Let's start, perhaps, with natural and. As the name implies, the first type includes ventilation and everything that has nothing to do with devices. Accordingly, to mechanical ventilation include fans, hoods, supply valves and other equipment for creating forced air flow.
It is good for the moderate speed of this flow, which creates comfortable indoor conditions for a person - the wind is not felt. Although correctly installed high-quality forced ventilation also does not bring drafts. But there is also a minus: at low air flow speed at natural ventilation a wider cross-section is needed to feed it. As a rule, the most effective ventilation is provided with complete open windows or doors, which speeds up the air exchange process, but can negatively affect the health of residents, especially in winter period of the year. If we ventilate the house by partially opening the windows or completely opening the vents, such ventilation requires about 30–75 minutes, and here the window frame may freeze, which may well lead to condensation, and cold air entering for a long time leads to health problems . Widely open windows speed up air exchange in the room; through ventilation will take approximately 4–10 minutes, which is safe for window frames, but with such ventilation almost all the heat in the house comes out, and for a long time indoor temperatures are quite low, which again increases the risk of disease.
We should also not forget about the increasingly popular supply valves, which are installed not only on windows, but also on walls inside rooms (wall supply valve), if the window design does not provide for such valves. The wall valve provides air infiltration and is an oblong pipe installed through the wall, closed on both sides with grilles and adjustable from the inside. It can be either completely open or completely closed. For convenience in the interior, it is recommended to place such a valve next to the window, since it can be hidden under tulle, and the flow of passing air will be heated by radiators located under the window sills.
For normal air circulation throughout the apartment, it is necessary to ensure its free movement. To do this on interior doors install transfer grilles so that the air moves smoothly from supply systems to the exhaust, passing throughout the house, through all the rooms. It is important to consider that the correct flow is considered to be the one in which the smelliest room (toilet, bathroom, kitchen) is the last. If it is not possible to install a flow grille, it is enough to simply leave a gap between the door and the floor, about 2 cm. This is enough for air to move easily around the house.
In cases where natural ventilation is not enough or there is no desire to provide it, they switch to using mechanical ventilation.
Favorable indoor microclimate - important condition human life activity. It is collectively determined by temperature, humidity and air mobility. Deviations in parameters negatively affect health and well-being and cause overheating or hypothermia of the body. Lack of oxygen leads to hypoxia of the brain and other organs.
Calculation and standards
Calculation of room ventilation is carried out when designing an object in accordance with SNiP 13330.2012, 41-01-2003, 2.08.01-89. But there are cases when its work is ineffective. If checking the draft with paper strips or a lighter flame does not reveal a violation of the patency of the ventilation ducts, it means exhaust ventilation does not cope with its functions due to an incorrectly selected section.
Why is ventilation needed?
The task of ventilation is to provide the necessary air exchange in the room, to create optimal or acceptable conditions for a person’s long stay.
Research has found that people spend 80% of their time indoors. In one hour at rest, a person secretes environment 100 kcal. Heat transfer occurs by convection, radiation and evaporation. If the air is not moving enough, the transfer of energy from the surface of the skin into space slows down. As a result, many body functions suffer and a number of diseases arise.
Lack or insufficient ventilation, especially in rooms with high humidity, leads to stagnation. They are accompanied by an invasion of difficult-to-remove mold fungi, unpleasant odors and constant dampness. Moisture has an adverse effect on building structures, leads to rotting of wood and corrosion of metal elements.
With excess draft, the release of air masses into the atmosphere increases, which in winter leads to loss of large quantity heat. Home heating costs are rising.
The quality and purity of air is the main factor that determines the effectiveness of ventilation. Pollutant fumes from building materials, furniture, dust and carbon dioxide must be removed from the premises in a timely manner.
There is the opposite situation, when the air in a house or apartment is much cleaner than outside. Exhaust gases on a busy highway, smoke or soot, toxic pollution industrial enterprises can poison the indoor atmosphere. For example, in the center big city carbon monoxide content is 4-6 times, nitrogen dioxide is 3-40 times, sulfur dioxide 2-10 times higher than in rural areas.
Ventilation calculations are carried out to determine the type of air exchange system, its parameters, which will combine the energy efficiency of housing and a favorable microclimate in the premises.
Microclimate parameters for calculation
Standards in accordance with GOST 30494-2011 determine the optimal and permissible air quality parameters in accordance with the purpose of the premises. They are classified by standards into the first and second categories. These are places where people relax, lying down or sitting, and engage in study and mental work.
Depending on the period of the year and the purpose of the room, the optimal and permissible temperature is 17-27°C, relative humidity 30-60% and air speed 0.15-0.30 m/s.
In residential premises, when calculating ventilation, the necessary air exchange is determined using specific standards, in industrial premises - according to the permissible concentration of pollutants. At the same time, the quantity carbon dioxide in the air should not exceed 400-600 cm³/m³.
On our website you can find contacts construction companies who offer interior remodeling services. You can communicate directly with representatives by visiting the “Low-Rise Country” exhibition of houses.
Types of ventilation systems according to the method of creating draft
The movement of air masses occurs as a result of pressure differences between layers of air. The greater the gradient, the stronger the driving force. To create it, a natural, forced or combined ventilation system is used, which uses supply, exhaust or recirculation (mixed) methods of air removal. In industrial and public buildings Emergency and smoke ventilation are provided.
Natural ventilation
Natural ventilation of rooms occurs according to physical laws - due to the difference in temperature and pressure between the external and internal air. Even during the times of the Roman Empire, engineers installed the likes of shafts in the houses of the nobility, which served for ventilation.
The natural ventilation complex includes external and internal openings, transoms, vents, wall and window valves, exhaust shafts, ventilation ducts, and deflectors.
The quality of ventilation depends on the volume of passing air masses and the trajectory of their movement. The most favorable option is when the windows and doors are located at opposite ends of the room. In this case, when air circulates, it is completely replaced throughout the room.
Exhaust ducts are placed in rooms with highest level pollution, pollution unpleasant odors and humidity - kitchens, bathrooms. Supply air comes from other rooms and pushes exhaust air out into the street.
In order for the hood to work in the desired mode, its top must be 0.5-1 m above the roof of the house. This creates the necessary pressure difference to move air.
Natural ventilation is silent, does not consume electricity, and does not require large investments in the device. Air masses penetrating from the outside do not acquire additional properties - they are not heated, purified or moistened.
Air recirculation is limited to one apartment. There should be no suction from neighboring rooms.
Forced ventilation began to be used from the mid-19th century. At first, large fans were used in mines, in the holds of ships, and in drying shops. With the advent of electric motors, a revolution occurred in room ventilation. Adjustable devices have appeared not only for industrial, but also for domestic needs.
Now, when passing through a forced ventilation system, outside air is given additional valuable qualities - it is purified, humidified or dried, ionized, heated or cooled.
Fans and ejectors move large volumes of air masses over large areas. The system includes electric motors, dust collectors, heaters, noise suppressors, control and automation devices. They are built into air ducts.
Video description
More information about calculating ventilation with a recuperator is described in this video:
Calculation of natural ventilation of residential premises
The calculation consists of determining the flow rate supply air L in cold and warm period of the year. Knowing this value, you can select the cross-sectional area of the air ducts.
A house or apartment is considered as a single air volume where gases circulate through open doors or canvas trimmed 2 cm from the floor.
The influx occurs through leaky windows, external fences and by ventilation, removal occurs through exhaust ventilation ducts.
The volume is found using three methods - multiplicity, sanitary standards and squares. The largest is selected from the obtained values. Before calculating ventilation, the purpose and characteristics of all rooms are determined.
Basic formula for the first calculation:
L=nхV, m³/h, where
- V is the volume of the room (the product of height and area),
- n - multiplicity determined according to SNiP 2.08.01-89 depending on the calculated temperature in the room in winter.
According to the second method, the volume is calculated based on the specific norm per person, regulated by SNiP 41-01-2003. They take into account the number of permanently residing people, the presence gas stove and a bathroom. According to Table M1, the flow rate is 60 m³/person per hour.
The third method is by area.
- A - room area, m²,
- k- standard flow rate per m².
Calculation of the ventilation system: example
Three-room house with total area 80 m². The height of the premises is 2.7 m. Three people live.
- Living room 25 m²,
- bedroom 15 m²,
- bedroom 17 m²,
- bathroom - 1.4² m²,
- bath - 2.6 m²,
- kitchen 14 m² with four-burner stove,
- corridor 5 m².
Separately find the flow rate for inlet and outlet so that the volume of incoming air is equal to the amount removed.
- living room L=25x3=75m³/h, multiplicity according to SNiP.
- bedrooms L=32x1=32 m³/h.
Total inflow flow:
L total=Lguest.+Lsleeping=75+32=107 m³/h.
- bathroom L= 50 m³/hour (tab.SNiP 41-01-2003),
- bath L= 25 m³/hour.
- kitchen L=90 m³/hour.
The inflow corridor is not standardized.
By hood:
L=Lkitchen+Lbathroom+L baths=90+50+25=165 m³/h.
The supply flow is less than the exhaust. For further calculations, the largest value L=165 m³/h is accepted.
According to sanitary standards, calculations are carried out based on the number of residents. Specific consumption per person is 60 m³.
L total=60x3=180m/h.
Taking into account temporary visitors, for whom the established air flow is 20 m3/h, we can take L = 200 m³/h.
By area, the flow rate is determined taking into account the standard air exchange rate of 3 m²/hour per 1 m² of living space.
L=57x3=171 m³/h.
According to the calculation results, the consumption according to sanitary standards is 200 m³/h, the multiplicity is 165 m³/h, and the area is 171 m³/h. Although all options are correct, the first option will make the conditions more comfortable for residents.
Bottom line
Knowing the air balance of a residential building, the size of the cross-section of the air ducts is selected. Most often, rectangular channels with an aspect ratio of 3:1 or round are used.
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To conveniently calculate the cross-section, you can use an online calculator or a diagram that takes into account the speed and air flow.
For natural ventilation, the speed in the main and branch air ducts is assumed to be 1 m/h. In the forced system, 5 and 3 m/h, respectively.
With a required air exchange of 200 m3/h, it is sufficient to implement a natural ventilation system. For large volumes of transported air, mixed recirculation is used. Devices designed for performance are installed in the channels, which will provide the necessary microclimate parameters.
To create a favorable microclimate in industrial and residential premises, it is necessary to install a high-quality ventilation system. Particular attention must be paid to the length and diameter of the pipe for natural ventilation, since the efficiency, productivity and reliability of air ducts depend on correct calculations.
What are the requirements for ventilation pipes?
The main purpose of the duct for natural ventilation is to remove exhaust air from the room.
When installing systems in homes, offices and other facilities, the following points must be taken into account:
- the diameter of the pipe for natural ventilation must be at least 15 cm;
- when installing in residential premises and food industry facilities, anti-corrosion characteristics are important, otherwise metal surfaces will rust under the influence of high humidity;
- the lighter the structure, the easier the installation and maintenance;
- performance also depends on the thickness of the air duct; the thinner, the greater the throughput;
- fire safety level – no harmful substances should be released during combustion.
If you do not comply with standards (norms) when designing, installing and choosing the material and diameter of PVC ventilation pipes or galvanized steel, then the indoor air will be “heavy” due to high humidity and lack of oxygen. In apartments and houses with poor ventilation, windows often fog up, the walls in the kitchen smoke, and fungus forms.
What material should I choose the air duct from?
There are several types of pipes on the market, differing in the material of manufacture:
Advantages of plastic pipes:
- low cost when compared with air ducts made of other materials;
- anti-corrosion surfaces do not require additional protection or treatment;
- easy to maintain, you can use any detergent for cleaning;
- large selection of pipe diameters for PVC ventilation pipes;
- simple installation, and, if necessary, the structure can be easily dismantled;
- dirt does not accumulate on the surface due to its smoothness;
- When heated, there is no release of harmful and toxic substances to human health.
Metal air ducts are made of galvanized or stainless steel; when considering the characteristics, the following advantages can be identified:
- galvanized and stainless steel pipes are allowed to be used in facilities with high humidity and frequent temperature changes;
- moisture resistance – structures are not subject to corrosion and rust;
- high heat resistance;
- relatively light weight;
- Easy installation - basic knowledge required.
Aluminum foil is used as a material for the manufacture of corrugated air ducts. Main advantages:
- during installation, a minimum number of connections is formed;
- ease of dismantling;
- if necessary, the pipeline is placed at any angle.
Advantages of fabric structures:
- mobility - easy to install and dismantle;
- there are no problems during transportation;
- no condensation under any operating conditions;
- low weight facilitates the fastening process;
- no need for additional insulation.
What are the different types of air ducts?
Depending on the scope and direction of use, not only the diameters of the PVC pipes are selected, but also the shape:
- Spiral shapes are distinguished by increased rigidity and attractive appearance. During installation, connections are made using cardboard or rubber seals and flanges. Systems do not need isolation.
Advice! If you have no experience in this area, then to save your own money and time, it is better to immediately turn to specialists, since calculating the diameter of the pipe for ventilation taking into account the air flow, and carrying out the installation yourself will be very problematic.
- For residential properties (country and country houses), flat shapes would be an ideal option due to the following advantages:
- if necessary, round and flat pipes can be easily combined;
- if the dimensions do not match, then the parameters can be easily adjusted using a construction knife;
- the structures are relatively lightweight;
- Tees and flanges are used as connecting elements.
- Installation of flexible structures occurs without additional elements for connection (flanges, etc.), which greatly simplifies the installation process. The manufacturing material used is laminated polyester film, woven fabric or aluminum foil.
- Round air ducts are more in demand, the demand is explained by the following advantages:
- minimum number of connecting elements;
- easy operation;
- air is well distributed;
- high levels of rigidity;
- simple installation work.
The material of manufacture and the shape of the pipes are determined at the stage of developing design documentation; a large list of points is taken into account here.
How is the diameter of the ventilation pipe determined?
On the territory of Russia there are a number of SNiP normative documents that say how to calculate the diameter of a pipe for natural ventilation. The choice is based on the air exchange rate - a determining indicator of how much and how many times per hour the air in the room is replaced.
First you need to do the following:
- calculations are made of the volume of each room in the building - you need to multiply the length, height and width;
- air volume is calculated using the formula: L=n (standardized air exchange rate)*V (room volume);
- the obtained L indicators are rounded up to a multiple of 5;
- the balance is drawn up so that the exhaust and supply air flows coincide in total volume;
- The maximum speed in the central air duct is also taken into account; the indicators should not exceed 5 m/s, and on branch sections of the network no more than 3 m/s.
The diameter of PVC ventilation pipes and other materials is selected according to the data obtained in the table presented:
How to determine the length of the ventilation pipe?
When writing a project, in addition to calculating the diameter of the pipe for natural ventilation, determining the length of the outer part of the air duct is considered an important point. The total value includes the length of all channels in the building through which air circulates and is discharged outside.
Calculations are made according to the table:
The following indicators are taken into account when calculating:
- if a flat duct is used in an installation above the roof, the minimum length should be 0.5 m;
- when installing a ventilation pipe next to the smoke, the height is made the same to prevent smoke from entering the room during the heating season.
The performance, efficiency and uninterrupted operation of the ventilation system largely depends on the correct calculations and compliance with installation requirements. It is better to choose proven companies with a positive reputation!
Comments:
- Why do you need to know about the area of air ducts?
- How to calculate the area of material used?
- Calculation of duct area
The possible concentration in enclosed spaces of air contaminated with dust, water vapor and gases, products of thermal processing of food, forces the installation of ventilation systems. For these systems to be effective, serious calculations have to be made, including calculation of the area of the air ducts.
Having found out a number of characteristics of the facility under construction, including the areas and volumes of individual premises, the features of their operation and the number of people who will be there, specialists, using a special formula, can establish the design ventilation performance. After this, it becomes possible to calculate the cross-sectional area of the air duct, which will ensure the optimal level of ventilation of the interior.
Why do you need to know about the area of air ducts?
Ventilation of premises is a rather complex system. One of the most important parts of the air distribution network is the air duct complex. Not only the correct location in the room or cost savings, but most importantly, the optimal ventilation parameters that guarantee a person comfortable living conditions depend on the high-quality calculation of its configuration and working area (both the pipe and the total material required for the manufacture of the air duct).
Figure 1. Formula for determining the diameter of the working line.
In particular, it is necessary to calculate the area in such a way that the result is a structure capable of passing the required volume of air while meeting other requirements for modern ventilation systems. It should be understood that correct calculation of the area leads to the elimination of air pressure losses, compliance with sanitary standards for the speed and noise level of air flowing through the air ducts.
At the same time, an accurate idea of the area occupied by pipes makes it possible to designate the most suitable place in the room for the ventilation system.
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How to calculate the area of material used?
Calculation of the optimal air duct area is directly dependent on factors such as the volume of air supplied to one or more rooms, its speed and air pressure loss.
At the same time, the calculation of the amount of material required for its manufacture depends both on the cross-sectional area (dimensions of the ventilation channel), and on the number of rooms into which it is necessary to pump, and on the design features of the ventilation system.
When calculating the cross-sectional area, it should be borne in mind that the larger it is, the lower the speed of air passage through the air duct pipes.
At the same time, there will be less aerodynamic noise in such a highway, and the operation of forced ventilation systems will require less electricity. To calculate the area of air ducts, you need to apply a special formula.
To calculate the total area of material that needs to be taken to assemble air ducts, you need to know the configuration and basic dimensions of the system being designed. In particular, to calculate for round air distribution pipes, quantities such as the diameter and total length of the entire line will be required. At the same time, the volume of material used for rectangular structures is calculated based on the width, height and total length of the air duct.
When making general calculations of material requirements for the entire highway, it is also necessary to take into account bends and half-bends of various configurations. Thus, correct calculations of a round element are impossible without knowing its diameter and angle of rotation. When calculating the area of material for a rectangular outlet, components such as width, height and angle of rotation of the outlet are involved.
It is worth noting that each such calculation uses its own formula. Most often, pipes and fittings are made of galvanized steel in accordance with the technical requirements of SNiP 41-01-2003 (Appendix N).
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Calculation of duct area
The size of the ventilation pipe is influenced by such characteristics as the mass of air pumped into the premises, the speed of the flow and the level of its pressure on the walls and other elements of the pipeline.
It is enough, without calculating all the consequences, to reduce the diameter of the line, but the air flow speed will immediately increase, which will lead to an increase in pressure along the entire length of the system and in places of resistance. In addition to the appearance of excessive noise and unpleasant vibration of the pipe, electric ones will also record an increase in energy consumption.
However, it is not always possible and necessary to increase the cross-section of the ventilation line in pursuit of eliminating these shortcomings. First of all, this can be prevented by the limited dimensions of the premises. Therefore, you should be especially careful when calculating the pipe area.
To determine this parameter, you must apply the following special formula:
Sc = L x 2.778/V, where
Sc is the calculated channel area (cm 2);
L - air flow moving through the pipe (m 3 / hour);
V is the speed of air movement along the ventilation line (m/sec);
2.778 - coefficient of coordination of dimensions (for example, meters and centimeters).
The result of the calculations - the estimated pipe area - is expressed in square centimeters, since in these units of measurement it is considered by specialists as the most convenient for analysis.
In addition to the calculated cross-sectional area of the pipeline, it is important to establish the actual cross-sectional area of the pipe. It should be borne in mind that for each of the main cross-section profiles - round and rectangular - its own separate calculation scheme has been adopted. So, to fix the actual area of a circular pipeline, the following special formula is used.
In order for air conditioning systems to operate without failures and ensure the specified performance, during their design, ventilation air ducts are calculated, including determining the throughput and selecting the cross section. Devices for transporting air - air ducts - are widely used in domestic and industrial ventilation and air conditioning systems, and are also used to supply air in various technological equipment in metallurgy, chemical and processing industries.
Today, in domestic and industrial air conditioning systems, regardless of their type (exhaust or supply, forced or natural), a single channel (exhaust) is provided, and air flow is assumed through windows and doors, as well as through cracks and gaps in the walls and floor building structure.
When creating a combined supply and exhaust system, the design and calculation of the ventilation duct in the supply duct is required.
In addition to determining the cross-section at which the required air exchange (performance) will be ensured, ventilation ducts are calculated for pressure loss and rigidity. The latter is caused by the use in modern complexes of technological equipment for air conditioning of plastic and flexible air ducts for ventilation, which have reduced strength and rigidity compared to traditional metal structures.
Features of modern designs
The production of individual parts and assembly units of ventilation and air conditioning systems (air pipes or ducts standardized in diameter and length) is carried out either at industrial enterprises or in repair and construction organizations that install ventilation air ducts according to an individual project tied to a specific constructed facility. At the same time, designers strive to maximize the use of standardized elements in order to reduce the range and number of original parts, the labor intensity and cost of manufacturing of which is much higher than that of mass-produced products.
According to their design and installation method, ventilation ducts are divided into:
- built-in channel pipelines (shafts);
- external air pipelines.
The first category of pipelines is usually provided for in the building design when developing an architectural and construction project. They are laid inside brick or concrete walls, and can also be built as a separate element into sandwich panels of prefabricated individual houses, warehouses and retail pavilions.
External pipelines are installed during reconstruction and major repairs of buildings, as well as when repurposing production premises for the production of a different range of products. External pipelines for air supply are made in the form of suspended or wall-hung boxes or pipes, consisting of prefabricated straight and shaped sections connected by special fittings or using flange connections.
External air ducts are also classified according to the material they are made of. Today, the following types of air pipelines are widely used for domestic purposes, in industry, warehousing and trading activities:
- metal box structures made of galvanized or stainless steel and aluminum;
- plastic structures, in the manufacture of which polypropylene or reinforced polyvinyl chloride is used;
- flexible (corrugated) pipelines made of aluminum, profiled tape or reinforced thermoplastic.
In modern construction, during the repair and reconstruction of industrial buildings, plastic air ducts for ventilation have become widespread, which, compared to metal structures, have a lower cost, weight and installation complexity.
Air duct calculation
At the first stage of the calculation work, a general diagram of the ventilation system is drawn up, indicating on it the length of straight sections, the presence and type of rotating parts, as well as places where the cross-section of pipelines changes. Based on the sanitary and hygienic requirements for the room and the specifics of the production process, the required air exchange (air exchange rate) is assigned. After this, the speed of air movement inside the pipeline is calculated, which depends on the type of ventilation - natural or forced.
Although there are many programs for this, many parameters are still determined the old fashioned way, using formulas. Calculation of the ventilation load, area, power and parameters of individual elements is carried out after drawing up the diagram and distribution of the equipment.
This is a difficult task that only professionals can do. But if you need to calculate the area of some ventilation elements or the cross-section of air ducts for a small cottage, you can really do it yourself.
Air exchange calculation
If there are no toxic emissions in the room or their volume is within acceptable limits, air exchange or ventilation load is calculated using the formula:
R= n * R1,
Here R1- air requirement of one employee, in cubic meters per hour, n- number of permanent employees in the premises.
If the volume of the room per employee is more than 40 cubic meters and natural ventilation is working, there is no need to calculate air exchange.
For domestic, sanitary and utility premises, ventilation calculations based on hazards are made based on approved air exchange rate standards:
- for administrative buildings (exhaust) - 1.5;
- halls (serving) - 2;
- conference rooms for up to 100 people with a capacity (for supply and exhaust) - 3;
- rest rooms: supply 5, exhaust 4.
For industrial premises in which hazardous substances are constantly or periodically released into the air, ventilation calculations are made based on hazardous substances.
Air exchange by pollutants (vapors and gases) is determined by the formula:
Q= K\(k2- k1),
Here TO- the amount of steam or gas appearing in the building, in mg/h, k2- steam or gas content in the outflow, usually the value is equal to the maximum permissible concentration, k1- gas or steam content in the inlet.
The concentration of harmful substances in the inlet is allowed to be up to 1/3 of the maximum permissible concentration.
For rooms with the release of excess heat, air exchange is calculated using the formula:
Q= Ghut\c(tyx - tn),
Here Gizb- excess heat drawn out is measured in W, With- specific heat capacity by mass, c=1 kJ, tyx- temperature of air removed from the room, tn- inlet temperature.
Calculation of thermal load
Calculation of the thermal load on ventilation is carried out according to the formula:
Qin=Vn*k * p * CR(tvn -tnro),
in the formula for calculating the thermal load on ventilation Vn- external volume of the building in cubic meters, k- air exchange rate, tvn- average temperature in the building, in degrees Celsius, tnro- outside air temperature used in heating calculations, in degrees Celsius, R- air density, in kg/cubic meter, Wed- heat capacity of air, in kJ/cubic meter Celsius.
If the air temperature is lower tnro the air exchange rate is reduced, and the heat consumption rate is considered equal to Qв, a constant value.
If, when calculating the heat load for ventilation, it is impossible to reduce the air exchange rate, the heat consumption is calculated based on the heating temperature.
Heat consumption for ventilation
The specific annual heat consumption for ventilation is calculated as follows:
Q= * b * (1-E),
in the formula for calculating heat consumption for ventilation Qo- total heat loss of the building during the heating season, Qb- domestic heat inputs, Qs- heat input from outside (sun), n- coefficient of thermal inertia of walls and ceilings, E- reduction factor. For individual heating systems 0,15 , for central 0,1 , b- heat loss coefficient:
- 1,11 - for tower buildings;
- 1,13 - for multi-section and multi-entry buildings;
- 1,07 - for buildings with warm attics and basements.
Calculation of the diameter of air ducts
Diameters and sections are calculated after the general diagram of the system has been drawn up. When calculating the diameters of ventilation air ducts, the following indicators are taken into account:
- Air volume (supply or exhaust air), which must pass through the pipe in a given period of time, cubic meters per hour;
- Air speed. If, when calculating ventilation pipes, the flow rate is underestimated, air ducts will be installed with a cross-section that is too large, which entails additional costs. Excessive speed leads to vibrations, increased aerodynamic noise and increased equipment power. The speed of movement on the inflow is 1.5 - 8 m/sec, it varies depending on the area;
- Ventilation pipe material. When calculating the diameter, this indicator affects the wall resistance. For example, black steel with rough walls has the highest resistance. Therefore, the calculated diameter of the ventilation duct will have to be slightly increased compared to the standards for plastic or stainless steel.
Table 1. Optimal air flow speed in ventilation pipes.
When the throughput of future air ducts is known, the cross-section of the ventilation duct can be calculated:
S= R\3600 v,
Here v- speed of air flow, in m/s, R- air consumption, cubic meters/h.
The number 3600 is a time coefficient.
Here: D- diameter of the ventilation pipe, m.
Calculation of the area of ventilation elements
Calculation of the ventilation area is necessary when the elements are made of sheet metal and it is necessary to determine the quantity and cost of the material.
The ventilation area is calculated using electronic calculators or special programs; many of them can be found on the Internet.
We will provide several tabular values of the most popular ventilation elements.
| Diameter, mm | Length, m | |||
| 1 | 1,5 | 2 | 2,5 | |
| 100 | 0,3 | 0,5 | 0,6 | 0,8 |
| 125 | 0,4 | 0,6 | 0,8 | 1 |
| 160 | 0,5 | 0,8 | 1 | 1,3 |
| 200 | 0,6 | 0,9 | 1,3 | 1,6 |
| 250 | 0,8 | 1,2 | 1,6 | 2 |
| 280 | 0,9 | 1,3 | 1,8 | 2,2 |
| 315 | 1 | 1,5 | 2 | 2,5 |
table 2. Area of straight round air ducts.
Area value in sq. m. at the intersection of horizontal and vertical stitching.
| Diameter, mm | Angle, degrees | ||||
| 15 | 30 | 45 | 60 | 90 | |
| 100 | 0,04 | 0,05 | 0,06 | 0,06 | 0,08 |
| 125 | 0,05 | 0,06 | 0,08 | 0,09 | 0,12 |
| 160 | 0,07 | 0,09 | 0,11 | 0,13 | 0,18 |
| 200 | 0,1 | 0,13 | 0,16 | 0,19 | 0,26 |
| 250 | 0,13 | 0,18 | 0,23 | 0,28 | 0,39 |
| 280 | 0,15 | 0,22 | 0,28 | 0,35 | 0,47 |
| 315 | 0,18 | 0,26 | 0,34 | 0,42 | 0,59 |
Table 3. Calculation of the area of bends and half-bends of circular cross-section.
Calculation of diffusers and grilles
Diffusers are used to supply or remove air from a room. The cleanliness and temperature of the air in every corner of the room depends on the correct calculation of the number and location of ventilation diffusers. If you install more diffusers, the pressure in the system will increase and the speed will drop.
The number of ventilation diffusers is calculated as follows:
N= R\(2820 * v *D*D),
Here R- throughput, in cubic meters per hour, v- air speed, m/s, D- diameter of one diffuser in meters.
The number of ventilation grilles can be calculated using the formula:
N= R\(3600 * v * S),
Here R- air flow in cubic meters per hour, v- air speed in the system, m/s, S- cross-sectional area of one grating, sq.m.
Calculation of a duct heater
The calculation of an electric ventilation heater is carried out as follows:
P= v * 0,36 * ∆ T
Here v- volume of air passed through the heater in cubic meters per hour, ∆T- the difference between the air temperature outside and inside, which must be provided by the heater.
This indicator varies between 10 - 20, the exact figure is set by the client.
Calculation of a heater for ventilation begins with calculating the frontal cross-sectional area:
Af=R * p\3600 * Vp,
Here R- volume of inlet flow, cubic meters per hour, p- density of atmospheric air, kg\cub.m, Vp- mass air speed in the area.
The cross-sectional size is necessary to determine the dimensions of the ventilation heater. If, according to calculations, the cross-sectional area turns out to be too large, it is necessary to consider the option of a cascade of heat exchangers with a total calculated area.
The mass velocity indicator is determined through the frontal area of the heat exchangers:
Vp= R * p\3600 * Af.fact
To further calculate the ventilation heater, we determine the amount of heat required to warm the air flow:
Q=0,278 * W * c (TP-Ty),
Here W- warm air consumption, kg/hour, Tp- supply air temperature, degrees Celsius, That- outside air temperature, degrees Celsius, c- specific heat capacity of air, constant value 1.005.
Ventilation of any room is a necessary condition, even if it is a warehouse not visited by people. And in public and residential buildings, the ventilation system must be carefully calculated and arranged in accordance with the standards. For each enclosed space, including the attic, it is necessary to take into account an air exchange system that promotes a comfortable stay for people. In any residential building you can see ventilation holes that are responsible for the supply of fresh air. In public spaces where people are expected to be present, supply and exhaust ventilation must be installed to circulate air masses. Sanitary standards strictly regulate the device ventilation systems taking into account the volume of the premises and the expected number of people in it. Below we will consider the types of ventilation systems and the methodology for calculating air exchange.
Ventilation systems vary in the degree of complexity of their design. There are several types:
- Simple, natural, providing a flow of clean air through channels made in the walls of the building.
- Supply and exhaust, having separate channels for air intake and air outflow.
- Supply and exhaust, forced, operating on duct fans built into the air ducts.
- Combined or complex, controlling and providing air supply and exhaust, as well as regulating temperature and humidity in the room.
The comfort of people inside the building depends on the quality of the ventilation system. Standards for the amount of incoming air have been developed and published by Rospotrebnadzor, which controls the operation of ventilation in public buildings.
General picture of ventilation in modern houses
What you need to know about air currents
Main stages of calculations
Natural ventilation in residential and public buildings is arranged during their construction and does not require additional calculations. Therefore, the conversation will focus on compulsory systems. The primary task for carrying out accurate calculations of ventilation systems is to take into account the microclimate of the premises. These are permissible and standard-recommended values of humidity, temperature and air circulation volumes. Depending on the types of the selected system given above, the tasks are determined - only air exchange or complex air conditioning of the room.
Calculation of air flow coming from outside is the first and most important parameter regulated by sanitary and hygienic standards. It is based on minimal volumes of air consumption and air flow due to exhaust channels and the operation of technological equipment. The determination of air exchange, which is measured in cubic meters of replaced air per hour, depends on the volume of the room and its purpose. For apartments, outside air is supplied to rooms where, as a rule, residents spend a long time. This is a living room and bedroom, less often an office and hallways. In corridors, kitchens and bathrooms, there is usually no air supply; only exhaust openings are installed in them. Air masses come naturally from neighboring rooms where the influx is made. This scheme forces the air flow to move through the living rooms into the technical rooms, “squeezing out” the waste air-gas mixture into the exhaust ducts. At the same time, unpleasant odors are removed without spreading throughout the apartment or house.
Calculations include two air exchange values:
- In terms of productivity - based on air mass standards per person.
- By frequency - how many times the air in the room is changed in one hour.
Important! To select the performance of the planned ventilation system, the largest of the obtained values is taken .
Air performance
For residential premises, the amount of air supplied must be calculated in accordance with building codes and regulations (SNiP) No. 41-01-2003. The amount of consumption by one person is indicated here - 60 cubic meters per hour. This volume must be compensated by the influx of external air. For bedrooms, a smaller volume is allowed - 30 cubic meters per hour per person. When making calculations, only permanently residing people should be taken into account, i.e. The number of guests visiting the room from time to time should not be taken into account when calculating air exchange. To make parties comfortable, there are systems that regulate air flow in different rooms. Such equipment will increase the air flow into the living room by reducing it in the bedroom.
Calculations are carried out according to the formula: L = N x Ln, where: L is the estimated volume of incoming air cubic meters per hour; N - estimated number of people; Ln - standard air flow for 1 person. – for bedrooms - 30 cubic meters per hour and for other premises - 60 cubic meters per hour.
Productivity by multiple
Calculation of the air exchange rate in rooms should be carried out based on the parameters of the room; this will require a house or apartment plan. The plan must indicate the purpose of the room and its dimensions (height, area or length and width). For a comfortable feeling, at least one exchange of the entire volume of air is required.
It should be noted that supply ducts, as a rule, provide a volume of air for a double exchange, while exhaust ducts are designed for a single air exchange. There is no contradiction in this, since air consumption also occurs naturally - through cracks, windows and doors. After calculating the air exchange for each room, we add up the values to calculate the performance of the ventilation system. After which it will be possible to correctly select the power of the supply and exhaust fans. Standard performance indicators for various premises are as follows:
- residential ventilation systems - 150-500 cubic meters per hour;
- in private houses and cottages - 550-2000 cubic meters per hour;
- in office premises - 1100-10000 cubic meters per hour.
The calculation is carried out using the formula: L = NxSxH, where: L is the estimated volume of incoming air cubic meters per hour; N is the standard air exchange rate: houses and apartments – 1-2, office premises – 2-3; S - area, sq.m; H - height, m;
Example of aerodynamic ventilation calculation
This calculator can also help you with your calculations.
One of the conditions for creating a comfortable microclimate in residential and industrial premises is the presence of an engineering system that ensures air circulation. To ensure its effective operation, it is necessary to correctly calculate the length and diameter of the ventilation pipe. To do this, several methods are used, depending on the characteristics of the engineering system.
Ventilation diagram for a private house
Consequences of poor ventilation
If the fresh air supply system is not properly organized, the rooms will experience a lack of oxygen and increased humidity. Errors in the design of the hood are fraught with the appearance of soot on the walls of the kitchen, fogging of the windows and the appearance of fungus on the surface of the walls.
Fogging of windows due to insufficient exhaust
It should be taken into account that round or square pipes can be used to install the ventilation system. When removing air without the use of special devices, it is advisable to install round air ducts, since they are stronger, more airtight and have good aerodynamic characteristics. Square pipes are best used for forced ventilation.
Calculation of the ventilation system
Standard volume of supply air
Typically, residential buildings use natural ventilation systems. In this case, outside air enters the premises through transoms, vents and special valves, and is removed using ventilation ducts. They can be attached or located in internal walls. The construction of ventilation ducts in external enclosing structures is not allowed due to the possible formation of condensation on the surface and subsequent damage to the structures. In addition, cooling can reduce the air exchange rate.
Ensuring natural air flow through ventilation
Determination of the parameters of ventilation pipes for residential buildings is carried out on the basis of the requirements regulated by SNiP and other regulatory documents. In addition, the exchange rate indicator, which reflects the efficiency of the ventilation system, is also important. According to it, the volume of air flow into the room depends on its purpose and is:
- For residential buildings -3 m 3 /hour per 1 m 2 area, regardless of the number of people staying on the territory. According to sanitary standards, 20 m 3 / hour is enough for temporary residents, and 60 m 3 / hour for permanent residents.
- For ancillary buildings (garage, etc.) - at least 180 m 3 /hour.
To calculate the diameter, a system with natural air flow is taken as a basis, without installing special devices. The simplest option is to use the ratio of the area of the room and the cross-section of the ventilation hole.
In residential buildings, 5.4 m2 of air duct cross-section is required per 1 m2, and in utility buildings - about 17.6 m2. However, its diameter cannot be less than 15 m2, otherwise air circulation will not be ensured. More accurate data is obtained using complex calculations.
Algorithm for determining the diameter of a ventilation pipe
Based on the table given in SNiP, the parameters of the ventilation pipe are determined based on the air exchange rate. It is a value that shows how many times per hour the air in the room is replaced, and depends on its volume. Before determining the diameter of the pipe for ventilation, do the following:
Diagram for determining the diameter of the ventilation pipe
Features of determining the length of ventilation pipes
Another important parameter when designing ventilation systems is the length of the outer pipe. It unites all the channels in the house through which air circulates and serves to remove it outside.
Calculation according to the table
The height of the ventilation pipe depends on its diameter and is determined from the table. Its cells indicate the cross-section of the air ducts, and the column on the left shows the width of the pipes. Their height is indicated in the top line and is indicated in mm.
Selecting the height of the ventilation pipe according to the table
In this case, you need to take into account:
- If the ventilation pipe is located next to, then their heights must match to avoid smoke entering the premises during the heating season.
- When the air duct is located from the ridge or parapet at a distance that does not exceed 1.5 m, its height must be more than 0.5 m. If the pipe is located within 1.5 to 3 m from the roof ridge, then it cannot be lower his.
- The height of the ventilation pipe above a flat roof cannot be less than 0.5 m.
Location of ventilation pipes relative to the roof ridge
When choosing a pipe for ventilation construction and determining its location, it is necessary to provide sufficient wind resistance. It must withstand a storm of 10 points, which is 40-60 kg per 1 m 2 of surface.
Using the Software
An example of calculating natural ventilation using special programs
Calculating natural ventilation is less labor-intensive if you use a special program for this. To do this, first determine the optimal volume of air flow, depending on the purpose of the room. Then, based on the data obtained and the features of the designed system, a calculation of the ventilation pipe is made. In this case, the program allows you to take into account:
- average temperature inside and outside;
- geometric shape of air ducts;
- roughness of the internal surface, which depends on the material of the pipes;
- resistance to air movement.
Ventilation system with round pipes
As a result, the required dimensions of ventilation pipes are obtained for the construction of an engineering system that must ensure air circulation under certain conditions.
When calculating the parameters of a ventilation pipe, you should also pay attention to the local resistance during air circulation. It can occur due to the presence of meshes, gratings, outlets and other design features.
.Correct calculation of the parameters of ventilation pipes will allow you to design and build an effective system that will make it possible to control the level of humidity in the premises and provide comfortable living conditions.