- What ventilation can do?
- How air flows in ventilated rooms?
- How air exchange is calculated?
- Natural ventilation
- How natural ventilation works?
- How to improve natural ventilation? Supply valves
- Pros and cons of natural ventilation
- Mechanical ventilation
- What is mechanical ventilation?
- Types of forced air ventilation
- What you need to know to select ventilation?
Why does a modern home have to have effective ventilation? What does the natural and mechanical ventilation system consist of, how does it work? What system should be organized at home? How to choose and order a working ventilation? We will answer these questions today.
What ventilation can do?
My home is my castle. Buildings are becoming more reliable and more economical every year. Not surprisingly, since the developers now have access to innovative energy-saving technologies and new insulation materials with previously unattainable characteristics. And the market does not stand still: inventors, manufacturers, marketers and salespeople work tirelessly. High-quality waterproofing of structures, multi-layer walls, insulated ceilings and roofs, sealed window blocks, efficient heating – all this does not give the slightest chance for precipitation and groundwater, city noise, winter cold and summer heat.
Yes, a person has learned very well to close off the unfavorable environmental conditions, but at the same time we have lost contact with the outside world, now the natural, natural mechanism of air self-purification has become inaccessible to us. The man in the street fell into another trap – moisture, carbon dioxide, harmful substances and chemical compounds emitted by the person himself, building materials, household items, household chemicals accumulate and concentrate inside the premises. Even in developed countries, the number of autoimmune and allergic diseases caused by the multiplication of bacteria, fungi, mold and viruses in the home is steadily growing. No less dangerous is dust, which consists of the smallest particles of soil, plant pollen, kitchen soot, animal hair, scraps of various fibers, skin flakes, microorganisms. Dust is not necessarily a visitor from the street, it forms even in a tightly closed non-residential apartment. Recent scientific studies have shown that in most cases, indoor air is several times more toxic and dirtier than outdoor air..
A decrease in the oxygen concentration in the room significantly reduces the level of performance, adversely affects the well-being of residents and their health in general.
That is why the issues of providing ventilation and air purification have become incredibly urgent, along with hydro and thermal insulation of buildings. Modern ventilation systems must effectively remove stagnant, “exhaust” air, replace it in the required volume with fresh air from the outside, if necessary, cleaning, heating or cooling it.
How air flows in ventilated rooms?
As we have already noted, the composition of the air inside the operated dwelling is not uniform. Moreover, gases, dust, vapors emitted in the room are constantly moving due to their special properties – density and dispersion (for dust). Depending on whether they are heavier than air or lighter, harmful substances rise or fall, accumulating in certain places. An even greater influence on the interior space is exerted by the movement of convective jets of heated air, for example, from working household appliances or a kitchen stove. Convective currents, rising, can carry even relatively heavy substances into the upper zone of the room – carbon dioxide, dust, dense vapors, soot.
The jets of home air interact in a special way with each other, as well as with various objects and building structures, which is why clearly defined temperature fields, zones of concentration of harmful substances, flowing streams of various speeds, directions and configurations are formed in the dwelling.
It is quite obvious that not all rooms are equally polluted and have excessive humidity. The most “dangerous” are kitchens, toilets, bathrooms. Precisely because the primary task of artificial air exchange is to remove harmful substances from places with the highest concentration of harmful substances, ventilation ducts with exhaust holes are arranged in the area of the kitchen and bathrooms.
The inflow is arranged in “clean” rooms. Thus, the “long-range” supply jets, which are stronger in comparison with other flows of substances, while moving, involve large masses of exhaust air in motion, and the necessary circulation appears. The main thing is that due to the direction of the air towards the “problem” rooms, unwanted substances do not get from kitchens and bathrooms into living rooms. That is why in the tables of building codes regarding the requirements for air exchange, the study, bedroom, living room are calculated only on the inflow, and the bathroom, toilet and kitchen only on the exhaust. Interestingly, in apartments with four or more rooms, it is recommended that the rooms farthest from the ventilation ducts of the bathroom be supplied with separate ventilation, with their own inflow and exhaust..
In this case, corridors, lobbies, hallways, smoke-free staircases may not have supply or exhaust openings, but only serve for air flow. But this flow must be ensured, only then the channelless ventilation system will function. Interior doors interfere with the movement of air flows. Therefore, they are equipped with transfer grids or arrange a ventilation gap of 20-30 mm, raising a blank canvas above the floor.
The nature of the movement of air masses depends not only on the technical and construction characteristics of the premises, the concentration and type of harmful substances, the features of convective flows. An important role here is played by the relative position of the air supply and exhaust points, especially for rooms containing both supply and exhaust openings (for example, kitchen-dining room, laundry …). In ventilation systems of residential premises, the most often used scheme is “top-up”, in some cases – “top-down”, “bottom-down”, “bottom-up”, as well as combined multi-zone, for example, the inflow at the top, and the two-zone hood – at the top and bottom … It depends on the correct choice of the scheme whether the air will be replaced in the required volume, or an annular circulation will form inside the room with the formation of stagnant zones.
How air exchange is calculated?
To design an efficient ventilation system, it is necessary to find out how much exhaust air should be removed from a room or group of rooms and how much fresh air should be supplied. Based on the data obtained, it will be possible to determine the type of ventilation system, select ventilation equipment, calculate the cross-section and configuration of ventilation networks.
It should be said that the parameters of air exchange in residential buildings are strictly regulated by various state regulatory documents. GOSTs, SNiPs, SanPiNs contain comprehensive information not only about the volume of air to be replaced and the principles, parameters of its supply and removal, but also indicate what type of system should be used for certain premises, what equipment is used, where it is located. It remains only to competently examine the room for excess heat and moisture, the presence of air pollution.
The tables, diagrams and formulas presented in these documents are created according to different principles, but in the end they give similar numerical indicators of the required air exchange. They can complement each other in the absence of certain information. Calculations of the amount of ventilation air are made on the basis of research, depending on the harmful substances emitted in specific premises and the norms of their maximum permissible concentration. If, for some reason, the amount of contamination cannot be found out, then the air exchange is counted by frequency, according to sanitary standards per person, by the area of the room.
Multiplicity calculation. SNiP contains a table that indicates how many times the air in a particular room must be replaced with a new one in one hour. For “problem” rooms, the minimum allowable volumes of air replacement are given: kitchen – 90 m3, bathroom – 25 m3, toilet – 50 m3. Ventilation air quantity (m3/ hour) is determined by the formula L = n * V, where n is the multiplicity value, and V is the volume of the room. If you need to calculate the air exchange of a group of rooms (apartment, floor of a private cottage …), then the L values of each ventilated room are summed up.
Another important point is that the volume of exhaust air must be equal to the volume of supply air. Then, if we take the sum of the indicators of air exchange in the kitchen, bathroom and toilet (for example, the minimum is 90 + 25 + 50 = 165 m3/ hour), and compare with the total one-time flow rate of the bedroom, living room, study (for example, it can be 220 m3/ hour), then we get the air balance equation. In other words, we will need to increase the hood up to 220 m3/hour. Sometimes it happens the other way around – you have to increase the flow.
Calculation by area is the simplest and most straightforward. Here we use the formula L = Spremises* 3. The fact is that for one square meter of the room, construction and sanitary standards regulate the replacement of at least 3 m3 air per hour.
The calculation according to sanitary and hygienic standards is based on the requirement that at least 60 m3 in hour. For one temporary – 20 m3.
All the above calculation options are normatively permissible; moreover, for the same room, their results may differ slightly. Practice shows that for a one-room or two-room apartment (30-60 m2) the performance of ventilation equipment will require about 200-350 m3/ hour, for three-, four-room (70-140 m2) – from 350 to 500 m3/hour. It is better to entrust the calculations of larger groups of premises to professionals..
So, the algorithm is simple: first we calculate the required air exchange – then we choose the ventilation system.
How natural ventilation works?
Natural (natural) ventilation system is characterized by the fact that the replacement of air in a room or group of rooms occurs under the influence of gravitational pressure and wind action on the building.
Usually, the air inside the room is warmer than the outside, it becomes more discharged, lighter, therefore it rises up and goes out through the ventilation ducts to the street. A vacuum appears in the room, and heavier air from the outside enters the dwelling through the enclosing structures. Under the influence of gravity, it tends downward and exerts pressure on the ascending currents, displacing the exhaust air. This is how gravitational pressure appears, without which natural ventilation cannot exist. The wind, in turn, helps this circulation. The greater the difference between the temperatures inside and outside the room, the higher the wind speed, the more air gets inside.
For more than a dozen years, such a system was used in Soviet-built apartments of 1930-1980, where the inflow was carried out through infiltration, through structures that let a large amount of air through – wooden windows, porous materials of the outer walls, loosely closing entrance doors. The amount of infiltration in old apartments is 0.5–0.75, depending on the degree of sealing of the cracks. Recall that for living rooms (bedroom, living room, study …), according to the norms, it is required that at least one air change occurs in one hour. There is an obvious need to increase air exchange, which is achieved by ventilation – opening vents, transoms, doors (unorganized ventilation). In fact, this entire system is an exhaust duct with a natural impulse, since the device of special supply openings was not intended. The exhaust of such ventilation is carried out through vertical ventilation ducts, the entrances to which are located in the kitchen and bathroom.
The force of gravitational pressure, which pushes the air out, largely depends on the distance between the ventilation grilles located in the room to the top of the shaft. On the lower floors of apartment buildings, the gravitational pressure is usually stronger due to the greater height of the vertical channel. If the draft in the ventilation duct of your apartment is weak or the so-called “overturning of draft” occurs, then polluted air from neighboring apartments may flow to you. In this case, the installation of a fan with a non-return valve or a louver grill that automatically closes in the event of a reverse draft can help. You can check the traction force by holding a lighted match to the exhaust opening. If the flame does not deviate towards the channel, then it may be clogged, for example with leaves, and cleaning is required.
Natural ventilation can also include short horizontal air ducts that are led out in certain areas of the room on the walls at least 500 mm from the ceiling or on the ceiling itself. The outlets of the exhaust ducts are closed with louvered grilles.
Vertical exhaust ducts of natural ventilation are usually made in the form of shafts made of bricks or special concrete blocks. The minimum permissible size of such ducts is 130×130 mm. There must be a 130 mm thick partition between adjacent shafts. It is allowed to manufacture prefabricated air ducts from non-combustible materials. In the attic, their walls are necessarily insulated, which prevents the formation of condensation. Exhaust ducts are led out above the roof, at least 500 mm above the ridge. From above, the exhaust shaft is covered with a deflector – a special nozzle that enhances air draft.
How to improve natural ventilation? Supply valves
Recently, the owners of the old housing stock have taken up energy conservation seriously. Almost sealed PVC or euro-windows are installed everywhere, walls are insulated and vapor-insulated. As a result, the infiltration process practically stops, air cannot enter the room, and regular ventilation through the window sashes is too impractical. In this case, the problem of air exchange is solved by installing supply valves..
Supply valves can be integrated into the profile system of plastic windows. Very often they are installed on Euro windows. The fact is that the ability of modern wooden windows to “breathe” is a little exaggerated, you will not wait for an inflow through them. Therefore, responsible manufacturers always suggest installing a valve.
Window valves are installed at the top of the frame, sash or in the form of a valve handle, they are made of aluminum or plastic, they can be of different colors. Supply valves for windows can not only be built into new windows, but also mounted on already installed window systems, without any dismantling work.
There is another way out – this is the installation of a wall supply valve. This device consists of a branch pipe passing through a wall, closed at both ends with gratings. Wall valves can have a chamber with filters and a sound-absorbing labyrinth. The inner grill is usually manually adjusted until fully closed, but options with automation through temperature and humidity sensors are possible.
As we have already said, air movement should be directed towards polluted premises (kitchen, toilet, bathroom), therefore, supply valves are installed in living rooms (bedroom, study, living room). Supply valves are placed at the top of the room to provide an effective top-up arrangement of ventilation openings for most apartments. Practice shows that removing the inflow into the radiator area in order to warm up the outside air is not the best solution, since the circulation of flows is disturbed.
Pros and cons of natural ventilation
Natural ventilation is practically not used in modern construction. The reason for this is low air exchange rates, the dependence of its power on natural factors, the lack of stability, strict restrictions on the length of air ducts and the cross-section of vertical channels..
But it cannot be said that such a system has no right to exist. Compared to forced “brothers”, natural ventilation is much more economical. After all, there is no need to purchase any equipment and long air ducts, there are no costs for electricity and maintenance. Rooms with natural ventilation are much more comfortable due to the absence of noise and the low speed of movement of the replaced air. Moreover, there is not always a constructive opportunity to mount ventilation ducts for mechanical ventilation, and then sheathe them with drywall boxes or false beams, for example, with a low ceiling height.
What is mechanical ventilation?
Forced (mechanical, artificial) ventilation is a system in which air movement is carried out using any injection devices – fans, ejectors, compressors, pumps.
This is a modern and very effective way of organizing air exchange in rooms of various purposes. The efficiency of mechanical ventilation does not depend on changing weather conditions (air temperature, pressure, wind force). This type of system allows you to replace any amount of air, transport it over a considerable distance, and create local ventilation. The air that is supplied to the room can be prepared in a special way – heated, cooled, dried, humidified, purified …
The disadvantages of mechanical ventilation include high initial costs, energy costs and maintenance costs. It is very difficult to implement duct mechanical ventilation in a residential area without more or less serious repairs.
Types of forced air ventilation
The best indicators of comfort and performance are shown by general exchange supply and exhaust mechanical ventilation. Balanced supply and exhaust air exchange allows avoiding drafts and forgetting about the effect of “slamming doors”. It is this system that is most common in new construction..
For certain reasons, either supply or exhaust ventilation is often used. Supply ventilation supplies fresh air to the room instead of exhaust air, which is removed through enclosing structures or passive exhaust ducts. Supply ventilation is structurally one of the most difficult. It consists of the following elements: fan, air heater, filter, silencer, control automation, air valve, air ducts, air intake grille, air distributors.
Depending on how the main components of the system are made, the supply unit can be monoblock or type-setting. A monoblock system is somewhat more expensive, but it has a greater assembly readiness, more compact dimensions. It only needs to be fixed in the right place and supply power and a network of channels to it. Monoblock installation saves a little on commissioning and design.
Often, in addition to filtration, the supply air requires special preparation, therefore the ventilation unit is equipped with additional equipment, for example, drying or humidifying equipment. Energy recovery systems are becoming increasingly popular, which cool or heat the supply air using electric air heaters, water heat exchangers or residential split air conditioning systems..
Exhaust ventilation is designed to remove air from rooms. Depending on whether the air exchange of the entire dwelling or individual zones is carried out, mechanical exhaust ventilation is local (for example, an exhaust hood over a stove, smoking room) or general exchange (a wall fan in a bathroom, toilet, kitchen). Fans of general exhaust ventilation can be placed in a through hole in the wall, in a window opening. Local ventilation is usually used in conjunction with general exchange.
Artificial ventilation can be performed with ventilation ducts – duct, or without the use of such – ductless. The duct system has a network of air ducts through which air is supplied, transported or removed from certain areas of the room. In a ductless system, air is supplied through the enclosing structures or intake ventilation openings, then it flows through the interior space of the room to the area of exhaust openings with fans. Ductless ventilation is cheaper and easier, but also less efficient.
Whatever the purpose of the room, in practice it is impossible to do with one type of ventilation system. The choice in each case is determined by the size of the room and its purpose, the type of pollutants (dust, heavy or light gases, moisture, vapors …) and the nature of their distribution in the total volume of air. Questions and economic feasibility of using a certain system are also important..
What you need to know to select ventilation?
So, your calculations show that natural ventilation will not cope with the tasks set – too much air needs to be removed, there are also questions with supply, since the walls are insulated, the windows are changed. Artificial ventilation is the way out. It is necessary to invite a representative of the company that installs climate systems, who will help you select the configuration of mechanical ventilation on site..
In general, it is better to design and implement ventilation at the stage of building a cottage or overhauling an apartment. Then it is possible to painlessly solve many design problems, for example, setting up a ventilation chamber, installing equipment, distributing ventilation ducts and hiding them with suspended ceilings. It is important that the ventilation system has a minimum of points of intersection with other communications, such as heating and water supply systems, electrical networks, low-current cables. Therefore, if you are carrying out repairs or construction, in order to search for general technical solutions, you must invite to the object and representatives of the contractor – installers, electricians, plumbers, engineers.
The result of joint work depends on the correct setting of tasks. The specialists will ask “tricky” questions that you need to answer. The following circumstances will be important:
- The number of people staying in the room.
- Floor plan. It is necessary to draw up a detailed layout of the rooms with an indication of their purpose, especially if redevelopment is possible.
- Wall thickness and material. Glazing features.
- Type and height of ceilings. The size of the interceiling space for suspended, hemmed, tensioning systems. Possibility of mounting false beams.
- Arrangement of furniture and heat-generating household appliances.
- Power and location of lighting and heating devices.
- Availability, type and condition of ventilation shafts.
- Features and performance of infiltration, natural ventilation.
- Local exhaust ventilation – cabinet, umbrella.
- Desired configuration of the supply system – type-setting or monoblock.
- The need to use noise insulation.
- Whether or not supply air preparation is required.
- Valve type – adjustable or non-adjustable grilles, diffusers.
- Air distributor locations – wall or ceiling.
- The nature of the system control – keys, shield, remote control, computer, smart home.
Based on the data obtained, equipment of a certain capacity, parameters of the ventilation network, and installation methods will be selected. If the customer is satisfied with the presented developments, then the contractor provides him with a working draft of the ventilation system and proceeds to installation. All we have to do is pay bills and enjoy clean air..