In the case when the natural supply and exhaust air exchange system in a domestic or industrial building does not work with sufficient efficiency, forced circulation is organized. Various systems are used for this, but in most cases a roof fan is the most economical and productive solution. The device and classification of these devices will be discussed in the following article.
According to the principle of installation in the system, the roof fan can be:
- Channel - mounted at the outlet to a structure such as soft top, using a special exhaust pipe running through the building, or a ventilation duct
- Channelless - installed on the roofs of buildings, usually single-level, where there are large solid premises - gyms, shopping centers, entertainment venues
- Universal - having the ability to install in any of the systems
If there is a need for continuous circulation, the fan can operate continuously.
If the natural air exchange is insufficient at certain moments, at peak loads, then the device turns on as needed, in manual mode, and with the appropriate sensors installed, for example, the air temperature inside the building, automatically.
In appearance, roof fans of various models and manufacturers may differ, but they have the same basic diagram:
- The base on which the device is attached to the ventilation outlet
- Motor frame
- inlet pipe
- Protective mesh
- Working impeller
- protective cap
- Engine
The structural difference of this fan from other varieties is that it is installed as an end device, it removes the air flow directly to the environment, without using its temperature and flow pressure.
Any roof fans have a protective cap - it protects the internal parts of the mechanism from the effects of precipitation.
Also, all models are equipped with protective nets - they protect the device from strong gusts of wind and the ingress of various debris from flat roof.
If the exhaust air stream contains aggressive impurities, then the device is made of corrosion-resistant materials. There are separate modifications specially designed for the removal of hot air and smoke, as well as explosion-proof ones.
ADVICE! There are special models of fans designed to increase the draft of chimneys. If you install such a device on the smoke channel of a fireplace or gas boiler, the normal functioning of the heater is guaranteed during its operation. The disadvantage of such a system is in the consumption of electricity, and also in the fact that when the device is turned off, the traction will be worse than without it at all.
The base for installing the device corresponds to the shape of the ventilation duct and can be:
- Round
- square
- Rectangular
There is also the possibility of fastening through special adapters or mounting cups.
Devices are classified according to the direction of the ejected air:
- Down
- To the sides
- Up
- Up and down
Typically, a top-drawn roof fan is used to exhaust hot or polluted air. The disadvantage of this design is the possibility of precipitation entering the system when the unit is turned off.
To prevent this trouble, such devices are equipped with valves and blades that open when power is applied.
Their normal state is closed, therefore, when the device is turned off, the return current to the system is automatically blocked. The lateral discharge system also has its own problem - this is an increased sensitivity to wind loads.
It is solved by installing protective grilles of an improved design.
Some manufacturers also offer a solution to both problems with an outer cup that is hermetically mounted on top of the entire fan structure and is equipped with a check valve that allows air to pass only to the outside.
Since rooftop blowers are often installed on the roof above residential or office premises, important requirements are placed on the noise and vibration generated by the device.
To reduce the sound impact, the cases of some models are equipped with special mufflers: tubular at the outlet of the flow, and plate at its inlet.
For special requirements, the body itself is soundproofed with a special sound-absorbing padding. To reduce vibration, special shock absorbers are provided, and when installed under the mounts, elastic gaskets are installed.
The standard sizes of fan air wheel diameters are in the range of 200-1400 mm, since smaller dimensions will not allow the system to work efficiently, and with larger ones, noise and vibration cannot be compensated to comfortable values.
ADVICE! Most modern private households are equipped with double-glazed windows and other hermetic structures, as a result of which the normal air circulation in the premises may be disturbed. In some cases, roof ventilation will help solve the problem - but you should choose a system with protection against noise and vibration, in such conditions the lack of insulation will definitely manifest itself.
The performance of the fans in terms of the volume of exhaust air is determined by the following parameters:
- Wheel size (increases with wheel size)
- Motor power (affects the speed of rotation of the installed impeller, and hence the higher or lower flow rate)
- The angle of the blades (it is always directed towards the wheel travel, ranges from 25 to 90 °. A larger angle provides high performance, but at the same time - higher electricity consumption)
Among this class of devices, according to the principle of operation, the roof radial fan is confidently leading, sometimes it is also called centrifugal.
From time to time, attempts are made to place the engine inside the wind wheel, which allows to reduce the size of the structure. But the motor itself covers a significant part of the cross section of the air channel - so the question remains open.
As a rule, the only “freedom” that manufacturers allow themselves is the horizontal or vertical arrangement of the engine and impeller.
Also, air exhaust systems are divided according to the degree of controllability of operating modes.
They can be switched manually or automatically, and can be as follows:
- Unregulated - having only states "on" - "off"
- With a fixed speed - there are 2-3 speeds, with a toggle switch
- Variable RPM - engine and wheel speed smoothly changes according to the current load (Systemair specializes in these)
ADVICE! Many buildings now have separate exhaust and smoke ventilation systems. If the regulatory requirements of SNiPs and GOSTs allow, their ventilation ducts are often combined at the exit points. Since smoke protection is an element of fire safety, and is used only in emergency situations, it is inactive most of the time. However, it must be equipped accordingly.If you install a universal roof fan in the place of such a combined outlet, this will save significant funds, without compromising the performance of each of the systems.
The buyer, when choosing a fan for his residential or commercial property, should pay attention, first of all, to the following characteristics:
- Air volume
- Weight
- The presence of adjustment modes
- Noise level
There may be special requirements - such as explosion protection (for rooms with combustible vapors) or work in a maritime climate.
It should also not be forgotten that a high power radial roof fan is not the only solution to a performance problem.
After all, you can install several weaker devices on different ventilation ducts. The result will be greater system flexibility - if necessary, they will give the same volume, but when the load decreases, they can be turned on and off in the desired mode, including automatically.
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