Automation of supply and exhaust ventilation system with recirculation

Contents

Contents

Introduction

1. Process Analysis

2. Functional Diagram Description

3. Structural Diagram Description

Specification for Automation Instruments and Tools

Conclusion

List of literature used

Calculation job

Introduction

Automation refers to the implementation of production processes without the direct participation of a person.

Automation of production process management can be partial if only individual operations, individual machines and units involved in the production process are automated. The main issue considered in this case is the task of automatic control of the production process.

A higher degree of automation is integrated automation. With this type of automation of technological processes, the site, workshop, plant perform their functions without the direct participation of a person in the process of their management. With complex automation of production, machines perform both simple and complex control functions associated with the impassability of making certain independent decisions.

In addition to the two previously listed types of automation, there is also a third - complete automation.

Automatic control is the maintenance of constancy or change by any given law of the value characterizing the production process carried out by changing the state of the control object or the disturbances acting on it and acting on the control body of the object.

Modern automatic regulation theory is a major part of control theory. The automatic control system consists of an adjustable object and control elements that affect the object when one or more adjustable variables change. Under the influence of input signals (control or disturbance), adjustable variables are changed. The purpose of regulation is to create laws in which output regulated variables differ little from the required values. The solution of this problem in many cases is complicated by the presence of random disturbances (interference). At the same time, it is necessary to choose a control law in which control signals pass through the system with small distortions, and noise signals are practically not transmitted.

The theory of automatic regulation has gone a significant way of its development. At the initial stage, methods were created to analyze the stability, quality and accuracy of regulation of continuous linear systems. Then, methods for analyzing discrete and discrete-continuous systems were developed. It can be noted that the methods of calculating continuous systems are based on frequency methods, and the calculations of discrete and discrete-continuous are based on z-conversion methods.

The development of the theory of automatic regulation based on the equations of state and zperformations, the principle of maximum and the method of dynamic programming improves the design methodology of control systems and allows creating highly efficient automatic systems for a wide variety of sectors of the national economy. The automatic control systems thus obtained provide high quality of the manufactured product, reduce its cost and increase labor productivity.

A process plan is a process that produces a product or product from raw materials or materials with pre-defined properties defined by regulatory documents.

Automation of production performs the following functions:

Technical equipment and installation management function;

function of technical parameters monitoring and measurement;

automatic control function;

function of the protective alarm system of blocking of technical devices, technical devices, etc.;

process control function. Systems that provide process control are called automated process control systems (APCS). APCS implements functions, both collecting information and making independent decisions in changing technological processes;

The automatic production control function implemented by the automatic production control system (ACMS).

In this course project, automation of the ventilation system will be considered. As part of the project, the graphic part, which contains two diagrams: functional and electrical schematic diagram of the air conditioner with recirculation, as well as an explanatory note, which will consider the following issues:

A brief description of the process

selection and description of the functional diagram of automation;

description of the schematic diagram of the conditioner with recirculation;

selection and description of automation tools used;

calculation part. Definition of level ECS transfer function.

Modern air conditioning systems can be classified according to the following characteristics:

• for the main purpose (object of application): comfortable and technological;

• according to the principle of air conditioner location in relation to the serviced room: central and local;

• by the presence of its own (included in the design of the air conditioner) source of heat and cold: autonomous and non-autonomous;

• according to the principle of action: direct-flow, recirculation and combined;

• according to the method of control of conditioned air output parameters: with qualitative (single-tube) and quantitative (double-tube) control;

• by the degree of ensuring meteorological conditions in the serviced room: first, second and third class;

• by the number of serviced rooms (local zones): single-zone and multi-zone;

• by the pressure developed by air conditioner fans: low, medium and high pressure.

In addition to the above classifications, there are various air conditioning systems serving special technological processes, including systems with time-varying (according to a certain program) meteorological parameters.

Single-zone central VMS are used to service large rooms with a relatively uniform distribution of heat, moisture emissions, for example, large halls of cinemas, audiences, etc. Such hard currencies, as a rule, are completed with devices for utilization of heat (heatutilizers) or mixing cameras for use in the served rooms of recirculation of air.

Multi-zone central SLE is used to service large premises where equipment is not evenly placed, as well as to service a number of relatively small premises. Such systems are more economical than individual systems for each zone or room. However, with their help, the same degree of accuracy of maintaining one or two specified parameters (humidity and temperature) cannot be achieved as autonomous SLE (split system air conditioners, etc.).

Direct-flow VMS fully operate in the outside air, which is processed in the air conditioner, and then supplied to the room.

Recirculation VMS, on the contrary, operate without inflow or with partial supply (up to 40%) of fresh outdoor air or in recirculation air (from 60 to 100%), which is taken from the room and after its treatment in the air conditioner is again supplied to the same room.

Classification of air conditioning according to the principle of operation for direct-flow and recirculation is mainly due to comfort requirements, production process conditions or technical and economic considerations.

Central VMS with high-quality control of meteorological parameters are a wide range of the most common, so-called single-channel systems, in which all treated air leaves the air conditioner in one channel and enters one or more rooms.

The control signal from the temperature controller installed in the serviced room is transmitted directly to the central air conditioner.

SCR with quantitative control is supplied to one or several rooms with cold and heated air through two parallel channels. The temperature in each room is controlled by a room temperature controller acting on local mixers (air valves), which change the ratio of cold and heated air flow rates in the supplied mixture.

Two-channel systems are used very rarely due to the difficulty of regulation, although they have some advantages, in particular, the absence of heat exchangers, coolant pipelines in the serviced rooms; the possibility of working together with a heating system, which is especially important for existing buildings, the heating systems of which can be stored during the arrangement of two-channel systems.

The disadvantage of such systems is the increased cost of thermal insulation of parallel air ducts supplied to each serviced room.

Two-channel systems, as well as single-channel systems, can be direct-flow and recirculated.

Process Analysis

One of the main components of modern air conditioning and ventilation systems (SLE) is automation equipment and systems. They implement various control functions, which must on the one hand ensure that the required microclimate is maintained in the serviced room, and on the other, that the process equipment operates economically and reliably. The range of control functions performed by automation systems by the number and complexity of implementation is quite wide: from simple switching on - off to centralized control of climatic or all engineering equipment of the building [1].

The main process functions of VMS control, as a rule, are implemented at the level of individual plants using automatic control systems (ACS). ACS is a combination of a control object (controlled process) and control devices, the interaction of which ensures the automatic flow of the process in accordance with a given program. In this case, the process refers to the sequence of operations that must be carried out in order to obtain the finished product from the feedstock. In the case of SLE, the finished product is air in the serviced room with the specified parameters (temperature, humidity, gas composition, etc.), and the raw material is external and exhaust air, heat carriers, electricity and others.

The operation of automatic control systems of SLE, like any control system, is based on the principle of feedback: generation of control actions based on information about the object obtained using sensors installed on the object.

Each specific ACS is developed on the basis of the specified technology of air inlet flow processing. These can be simple ventilation systems or central air conditioners in combination with autonomous devices (dryers, autonomous air conditioners, humidifiers).

When using stand-alone devices or complete process units for air treatment, ACS are supplied with already built-in equipment and already installed certain control functions, which are usually described in detail in the technical documentation. In this case, adjustment, maintenance and operation of such control systems should be carried out in exact accordance with the specified documentation.

If ACS requires the development of automation tools of other manufacturers for a specific process diagram and equipment, then the determination of the optimal program and specific control functions should be carried out jointly by air conditioning and ventilation specialists and automation specialists. This approach takes into account both the requirements for the automation system and the object being automated.

Modern ACS typically use microprocessor-based electronic digital devices as controls. By their technical capabilities, these devices allow you to provide control of many parameters. This is the start and stop of individual process devices and the entire system, the blocking and protection of equipment in emergency situations, indication, switching from mode to mode, and so on. Devices that comprehensively solve control and control functions are called control controllers. When used in most cases, it is not necessary to use automation elements such as relays, transducers, switches, counters, indicators, measuring instruments and the like. This in turn allows:

- increase accuracy of control parameters maintenance and system operation reliability;

- reduce the dimensions of the controls;

- simplify the installation and reduce the time of its execution;

- facilitate operation of the system.

In some cases, at the expense of the listed advantages, it is possible to reduce the actual cost of the automation tool taking into account capital and operating costs.

2.1 Process equipment

The composition of the ventilation system depends on its type. The most complex and frequently used are plenum artificial (mechanical) ventilation systems. Typical plenum mechanical ventilation system consists of the following components (located in the direction of air movement, from inlet to outlet).

Air intake screen - external air enters the system through it. Ventilation grids, like all other elements of the ventilation system, are round or rectangular in shape. These grates not only perform decorative functions, but also protect the ventilation system from ingress of rain drops and foreign objects.

The air valve prevents outside air from entering the room when the ventilation system is turned off. An air valve is especially necessary in winter, since cold air and snow will enter the room without it. As a rule, electrically driven valves are installed in plenum ventilation systems, which allows you to fully automate the system control - when the fan (and heater) is turned on, the valve opens, when the switch is off, it closes.

Filter - is necessary to protect both the ventilation system itself and ventilated rooms from dust, fluff, insects. Typically, a single coarse filter is installed that retains particles greater than 10 μm. If the air purity is subject to increased requirements, fine filters (trapping particles up to 1 μm) and extra fine filters (trapping particles up to 0.1 μm) can be additionally installed. The filter material in the coarse filter is a fabric of synthetic fibers, for example acrylic. The filter must be cleaned periodically of dirt and dust, usually at least once a month. To monitor filter contamination, a differential pressure sensor can be installed, which monitors the difference in air pressure at the inlet and outlet of the filter - during contamination, the pressure difference increases.

Calorifer or air heater is designed to heat the air supplied from the street in the winter. The calorifer may be water or electric. For small supply units, it is more profitable to use electric heaters, since the installation of such a system is less expensive. For a large number of rooms, it is desirable to use water heaters, otherwise the cost of electricity will be very high. There is a method to reduce the cost of heating incoming air several times. To do this, a recuperator is used - a device in which cold supply air is heated by heat exchange with removed warm air. Of course, air flows do not mix.

The fan is the basis of any ventilation system. It is selected taking into account two main parameters: productivity, that is, the amount of pumped air and full pressure. According to the design, the fans are divided into axial (for example, household fans "on the leg") and radial or centrifugal ("squirrel wheel"). Axial fans provide good performance, but are characterized by low full pressure, that is, if an obstacle occurs in the air flow path (long air duct with turns, grille and the like), then the flow speed is significantly reduced. Therefore, in ventilation systems with a branched network of air ducts, radial fans are used, which are distinguished by the high pressure of the created air flow. Other important characteristics of the fans are noise level and dimensions. These parameters depend to a large extent on the equipment grade.

Silencer - Since the fan is a source of noise, a silencer must be installed after it to prevent the spread of noise through the ducts. The main source of noise during operation of the fan is turbulent swirls of air on its blades, that is, aerodynamic noises. To reduce these noises, a sound absorbing material of a certain thickness is used, which is lined with one or more walls of the silencer. As the sound absorbing material, mineral wool, fiberglass and the like are generally used.

Air ducts - after leaving the silencer, the treated air flow is ready for distribution to the rooms. For these purposes, an air duct network consisting of ducts and shaped products (tees, turns, adapters) is used. The main characteristics of ducts are section area, shape (round or rectangular) and stiffness (there are rigid, semi-flexible and flexible ducts).

The flow velocity in the duct must not exceed a certain value, otherwise the duct will become a source of noise. Therefore, the area of ​ ​ the duct section determines the volume of pumped air, that is, the size of the ducts is selected based on the calculated value of air exchange and the maximum permissible air speed.

Rigid ducts are made of galvanized tin and can have a circular or rectangular shape. Semi-flexible and flexible air ducts have a circular shape and are made of multilayer aluminum foil. Such air ducts are formed in a circular shape by a skeleton of helical steel wire. Such a design is convenient in that the ducts during transportation and installation can be folded with an accordion. The disadvantage of flexible air ducts is the high aerodynamic resistance caused by an uneven internal surface, so they are used only in areas of small length.

Air distributors - through them air from the duct enters the room. As a rule, grilles (round or rectangular, wall or ceiling) or diffusers (plafons) are used as air terminals. In addition to decorative functions, air distributors serve to uniformly disperse the air flow through the room, as well as to individually adjust the air flow directed from the air distribution network to each room. Control and automation systems - the last element of the ventilation system is the electric shield, in which the ventilation control system is usually mounted. In the simplest case, the control system consists only of a switch with an indicator that allows you to turn on and off the fan. However, most often, a control system with automation elements is used, which includes a calorifer when the supply air temperature decreases, monitors the purity of the filter, controls the air valve, and so on. Thermostats, hygrostats, pressure sensors and the like are used as sensors for the control system.

2.2 Setting and decomposition of general task of process control

Control functions can be divided into two categories. The first combines control functions defined by air processing technology and equipment. The second is additional functions, which are mostly service functions.

The process functions of SLE control are practically unchanged, that is, they are typical and differ mainly in the method of implementation, and therefore in the quality and reliability of operation. Most of these functions are determined by the requirements set for ACS by regulatory documents (SNiP, PUE, GOST and others) [2, 3].

In general, the main process functions of SCR control can be divided into the following groups:

- monitoring and recording of parameters;

- operational and software management;

- protection and blocking functions;

- regulating functions.

2.2.1 Monitoring and recording of parameters

Mandatory control parameters are:

- temperature and pressure in the common supply and return pipelines and at the outlet of each heat exchanger;

- air temperature of external, recirculation and supply air downstream the heat exchanger, as well as temperature and relative humidity (at its regulation) in the room in air conditioning systems.

Other parameters in ventilation and air conditioning systems shall be controlled on demand of technical specifications for equipment or according to operating conditions.

Remote monitoring is provided for measuring the main process parameters or parameters involved in the implementation of other control functions. Such monitoring is carried out using sensors and transmitters with output (if necessary) of measured parameters to the indicator or screen of the control device.

For measuring other parameters, local (portable or stationary) devices are usually used - showing thermometers, pressure gauges or thermomanometers.

The use of local monitoring devices does not violate the basic principle of control systems - the feedback principle. In this case, it is implemented with the help of a person (operator or maintenance personnel).

Recording of basic parameters should be provided only according to technological requirements.

Conclusion

In this course work, a functional diagram of the plenum-exhaust system with recirculation was developed and the following issues were considered: process analysis, description of the functional diagram and description of the structural control diagram.

The use of modern controls, actuators and fast-acting reliable regulators make the ventilation system reliable and economical, and the alarm and blocking systems ensure its safety.

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