Calculation of ventilation
When choosing equipment for the ventilation system, the following parameters must be calculated:
Air performance; Califf power; Working pressure created by the fan; Air flow rate and air ducts area; Permissible noise level.
The following is a simplified methodology for selecting the main elements of the supply ventilation system used in domestic conditions
Full Pitch and Short Pitch Winding (Worked Example)
We deal with the general ventilation calculation
When performing aerodynamic calculation of air ducts, you are required to take into account all the characteristics of the ventilation mine (these characteristics are given below in the form of a list).
- Dynamic pressure (the formula is used to determine. DPE?/2 = p).
- The consumption of air masses (it is indicated by the letter L and is measured in cubic meters per hour).
- Pressure losses as a result of air friction on the internal walls (indicated by the letter R, measured in pascals per meter).
- The diameter of the air ducts (for calculating this indicator, the following formula is used: 2AB/(AB); in this formula, the values of the channel cross section are and measured in millimeters).
- Finally, speed is V, measured in meters in a second, which we have already mentioned earlier.
As for the sequence of actions during the calculation, it should look approximately as follows.
Step one. First, the required channel area should be determined, for which the formula below is used:
- F in this case, of course, is an area that is measured in square meters;
- VPEK is the desirable speed of air, which is measured in meters per second (for channels, a speed of 0.5-1.0 meters per second is taken, for mines-about 1.5 meters).
Step third. The next step is the determination of the corresponding diameter of the duct (indicated by the letter D).
Step fourth. Then the remaining indicators are determined: pressure (designated as p), speed (abbreviated V) and, therefore, a decrease (abbreviated R). To do this, use nomograms according to D and L, as well as the corresponding tables of coefficients.
Step Five using other tables of coefficients (we are talking about local resistance indicators), it is necessary to determine how much the exposure of the air will decrease due to the local resistance Z.
The sixth step. At the last stage of calculations, it is necessary to determine the total losses on each individual segment of the ventilation line.
Pay attention to one important point! So, if total losses are lower than existing pressure, then such a ventilation system can be considered effective. But if the losses exceed the pressure indicator, then the installation of a special throttle diaphragm in the ventilation system may be required
Thanks to this diaphragm, excess pressure will be extinguished.
We also note that if the ventilation system is calculated for maintenance of several rooms at once, for which the air pressure must be different, then during the calculations it is required to take into account the opening indicator or backbone, which must be added to the overall loss indicator.
Fan Laws How to Calculate CFM BHP SP RPM
And the effective functioning of ventilation, in turn, ensures the maximum comfort of your residence in the house.
An example of calculations. The conditions in this case are as follows: an administrative building, has three floors.
Although there are many programs for, many parameters are still determined by the old fashioned way, using the formulas. The calculation of the load on ventilation, area, power and parameters of individual elements is made after compiling the scheme and distribution of equipment.
This is a difficult task, which is only possible for professionals. But if it is necessary to calculate the area of some ventilation elements or a section of air ducts for a small cottage, it is really possible to cope on your own.
Recommendation 2.
In systems with a large duration of ducts and a large number of ventilation grilles, it is advisable to place a fan in the middle of the ventilation system. This solution has several advantages. On the one hand, pressure losses are reduced, and on the other hand, you can use smaller air ducts.
What else needs to be taken into account when choosing an exhaust fan
The equipment must meet the requirements:
Safety. the device works from electricity and is mounted in a damp room, it is recommended to choose devices with an increased level of moisture protection. The fan must withstand the effects of hot steam.
Noise indicators during the operation of the device should not exceed 35 dB marks. Otherwise, a strong hum will begin to annoy the household. There are times that the neighbors are also complaining about the noise from ventilation. Owners will have to establish noise insulation, and this is additional expenses.
The capacity of the device-the fan must provide a change in air flows 6-8 times in one hour.
To correctly choose an exhaust device, the instructions follow:
measure the diameter of the ventilation duct in the bathroom;
calculate the productivity of equipment;
selects optimal functions of the fan for convenience and according to the requirements of the room;
are determined with the manufacturer’s brand and the design of the device;
If you correctly calculate the power of an exhaust fan for the bathroom, then mold and fungus on the wall will not appear in the room, an unpleasant odor will not linger. When choosing equipment, take into account the design of the bathroom and electricity costs.
Aerodynamic parameters of fans
The application of the schedule of aerodynamic characteristics is a prerequisite and individual condition when choosing a ventilation system. The working point on such a graph will mean the efficiency and frequency of rotation of the working wheel of the mechanism. It can be determined by pressure and air flow. Preference is given to the fans with the largest indicator of the efficiency at a given value of pressure and air flow, while comparing the position of the working point.
How to calculate the desired power for the fan drive?
The desired power for the fan drive is directly related to the pressure of HB (PA), which is created by it, the volume of the moving air of QV, as well as the efficiency. The formula for the calculation will be as follows: NV = HV QV/1000 efficiency (kW); NV = 2200 Pa; QV = 6000/3600 = 1.67 m³/s.
How to calculate the power of the electric motor for the fan drive?
Type of power transmission of the electric motor from the engine shaft to the fan shaft parameter on which the power of the electric motor depends. It is customary to consider it in the calculation by the corresponding coefficient (kper). Lack of power loss when planting the fan wheel of the fan on the shaft of the electric motor means that the efficiency of this transmission will be 1. If you use a coupling to connect the fan and electric motor shafts, then the efficiency in this case will be 0.98. To get the desired rotation frequency of the fan of the fan, we use a cuneiform gear and then the efficiency will equalize 0.95. Losses in bearings are taken into account by a coefficient of 0.98. According to the formula used to calculate the power of the electric motor: NEL = NV / kper kp. The resulting power is taken into account with the stock coefficient. If the power is less than 5 kW, then it will be 1.15. With a power of more than 5 kW, it is 1.1. So, having calculated the necessary parameters, you can install which fan you will need. In the process of choice, you can ask any questions you are interested in to our managers. To familiarize yourself with the assortment and prices, use our site.
Description of calculations of the parameters of a blower machine
The calculation of the ventilation unit of any type is performed according to individual aerodynamic characteristics, the axial fan is not an exception. These characteristics:
- Volumetric consumption or performance.
- Efficiency.
- The power required to drive the unit.
- Actual pressure developed by the aggregate.
Productivity was determined earlier, when the calculation of the ventilation system itself was performed. The fan must provide it, so the value of the air flow remains unchanged for calculating. If the air temperature in the working area differs from the temperature of the air passing through the fan, then the performance should be counted by the formula:
- LN. necessary performance, m³/h;
- t is the temperature of the air passing through the fan, ° C;
- tr. air temperature in the working area of the room, ° C.
Exhaust ventilation in the kitchen
Thanks to exhaust kitchen ventilation, air exchange manages in the most problematic zones of the room. For example, improve the quality of air in the kitchen at the time of cooking. Not only the general well.being of people living here depends on the use of such structures, but also the condition of the walls in the living room. Technical standards recommended for SNiP when organizing ventilation:
This value should be multiplied by the area of the room to find out the set productivity of the ventilation system. It is precisely by the value that the device should be selected, with the corresponding electric motor. The installation of hood over the hob allows you to provide additional air exchange, preventing the spread of food aromas throughout housing. When connecting these elements, all components should be correctly selected, with equal sections.
With proper installation of the kitchen hood, a ventilation shaft is connected to an attached device. Thanks to this, the complete removal of harmful chemical compounds from the components formed at the time of cooking.
Exhaust ventilation in the kitchen
But external beauty is not the most important thing. The main task of this device is to save the kitchen premises from smells, burning, soot and fat that appear during cooking. Exhaust ventilation removes evaporation emanating from various kinds of heating devices. It prevents the appearance of dirty plaque on the ceiling and on the surface of the walls. This allows cosmetic repairs to be much less common, which will save a significant amount of money. Less time will need to carry out general cleaning.
A device that can pass through their filters a certain amount of air 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 desired power. How to calculate the power of the device?
Air flow or air performance
The design of the system begins with calculating the required performance by air measured in cubic meters per hour. This requires a poetry plan of rooms with explication, which indicates the names (purpose) of each room and its area.
The ventilation calculation begins with determining the required increase in air exchange, which shows how many times during one hour there is a complete change of air in the room. For example, for a room with an area of 50 square meters with a ceiling height of 3 meters (volume 150 cubic meters), two.time air exchange corresponds to 300 cubic meters per hour.
The required frequency of air exchange depends on the purpose of the room, the number of people located in it, the power of the heat alternating equipment and is determined by SNiP (construction standards and rules).
So, for most residential premises there is enough single air exchange, for office premises, 2-3 multiple air exchange is required.
But, we emphasize, this is not a rule. If this is an office room 100 square meters.m. And 50 people work in it (say the operating room), then to ensure ventilation, a supply of about 3000 m3/h is needed.
To determine the required performance, two values of air exchange must be calculated: by multiplicity and by the number of people. then choose a larger of these two values.
