(A) the task of ventilation engineering
Improving the indoor air environment through ventilation is to discharge the dirty air that does not meet the hygiene standards to the outside and send the fresh air or the purified air that meets the hygiene requirements to the room. The purpose of ventilation is to ensure good air quality in environmental space by controlling pollutants in the air and adopting purification, removal or dilution technology.
(2) Composition of ventilation system
Ventilation system is divided into two categories: air supply system and exhaust system. The basic function of air supply system is to send clean air into the room. The basic function of exhaust system is to eliminate indoor polluted air.
(3) Ventilation mode
1. Fully ventilated
That is, the entire control space is ventilated to make the indoor pollutant concentration lower than the allowable concentration. The essence of total ventilation is to dilute the pollutants in the ambient air.
(1) comprehensive ventilation setting conditions
1) In workshops or other rooms where hot, wet or harmful substances are emitted, when local ventilation cannot be used or cannot meet the hygiene requirements, full ventilation should be supplemented or adopted.
2) When designing comprehensive ventilation, natural ventilation should be adopted as far as possible to save energy and investment. When natural ventilation cannot meet the requirements of indoor safety, hygiene, environmental protection or production, mechanical ventilation or natural and mechanical combined ventilation should be set up.
3) Kitchen, toilet, washroom and bathroom in civil buildings should be fully ventilated by natural ventilation or mechanical ventilation.
4) For buildings with central heating and mechanical ventilation, when natural air supply can't meet indoor sanitary conditions, production requirements or technical and economic irrationality, a mechanical air supply system should be set up.
(2) Comprehensive ventilation classification
Total ventilation can be divided into dilution ventilation, one-way ventilation, uniform ventilation and displacement ventilation.
1) dilution ventilation. Ventilate the whole room (or workshop) and dilute the concentration of harmful substances in the whole workshop to below the allowable concentration with fresh air. This method needs a lot of overall ventilation and has poor control effect.
2) One-way ventilation. Control the diffusion and transfer of harmful substances through organized airflow movement. Ensure that the breathing area of the operator meets the requirements of hygiene standards. This method has the advantages of small ventilation and good control effect.
3) Uniform ventilation. In principle, the airflow speed should be controlled between 0.2-0.5m/s, which can effectively exhaust indoor polluted air. At present, it is mainly used in automobile painting room and other occasions with high requirements for airflow and temperature and humidity control.
4) Displacement ventilation. Low-speed, low-temperature air supply and indoor flow pattern are important characteristics of displacement ventilation. Therefore, displacement ventilation requires high air distributor for air supply, which requires the air distributor to send out low-temperature fresh air evenly at a small wind speed and spread it outwards.
(3) Air distribution of comprehensive ventilation
The overall ventilation effect depends not only on the ventilation volume, but also on the ventilation airflow organization. The so-called airflow organization is to reasonably arrange the air supply, exhaust and distribution, select the corresponding tuyere form, and obtain the ventilation effect with the minimum ventilation. The basic principles that should be observed when designing a comprehensive ventilation system are as follows: clean air should be sent directly to the place where the staff are located or where the concentration of pollutants is low; Avoid short circuit of ventilation airflow. The commonly used air supply and exhaust methods are upper air supply and upper air exhaust, lower air supply and upper air exhaust, and middle air supply and upper air exhaust.
(4) Emergency ventilation
There are some technological processes in the factory, which suddenly produce a large number of toxic gases or gases with the danger of burning and explosion due to operational accidents and equipment failures. In order to prevent injury to staff and further accidents, it is necessary to set up a temporary exhaust system-emergency ventilation system. The emergency ventilation fan can be centrifugal or axial.
2. Local ventilation
That is, the gas containing pollutants is captured, purified and discharged to the outside at the source of pollutants; For areas that need to ensure the air conditions in local places, local air supply ventilation should be adopted. Local ventilation should be given priority as a technical measure to ensure the air quality of working and living environment and prevent indoor environmental pollution.
Local ventilation includes local air supply and local air exhaust.
(1) local air supply. Local air supply is more suitable for large space and places where people are not densely distributed.
(2) Local ventilation. Local exhaust is to collect pollutants directly in the place where pollutants are produced, and then put them outdoors after treatment. In the exhaust system, local exhaust is the most economical and effective. When pollutants are concentrated in a certain place, local exhaust is the most effective ventilation method to control the harm of pollutants to the environment.
3. Mechanical ventilation
Rely on mechanical power (such as fans) for organized ventilation. Include mechanical air intake and mechanical air exhaust.
4. Natural ventilation
It is an economical and effective measure to make full and reasonable use of natural ventilation. Therefore, when there are no strict requirements for indoor air temperature, humidity, cleanliness and airflow speed, natural ventilation should be given priority when conditions permit.
(4) industrial building dust removal system
1. Dust removal on site. That is, the dust collector is directly placed near the production equipment to collect and recover dust on the spot, and basically no laying or only a short dust removal pipeline is needed. The system has compact structure, simple layout and easy maintenance and management.
2. Decentralized dust removal system. When the exhaust points in the workshop are scattered, the exhaust points can be combined appropriately, and several exhaust points can be combined into a system according to the nature of the transported gas and the working shifts. The dust collector and fan of decentralized dust removal system should be as close as possible to the dust-producing equipment. The system has short air duct, simple layout and easy pressure balance. Because of the scattered arrangement of dust collectors, it is more troublesome to deal with the dust recovered by dust collectors.
3. Centralized dust removal system. Centralized dust removal system is suitable for workshops with centralized dust removal points and large dust removal facilities. All the exhaust points can be concentrated in one dust removal system, or the dust removal equipment of several dust removal systems can be arranged together. Due to the centralized maintenance and management of dust removal equipment, it is easy to realize the mechanized treatment of recycled dust. However, the pipeline of the system is long and complicated, the pressure balance is difficult, and the initial investment is large. Therefore, this system is only suitable for a few large factories.
(5) Pneumatic conveying system
Pneumatic conveying is a way of conveying materials by air flow. In HVAC, airflow is often used to transport smoke (powder) collected from dust collectors, cooling equipment and flue to the needed places. Pneumatic conveying system can be divided into four types according to its device form and working characteristics: suction conveying type, pressure conveying type, mixed type and circulating type, and the first two are commonly used.
(6) Air curtain
The strip air distributor is used to spray curtain airflow with a certain speed and temperature to close doors, corridors, passages, doorways, counters, etc. , reduce or isolate the invasion of external air flow, maintain the environmental conditions indoors or in a working area, and block the entry of dust, harmful gases and insects. The characteristics of air curtain, such as heat insulation, cold insulation, dust isolation and insect prevention, can not only maintain indoor environment but also save building energy consumption.
The air curtain can be composed of air handling equipment, fans, air duct systems and air distributors. According to the installation position of the air distributor, the air curtain can be divided into three types: upward transportation, lateral transportation and downward transportation.
1. Upward air curtain. Installed in the upper part of the doorway. The upward air curtain is convenient to install, does not occupy the building area, does not affect the beauty of the building, and has good sanitary conditions for air supply and airflow, which is suitable for general public buildings. Although the upward air curtain is not as effective as the downward air curtain in blocking outdoor cold air, it is still the most promising form.
2. Side air curtain. Installed at the door side, it can be divided into unilateral and bilateral. Single-sided air curtain is suitable for doorways with a width less than 4m and industrial workshops with short time for vehicles to pass through doorways. Double-sided air curtain is suitable for occasions where the width of the doorway is more than 4m, or vehicles pass through the doorway for a long time. The wind-proof efficiency of the side air curtain is not as good as that of the lower air curtain, but the sanitary conditions are better than that of the lower air curtain. Side air curtain is often used in industrial buildings with high doorways, but its use is limited because of its occupied building area. In order not to block the airflow, it is forbidden to open the door with side air curtain inward.
3. Downward air curtain. It is installed underground. Because the spraying area of the downward air curtain is at the lower part of the door opening, it can resist the wind-proof effect when cold air invades from the lower part of the door opening in winter, and is not affected by the opening direction of the door. However, the air outlet of the downward air curtain is under the ground, which is easy to be blocked by dirt, and the downward air flow is easy to lift clothes, which is unpopular.
Air curtain is divided into non-heated air curtain (isothermal air curtain) and hot air curtain according to the heating state of air supply flow.
1. Hot air curtain. There is a heater in the air curtain, and the heating medium is hot water, steam or electricity. The hot air curtain can heat the air curtain to the required temperature. Suitable for buildings that need heating, often used in cold areas.
2. Unheated air curtain (isothermal air curtain). There is no heating device in the air curtain, which has simple structure, small volume and wide application range. Commonly used in air-conditioned buildings and non-cold areas.
(seven) building fire prevention and smoke control
There are two kinds of smoke exhaust parts: fire area and evacuation passage. The purpose of smoke exhaust in the fire area is to exhaust the smoke (including the air volume expanded by heating) from the fire area outdoors, reduce the pressure in the fire area, and prevent the smoke from flowing to the non-fire area, so as to facilitate the evacuation of fire area personnel and firefighters. The purpose of smoke exhaust in the evacuation passage is to eliminate the smoke that may invade, ensure that there is no smoke or less smoke in the evacuation passage, and facilitate the safe evacuation of personnel and the passage of firefighters.
Master the advantages and disadvantages of natural smoke exhaust, mechanical smoke exhaust and pressurized smoke prevention.
(eight) the main equipment and components of ventilation (air conditioning)
1 fan
Master the types of commonly used ventilators and their applicable places.
2. Valve of the snorkel
The air valve is the control and adjustment mechanism of the air distribution network, and its basic function is to cut off or open the air circulation pipeline and adjust or distribute the pipeline flow.
(1) Air valves with both control and adjustment functions are: 1) butterfly valves; 2) diamond-shaped single-leaf regulating valve; 3) Insert the valve; 4) Multi-leaf regulating valve is connected in parallel; 5) Split multi-leaf regulating valve; 6) rhombic multi-leaf regulating valve; 7) compound multi-leaf regulating valve; 8) Three-way regulating valve, etc. 1) ~ 3) Air valves are mainly used for small-section air ducts; 4) ~ 6) Various air valves are mainly used for large-section air ducts; 7) and 8) two kinds of air valves are used to adjust the air volume of each branch at the branch, confluence or bypass of the pipe network.
Butterfly, parallel and split multi-leaf control valves adjust the air volume by changing the blade angle, and the blades of parallel multi-leaf control valves rotate in the same direction; Two adjacent blades of the split multi-blade regulating valve rotate in opposite directions. The flashboard valve adjusts the air volume according to the depth of the flashboard inserted into the pipeline. The diamond regulating valve adjusts the air volume by changing the opening angle of the blades.
(2) The damper with control function only includes check valve, fire valve and smoke exhaust valve. The check valve controls the direction of air flow, and only allows the air flow in the specified direction to prevent the air flow from flowing in the opposite direction. Fire dampers are generally fully opened and closed in case of fire, so as to cut off the airflow and prevent the fire from spreading through the air duct; The smoke exhaust valve is normally closed and fully opened when smoke is exhausted, so as to eliminate indoor smoke.
3. Blowhole
The basic function of tuyere is to suck or exhaust gas from the pipe network. Aluminum alloy tuyere is widely used in ventilation (air conditioning) engineering, and its surface is oxidized, which has good anti-corrosion and waterproof properties.
(1) Common types
At present, the commonly used tuyeres are grille tuyere, landing return air tuyere, slit tuyere, louver tuyere (including fixed louver tuyere and movable louver tuyere) and diffuser.
(2) The tuyere can be divided into fresh air tuyere, exhaust tuyere, air supply tuyere and return air tuyere according to specific functions.
4. Local exhaust hood
The main function of the range hood is to remove dusty gas, waste heat, residual temperature, toxic gas, oil fume, etc. In a process or equipment.
According to different working principles, local exhaust hoods can be divided into closed exhaust hoods, cabinet exhaust hoods (fume hoods), external suction exhaust hoods, connecting exhaust hoods and blowing exhaust hoods.
5. Dust catcher
The technical performance indexes of dust collector mainly include dust removal efficiency, pressure loss, gas volume and load adaptability.
(1) inertial vacuum cleaner. It is a device that uses its own inertia force to separate dust particles from dusty airflow when the direction of dusty airflow changes sharply or collides with obstacles such as baffles and shutters. Its performance mainly depends on the characteristic speed, turning radius and turning angle. It can be used to collect dust particles with particle size greater than 20μ m. Due to different structural forms, the pressure loss varies greatly, generally 100 ~ 400 Pa. It is suggested to take LOM/s as the airflow velocity in the intake pipe. Commonly used inertial dust collectors include airflow folding type, gravity baffle type, louver type and combined type.
(2) Cyclone dust collector. It is a device that uses centrifugal force to remove dust particles from airflow. After the dust-containing gas enters the dust collector, due to the centrifugal force, the dust particles rotate and fall along the cylinder wall, and the purified gas is discharged through the exhaust pipe. The separated dust particles enter the dust unloading device at the lower part through the dust outlet. This kind of dust collector has simple structure, no moving parts, low cost and convenient maintenance and management. The dust removal efficiency can generally reach about 85%, and the dust removal efficiency of high-efficiency cyclone can reach more than 90%.
(3) Wet dust collector. Mainly through the contact between the dusty airflow and liquid droplets or liquid films, under the interaction of purification mechanisms such as collision and detention of liquid and coarse dust particles, diffusion and mutual cohesion of fine dust particles, the dust particles are separated from the airflow, thus purifying the airflow. Dust collector has the advantages of simple structure, less investment, small floor space and high dust removal efficiency, and can purify harmful gases at the same time, but it is difficult to recover materials by dry method, and sometimes it is necessary to set up a special wastewater treatment system.
There are many kinds of wet dust collectors, such as water bath type, pulse type, horizontal cyclone water film type, vertical cyclone water film type, venturi tube type and so on.
(4) Filter dust collector. It is a device that collects dust from gas-solid two-phase flow and purifies gas through the action of porous filter materials. According to different filtering materials and working objects, it can be divided into three types: bag filter, granular layer filter and air filter. Filter dust collector is a kind of efficient filtering equipment, which is widely used.
(5) Small dust removal device.
(6) electrostatic precipitator. It is a kind of dust removal equipment which uses electrostatic force to separate dust from gas. Electrostatic precipitator has high dust removal efficiency, good temperature resistance and low pressure loss; But the one-time investment is high, the steel consumption is large, the manufacturing and installation accuracy is high, and the specific resistance of purified dust is certain. According to the different cleaning methods of electrodes, they can be divided into dry electrostatic precipitator, wesp electrostatic precipitator and semi-dry semi-wet electrostatic precipitator. According to the direction of airflow in electrostatic precipitator, it can be divided into vertical electrostatic precipitator and horizontal electrostatic precipitator. According to the form of dust collecting electrode, it can be divided into tube electrostatic precipitator and plate electrostatic precipitator.
6. Heat recovery exchanger
Device for recovering heat from waste gas and heating intake air in winter. There are several types of heat exchangers, such as runner type, plate-fin type, heat pipe type and intermediate medium type.
7.scarf
Muffler is a device that can prevent noise from spreading and let airflow pass smoothly. Its types are: resistive muffler, reactive muffler, diffusion muffler, buffer muffler, interference muffler and impedance compound muffler.
8. Air curtain equipment
In recent years, some factories have produced integrally assembled air curtains and tubular air curtains. The former is equipped with heaters, which are suitable for civil and industrial buildings in cold areas, while the latter is small in size and suitable for all kinds of civil buildings and cold storage. There is no heating (cooling) device.
9. Air purification equipment
There are many methods to deal with harmful gases, including absorption and adsorption.
(1) absorption equipment
Absorption is to use a suitable liquid to contact the waste gas containing harmful gases, and to remove one or more harmful gases by using the different solubility of gases in the liquid, so as to achieve the purpose of purifying harmful gases and at the same time play a role in dust removal. Therefore, it is used in the exhaust system that needs to purify harmful gases and remove dust at the same time. Commonly used absorbents include water, alkaline absorbents, acidic absorbents, organic absorbents and oxidant absorbents. Commonly used absorption equipment: spray tower, packed tower and turbulent tower.
(2) adsorption equipment
Adsorption is a diffusion process in which harmful gases contact with solid substances at the interface. During adsorption, the adsorbed substances are only adsorbed on the surface of solid substances, forming an adsorption layer. In the adsorption phenomenon, the solid substance with large adsorption capacity is called adsorbent, and the adsorbed substance is called adsorbate. Activated carbon adsorption equipment includes fixed bed activated carbon adsorption equipment, moving bed adsorption equipment and moving bed adsorption equipment.