Recovery(from Latin recuperatio - “return receipt”) - the return of part of materials or energy for reuse in the same technological process.
Recovery during processing of raw materials is called desorption. Desorption, like other mass transfer processes, is usually reversible, and the primary process is called adsorption. These processes are widely used in the chemical industry for purification and drying of gases, purification and clarification of solutions, separation of mixtures of gases or vapors, in particular when extracting volatile solvents from a mixture of gases (recovery of volatile solvents). Recovery of liquid solvents is used in the production of hydrocarbons, alcohols, ethers and esters, etc. Adsorption and desorption processes are carried out in specialized adsorption units.
Recovery– the process of partial energy recovery for reuse. In this topic we are talking about air recovery in ventilation systems.
The principle of operation of the recuperator
We have supply and exhaust ventilation. In winter, the supply air is cleaned by air filters and heated by air heaters. It enters the room, warms it and dilutes harmful gases, dust and other emissions. Then it enters the exhaust ventilation and is thrown out into the street... Hence the thought... Why don't we heat the cold supply air with the exhaust air. After all, we are essentially throwing money away. So, we have exhaust air with a temperature of 21 C and supply air, which before the heater has a temperature of -10 C. We install, for example, a recuperator with a plate heat exchanger. To understand the principle of operation of a recuperator with a plate heat exchanger, imagine a square in which the exhaust air passes from bottom to top, and the supply air from left to right. Moreover, these flows do not mix with each other due to the use of special heat-conducting plates that separate these two flows.
As a result, the exhaust air gives up to 70% of the heat to the supply air and at the exit from the recuperator has a temperature of 2-6 C, and the supply air, in turn, has a temperature at the exit from the recuperator of 12-16 C. Consequently, the heater will not heat the air -10 C , and +12 C and this will allow us to significantly save on electrical or thermal energy spent on heating the supply air.
Types of recuperators
Although a recuperator with a plate heat exchanger is most common in the Russian Federation, there are other types of recuperators, which in some cases are more efficient or, in general, only they can cope with the tasks. We invite you to consider the four most popular types of recuperators:
Recuperator with plate heat exchanger (Plate recuperator)
Recuperator with rotary heat exchanger (Rotary recuperator)
Water recirculation heat exchanger
Roof recuperator
Plate recuperator
The most common type is a plate or cross-flow air recuperator for apartments.
It is a small cassette. Two channels are created in it, which are separated from each other by sheets of steel. They carry separate supply and exhaust air flows. Steel acts as a heat “filter”. That is, a temperature exchange occurs, but air mixing is not allowed. The prevalence of this type of device is due to its simplicity, compactness and low cost. The plate air recuperator for apartments has some disadvantages, but they are not so significant when installed in small residential premises.
Advantages: - the device is easily built into any part of the air duct; - there are no moving parts (easier maintenance, no risk of air flow displacement, etc.); - relatively high efficiency – 50...90%; - can work with high-temperature gas and air mixtures (up to +200°C); - aerodynamic resistance to passing air flows increases slightly; - simple performance adjustment via a bypass valve.
Plate recuperators are designed in such a way that the air flows in them do not mix, but contact each other through the walls of the heat exchange cassette. This cassette consists of many plates that separate cold air flows from warm ones. Most often, the plates are made of aluminum foil, which has excellent thermal conductivity properties. The plates can also be made of special plastic. These are more expensive than aluminum ones, but increase the efficiency of the equipment. 
Plate heat exchangers have a significant drawback: as a result of the temperature difference, condensation forms on cold surfaces, which turns into ice. An ice-covered recuperator stops working effectively. To defrost it, the incoming flow is automatically bypassed by the heat exchanger and heated by a heater. Meanwhile, the escaping warm air melts the ice on the plates. In this mode, of course, there is no energy saving, and the defrosting period can take from 5 to 25 minutes per hour. To heat the incoming air during the defrosting phase, air heaters with a power of 1-5 kW are used.
Some plate heat exchangers use preheating of the incoming air to a temperature that prevents the formation of ice. This reduces the efficiency of the recuperator by approximately 20%.
Another solution to the icing problem is hygroscopic cellulose cassettes. This material absorbs moisture from the exhaust air flow and transfers it to the incoming air, thereby returning moisture back. Such recuperators are justified only in buildings where there is no problem of air humidification. The undoubted advantage of hygrocellulose recuperators is that they do not require electrical heating of the air, which means they are more economical. Recuperators with double plate heat exchangers have an efficiency of up to 90%. Ice does not form in them due to heat transfer through the intermediate zone.
Famous manufacturers plate recuperators: SCHRAG (Germany), MITSUBISHI (Japan), ELECTROLUX, SYSTEMAIR (Sweden), SHUFT (Denmark), REMAK, 2W (Czech Republic), MIDEA (China).
Electric motors are designed to drive various mechanisms, but after completing the movement, the mechanism must be stopped. For this you can also use electric car and recovery method. This article explains what energy recovery is.
What is recovery
The name of this process comes from the Latin word “recuperatio”, which translates as “receiving back”. This is the return of some of the energy or materials used for reuse.
This process is widely used in electric vehicles, especially those powered by batteries. When driving downhill and during braking, the recuperation system returns the kinetic energy of movement back to the battery, recharging them. This allows you to travel a longer distance without recharging.
Regenerative braking
One type of braking is regenerative. In this case, the rotation speed of the electric motor is greater than that specified by the network parameters: the voltage on the armature and the field winding in the motors DC or the frequency of the supply voltage in synchronous or asynchronous motors. In this case, the electric motor switches to generator mode and releases the generated energy back into the network.
The main advantage of the recuperator is energy saving. This is especially noticeable when driving around the city with constantly changing speeds, commuter electric transport and subways with a large number of stops and braking in front of them.
In addition to its advantages, recovery has disadvantages:
- impossibility of completely stopping transport;
- slow stop at low speeds;
- lack of braking force when parking.
To compensate for these shortcomings, vehicles an additional mechanical brake system is installed.
How does the recovery system work?
To operate, this system must provide power to the electric motor and return energy during braking. This is most easily done in urban electric vehicles, as well as in older electric vehicles equipped with lead batteries, DC motors and contactors - when downshifting at high speed, the energy return mode is automatically activated.
In modern transport, a PWM controller is used instead of contactors. This device allows you to return energy to both direct and alternating current networks. During operation, it acts as a rectifier, and during braking it determines the frequency and phase of the network, creating a reverse current.
Interesting. When dynamic braking of DC electric motors occurs, they also switch to generator mode, but the generated energy is not returned to the network, but is dissipated in the additional resistance.
Power descent
In addition to braking, the recuperator is used to reduce speed when lowering loads using lifting mechanisms and when driving down an inclined road of electric vehicles. This eliminates the need to use a wear-out mechanical brake.
Application of recovery in transport
This braking method has been used for many years. Depending on the type of transport, its application has its own characteristics.
In electric cars and electric bicycles
When driving on the road, and even more so off-road, the electric drive operates almost all the time in traction mode, and before stopping or at an intersection - “coasting”. Stopping is done using mechanical brakes due to the fact that recuperation is ineffective at low speeds.
In addition, the efficiency of batteries in the charge-discharge cycle is far from 100%. Therefore, although such systems are installed on electric vehicles, they do not provide great battery savings.
On the railway
Recuperation in electric locomotives is carried out by traction motors. At the same time, they turn on in generator mode, converting the kinetic energy of the train into electricity. This energy is given back to the network, in contrast to rheostatic braking, which causes the rheostats to heat up.
Recuperation is also used during long downhill runs to maintain a constant speed. This method saves electricity, which is fed back into the grid and used by other trains.
Previously, only locomotives operating on DC power were equipped with this system. In devices operating from an alternating current network, it is difficult to synchronize the frequency of the supplied energy with the frequency of the network. Now this problem is solved using thyristor converters.
On the subway
In the subway, while trains are moving, cars are constantly accelerating and braking. Therefore, energy recovery has a great economic effect. It reaches a maximum if this happens simultaneously in different trains at the same station. This is taken into account when creating the schedule.
In city public transport
In urban electric transport, this system is installed in almost all models. It is used as the main one up to a speed of 1-2 km/h, after which it becomes ineffective and the parking brake is activated instead.
In Formula 1
Since 2009, some cars have been equipped with a recovery system. This year, such devices have not yet provided tangible superiority.
In 2010, such systems were not used. Their installation, with restrictions on power and volume of recovered energy, resumed in 2011.
Braking of asynchronous motors
Reducing the speed of asynchronous electric motors is carried out in three ways:
- recovery;
- opposition;
- dynamic.
Regenerative braking of an asynchronous motor
Recovery asynchronous motors possible in three cases:
- Changing the frequency of the supply voltage. Possible when powering the electric motor from a frequency converter. To switch to braking mode, the frequency is reduced so that the rotor rotation speed is greater than synchronous;
- Switching windings and changing the number of poles. Possible only in two- and multi-speed electric motors, in which several speeds are provided structurally;
- Power descent. Applicable in lifting mechanisms. These devices are equipped with electric motors with a wound rotor, the speed of which is adjusted by changing the value of the resistance connected to the rotor windings.
In any case, when braking, the rotor begins to overtake the stator field, the slip becomes greater than 1, and the electric machine begins to work as a generator, delivering energy to the network.
Opposition
The counter-switching mode is carried out by switching the two phases powering the electric machine between each other and turning on the rotation of the device in the opposite direction.
It is possible to switch on with counter-connection of additional resistances in the stator circuit or wound rotor windings. This reduces current and braking torque.
Important! In practice, this method is rarely used due to currents exceeding 8-10 times higher than rated (with the exception of motors with wound rotor). In addition, the device must be turned off in time, otherwise it will begin to rotate in the opposite direction.
Dynamic braking of an asynchronous motor
This method is carried out by applying a constant voltage to the stator winding. To ensure trouble-free operation of the electric machine, the braking current should not exceed 4-5 currents idle speed. This is achieved by including additional resistance in the stator circuit or using a step-down transformer.
Direct current flowing in the stator windings creates a magnetic field. When it crosses, an EMF is induced in the rotor windings and current flows. The released power creates a braking torque, the strength of which is greater, the higher the rotation speed of the electric machine.
In fact, an asynchronous electric motor in mode dynamic braking turns into a direct current generator, the output terminals of which are short-circuited (in a machine with a squirrel-cage rotor) or connected to additional resistance (an electric machine with a wound rotor).
Regeneration in electric cars is a type of braking that allows you to save energy and avoid wear and tear on mechanical brakes.
Video
Ecology of consumption. Estate: Heat loss is a serious problem that construction science is struggling with. Effective insulation, sealed windows and doors only partially solve this problem. Heat leakage through walls, windows, roofs and floors can be significantly reduced. Despite this, energy still has one more wide path to “escape.” This is ventilation, which is impossible to do without in any building.
Heat loss is a serious problem that construction science is struggling with. Effective insulation, sealed windows and doors only partially solve this problem. Heat leakage through walls, windows, roofs and floors can be significantly reduced. Despite this, energy still has one more wide path to “escape.” This is ventilation, which is impossible to do without in any building.
It turns out that in winter we spend precious fuel on heating rooms and at the same time continuously throw out heat outside, letting in cold air.
The problem of energy saving can be solved using a heat recuperator. This device is warm room air heats up outdoor. This achieves considerable savings on heating costs (up to 25% of total amount costs).
In the summer, when it is hot outside and the air conditioner is running in the house, the recuperator also brings benefits. It cools the hot incoming stream, reducing air conditioning costs.
Let's take a closer look at household heat recovery units in order to have an idea of their design, advantages and features of choice.
Types, principle of operation and design of recuperators
The idea of using the heat from indoor air to heat outdoor air turned out to be very fruitful. It was the basis for the operation of all recuperators.
Today, three types of such devices are used:
- lamellar;
- rotary;
- recirculating water.
The most common and simplest in design are plate recuperators. They are non-volatile, compact, reliable in operation and have sufficient high efficiency (40-65%).
The main working part of such a device is a cassette, inside of which parallel plates are installed. The air leaving and entering the room is cut by them into narrow streams, each of which goes through its own channel. Heat exchange occurs through the plates. Street air is heated, and indoor air cools and is released into the atmosphere.
Operating principle of a plate recuperator
The main disadvantage of plate installations is freezing in severe frosts. Condensate settling in the recovery unit turns into ice and sharply reduces the performance of the device. Three ways have been found to combat this phenomenon.
The first is installing a bypass valve. Having received a signal from the sensor, it allows a cold flow to bypass the block. Only warm air passes through the plates, defrosting the ice. After defrosting and draining the condensate, the valve restores normal operation of the system.
The second option is to use plates made of hygroscopic cellulose. Water settling on the walls of the cassette is absorbed into them and penetrates into the channels through which the supply air moves. This solves two problems at once: eliminating condensation and humidification.
The third method is to preheat the cold stream to a temperature that prevents the water from freezing. To do this, the server ventilation duct install heating element. The need for it arises when the outside air temperature is below -10C.
IN recent years Plate reversible units appeared on the market. Unlike direct-flow devices, they operate in two strokes: the first is release warm air to the street, the second is the suction of cold air through a heated block.
Operating principle of reversible installation
Another type of installation is rotary recuperators. The efficiency of such devices is significantly higher than that of plate devices (74-87%).
The operating principle of the rotary unit is to rotate a cassette with cells in the flow of incoming and outgoing air. Moving in a circle, the channels alternately pass warm internal and cold external flows. In this case, the moisture does not freeze, but saturates the supply air.
It should be noted that the supply and exhaust unit with a rotary type recuperator allows you to smoothly regulate heat transfer. This is done by changing the rotation speed of the cassette. The main disadvantage of rotary systems is the high cost of maintenance. In terms of reliability, they are also inferior to plate ones.
The next type is recirculation water installation. It is the most complex in design. Heat transfer here is carried out not through the plates or rotor, but with the help of antifreeze or water.
The first liquid-air heat exchanger is installed on the exhaust duct, and the second on the suction duct. The work is carried out according to the principle of a heater: indoor air heats water, and it heats outdoor air.
The efficiency of such a system does not exceed that of plate recuperators (50-65%). High price which you have to pay for the complexity of the design, is justified by the only advantage: the units of such an installation can be placed not in one building, but in supply and exhaust ventilation areas remote from each other. For the powerful industrial systems it has great value. Such devices are not installed in small buildings.
Features of choosing a recuperator
Having become familiar with the operating features of recuperation units, it’s time to move on to the practical part – the selection criteria for performing specific tasks.
The first thing you need to pay attention to is the installation method. Domestic supply and exhaust ventilation with heat recovery can be installed in its working position in several ways:
- Inside the wall. The housing is mounted in a pre-drilled hole. A cap is placed on the outside, and a grille and control unit on the inside.
- Indoors. The installation is hung on the wall. A grille or cap is placed outside.
- Outdoor placement. The advantages of this solution are obvious: minimum noise and space saving. The duct design of the device allows it to be placed on balconies and loggias, as well as simply on the facade of a building.
Another parameter that needs to be taken into account when purchasing is the number of fans. Budget air recuperators for the home are equipped with one ventilation unit that operates for both supply and exhaust.
More expensive devices have 2 fans. One of them pumps in and the other exhausts air. The performance of such devices is higher than that of single-fan devices.
When purchasing, you should also pay attention to the presence of an electric heater. With its help, freezing of the cassette is prevented and the lower temperature limit of the device’s operation is increased.
Climate control function. Allows you to accurately set the temperature to which the recuperator will heat the air.
Possibility of humidity control. This parameter significantly affects the comfort of the microclimate. A standard recuperator dries the air, removing moisture from it.
Presence or absence of a filter. Additional option, which has a positive effect on the sanitary characteristics of the air mixture.
An important parameter that requires attention is the temperature of the pumped air. IN different models its meaning may vary significantly. The widest range of operating temperatures from -40 to +50С household devices is rare.
Therefore, in addition to taking into account the optimal performance in m3/hour, when purchasing, choose a device that can fully operate in your climatic conditions.
Performance calculation
Detailed calculations of the operation of recuperators in the supply and exhaust ventilation system are quite complex. Here we have to take into account many factors: the frequency of air exchange in the premises, the cross-section of the channels, the speed of air movement, the need to install mufflers, etc. Only experienced engineers can competently perform such a task.
The average consumer can use a simplified method to correctly navigate when purchasing a device.
The performance of the recuperator directly depends on the sanitary standard of air flow per person. Its average value is 30 m3/hour. Therefore, if 4 people permanently live in an apartment or private house, then the installation productivity should be at least 4x30 = 120 m3/hour.
The own electrical power of household recuperators is small (25-80 W). It is determined by the level of energy consumption of duct fans. In installations with electric heating of the incoming flow, heating elements with a total power of 0.8 to 2.0 kW are installed.
Popular brands and approximate prices
When choosing a household recuperator, you should focus on manufacturers and models that have earned high customer ratings. As an example, we can cite the products of foreign companies Electrolux, Mitsubishi, Marley.
Recuperator for small premises Mitsubishi Electric VL-100EU5-E. Air consumption 105 m3/h. Price from 21,000 rub.
Popular model from Electrolux. Estimated retail price from 42,000 rubles.
The 2017 price tags for household installations of these brands start at 22,000 rubles and end at 60,000 rubles.
MARLEY MENV-180. Air consumption 90 m3/hour. Cost from 27,500 rub.
The equipment of Russian and Ukrainian companies Vents (Vents), Vakio (Vakio), Prana and Zilant has proven itself well. Not inferior to foreign analogues in performance and reliability, they are often more affordable.
Installation of Vakio. Capacity 60 m3/h in recovery mode, up to 120 m3/h in supply ventilation. Price from 17,000 rub.
The estimated cost of air recovery systems from these companies (capacity from 120 to 250 m3/hour) ranges from 17,000 to 55,000 rubles.
Prava 200G. Inflow - 135 m3/h, exhaust - 125 m3/h. The recommended area for servicing the system is up to 60 m2.
The nature of reviews about air recuperators is mostly positive. Many owners note that with their help, the problem of excess humidity, which caused the appearance of mold and mildew in the premises, was solved.
In calculations of payback period of this equipment figures are given from 3 to 7 years. We did not find any data from instrumental measurements regarding real energy savings on forums dedicated to this topic.
Briefly about self-assembly
Most photo and video instructions for making recuperators yourself discuss plate models. This is the simplest and affordable option for the home handyman.
The main part of the structure is the heat exchanger. It is made from galvanized steel, cut into plates measuring 30x30 cm. To create channels at the edges and in the middle of each section, plastic strips 4 mm thick and 2-3 cm wide are glued with silicone.
The heat exchanger is assembled by placing and alternately rotating the plates at an angle of 90 degrees relative to each other. That's how they get it isolated channels for counter movement of cold and warm air.
After this, a housing made of metal, chipboard or plastic is made to fit the dimensions of the heat exchanger. There are four holes in it for air supply. Two of them have fans. The heat exchanger is rotated at an angle of 45 degrees and secured in the housing.
The work is completed by thoroughly sealing all installation joints with silicone.
Until recently, supply and exhaust ventilation with an air recuperator was used quite rarely in Russia, until experts came to the conclusion that such a system was a necessity. The operation of ventilation is based on the principle of recovery. This is the name of the process in which part of the heat is returned from exhaust air. Leaving the room, warm air partially heats the oncoming cold flow in the heat exchanger. Thus, completely “exhausted” air goes outside, and not only fresh, but also already heated air enters the room.
Why is it high time to abandon the old type of exhaust ventilation?
Why is traditional natural exhaust ventilation, which has been installed in private houses, apartments and buildings for many years, no longer effective? The fact is that in this case, through frames, doorways and cracks, there should be continuous penetration of air into the room, but in the case of installing sealed plastic double-glazed windows, the air flow is greatly reduced and, as a result, natural exhaust system ventilation stops functioning normally.
To ensure that the air temperature in the rooms is comfortable, winter period the air needs to be heated, for which in our country, homeowners spend huge amounts of money, because... cold weather in our country lasts 5-6 months. And although heating season- in short, huge resources are still spent on heating the supply air. However, the disadvantages of natural exhaust ventilation do not end there. Not only cold but also dirty air enters the room from the street, and drafts also occur periodically. There is no way to control the volume of these air flows. It turns out that due to unbalanced ventilation, a lot of money is literally wasted, because people are forced to pay for heating the air, which flies down the chimney in a couple of minutes. Since energy prices are rising year after year, it is not surprising that the question of reducing heating costs sooner or later arises in every thrifty person who does not want to “heat the street” at his own expense.
How to save heat in your home
To save heat in the ventilation system - heating the supply cold air due to the warm air removed from the room, special recuperator units are designed. A cassette is built into supply and exhaust ventilation units to ensure air heat exchange. Coming out through it, the exhaust air transfers heat to the walls of the heat exchanger, while the cold air flowing into the room is heated by the walls. This principle is the basis for the operation of plate and rotary recuperators, which at the moment have gained popularity in the ventilation unit market.
Are there any disadvantages to plate recuperators?
In devices of this type, air flows are, as it were, cut by plates. These supply and exhaust systems, in addition to many advantages, which will be discussed later, also have one drawback: on the side where the exhaust air exits, ice forms on the plates. The problem is explained simply: as a result of the fact that the heat exchange plate and the exhaust air have different temperatures, condensation forms, which, in fact, turns into ice. Air begins to pass through frozen plates with enormous resistance, and ventilation performance drops sharply, and the recovery process practically stops until the plates are completely thawed.
The process can be compared to freezer got a bottle of lemonade. The glass would instantly be covered first with a white film, and then with drops of water. Is it possible to combat the problem of recuperator freezing? Experts found a way out by installing a special bypass valve in ventilation systems with recovery. As soon as the plates are covered with a layer of ice, the bypass opens, and the supply air for some time bypasses the recuperator cassette, entering the room with virtually no heating. At the same time, the recuperator plates are defrosted quite quickly due to the removed exhaust air, and the resulting water is collected in the drainage bath. The bath is connected to a drainage system that goes into the sewer system, and all condensate is drained there. The recuperator begins to work effectively again, and air exchange is restored.
When the cassette defrosts, the valve closes again, however, there is one “but” here. When air does not enter the heat exchanger and bypasses it, energy savings are minimized. This is due to the fact that the supply air, as a rule, in addition to the heat exchanger plates, heats up the built-in air heater - exactly the same as that found in simple air supply units, but with significantly less power. How to deal with this? Is it possible to deal with ice without losing money?
Supply and exhaust ventilation units with heat recovery
Manufacturers of recuperators have found a solution to this serious problem. Thanks to the invention new technology, the moisture that settles on the walls of the heat exchanger on the outgoing air side begins to be absorbed into them and moves to the supply air side - moistening it. Thus, almost all the moisture in the removed air gets back into the room. What makes this process possible? Engineers achieved this effect by creating cassettes made of hygroscopic cellulose. In addition, many of the hygroscopic celluloses do not have bypasses and do not connect to drainage system with bath and running water. All moisture is utilized by air currents, and it remains almost entirely in the room. So, using a cellulose heat exchanger in the recuperator, you no longer need to use a bypass and direct air bypassing the recuperator plates.
As a result, the efficiency of the recuperator was increased to 90%! This means that the supply air from the street will be 90% heated by the exhaust air. At the same time, recuperators can operate without problems even in cold weather, down to -30 degrees Celsius. Such installations are perfect for residential premises, apartments, country houses and cottages, preserving and maintaining the necessary humidity and air exchange in winter and summer, they create and maintain the necessary indoor microclimate all year round, while saving quite a bit of money. However, it should be remembered that recuperators with cellulose heat exchangers, like all others, are capable of freezing, which over time can lead to failure of the heat exchange cassette. In order to completely eliminate the possibility of freezing, it is necessary to install frost protection. Also, with all their positive qualities, recuperators with a paper heat exchanger cannot be used for rooms with a high moisture content, in particular for. For wet rooms, including swimming pools, it is necessary to use supply and exhaust ventilation units with an aluminum plate heat exchanger.
Diagram and operating principle of a supply and exhaust ventilation system with a recuperator
Let's assume that it is winter outside and the air temperature outside the window is -23 0 C. When the air handling unit is turned on, street air is sucked in by the unit using a built-in fan, passes through the filter and hits the heat exchange cassette. Passing through it, it heats up to +14 0 C. As we see, in winter cold, the installation is not able to completely warm the air to room temperature, although for many, such heating may be sufficient, therefore, after the recuperator, the supply air can go directly into the room, or if the recuperator has the so-called “air reheating”, passing through it, the air is heated to +20 0 C and only fully heated air enters room. The reheater is a low-power electric or water heater with a power of 1-2 kW, which can, if necessary, turn on at low outside temperatures and heat the air to a comfortable room temperature. In the configurations of recuperators from various manufacturers, as a rule, it is possible to choose a water or electric reheater. On the contrary, room air with a temperature of +18 0 C (+20 0 C), sucked from the room by a fan built into the installation, passing through a heat exchange cassette, is cooled by the supply air and goes outside from the recuperator, having a temperature of -15 0 C.
What will the air temperature be after the recuperator in winter and summer?
There is a fairly simple way to calculate for yourself what temperature the air will enter the room after the recuperator. How effectively will the supply air be heated and will it be heated at all? What will happen to the air in the recuperator in the summer?
Winter
The picture shows that the street air is 0 0 C, the efficiency of the recuperator is 77%, while the temperature of the air entering the room is 15.4 0 C. How much will the air warm up if the temperature outside is, for example, -20 0 C? There is a formula for calculating the supply air for a recuperator depending on its efficiency, outdoor and indoor air temperature:
t (after the recuperator)=(t (indoors)-t (outdoors))xK (recuperator efficiency)+t (outdoors)
For our example, it turns out: 15.4 0 C = (20 0 C - 0 0 C)x77% + 0 0 C If the temperature outside the window is -20 0 C, in the room +20 0 C, the recuperator efficiency is 77%, then the air temperature after the recuperator it will be: t=((20-(-20))x77%-20=10.8 0 C. But this is, of course, a theoretical calculation, in practice the temperature will be slightly lower, about +8 0 C.
Summer
The air temperature after the recuperator in summer is calculated similarly:
t (after the recuperator)=t (outdoors)+(t (indoors)-t (outdoors))xK (recuperator efficiency)
For our example it turns out: 24.2 0 С=35 0 С+(21 0 С-35 0 С)х77%
Diagram and principle of operation of a supply and exhaust ventilation system with a rotary recuperator
The principle of operation of a rotary recuperator is based on the exchange of heat between the incoming and outgoing air flow in the ventilation system through a rotary aluminum heat exchanger, which, rotating at different speeds, allows this process to be carried out with different intensities.
Which recuperator is better?
Today, recuperators from different manufacturers are available for sale, differing in many respects: operating principle, efficiency, reliability, economy, etc. Let's look at the most popular types of recuperators and compare their advantages and disadvantages.
1. Plate recuperator with aluminum heat exchanger.
The price of such a recuperator is quite low compared to other types of recuperators, which is undoubtedly one of its advantages. The air flows in the device do not mix; they are separated by aluminum foil. One of the disadvantages is not high performance when low temperatures, because The heat exchanger freezes periodically and must thaw frequently. It is logical that energy costs are rising. It is also not advisable to install them in residential premises, because in winter, during the operation of the recuperator, all moisture is removed from the air in the room and its constant humidification is required. The main advantage of aluminum plate heat exchangers is that they can be installed for ventilation of swimming pools.
2. Plate recuperator with a plastic heat exchanger. The advantages are the same as the previous option, but the efficiency is higher due to the properties of plastic. 
3. Plate recuperator with a cellulose heat exchanger and a single cassette. Despite the fact that the air flows are separated by paper partitions, moisture quietly permeates the walls of the heat exchanger. An important advantage is that the saved heat and moisture are returned to the room. Due to the fact that the heat exchanger is practically not subject to freezing, no time is wasted on defrosting it, and the efficiency of the device increases significantly. If we talk about the disadvantages, they are as follows: recuperators of this type cannot be installed in swimming pools, as well as in any other rooms where there is excess humidity. In addition, the recuperator cannot be used for drying. Very often, like this.
4. Rotary recuperator. It is characterized by high efficiency, but this figure still remains lower than if it were used plate installation with double cassette. Distinctive feature is low energy consumption. As for the shortcomings, we note the following points, since the oncoming air flows of the rotary heat exchanger are not ideally separated; a small amount of air removed from the room (albeit insignificant) enters the supply air. The device itself is quite expensive, because... complex mechanics are used. Finally, the rotary heat exchanger must be serviced more often than other air handling units and its installation in wet areas not desirable.
Recuperators for apartments and country houses
| Mitsubishi Lossney | Electrolux EPVS |
DAIKIN |
Systemair | SHUFT |
What determines the price of a recuperator?
First of all, the price of a recuperator depends on the performance of the entire ventilation system. A professional designer will be able to develop a competent project that satisfies exactly your conditions and requirements, the quality of which will determine not only the efficiency of the entire system, but also your further costs for its maintenance. Of course, you can select the equipment yourself, including air ducts and grilles, but it is advisable that a specialist deal with the identified issues. Project development costs extra money and at first glance, such expenses will seem quite substantial to someone, but if you calculate how much money will remain in your budget as a result thanks to a competent investment, you will be surprised.
When choosing a recuperator yourself, first of all pay attention to the price and the promised quality. Is the device worth the stated amount? Or will you simply overpay for a new product or brand? The equipment is not cheap and takes several years to pay for itself, so the choice of device should be approached very responsibly.
Be sure to check the availability of product certificates and find out how long the warranty period is valid. Usually the warranty is given not for the recuperator, but for its components. How better quality components, assemblies and other components - the more expensive the purchase will be. System reliability is assessed by strong and weaknesses goods. natural, ideal option no one suggests, but find best solution for a specific room - quite possible.
How to choose an air handling unit with a recuperator
First of all, ask the seller the following questions:
1. Which company produces the product? What is known about her? How many years on the market? What are the reviews?
2. What is the system performance? These data can be calculated by specialists whom you contact for advice, including specialists from our company. To do this, you must indicate the exact parameters of the room, it is advisable to provide the layout of the apartment, office, country house, cottage, etc.
3. What will be the resistance of the air duct system to air flow after installing a particular model? These data must also be calculated by designers for each individual case. The calculations take into account all diffusers, duct bends and much more. The model and power of the recuperator are selected taking into account the so-called “operating point” - the ratio of air flow and air duct resistance.
4. What energy consumption class does the recuperator belong to? How much will it cost to maintain the system? How much electricity can you save? You need to know this in order to calculate expenses for the heating season.
5. What is the declared Efficiency Factor of the installation and the real one? The efficiency of recuperators depends on the temperature difference between indoors and outdoors. This indicator is also influenced by such parameters as: type of heat exchange cassette, air humidity, layout of the system as a whole, correct placement of all components, etc.
Let's see how efficiency can be calculated for different types recuperators.
- If the heat exchanger of a plate recuperator is made of paper, then the efficiency will be, on average, 60-70%. The installation does not freeze, or rather, this happens extremely rarely. If the heat exchanger needs to be defrosted, the system itself reduces the performance of the installation for some time.
- The aluminum plate heat exchanger demonstrates high efficiency - up to 63%. But the recuperator will be less productive. The efficiency here will be 42-45%. This is due to the fact that the heat exchanger must often thaw. If you want to eliminate freezing, you will have to use much more electricity.
- A rotary recuperator shows high efficiency if the rotor speed is regulated by “automation”, guided by the readings of temperature sensors that are installed both indoors and outdoors. Rotary recuperators they are also susceptible to freezing, as a result of which the efficiency decreases in the same way as with plate heat exchangers made of aluminum.