating, ventilation and hot water supply of residential, public and industrial buildings, water should be taken as heat carrier.

5. Control of heat release

Heat generated and transmitted by the heat supply system is used by consumers for various needs: heating, ventilation and air conditioning of buildings, hot water supply.

The heat load of the subscribers is not constant. It varies depending on the temperature of the outside air, wind speed, insolation, water flow modes for hot water supply and the operation of technological equipment, a number of other factors. To ensure economical operation of the system and high quality of heat supply, heat release control is used. The high quality of control is expressed in maintaining the specified air temperature in heated rooms, at external climatic conditions varying during the heating period and the specified temperature of water entering the hot water supply system at the varying flow rate of this water during the day.

This project provides for a central qualitative control of heat release.

The central qualitative control consists in maintaining a temperature schedule in the heat source, which ensures during the entire heating period the specified temperature of the internal air of the heated rooms at a constant flow of network water. Such a temperature plot is called heating.

6. Heat networks

Heat networks should be placed within the transverse profiles of streets and roads - under sidewalks or dividing strips. On streets that do not have dividing lanes, it is allowed to place networks under the carriageway, provided that they are placed in channels.

Crossing of residential and public buildings with a diameter of up to 300 mm by breeding networks is allowed, provided that the networks are laid in technical underground, corridors and tunnels with a height of at least 1.8 m.

The slope of heat networks regardless of the direction of movement of the coolant and the method of laying should be at least 0.002. The slope to individual buildings during underground laying shall be taken from the building to the nearest heat chamber.

Diameters of pipelines laid in quarters under safety conditions shall be not more than 500 mm, and their route shall not pass in places of possible population accumulation.

Choice of piping method and structures is determined by pipeline diameter, reliability requirements, cost-effectiveness and method of works execution.

This project provides for underground laying of heating networks in impassable channels.

7.hydraulic calculation of heat networks

Hydraulic calculation is one of the most important sections of design and operation of heat networks.

During design as a result of hydraulic calculation, the following is determined:

• diameter of pipelines;

• pressure drop (head) in the sections;

• pressure (head) at different points of the system;

• perform pressure matching at different points of the system in static and dynamic modes in order to ensure allowable pressures and required head in the network and subscriber systems.

The results of the hydraulic calculation give the source material for solving the following problems:

• determination of investments in the construction of heating networks, metal consumption (pipes, rolled stock) and the main scope of work on the construction of the heating network;

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

• determination of operating conditions of the thermal network and subscriber systems and selection of schemes for connection of subscriber units to the thermal network;

• selection of automatic regulators installed at the thermal network facilities and subscriber inputs.

For hydraulic calculation, the diagram and profile of the heat network should be developed, the location of the heat source and consumers, design loads and section lengths should be indicated.

According to [2], specific friction pressure losses during hydraulic calculations of water heating networks should be determined on the basis of technical and economic calculations. It is recommended to take the following values of specific friction pressure losses:

• for the main design direction (main line) from the heat source to the most distant consumer - up to 80 Pa/m;

• for other sections - by the available pressure drop, but not more than 300 Pa/m.

The water velocity in the pipelines shall not exceed 3.5 m/s.

After preliminary calculation, the type and required number of compensators are selected for each section, depending on which the number of intermediate fixed supports is determined.

Performing the refined calculation of the branches, we determine the design pressure losses in the branch. At the same time, as a rule, due to the limited variety of pipe material, it is not possible to achieve an exact correspondence of pressure losses in the from-branching to the located head. In such cases, the following should be done. If the non-binding value is less than 25%, the calculation can be considered complete. Insignificant overpressure can be extinguished by valves installed on the branch. If the amount of non-binding is greater, the throttle diaphragm must be selected.

8.hydraulic mode of thermal network operation

In order to ensure safe operating conditions of the heat supply system and the necessary pressures at various points of the system that provide the design mode of the heat supply system, the hydraulic mode of the heat networks is developed.

The hydraulic mode is developed at the dynamic state of the system, that is, at the operating circulation (network) pumps and at the static state of the system (hydrostatic mode), when the circulation pumps do not work. As a result, lines of maximum pressures in supply and return pipelines are determined from condition of mechanical strength of system elements and lines of minimum pressures from condition of prevention of boiling of high-temperature heat carrier and formation of vacuum in system elements. Pressure lines of the designed system shall not go beyond these extreme limits.

8.1 Construction of piezometric graph

To take into account the mutual influence of the terrain, the height of subscriber systems, pressure losses in thermal networks and requirements in the process of developing the hydraulic mode of the thermal network, a piezometric graph is built. In piezometric graphs, the values ​ ​ of the hydraulic potential are expressed in units of head .

On a piezometric plot on a certain scale, the terrain, the height of the connected buildings, and the pressure values ​ ​ in the network are applied .

On the horizontal axis of the graph, the length of the network is deposited, and on the vertical head.

8.2 Mains and makeup pumps

The required pump is selected according to the obtained efficiency and head values taking into account the up-to-start temperature of pumped water and the head at the pump inlet, according to the corresponding tables [5].

We accept one network pump and one make-up pump for installation.

8.3 Water jet pumps (elevators)

Since the temperature of the water in the heating network is generally higher than required for heating systems, the latter are connected to the heating network through mixing devices providing the required mixing ratio of the return water after the heating system to the supply pipeline of the local heating system. Mixing devices, in addition to the main purpose, also create the head necessary for the circulation of water in the system.

As mixing devices, water jet pumps - elevators were most widely used.

9. Construction structures of the heating system

When placing pipelines in channels, it is necessary to maintain the minimum permissible distances in the light between construction structures and pipelines, as well as between the surfaces of thermal insulation structures of neighboring pipelines.

During the construction of heat networks, prefabricated reinforced concrete channels made of cable tray elements manufactured according to a typical series are used. Chambers for arrangement of gate valves, drain and air cranes, gland compensators are arranged from prefabricated reinforced concrete. The dimensions of the chambers are taken from the conditions of normal maintenance of the equipment placed in them according to [7] and must be a multiple of 600 mm.

When designing cameras, it is necessary to provide:

• hatches D = 700 mm with internal area of chambers from 2.5 to 8 m2 - at least two, located diagonally, and with area more than 8 m2 - chet-re;

• stairs for descent and drainage pit under one of the hatches.

This design also provides for fixed supports of the shield type and movable supports of the sliding type.

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