Fundamentals of industrial ventilation: all about calculations and types of systems

The ventilation system of the industrial premises creates and maintains climatic indicators, the norms of which are regulated by the instructions of the sanitary and epidemiological supervision.

Humidity, temperature, and air flow rate are important to the health of plant personnel and process compliance. In contrast to household facilities, in production facilities such indicators as the amount of mechanical and chemical impurities in the air are also monitored.

In some cases, the microclimate in the room must provide optimal conditions for storage (for example, in the depositories of museums or libraries), then the convenience of the staff fades into the background.

Classification of ventilation systems in production

Industrial ventilation systems and installations can be classified according to the following properties:

• Method of movement of air masses: free and forced;
• The nature of the action: exhaust or supply;
• Serviced area: local or general exchange;
• Design features: channelless or channel.

Natural motivation

Natural flow ventilation has the following properties:

• the movement of air flows is provided by the aeration method;
• due to the pressure difference between the workshop and the end of the exhaust duct located above the roof of the building;
• due to the pressure of the wind.

According to the basics of ventilation of industrial-type premises, natural motivation is implemented in industries with a powerful heat release and a content of mechanical impurities of no more than 30% of the PDN in the workplaces of personnel.

If it needs to be treated before air is supplied, aeration method is not suitable.

For a stable movement of air masses due to the pressure difference, the height difference between the points of intake and discharge should be from 3 meters. In ventilation calculations for rooms of this type, the maximum duration of horizontal ventilation ducts is 3 meters. The air in the system moves at a speed not exceeding one meter per second.

The ventilation system of the premises, built according to this principle, is cheap, it is easy to install and operate. However, its effectiveness is unstable and varies from many external factors.

Mechanical impulsion

In ventilation systems of rooms operating on mechanical traction, devices are used that transport air masses to the required distances.

Air is supplied and removed from the working area in the required volumes under any ambient conditions. If required, the supply air can be filtered, cooled, heated, dried or humidified. Natural ventilation does not allow for optimal air performance. Inflow parameters are similar to those of atmospheric air.

The most common ventilation systems are with mixed motivation.

Supply equipment supplies fresh air to the manned building.At the same time, the exhaust mechanisms draw out dirty, hot or damp vapors.

When calculating the ventilation of premises, it is important to correctly balance the volume of supplied and removed used air.

Local ventilation

The fundamental difference between the local air exchange scheme is that air is supplied pointwise to a specific place (local supply) and is discharged in the same way (local exhaust).

Here is a list of local ventilation components used in industrial premises:

• air showers (streams of air going to a certain place at high speed);
• areas fenced off from the total area, where a special atmosphere is created;
• air curtains.

Due to the high efficiency and cost-effectiveness of local ventilation, it is widely used in various types of industries.

Exhaust local ventilation is necessary when poisonous substances or heat are released pointwise and it is necessary to prevent their spread.

Local exhaust ventilation elements:

• exhaust umbrellas;
• side hoods;
• covers over equipment;
• air curtains.

When calculating the ventilation of the room, the following requirements are taken into account:

• local exhaust should not interfere with the course of the technological process;
• the entire surface of the emission of hazards must be covered;
• secretions are removed in the course of their physical movement (cold ones are directed downward, and hot, according to the laws of physics, upward).

The exhaust air must be cleaned before being released into the environment. Sometimes only one coarse filter is enough; if necessary, a cascade of filters of different degrees of purification is installed. Despite the efficiency of local systems, they do not always cope with maintaining the required microclimate.

General ventilation

A general ventilation system is needed when harmful impurities, moisture and heat are distributed throughout the entire volume of the room.

The supply general exchange system reduces the concentration of harmful substances and displaces polluted air masses.

Exhaust general ventilation is a duct system and a fan. If the length of the ventilation duct is not more than 40 m, an axial fan is installed, otherwise a centrifugal fan, as a more powerful one.

Features of calculations of ventilation systems

The calculations and type of ventilation of the room depend on its purpose. Ventilation of the production area should remove the following types of contaminants emitted during the operation of equipment and people:

• hot air;
• explosive and toxic impurities in the air;
• water vapor.

Room ventilation is calculated for each type of air pollution.

The calculation is based on the amount of supply air required for normal operating conditions.

Calculation of ventilation for excess heat:

Q = Qu + (3.6V - cQu (Tz - Tp) / c (T1 - Tp),

WhereQu - the volume of air removed by local suction, in cubic meters \ h,V - the amount of heat generated by equipment and products, in watts,c - heat capacity, taken from reference books, is equal to 1.2 kJ,Tz - the temperature of the exhaust air removed from the workplace, in degrees Celsius,Tp - supply air temperature, in degrees Celsius,T1 - temperature of the air removed by general ventilation.

Calculation for explosive and toxic industries

When calculating ventilation for industries with explosive or toxic emissions, the task is to dilute them to the maximum permissible level.

Q = Qu + (M - Qu (Km - Kp) / (Ku - Kp),

WhereM - the mass of toxic substances released into the air in 1 hour, in mg,Km - the content of toxic substances in the air discharged by local systems, in mg / m3,Kp - the content of toxic substances in the supply air, mg / cubic meter,Ku - the content of toxic substances in the air removed by the general exchange system, mg / cubic meter.

Calculation with increased moisture content

Q = Qu + (W - 1.2 (Om - ABOUTp) / (О1 - Оp)),

hereW - the amount of moisture that gets into the air of the workshop for 1 hour, in mg / h,Оm - the amount of steam discharged by the local system, in g / kg,Op - supply air humidity, g / kg,О1 - the amount of steam in the air removed by the general exchange system, g / kg.

Calculation of personnel emissions

When calculating the ventilation of some rooms, it is important to take into account every gram of moisture that enters the air. Then the calculation is carried out according to the number of employees:

Q = N * m,

hereN - the number of employees,m - the consumption of atmospheric air per person per hour.

Categories of premises for fire safety

Premises for any purpose: industrial, warehouse, residential or public are divided into categories for ventilation and fire safety:

• BUT - increased danger of explosions, fires. Buildings that use or emit flammable gases and substances or substances that, on contact with air (water), can ignite or explode with a flash point of up to 28 degrees;
• B - danger of fires or explosions. Buildings with dust or vapor in the atmosphere that are flammable and have a flash point above 28 degrees;
• B1 - B4 - risk of fire. Buildings in which liquids, solids or volatile substances are emitted or present, which are difficult to ignite when in contact with air, water or other substances;
• D - moderate fire hazard. Rooms in which substances are present in a heated or molten form, an abundance of heat and flame are emitted. As well as substances used in the form of fuel or utilized by the method of combustion;
• D - low risk of fire. Buildings containing non-flammable substances at ambient temperatures.

When creating ventilation for warehouse or industrial premises, a single system is provided in the following cases:

• for residential buildings;
• for office buildings, domestic, public or industrial premises with ventilation category D;
• industrial with ventilation category B or A, occupying up to 3 floors;
• industrial with a single category D, D or V;
• warehouse, occupying up to 3 floors, with category B, A or B.

Features of warehouse ventilation

Selecting the ventilation of the warehouse, it is necessary to be guided by the SNiP "General sanitary and hygienic requirements for the air of the working area", "Warehouse buildings", "Fire safety of buildings and structures."

If typical room ventilation with natural draft is not able to create the required microclimate, mechanical induction is used. For example, it is not recommended to use aeration for ventilation of warehouses with food storage. Outdoor air is polluted, and it is often impossible to clean it.

In some cases, it is impossible to organize aeration due to the architecture of the building or its location. Then they resort to the mechanical type of ventilation of the warehouse.

If the warehouse stores substances that emit harmful or explosive gases (vapors), mechanical ventilation is arranged.

Nevertheless, in the overwhelming majority of storages, a general exchange system with natural draft and a single air exchange is organized.

Before calculating the ventilation of the warehouse, it is necessary to determine the nature of the stored materials. So, when calculating air exchange, the type and amount of harmful emissions are taken into account.

Infiltration

As a rule, warehouses are not sealed. The process of air exchange between the warehouse and the street is called infiltration. With a large temperature difference, infiltration can be 1.5 - 2 air changes. This parameter is certainly taken into account when designing the basics of storage ventilation.

If a 1-fold air exchange is sufficient for the warehouse, only exhaust air can be blown out. The inflow will be replenished by infiltration.

More often, channelless systems are installed in warehouses. It is advisable to use channels with natural draft in small auxiliary buildings with an estimated air exchange of no more than 1.

During aeration, the air flow is ensured by open vents. If the concentration of impurities in the air is more than a third of the MPC, aeration is not applied.

In the warm season, air is supplied to the warehouse through openings in the walls located at a height of no more than 1.5 meters from the ground. These can be gates, windows, sliding partitions.

In winter, the openings for the inflow are equipped at a height of 3-4 meters from the ground. They must be covered with rain and snow canopies.

Exhaust air is removed through exhaust shafts or vents. The thrust in the system is increased by installing a deflector at the outlet of the exhaust shaft. And the intensity of traction is regulated by various dampers, gates, blinds.

The height of the exhaust shaft head must exceed the height of the roof ridge by 50 cm or more. Otherwise, in strong winds, reverse thrust is observed.

Supply air volume calculation:

Def = 3600 *S*m*n,

WhereS - the area of ​​the vents in sq. M,m - air speed in m / s, is 1 - 1.5 with natural draft,n - flow coefficient, depends on the opening angle of the window: at 90 degrees 0.65, at 45 - 0.44, at 30 degrees - 0.32.

Table 1. The volume of air penetrating through 1 sq. M of vents

Features of ventilation of commercial premises

All retail premises can be roughly divided into 2 types:

• Warehouse stores (large hypermarkets such as Metro);
• Zoned shopping malls (Mega-type malls).

Warehouse shops

In the first case, it is not required to supply air to separate rooms. Therefore, the ventilation of a retail space of the first type is most often a powerful supply and exhaust unit without zoning of climatic indicators.

Rooftop air conditioners are the standard solution for warehouse stores. This is a one-piece equipment that is installed on the roof of the building and connected to the hall by air ducts. The air ducts are distributed under the false ceiling. In addition to ventilation, the rooftop performs the function of heating and air conditioning.

Sometimes several rooftops of lower power are installed instead of one large one.

Rooftop air conditioners are reliable, durable, quiet and economical enough. The only disadvantage of using this type of retail space ventilation is the impossibility of zoning air indicators.

Shopping malls

In shopping malls there are zones for various purposes: boutiques, beauty salons, cafes, warehouses. Which need to create a different microclimate. Therefore, for each type of premises, a calculation is made depending on the number of visitors, heat release, moisture (spas), smoke (smoking rooms).

An additional complication is the placement of shopping complexes on several levels, as well as the architectural features of each room.

Central air conditioners are the standard choice for ventilation of this type of retail space. This is a sectional equipment including sections:

• heating;
• noise reduction;
• fans;
• humidification;
• filtration.

The modules are enclosed in a common building, which is located in a special compartment of the building. Since the central air conditioner does not include sources of cold and heat, it must be combined with a chiller-fan coil unit. This combination of equipment allows you to set individual air parameters for each room, serves buildings of any size.Moreover, this type of equipment for ventilation of premises can be simultaneously used for heating water in a pool and freezing ice on a skating rink.

Such sophisticated climatic equipment is controlled only automatically through a central control panel.

Features of ventilation of clean rooms

The main task of ventilation in a clean room is to ensure the following indicators:

• Concentration of dust particles in 1 cu. m of air. To do this, air is passed through absolute filters, maintaining the specified cleanliness class. The supply air is cleaned using four-stage filters that trap inclusions down to 0.01 microns;
• Temperature, humidity and air velocity. The microclimate is important not so much for the work of personnel as for the technological process. If the air is too dry, it will generate static electricity. If it is too humid, condensation may settle;
• The pressure difference between the clean room and the adjacent room. To prevent dust and moisture from entering the cleanroom from neighboring rooms, a slightly increased pressure is maintained inside. Ventilation of the cleanroom ensures the predominance of the supply over the exhaust;
• Availability of fresh air. People work in the room, so they must be provided with clean air in volumes regulated by sanitary standards.

Creation of "clean zones"

Using directional or laminar airflow, you can create a clean area in the room. Air moving in one direction without turbulence displaces dust particles from the required zone. Then they are pulled out of the bounds along the duct system. Due to the special direction of the flow, particles are removed instantly. The effect is achieved through the use of special laminar air distributors.

As a rule, the basis of ventilation in a clean room is a specially modified central air conditioner.

It is controlled automatically. And the necessary air parameters are maintained using a whole network of sensors and a fully automated dispatching unit.

Design and installation of industrial ventilation is a complex multi-stage process. Many firms offer comprehensive services: from design to maintenance. Such a solution removes all problems with the microclimate of the enterprise from the customer.

Video about automation of ventilation control in clean rooms: