Calculation of the ventilation system and its individual elements: area, pipe diameters, parameters of heaters and diffusers. How to calculate the diameter and length of ventilation pipes Calculate ventilation ducts if we know the volume
A favorable indoor climate is an important condition for human life. It is collectively determined by temperature, humidity and air mobility. Deviations of parameters negatively affect health and well-being, cause overheating or hypothermia of the body. Lack of oxygen leads to hypoxia of the brain and other organs.
Calculation and standards
The ventilation of the room is calculated when designing the facility 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 did not reveal a violation of the patency of the ventilation ducts, it means that the exhaust ventilation does not cope with its functions due to an incorrectly selected section.
What is ventilation for?
The task of ventilation is to provide the necessary air exchange in the room, to create optimal or acceptable conditions for a long stay of a person.
Studies have found that people spend 80% of their time indoors. For one hour in a calm state, a person releases 100 kcal into the environment. Heat transfer occurs by convection, radiation and evaporation. With insufficiently mobile air, the transfer of energy from the surface of the skin into space slows down. As a result, many functions of the body suffer, a number of diseases occur.
Lack or insufficient ventilation, especially in rooms with high humidity, leads to stagnation. They are accompanied by an invasion of hard-to-remove mold fungi, unpleasant odors and constant dampness. Moisture adversely affects building structures, leads to decay of wood and corrosion of metal elements.
With excess thrust, the release of air masses into the atmosphere increases, which in winter leads to the loss of a large amount of heat. House heating costs are rising.
The quality and purity of the air is the main factor that determines the effectiveness of ventilation. Polluting fumes from building materials, furniture, dust and carbon dioxide must be removed from the premises in a timely manner.
There is an opposite situation, when the air in a house or apartment is much cleaner than on the street. Exhaust gases on a busy highway, smoke or soot, toxic pollution from industrial enterprises can poison the indoor atmosphere. For example, in the center of a large city, the content of carbon monoxide is 4-6 times higher, nitrogen dioxide is 3-40 times higher, and sulfur dioxide is 2-10 times higher than in rural areas.
The calculation of ventilation is carried out in order 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 according to 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 category. These are places where people rest in a lying or sitting position, study, do mental work.
Depending on the period of the year and the purpose of the premises, 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 norms, in industrial premises - according to the permissible concentration of pollutants. At the same time, the amount of carbon dioxide in the air should not exceed 400-600 cm³/m³.
On our website you can find contacts of construction companies that offer interior redevelopment services. You can directly communicate with representatives by visiting the exhibition of houses "Low-Rise Country".
Types of ventilation systems according to the method of creating traction
The movement of air masses occurs as a result of the pressure difference between the layers of air. The larger the gradient, the stronger the driving force. To create it, a natural, forced or combined ventilation system is used, where supply, exhaust or recirculation (mixed) methods of air removal are used. Industrial and public buildings are provided with emergency and smoke ventilation.
natural ventilation
Natural ventilation of premises occurs according to physical laws - due to the difference in temperature and pressure between the outside and inside air. Back in the days of the Roman Empire, engineers installed semblances of mines in the houses of the nobility, which served for ventilation.
The complex of natural ventilation includes external and internal openings, transoms, vents, wall and window valves, exhaust shafts, ventilation ducts, 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 windows and doors are located at opposite ends of the room. In this case, when air circulates, it is fully replaced throughout the room.
Exhaust ducts are placed in rooms with the highest level of pollution, unpleasant odors and humidity - kitchens, bathrooms. The supply air comes from other rooms and squeezes the 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, does not require large investments in the device. Air masses penetrating from the outside do not acquire additional properties - they are not heated, cleaned or moistened.
Air recirculation is limited to one apartment. There should be no suction from adjacent rooms.
Forced ventilation began to be used from the middle of the 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 has taken place in the ventilation of rooms. Adjustable devices appeared not only for industrial, but also for domestic needs.
Now, when passing through the forced ventilation system, the outside air is given additional valuable qualities - it is cleaned, 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, silencers, control and automation devices. They are built into the air ducts.
Video description
Read more about the calculation of ventilation with a heat exchanger in this video:
Calculation of natural ventilation of residential premises
The calculation consists in determining the supply air flow rate L in the cold and warm periods of the year. Knowing this value, you can choose the cross-sectional area of air ducts.
A house or apartment is considered as a single air volume, where gases circulate through open doors or a canvas cut 2 cm from the floor.
The inflow occurs through leaky windows, external fences and by ventilation, removal - through exhaust ventilation ducts.
The volume is found by three methods - multiplicity, sanitary standards and area. From the obtained values, choose the largest. Before calculating ventilation, determine the purpose and characteristics of all rooms.
Basic formula for the first calculation:
L=nхV, m³/h, where
- V is the volume of the room (the product of the height and the area),
- n - multiplicity, determined according to SNiP 2.08.01-89, depending on the design 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. The number of permanent residents, the presence of a gas stove and a bathroom are taken into account. According to tab. M1, the consumption is 60 m³ / person per hour.
The third way is by area.
- A - area of the room, m²,
- k - standard consumption per m².
Calculation of the ventilation system: example
Three-room house with a total area of 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, they find the flow rate for the inflow and exhaust, 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=32х1=32 m³/h.
Total consumption by inflow:
L total \u003d Lguest. + Lsleep \u003d 75 + 32 \u003d 107 m³ / h.
- bathroom L= 50 m³/hour (tab. SNiP 41-01-2003),
- bath L= 25 m³/h.
- kitchen L=90 m³/hour.
The inflow corridor is not regulated.
By extract:
L=Lkitchen+Lbathroom+L bath=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 taken.
According to sanitary standards, the calculation is carried out based on the number of residents. Specific consumption per person is 60 m³.
L total \u003d 60x3 \u003d 180m / h.
Taking into account temporary visitors, for whom the set air flow is 20 m3/h, we can assume 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 the dwelling.
L=57х3=171 m³/h.
According to the results of calculations, the flow rate according to sanitary standards is 200 m³/h, the multiplicity is 165 m³/h, over the area 171 m³/h. Although all options are correct, the first option will make living conditions more comfortable.
Outcome
Knowing the air balance of a residential building, they select the size of the cross section of the air ducts. Most often, rectangular channels with an aspect ratio of 3: 1 or round are used.
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For a convenient calculation of the cross section, you can use an online calculator or a diagram that takes into account the speed and air flow.
During ventilation with natural impulse, the speed in the main and branching air ducts is assumed to be 1 m/h. In the forced system, 5 and 3 m/h, respectively.
With the required air exchange of 200 m/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 mounted in the channels, which will provide the necessary microclimate parameters.
Natural ventilation of a room is a spontaneous movement of air masses due to the difference in its temperature regimes. in not at home and inside. This type of ventilation is divided into ductless and ducted, relatively capable of operation to be continuous and periodic.
The systematic movement of transoms, vents, doors and windows means by the very ventilation procedure. Channelless ventilation, formed on a stable basis in industrial-type rooms with tangible heat emissions, organizing the desired frequency of air mass exchange in the middle of them, this process is called aeration.
In private and high-rise buildings, a natural duct-type ventilation system is more used, the channels in which are located in vertical position in specialized blocks, shafts or located in the walls themselves.
Aeration calculation
Aeration of industrial rooms in summer guarantees the flow of air currents through gaps below gates and entrance doors. In the cool months, the intake in the required sizes is made under the means of upper gaps, from 4 m or more above the floor level. Ventilation throughout the whole year was carried out with the help of shafts, deflectors and vents.
In winter, transoms are opened only in areas above the generators enhanced heat release. During the generation of excess apparent heat in the rooms of the building, the temperature regime of the air in it is constantly greater than the temperature regime outside the building, and, accordingly, the density is less.
This phenomenon leads to the presence of a pressure difference in the atmosphere. outside and inside rooms. In a plane at a specific height of the room, which is referred to as the plane of equal pressures, this difference is absent, that is, it is equated to zero.
Above this plane, there is some excessive stress, which leads to removing the hot atmosphere to the outside, and below this plane, a rarefaction, which causes an influx of fresh air. The pressure that forces the air masses to move in the process of natural ventilation can be set based on their calculations:
Natural ventilation formula
Pe \u003d (in - n) hg
- where n is the air density outside the room, kg/m3;
- vn is the density of air masses in the room, kg/m3;
- h is the distance between the supply opening and the center of the exhaust, m;
- g is the free fall acceleration, 9.81 m/s2.
The method of ventilation (aeration) of buildings with the help of drop-down transoms is considered to be quite correct and effective.
When calculating the natural ventilation of the premises, the establishment of the area of the lower and upper gaps is taken into account. First, the value of the area of the lower gaps is obtained. The building aeration model is set.
Calculation of natural exhaust ventilation
Then, in connection with the opening section of the upper and lower, respectively, supply and exhaust transoms in the room approximately in the center of the height of the structure, the degree of equal pressure is obtained, in this place the influence is exactly the same as zero. In accordance, the influence in the degree of concentration of the lower gaps will be equal to:
- where cp is equal to the average temperature of the density of air masses in the room, kg/m3;
- h1 is the height from the plane of equal pressures to the lower gaps, m.
At the level of the centers of the upper gaps, above the plane of equal pressures, an excess stress is formed, Pa, equal to:
It is this pressure that affects the air extraction. The total voltage available for the exchange of air flows in the room:
Natural ventilation rate
Air speed in the center of the lower gaps, m/s:
- where L is the required exchange of air masses, m3/h;
- 1 – flow coefficient, depending on the design of the flaps of the lower gaps and the angle of their opening (at 90 opening, = 0.6; 30 - = 0.32);
- F1– area of lower gaps, m2
Then the losses, Pa, in the lower gaps are calculated:
Assuming that Pe = P1 + P2 = h(n - cf), and the temperature of the exhaust air tsp = trz + (10 - 15oC), we determine the densities h and cf, which correspond to temperatures tn and tcp.
Excess pressure in the plane of the upper lumens:
Their required area (m2):
F2 \u003d L / (2V22) \u003d L / (2 (2Р2g / cp) 1⁄2)
Calculation and calculation of ventilation ducts
The calculation of a natural ventilation system of a duct type is approaching the establishment of an active section of air ducts, which, in order to access the required amount of air, express a counteraction corresponding to the calculated voltage.
For the longest network path, the voltage costs in the duct channels are set as the sum of the voltage costs in absolutely all of its places. In each of them, pressure costs are formed from friction losses (RI) and costs at counteraction points (Z):
- where R is the specific loss of stress along the length of the section due to friction, Pa/m;
- l is the length of the section, m.
Air duct area, m2:
- where L is the air flow rate, m3/h;
- v is the speed of air movement in the duct, m/s (equal to 0.5 ... 1.0 m/s).
Setting the speed of air movement through ventilation, and read the area of its active section and scale. With the help of specialized nomograms or tabular calculations for the rounded shape of air ducts, the stress costs for friction are established.
Natural ventilation calculation of air ducts
For rectangular air ducts of this ventilation concept, the diameter dE is planned to be equal to the rounded air duct:
dE \u003d 2 a b / (a + b)
- where, a and b are the length of the sides of a rectangular duct, m.
In the case of using non-metal air ducts, their specific friction pressure costs R, taken from the nomogram for steel air ducts, are changed by multiplying by the corresponding coefficient k:
- for slag-gypsum - 1.1;
- for slag concrete - 1.15;
- for brick - 1.3.
Excess pressure, Pa, to overcome certain resistances for different sections is calculated using the equation:
- where - the sum of the coefficients of counteraction on the site;
- v2/2 - dynamic stress, Pa, taken from the standards.
To create a concept of free ventilation, it is preferable to beware of winding twists, multiple gates and valves, since losses due to local resistances usually reach up to 91% of all costs in ducts.
Natural ventilation contains a small radius of influence and an average efficiency for rooms with very little excess heat, which can be attributed to disadvantages, and the advantage is the ease of the system, low price and ease of maintenance.
Natural ventilation calculation example
Total area - 60 m2;
bathroom, kitchen with gas stove, toilet;
storage room - 4.5 m2;
ceiling height - 3 m.
Concrete blocks will be used for the equipment of air ducts.
Air inflow from the street according to the standards: 60 * 3 * 1 = 180 m3 / hour.
Exhaust air from the room:
kitchens - 90 m3 / hour;
bathroom - 25 m3 / hour;
toilet - 25 m3 / hour;
90 + 25 + 25 = 140 m3/h
The frequency of renewal of air masses in the pantry is 0.2 per 1 / hour.
4.5 * 3 * 0.2 = 2.7 m3/h
Desired air outlet: 140 + 2.7 = 142.7 m3/h.
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.
Fresh air 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, eliminating the possibility of the spread of unpleasant odors throughout the 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 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- the number of people;
lnorm- the rate of air consumption 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 estimated 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 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: |
||||||
| 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). In order to reduce air velocity and reduce noise, the dimensions of the main duct are often chosen larger than the dimensions of the ventilation unit 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 ).
To select a 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 duct 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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Let's start with the natural and . As the name implies, the first type includes ventilation and everything that has nothing to do with devices. Accordingly, mechanical ventilation includes fans, hoods, air inlets and other equipment for creating a forced air flow.
The moderate speed of this flow is good, which creates comfortable conditions in the room for a person - the wind is not felt. Although properly installed high-quality forced ventilation also does not bring drafts. But there is also a minus: at a low air flow rate during natural ventilation, a wider cross section is needed for its supply. As a rule, the most effective ventilation is provided with windows or doors completely open, which speeds up the process of air exchange, but can adversely affect the health of residents, especially in the winter season. If we ventilate the house by partially opening the windows or fully opening the vents, it takes about 30–75 minutes for such ventilation, and here the window frame may freeze, which may well lead to condensation, and cold air that enters for a long time leads to health problems . Wide open windows speed up the air exchange in the room, cross-ventilation will take about 4-10 minutes, which is safe for window frames, but with such ventilation almost all the heat in the house goes outside, and for a long time the temperature inside the premises is quite low, which again increases the risk diseases.
You should also not forget about the supply valves, which are gaining popularity, which are installed not only on windows, but also on the walls inside the rooms (wall supply valve), if the design of the windows does not provide for such valves. The wall valve performs air infiltration and is an elongated branch pipe installed through the wall, closed on both sides with gratings 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 the 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, overflow grilles are placed on the interior doors so that the air moves calmly from the supply systems to the exhaust systems, passing through the whole house, through all the rooms. It is important to consider that such a flow is considered correct in which the smelliest room (toilet, bathroom, kitchen) is the last one. If it is not possible to install an overflow grill, it is enough just to leave a gap between the door and the floor, about 2 cm. This is quite enough for the air to move easily around the house.
In cases where natural ventilation is not enough or there is no desire to arrange it, they switch to the use of mechanical ventilation.
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 the air exchange system, which contributes to the comfortable stay of people. In any residential building, you can see ventilation openings that are responsible for the supply of fresh air. In public premises where people are supposed to be, supply and exhaust ventilation should be arranged to circulate air masses. Sanitary standards strictly regulate the arrangement of ventilation systems, taking into account the volume of premises and the expected number of people in it. Below we consider the types of ventilation systems and the method of calculating air exchange.
Ventilation systems vary in the degree of complexity of their design. There are several types:
- Simple, natural, carrying out the flow of clean air through channels made in the walls of the building.
- Supply and exhaust, having separate channels for the inflow and outflow of air.
- 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 the temperature and humidity in the room.
The comfort of people inside the building depends on the quality of the ventilation system. The standards for the amount of incoming air are developed and published by Rospotrebnadzor, which controls the operation of ventilation in public buildings.
General picture of ventilation of 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, we will talk about coercive systems. The primary task for accurate calculations of ventilation systems is to take into account the microclimate of the premises. These are the permissible and normative-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.
The calculation of the air flow coming from outside is the first and most important parameter regulated by sanitary and hygienic standards. It is built on the minimum volumes of consumption and air consumption due to outflow channels and the operation of process equipment. The definition 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, outdoor air is supplied to rooms where, as a rule, residents stay for a long time. This is a living room and a bedroom, less often an office and halls. In corridors, kitchens and bathrooms, they usually do not make inflows; only exhaust holes are installed in them. Air masses come naturally from neighboring rooms where an inflow is made. Such a scheme makes the air flow move through the living rooms to the technical ones, “squeezing out” the spent air-gas mixture into the exhaust ducts. At the same time, unpleasant odors are removed without spreading throughout the apartment or house.
The calculations include two air exchange values:
- In terms of productivity - based on the standards of air mass per person.
- By multiplicity - how many times the air in the room changes 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. Here the amount of consumption by one person is indicated - 60 cubic meters per hour. This volume must be compensated by the inflow of external air. For bedrooms, a smaller volume is allowed - 30 cubic meters per hour per person. When making calculations, only permanent residents should be taken into account, i.e. the number of guests visiting the room from time to time should not be taken to calculate the air exchange. For comfortable parties, there are systems that regulate the flow of air in different rooms. Such equipment will increase the flow of air into the living room, by reducing it in the bedroom.
Calculations are carried out according to the formula: L = N x Ln, where: L - estimated volume of incoming air cubic meters per hour; N is the estimated number of people; Ln - standard air consumption 1 person. - for bedrooms - 30 cubic meters per hour and for other premises - 60 cubic meters per hour.
Performance by multiplicity
The calculation of the frequency of air exchange in the premises should be carried out based on the parameters of the room; this will require a plan of the house or apartment. The plan should indicate the purpose of the room and its dimensions (height, area or length and width). For a comfortable feeling, a minimum of a single exchange of the entire volume of air is required.
It should be noted that the supply channels, as a rule, provide the volume of air for a double exchange, while the exhaust channels 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 that, it will be possible to choose the right power supply and exhaust fans. The standard performance indicators for various rooms 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 according to the formula: L = NxSxH, where: L - the estimated volume of incoming air cubic meters per hour; N - air exchange rate standard: houses and apartments - 1-2, office premises - 2-3; S - area, sq.m; H - height, m;
An example of calculating the aerodynamic calculation of ventilation
This calculator can also help you with calculations.