Heat supply to the microdistrict of the city

Contents

1. Source Data

Introduction

EXPLANATORY PART

1. Method for determination of heat loads for heating, ventilation and hot water supply

2. Selection of heat supply system and heat carriers

3. Diagram of connection of water heaters

4. Total hourly and annual heat consumption schedules

5. Control of heat release

6. Thermal networks

7. Development of calculation scheme

8. Hydraulic calculation of heat networks

9. Hydraulic mode of thermal network operation

9.1 Construction of piezometric graph

9.2 Mains and makeup pumps

9.3 Water jet pumps (elevators)

DESIGN PART

1. Definition of heat loads

1.1. Determination of heat flows for heating

1.2. Determination of heat flow for ventilation

1.3. Definition of heat flow to hot water supply

2. Hourly and annual schedules

heat flow rate

3. Schedule Regulation

coolant temperature

4. Determination of design coolant flow rates

5. Preliminary hydraulic calculation

6. Final hydraulic calculation

7. Selection of mains and makeup pumps

8 Selection of water jet pump (elevator)

Literature

Applications

Appendix A

Appendix B

Appendix B

Appendix D

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 it largely depends on the creation of comfortable conditions for work and living of people and optimal conditions for various technological processes.

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

In centralized systems, heat generation is carried out in separate sources (CHP or boiler houses), and coolant supply to heat consumption systems occurs 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 facilities, carried out in the order of compaction of existing buildings. 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.

Explanatory part

1. Method for determination of heat loads for heating, ventilation and hot water supply

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 the specific conditions: the design stage, scale, and the degree of detail of the image on the plot 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.

2. 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 among 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 closed 4-pipe heat 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 station is obtained in such a case as if blocked with a 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. It is also necessary to check the possibility of using water as a coolant for technological processes.

3. Diagram of connection of water heaters

With closed heat supply systems, depending on the ratio of maximum heat flows to hot water supply and to heating, the connection of hot water heaters should be accepted:

A distinctive feature of this scheme is that during the period of maximum load on hot water supply, heat consumption for heating is reduced. Such a solution is implemented by the so-called related regulation. Using the flow controller installed at the subscriber input, a constant flow of network water is maintained to satisfy the total heat load on heating and hot water supply.

4. Total hourly and annual heat consumption schedules

To solve a number of issues of district heat supply, namely: determination of annual heat consumption by heat-using facilities, selection of heat source equipment, its loading and repair mode, etc., frequency graphs of heat hour consumption during the year are used.

The more hours the maximum heat load is used, the more evenly the generated heat is consumed during the year, the more efficiently the heat supply system equipment is used.

5. Control of heat release

Heat release control is provided for: centralized - at the heat source, group - at the control units or at the CTP, individual in ITP.

For water heating networks, as a rule, qualitative control of heat release by heating load or combined heating and hot water supply load should be taken according to the schedule of water temperature change depending on ambient air temperature.

Centralized qualitative control of heat release is limited by the lowest water temperatures in the supply pipeline required to heat the water supplied to the consumer hot water supply system (for closed heat supply systems - at least 700C).

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, the modes of water consumption 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.

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

6. Thermal 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. Development of calculation scheme

After the heat network route is placed on the plot plan, a piping scheme is developed.

In the initial stage, places of installation of shutoff valves, fixed supports, compensating devices are indicated. Once the hydraulic calculation has been performed and the piezometric graph has been plotted, the need for any facilities (pumping stations, safety or measuring devices) may be determined.

Fixed supports shall be placed in the following places:

- at the outlet of their source, at the inlet and outlet of CTP, pump substations and other structures (to relieve forces on equipment and valves);

- in places of branches from the heat network (to eliminate mutual influence of sections running in perpendicular directions);

- at route turns (to eliminate the influence of bending and torques arising from natural compensation).

As a result of said arrangement of fixed supports, the route is divided into straight sections having different lengths and diameters of pipelines.

Type and number of compensators are selected for each of said sections, depending on which number of fixed intermediate supports is determined (one less than compensators).

8. 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 range of pipes, it is not possible to achieve an exact correspondence of the pressure loss in the branch 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.

9. Hydraulic mode of thermal network operation

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.

9.1 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.

9.2 Mains and makeup pumps

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

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

9.3 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. The most perfect elevator in terms of design is the VTITeploset Mosenergo.