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How to choose a fan?

Views: 24     Author: belmont     Publish Time: 2023-04-28      Origin: https://www.belmont-tech.com/


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How to choose a fan?

In the fan application, the correct selection of the fan is essential, it requires us to use some basic knowledge of simple, fast and accurate selection to meet the conditions of use of the fan. Fan selection, in addition to meeting the requirements of its flow, wind pressure, but also to ensure that the fan can operate economically and safely. The following fan selection issues for the fan to make a detailed explanation.

We should first be clear: the five elements affecting the selection of fans:

1. air volume, air pressure

2. Use of working conditions

3. The composition of the exhaust gas

4. Installation location, installation form

5. Accessories, noise and other requirements.

I. Fan air volume is defined as the product of wind speed V and duct cross-sectional area F.

Large fans can accurately measure the wind speed with anemometers, so the air volume calculation is also very simple, directly with the formula Q = VF, you can calculate the air volume.

The number of fans need to determine the number of air changes in the selected room, calculate the total air volume required for the plant, and then calculate the number of fans.

Calculation formula: N = V × n / Q where: N - the number of fans (units); V - site volume (m3); n - the number of air changes (times / hour); Q --the single air volume of the selected fan model (m3/h).

The choice of fan model should be based on the actual situation of the plant, try to select the fan model matching the original window size, the fan and the wet curtain try to maintain a certain distance (as far as possible, respectively, installed in the plant on both sides of the mountain wall), to achieve good ventilation and air exchange effect. Exhaust side as far as possible not close to nearby buildings, to prevent the impact of nearby households. Fan wind pressure: refers to the resistance to be overcome in the process of conveying so much air volume, referring to the pressure rise.

However, the domestic fan selection is generally according to the full pressure, foreign countries are generally according to the pressure rise. Outside the machine residual pressure = fan full pressure - wind cabinet resistance of each processing section, air supply and return ducts generally according to 7 ~ 8Pa / m, 90 degree elbow according to 10Pa / one to calculate the resistance.

Empirical formula: Outside the machine residual pressure = fan full pressure - each processing section resistance fan power (W) = air volume (L / S) * wind pressure (Kpa) / efficiency (75%) / force rate (75%) full pressure = static pressure + dynamic pressure.

Fan motor power (W) = fan power (W) * 130% = air volume (L/S) * wind pressure (Kpa) / efficiency (75%) / force rate (75%) * 130%

II. What are the differences in the selection of fans for different occasions?

1. Need to exhaust heat or exhaust hot steam, should try to set the roof exhaust fan as a priority.

2. Need to heating, cooling or sending fresh air, should try to let the warm airflow or cold airflow flow through the staff location, so more duct fans or sidewall fans.

3. Fire smoke exhaust, should take priority to the roof fan or suspended duct, so more duct fans.

Note: Try to use the natural wind airflow (fan location and form should be set reasonably) specific occasion fan selection

1. Warehouse ventilation

(1) to see whether the storage goods are flammable and explosive goods, such as: paint warehouses, etc., must choose explosion-proof series fans.

(2) look at the noise requirements of high and low, you can choose the roof fan or environmental protection centrifugal fan. 3) look at the size of the required air exchange in the warehouse, you can choose the most conventional axial fan SF type or exhaust fan FA type.

2. Kitchen exhaust air

(1) For kitchens with direct indoor fumes (i.e., the exhaust vent is on the indoor wall), you can choose SF type axial flow fan or FA type exhaust fan according to the size of fumes.

(2) For kitchens with large fumes, and fumes need to go through long pipes, and pipes with bending treatment, it is highly recommended to use centrifugal fans, because the pressure of centrifugal fans is larger than axial fans, and fumes do not go through the motor, so it is easier to maintain and change the motor.

(3) It is recommended that the kitchen with strong fumes choose the above two options and use, the effect is better. 3. High-grade places ventilation. For hotels, tea houses, coffee bars, chess rooms, karaoke halls and other high-grade places ventilation, it is not suitable to use conventional fans.

(1) for the ventilation of small rooms, so that ventilation pipes connected to the central ventilation pipe room, you can take into account the appearance and noise based on the choice of small axial fans, small size, plastic or aluminum appearance, low noise and high air volume coexist.

(2) air volume and noise requirements more stringent perspective, said the fan box is the best choice. Box internal silencing cotton, external central ventilation ducts can be achieved after the significant effect of noise reduction.

(3) To add, for the indoor air blowing in the gym, it is necessary to choose the large air volume industrial electric fan, rather than SF type post axial flow fan. This is from the appearance and safety considerations.

Third, what kind of working environment is the fan in? What kind of gas is discharged?

Need to determine whether the fan is used for ordinary room temperature clean gas exhaust, process exhaust, or fire exhaust, explosion-proof exhaust, anti-corrosion exhaust, kitchen exhaust fumes, etc.

1. Ordinary exhaust: no special requirements for the fan, as long as the design conditions and customer requirements can be met. But the speed of the fan should generally be controlled below 1500rpm, because the speed is too high, the fan and its components will be easily damaged, such as bearings and shafts, belts and pulleys wear out in advance, leading to frequent replacement of parts, raising maintenance costs.

2. Process exhaust: there are many kinds, some of which may contain welding slag, paint, explosive gases, sometimes need to be resistant to high temperatures, exhaust fumes, etc.; different components have different treatment methods and different requirements for fans.

(1) gas with welding slag: welding workshop or down shop exhaust, usually to take into account the exhaust gas contains impurities such as metal chips and welding slag; to add filters, and the motor can not be built-in. These impurities, if they enter the fan, may scratch and wear the bearing belt and other accessories, more serious will damage the motor, resulting in motor scrap. So require the addition of primary filter aluminum mesh (filter particles greater than one millimeter in diameter), and the motor is external (to prevent metal chips into the motor)

(2) gas containing paint: most of them should be added to the filter, with explosion-proof fan, with explosion-proof motor, shaft seal, and external motor; paint contains volatile organic solvents, is flammable and explosive gases, if encountered with open flame, such as electric sparks may cause an explosion. Therefore, the requirement that the fan explosion-proof;

(3) exhaust gas containing explosive gases or explosive dust: must be equipped with explosion-proof fans and explosion-proof motors;

(4) the exhaust gas contains corrosive gas: first of all, we must be clear what corrosive gas, what kind of composition, if it is acid and alkali, choose FRP (glass fiber reinforced plastic material) or plastic material; if it is a medium corrosive, stainless steel; if it is weak acid and alkali exhaust or corrosive gas content in the air is relatively low, it can be achieved through the method of anti-corrosion coating on the impeller, single-layer coating can achieve 10 Micron, double coating can reach about 20 microns.

3. Fire exhaust: you should choose the fan that has passed the national fire certification.

4. Exhaust fumes: you should choose the type of fan that has done non-stick coating of the impeller and can collect oil droplets for easy cleaning.

Fourth, how is the fan installed?

The installation position of the fan is different, the selected model is also different. Common forms of installation are: roof installation, side wall installation, hanging ducts, etc. If installed on the roof of the steel frame structure, then you should choose a lighter all-aluminum roof fan, which can save the cost of the roof to do to strengthen, if the side wall installation, you should advise customers to match the rain cover, check the air valve and insect net and other accessories.

Fifth, is not the fan selection, the less noise the better?

With the normal operation of the fan, the noise cannot be eliminated. The latest research shows that as long as the wind speed exceeds 0.75m/s, noise will be generated. Of course, the lower the wind speed, the less noise generated. Noise is harmful pollution. In our design, we always try to reduce the noise of fan equipment as much as possible. With the development of fan technology, the noise pollution that we can do is getting smaller and smaller. So is it the fan selection, the less noise the better?

The noise is certainly good, but must take into account its economy. The lower the required noise, the higher the cost of the required fan. Approximately every 10 decibels reduction, fan costs rise by a factor of 1 (empirical value, non-linear). Most of the fan noise is unlikely to be less than 35 dBA, so when choosing a fan, it is not necessary to pursue low noise, in their own acceptable reasonable range can be.