Exhaust with recirculation: exhaust device and ventilation

Whereas when using a flow hood, dirty air escapes from 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 undesirable odor, and then re-enters the room.

In this material we will talk about the principles of operation of such equipment, we will designate the subtleties of choice and the ventilation arrangement scheme.

How does recirculation hood work?

Exhaust recirculation type works in a closed loop. In fact, the exhaust device can only be called 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 cooker.

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.

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 one-time product, therefore, as it becomes soiled, it must 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 the filter hood has 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

Cons 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.

The hoods of the latest releases, as a rule, can work in the mode of removing air masses, and as recirculation. Such a device must have 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 are flat, mounted above the slab and having low productivity. There are built-in hoodsand integrated into the furniture elements placed above the hob. 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.

According to 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 changes.

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 model maximally meets specific requirements. Paying for unclaimed functions is irrational.

Filters for exhaust with recycling

So high quality will be recycling air depends on the number of filters in it. The models of the latest issue 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.

The fat filter made of metal resembles 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.

Read more about fat filters in this material.

For the fat follows a 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 models with manufacturers.

Additional filters that provide finer cleaning are:

1. Acrylic, intended for reusable use. They have a very delicate structure, so they need to be washed by hand and in no case be pressed, 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 unpleasant odors.

The first three are used in economy class hoods, called flat. Visually, these filters resemble a lightweight mat. 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.

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

To extend the duration of the use of carbon filters, after using the hood, it is necessary 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 the sizes do not match, they either fail to insert 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 use of the coal filter has expired, its replacement is necessary. To do this, the exhaust device is disconnected from the electrical network, otherwise the motor may accidentally turn on spontaneously.

Next, dismantle the grease filters and remove the cartridge from the case with the failed carbon filter.

A new filter is inserted into the cassette, then the latter is closed and placed in the appropriate place on the hood. A well-executed operation is indicated by a characteristic click. After this, the coarse filter is returned to its place, the device is connected to the power grid 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 carry out cleaning from 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 the filter is cleaned, dried and put into 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.

Stainless steel filters are manufactured by Titan. The working environment temperature for them is 70 70С. Product thickness - 0.5 mm. Up to 80 ⁰С - 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 famous manufacturers as Electrolux, Gorenje, Folter, Hansa, Krona.

Ventilation with recirculation function

The very concept of ventilation with air recirculation means that the process is carried out with the return all or part of the air removed from the room with the possible addition of air to it 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. Part of this air mass is thrown out, and the residue goes into 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.

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 using 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. In ventilation systems fan coils not often used, because they do not ventilate the room, but only affect the internal temperature.

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 with a channel indoor unit and 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 allows air through the outside, you get full recycling. In this case, the ventilation system 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 little power, there is no mixing chamber, automatic equipment and there is no heat utilization.

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 desired 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.

Disadvantages of ventilation with recycling

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 outdoor 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 expressed 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 installing a 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.

Perhaps you have experience using recirculating hoods? Tell us what device you are using and are you satisfied with its work? Please leave your comments at the bottom of the article.