How does recirculation hood work + typical ventilation schemes with air recirculation

Whereas when using a flow hood, dirty air leaves the room through an air duct, the exhaust hood with recirculation has a completely different principle of operation.

Here, there is no such element as the air duct, and the device itself is equipped with efficient filter-catchers. When passing through them, the air is freed from all harmful trace impurities and unwanted odor, and then re-injected into the room.

How the recirculation hood works

Exhaust recirculation type operates in a closed loop. In fact, the exhaust device can be called only conditionally, since it does not remove air from the room, but only cleans it and returns it back. Contaminated air enters the enclosure of the device under the influence of thrust generated by the blades of the fan, which rotates in the horizontal plane to the surface with a cooking stove.

Moving along a given trajectory, the air mass collides with the coarse filter. After passing through it, it leaves fatty inclusions, particles of soot and dust on its thin-mesh surface.

Ventilation work
An exhaust hood of this type will help out when the ventilation system at home is not working at full capacity or the ventilation channels are so clogged that there is no traction in them.

Further, the air flow under the influence of pressure passes through the fine filter, where it gets rid of odors and residues of the smallest parts, then returns to the room. This filter is an ordinary cartridge, the filler of which is granulated carbon. The carbon filter is a disposable item, so as it becomes soiled it should be replaced.

Since this type of hood does not interact with the ventilation system, designers have developed telescopic hoods. When working, they create a powerful side thrust, due to which all the dirty air masses are sucked. As soon as the need for this disappears, the device hides in the tabletop. This solution is not only original, but also very convenient.

Positive and negative points

Despite the fact that filtering hoods have a small performance, they have many advantages. These include:

  • ease of installation and operation;
  • unlimited choice of plate placement, because ventilation shaft is not needed for this;
  • easy care

Disadvantages of these exhaust devices are also available. This is a small efficiency - up to 70%, the need for frequent replacement of disposable filters - 3-4 times in 24 months. The hood does not affect the level of humidity in the room. The electric device in the on state creates a certain noise.

retractable hood
Small compact hoods are becoming increasingly popular because they save space. You can install this design anywhere.

Extracts of the latest releases, as a rule, can work in the mode of removing air masses, and as recirculation. Such a device must have a connection to the ventilation shaft. Since the autonomous exhaust does not supply fresh air, after it is turned off, the room must be ventilated.

Types of autonomous hoods

Depending on the fastening system, exhaust hoods with recirculation can be flat, mounted above the slab and having low productivity.There are built-in hoods that are integrated into the furniture elements placed above the cooking surface. They are compact and have more performance than the first.

Suspended hoods are placed under kitchen cabinets. In this category there is a slider options with a working surface moving forward. At a certain angle to the mounting surface have angular hoods. They are ergonomic, convenient in operation, high-performance, have a low noise level.

Hood selection
Flat hood - a classic version. They are well suited to any interior, are inexpensive, have a large product range.

At the place of installation hoods are divided into wall, corner, island. The first are used to complete the zones located near the wall, the second - at the junction of the walls. Island - ideal for spacious kitchen facilities.

Features of the choice of hood

Basically, the hood is chosen for parameters such as depth and width. They are determined by the dimensions of the hob. Ideally, the unit should be wider than the plate by a few centimeters. This has a positive effect on the efficiency of the collection of waste air mass.

Different models of autonomous hoods differ in a set of functions. The more of them, the more expensive appliances. Manufacturers equip them with electronic panels with displays for more convenient control and monitoring of the device. Sometimes there are programmable timers, sensors that automatically turn on the fan when the humidity and temperature values ​​change.

Special sensors can independently adjust the performance of the hood. The presence of the remote control in the kit allows you to start and shut down the unit without direct contact. When choosing, it is necessary to strive to ensure that the functional of the model maximally meets specific requirements. Paying for unclaimed functions is irrational.

Filters for exhaust with recycling

So high quality will be recycled air, depending on the number of filters in it. The most recent models of hoods are equipped with two types of filters. The first, made of metal (aluminum or stainless steel), is called fat. Its purpose is rough cleaning. As a necessary minimum, it is always in the complete set of the unit.Without it, any engine simply could not function.

Fat filter
The metal fat filter is similar to a cassette. It includes a metal frame and the filter itself. The perforation of the filter element is asymmetric and symmetrical

The metal fat filter is similar to a cassette. It includes a metal frame and the filter itself. The perforation of the filter element is asymmetric and symmetrical. Caring for him is a periodic cleaning with household chemicals. Attach it to the outside of the cleaning appliance. It can be both disposable and reusable. The effectiveness of the work depends on the shape and size of the grid cells.

For the fat follows the second filter - coal. It cleans the air that has passed through the first filter, depriving it of odors. These filters are not cleaned; when clogged, they are simply changed to new ones. That the time has come to change the filters of the second type is indicated by special sensors. They are sure to equip their new model manufacturers. Additional filters that provide finer cleaning are:

  1. Acrylic, intended for reusable use.They have a very delicate structure, so they must be washed by hand and in no case be squeezed, otherwise the fibers will change their original position.
  2. In the form of disposable liners - sinteponovye, paper or non-woven. When the pattern on them is not visible because of the layer of dirt, they are replaced with new ones.
  3. Coal endowed with absorbent property. They are much denser than the first two, well hold odors.

The first three are used in economy class hoods, called flat. Visually, these filters resemble a lightweight rug. Although some housewives wash them and then reuse them, this procedure does not return the synthetic material to its original properties. The quality of air purification after that decreases.

Coal filter
The carbon filter, the basis of which is an absorbent such as activated carbon, well absorbs and holds harmful substances

The density of coal filters is different. As it fills, the air passes through it more and more slowly, so it is necessary to change the cartridges in a timely manner. Usually they are not included in the hood.

To prolong the duration of their use, it is necessary after use of the hood to leave it in the on state for another five minutes. This short time is enough to remove the residual moisture from the filter, contributing to the caking of the coal and a decrease in its adsorption capacity.

The frequency of replacing cassettes with fine filters depends on how intensively the technique is used. Usually, the instructions that manufacturers attach to the product specify the frequency of such a replacement. When choosing filters for your recirculation hood, you should definitely check the parameters of the slots for cassettes. If their sizes do not match, they either fail to be inserted correctly, or gaps are formed, which is unacceptable.

If the hood is used occasionally, universal filters can be applied. They are made of polyester and impregnated with activated carbon. The fabric is able to absorb both fat and odors.

How to replace the carbon filter

If the term of use of the coal filter has expired, its replacement is necessary. To do this, the exhaust device is disconnected from the mains, otherwise the motor may accidentally turn on spontaneously.Next, remove the grease filters and remove the cartridge from the body with the failed carbon filter.

Carbon filter change
Replacing the carbon filter, you need to check the hood for the absence of vibration and extraneous noise. If the installation is incorrect or the cassette is loose, such a phenomenon is inevitable.

A new filter is inserted into the cassette, then the latter is closed and placed in the appropriate place on the hood. On the correct operation performed shows a characteristic click. After this, the coarse filter is returned to its place, the device is connected to the mains and its operability is checked.

As a rule, the manufacturer applies the installation instructions to the carbon filters. If the body of the carbon element is designed so that it can be opened, this means that it is possible to replace its contents - replacing the spent granules with new ones.

Washing the grease filter

In order to wash the grease filter, it is removed from the device. The pelvis is filled with water, add the tool used to remove fat. After take a stiff brush and perform the cleaning of fat deposits and soot.

If this method was ineffective, you should soak the filter in a solution consisting of soap and soda for 3 hours. After soaking, clean the filter, dry it and put it in place.

Top Filter Samples

Grease filters are manufactured by many manufacturers. Among the best is the Russian enterprise Lissant-Yug. Here produce non-separable cassettes of stainless steel or galvanized steel. A five-plate filter withstands temperatures up to 70⁰.

Modern hood
Modern hoods with recirculation are equipped with several functions: mode switching, sensors indicating that it is time to change the filters. There are sensors that automatically turn the engine on and off

Stainless steel filters are manufactured by Titan. The temperature of the working environment for them is 70⁰С. Product thickness - 0.5 mm. Up to 80⁰С - limiting temperature for filters made of galvanized material or stainless steel, produced by the manufacturer ROVEN. Element includes from three to five plates. The best samples of carbon filters include elements produced by such well-known manufacturers as Electrolux, Gorenje, Folter, Hansa, Krona.

Ventilation with recirculation function

The concept of ventilation with recirculation of air means that the process is carried out with the return of all or part of the air removed from the room with possible mixing of air coming from outside. In what ratio the air masses are mixed, determines the design decision, taking into account the specific circumstances.

Ventilation scheme with recirculation

Supply and exhaust ventilation with recirculation works according to a specific scheme. In the room through the mine enters the air from the street. After some time, it draws a hood. A part of this air mass is thrown out, and the rest goes to the mixing chamber, where it mixes with the new influx.

Depending on how the system is set up, the air entering the chamber is heated or cooled. Further his way - air conditioning or heater and return to the room.

Full recycling
When a ventilating system with full recirculation is set up, the entire volume of air drawn from the room passes through filtration and enters again.

Recycling significantly reduces the load on systems designed to handle air masses.The air will always have indicators that make it suitable for breathing, if two main conditions are met:

  1. The minimum volume of air coming in from the street is 10% of the volume processed by the air handling unit per unit of time.
  2. In the air mass entering the room, is 30% of the permissible concentration of harmful impurities as a maximum.

With the participation of recycling, the system operates with a constant flow of thermal energy, as well as a constant speed of transported air flow, regardless of the time of year. This fact is a guarantee that the air entering the room will be evenly distributed throughout the volume.

Options for the implementation of schemes

There are various options for the implementation of ventilation schemes with recycling. This is recirculation with the help of a fan installed under the ceiling of the room, and through the ceiling channel, and through the central air supply unit. Air exchange in the first way can only conditionally be called recirculation.

There is no heat exchanger here, and if you connect it to a fan and separate them into a separate unit, you will get a fan coil or a fan closer.In the heat exchanger, in this case, the recirculated air is cooled or heated. Outdoor air is supplied separately and has its own individual parameters.

Removal of harmful substances occurs only through the outside air. Fan coils in ventilation systems are not often used, because they do not ventilate the room, but only affect the internal temperature.

Localized heat transfer
Such a device as a fan provides a localized heat exchange. There is equipment working on the exhaust and removal of exhaust air, but there are also units that work on the influx

When recycling the second option, through the ceiling channel, the length of the ducts is negligible. Sometimes a heat exchanger and a fan are placed in the channel. This is the standard scheme for air conditioners that have a channel indoor unit and are used in rooms with medium and small volume.

If in the main air handling unit with recirculation before the heater to close the valve that lets air through the outside, you get full recycling. The ventilation system in this case is used as air heating. The blocks inside the split air conditioners and fan coil units often have a design that makes it possible to blend in the outside air.

At the same time, the air flow with the required temperature gets into the room through one air distributor. Air conditioning installations are arranged according to this principle. For large rooms, this scheme is not suitable, because there is a small capacity, there is no mixing chamber, automatic equipment and there is no heat utilization.

Recirculation system layout
The recirculation system installation in the ventilation system consists of an inlet valve (1), a mixing section (2), an air filter (3), a heating calyx (4), a supply fan (5), a recirculation valve (6), an exhaust valve (7) , recirculation section on exhaust (8), exhaust fan (9)

Ventilation of large enough rooms is carried out with the use of large-scale central installations, including a large set of equipment. The recirculation scheme used for this purpose ensures economical operation by means of flexible system management. Maintaining the right ratio of external and exhaust air is carried out by means of valves.

When the recirculation valve is closed and there is no open exhaust and flow recirculation. If you close the last two valves and open the first one, there is complete recycling.

Disposable ventilation with recirculation

The use of air recirculation limits the SNiP 41-01-2003. It does not allow its use from rooms where substances of 1-2 classes of hazard are released and the flow of street air is governed by their mass.

Recycling should not be used where the concentration of fungi and bacteria in the air exceeds the norm or there are clearly pronounced unpleasant odors. Laboratory rooms where they work with flammable or hazardous gases are not suitable for recycling.

Conclusions and useful video on the topic

Video of the flat kitchen hood:

About installation of the carbon filter in the kitchen hood:

Air recirculation hoods prevent their connection to the ventilation shaft. With the help of integrated filters, they effectively clean the exhaust air. In this case, it is necessary to replenish the supply of fresh air in the room through the vents.

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