Calculation of supply and exhaust ventilation calculation examples. What is the advantage of a ventilation system with heat recovery? How to check the efficiency of ventilation
The task of ventilation is the removal of old stale air from the premises and its obligatory replacement with fresh outdoor air. Only full ventilation is able to ensure the creation and maintenance of a favorable climate in the rooms. human body atmosphere. When thinking about how to calculate ventilation in a room, you need to understand that in addition to its main purpose, it is the key to maintaining dryness for house structures. It is the correct operation of this system that will not allow rot and mold to form on the surface of the walls, even in rooms with high humidity.
Well-designed ventilation is a prerequisite for creating optimal microclimate in any modern home. Centralized heating, anti-draught equipment, careful thermal insulation - all this requires a meticulous approach to design. ventilation system. Lack of constant air exchange leads to stuffiness. In turn, high levels of humidity in the room lead to condensation.
To calculate ventilation as correctly as possible, we can take as an example natural convection, which works to remove unpleasant odors and air with high humidity from the premises. Natural convection supplies warm air layers from the house to its roof. For such a wire, duct pipes are used, through which the flows are directed through the ridge ventilation elements, and then brought out. This type of ventilation belongs to self-regulating types. It does not have fans, which eliminates the need to use electricity.
Ventilation in the room must be mandatory. At the same time, modern technical constructions, which include air purification from almost all street pollution, are not as useful as they might seem at first glance. They are able to purify the outdoor air so much that it becomes completely artificial, and loses its natural properties and characteristics. That is why the choice of place of residence is fundamental to creating a healthy atmosphere in a house or apartment. Clean air outside provides clean natural air inside and eliminates the need for powerful air purifiers in ventilation systems.
Exhaust ventilation
The purpose of exhaust ventilation is ventilation. In other words, such a constructive structure contributes to the high-quality removal of already exhausted air flows from the premises, and ensures their replacement with fresh flows from the street. Modern technical development allows, along with solving the main problem, to install air conditioning, heating-cooling, and filtration equipment in such systems. However, the extent to which this is necessary and appropriate should be decided in each individual case.
Compliance with sanitary and hygiene conditions indoors can only be ensured by constant ventilation of the room atmosphere. Correctly calculating exhaust ventilation means creating an environment in the building that is favorable for well-being and human health, which will meet all existing sanitary requirements. Exhaust ventilation is necessary to combat harmful emissions indoors. These allocations in a residential building can be defined as follows:
- dust;
- excess moisture (not only the bathroom, toilet, kitchen, dining room, but also living rooms are often characterized by high humidity);
- excess heat;
- vapors of harmful substances and accumulations of various gases.
Exhaust type ventilation can be a whole system of different structural elements, the common goal of which is the complete removal of used (exhaust) air from any premises. Checking its functionality is very simple: if after a walk you enter the apartment, and the feeling of freshness in it is no different from the sensations that you experienced on the street, then the exhaust ventilation of your house works just perfect.
Of course, this method of verification is effective where the air around the house is clean, which is impossible in a gassy urban environment or close to industrial enterprises. Thus, if at the entrance to the apartment you feel even a slight presence of an unpleasant smell or stuffiness, then the ventilation system must be checked for efficiency. If any problems are found, they should be corrected in without fail. Remember that the human body tends to get used to the surrounding smells and atmosphere. However, even if you do not feel obvious discomfort from the consumption of stale air, it will continue to affect your well-being as negatively as possible.
Forced ventilation
The task of supply ventilation is an uninterrupted supply to the building required amount fresh air. At the same time, today's technologies allow this feed stream to either be warmed (in winter) or cooled (in summer). Supply ventilation can be both local and general.
The local system involves the supply of air from the street to a certain place in the building, for example, to the zone of localization of air pollution (stove, toilet). In this case, exhaust ventilation is also made point, focusing on those areas of the room where the use of clean air is especially intensive. General ventilation is the most acceptable in domestic conditions and is used everywhere. She is mechanical.
The design features of ventilation, both supply and exhaust, can be reduced to a duct or non-duct type. Calculate supply ventilation you can on your own. However, for this, it is necessary to additionally determine the volume of the required fresh air inflow, and suitable methods for processing the supplied flows: purification, heating or cooling, humidification (in winter) and calculate the ventilation pipes.
Supply ventilation in conjunction with an air purifier, such as a photocatalytic one, provides air layers into the room that do not contain the following:
- traffic fumes;
- industrial and household toxic organic compounds;
- allergens of animal and vegetable origin;
- soot and gases;
- unpleasant odors and smoke of tobacco origin;
- carbon monoxide, ozone, phenol, formaldehyde and nitrogen oxides.
However, such serious cleaning systems are justified only if your housing is located in a really very polluted area of the metropolis or located close to factories and manufacturing concerns. If you live in a quiet suburb or surrounded by gardens and forests, the use of powerful air purifiers becomes impractical.
Calculation of the volume of air in the room
To understand how to calculate the ventilation in the room will help the recommendations of experts. It is advisable to entrust the creation of such a project and its full-fledged calculation to a professional OM designer. His competence will save on finances, time and nerves, and will also help you choose the most appropriate type of ventilation, tell you which additions to the system you need to install and which are not necessary.
Before giving preference to one or another type of equipment, you need to calculate the volume of air in the room. Knowing the required amount of air, you can proceed to the selection of equipment, which is also calculated depending on certain parameters:
- Heater power indicators.
- Air flow performance indicators.
- Indicators of air velocity and cross-sectional area of air duct structures.
- The level of pressure that is created by the fan during operation.
- The level of emitted noise.
You can determine the air flow by measuring the consumption of its cubic meters per hour. This work will require a floor plan of the premises indicating their purpose and with an explication.
Calculations begin with the determination of the air flow rate required for each specific room. In other words, calculations are carried out showing how many times a complete air exchange takes place in the rooms within 60 minutes. These calculations, to a large extent, depend on the area of the object. So, for example, in a room with an area of 50 m2 and with a ceiling height of 3 meters, the total volume is 150 m3, which provides a double air exchange, which is equal to 300 m3 in one hour. It must be remembered that, in many respects, the air exchange rates directly depend on the power level of the equipment that generates heat, as well as on the number of people who are constantly in the rooms and on the direct purpose of these rooms.
For uninterrupted and long-term operation of the ventilation system in apartments of high-rise buildings or private cottages, especially when you install it again, a competent calculation is required. Usually, only the supply ventilation system is considered, because the natural one is already provided and installed during the construction of the building. At the same time, we note that the design of the exhaust outlet is designed for a single exchange, while the air inflow exceeds the exhaust twice.
A constant and uninterrupted supply of fresh air is necessary only in those rooms where you will be staying for a long time (kitchen, bedroom and living room, etc.) therefore, the calculation of the ventilation system begins with a building plan or a separate apartment, which indicates the area of \u200b\u200ball available rooms . Air exchange is measured in cubic meters per hour. In this case, the air exchange scheme will look like this: clean air enters the rooms, from there, in a slightly polluted form, it goes out into the corridor, then into the kitchen and bathroom and is discharged outside through the ventilation shafts.
You need to know that for rooms without natural ventilation the norm is the consumption of fresh air per tenant is not less than 60 square meters. m / hour. In the bedroom, a smaller number is allowed - up to 30 square meters. m / hour for one, this is due to the fact that at night we consume less oxygen. It is necessary to take into account the needs of only people permanently residing in the dwelling. After you have calculated the air exchange according to the needs of the residents, you should find out the multiplicity of air mass exchange, that is, how many times the entire volume of air is replaced in one hour. This indicator must be at least one.
Using the formulas below, calculate both of these indicators (air exchange by the number of people and the multiplicity) and select a larger value as the most consistent with safety standards:
L (required performance of the supply ventilation system) is equal to N (number of residents) multiplied by Lnorm (expenditure rate per one), this applies to the number of residents.
The multiplicity is calculated as follows - L (required ventilation system performance) is equal to n (normalized air exchange rate) times S (room area) times H (room height).
By making calculations and adding up the numbers obtained, you will find out the overall performance of the ventilation system. The indicators of this value in normative documents the following:
In apartments and rooms 100 - 500 sq. m / hour.
In cottages 500 - 2000 sq. m / hour.
How to make ventilation
A natural ventilation system can be designed and built in a ductless or ducted way. At the same time, the calculation of natural ventilation is possible only in the presence of ventilation ducts, since with ductless ventilation, air cannot be accounted for.
The calculation is made according to the above formulas. If simple ventilation does not help air exchange, mechanical ventilation is installed. In this case, if the area of the room is large, it is required to install two fans.
Properly arranged ventilation is considered, the calculation of which coincided with the indications of the inflow of fresh air and its output.
Calculation of supply and exhaust ventilation
After the fresh air needs and the performance of the ventilation system have been determined, proceed to the air distribution project for the apartment or building. It consists of: an air duct, various fittings, air distributors (grilles) and throttle valves. Before you calculate the ventilation, you need to draw a diagram of the future duct in such a way that its length is minimal and the performance is sufficient.
Choose which section of the duct will be more optimal for you - round or rectangular. The first has a lower height, which saves ceiling space, and the second is easier to install. It should be noted that the speed of the air flow should be limited to 3-4 meters per second. If it is more - there will be a strong noise.
The required calculated cross-sectional area at the duct is calculated as follows:
Sc (cross-sectional area) = L (air flow rate) times 2.778 (generally accepted coefficient of different dimensions) and divided by V (air flow rate through the duct).
The result will be in square centimeters for greater convenience.
For round air outlets, it is calculated as follows: S = tt times D / 400
For rectangular S = A times B / 100.
S actual area, D diameter, A and B width and height.
You need to read these indicators for each branch of the duct. For domestic engineering networks, round air outlets are chosen from 100 to 250 mm, if your choice is rectangular products, their diameter must be completely equivalent.
Exhaust ventilation calculation
In addition to all these indicators, it is necessary to calculate the ventilation systems, taking into account the resistance of the network, the power of the heater (if it is supposed to be installed), find out how much electricity the ventilation equipment will consume. This is very important for supply systems.
Additional (forced) kitchen exhaust ventilation, which is calculated according to the formula:
P (power) = S (area) multiplied by H (ceiling height) and multiplied by 12 (average SES rate).
Comments:
- Exhaust ventilation in the kitchen
- Fan power calculation
- Air change rate
- Another way to determine the power of the device
Nowadays it is impossible to imagine our life without ventilation systems. They are installed in industrial buildings, in offices, educational institutions, in shops, in apartments. The operation of these systems is unthinkable without the use of exhaust fans of various capacities. A widely used element of apartment ventilation is a kitchen hood. It can have different shapes, sizes, designs.
From fan power calculation kitchen hood will depend on the amount of purified air in the room.
Exhaust ventilation in the kitchen
But external beauty is not the most important thing. The main task of this appliance is to rid the kitchen of odors, burning, soot and grease that appear during cooking. Exhaust ventilation removes fumes from various heating devices. It prevents the appearance of dirty plaque on the ceiling and on the surface of the walls. This allows you to perform cosmetic repairs much less often, which will save a significant amount of money. Less time will be needed for general cleaning.
A device capable of passing a certain amount of air through its filters can cope with the task of cleaning the atmosphere in the room. And for this you need to choose a device with a fan of the required power. How to calculate the power of the device?
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Fan power calculation
- Using a tape measure, measure the size of the kitchen and determine its volume in meters. To do this, multiply the length by the width and height. The BTI documents indicate the area of \u200b\u200bthe premises. Example: the kitchen area is 10 m². The height from floor to ceiling is 3 m. We multiply the area by the height and get 30 m³. This is the size of the kitchen.
- Next, the value characterizing the air exchange is calculated. To do this, multiply the volume of the kitchen by the number of complete air updates per hour. Building codes and regulations (SNiP) provide for an air exchange rate of 10-12. So to calculate the power exhaust system you need to multiply 30 m³ by 12. The result is a figure of 360 m³ / h. So much air must be renewed every hour.
- To carry out the exchange in such a volume, a fan with a capacity of 400-800 m³ / h is needed. But standard ventilation ducts can only pass about 180 m³. Therefore, the fan will not help much here.
- In this case, the recirculation hood system will help, which passes the air through the filters and sends it back to the room. Power is also required to overcome the resistance of the filters. Therefore, 40% should be added to the calculated figure. It will turn out 560-1120 m³. This should be the power of the hood fan in a 30 m³ kitchen.
- In some cases, you can do without a ventilation duct. To do this, the exhaust fan is installed in a specially equipped opening in the wall, in the ceiling or at the junction of the ceiling and wall. This installation allows the use of a less powerful fan.
This is just a simple calculation. required power exhaust fan. If the kitchen does not have doors, then the volume of the adjacent room must also be taken into account. So, the formula for calculating the fan power for common cases: room width x length x height x exchange rate = desired value. You can calculate the volume of the room without any problems. It is enough to measure the length, width and height and multiply them.
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Air change rate
Multiplicity for rooms different type is defined like this:
| Room type | multiplicity |
| Bakery | 20-30 |
| Greenhouse | 25-50 |
| Office | 6-8 |
| Bathroom, shower | 3-8 |
| Salon | 10-15 |
| Restaurant, bar | 6-10 |
| Bedroom | 2-4 |
| Lobby | 3-5 |
| Classroom at school | 2-3 |
| Cafeteria | 10-12 |
| Hospital chamber | 4-6 |
| Score | 8-10 |
| Basement | 8-12 |
| Kitchen in the house or in the apartment | 10-15 |
| Gym | 6-8 |
| Attic space | 3-10 |
| Catering kitchen | 15-20 |
| Pantry | 3-6 |
| Changing room with shower | 15-20 |
| Laundry | 10-15 |
| Toilet in the house, in the apartment | 3-10 |
| Conference hall | 8-12 |
| Living room | 3-6 |
| billiard room | 6-8 |
| public toilet | 10-15 |
| Garage | 6-8 |
| Meeting room | 4-8 |
| Utility room | 15-20 |
| Library | 3-4 |
| Canteen | 8-12 |
The highest magnification is chosen for use in rooms with a lot of people, with high humidity and temperature, with a lot of dust and strong odors. In a kitchen with an electric hob, you can choose a lower indicator, with a gas stove - a larger one. This is due to the fact that when the stove is turned on, the gas emits combustion products. The fan, selected taking into account the above data, can be mounted in the wall, window, ceiling of the room.
Comments:
- Calculation of the size of the ducts
- Correspondence of area and flow
- Calculations for the heater
- Calculation of a natural channel system
In order for the ventilation system in the house to work efficiently, it is necessary to make calculations during its design. This will not only allow you to use the equipment with optimal power, but also save on the system, fully preserving all the required parameters. It is carried out according to certain parameters, while completely different formulas are used for natural and forced systems. Separate attention should be paid to the fact that a forced system is not always required. For example, for a city apartment, natural air exchange is quite enough, but subject to certain requirements and norms.
Calculation of the size of the ducts
In order for the premises, it is necessary to determine what the cross section of the pipe will be, the volume of air passing through the ducts, and the flow rate. Such calculations are important, since the slightest errors lead to poor air exchange, noise of the entire air conditioning system, or large cost overruns during installation, electricity for the operation of equipment that provides for ventilation.
To calculate the ventilation for a room, find out the area of the air duct, you must use the following formula:
Sc = L * 2.778 / V, where:
- Sc is the estimated area of the channel;
- L is the value of the air flow passing through the channel;
- V is the value of the air velocity passing through the air duct;
- 2.778 is a special coefficient that is needed to match the dimensions - these are hours and seconds, meters and centimeters, used when including data in the formula.
To find out what the actual area of the duct pipe will be, you need to use a formula based on the type of duct. For a round pipe, the formula applies: S = π * D² / 400, where:
- S is the number for the actual cross-sectional area;
- D is the number for the channel diameter;
- π is a constant equal to 3.14.
For rectangular pipes, you will need the formula S = A * B / 100, where:
- S is the value for the actual cross-sectional area:
- A, B is the length of the sides of the rectangle.
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Correspondence of area and flow
The pipe diameter is 100mm, it corresponds to a rectangular air duct of 80*90mm, 63*125mm, 63*140mm. The areas of rectangular channels will be 72, 79, 88 cm². respectively. The speed of the air flow can be different, the following values are usually used: 2, 3, 4, 5, 6 m / s. In this case, the air flow in a rectangular duct will be:
- when moving at 2 m / s - 52-63 m³ / h;
- when moving at 3 m / s - 78-95 m³ / h;
- when moving at 4 m / s - 104-127 m³ / h;
- at a speed of 5 m / s - 130-159 m³ / h;
- at a speed of 6 m / s - 156-190 m³ / h.
If the calculation of ventilation is carried out for a round duct with a diameter of 160 mm, then it will correspond to rectangular air ducts of 100 * 200 mm, 90 * 250 mm with cross-sectional areas of 200 cm² and 225 cm², respectively. In order for the room to be well ventilated, the following flow rate must be observed at certain speeds of air mass movement:
- at a speed of 2 m / s - 162-184 m³ / h;
- at a speed of 3 m / s - 243-276 m³ / h;
- when moving at 4 m / s - 324-369 m³ / h;
- when moving at 5 m / s - 405-461 m³ / h;
- when moving at 6 m / s - 486-553 m³ / h.
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Calculations for the heater
A heater is a piece of equipment designed for air conditioning of a premise with heated air masses. This device is used to create a more comfortable environment in the cold season. Heaters are used in the forced air conditioning system. Even at the design stage, it is important to calculate the power of the equipment. This is done based on system performance, the difference between outdoor temperature and room temperature. The last two values are determined according to SNiPs. At the same time, it must be taken into account that air must enter the room, the temperature of which is not less than +18 ° C.
The difference between outdoor and indoor conditions is determined by taking into account the climatic zone. On average, during switching on, the air heater provides heating of the air up to 40 ° C, in order to compensate for the difference between the warm internal and external cold flow.
I = P / U, where:
- I is the number for the maximum current consumed by the equipment;
- P is the power of the device required for the room;
- U - voltage for powering the heater.
If the load is less than required, then the device must be chosen not so powerful. The temperature at which the air heater can heat the air is calculated using the following formula:
ΔT = 2.98 * P / L, where:
- ΔT is the number of air temperature difference observed at the inlet and outlet of the air conditioning system;
- P is the power of the device;
- L is the value of equipment productivity.
In a residential area (for apartments and private houses), a heater can have a power of 1-5 kW, but for office space, a larger value is taken - this is 5-50 kW. In some cases, electric heaters are not used, the equipment here is connected to water heating, which saves electricity.
It is not always possible to invite a specialist to design a system of engineering networks. What to do if during the repair or construction of your facility, the calculation of ventilation ducts was required? Is it possible to make it on your own?
The calculation of ventilation and air ducts for it will allow you to create an effective system that will ensure the uninterrupted operation of units, fans and air handling units. If everything is calculated correctly, this will reduce the cost of purchasing materials and equipment, for further maintenance of the system.
Calculation of air ducts of the ventilation system can be carried out by different methods. For example, like this:
- constant pressure loss;
- allowed speeds.
Types and types of air ducts
Before calculating networks, you need to determine what they will be made of. Nowadays, products made of steel, plastic, fabric, aluminum foil, etc. are used. Air ducts are often made of galvanized or stainless steel, this can be arranged even in a small workshop. Such products are convenient to mount and the calculation of such ventilation does not cause problems.
In addition, air ducts may differ in appearance. They can be square, rectangular, oval. Each type has its own merits. Rectangular allow you to make ventilation systems of small height or width, while maintaining the desired cross-sectional area. In round systems less material, oval combine the pros and cons of other types.
For an example of calculating ventilation, we choose round pipes made of tin. These are products that are used for ventilation of housing, office and retail space. The calculation will be carried out by one of the methods that allows you to accurately select the network of air ducts and find its characteristics.
Method for calculating air ducts by the method of constant speeds
The calculation of ventilation ducts must begin with a floor plan. Using all the norms, determine the required amount of air in each zone and draw a wiring diagram. It shows all gratings, diffusers, cross-section changes and taps. The calculation is made for the most remote point of the ventilation system, divided into sections limited by branches or gratings.
The calculation of the air duct for the installation of a ventilation system consists in choosing the desired section along the entire length and finding the pressure loss for selecting a fan or air handling unit. The initial data are the values of the amount of passing air in the ventilation network. Using the scheme, we will calculate the diameter of the duct. To do this, you need a pressure loss graph.
For each type of air duct, the schedule is different. Typically, manufacturers provide this information for their products, or you can find it in reference books. We calculate round tin ducts, the graph for which is shown in the figure.
According to the chosen method, we set the air velocity of each section. It must be within the limits for buildings and premises of the selected purpose. For main supply air ducts and exhaust ventilation the following values are recommended:
- living quarters - 3.5–5.0 m/s;
- production - 6.0–11.0 m/s;
- offices - 3.5–6.0 m/s.
For branches:
- offices - 3.0–6.5 m/s;
- living quarters - 3.0–5.0 m/s;
- production - 4.0–9.0 m/s.
When the speed exceeds the permissible level, the noise level rises to an uncomfortable level for a person.
After determining the speed (in the example 4.0 m/s), we find the desired section of the air ducts according to the graph. There are also pressure losses per 1 m of the network, which will be needed for the calculation. The total pressure loss in Pascals is found by multiplying the specific value by the length of the section:
Ruch=Rch·lch.
Network elements and local resistances
Losses on network elements (lattices, diffusers, tees, turns, changes in section, etc.) are also important. For lattices and some elements, these values are specified in the documentation. They can also be calculated by multiplying the coefficient of local resistance (c.m.s.) by the dynamic pressure in it:
Pm. s.=ζ Pd.
Where Pd \u003d V2 ρ / 2 (ρ is the air density).
K. m. s. determined from reference books and factory characteristics of products. We summarize all types of pressure losses for each section and for the entire network. For convenience, we will do this in a tabular way.
The sum of all pressures will be available for this duct network and the branch losses must be within 10% of the total available pressure. If the difference is greater, it is necessary to mount dampers or diaphragms on the outlets. To do this, we calculate the required c.m.s. according to the formula:
where Pex is the difference between available pressure and branch losses. According to the table, select the diameter of the diaphragm.
The required diameter of the diaphragm for air ducts.
The correct calculation of ventilation ducts will allow you to choose the right fan according to the manufacturer's schedules. Using the found available pressure and the total air flow in the network, this will be easy to do.
