How to make a calculation of ventilation: formulas and an example of calculating the supply and exhaust system
Do you dream that the house has a healthy microclimate and in no room does it smell of mustiness and dampness? In order for the house to be truly comfortable, it is necessary to carry out a competent calculation of ventilation even at the design stage.
If during the construction of the house to miss this important point, in the future will have to solve a number of problems: from the removal of mold in the bathroom to the new repair and installation of the duct system. Agree, it is not too pleasant to see black molds nurseries in the kitchen on the windowsill or in the corners of the children's room, or to re-plunge into repair work.
Want to independently calculate the ventilation system, ranging from the diameter of the ducts and ending with their length for all rooms in the house, but do not know how to do it right? We will help you with this - the article contains useful materials for the calculation, including formulas and a real example for various premises and a certain area.
Also selected are tables from reference books that comply with the standards, illustrative photos and video clips, which demonstrate an example of how to perform an independent calculation of the ventilation system in accordance with the standards.
Causes of ventilation problems
With proper calculations and proper installation, ventilation of the house is carried out in a suitable mode. This means that the air in the premises will be fresh, with normal humidity and without unpleasant odors.
If there is a reverse pattern, for example, constant stuffiness, mold and fungus in the bathroom or other negative phenomena, then you need to check the condition of the ventilation system.
A lot of problems are caused by the absence of micro gaps, provoked by the installation of hermetic plastic windows.In this case, the house gets too little fresh air, you need to take care of its inflow.
Clogging and depressurization of air ducts can cause serious problems with the removal of exhaust air, which is saturated with unpleasant odors, as well as excess water vapor.
As a result, mold and fungus can appear in the office space, which has a bad effect on people's health and can provoke a number of serious diseases.
But it also happens that the elements of the ventilation system work fine, but the problems described above remain unsolved. Perhaps the calculations of the ventilation system for a particular house or apartment were carried out incorrectly.
Their alteration, redevelopment, the appearance of extensions, the installation of the previously mentioned plastic windows, etc. can negatively affect the ventilation of the premises.
In case of such significant changes, it does not make it necessary to re-calculate and modernize the existing ventilation system in accordance with the new data.
One of the easiest ways to detect ventilation problems is to check for traction. You need to bring a lit match or a piece of thin paper to the exhaust grille.
It is not necessary to use open fire for such a test, if gas heating equipment is used indoors..
If the flame or paper is surely deflected towards the exhaust side, there is a draft, if this does not happen or the deflection is weak, irregular, the problem with exhaust air discharge becomes obvious.
The cause may be blockages or damage to the duct as a result of inept repair.
It is not always possible to eliminate the damage, the installation of additional exhaust ventilation equipment often becomes a solution. Before installing them also does not hurt to carry out the necessary calculations.
How to calculate the air exchange?
All calculations for ventilation systems are to determine the amount of air in the room. As such a room can be considered as a separate room, and a set of rooms in a particular house or apartment.
Based on these data, as well as information from regulatory documents, the main parameters of the ventilation system are calculated, such as the section and number of ducts, fan power, etc.
There are specialized calculation methods that allow calculating not only the renewal of air masses in the room, but also the removal of thermal energy, changes in humidity, removal of contaminants, etc.
Similar calculations are usually performed for industrial, social, or any specialized buildings.
If there is a need or desire to perform such detailed calculations, it is best to contact an engineer who has studied such techniques. For self-calculations for residential premises use the following options:
- by multiplicities;
- on sanitary and hygienic standards;
- by area.
All these techniques are relatively simple, having understood their essence, even a non-specialist can calculate the main parameters of his ventilation system.
The easiest way to use the calculations for the area.The following norm is taken as a basis: every hour three cubic meters of fresh air per square meter of space should be supplied to the house.
The number of people who permanently live in the house is not taken into account.
The calculation for sanitary and hygienic standards is also relatively simple. In this case, for calculations, not the area is used, but data on the number of permanent and temporary residents.
For each resident, it is necessary to ensure the flow of fresh air in the amount of 60 cubic meters per hour.
If temporary visitors are regularly present in the room, then for each such person you need to add another 20 cubic meters per hour.
Calculation by multiplicity is somewhat more complicated. When performing it, the purpose of each individual room and the standards for the rate of air exchange for each of them are taken into account.
Air exchange rate is the coefficient reflecting the amount of complete replacement of exhaust air in a room within one hour.Relevant information is contained in a special regulatory table (SNiP 2.08.01-89 * Residential buildings, adj. 4).
Calculate the amount of air that must be updated within an hour, can be according to the formula:
L = N * V,
Where:
- N- the frequency of air exchange per hour, taken from the table;
- V- volume of the room, m 3
The volume of each room is very simple to calculate, for this you need to multiply the area of the room by its height. Then, for each room, the volume of air exchange per hour is calculated using the above formula.
The indicator L for each room is summed up, the final value allows us to get an idea of how much fresh air should be delivered to the room per unit of time.
Of course, exactly the same amount of exhaust air must be removed through exhaust ventilation. In the same room do not install and ventilation, and exhaust ventilation.
Typically, the air flow through the “clean” rooms: bedroom, nursery, living room, office, etc.
Remove the same air from the rooms of official appointment: bathroom, bathroom, kitchen, etc. This is reasonable, since the unpleasant odors characteristic of these rooms do not spread through the dwelling, but are immediately brought outside, which makes living in the house more comfortable.
Therefore, in the calculations, the standard is taken only for supply air or only for exhaust ventilation, as reflected in the standard table.
If the air does not need to be supplied to a specific room or removed from it, there is a dash in the corresponding box. For some rooms the minimum value of the air exchange rate is indicated.
If the calculated value is lower than the minimum, a table value should be used for calculations.
Of course, there may be rooms in the house whose purpose is not displayed in the table. In such cases, the standards adopted for residential premises are used, i.e. 3 cubic meters for each square meter of the room.
You just need to multiply the area of the room by 3, the resulting value is taken as the standard rate of air exchange.
All values of air exchange rate L should be rounded upwards so that they are multiples of five. Now we need to calculate the sum of the air exchange rate L for the rooms through which the air flow is carried out.
Separately summarize the air exchange rate L of those rooms from which exhaust air is discharged.
Then you should compare these two indicators. If L in inflow is higher than L in exhaust air, then you need to increase the indicators for those rooms for which the minimum values were used in the calculations.
Examples of calculations of the volume of air
To make a calculation for the ventilation system by multiplicity, first you need to make a list of all the rooms in the house, record their area and height of the ceilings.
For example, in a hypothetical house there are the following premises:
- Bedroom - 27 sq.m .;
- Living room - 38 sq.m .;
- Cabinet - 18 sq.m .;
- Children's - 12 sq.m .;
- Kitchen - 20 sq.m .;
- Bathroom - 3 sq.m .;
- Bathroom - 4 sq.m .;
- Corridor - 8 sq.m.
Given that the height of the ceiling in all rooms is three meters, we calculate the corresponding volumes of air:
- Bedroom - 81 cubic meters;
- Living room - 114 cubic meters;
- Cabinet - 54 cubic meters;
- Children's - 36 cubic meters;
- Kitchen - 60 cubic meters;
- Bathroom - 9 cubic meters;
- Bathroom - 12 cubic meters;
- Corridor - 24 cubic meters.
Now, using the above table, it is necessary to make calculations of the ventilation of the room taking into account the rate of air exchange, increasing each indicator to a value multiple of five:
- Bedroom - 81 cubic meters. * 1 = 85 cubic meters;
- Living room - 38 sq.m. * 3 = 115 cubic meters;
- Cabinet - 54 cubic meters. * 1 = 55 cubic meters;
- Children’s - 36 cubic meters. * 1 = 40 cubic meters;
- Kitchen - 60 cubic meters. - not less than 90 cubic meters;
- Bathroom - 9 cubic meters. not less than 50 cubic meters;
- Bathroom - 12 cubic meters. not less than 25 cubic meters
Information about the standards for the corridor in the table are not available, so the data for this small room are not taken into account in the calculation. For the living room, a square calculation was made taking into account the standard three cubic meters meters per square meter.
Now you need to separately summarize the information on the rooms in which air flow is carried out, and separately - rooms,where exhaust ventilation devices are installed.
Air exchange volume by inflow:
- Bedroom - 81 cubic meters. * 1 = 85 cubic meters / hour;
- Living room - 38 sq.m. * 3 = 115 cubic meters / h;
- Cabinet - 54 cubic meters. * 1 = 55 cubic meters / h;
- Children’s - 36 cubic meters. * 1 = 40 cubic meters / h;
Total: 295 m³ / h
Air volume on the hood:
- Kitchen - 60 cubic meters. - not less than 90 cubic meters / h;
- Bathroom - 9 cubic meters. - not less than 50 cubic meters / h;
- Bathroom - 12 cubic meters. - not less than 25 cubic meters / h.
Total: 165 cubic meters / h.
Now you should compare the amount received. Obviously, the required inflow exceeds exhaust by 130 cubic meters / h (295 cubic meters / h-165 cubic meters / h).
To eliminate this difference, you need to increase the volume of air exchange on the hood, for example, by increasing the figures for the kitchen. After editing, the calculation results will be as follows:
Air exchange volume by inflow:
- Bedroom - 81 cubic meters. * 1 = 85 cubic meters / hour;
- Living room - 38 sq.m. * 3 = 115 cubic meters / h;
- Cabinet - 54 cubic meters. * 1 = 55 cubic meters / h;
- Children’s - 36 cubic meters. * 1 = 40 cubic meters / h;
Total: 295 m³ / h
Air exchange on the hood:
- Kitchen - 60 cubic meters. - 220 cubic meters / h;
- Bathroom - 9 cubic meters. - not less than 50 cubic meters / h;
- Bathroom - 12 cubic meters. - not less than 25 cubic meters / h.
Total: 295 m³ / h
Volumes for inflow and exhaust are equal, which meets the requirements for calculations of air exchange by multiplicity.
The calculation of air exchange in accordance with sanitary standards is much easier. Suppose that in the house discussed above, two people live permanently and two others stay in the room irregularly.
The calculation is carried out separately for each room in accordance with the norm of 60 cubic meters per person for permanent residents and 20 cubic meters per hour for temporary visitors:
- Bedroom - 2 people * 60 = 120 cubic meters per hour;
- Cabinet - 1 person. * 60 = 60 cubic meters per hour;
- Living room 2 people * 60 + 2 people * 20 = 160 cubic meters per hour;
- Children's 1 pers. * 60 = 60 cubic meters \ hour.
Totalby inflow- 400 cubic meters per hour.
For the number of permanent and temporary inhabitants of the house there are no strict rules, these figures are determined based on the real situation and common sense.
The exhaust is calculated according to the standards set forth in the table above, and increased to a total figure for the influx:
- Kitchen - 60 cubic meters. - 300 m³ / h;
- Bathroom - 9 cubic meters. - not less than 50 cubic meters / h;
- Bathroom - 12 cubic meters. - not less than 50 cubic meters / h.
Total hood: 400 cubic meters / h.
Increased air exchange for the kitchen and bathroom.Insufficient exhaust volume can be divided between all rooms in which exhaust ventilation is installed.
Or increase this figure for only one room, as was done in the calculation of multiplicity.
In accordance with sanitary norms, air exchange is calculated in a similar way. Suppose the area of the house is 130 sq.m.
Then the air exchange at the inflow should be 130 sq.m * 3 cubic meters \ hour = 390 cubic meters per hour.
It remains to distribute this volume to the premises by the hood, for example, in this way:
- Kitchen - 60 cubic meters. - 290 cubic meters / h;
- Bathroom - 9 cubic meters. - not less than 50 cubic meters / h;
- Bathroom - 12 cubic meters. - not less than 50 cubic meters / h.
Total hood: 390 m 3 / h.
Air exchange balance is one of the main indicators in the design of ventilation systems. Further calculations are performed based on this information.
How to choose the cross section of the duct?
The ventilation system, as is known, can be channel or non-channel. In the first case, you need to choose the correct cross-section of channels.
If it is decided to install structures with a rectangular section, then the ratio of its length and width should approach 3: 1.
The speed of movement of air masses on the main line should be about five meters per hour, and on the branches - up to three meters per hour.
This will ensure that the system operates with minimal noise. The speed of air movement is largely dependent on the cross-sectional area of the duct.
To choose the size of the structure, you can use special calculation tables. In such a table, you need to select the volume of air exchange on the left, for example, 400 cubic meters / h, and from the top choose the speed value - five meters per hour.
Then you need to find the intersection of the horizontal line for air exchange with a vertical line for speed.
From this point of intersection, a line is drawn down to the curve, along which a suitable cross section can be determined. For a rectangular duct, this will be the area value, and for a round one, the diameter is in millimeters.
First, make calculations for the main duct, and then - for branches.
Thus, calculations are made if only one exhaust duct is planned in the house.If it is planned to install several exhaust channels, then the total volume of the duct should be divided by the number of channels, and then the calculations should be made according to the principle outlined.
In addition, there are specialized calculation programs with which you can perform similar calculations. For apartments and residential houses, such programs may even be more convenient, since they give a more accurate result.
Conclusions and useful video on the topic
Useful information on the principles of the ventilation system can be found in this video:
Together with the exhaust air leaves the home and heat. Calculations of heat losses associated with the operation of the ventilation system are clearly demonstrated here:
The correct calculation of ventilation is the basis of its safe operation and a guarantee of a favorable microclimate in a house or apartment.. Knowledge of the basic parameters on which such calculations are based, will allow not only to properly design the ventilation system during construction, but also to correct its state if circumstances change.