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The anatomy of a hood – which one to choose??

Young children often begin their technical cognition of the world with whatever is at hand – a new car or a doll. And very quickly losing interest in the “properties”, they are trying to get to know the “essence”, in other words, to find out what’s inside. Toys are disassembled and then reassembled, but with the newfound knowledge and a pile of “extra” parts . This approach has not left us indifferent, continuing the conversation about hoods, we also decided, after a deep dive into the subject of design, to look inside and understand the technical equipment.

A kitchen with an extractor hood

TO RECOIL OR FLY AROUND IN CIRCLES?

Hood design

The cooker hood has long been one of the most common attributes of the modern kitchen. Without it, cooking smells would spread unhindered around the house, but this appliance works as a “trap” for stove fumes and thus guarantees a comfortable living environment.

The hood is installed above the stove hob, it absorbs air flows coming from pots and pans and together with them pleasant and not so smells, a whole “bouquet” of different substances, microscopic drops of fat and soot. All of this mixture passes through a filter that separates the grease particles from it, which is why it’s called a grease trap.

The next stage can be implemented in two “scenarios”. According to the first one, the flow is led out of the kitchen into the ventilation shaft. This operation of the appliance is so called – recirculation.

According to the second one, the air is directed to another filter which is a carbon filter where all the rest of the dirt is adsorbed and then the air is blown back to the room.

This process is called recirculation. The word “recirculation” is Latin in origin. “Re” from re, i.e. repetitive action and “circulatio”, i.e. circular rotation. According to the “Great Soviet Encyclopedia” “repeated total or partial reversal of the flow of gases, liquids or solids in a process, installation, apparatus, etc.”.

Exhaust hoods can have a strict “specialization”, most often this applies to appliances designed to work in extraction mode. Most models can be used in either of two ways.

Two scenarios for the hood

Terms

Features

Maintenance

Recirculation

The presence of a separate ventilation hole

Fully harnessing the power of the hood.

Constantly updating the volume of air in the kitchen.

Cleaning or replacing the grease filters

Recirculation

No additional ventilation hole. Buying a set of activated charcoal filters and installing them

Reduced extraction performance because of the losses produced by the passage of the activated charcoal filters, hence the need to choose a more powerful extraction unit.

No renewable air volume and therefore no heat loss.

Easy to replace or clean grease filters and replacement of the charcoal filters.

WHAT’S INTO THERE

At first sight, the hood arrangement does not seem to be particularly complicated. Here are its main parts:

– turbine,

– sound attenuator,

– grease filter,

– air ducts,

– Anti-return valve,

– carbon filter,

– control system,

– illumination,

– casing.

LET’S DECOMPOSE THE “HEART” INTO TURBINE BLADES

Exhaust turbine or fan – this is the main working unit of the device, its “heart”. It creates the necessary pressure difference at the inlet and outlet, which ensures air suction. This unit itself is made up of a motor and the elements that it drives.

Fans differ in design, in addition, they redirect air flows through themselves in different ways, which defines their names: axial, radial, tangential.

Axial fans have an impeller – a wheel in a cylindrical casing with several blades. impeller is threaded directly on the motor axis at a slight angle . As the blades rotate, they catch the airflow and direct it along the axis of the fan.

Axial turbines are unobtrusive, so they can be installed even in the most compact of units. At the same time the efficiency of these devices is rather high.

The impeller is also the driving element in radial or centrifugal fans. It looks like a cylinder but it has blades instead of walls. They are attached to flat discs, and these in turn are threaded on the motor shaft through the hub. When the impeller rotates, the air moves radially from the center to the periphery and is compressed by centrifugal force. The fan casing is a spiral casing through which the air jet passes under pressure.

Turbine blades can be oriented forward or backward, each option has its own advantages. If the blades bent forward are used in the design, the size of the wheel will be smaller. Lower speeds are required for operation, and therefore the noise level will be more modest. But fans with backward-facing blades use less energy about 20% savings and are more forgiving of overloading.

Tangential turbines move air in the plane perpendicular to the axis of rotation. The wheel of these fans is almost the same as that of a radial fan with the blades curved forward. The housing is similar, but has a nozzle on the air inlet and a diffuser on the outlet. The spigot directs the air in, and the diffuser gives it acceleration, sets the direction of movement. But unlike radial suction, the suction takes place in the entire frontal area of the turbine rather than at the turbine end, resulting in a flat, even jet of air. Tangential blowers have compact dimensions, high efficiency.

HOW MUCH WE PUMP?

The turbine’s performance is an important indicator of its performance. This parameter shows how much air is pumped through the turbine per unit of time. measured in cubic meters per hour. For yourself, the required capacity is determined by the formula:

M=PxBx10+20%, M is the hood power, P is the kitchen area, B is the ceiling height, 10 is the coefficient corresponding to the SES norm for air renewal in kitchen rooms 10 times per hour , it is increased by 20%, for the air resistance tolerance.

Two figures are usually given in the technical specifications – extraction capacity with free outlet, i.e. without connecting a duct, and with a load in the form of an elbow rising up 30 cm and extending 1 m to the side. In recirculation mode, the power will be lower.

Kitchen hood

FILTERS WITH AND WITHOUT LOSS

The first obstacle to the intake air flow of a hood is the grease filters. It is an obligatory attribute of all air purifiers without exception.

In most devices you can easily see them – they are located on the border of the intake area. The perimeter suction models have the filters on the inside, behind a decorative panel. Like any obstacle, the filters will reduce the power of the hood.

Grease traps come in two types: disposable and permanent. Disposable ones are made of highly porous acrylic, fleecerin, synthetic. These can look like felt mats. Approximately every 1-2 months they need to be replaced with new ones.

Permanent or reusable filters are made of aluminum or steel. These are cassettes that have several perforated or mesh layers in their frames. The cassettes must be removed from the hood every 2-3 months and washed by hand or in the dishwasher.

Since filters require attention, their dimensions must be large enough for all user manipulations – taking out, washing, drying. That’s why the hood doesn’t only have one large filter cassette, but two or three, or even four.

The principle of operation of filters is very simple. The air is sucked inside the body by a turbine. It passes through the cassettes, where the flow is dispersed, “looking” into the numerous holes-cells, thin jets follow inside the filter, constantly changing its direction. As a result, thanks to this “ornate voyage” on the walls of the filter remain tiny droplets of grease, and the air purified from them rushes into the fan.

As you understand, metal cassettes can be a “great” source of noise. Therefore, engineers are looking for even simpler and more effective solutions. One of the already held, has become a grease collector – a container in which contaminants accumulate. The air stream in such a case is cleaned with the help of centrifugal force like in vacuum cleaners . It is important that there is no loss of power or additional noise.

THE CHIMNEY MUST COMPLY WITH THE PASSPORT DATA

If you follow the air flow inside the hood, its last and shortest “resting place” will be the air duct. The air stream rushes directly into the interior of the fan after the removal of impurities and then, by-passing the anti-return valve, exits through the drain pipe into the ventilation shaft.

The anti-return valve is a very useful thing, which is a kind of an air guard. It only lets air pass out of the kitchen and prevents it from flowing back in if the hood is not turned on.

Two factors are relevant to hood ducting – size and material. The efficiency of the whole appliance and the level of noise it makes largely depends on what the pipe is made of. Flexible corrugated pipes are affordable, but their numerous accordions reduce productivity because they create a resistance to the air flow.

Aluminium pipes filled with moving air make an unpleasant rustling noise. PVC ducts are the most suitable, they make almost no noise and their smooth surface does not affect the performance.

The cross-section of the pipe can be round or rectangular, it is important that the cross-sectional area of the pipe corresponds to the passport data, as it takes into account the capabilities of the motor. When the extractor hood works, it tends to extract a certain amount of air. Narrowing the duct will cause the appliance to need more power. As a result, the hood will constantly work at the limit of possibility, the noise produced by the device will increase, and most importantly the wear and tear of the motor.

When calculating the length of the ductwork, make sure that it is as short as possible and has as few bends as possible, because each bend reduces the hood capacity by 7 to 15%. The ideal length is no more than 5 meters, if there is one bend, it is already 3.8 m, and two – 2.6 m.

CHARCOAL FILTERS MUST BE REPLACED 4 TIMES A YEAR

In recirculation mode, the same amount of air returns to the kitchen as was sucked into the hood. For more thorough cleaning carbon filters are used. The air stream cleaned by the grease traps enters the turbine and the carbon filters are placed at the outlet of the turbine.

Their main and only working “agent” is activated carbon, which is one of the most affordable and effective absorbers. It absorbs very fine impurities: various chemical compounds, odors, smoke.

About 4 months of operation and all surfaces of charcoal grains are clogged – it’s time to change the filter for a new one.

Elica uses a long-life activated charcoal filter that lasts three years. Every few months it should be machine washed, oven dried, and ready to go again.

THE HOOD IS INVITED TO THE SMART HOME

The control system of any appliance is a kind of a way to find a common language between the user and the appliance. There are two types of hoods – mechanical and electronic. The mechanical one is either push-button, where the modes of operation are selected by pressing the desired button, it remains recessed when the function is activated, or slider – the selection is made by moving the slider to the right or left to the desired position. For convenience the panel may be equipped with indicator.

More varied and interesting control of the electronics. The function is achieved by means of pseudo sensor buttons when pressed, they rise to their initial position , touch sensors, remote controls and sensors that respond to light, heat and movement.

Electronic panels have backlit buttons including multi-colored , digital and text displays for displaying information about the work or special data time, contamination of filters, air temperature, humidity . Some models have a connection to the “smart home” system, can be equipped with a small screen to watch movies, and even have Internet access.

However, the most important and basic control task is to choose the speed of the machine. Most often set three speeds – the first – with the lowest noise level and optimal performance, it is used for slow removal of small dirt.

The second – with medium parameters, and the third – with maximum speed for emergencies. But sometimes there are more speeds – four or five, and even seven. The capacity for each is determined by the engineers in the design based on the size of the room. Another mandatory element of control is the inclusion of lighting.

ALWAYS LIGHT

The hood is sometimes called “the most expensive kitchen light”. After all, the lighting of the cooking area is an important part of its work. A variety of elements are used as light sources: incandescent, halogen, fluorescent, neon and fiber optic lamps. Lights are usually placed in a row along one or two edges of the hood. A model with lights all around the perimeter looks more interesting.

The lighting can also be controlled electronically. It is possible to change the intensity of the radiation, to focus it. With sensors, the light can turn on with a certain level of light and turn off automatically.

cooker hood in the kitchen

THE TECHNOLOGY IS ON THE INSIDE, THE DESIGN IS ON THE OUTSIDE

All of the above “household” described above is placed inside the body of the appliance. It is a supporting structure for the turbine, the grease filters are mounted on it, the control unit is installed on the front or side panel, the bottom is the location of the light bulbs.

The body is made of plastic or metal. The most popular metals are stainless steel and aluminum, in expensive models copper and brass are used. Functional and decorative elements are made of glass modern design , wood rustic and polymers.

DID WE MAKE ANY NOISE?

The noise produced by the hood is one of the most important annoying factors, so it is always in the focus of the designers’ attention.

The first “supplier” of sounds of the appliance is the fan, it is possible to reduce its noisiness:

– Structurally, that is, by choosing the best type of fan device and the motor itself. For example, motors with hermetic winding and there are also open and semi-hermetic ones and special bearings that work almost silently. Fan impellers made of metal, easier to achieve balance – another factor.

Less vibration and therefore less noise produced by compact turbines. Other design solutions include an alternative air intake system around the perimeter of the intake area. The air is not drawn in through the entire surface of the housing, but through narrow slots, and the flow velocity inside the housing increases, which gives a higher output, but at a lower noise level.

There is another very witty option – using not one but two powerful units. With a combined output exceeding that of a single fan, they can reliably remove or purify air at lower speeds, plus they each produce far less noise.

– by choosing “quieter” materials, such as aluminum alloys.

– Due to the use of noise absorbers, i.e. special boxes for fans and special vibration absorbing gaskets that close the gap between the turbine and the hood body.

cooker hood in the kitchen

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John Techno

Greetings, everyone! I am John Techno, and my expedition in the realm of household appliances has been a thrilling adventure spanning over 30 years. What began as a curiosity about the mechanics of these everyday marvels transformed into a fulfilling career journey.

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Comments: 4
  1. Giselle

    When it comes to choosing a hood, the options seem endless! But what factors should we consider? Is it the type of hood, the material, or the size that matters most? What are the pros and cons of each? It would be great to hear your insights and recommendations for selecting the perfect hood that suits our individual needs.

    Reply
  2. Juniper

    When it comes to selecting a hood, the variety of options can be overwhelming. So, which one is the right choice for you? What factors should be considered – style, material, or functionality? Could you please share any tips or recommendations to help us navigate through the intricacies of hood selection?

    Reply
  3. Samuel Foster

    Hi there! I’m curious to know about the different types of hoods available. Could you help me understand the anatomy of a hood and advise me on how to choose the right one? I’d appreciate any insights or recommendations you can provide. Thanks!

    Reply
    1. Juniper

      Sure! Hoods come in various styles such as under-cabinet, wall-mounted, island, and downdraft hoods. The anatomy of a hood usually consists of a fan, filter, and ductwork to remove smoke, odors, and grease from your kitchen. When choosing a hood, consider the size of your kitchen, the amount of cooking you do, and the layout of your stove. Make sure to check the CFM (cubic feet per minute) rating to ensure adequate ventilation. Also, consider the noise level, lighting options, and design to complement your kitchen. I hope this helps you choose the right hood for your kitchen!

      Reply
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