Ventilation in a room, especially in a residential or industrial one, must function 100%. Of course, many may say that you can simply open a window or door to ventilate. But this option can only work in summer or spring. But what to do in winter, when it’s cold outside?
Need for ventilation
Firstly, it is immediately worth noting that without fresh air, a person’s lungs begin to function worse. It is also possible that a variety of diseases will appear, which with a high percentage of probability will develop into chronic ones. Secondly, if the building is a residential building in which there are children, then the need for ventilation increases even more, since some ailments that can infect a child will most likely remain with him for life. In order to avoid such problems, it is best to arrange ventilation. There are several options worth considering. For example, you can start calculating the supply ventilation system and installing it. It is also worth adding that diseases are not the only problem.
In a room or building where there is no constant exchange of air, all furniture and walls will become covered with a coating from any substance that is sprayed into the air. Let's say, if this is a kitchen, then everything that is fried, boiled, etc. will leave its sediment. In addition, dust is a terrible enemy. Even cleaning products that are designed to clean will still leave a residue that will negatively impact the occupants.
Type of ventilation system
Of course, before you start designing, calculating a ventilation system or installing it, you need to decide on the type of network that is best suited. Currently, there are three main distinctions: different types, the main difference between them is in their functioning.
The second group is the exhaust group. In other words, this is a regular hood, which is most often installed in the kitchen areas of a building. The main task of ventilation is to extract air from the room to the outside.
Recirculation. Such a system is perhaps the most effective, since it simultaneously pumps air out of the room and at the same time supplies fresh air from the street.
The only question that everyone has next is how the ventilation system works, why does the air move in one direction or another? For this, two types of sources of awakening the air mass are used. They can be natural or mechanical, that is, artificial. To ensure their normal operation, it is necessary to correctly calculate the ventilation system.
General network calculation
As mentioned above, simply selecting and installing a specific type will not be enough. It is necessary to clearly determine exactly how much air needs to be removed from the room and how much needs to be pumped back in. Experts call this air exchange, which needs to be calculated. Depending on the data obtained when calculating the ventilation system, it is necessary to make a starting point when choosing the type of device.
Today, a large number of different calculation methods are known. They are aimed at determining various parameters. For some systems, calculations are carried out to find out how much warm air or evaporation needs to be removed. Some are carried out in order to find out how much air is needed to dilute contaminants, if this is an industrial building. However, the disadvantage of all these methods is the requirement of professional knowledge and skills.
What to do if it is necessary to calculate the ventilation system, but there is no such experience? The very first thing that is recommended to do is to familiarize yourself with the various regulatory documents available in each state or even region (GOST, SNiP, etc.). These papers contain all the indications that any type of system must comply with.
Multiple calculation
One example of ventilation can be calculation by multiples. This method is quite complicated. However, it is quite feasible and will give good results.
The first thing you need to understand is what multiplicity is. A similar term describes how many times the air in a room is changed to fresh in 1 hour. This parameter depends on two components - the specifics of the structure and its area. For a clear demonstration, a calculation using the formula for a building with a single air exchange will be shown. This indicates that a certain amount of air was removed from the room and at the same time an amount of fresh air was introduced that corresponded to the volume of the same building.
The formula for calculation is: L = n * V.
Measurement is carried out in cubic meters/hour. V is the volume of the room, and n is the multiplicity value, which is taken from the table.
If you are calculating a system with several rooms, then the formula must take into account the volume of the entire building without walls. In other words, you must first calculate the volume of each room, then add up all the available results, and substitute the final value into the formula.
Ventilation with mechanical type device
Calculation of the mechanical ventilation system and its installation must take place according to a specific plan.
The first stage is to determine the numerical value of air exchange. It is necessary to determine the amount of substance that must enter the structure in order to meet the requirements.
The second stage is determining the minimum dimensions of the air duct. It is very important to choose the correct cross-section of the device, since such things as the cleanliness and freshness of the incoming air depend on it.
The third stage is the selection of the type of system for installation. This is an important point.
The fourth stage is the design of the ventilation system. It is important to clearly draw up a plan according to which the installation will be carried out.
Need for mechanical ventilation occurs only if the natural influx fails to cope. Any of the networks is calculated on such parameters as its air volume and the speed of this flow. For mechanical systems this figure can reach 5 m 3 / h.
For example, if it is necessary to provide natural ventilation to an area of 300 m 3 /h, then you will need a 350 mm caliber. If mounted mechanical system, then the volume can be reduced by 1.5-2 times.
Exhaust ventilation
The calculation, like any other, must begin with the fact that productivity is determined. The units of measurement for this parameter for the network are m 3 /h.
To carry out an effective calculation, you need to know three things: the height and area of the rooms, the main purpose of each room, the average number of people who will be in each room at the same time.
In order to begin calculating a ventilation and air conditioning system of this type, it is necessary to determine the multiplicity. The numerical value of this parameter is set by SNiP. It is important to know here that the parameter for residential, commercial or industrial premises will be different.
If calculations are carried out for a domestic building, then the multiplicity is 1. If we are talking about installing ventilation in an administrative building, then the indicator is 2-3. It depends on some other conditions. To successfully carry out the calculation, you need to know the amount of exchange by multiplicity, as well as by the number of people. Must be taken highest value flow rate to determine the required system power.
To find out the air exchange rate, you need to multiply the area of the room by its height, and then by the value of the rate (1 for domestic, 2-3 for others).
In order to calculate the ventilation and air conditioning system per person, it is necessary to know the amount of air consumed by one person and multiply this value by the number of people. On average, with minimal activity, one person consumes about 20 m 3 / h; with average activity, the figure increases to 40 m 3 / h; with intense physical activity the volume increases to 60 m 3 / h.
Acoustic calculation of the ventilation system
Acoustic calculation is a mandatory operation that is attached to the calculation of any room ventilation system. This operation is carried out in order to perform several specific tasks:
- determine the octave spectrum of airborne and structural ventilation noise at design points;
- compare the existing noise with the permissible noise according to hygienic standards;
- determine a way to reduce noise.
All calculations must be carried out at strictly established design points.
After all measures have been selected according to building and acoustic standards, which are designed to eliminate excess noise in the room, a verification calculation of the entire system is carried out at the same points that were determined earlier. However, the effective values obtained during this noise reduction measure must also be added to this.
To carry out calculations, certain initial data are needed. They became the noise characteristics of the equipment, which were called sound power levels (SPL). For calculations, geometric mean frequencies in Hz are used. If an approximate calculation is carried out, then correction noise levels in dBA can be used.
If we talk about design points, they are located in human habitats, as well as in places where the fan is installed.
Aerodynamic calculation of the ventilation system
This calculation process is performed only after the air exchange calculation for the building has already been carried out, and a decision has been made on the routing of air ducts and channels. In order to successfully carry out these calculations, it is necessary to create a ventilation system, in which it is necessary to highlight such parts as the fittings of all air ducts.
Using information and plans, you need to determine the length of individual branches of the ventilation network. It is important to understand here that the calculation of such a system can be carried out to solve two different problems - direct or inverse. The purpose of the calculations depends on the type of task at hand:
- straight - it is necessary to determine the cross-sectional dimensions for all sections of the system, while setting a certain level of air flow that will pass through them;
- the reverse is to determine the air flow by setting a certain cross-section for all ventilation sections.
In order to carry out calculations of this type, it is necessary to divide the entire system into several separate sections. The main characteristic of each selected fragment is constant flow air.
Calculation programs
Since carrying out calculations and building a ventilation scheme manually is a very labor-intensive and time-consuming process, we have developed simple programs who are able to do all the actions themselves. Let's look at a few. One such ventilation system calculation program is Vent-Clac. Why is she so good?
A similar program for calculations and network design is considered one of the most convenient and effective. The operating algorithm of this application is based on the use of the Altschul formula. The peculiarity of the program is that it copes well with both ventilation calculations natural type, and mechanical type.
Since the software is constantly updated, it is worth noting that the latest version of the application is capable of carrying out such work as aerodynamic calculations resistance of the entire ventilation system. It can also effectively calculate other additional parameters that will help in the selection of preliminary equipment. In order to make these calculations, the program will need data such as air flow at the beginning and end of the system, as well as the length of the main air duct of the room.
Since manually calculating all this takes a long time and you have to break the calculations into stages, this application will provide significant support and save a lot of time.
Sanitary standards
Another option for calculating ventilation is according to sanitary standards. Similar calculations are carried out for public and administrative facilities. To make correct calculations, you need to know the average number of people who will constantly be inside the building. If we talk about regular consumers of indoor air, they need about 60 cubic meters per hour per person. But since public facilities are also visited by temporary persons, they must also be taken into account. The amount of air consumed by such a person is about 20 cubic meters per hour.
If you carry out all the calculations based on the initial data from the tables, then when you receive the final results, it will become clearly visible that the amount of air coming from the street is much greater than that consumed inside the building. In such situations, most often resort to the most simple solution- hoods at approximately 195 cubic meters per hour. In most cases, adding such a network will create an acceptable balance for the existence of the entire ventilation system.
Designing ventilation for a residential, public or industrial building takes place in several stages. Air exchange is determined based on regulatory data, the equipment used and the individual wishes of the customer. The scope of the project depends on the type of building: a one-story residential building or apartment is calculated quickly, with minimum quantity formulas, and for production facility serious work is required. The methodology for calculating ventilation is strictly regulated, and the initial data is specified in SNiP, GOST and SP.
The selection of the optimal air exchange system in terms of power and cost is carried out step by step. The design order is very important, since the efficiency of the final product depends on its observance:
- Determination of the type of ventilation system. The designer analyzes the source data. If you need to ventilate a small living space, then the choice falls on a supply and exhaust system with natural impulse. This will be enough when the air flow is small and there are no harmful impurities. If you need to calculate a large ventilation complex for a factory or public building, then preference is given to mechanical ventilation with the function of heating/cooling the inlet, and if necessary, then with calculations based on hazards.
- Outlier analysis. This includes: thermal energy from lighting fixtures and machines; fumes from machines; emissions (gases, chemicals, heavy metals).
- Calculation of air exchange. The task of ventilation systems is to remove excess heat, moisture, and impurities from the room with an equilibrium or slightly different supply of fresh air. To do this, the air exchange rate is determined, according to which the equipment is selected.
- Equipment selection. Produced according to the obtained parameters: required volume of air for supply/exhaust; indoor temperature and humidity; the presence of harmful emissions, ventilation units or ready-made multi-complexes are selected. The most important parameter is the volume of air required to maintain the design expansion ratio. Filters, heaters, recuperators, air conditioners and hydraulic pumps come as additional devices networks that ensure air quality.
Emissions calculation
The volume of air exchange and the intensity of the system depend on these two parameters:
- Standards, requirements and recommendations prescribed in SNiP 41-01-2003 “Heating, ventilation and air conditioning”, as well as other, more highly specialized regulatory documentation.
- Actual emissions. They are calculated using special formulas for each source and are shown in the table:
|
Heat release, J |
||
| Electric motor | N – nominal motor power, W; K1 – load factor 0.7-0.9 k2η - work coefficient at one time 0.5-1. |
|
| Lighting devices | ||
| Human | n – estimated number of people for this room; q is the amount of heat released by the body of one person. Depends on air temperature and work intensity. |
|
| Pool surface | 
|
V – speed of air movement over the water surface, m/s; T – water temperature, 0 C F – water surface area, m2 |
|
Moisture release, kg/h |
||
| Water surface, such as a swimming pool | P - mass transfer coefficient; F-evaporation surface area, m 2 ; Рн1, Рн2 - partial pressures of saturated water vapor at a certain temperature of water and air in the room, Pa; RB – barometric pressure. Pa. |
|
| Wet floor | F - wet floor surface area, m2; t s, t m – temperatures of air masses, measured by dry/wet thermometer, 0 C. |
|
Using the data obtained as a result of the calculation harmful secretions, the designer continues to calculate the parameters of the ventilation system.
Air exchange calculation
Experts use two main schemes:
- According to aggregated indicators. This technique does not involve harmful emissions such as heat and water. Let's call it “Method No. 1”.
- Method taking into account excess heat and moisture. Conventional name “Method No. 2”.
Method No. 1
Unit of measurement - m 3 / h ( Cubic Meters at one o'clock). Two simplified formulas are used:
L=K ×V(m 3 /h); L=Z ×n (m 3 / h), where
K – air exchange rate. The ratio of the air supply volume in one hour to the total air in the room, times per hour;
V – volume of the room, m3;
Z – value of specific air exchange per unit of rotation,
n – number of units of measurement.
The selection of ventilation grilles is carried out according to a special table. The selection also takes into account the average speed of air flow through the channel.
Method No. 2
The calculation takes into account the assimilation of heat and moisture. If in production or public building excess heat, then the formula is used:
where ΣQ is the sum of heat releases from all sources, W;
с – thermal capacity of air, 1 kJ/(kg*K);
tyx – temperature of air directed to the exhaust, °C;
tnp - temperature of air directed to the inlet, °C;
Exhaust air temperature:
where tp.3 is the standard temperature in the work area, 0 C;
ψ - temperature increase coefficient, depending on the measurement height, equal to 0.5-1.5 0 C/m;
H – arm length from the floor to the middle of the hood, m.
When the technological process involves the release of a large volume of moisture, a different formula is used:
where G is the volume of moisture, kg/h;
dyx and dnp – water content per kilogram of dry supply and exhaust air.
There are several cases, described in more detail in the regulatory documentation, when the required air exchange is determined by the multiplicity:
k – frequency of indoor air changes, once per hour;
V is the volume of the room, m3.
Section calculation
The cross-sectional area of the duct is measured in m2. It can be calculated using the formula:
where v is the speed of air masses inside the channel, m/s.
It varies for main air ducts 6-12 m/s and side appendages no more than 8 m/s. Quadrature affects throughput channel, the load on it, as well as the noise level and installation method.
Calculation of pressure loss
The walls of the air duct are not smooth, and the internal cavity is not filled with vacuum, so part of the energy of the air masses during movement is lost to overcome these resistances. The amount of loss is calculated using the formula:
where ג is friction resistance, defined as:
The formulas given above are correct for channels round section. If the duct is square or rectangular, then there is a formula for converting to an equivalent diameter:
where a,b are the dimensions of the channel sides, m.
Pressure and engine power
The air pressure from the blades H must completely compensate for the pressure loss P, while creating the calculated dynamic P d at the outlet.
Power electric motor fan:
Selection of heater
Often heating is integrated into the ventilation system. For this purpose, air heaters are used, as well as the recirculation method. The choice of device is carried out according to two parameters:
- Q in – maximum consumption of thermal energy, W/h;
- F k – determination of the heating surface for the heater.
Calculation of gravitational pressure
Applies only to natural system ventilation. With its help, its performance is determined without mechanical stimulation.
Equipment selection
Based on the data obtained on air exchange, the shape and size of the cross-section of air ducts and grilles, the amount of energy for heating, the main equipment is selected, as well as fittings, a deflector, adapters and other related parts. Fans are selected with a power reserve for peak operating periods, air ducts are selected taking into account the aggressiveness of the environment and ventilation volumes, and air heaters and recuperators are selected based on the thermal demands of the system.
Design errors
At the project creation stage, errors and shortcomings are often encountered. This could be reverse or insufficient draft, blowing ( upper floors multi-storey residential buildings) and other problems. Some of them can be solved after installation is completed, using additional installations.
A striking example of low-skilled calculation is insufficient draft on the exhaust production premises without particularly harmful emissions. Let's say the ventilation duct ends in a round shaft, rising 2,000 - 2,500 mm above the roof. Raising it higher is not always possible or advisable, and in such cases the principle of flare emission is used. A tip with a smaller diameter of the working hole is installed in the upper part of the round ventilation shaft. An artificial narrowing of the cross-section is created, which affects the rate of gas release into the atmosphere - it increases many times over.
The method for calculating ventilation allows you to obtain a high-quality internal environment by correctly assessing the negative factors that worsen it. The Mega.ru company employs professional designers engineering systems of any complexity. We provide services in Moscow and neighboring regions. The company also successfully engages in remote collaboration. All communication methods are listed on the page, please contact us.
Local ventilation is used in all cases where harmful substances are released as a result of technological process, when processing metals by cutting, welding, foundry, forging, thermal, painting, tire repair, copper work, as well as when soldering metal, charging batteries, chemical processes and other types of work.
Removal of harmful substances can be carried out using various gas and dust receivers located on the equipment or workplace where harmful substances are released (or using suction built into the equipment or its individual elements). For example, on automatic welding machines ADS-1000-ZU, ASU-6M, welding torches E.M. Tupchia, on semi-automatic machines A-537, A-547, PSh-5u, with chip collector cutters designed by VTSNIIOT, on sharpening grinders and other metalworking machines, etc.
Dust and gas receivers can be of various types: closed (fume hoods), semi-closed (umbrellas) and open (uniform suction panels). Technical characteristics of some suction units for stationary and non-stationary welding stations are given in the table.
3.1. Calculation of exhaust hoods. Volume of air sucked exhaust hood, determined by the formula
a and b – dimensions of the umbrella in plan, m;
V– the speed of the sucked air in the cross-sectional plane along the edge of the umbrella (receiving hole of the umbrella), usually V accepted from 0.5 to 1.5 m/s depending on the design of the umbrella. According to GOST 12.2.046-80 “Foundry equipment. General requirements safety: the speed of exhaust air for exhaust casings of foundry conveyors is assumed to be 4 m/s, for tumbling drums in a journal up to 24 m/s, for sanding machines 30% of the peripheral speed, but not less than 2 m/s per mm of circle diameter.
3.2. Calculation of fume hoods. The volume of air removed from fume hoods is determined by the formula
F– area of the working opening (open openings and leaks), ;
v – speed of air suction through open working holes, m/s.
For welding work v accepted according to the table.
3.3 Amount of air removed from grinding and polishing machines,
Where dkp– circle diameter, mm;
k– coefficient taken depending on the material and
circle diameter;
n- number of laps.
For ground wheels: when dkp= 250 mm k= 1.6. For cloth polishing wheels k= 6, for felt polishing wheels k = 4.
3.4. To determine the air flow removed by local suction during semi-automatic welding, you can apply the formula
Where TO– experimental coefficient equal to 12 for slot suction and 16 for double suction;
I– value of welding current.
Table 3.1.
Design air speed at various technological operations and types of local suctions
This article will discuss the design of general mechanical ventilation mainly in public/administrative and industrial buildings. We will not touch here on the issues of emergency and smoke ventilation, as well as local suction, showering and thermal curtains.
Let's consider the fundamental stages of calculation.
Let’s say in advance that nothing new will be written in this article. The calculation is based on existing regulatory documentation, specifically SP 60.13330.2012 “Heating, ventilation and air conditioning”, and the author’s favorite reference books of the Soviet and post-Soviet period, recommendations of foreign equipment manufacturers.
Let’s immediately make a reservation that to carry out the calculation it is necessary to have at least a minimum base - a plan of the premises with their purpose.
Calculation of ventilation systems and their design must be carried out by qualified specialists. The technical and design departments of the Airkat Klimatekhnik company have the necessary competencies and resources for the competent selection of ventilation equipment and the development of ventilation and air conditioning projects.
If you have a ready-made project
You can compare economic performance indicators ventilation units various suppliers COMPAREThe main stages of calculating the ventilation system
1. Required indoor microclimate parameters
First of all, the microclimate parameters of the serviced premises are determined. Here it is necessary to note the following important point - what parameters we provide: acceptable or optimal. At this stage, it is determined what kind of system we are calculating: ventilation or air conditioning?
This question is important, and is quite specifically stated in paragraphs 5.1-5.16 of SP 60.13330.2012.
2. Consumption supply air
According to clause 7.4.1 SP 60.13330.2012: “The required flow rate of supply air (external or a mixture of external and recirculated air) should be determined by calculation in accordance with Appendix I, and take the greater of the values necessary to ensure sanitary and hygienic standards or fire and explosion hazard standards ", - and clause 7.4.2 - "The outdoor air flow rate in the room should be no less than:
A) minimum flow outside air, calculated according to Appendices I and K;
b) air flow removed by local suction systems, general exhaust ventilation, technological equipment, taking into account the normalized imbalance.”
If we simplify the formulas given in Appendix I, we get the following output:
1. To assimilate predominantly sensible heat (when the value slope process beam greater than or equal to 40,000 kJ/kg):
2. To assimilate excess moisture:
3. According to the normalized multiplicity: 
4. The amount of outside air per person indoors: 
Where: 
– excess sensible and total heat flows in the room, W;
W – moisture gain in the room, kg/h;
k – air exchange rate, 1/h;
S – room area, m2;
H – room height (for rooms with a height of more than 6 meters, you should stop at this mark), m;
N – number of people in the room, pcs;
Standard multiplicities are given in the relevant regulatory documents.
Even if we calculate the flow rate of supply air by multiplicity, we, nevertheless, must set certain temperatures of supply and exhaust (exhaust air).
If the room is an office space, then the parameters of the exhaust air can be assumed to be equal to the parameters of the internal air.
The inflow temperature should be calculated, but there are certain difficulties. As we can see from the formula for sensible heat assimilation, the air flow will vary depending on the temperature difference, i.e. with a difference of 1°C there will be one flow rate, and if it is 3°C, then the required flow rate will be less. But the main thing here is not to “go too far” in pursuit of low flow, because the set temperature must be somehow ensured. And on the plus side, you may end up with a situation that many are probably familiar with - when you sit under the flow of a split-system air conditioner.
3. Calculation of air distribution
“Air distribution in most public spaces (schools, retail stores and businesses Catering; recreation, tourism and treatment institutions; clubs, etc.) have practically not been studied.
The calculation mainly determines the quantity and temperature of air supplied to the room, and the size, number and location of supply and exhaust devices are taken intuitively. This often leads to the emergence of uncomfortable zones in rooms, and, as a result, to a deterioration in the well-being of the people in them, and sometimes to turning off the ventilation.”
At the moment, there are many manufacturers of air distributors on the ventilation equipment market, and each of them has recommendations for calculating one or another type of air distributor. They also produce a software package to make calculations easier.
Highlighting the essence:
1. There are Various types jets (flat, conical, fan-shaped for example), each of which better solves certain problems.
2. When choosing an air distributor, you need to remember its jet length.
3. If the temperature of the jet differs from the air temperature in the room, then it will deviate from the original direction (for example, in systems air heating the jets “float up”).
4. In SP 60.13330.2012, in appendices B and C, there are regulations on the permissible speed and temperature in the supply air stream at the entrance to the work/service area.
3.1 Calculation of the number of diffusers and grilles
The number of air distributors is determined by one of the following dependencies:
The immediate end of the air distribution calculation is a theoretical assessment of the correspondence of the obtained parameters of speed and air temperature at the inlet work area permissible limits, see appendices B and C SP 60.13330.2012.
4. Aerodynamic calculation of the network
There are a lot of CAD systems in this field, so I think it is sufficient to give the formula for finding the diameters of the air duct:
2-4 m/s – on branches to air distributors;
4-6 m/s – on highway sections;
6-8 m/s – in the area after the fan.
5. Selection of equipment
The selection of equipment is carried out according to the required air treatment scheme, aerodynamic parameters of the network, requirements for the energy efficiency of the system, purity of the supplied air, acoustic characteristics, etc.
AirCut specialists carry out professional calculations of ventilation and air conditioning systems of any complexity. Get advice on ventilation systems, order a ventilation system design, select necessary equipment possible at any of the branches of the Airkat Klimatekhnik company.
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Only proven solutions from AirCut. We are the best in our field, thanks to our wealth of experience.In residential and office buildings where people are constantly present, comfortable conditions must be created for their work and life. These conditions are regulated by state sanitary standards and other documents. Options and required amount air requirements for residential and administrative buildings are specified in the relevant building regulations. To calculate ventilation in a room, you should be guided by these documents.
Initial data for calculating air exchange
The purpose of the calculation is to determine how much clean air required to be supplied to each room and how much waste to remove from it. After this, they choose a method for organizing air exchange and, for the cold season, calculate the thermal power that needs to be spent to heat the influx from the street. First you need to determine the exchange rate for each room of a residential building.
Exchange rate is a number showing how many times per everyone volume The air in the room will be completely renewed within 1 hour.
Multiplicity values for offices and rooms for various purposes are prescribed in SNiP 31-01-2003, for convenience they are given in Table 1.
SNiP indicates the calculated values of flow rate and multiplicity, but for combustion chambers the amount of combustion air must be specified according to technical specifications hot water boiler.
Methods for performing calculations
Building codes allow for the calculation of the supply ventilation of a room in several ways:
- According to the frequency of exchange, the value of which for each room is fixed by standards.
- According to the standardized specific air mass flow rate per 1 m2 of room.
- Based on the specific volume of fresh air mixture per 1 person staying in the house for more than 2 hours daily.
In accordance with SNiP 41–01-2003 “Ventilation and air conditioning”, the following formula for calculating ventilation according to the normalized multiplicity is used for residential buildings:
- L – required amount of supply air, m 3 /h;
- V – volume of the office or room, m3;
- n – calculated air exchange rate (Table 1).
The volume of each room is determined by measurements of its dimensions or, in the case of a house under construction, according to the drawings included in the project. The inflow flow rate for some rooms has a certain standardized value, for example, in bathrooms or laundry rooms. Then there is no need to determine the dimensions; it is accepted fixed value, indicated in Table 1. After calculating each room, the results are summed up and the total amount of supply air required for the entire house is obtained.
Determining the influx based on the specific consumption of fresh air mixture for each person is carried out using the following method:
In this formula:
- L – the same as in the previous formula, m 3 / h;
- N – number of people staying in the building for more than 2 hours during the day, people;
- m – specific amount of supply air per 1 person, m 3 /h (Table 2).
This method can be used not only for residential buildings, but also for administrative buildings where many people work in the offices. In this case, the specific flow rate is standardized by Appendix M SNiP 41–01-2003, which is reflected in Table 2.
To maintain balance, the volume of exhaust from the office is equal to the inflow - 1200 m 3 /h.
If, in terms of 1 resident, there is less than 20 m2 of the total area of a residential building, then the calculation is made based on the area of the premises:
- L – required inflow value, m 3 /h;
- A – area of the office or room, m2;
- k – specific consumption of clean air supplied per 1 m2 of room area.
SNiP 41-01-2003 sets the value of k at 3 m 3 per 1 m 2 of living space. That is, a bedroom with an area of 10 m2 will need to supply at least 10 x 3 = 30 m3 / h of fresh air mixture.
General ventilation device in the house
After the need for supply and exhaust for all rooms of the house has been calculated using one of the methods described above, you should choose the type of general ventilation: with natural or mechanical impulse. The first type is suitable for apartments, small private houses and offices. Here the main role will be played by natural exhaust, since it is it that creates a vacuum inside the house and encourages air masses to move in their direction, drawing in fresh ones from the street. In this case, the calculation natural ventilation premises is reduced to calculating the height of the vertical exhaust shaft.
Example of ventilation in a residential building
Calculations are made using the selection method, since vertical exhaust ducts make standard sizes and heights. Having accepted a certain value for the height of the shaft, it is substituted into the formula:
p = h (ρ H - ρ B)
- h – channel height, m;
- ρ Н – density of outside air, on average is taken equal to 1.27 kg/m 3 at a temperature of +5ºС;
- ρ B – the density of the air mixture removed from the apartment is taken according to its temperature.
When air masses move in a shaft, resistance to friction against its walls arises; the traction force must overcome it. The calculation and design of a vertical channel is to ensure that the traction force in it is slightly greater than the friction resistance and that the condition is met:
H ≤ 0.9 r
- р – gravitational pressure in the channel, kgf/m2;
- N – resistance of the exhaust shaft, kgf/m2.
The value of H is calculated using the following formula:
In this formula:
- R – pressure loss per 1 m.p. mine, is a reference value, kgf/m 2 ;
- h – channel height, m;
Substituting the values of the height of the exhaust shaft into the above formulas, calculations are made until the condition for the operation of the draft is met.
Forced ventilation
When using local and centralized ventilation units in organizing air exchange, the most important indicator remains the consumption of external air masses to ensure required inflow into the building. If local air supply units with cleaning and heating are installed in the rooms, then their total performance should be equal to the volume of inflow into the building calculated earlier.
Air exchange in rooms
When selecting the performance of the air supply unit, it must be taken into account that not all rooms are located near external walls. The installation will serve not only its own office, but also the adjacent one located in the back of the house.
Centralized air handling units it is better to select with the help of specialists, since you will need to perform a rather complex calculation ventilation systems. The installation can use the heat of the exhaust air, heating the outdoor air with its help; here it is important to choose the right heat exchanger.
The treated air mixture will be distributed into the premises through a network of air ducts; it will be necessary to determine their parameters (diameter, length, pressure loss). This is needed for the right choice ventilation unit, which for stable operation of the system must develop the necessary pressure to overcome all resistance.
Conclusion
Calculate the required volume of supply air in a residential or administrative building- not such a difficult task. This is the first step to creating comfortable conditions for the life or work of people. Knowing the required supply and exhaust costs, you can make an estimate of the total cost of work and equipment for installing general ventilation. It is preferable to entrust further development and implementation to specialists.
How to do supply ventilation with your own hands
How to make ventilation in a private house
Everything about ventilation in an apartment building
