Calculation of the section of exhaust ventilation. Calculation of the ventilation system of the industrial premises. About electricity consumption
It is known that the quantitative parameters of air exchange are determined by the dominant types of harmful emissions in industrial buildings (by heat, by water vapor, harmful gases and vapors, taking into account their summation when exposed to a person).
Depending on the technological features of production processes, to ensure the parameters of the microclimate in industrial premises, the simultaneous operation of general exchange and local supply and exhaust systems is often used.
Local air ventilation systems are assembled into systems:
on technological production lines,
by the simultaneous operation of the equipment,
by types of harmful emissions,
· Optimum radius of action and air consumption.
Local exhaust ventilation is a set of interconnected and interacting components such as hazardous substances released from process equipment, process equipment itself and a set of elements and devices designed to localize emitted hazards and remove polluted air outside the premises.
The main elements of local exhaust ventilation systems are:
local suction - devices designed to collect harmful substances from technological equipment or places of their formation;
Branches
main air duct.
Depending on whether the system is mechanical or gravitational, it may include, if necessary, cleaning equipment (filters, dust collectors, cyclones) and a ventilation unit.
The formation of harmful substances in the air of industrial premises imposes the following requirements on the organization of air exchange:
1. The supply jets should not cross the trajectory of the local suction jet;
2. It is forbidden to install air diffusers above technological equipment and technological lines;
3. The air ducts of the supply systems should be placed in places that do not interfere with technological production;
4. Air distributors should be located above workplaces and driveways to ensure the required weather conditions in the working area in such a way that there is a minimum trajectory from the air distributor to the human breathing zone;
5. The type of air distribution devices is determined by the type technological operations and features of indoor production.
The concentration of harmful substances in the air removed by local exhaust systems exceeds the concentration of these substances in the air removed by general exchange systems, so the efficiency of local exhaust systems in removing harmful substances is higher than that of general exchange systems. To achieve the same effect, general exchange systems must have significantly higher costs, so local exhaust systems are not climatic, they are technological ventilation systems.
Requirements for local suctions.
Sanitary and hygienic requirements - requirements that determine
the need for complete trapping by local suction of released harmful substances and preventing them from entering the human breathing zone in order to maintain the required climatic conditions in the working zone.
Technological requirements:
1) local suction must completely cover the place of formation of harmful substances and have a minimum technological opening (working opening) for servicing processes;
2) local suction should be located in places that ensure maximum productivity and safety technological processes;
3) local suctions must have minimal aerodynamic resistance;
4) the removal of harmful substances must coincide with the direction of action of the forces of inertia of harmful substances;
5) local suctions must be manufactured by industrial methods and be easily dismantled.
Classification of local suctions.
There is the following conditional classification of local suctions:
semi-open
open;
completely enclosed.
Semi open local sucks- local exhausts, completely covering the place of formation of harmful substances and having a working opening for servicing technological processes (fume hoods and fume hoods).
Open local sucks- local suctions located outside the process equipment and the production line (umbrellas, canopy umbrellas, side suctions).
Fully closed local suctions- local suctions, which are part of the casing of the process equipment. For air intake, they have special slot-like holes in the casing.
When choosing a suction scheme and during its constructive study, it is necessary to be guided by the following basic provisions:
The suction should be as close as possible to the source and, if possible, isolate the source from the room;
· The best solution is complete containment of the source;
The suction opening should be oriented so that the flow of harmful emissions deviates minimally from the original direction of movement and, at the same time, the removed air does not pass through the breathing zone of the worker.
· Reducing the size of the suction inlet leads to an increase in the air flow required to trap harmful emissions.
The air flow rate for suction from a source that releases heat and gases is proportional to the characteristic air flow rate in the convective flow rising above the source:
where L 0 - typical flow rate, m3/h;
k n is a dimensionless factor that takes into account the influence of geometric
and regime parameters characterizing the "source - suction" system;
k c - coefficient taking into account the influence of the air velocity in the room;
k m is a coefficient taking into account the toxicity of harmful emissions.
For suction from shelters with working openings and leaks, the formula is also used
, (..)
where F- area of working openings and leaks, m2;
v 0 - average suction speed over the area of working openings and leaks, m/s.
Air speed v o depends on the nature of the technological process and the toxicity of harmful emissions and is usually determined experimentally.
When calculating suction from heat sources, it is necessary to know their convective heat transfer, which is calculated by the formulas:
horizontal surface
vertical surface
where are the temperatures of the heated surface and the air in the room, °C;
And are the areas of the horizontal and vertical surfaces of the source, .
Coefficient value n accepted depending on:
, °С……….. 50 100 200 300 400 500 1000
n………………. 1,63 1,58 1,53 1,45 1,4 1,35 1,18
When calculating suction from volumetric heat sources, the total heat transfer of all surfaces is taken
The quality of the air environment in the workshops is regulated by law, the standards are set in SNiP and TB. At most facilities, effective air exchange cannot be formed by means of natural system, and hardware needs to be installed. It is important to achieve standards. For this, the calculation of the supply exhaust ventilation production premises.
The regulations provide different kinds pollution:
- excess heat from the operation of machines and mechanisms;
- fumes containing harmful substances;
- excess moisture;
- various gases;
- human secretions.
The calculation method offers an analysis for each type of pollution. The results are not summarized, but accepted for work highest value. So, if in production the maximum volume is needed to remove excess heat, it is this indicator that is taken for calculations technical parameters structures. Let us give an example of calculating the ventilation of a production facility with an area of 100 m 2.
Air exchange at an industrial site with an area of 100 m 2
In production, it must perform the following functions:
- remove harmful substances;
- clean the environment from pollution;
- remove excess moisture;
- remove harmful emissions from the building;
- regulate the temperature;
- form an inflow of a clean stream;
- depending on the characteristics of the site and weather conditions, heat, humidify or cool the incoming air.
Since each function requires additional power from the ventilation structure, therefore, the choice of equipment should be made taking into account all indicators.
Local exhaust
If in the technological processes of production at one of the sites emissions of harmful substances occur, then next to the source, according to the regulations, it is necessary to install a local exhaust. So the removal will be more effective.
Most often, such a source is technological tanks. For such objects, special installations are used - suction in the form of umbrellas. Its dimensions and power are calculated using the following parameters:
- source dimensions depending on the shape: side length (a*b) or diameter (d);
- flow velocity in the source zone (vv);
- suction speed of the unit (vz);
- suction height above the tank (z).
The sides of a rectangular suction are calculated by the formula:
A \u003d a + 0.8z,
where A is the suction side, a is the tank side, z is the distance between the source and the device.
The sides of a circular device are calculated using the formula:
D=d+0.8z,
where D is the diameter of the device, d is the diameter of the source, z is the distance between the suction and the reservoir.
Predominantly has the shape of a cone, the angle of which should not exceed 60 degrees. If the speed of the masses in the workshop is more than 0.4 m/s, then the device should be equipped with an apron. The amount of extract air is determined by the formula:
L=3600vz*Sa,
where L– air consumption in m3/h, vz – flow rate in the hood, Sa – suction working area.
Expert opinion
Ask an expertThe result must be taken into account in the design and calculations of the general exchange system.
General ventilation
When the calculation of the local exhaust, types and volumes of pollution, it is possible to do a mathematical analysis of the required volume of air exchange. The simplest option is when there are no technological pollution on the site, and only human emissions are taken into account.
In this case, the task is to achieve sanitary standards and cleanliness of production processes. The required volume for employees is calculated by the formula:
L=N*m,
where L is the amount of air in m 3 / hour, N is the number of employees, m is the volume of air per person per hour. The last parameter is normalized by SNiP and is 30 m 3 / hour - in a ventilated workshop, 60 m 3 / hour - in a closed one.
If harmful sources exist, then the task ventilation system reduce pollution to the maximum standards (MAC). Mathematical analysis is performed according to the formula:
O \u003d Mv \ (Ko - Kp),
where O is the air flow rate, Mw is the mass of harmful substances emitted into the air in 1 hour, Ko is the concentration of harmful substances, Kp is the number of pollutants in the inflow.
The influx of pollution is also calculated, for this I use the following formula:
L \u003d Mv / (ypom - yp),
where L is the volume of inflow in m3/h, Mw is the weight value of harmful substances emitted in the workshop in mg/h, yp is the specific concentration of pollutants in m3/h, yp is the concentration of pollutants from the supply air.
The calculation of general ventilation of industrial premises does not depend on its area, other factors are important here. Mathematical analysis for a particular object is complex, it needs to take into account a lot of data and variables, you should use special literature and tables.
Forced ventilation
It is advisable to calculate industrial premises according to aggregated indicators, which express the flow of incoming air per unit volume of the room, per 1 person or 1 source of pollution. The standards set their own standards for various industries.
The formula is:
L=Vk
where L is the volume of supply masses in m 3 / hour, V is the volume of the room in m 3, k is the frequency of air exchange.
For a room with an area of 100 m 3 and a height of 3 meters for a 3-fold air change, you will need: 100 * 3 * 3 + = 900 m 3 / hour.
The calculation of exhaust ventilation of industrial premises is carried out after determining required volumes supply masses. Their parameters should be similar, so for an object with an area of 100 m 3 with a ceiling height of 3 meters and a three-fold exchange, the exhaust system should pump out the same 900 m 3 / hour.
Design includes many aspects. It all starts with compiling terms of reference, which determines the orientation of the object to the cardinal points, purpose, layout, materials of building structures, features of the technologies used and the mode of operation.
Computing volumes are large:
- climatic indicators;
- air exchange rate;
- distribution of air masses inside the building;
- determination of air ducts, including their shapes, location, capacities and other parameters.
Then a general scheme is drawn up, and the calculations continue. At this stage, the nominal pressure in the system and its loss, the noise level in production, the length of the duct system, the number of bends and other aspects are taken into account.
Summarizing
The correct mathematical analysis for determining the parameters of air exchange in production can only be done by a specialist using various data, variables and formulas.
Independent work will lead to errors, and as a result: violation of sanitary standards and technological processes. Therefore, if your company does not have a specialist with the proper level of qualifications, it is better to use the services of a specialized company.
air performance
The calculation of the ventilation system begins with the determination of the air capacity (air exchange), measured in cubic meters per hour. For calculations, we need a plan of the object, which indicates the names (appointments) and areas of all premises.
Serve Fresh air it is required only in those rooms where people can stay for a long time: bedrooms, living rooms, offices, etc. Air is not supplied to the corridors, and is removed from the kitchen and bathrooms through exhaust ducts. Thus, the air flow pattern will look like this: fresh air is supplied to the living quarters, from there it (already partially polluted) enters the corridor, from the corridor - to the bathrooms and the kitchen, from where it is removed through the exhaust ventilation, taking with it unpleasant odors and pollutants. Such a scheme of air movement provides air support for "dirty" premises, excluding the possibility of spreading unpleasant odors by apartment or cottage.
For each dwelling, the amount of air supplied is determined. The calculation is usually carried out in accordance with SNiP 41-01-2003 and MGSN 3.01.01. Since SNiP sets more stringent requirements, in the calculations we will focus on this document. It states that for residential premises without natural ventilation (that is, where the windows are not opened), the air flow must be at least 60 m³ / h per person. For bedrooms, a lower value is sometimes used - 30 m³ / h per person, since in a state of sleep a person consumes less oxygen (this is permissible according to MGSN, as well as according to SNiP for rooms with natural ventilation). The calculation takes into account only people who are in the room for a long time. For example, if a large company gathers in your living room a couple of times a year, then you do not need to increase the ventilation performance because of them. If you want your guests to feel comfortable, you can install a VAV system that allows you to adjust the air flow separately in each room. With such a system, you can increase the air exchange in the living room by reducing it in the bedroom and other rooms.
After calculating the air exchange for people, we need to calculate the air exchange by the multiplicity (this parameter shows how many times a complete change of air occurs in the room within one hour). In order for the air in the room not to stagnate, it is necessary to provide at least a single air exchange.
Thus, to determine the required air flow, we need to calculate two air exchange values: according to number of people and by multiplicities and then choose more from these two values:
- Calculation of air exchange by the number of people:
L = N * Lnorm, where
L
N number of people;
lnorm air consumption rate per person:
- at rest (sleep) 30 m³/h;
- typical value (according to SNiP) 60 m³/h;
- Calculation of air exchange by multiplicity:
L=n*S*H, where
L required capacity of supply ventilation, m³/h;
n normalized air exchange rate:
for residential premises - from 1 to 2, for offices - from 2 to 3;
S room area, m²;
H room height, m;
Having calculated the required air exchange for each serviced room, and adding the obtained values, we will find out the overall performance of the ventilation system. For reference, typical ventilation system performance values:
Calculation of the air distribution network
After determining the ventilation performance, you can proceed to the design of the air distribution network, which consists of air ducts, fittings (adapters, splitters, turns), throttle valves and air distributors (grilles or diffusers). The calculation of the air distribution network begins with the drawing up of a duct diagram. The scheme is drawn up in such a way that, with a minimum total length of the route, the ventilation system can supply the calculated amount of air to all serviced premises. Further, according to this scheme, the dimensions of the air ducts are calculated and air distributors are selected.
Calculation of the dimensions of the ducts
To calculate the dimensions (cross-sectional area) of air ducts, we need to know the volume of air passing through the duct per unit time, as well as the maximum allowable air velocity in the duct. As the air speed increases, the dimensions of the ducts decrease, but the noise level and network resistance increase. In practice, for apartments and cottages, the air speed in the ducts is limited to 3-4 m / s, since at higher air velocities the noise from its movement in the ducts and distributors may become too noticeable.
It should also be taken into account that it is not always possible to use "quiet" low-velocity air ducts of a large cross section, since they are difficult to place in the overhead space. Reducing the height of the ceiling space allows the use of rectangular air ducts, which, with the same cross-sectional area, have a lower height than round ones (for example, a round air duct with a diameter of 160 mm has the same cross-sectional area as a rectangular air duct with a size of 200 × 100 mm). At the same time, it is easier and faster to mount a network of round flexible ducts.
So, the calculated cross-sectional area of the duct is determined by the formula:
Sc = L * 2.778 / V, where
Sc- the estimated cross-sectional area of the duct, cm²;
L— air flow through the duct, m³/h;
V— air velocity in the duct, m/s;
2,778 — coefficient for coordinating different dimensions (hours and seconds, meters and centimeters).
We get the final result in square centimeters, since in such units of measurement it is more convenient for perception.
The actual cross-sectional area of the duct is determined by the formula:
S = π * D² / 400- for round ducts,
S=A*B/100- for rectangular ducts, where
S— actual cross-sectional area of the duct, cm²;
D— diameter of the round air duct, mm;
A and B- width and height of a rectangular duct, mm.
The table shows data on air flow in round and rectangular ducts at different air speeds.
Table 1. Air flow in ducts
| Duct parameters | Air consumption (m³/h) at air speed: |
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| Diameter round duct | Dimensions rectangular duct | Square sections duct | 2 m/s | 3 m/s | 4 m/s | 5 m/s | 6 m/s |
| 80×90 mm | 72 cm² | 52 | 78 | 104 | 130 | 156 | |
| Ø 100 mm | 63×125 mm | 79 cm² | 57 | 85 | 113 | 142 | 170 |
| 63×140 mm | 88 cm² | 63 | 95 | 127 | 159 | 190 | |
| Ø 110 mm | 90×100 mm | 90 cm² | 65 | 97 | 130 | 162 | 194 |
| 80×140 mm | 112 cm² | 81 | 121 | 161 | 202 | 242 | |
| Ø 125 mm | 100×125 mm | 125 cm² | 90 | 135 | 180 | 225 | 270 |
| 100×140 mm | 140 cm² | 101 | 151 | 202 | 252 | 302 | |
| Ø 140 mm | 125×125 mm | 156 cm² | 112 | 169 | 225 | 281 | 337 |
| 90×200 mm | 180 cm² | 130 | 194 | 259 | 324 | 389 | |
| Ø 160 mm | 100×200 mm | 200 cm² | 144 | 216 | 288 | 360 | 432 |
| 90×250 mm | 225 cm² | 162 | 243 | 324 | 405 | 486 | |
| Ø 180 mm | 160×160 mm | 256 cm² | 184 | 276 | 369 | 461 | 553 |
| 90×315 mm | 283 cm² | 204 | 306 | 408 | 510 | 612 | |
| Ø 200 mm | 100×315 mm | 315 cm² | 227 | 340 | 454 | 567 | 680 |
| 100×355 mm | 355 cm² | 256 | 383 | 511 | 639 | 767 | |
| Ø 225 mm | 160×250 mm | 400 cm² | 288 | 432 | 576 | 720 | 864 |
| 125×355 mm | 443 cm² | 319 | 479 | 639 | 799 | 958 | |
| Ø 250 mm | 125×400 mm | 500 cm² | 360 | 540 | 720 | 900 | 1080 |
| 200×315 mm | 630 cm² | 454 | 680 | 907 | 1134 | 1361 | |
| Ø 300 mm | 200×355 mm | 710 cm² | 511 | 767 | 1022 | 1278 | 1533 |
| 160×450 mm | 720 cm² | 518 | 778 | 1037 | 1296 | 1555 | |
| Ø 315 mm | 250×315 mm | 787 cm² | 567 | 850 | 1134 | 1417 | 1701 |
| 250×355 mm | 887 cm² | 639 | 958 | 1278 | 1597 | 1917 | |
| Ø 350 mm | 200×500 mm | 1000 cm² | 720 | 1080 | 1440 | 1800 | 2160 |
| 250×450 mm | 1125 cm² | 810 | 1215 | 1620 | 2025 | 2430 | |
| Ø 400 mm | 250×500 mm | 1250 cm² | 900 | 1350 | 1800 | 2250 | 2700 |
The calculation of the dimensions of the air duct is carried out separately for each branch, starting from the main channel to which the ventilation unit is connected. It should be noted that the air velocity at its outlet can reach 6-8 m/s, since the dimensions of the connecting flange of the ventilation unit are limited by the size of its housing (the noise that occurs inside it is damped by a silencer). To reduce air velocity and reduce noise, main duct sizes are often chosen more sizes ventilation flange. In this case, the connection of the main air duct to the ventilation unit is made through an adapter.
In domestic ventilation systems, round ducts with a diameter of 100 to 250 mm or rectangular equivalent sections are usually used.
Selection of air terminals
Knowing the air flow rate, it is possible to select air distributors from the catalog, taking into account the ratio of their sizes and noise level (the cross-sectional area of the air distributor, as a rule, is 1.5-2 times larger than the cross-sectional area of \u200b\u200bthe air duct). For example, consider the parameters of popular air distribution grilles Arktos series AMN, ADN, AMP, ADR:
Air handling unit selection
To select an air handling unit, we need the values of three parameters: total performance, heater power and resistance of the air duct network. We have already calculated the performance and power of the heater. The network resistance can be found using or, when manually calculated, taken equal to the typical value (see section ).
For selection suitable model we need to select ventilation units, the maximum performance of which is slightly higher than the calculated value. After that, according to the ventilation characteristic, we determine the performance of the system for a given network resistance. If the value obtained is slightly higher than the required performance of the ventilation system, then the selected model suits us.
For example, let's check whether the ventilation unit with the ventilation characteristics shown in the figure is suitable for a cottage with an area of 200 m².
Estimated value of productivity - 450 m³ / h. We take the resistance of the network equal to 120 Pa. To determine the actual performance, we must draw a horizontal line from the value of 120 Pa, and then draw a vertical line down from the point of its intersection with the graph. The intersection point of this line with the "Productivity" axis will give us the desired value - about 480 m³ / h, which is slightly more than the calculated value. Thus, this model suits us.
Note that many modern fans have flat ventilation characteristics. This means that possible errors in determining the network resistance have almost no effect on the actual performance of the ventilation system. If in our example we made a mistake in determining the resistance of the air network by 50 Pa (that is, the actual resistance of the network would not be 120, but 180 Pa), the system performance would drop by only 20 m³ / h to 460 m³ / h, which would not affect on the result of our choice.
After choosing an air handling unit (or a fan, if a stacked system is used), it may turn out that its actual performance is noticeably higher than the calculated one, and the previous model of the air handling unit is not suitable, since its performance is not enough. In this case, we have several options:
- Leave everything as it is, while the actual ventilation performance will be higher than the calculated one. This will lead to an increased consumption of energy spent on heating the air during the cold season.
- “Suffocate” the ventilation unit with the help of balancing throttle valves, closing them until the air flow in each room drops to the calculated level. This will also lead to energy overruns (although not as much as in the first option), since the fan will work with an excess load, overcoming the increased resistance of the network.
- Do not include maximum speed. This will help if the ventilation unit has 5-8 fan speeds (or smooth speed control). However, most budget ventilation units have only 3-speed speed control, which, most likely, will not allow you to accurately select the desired performance.
- Reduce the maximum capacity of the air handling unit exactly to the specified level. This is possible if the automation of the ventilation unit allows you to set the maximum fan speed.
Do I need to focus on SNiP?
In all calculations that we carried out, the recommendations of SNiP and MGSN were used. This regulatory documentation allows you to determine the minimum allowable ventilation performance that ensures a comfortable stay of people in the room. In other words, the requirements of SNiP are primarily aimed at minimizing the cost of the ventilation system and the cost of its operation, which is relevant when designing ventilation systems for administrative and public buildings.
In apartments and cottages, the situation is different, because you are designing ventilation for yourself, and not for the average resident, and no one forces you to adhere to the recommendations of SNiP. For this reason, the performance of the system can be either higher than the calculated value (for greater comfort) or lower (to reduce energy consumption and system cost). In addition, the subjective feeling of comfort is different for everyone: 30-40 m³ / h per person is enough for someone, and 60 m³ / h will not be enough for someone.
However, if you do not know what kind of air exchange you need to feel comfortable, it is better to follow the recommendations of SNiP. Since modern air handling units allow you to adjust the performance from the control panel, you can find a compromise between comfort and economy already during the operation of the ventilation system.
Noise level of the ventilation system
How to make a "quiet" ventilation system that will not interfere with sleep at night is described in the section.
Ventilation system design
For an accurate calculation of the parameters of the ventilation system and project development, please contact. You can also use the calculator to calculate the approximate.
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- The performance of a system serving up to 4 rooms.
- Dimensions of air ducts and air distribution grilles.
- Air line resistance.
- Heater power and estimated electricity costs (when using an electric heater).
If you need to choose a model with humidification, cooling or recuperation, use the calculator on the Breezart website.
An example of calculating ventilation using a calculator
In this example, we will show how to calculate the supply ventilation for 3 room apartment in which a family of three lives (two adults and a child). During the day, relatives sometimes come to them, so up to 5 people can stay in the living room for a long time. The ceiling height of the apartment is 2.8 meters. Room options:
We will set the consumption rates for the bedroom and the nursery in accordance with the recommendations of SNiP - 60 m³ / h per person. For the living room, we will limit ourselves to 30 m³ / h, since a large number of there are not many people in this room. According to SNiP, such air flow is acceptable for rooms with natural ventilation (you can open a window for ventilation). If we also set an air flow rate of 60 m³/h per person for the living room, then the required performance for this room would be 300 m³/h. The cost of electricity to heat this amount of air would be very high, so we made a compromise between comfort and economy. To calculate the air exchange by the multiplicity for all rooms, we will choose a comfortable double air exchange.
The main air duct will be rectangular rigid, the branches will be flexible and soundproof (this combination of duct types is not the most common, but we chose it for demonstration purposes). For additional purification of the supply air, a carbon-dust filter will be installed. fine cleaning EU5 class (we will calculate the network resistance with dirty filters). The air velocities in the air ducts and the permissible noise level on the gratings will be left equal to the recommended values that are set by default.
Let's start the calculation by drawing up a diagram of the air distribution network. This scheme will allow us to determine the length of the ducts and the number of turns that can be both in the horizontal and vertical plane (we need to count all the turns at a right angle). So our schema is:
The resistance of the air distribution network is equal to the resistance of the longest section. This section can be divided into two parts: the main duct and the longest branch. If you have two branches of approximately the same length, then you need to determine which one has more resistance. To do this, we can assume that the resistance of one turn is equal to the resistance of 2.5 meters of the duct, then the branch with the maximum value (2.5 * number of turns + duct length) will have the greatest resistance. It is necessary to select two parts from the route in order to be able to set different type ducts and different air speeds for the main section and branches.
In our system, balancing throttle valves are installed on all branches, allowing you to adjust the air flow in each room in accordance with the project. Their resistance (in the open state) has already been taken into account, since this is a standard element of the ventilation system.
The length of the main air duct (from the air intake grille to the branch to room No. 1) is 15 meters, there are 4 right-angle turns in this section. The length of the supply unit and the air filter can be ignored (their resistance will be taken into account separately), and the silencer resistance can be taken equal to the resistance of an air duct of the same length, that is, simply consider it a part of the main air duct. The longest branch is 7 meters long and has 3 right angle bends (one at the branch, one at the duct and one at the adapter). Thus, we have set all the necessary initial data and now we can proceed to the calculations (screenshot). The calculation results are summarized in tables:
Calculation results for roomsResults of the calculation of general parameters
| Type of ventilation system | Plain | VAV |
| Performance | 365 m³/h | 243 m³/h |
| Cross-sectional area of the main air duct | 253 cm² | 169 cm² |
| Recommended main duct dimensions | 160x160mm 90x315mm 125x250mm |
125x140 mm 90x200mm 140x140 mm |
| Air network resistance | 219 Pa | 228 Pa |
| Heater power | 5.40 kW | 3.59 kW |
| Recommended Supply unit | Breezart 550 Lux (in 550 m³/h configuration) |
Breezart 550 Lux (VAV) |
| Maximum performance recommended PU |
438 m³/h | 433 m³/h |
| Electric power heater PU | 4.8 kW | 4.8 kW |
| Average monthly electricity costs | 2698 rubles | 1619 rubles |
Calculation of the air duct network
- For each room (subsection 1.2), the performance is calculated, the cross-section of the duct is determined, and a suitable duct of standard diameter is selected. According to the Arktos catalog, the dimensions of distribution grids with a given noise level are determined (data for the AMN, ADN, AMR, ADR series are used). You can use other gratings with the same dimensions - in this case, there may be a slight change in the noise level and network resistance. In our case, the grilles for all rooms turned out to be the same, since at a noise level of 25 dB(A) the allowable air flow through them is 180 m³/h (there are no smaller grilles in these series).
- The sum of the air flow rates for all three rooms gives us the total system performance (subsection 1.3). When using a VAV system, the system performance will be one third lower due to the separate adjustment of the air flow in each room. Next, the cross section of the main air duct is calculated (in the right column - for the VAV system) and air ducts that are suitable in size are selected rectangular section(usually given several options with different aspect ratios). At the end of the section, the resistance of the air duct network is calculated, which turned out to be very large - this is due to the use of a fine filter in the ventilation system, which has a high resistance.
- We have received all the necessary data to complete the air distribution network, with the exception of the size of the main air duct between branches 1 and 3 (this parameter is not calculated in the calculator, since the network configuration is not known in advance). However, the cross-sectional area of this section can be easily calculated manually: from the cross-sectional area of the main duct, you need to subtract the cross-sectional area of \u200b\u200bbranch No. 3. Having obtained the cross-sectional area of \u200b\u200bthe duct, its size can be determined by.
Calculation of heater power and selection of air handling unit
The recommended Breezart 550 Lux model has programmable parameters (capacity and power of the heater), therefore, the performance that should be selected when setting up the remote control is indicated in brackets. It can be seen that the maximum possible power of the heater of this launcher is 11% lower than the calculated value. The lack of power will be noticeable only at outdoor temperatures below -22 ° C, and this does not happen often. In such cases, the air handling unit will automatically switch to a lower speed to maintain the set outlet temperature (Comfort function).
In the calculation results, in addition to the required performance of the ventilation system, the maximum performance of the PU at a given network resistance is indicated. If this performance turns out to be noticeably higher than the required value, you can take advantage of the possibility of programmatically limiting the maximum performance, which is available for all Breezart ventilation units. For a VAV system, the maximum performance is indicated for reference, since its performance is adjusted automatically during the operation of the system.
Calculation of the cost of operation
This section calculates the cost of electricity used to heat the air during the cold season. The costs for a VAV system depend on its configuration and mode of operation, so they are assumed to be equal to the average value: 60% of the costs of a conventional ventilation system. In our case, you can save money by reducing the air consumption at night in the living room, and during the day in the bedroom.
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This article will focus on 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 exhausts, showering and thermal curtains.
Consider the fundamental stages of the calculation.
Let's say in advance that nothing new will be written in this article. The calculation is based on the existing normative documentation, and specifically SP 60.13330.2012 "Heating, ventilation and air conditioning", and reference books of the Soviet and post-Soviet period, especially beloved by the author, recommendations of foreign equipment manufacturers.
We will immediately make a reservation that in order to make a 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 should be carried out by qualified specialists. The technical and design departments of Airkat Klimatekhnik 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 finished project
you can compare economic indicators operation of ventilation units from various suppliers COMPAREThe main stages of the calculation of the ventilation system
1. Required indoor climate parameters
First of all, the parameters of the microclimate of the serviced premises are determined. Here it is necessary to note the following important remark - what parameters we provide: acceptable or optimal. At this stage, it is determined what kind of system we are counting on: ventilation or air conditioning?
This question is important, and quite specifically set out in paragraphs 5.1-5.16 of SP 60.13330.2012.
2. Supply air flow
According to clause 7.4.1 of SP 60.13330.2012: “The required flow rate of supply air (outdoor or a mixture of outdoor and recirculation) should be determined by calculation in accordance with Appendix I, and take the largest of the values \u200b\u200bnecessary to ensure sanitary and hygienic standards or explosion and fire hazard standards ”, - and clause 7.4.2 - “Outdoor air flow in the room should be taken at least:
a) the minimum outdoor air flow, calculated according to Annexes I and K;
b) air flow rate removed by local exhaust systems, general exhaust ventilation, technological equipment, taking into account the normalized imbalance.
If we simplify the formulas given in Appendix AND, then at the output we get the following:
1. For predominantly sensible heat assimilation (when the value of the process beam slope is greater than or equal to 40,000 kJ/kg):
2. For the assimilation of excess moisture:
3. According to the normalized multiplicity: 
4. The amount of outdoor air per person in the room: 
where: 
- excess apparent and total heat fluxes in the room, W;
W – moisture input in the room, kg/h;
k is the air exchange rate, 1/h;
S is the area of the room, m2;
H - the height of the room (for rooms with a height of more than 6 meters, you should stop at this mark), m;
N is the number of people in the room, pcs;
Normative multiplicity are given in the relevant regulatory documents.
Even if we calculate the supply air flow rate by multiplicity, we, nevertheless, must be given certain supply and exhaust temperatures (exhaust air).
If the room is an office, then the parameters of the removed air can be taken equal to the parameters of the internal one.
The inflow temperature must be calculated, but there are certain difficulties. As we can see from the formula for sensible heat assimilation, the air flow will change 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 here the main thing is not to "go too far" in pursuit of low consumption, because the set temperature must be somehow ensured. Yes, and plus, a situation can turn out that many are probably familiar with - when you sit under a stream from a split-system air conditioner.
3. Air distribution calculation
“Air distribution in most public buildings (schools; trade shops and public catering establishments; recreation, tourism and treatment institutions; clubs, etc.) is practically not studied.
The calculation mainly determines the amount and temperature of the air supplied to the room, and the dimensions, number and location of the supply and exhaust devices are accepted intuitively. This often leads to the emergence of uncomfortable zones in the premises, 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 release a software package to simplify calculations.
Highlighting the point:
1. Exist different types jets (flat, conical, fan for example), each of which better solves certain problems.
2. When choosing an air diffuser, keep in mind its throw 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 air heating systems, the jets “float up”).
4. In SP 60.13330.2012, in appendices B and C, there is a regulation on the permissible speed and temperature in the supply air jet at the inlet to the working / serviced 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 between the obtained parameters of the velocity and the air temperature at the inlet to the working area permissible limits, see Annexes B and C of SP 60.13330.2012.
4. Aerodynamic calculation of the network
There are a lot of CAD systems in this field, so I consider it sufficient to give a formula for finding the diameters of the duct:
2-4 m / s - on the branches to the air distributors;
4-6 m / s - on the main sections;
6-8 m/s - in the area after the fan.
5. Equipment selection
The selection of equipment is carried out according to the required air treatment scheme, the aerodynamic parameters of the network, the requirements for the energy efficiency of the system, the purity of the supplied air, acoustic characteristics, etc.
AirCut specialists carry out professional calculation of ventilation and air conditioning systems of any complexity. Get advice on ventilation installations, order a ventilation system project, select necessary equipment can be in any of the branches of the company "Airkat Klimatekhnik".