# Duct fans for round ducts

The beginning of the narrative concerns the holiday: November 11 is the Day of saving energy. Got a video: duct fans were equipped with new EC motors, quiet and economical than AC.As the reader looks at the lines, having little understanding, so the authors see materials that forget to explain the details. It leads to disputes, incomprehensible moments. Portal VashTehnik clearly trying to figure out until the end of the little things. Let's start with asynchronous motors, smoothly move on to consider duct fans for round ducts.

## Definition of

A duct fan is built into the duct, forming an integral section. The first operation plan takes up the noise level, the device literally hangs in the air. Reducing sound pressure using asynchronous motors, an additional effect is achieved by choosing the method of adjusting the speed.

## Asynchronous motors

In the 19th century, one pundit hinted at a journal: three-phase AC motors have no prospects. In the same year, Nikola Tesla outlined the basics of device operation theoretically. Press statements were received by the call, a year later a certain Russian came up with a patent for the first three-phase motor. The unit is called asynchronous: the rotational speed does not coincide with the frequency of the feeding pulses. The formula for speed is as follows:

n =( 60 · f1 / p)( 1 - s), where

f1 is the frequency of the supply voltage;

p - the number of pole pairs of the motor coils;

s is the slip coefficient determined by the rotor parameters.

The three-phase motor is equipped with six coils, where the pulses of the desired phase and polarity are fed. Avoid considering, leave the electronics. There are half a dozen ways to control, the main - three, so there is a choice. Each choice raises doubts, makes it difficult to justify preferences. Regarding the latter, we note: it is used for asynchronous motors with a phase rotor, requires the inclusion in the winding of the last rheostat, which will lose some power, efficiency. However, the adjustment range can be significant.

The second method of VashTehnik portal seems to some other authors unpromising when it comes to smooth adjustment. The speed of rotation of the rotor of the asynchronous engine is graded by steps. For duct fans option, most of the way it works. It is recommended to use a thyristor voltage variator capable of giving three levels. Immediately make a reservation, the methods are different, the result is the same - a discrete change in speed.

A change in the number of pole pairs is assumed, the windings are divided into 3-6 coils, they can:

1. Work in phase or out of phase, creating the desired effect.
2. Power up in parallel instead of in series.

Not enough to disassemble the method in detail, applies to asynchronous motors with a squirrel cage rotor. Otherwise, the number of rotating windings would have to be changed. Not so much uncomfortable as problematic. In the case of a short-circuited rotor, the mass of the device increases, a couple of speeds cause titanic efforts from the side of the relay, contactors. It seems outdated.

It is much easier to change the frequency of the supply voltage. So eventually work invertor circuits. Microelectronics does not cost anything to make a network of 50 Hz ultrasound of a sufficiently large amplitude. Achieved smooth adjustment of speed, power. Easily provided by PWM devices( pulse width modulation).

According to science, it is necessary to feed an asynchronous motor with smoothed pulses, like a sinusoid cut off by a diode;Generators of rectangular pulses of the desired phase are used, driving the rotor. However, the noise is obtained. Apparently, the shape of the effect has. Dodged the topic. The parameters of the asynchronous motor are changed as follows:

1. Frequency - pulse repetition rate.
2. Power - pulse width( variation of duty ratio).

## Channel Fans and Asynchronous Motors

A long conversation about asynchronous motors in the topic of channel fans is caused by a number of reasons. One pundit in the video( Youtube) said: for the regulation of the rotational speed, it is better to use the triacistic CPM - 2.5.When it came to the details, it turned out that the frequency parameters of the centrifugal fan of the type Snail varied by variations in the voltage amplitude.

We list:

• first speed 100 V;
• second speed 160 V;
• third speed 220 V.

Honestly, I was surprised that I wanted to open the question in more detail. Why do we need in nature a centrifugal fan for the duct, which will react to every voltage instability by changing the speed? It turned out that the fact is that in practice there is a desire to use asynchronous motors with both a phase rotor and a short-circuited one. Methods of regulation of revolutions are different. However, there is one common.

It turned out the key is the change in the magnitude of the supply voltage. To release a universal regulator that is able to act on any fan in the duct, produced CPM - 2.5 and similar devices. The principle is to change the slip, denoted by S by the formula given above. Changing the frequency of the supply voltage is used mainly for asynchronous motors with a squirrel-cage rotor( dominated in industry).The method of changing the amplitude is suitable for both types.

However, we approve variable frequency inverter power supply circuits for a reason. Channel fans of rectangular ducts, other for round ones, demonstrate high efficiency.

. It is possible to change the number of pairs of poles, it will allow to achieve stepped regulation with increasing mass of the engine with a short-circuited rotor. The remaining methods reduce the efficiency. Single-phase motors do not have such high rates as three-phase ones. Why bother using an asynchronous machine? Cheap, reliable, easy to manufacture. Change the power scheme - a matter of technology.

## Origin of the name of the channel fan

The channel fan forms a pipeline segment. It is not mounted, like an axial one, on the kitchen grate, it is built in along the length of the path. For an apartment building is useless, for a private cottage - just a godsend.

Round duct fan:

1. You can install behind a fork to pull air into several rooms, saving equipment at the price.
2. Is placed away from the children's rooms, classrooms, does not interfere with work or sleep noise.
3. For maintenance, the fans for round ducts are removed from the fixing clamps, and then installed just as easily. Residents or employees will not even know that a repairman came to work in the attic.
4. It is permissible to install equipment anywhere in the path. Where operating conditions are optimal.

Powerless to provide any other type of fan. However, the channel equipment is not only round and axial, there are "snails", centrifugal models. Curiously look instances designed for installation on the wall of the series CFW( Shuft).Suppose W stands for Wall - Wall. CFW single-phase are of the following sizes:

1. Round duct fan 100 mm.
2. Round duct fan 125 mm.
3. Round duct fan 160 mm.
4. Round duct fan 200 mm.
5. Round duct fan 250 mm.
6. Round duct fan 315 mm.

In mm is the diameter of the duct for installation. Channel fans for round channels are seemingly rectangular in shape. Will mask near the ceiling under the elements of power structures. These are the ICF( Shuft) models with thermal insulation and sound insulation. The rotation of the blades does not place the servants, into the house is not put from the hand. The view is too office. There are 7 sizes up to 400 mm.

Flow duct plastic round fan of the Flow( Ballu Machine) series weighs less, cost is lower. Can only be operated indoors. Very quiet equipment. A volume of 16 - 19 dB is much better than a dishwasher. ABS plastic, deceptively fragile type, little susceptible to corrosion, not afraid of shock. The equipment is intended for hospitals, laboratories, and other premises that place increased demands on the level of noise. You can fearlessly put near children. The child will not hear the sound of work. For comparison, the noise level of a tightly closed room in a city apartment is 40 dB.

Duct round duct fans can be used to create your own hoods. Device performance is sufficient for the implementation of ideas. It remains to make an umbrella. The advantage is that by leaving the outlet in front of the fan, it is possible in one person to get the ventilation system. Device control methods discussed above. It is enough to buy a round channel fan, you can get down to business.

We wish you success Kulibin, say goodbye exactly until the next time!

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