The atmosphere of the house is more or less protected from dusty and polluted streets, but is defenseless against air pollutants produced by the kitchen. Agree that the open window when cooking food is extremely small.
You need an exhaust umbrella over the stove and a ventilation channel with output to the “street”, but first of all - calculation of the hood for the kitchen for the selection of equipment with suitable power. But how to do it in order not to attract specialists?
We will try to give you a hint - in this material the procedure for performing the calculation is described in detail, formulas and specific examples of calculations are given. Also selected pictorial photos and useful video tips on the selection and installation of hoods.
Following the recommendations, you can independently calculate the required power of the exhaust device, which will remove exhaust air in a timely manner and in full.
The content of the article:
- How does the hood differ from ventilation?
- Kitchen hood feature
Calculation procedure exhaust hood
- Stage # 1 - calculation of total heat output
- Stage # 2 - Calculate Hydraulic Diameter and Flow
- Stage # 3 - Calculation of exhaust hood power
- Why a powerful hood "does not pull"?
- Conclusions and useful video on the topic
How does the hood differ from ventilation?
Located in modern apartments above the stove exhaust umbrella, better known as the hood. Many homeowners are convinced that this air collector is responsible for the ventilation of the kitchen.
Therefore, with a clear conscience, they lead the ventchannel pipe from the exhaust hood into the vent hole, designed and built by the designers of a high-rise building.
What happens if the standard ventilation in the kitchen is blocked by a duct from the exhaust hood? The intensity of air in the apartment will decrease dramatically.
Kitchen hood installers and kitchen umbrellas usually state the opposite. They will say: this technique will significantly improve the quality of air supply at home, because it has a powerful fan heater.
However, the power of plate extraction is in no way connected with ventilation. The reason - the air in the apartments of most residential high-rises, especially those built before 2000, were designed with the expectation of supply and exhaust ventilation.
The principle of air exchange in a high-rise building is based on the sources of fresh air (windows, air vents, etc.) and exhaust ducts (Fig. left). The latter are displayed vertically through all floors of the building. A kitchen hood can be connected to a canal (Fig. right) or not connected
Street air entered through the slots of the window frames and the front door. And the channels ventilation in the kitchen, in a bathroom and a bathroom were used for a conclusion of "stale" air. It would seem - what is it?
Exhaust in the kitchen - to pull the air. So why it is impossible to "stick" into it the duct from the exhaust hood? The point here is the performance by air.
Kitchen hood that is not connected to the general house ventilation system removes polluted air through a separate air vent or works as a heat exchanger without the function of air outlet the masses
Duct ducts in residential apartment buildings are designed for a certain load. In general, the capacity of any communication is carefully calculated at the design stage.
And in ideal conditions (clean walls of the ventilation channel, no noise at the entrance-exit, etc.), the performance of natural ventilation in a high-rise apartment will be 160-180 m3/ h
You may also be interested in information about the standard air velocity in the ducts, considered in this article.
Kitchen hood feature
At models of exhaust umbrellas, the power is significantly higher - 200-1100 m3/ h Such power is necessary for pulling volatile pollutants generated during cooking into the duct.
However, sellers of exhaust hoods declare a different reason for choosing the power of the exhaust device - the need for frequent air exchange in the kitchen.
The exhaust box mounted above the stove is not responsible for air exchange in the kitchen. This device only removes volatile food preparation products. Legend: A - removal of combustion products from the stove, B and C - direction of air movement in the process of air exchange
Standards of mechanical ventilation really claim 10-12 times the change of air in the volume of the room serviced (SNiP 41-01-2003).
But the hood hood located above the kitchen stove does not perform the function of “room ventilation” because it is not capable.
In need of updating (replacing) air accumulates near the ceiling. It is not capable of sucking it into the ventchanal exhaust umbrella - its socket is not set high enough. And the air flow during discharge and injection behaves differently.
Electromechanical installation pulls air from a distance not exceeding the diameter of the suction socket. Those. at 400 mm width of the hood hood, air will be drawn into it that is not further than 400 mm from the socket.
Meanwhile, the emission of air flow occurs over a distance exceeding 15 diameters of the exhaust opening.
A simple "home" example: the included household fan. From its reverse side, the movement of air is barely noticeable, but from the front - a powerful air flow. By the way, the vacuum cleaner works on suction of dust only at a minimum distance from the carpet.
The only effective way to remove volatile food preparation products is through an independent ventilation channel. Otherwise, smells will remain in the house.
Exhaust umbrella above the stove performs a single task - the removal of air that came to him from the surface of the cooking stove.
Of course, instead of the injected air, another portion of it will come to the stove from the window, open the door to the next room, etc. But a complete change of air volume in the kitchen will not occur.
If smells of cooking food rise to the ceiling - they will not participate in mixing and they are difficult to remove.
For this reason, the instructions for exhaust umbrellas contain the following conditions accommodation hoods and works: 600 mm from an electric stove; 750 mm from gas plates; Air currents (drafts) during the operation of the hood should not be allowed, otherwise smells will spread around the room.
Plate hood does not provide a change of air in the kitchen. When choosing her model air volume of the room does not matter. The relationship between the size of the kitchen and the power of the exhaust hood was invented by the sellers of kitchen appliances.
How to calculate the required drawing power? Of course, based on the performance of the cooker.
When performing calculations for the selection of the kitchen hood, consider the following factors:
A photo of
The area of the working surface of the hood must be equal to or more than the working surface of the plate. It is recommended that the hood be better wider.
The performance of the recirculation hood should be three times greater than that of the device with the output in the duct, because equipment constantly pushes air through filters
The calculated value of the extraction power installed above the gas stove should be doubled. After all, the device must fully remove the products of combustion of blue fuel
The exhaust system for an electric cooking surface must be one and a half times more powerful than the calculated value. She needs to remove moisture to prevent breakdowns.
Airways without turns do not affect the calculated data, for example, with direct connection to a separate ventilation riser in a private house
The power of the exhaust unit connected to the duct requires an increase of 1.3 times, plus 10% for each turn of the system
The wider the duct, the lower the load on the hood. When connecting it to a pipe with a large cross section, multiply the rated power by 1.3
Estimated hood power for a small-sized kitchen with an area of less than 9 m² is increased 1.3 - 1.5 times, because smells and volatile fat spread faster in small rooms
Extraction hood with increased coverage
Recycling device in the kitchen
Exhaust installation over the gas stove
Hood over the electric hob
Ventchanal with access to the attic space
Ventilation duct with turns
Connecting the device to a wide channel
Installing hood in a small kitchen
Calculation procedure exhaust hood
To calculate the required hood performance, you need to know the parameters of the cooker.
In the calculation given below as an example, the characteristics of a gas stove from a Slovenian manufacturer Gorenje (model GI633E35WKB) are used. Note that the brand and model of the plate are chosen arbitrarily.
You may also find information about how hang the hood over the gas stoveconsidered in our other article.
No 10-time change of air in the kitchen hood can not perform. To calculate its power, you need to know the heat output and dimensions of the kitchen stove.
The calculations made below are performed by the method R NP ABOK 7.3-2007. Despite the “industrial” purpose of this method (ventilation of hot food service shops), its formulas can be used to calculate the parameters of a household hood for the kitchen.
When cooking, the stove produces heat that needs to be disposed of (exhaust). The heat dissipation of the plate forms convection air flows over it, which simplifies the operation of the exhaust hood. But it is impossible to completely eliminate the air pollution arising above the cooker, relying only on convection.
Stage # 1 - calculation of total heat output
To the exhaust hood or panel, volatile particles formed during cooking are delivered by convection air flow. It is the heat developed by the burners that provides air volumes for elimination. Therefore, it is required to calculate their total thermal power.
To define it, use the formula:
QT= q1+ q2+ q3+ q4,
Here q - nameplate thermal power of one burner, kW.
In the model of cooking stove, there are four gas burners on the surface, their heat capacities must be summed up.
We consider: QT= 1.9 + 1.9 + 1.0 + 3.5 = 8.3 kW. The obtained value of heat output is valid when cooking on all burners at the same time, which is rare.
The power of the kitchen hood is directly dependent on the thermal parameters of the stove. It burners form convection flow, which requires exhaust. Legend: Lo is air flow, A / B is the width and depth of the slab, h is the height of the slab, Z is the height from the stove to the exhaust, Qk is the total thermal power of the convective flow
In principle, it is possible to take into account the heat release of only three burners with the highest heat output. But let's leave it so - just in case.
To calculate the exhaust power, it is necessary to determine the air flow (Lo) according to the parameters of the stove. However, the air flow formula requires the calculation of intermediate parameters — the hydraulic diameter of the plate surface (D), air flow in a convective flow (Lki) and volumetric flow rate of combustion products (Lri).
Also in the process of calculations used coefficients developed by specialists of NP "ABOK". The values of the coefficients are chosen according to parameters suitable for domestic stoves.
Stage # 2 - Calculate Hydraulic Diameter and Flow
Let's calculate the hydraulic diameter and convective air flow. The first parameter is determined by the formula:
D = 2 * A * B / (A + B),
- A - width of the cooker, m;
- B - kitchen plate length, m.
Substitute the values of the width and length of the model of the gas stove, selected for the approximate calculation: D = 2 * 0.6 * 0.6 / (0.6 + 0.6) = 0.6 m.
In addition, the choice of power hood is associated with the upcoming location of the device. The more free space around the umbrella, the more powerful the hood must be. For a device located in a corner, a correction factor of 0.8 is introduced; for an “island” system, 1.1
To determine the volume of convective flow, it is necessary first to clarify the proportion of convective heat release of our stove. It is calculated using the formula:
Qk= QT* KI* KK,
- QT - the power of the plate determined above, kW;
- KI - a fraction of the apparent heat from the heat capacity of kitchen equipment. For a domestic cooker, the value 250 W / kW is assumed;
- KK - a fraction of the convective heat with respect to the apparent heat of the kitchen equipment. Accepts a value of 0.5.
Substitute numerical data in the formula, we consider: Qk= 8.3 * 250 * 0.5 = 1037.5 W. We move on and proceed to the calculation of convective air flow.
The formula is as follows:
Lki= k * Qk1/3* (z + 1.7 * D)5/3* r,
- k - coefficient obtained by NPO ABOK experimentally. It is assumed to be 5 · 10-3;
- Qk - calculated above the proportion of convective heat dissipation of the plate, W;
- z - the distance from the surface of the stove to the exhaust hood, m. The minimum distance for placing the hood vertically from the gas stove is 0.75 m;
- D - hydraulic diameter of the tile surface, m. The formula for its calculation and an example of calculation are presented above;
- r - correction factor, the value of which depends on the conditions of placement of the hood (see image table above). In our example, the position of the exhaust hood “near the wall” will be chosen, with a coefficient value of 0.75 (due to the conditional “proximity” of the cabinet furniture in the neighborhood, which is usually for kitchens).
Determine the convective flow rate, substituting numerical data in the formula:
Lki=5·10-3*1037,51/3*(0,75+1,7*0,6)5/3* 0.75 = 0.061 m3/with
As the results of the calculations show, the air flow due to convection over the cooker is quite intense. Given these data, it will turn out to choose a fair power exhaust system.
Stage # 3 - Calculation of exhaust hood power
In the process of cooking food, the electric cooker does not emit combustion products, since the heating of the burners takes place without open burning - thanks to the shadows. But the gas burners produce combustion products and the hood will have to remove them.
The formula for calculating the volumetric flow rate for methane combustion products:
Here QT - installed capacity of the cooker, kW. This parameter was previously found by us.
Enter its data in the formula and we get: Lri=3,75*10-7*8,3= 3,1125*10-6.
From the example it is clear that the value of the volumetric flow rate of the combustion products of a household gas stove is small. Therefore, when determining the parameters of the kitchen hood, it is permissible to neglect them.
The edges of the hood should go slightly beyond the plate boundaries. A - the width of the exhaust hood, B - the depth of the exhaust hood. A 100 mm overhang is sufficient to prevent the convection flow from the stove to mix with the atmosphere of the house.
So, it is the turn of the calculation of the air flow for our stove. This is the determining parameter when choosing a hood hood.
The formula for counting it:
Lo= Lki+ Lri,
- Lki - value of air flow from the convective flow ascending above the stove, m3/with;
- Lri - data on the volumetric consumption of products of combustion of natural gas in the burners of the stove, m3/with.
It remains to enter the data and calculate the required air flow rate with rounding the result to three decimal places: Lo=0,061+3,1125*10-6= 0.061 m3/with. We found air flow in cubic meters per second, but for the selection of a model of an exhaust hood, cubic meters per hour are needed (L).
To translate m3/ s in m3/ h should multiply the air flow rate obtained (Lo) on the number of seconds in one hour and on the hydraulic diameter of the plate (D) / L = 0.061 * 3600 * 0.6 = 131.76 m3/ h.
Thus, a sufficient maximum power of the exhaust hood for the Gorenje gas stove model, shown in the example, with rounding “in reserve” will be 150 m.3/ h Big power is simply not needed - empty power consumption.
Why a powerful hood "does not pull"?
First, you should check the condition of the ventilation channel in the exhaust device itself, remove and wash (or replace) the filters - fatty and, perhaps coalthat depends on the model of the hood. The best methods of cleaning the kitchen hood from fat considered in this article.
You also need to make sure that the ventilation unit is in good condition and that there is power supply to it.
Drafts may also interfere with the operation of the hood, preventing vertical movement of the convection air flow from the stove. If the problem of "weak" hood is not detected - its source is outside the kitchen.
Capacity of the exhaust hood depends on the cross-section of the ventilation channel, where the evaporation from the cooker goes. And homeowners often set an excessively powerful hood, or assign it an exaggerated mode of operation.
Residential property owners follow a simple logic - the stronger the fan draws, the better the volatile contaminants are removed from the stove.
This is not true. The performance and availability of a kitchen hood system directly depend on the throughput characteristics of the ventilation duct.
The output of the ventilation channel for the kitchen hood on the facade of the building will ensure the safety of traction in the ventilation duct. Mandatory installation of check valve and grid cover
For example, the ventilation channel of the supply and exhaust air exchange existing in the wall of the house is more than 150 m.3/ h of air, he can not bring.
Firstly, the cross section of such ventilation channels does not exceed 130-140 mm, which is not enough for mechanical ventilation. Secondly, the standard duct ventilation in high-rise buildings is long and contains multiple irregularities.
The manual for the ventilation unit usually contains a diagram showing the relationship between the pressure in the ventilation duct and the capacity. The increase in pressure causes a decrease in the performance of the hood.
Ventkanaly in houses collected clumsily: uneven walls; drip solution; narrowing due to shifted blocks; a lot of turns. Or at all - mine ventilation may be clogged. In such a situation without cleaning is not enough.
Attempts to set the increased performance of the ventilation hood connected to the house ventilation channel have the opposite effect.
The stronger the air flow, the more intensively it is prevented by defects in the section of the ventilation channel. And if the actively injected air cannot move forward, it moves backward.
A simple example is a soccer ball. The more air in such a ball to pump, the harder it is to operate the pump. The pressure becomes an obstacle - there is a lot of air; it tends to go back through the tube, pushing the pump handle.
The situation is similar with the increased power hood - the more intensively the air is supplied, the more blocked its work.
In addition to the correct selection of exhaust devices for the kitchen on the power it is important to choose the perfect place for its installation
The ideal ventilation duct under the kitchen hood is short, with a minimum of bends. Therefore, it is not necessary to remove air from the stove through the supply and exhaust duct, but according to the tailor-made air vent.
Hole in the facade wall, rigid or flexible duct (ideally circular), check valve and air intake at the exit channel. So you should equip the kitchen hood.
More arrangement exhaust valve through the wall We looked at the street in our other article.
Conclusions and useful video on the topic
The power, brand, design and principle of placement of the hood hood - sellers of kitchen appliances salons colorfully tell about all this.
From the video below, you will learn about the nuances of choice, not mentioned by sales staff. Hood models are distinguished not by design, but by the quality of assembly and configuration:
In the next video, the masters perform the drilling of a wall in a high-rise building under the air duct of an exhaust hood. Work is carried out by a professional tool quickly and accurately.
A ventilation channel is mounted to the prepared opening, which will be connected to the exhaust hood after finishing the kitchen:
Most videos about exhaust umbrellas for household use contain either advertisements or simplified information of their choice. Moreover, the procedure for calculating the power is not given anywhere - completely “kitchen volumes” and “10-fold renewal of the atmosphere.”
We are sure thatYou can balance the home atmosphere in the only way - by the correct calculation of air-cleaning equipment..
Does your kitchen hood do an excellent job of removing exhaust air? Share your power calculation experience. Or maybe instead of formulas and complex calculations, you used a simpler method? Tell us about it - leave your comments in the block below.