Ventilation deflector: device, varieties, installation rules
A properly designed room ventilation system is the key to a healthy microclimate. One of the priority conditions for natural air circulation is the presence of traction. To normalize the pressure, a ventilation deflector is often used - the device enhances the intake from the ventilation duct due to the wind pressure.
Despite the simplicity of design and affordable price, such a cap significantly increases traction. The only difficulty is choosing the best option among the variety of offers.
We will help you sort this out. The article provides a detailed overview of the devices and principles of operation of various deflectors, provides practical recommendations for the selection and installation of caps.
To make it easier for you to decide on a model and understand the order of installation of the air “driver”, we have prepared a thematic photo and video selection.
The content of the article:
- The main tasks of the “ventilation hood”
- The scheme of the device and the principle of operation of the deflector
- Wind nozzle classification
- Browse Popular Models
- Nuances of mounting wind-driven hoods
- Conclusions and useful video on the topic
The main tasks of the “ventilation hood”
Efficiency ventilation systems with the natural impulse of air is largely determined by atmospheric conditions. Air flows circulate due to the lifting force arising due to the temperature difference inside and outside the room.
The wind also “corrects” the ventilation operation - it can both accelerate and impede natural air exchange.
Partially reduce the influence of weather factors, direct them to the benefit of the functioning of the ventilation system and increase air speed allows installation of a deflector. A module that resembles a cap is mounted at the top of the exhaust duct.
The deflector solves two main tasks:
- Protects the mine from clogging and bird entry.
- Minimizes the negative impact of precipitation on ventilation equipment.
- It activates and enhances traction, generating and redirecting wind flows - the efficiency of the ventilation system increases by 15-20%. The baffle reduces the likelihood of occurrence reverse thrust.
Umbrella design is used to increase traction in the chimney. Besides, chimney deflector additionally plays the role of a spark arrester.
The scheme of the device and the principle of operation of the deflector
To get an accurate idea of what a deflector is and how it functions, let’s take a look at a typical circuit of its device.
The main parts of the ventilation nozzle:
- Diffuser - base in the form of a truncated cone. The lower part of the cylindrical flask is mounted on the top of the ventilation duct discharged through the roof. It is in the diffuser that the airflow slows down and the pressure rises.
- Umbrella - The upper protective cap attached to the diffuser struts. The element prevents debris from entering the ventilation duct.
- Housing - ring or shell. The visible part of the deflector, connected to the diffuser by two or three brackets. The plane of the body cuts through the air flow and creates a region of reduced pressure inside the cylinder.
In some versions, a mesh is installed to detain small debris. The filter insert weakens the draft somewhat.
The action of the ventilation nozzle is based on the Bernoulli effect - the relationship between pressure and the flow velocity of the air flow in the channel. During acceleration, provoked by the narrowing of the duct, the pressure in the system drops, forming a vacuum in the pipeline.
Principle of operation:
- The baffle catches the wind.
- Air masses rush into the diffuser, branch and provoke a decrease in pressure at the top of the ventilation duct.
- Exhausted air from the room rushes into the discharged void.
With the right choice and installation of the deflector at the end of the exhaust duct, the pressure difference increases, and accordingly, the air exchange rate increases.
Wind nozzle classification
Despite the same purpose, exhaust hoods differ from each other.
Determining the optimal device model, it is necessary to evaluate:
- material of manufacture;
- principle of operation;
- design features.
Production material. The production uses aluminum, stainless steel, galvanization, copper, plastic and ceramics.
The best solution from the point of view of the balance “cost / quality” are steel and aluminum products. Copper deflectors are rarely used due to the high cost.
The symbiosis of strength and decorativeness - combined metal caps covered with plastic.
Principle of operation. Based on the functional features, ventilation devices are divided into 4 groups.
- static nozzles;
- rotary deflectors;
- static installations with an ejection fan;
- models with a rotary housing.
The first group includes models of the traditional type. Static deflectors are characterized by simplicity of design and the possibility of self-assembly. Valves are mounted on exhaust shafts of apartment and industrial aeration ducts.
The second group (rotary deflectors) is equipped with a system of rotating blades. The complex mechanism consists of an active head and a static base.
Static exhaust baffle with an ejection fan - modern technology. A fixed hood is installed at the end of the ventilation duct; a low-pressure axial fan is mounted directly under it inside the shaft.
Under normal environmental conditions, the system functions as a traditional static deflector. As the wind and thermal pressure decreases, the sensor is triggered - the axial fan is turned on and the draft is normalized.
An interesting development that deserves attention is an ejection-type deflector with a rotary body. A rotating cap is mounted above the shaft.
The model consists of horizontal and vertical pipes, which are interconnected by a swivel mechanism. At the top of the deflector there is a partition - a weather vane.
Design Features. Models with the same principle of inducing natural ventilation have some differences in the device.
Deflectors are open or closed, square or round, with one cap or several conical umbrellas. The characteristics of the most popular and effective modifications are described below.
Browse Popular Models
In practice, the following types have proven themselves well: Grigorovich, Volper, TsAGI, double and H-shaped deflector, rotary weather vane of the “Sachet” or “Hood” type.
View # 1 - Grigorovich's classic cap
The most common option used in ventilation and smoke exhaust systems.Because of its simplicity and accessibility, the Grigorovich deflector holds a leading position among analogues.
The device is represented by a pair of umbrellas connected in a single "plate".
The cap is mounted on circular pipelines or mounted through an adapter plate on rectangular and square shafts.
Thanks to the design, double ejection of air is carried out - in the direction of the expanded part of the diffuser and in the direction of the return hood.
The flow rate under the lower cone increases due to the narrowing of the channel section, as a result, the pressure difference increases.
View # 2 - TsAGI universal nozzle
The ventilation hood, designed by the Aerohydrodynamic Institute, enhances traction due to wind pressure and pressure differences at different heights.
The nozzle is complemented by a cylindrical screen, inside of which a prototype of a traditional deflector is placed.
- permissible bandage, rack, flange and nipple connection with the duct, depending on the shape of the neck of the mine;
- the ability to transport air, chemically non-aggressive environment (steel models withstand temperatures up to +800 ° C);
- in winter, ice may form on the inner walls of the cylinder, which can block the passage section.
The deflector is susceptible to wind currents - in calm weather it creates traction resistance.
View # 3 - Astato Static Dynamic Cap
Stato-mechanical deflector - development of a French company Astato. The device enhances the exhaust draft of the natural ventilation system due to wind and fan.
The nozzle is mounted on houses of any number of floors, reconstructed and new buildings.
After turning on the electric motor, the ventilation duct aerodynamics is maintained, the degree of vacuum is the total value of the fan head and pressure.
- Installation methods. Nipple connection for round ventilation ducts, through an adapter - for a group of ducts or shafts of rectangular cross section.
- Control modes. Manual control and automatic are permissible - by means of a pressure sensor, time switch.
- Production material - aluminum.
- The lineup. The Astato deflector is presented in six positions, with a nominal diameter of 16-50 cm.
Series Modifications DYN-Astato equipped with a two-speed fan, the cost of products - 1300-4000 cu depending on the dimensions of the deflector.
View # 4 - deflector series DS
The open-type static nozzle DS looks like an Astato deflector. But, unlike the French cap, the DS series models do not have moving parts.The cap has three conical shaped discs.
The highest speed of wind turbulence is observed in the truncated channel of the hood - above the ventilation pipe. The pressure difference inside the deflector and remotely from it causes an additional vacuum that increases traction.
Features of the DS series model:
- the deflector is compatible with forced means of inducing air exchange - fans;
- a wind speed of 5-10 m / s increases traction by 10-40 Pa - the data are relevant at a relative humidity of 50 °, air temperature +25 ° C and a deviation of the wind flow up to 30 ° from the horizontal plane.
Deflectors are available in 13 sizes. Designation of ventilation hoods: DS - ***where *** - inner diameter in mm. The minimum dimensions are the model DS-100, the maximum - DS-900.
View # 5 - rotary turbine or turbo deflector
The dynamic deflector consists of a fixed base and a rotating turbine head.
The elements of the spherical cap are made of light, thin metal, which allows the drum with blades to be put into operation with a slight wind - from 0.5 m / s.
Advantages of a turbo deflector:
- efficiency work 2-4 times higher than static models;
- room protection from overheating in the summer and lowering the costs of air conditioning in the heat;
- aesthetic appearance - the deflector head is made in the form of an elegant spherical cap;
- condensation prevention inside the roof by lowering the temperature in hot weather;
- profitability of work - The active deflector operates without electricity.
The turbo deflector draws excess heat, moisture, dust, vapors and harmful gases from the building and the roof space from the mine, thereby increasing the life of the structural elements of the house.
The disadvantage of an active deflector is zero productivity in calm weather.
Dynamic nozzles are available wide assortment. Demand is for the goods of companies: Aerotech (Russia), Turbovent (Ukraine), Rotowent (Poland) and Turbomax (Belarus).
View # 6 - rotary weather vane type "hood"
Swivel hood type "hood" or "net" - a semicircular rotating catcher of air flow, mounted on a rod.
Its curved visors are fastened to the bearing assembly. At the top of the hull is a weather vane, allowing the structure to follow the direction of the wind.
The principle of operation of the ventilation "hood":
- Under the pressure of the wind, the weather vane turns, being located along the line of air flow.
- Jets of air pass through the space between the curved visors.
- Streams change the vector and rush up.
- In this zone, according to the postulates of aerodynamics, the speed of air movement increases, and the pressure drops - a deep vacuum is formed.
- The draft from the ventilation shaft increases, providing additional exhaust air extraction.
A weather vane-deflector is more difficult for independent manufacture than static models. The nozzle is operational with a wind load of up to 0.8 kPa (not more than 800 kgf / sq.m).
View # 7 - H-type module
The H-shaped deflector is preferably mounted on manufacturing enterprises. Its purpose is to increase traction in the ventilation and chimney.
The design does not require the use of a visor, since the top of the duct is protected by a horizontal element.
The main advantage of the H-shaped hood is its operability with strong gusts of wind. For operation, the deflector is able to use the force of wind flows directed from the bottom up.
Nuances of mounting wind-driven hoods
When installing the deflector should be guided by the norms of SNiP.
The focus is on the height of the ventilation pipe and hood:
- from 500 mm above the roof parapet / ridge if the duct is 1.5 m or less from the top of the roof;
- flush with the ridge or higher, if the distance from the ventilation duct to the parapet is 1.5-3 m;
- not lower than the deviation line drawn at an angle of 10 ° from the ridge down, provided the distance of the pipe is more than 3 m.
On a flat roof, the deflector is installed at a height of 50 cm and above.
Additional installation nuances:
- installation in the field of aerodynamic shadow of neighboring buildings is unacceptable;
- the deflector is located in the free-blowing zone, optimally if the hood is the highest part of the roof.
The installation of a nozzle of circular cross section on a square duct is carried out through a transition pipe.
Requirements and installation methods of the deflector on the boiler chimney are described in this article.
Conclusions and useful video on the topic
Comparison of the characteristics of a rotary turbine and TsAGI model:
The principle of operation of the rotary vane-deflector:
Technology for installing a turbo deflector on a flat roof:
Such a simple device as a deflector can solve the common problem of natural ventilation - the lack of exhaust draft.
In addition to increasing the efficiency of air circulation, the hood has a protective role, preventing the ventilation duct from clogging with debris.
Have experience in installing and operating a ventilation deflector? Or have questions about the topic? Please share your opinion and leave comments. The feedback box is located below.