Until recently, natural ventilation systems have been favorites of industrial and civil construction. The combination of simplicity and reliability attract both professionals and homeowners.
Penetrating into the house through leaks of window blocks, cracks or specially installed ventilation devices, the air is drawn out due to the laws of physics. Before calculating natural ventilation, familiarize yourself with the existing types, advantages and disadvantages. With the help of our tips, you can easily and competently design the natural ventilation of a private house with your own hands.
The principle of natural ventilation
We will explain in detail how natural ventilation works so that the apparent simplicity does not deceive anyone.
In cold weather, warm streams are actively drawn from the premises through the ventilation ducts. An area of reduced pressure is created, which is leveled by suction of the air masses from the outside. Cool street air warms up, the cycle of work is repeated according to the same principle, until the temperature outside and the house is even out.
Therefore, we feel particularly stuffy: our natural ventilation is not able to provide sanitary standards.
In summer, when atmospheric air is hot, natural exhaust ventilation stops working.
Successful work is directly ensured by the following conditions:
- ventilation ducts are installed in rooms with maximum heat gain (kitchen, bathroom);
- ventilation shafts are designed strictly vertically, channels from apartments are connected to them;
- uninterrupted air flow from the street is provided in each of the rooms of the house (air inlets, ventilators, leaky wooden windows);
- air between rooms moves freely. To do this, a 1.5 cm gap is left under the doors or a ventilation grill is installed in the lower half of the door leaf.
The operation of the system is based solely on a significant difference in climatic indicators in the building and on the street.
Types of natural ventilation
In buildings with natural ventilation, the use of any type of fan is completely excluded.
There are two types:
- Unorganized or spontaneous. Air flows enter the house through specially designed slots, and are discharged through the chimney. No ventilation vents do this.
- Organized. Air enters the building and leaves it through specially equipped vents. The locations of the products and their diameter are calculated depending on the volume of the room. The movement of air masses is regulated in different ways, depending on which the system happens:
- gravitational;
- longline;
- aeration.
In order to correctly calculate the system in a private house and make a project, it is important to choose the appropriate method of air movement.
The device has many advantages:
- it is possible to equip the natural ventilation of a private house with your own hands, spending a little money and having minimal knowledge in physics;
- Effectively working under certain conditions and proper design;
- Calculating natural ventilation for a private home is quite simple.
A simple, but not always reliable principle of natural ventilation is used in residential buildings, public buildings of the old construction, small warehouses, workshops. But when natural ventilation is not able to maintain the desired microclimate, while maintaining it, auxiliary fans are connected, which can enhance the flow of air or exhaust air.
Natural ventilation schemes
There are several types of schemes for a private house:
- channelless;
- channel;
- Permanent
- periodic.
Air enters the house through the “dry” rooms: bedroom, guest room, and is discharged through the “wet” rooms with any ventilation device.
Projects without the use of ventilation ducts are often done for industrial premises. A constant circuit is characterized by continuous air movement. Periodic natural ventilation involves periodic ventilation.
The well-known channel scheme of natural ventilation of a private house is quite simple, it consists of mines located vertically. The lower ends of the mines go into the room and hide behind ventilation grills. Upper raise above the roof.
Most of all, bathrooms, toilets, kitchens, storage rooms, boiler rooms need exhaust ventilation. With this in mind, calculate the scheme.
Supply devices are located at the top of the sash. Exhaust - as high as possible to the ceiling. For the free movement of air through the house under the interior doors leave cracks.
If it is necessary to ventilate the basement or attic floors, additional air ducts are equipped.
Usually, all calculations and diagrams are prepared during the design period of the building. During construction, cavities or shafts are provided.
Traction directly affects the air speed.
Which largely depends on the properties of ventilation ducts:
- sections;
- heights;
- thermal insulation;
- number of turns.
Ducts suitable for the natural ventilation of the cottage are installed during the construction of the walls. Often they hide quite quietly inside partitions.
The higher the head of the ventilation duct rises above the roof, the higher the air speed. This is due to the greater pressure difference below and above.
Norms of air exchange during natural ventilation
Norms according to ABOK-1-2002 are:
| Living rooms | 3 cubic meters of air per hour per 1 sq. Km. m. with a living space of less than 20 square meters. m per person |
| 30 cubic meters per hour is the norm of natural ventilation for an adult | |
| Kitchen | 90 cubic meters per hour for a gas stove |
| 60 m3 / h (electric cooker) | |
| Toilet and bathroom | 50 m3 / h (joint) |
| 25 cubic meters / hour (separate) | |
| Laundry | 5 times per hour |
| Storerooms and utility rooms | 1 time / h |
The project is initially based on sanitary standards. The natural ventilation scheme will not provide a healthy microclimate in the house if they are not taken into account. So, with excessive air exchange, drafts and colds are expected for residents, and with weak air, stuffiness, accumulation of dust and allergens are expected.
Calculation of natural ventilation ducts
Ducts are one of the main components of the natural ventilation of an apartment or house. On them from the premises exhaust air is discharged. In order for the system to function correctly, a calculation of the pipe sections is needed.
Formula 1. First, specific losses are calculated:
In the numerator, gravitational pressure, in the denominator, the design length of the track in meters.
Formula 2. Gravity pressure in Pascals:
here h - the height of the air column,Rat - air density in the room,Rn - street air density in kg / m3.
Pipe dimensions are calculated as follows:
- Designation of ducts and ventilation grilles on the plan of natural exhaust ventilation;
- Drawing up an axonometric diagram.
When drawing up the axonometric diagram, the vertical channels should be placed evenly and ensure the movement of equal volumes of air.
The procedure for doing a do-it-yourself aerodynamic calculation for a private house system:
- The first to calculate the areas farthest from the mine;
- For each branch, gravity pressure is calculated using Formula 2;
- Calculation of the cross section of the ducts:
Here L - air flow for ventilation, VR - gas velocity; - Having calculated the dimensions of the ducts, they select the most suitable pipes for the diameter;
- The cross-sectional diameter of a rectangular duct is calculated by the diameter of a round, similar in friction: D = 2cb / (c + b), here c and b are the sides of the cross-section of the duct in meters.
For calculations, averaged indicators of air velocity in natural ventilation are taken: from 0.5 to 1 m / s.
As ducts for the natural ventilation device, choose round plastic pipes.
Their smooth inner surface freely passes air through itself, without creating obstacles. They are easily interconnected and easy to maintain. It is advisable to arrange plastic pipes with antistatic solution before arranging natural ventilation in a private house.
Natural Ventilation Issues
Even properly designed natural ventilation has several disadvantages. Dependence on external conditions we have already mentioned.
And the last factor that negates the presence of exhaust natural ventilation: sealed windows. Air does not enter through PVC window seals; modern wall materials completely isolate the housing. Therefore, common house hoods do not work.
Testing effectiveness is very simple:
- Open the window in the kitchen;
- Bring a palm-sized piece of tissue paper to the ventilation grill of the ventilation duct;
- If the sheet is held, then natural ventilation works like a clock.
Checking natural ventilation with a lit match is also common. This method is dangerous and may cause a fire or explosion in the ventilation shaft. Therefore, professionals check only with a paper sheet.
Heat is removed from the apartment or cottage through natural ventilation ducts along with stale air. Street air carries dust and allergens. And in the kitchen, natural supply and exhaust ventilation will not cope with steam and heat on days of large cooking.
Problem solving
You can create a constant or controlled air flow for the natural ventilation of the apartment by installing a supply valve. Supply valves are wall or window. With some skills, it is possible to normalize the work of natural ventilation with your own hands.
Supply devices are necessarily supplied with nets that will not let dust and insects pass into the apartment.
As an auxiliary exhaust device, hoods are widely used. It is necessary to correctly connect the cooker hood while maintaining natural ventilation. The ventilation grill in the kitchen does not overlap, as there is a separate outlet for the hood. The natural ventilation of the kitchen is preserved, while the fan drives the humid, saturated air with particles of fat from the room intensely.
Bring the end of the duct into the street. This is the most appropriate option for those who want to connect a cooker hood while maintaining natural ventilation.
Outside, the duct is covered by a check valve, its surface is covered with thermal insulation. The method is more costly, but competent.
Having resorted to our recommendations, you will provide the apartment or house with effective natural ventilation all year round, regardless of the weather.
Video on how to install a window inlet valve yourself:
