Recovery in the ventilation system. Supply and exhaust ventilation systems with heat recovery and recirculation. The device and principle of operation of supply and exhaust ventilation with heat recovery

The intake of fresh air during the cold period of time leads to the need to heat it to ensure the correct microclimate of the premises. To minimize energy costs, supply and exhaust ventilation with heat recovery can be used.

Understanding the principles of its operation will allow you to reduce heat losses as efficiently as possible while maintaining a sufficient volume of replaced air. Let's try to understand this issue.

In the autumn-spring period, when ventilating rooms, a serious problem is the large temperature difference between the incoming and inside air. The cold stream rushes down and creates an unfavorable microclimate in residential buildings, offices and production or an unacceptable vertical temperature gradient in the warehouse.

A common solution to the problem is integration into the supply ventilation, with the help of which the flow is heated. Such a system requires electricity, while a significant amount of warm air coming out leads to significant heat losses.

The exit of air to the outside with intense steam serves as an indicator of significant heat loss, which can be used to heat the incoming flow

If the air inlet and outlet channels are located nearby, then it is possible to partially transfer the heat of the outgoing stream to the incoming one. This will reduce the consumption of electricity by the heater or completely abandon it. A device for ensuring heat exchange between different-temperature gas flows is called a recuperator.

In the warm season, when the outdoor air temperature is much higher than the room temperature, a heat exchanger can be used to cool the incoming flow.

Block device with recuperator

Systems internals supply and exhaust ventilation s is quite simple, so their independent item-by-item purchase and installation is possible. If the assembly or self-assembly causes difficulties, you can purchase ready-made solutions in the form of standard monoblock or individual prefabricated structures on order.

An elementary device for collecting and draining condensate is a tray located under the heat exchanger with a slope towards the drain hole

The output of moisture is carried out in a closed container. It is placed only indoors in order to avoid freezing of the outflow channels at sub-zero temperatures. There is no algorithm for reliable calculation of the volume of water received when using systems with a recuperator, so it is determined experimentally.

The reuse of condensate for air humidification is undesirable, since the water absorbs many pollutants such as human sweat, odors, etc.

Significantly reduce the amount of condensate and avoid the problems associated with its appearance by organizing a separate exhaust system from the bathroom and kitchen. It is in these rooms that the air has the highest humidity. If there are several exhaust systems, the air exchange between the technical and residential area must be limited by installing non-return valves.

In the case of cooling of the outgoing air flow to negative temperatures inside the heat exchanger, the condensate passes into frost, which causes a reduction in the effective cross section of the flow and, as a result, a decrease in the volume or a complete cessation of ventilation.

For periodic or one-time defrosting of the heat exchanger, a bypass is installed - a bypass channel for the movement of supply air. When the flow bypasses the device, the heat transfer stops, the heat exchanger heats up and the ice passes into a liquid state. Water flows into the condensate collection tank or it evaporates to the outside.

The principle of the bypass device is simple, therefore, if there is a risk of ice formation, it is advisable to provide such a solution, since heating the heat exchanger in other ways is complicated and time-consuming

When the flow passes through the bypass, there is no heating of the supply air through the heat exchanger. Therefore, when this mode is activated, it is necessary to automatically turn on the heater.

Features of various types of recuperators

There are several structurally different options for implementing heat transfer between cold and heated air flows. Each of them has its own distinctive features, which determine the main purpose for each type of recuperator.

The design of a plate heat exchanger is based on thin-walled panels connected in turn in such a way as to alternate the passage of different temperature flows between them at an angle of 90 degrees. One of the modifications of this model is a device with finned channels for air passage. It has a higher heat transfer coefficient.

The alternating passage of warm and cold air flow through the plates is realized by bending the edges of the plates and sealing the joints with polyester resin

Heat exchange panels can be made of various materials:

copper, brass and aluminum-based alloys have good thermal conductivity and are not susceptible to rust;
plastics made of polymeric hydrophobic material with a high coefficient of thermal conductivity are lightweight;
hygroscopic cellulose allows condensate to penetrate through the plate and back into the room.

The disadvantage is the possibility of condensation at low temperatures. Due to the small distance between the plates, moisture or frost significantly increases the aerodynamic drag. In case of freezing, it is necessary to shut off the incoming air flow to warm up the plates.

The advantages of plate heat exchangers are as follows:

low cost;
long service life;
long period between preventive maintenance and ease of its implementation;
small dimensions and weight.

This type of heat exchanger is most common for residential and office premises. It is also used in some technological processes, for example, to optimize fuel combustion during the operation of furnaces.

Drum or rotary type

The principle of operation of a rotary heat exchanger is based on the rotation of the heat exchanger, inside which there are layers of corrugated metal with a high heat capacity. As a result of interaction with the outgoing flow, the drum sector is heated, which subsequently gives off heat to the incoming air.

The fine-mesh heat exchanger of a rotary heat exchanger is prone to clogging, so you need to pay special attention to the quality work of fine filters

The advantages of rotary recuperators are as follows:

sufficiently high efficiency compared to competing types;
return a large number moisture that remains in the form of condensate on the drum and evaporates when it comes into contact with the incoming dry air.

This type of heat exchanger is less commonly used for residential buildings with apartment or cottage ventilation. It is often used in large boiler houses to return heat to furnaces or for large industrial or commercial and entertainment premises.

However, this type of device has significant disadvantages:

a relatively complex design with moving parts, including an electric motor, a drum and a belt drive, which requires constant maintenance;
increased noise level.

Sometimes for devices of this type you can find the term "regenerative heat exchanger", which is more correct than "recuperator". The fact is that a small part of the outgoing air gets back due to the loose fit of the drum to the body of the structure.

This imposes additional restrictions on the possibility of using devices of this type. For example, polluted air from heating furnaces cannot be used as a heat carrier.

Tube and shell system

The tubular type heat exchanger consists of a system of thin-walled tubes of small diameter located in an insulated casing, through which outside air is supplied. A warm air mass is removed from the room through the casing, which heats the incoming flow.

Warm air must be exhausted through the casing, and not through the pipe system, since it is impossible to remove condensate from them

The main advantages of tubular heat exchangers are as follows:

high efficiency, due to the countercurrent principle of movement of the coolant and incoming air;
simplicity of design and the absence of moving parts ensures low noise levels and a rarely occurring need for maintenance;
long service life;
the smallest section among all types of recuperation devices.

Tubes for this type of device use either light-alloy metal or, less commonly, polymer. These materials are not hygroscopic, therefore, with a significant difference in flow temperatures, intense condensate may form in the casing, which requires a constructive solution for its removal. Another disadvantage is that the metal filling has a significant weight, despite the small size.

The simplicity of the design of the tubular heat exchanger makes this type of device popular for self-manufacturing. As an external casing, plastic pipes for air ducts, insulated with polyurethane foam shells, are usually used.

Device with intermediate heat carrier

Sometimes the supply and exhaust air ducts are located at some distance from each other. This situation may arise due to the technological features of the building or sanitary requirements for reliable separation of air flows.

In this case, an intermediate heat carrier is used, which circulates between the air ducts through an insulated pipeline. As a medium for the transfer of thermal energy, water or a water-glycol solution is used, the circulation of which is provided by work.

The recuperator with an intermediate heat carrier is a volumetric and expensive device, whose use is economically justified for rooms with large areas

In the event that it is possible to use another type of heat exchanger, it is better not to use a system with an intermediate heat carrier, since it has the following significant disadvantages:

low efficiency compared to other types of devices, therefore, such devices are not used for small rooms with low air flow;
significant volume and weight of the entire system;
the need for an additional electric pump for fluid circulation;
increased noise from the pump.

There is a modification of this system, when instead of forced circulation of the heat exchange fluid, a medium with a low boiling point, such as freon, is used. In this case, movement along the contour is possible in a natural way, but only if the supply air duct is located above the exhaust duct.

Such a system does not require additional energy costs, but works for heating only with a significant temperature difference. In addition, it is necessary to fine-tune the point of change in the state of aggregation of the heat exchange fluid, which can be implemented by creating the desired pressure or a certain chemical composition.

Main technical parameters

Knowing the required performance of the ventilation system and the heat exchange efficiency of the heat exchanger, it is easy to calculate the savings on air heating for a room under specific climatic conditions. By comparing the potential benefits with the costs of purchasing and maintaining the system, you can reasonably make a choice in favor of a heat exchanger or a standard heater.

Often, equipment manufacturers offer a model line in which ventilation units with similar functionality differ in air exchange volume. For residential premises, this parameter must be calculated according to Table 9.1. SP 54.13330.2016

Efficiency

The efficiency of a heat exchanger is understood as the efficiency of heat transfer, which is calculated using the following formula:

K \u003d (T p - T n) / (T in - T n)

Wherein:

T p - the temperature of the incoming air inside the room;
T n - outdoor air temperature;
T in - the air temperature in the room.

The maximum efficiency value at standard and certain temperature conditions is indicated in the technical documentation of the device. His real figure will be slightly less.

In the case of self-manufacturing of a plate or tube heat exchanger, in order to achieve maximum heat transfer efficiency, it is necessary to adhere to the following rules:

The best heat transfer is provided by countercurrent devices, then by cross-flow devices, and the smallest - with unidirectional movement of both flows.
The intensity of heat transfer depends on the material and thickness of the walls separating the flows, as well as on the duration of the presence of air inside the device.

E (W) \u003d 0.36 x P x K x (T in - T n)

where P (m 3 / hour) - air consumption.

Calculation of the efficiency of the heat exchanger in monetary terms and comparison with the cost of its purchase and installation for two-storey cottage with a total area of 270 m2 shows the feasibility of installing such a system

The cost of recuperators high efficiency large enough they have complex structure and significant size. Sometimes you can get around these problems by installing a few more simple devices so that the incoming air passes through them in sequence.

Ventilation system performance

The volume of air passed through is determined by the static pressure, which depends on the power of the fan and the main components that create aerodynamic resistance. As a rule, its exact calculation is impossible due to the complexity mathematical model Therefore, for typical monoblock structures, experimental studies are carried out, and for individual devices, components are selected.

The fan power must be selected taking into account the throughput of any type of heat exchangers installed, which is indicated in the technical documentation as the recommended flow rate or the amount of air passed by the device per unit of time. Usually, allowable speed air inside the device does not exceed 2 m/s.

Otherwise, at high speeds, a sharp increase in aerodynamic resistance occurs in the narrow elements of the recuperator. This leads to extra costs electricity, inefficient heating of the outside air and reduced life of the fans.

The graph of dependence of pressure loss on air flow rate for several models of high-performance heat exchangers shows a non-linear increase in resistance, therefore, it is necessary to adhere to the requirements for the recommended air exchange volume indicated in the technical documentation of the device

Changing the direction of the air flow creates additional aerodynamic drag. Therefore, when modeling the geometry of an indoor duct, it is desirable to minimize the number of pipe turns by 90 degrees. Diffusers to disperse air also increase resistance, so it is advisable not to use elements with a complex pattern.

Dirty filters and gratings create significant flow problems and must be cleaned or replaced periodically. One of effective ways clogging assessment is the installation of sensors that monitor the pressure drop in the areas before and after the filter.

Conclusions and useful video on the topic

The principle of operation of a rotary and plate heat exchanger:

Measurement of the efficiency of a plate-type heat exchanger:

Domestic and industrial ventilation systems with an integrated heat exchanger have proven their energy efficiency in keeping indoor heat. Now there are many offers for the sale and installation of such devices, both in the form of ready-made and tested models, and for custom order. You can calculate the necessary parameters and perform the installation yourself.

If you have questions or find inaccuracies in our material while reading the information, please leave your comments in the block below.

Heat recovery ventilation is equipment designed to process air to such parameters that a person could feel comfortable and safe. Such parameters are regulated by the norms and lie within the following limits: temperature 23÷26 С, humidity 30÷60%, air velocity 0.1÷0.15 m/s.

There is another indicator that is directly related to the safety of a person being indoors - this is the presence of oxygen, or more precisely, the percentage of carbon dioxide in the air. Carbon dioxide displaces oxygen and, at a content of 2 to 3% carbon dioxide in the air, can lead a person to unconsciousness or death.

It is to maintain these four parameters that they serve ventilation units with recovery. This is especially true for modern business centers, where there is no natural influx of fresh air. Industrial, administrative, commercial, residential and other premises cannot do without modern ventilation equipment. With today's air pollution, the issue of installing ventilation units with recuperation is the most relevant.

It is possible to install additional filters and other devices in ventilation with recuperation, which allow you to even better clean and process the air to the specified parameters.

All this can be done with Dantex ventilation units.

The principle of operation of the supply and exhaust ventilation system with heat recovery

Thanks to the supply and exhaust ventilation system, clean air is pumped into the room, and the heated exhaust air is discharged outside. Passing through the heat exchanger, the heated air leaves part of the heat to the walls of the structure, as a result of which the cold air coming from the street is heated from the heat exchanger without spending additional energy on heating. This system is more efficient and less energy intensive than a ventilation system without heat recovery.

The efficiency of the heat exchanger varies with the outdoor temperature, it can be calculated using the general formula:

S = (T1 - T2) : (T3 - T2)
where:

S– recovery efficiency;
T1- the temperature of the air entering the room;
T2- outdoor air temperature;
T3- the air temperature in the room.

Types of recuperators

Plate heat exchangers

This type of heat exchanger consists of a set of thin plates made of aluminum or any other material preferably with good heat transfer characteristics). This is the most inexpensive and most popular type of device (recuperator). The efficiency of a plate heat exchanger can range from 50% to 90%, and the service life is very long due to the absence of moving parts.

The main disadvantage of such recuperators is the formation of ice due to temperature differences. There are three options for solving this problem:

Do not use heat recovery at extremely low temperatures
Use models of automated recovery process. In this case, cold air bypasses the plates, and warm air warms the ice. But it is worth considering that the efficiency of such models in the cold will decrease by 20%.

Rotary heat exchangers

The heat exchanger has a movable part - a cylindrical rotor (recuperator), which consists of profiled plates. Heat transfer occurs when the rotor rotates. The efficiency is from 75 to 90%. In this case, the rotation speed affects the level of recuperation. The speed can be adjusted independently.

Ice does not form on rotary heat exchangers, but they are more difficult to maintain, unlike plate heat exchangers.

With intermediate coolant

In the case of an intermediate heat carrier, as in plate heat exchangers, there are two channels for clean and exhaust air, but heat exchange occurs through a water-glycol solution or water. The efficiency of such a device is below 50%.

Chamber recuperators

In this form, the air passes through a special chamber (recuperator), in which a movable damper is provided. It is the damper that has the ability to redirect the flow of cold and hot air. Due to this periodic switching of air flows, recuperation occurs. However, in such a system, there is a partial mixing of the outgoing and incoming air flows, which leads to the ingress of foreign odors back into the room, but, in turn, this design has a high efficiency of 80%.

heat pipes

Such a mechanism has many tubes that are assembled into a single sealed unit, and inside the tube are filled with a special easily condensing and evaporating substance, most often freon. Warm air, passing through a certain part of the tubes, heats and evaporates it. It moves to the area of the tubes through which cold air passes and heats it with its heat, while freon cools and this can lead to condensation. The advantage of this design is that polluted air does not enter the room. Optimal use of heat pipes is possible in small rooms in climatic zones with a small difference between internal and external temperatures.

Sometimes recovery is not enough to heat the room at low outdoor temperatures, so often electric or water heaters are used in addition to recovery. In some models, heaters perform the function of protecting the heat exchanger from icing.

Recuperators

Supply and exhaust ventilation is an integrated approach to the problem of ventilation.

Supply and exhaust units provide an active inflow of fresh air into the room and removal of exhaust air masses from the room. Recuperators are becoming increasingly popular, the advantage of which is the supply of fresh air heated to room temperature, with minimal annual energy consumption.

Recuperators return up to 95% of heat back to the room, practically without creating additional energy costs. Thus, recuperators are the most economical type of ventilation unit with the supply of warm air into the room. This is achieved by storing heat from the exhaust room air on heat exchangers.

The latest models of recuperators combine the functions of supply and exhaust ventilation and fine air purification from allergens, are equipped with carbon dioxide sensors, heat exchangers of a special design to maintain optimal humidity conditions, and can be controlled from a smartphone.

Installing a heat exchanger effectively helps to cope with stuffiness, humidity control in rooms, mold and dampness in the house, and condensation on plastic windows.

We are the official dealer of leading manufacturers, and we can provide a guarantee the best price. You can choose and buy any model of the recuperator from us with delivery in Moscow and Russia.

Supply and exhaust ventilation units with heat recovery appeared relatively recently, but quickly gained popularity and became a fairly popular system. The devices are able to fully ventilate the room during the cold period, while maintaining optimal temperature regime incoming air.

What it is?

When using supply and exhaust ventilation in the autumn-winter period, the question of maintaining heat in the room often arises. The flow of cold air coming from the ventilation rushes to the floor and contributes to the creation of an unfavorable microclimate. The most common way to solve this problem is to install a heater that heats cold outdoor air flows before supplying them to the room. However, this method is quite energy-intensive and does not prevent heat losses in the room.

The best option The solution to the problem is to equip the ventilation system with a heat exchanger. The heat exchanger is a device in which the outflow and air supply channels are located in close proximity to each other. The heat recovery unit allows you to partially transfer heat from the air leaving the room to the incoming air. Thanks to the technology of heat exchange between multidirectional air flows, it is possible to save up to 90% of electricity, in addition, in the summer, the device can be used to cool the incoming air masses.

Specifications

The heat recuperator consists of a housing, which is covered with heat and noise insulating materials and is made of sheet steel. The case of the device is strong enough and able to withstand weight and vibration loads. There are inflow and outflow openings on the case, and air movement through the device is provided by two fans, usually of axial or centrifugal type. The need for their installation is due to a significant slowdown in the natural circulation of air, which is caused by the high aerodynamic resistance of the heat exchanger. In order to prevent the suction of fallen leaves, small birds or mechanical debris, an air intake grille is installed on the inlet located on the street side. The same hole, but from the side of the room, is also equipped with a grill or diffuser that evenly distributes air flows. When installing branched systems, air ducts are mounted to the holes.

In addition, the inlets of both streams are equipped with fine filters that protect the system from dust and grease drops. This prevents the heat exchanger channels from clogging and significantly extends the life of the equipment. However, the installation of filters is complicated by the need for constant monitoring of their condition, cleaning, and, if necessary, replacing them. Otherwise, the clogged filter will act as a natural barrier to air flow, as a result of which the resistance to it will increase and the fan will break.

According to the type of construction, heat exchanger filters can be dry, wet and electrostatic. The choice of the desired model depends on the power of the device, physical properties and the chemical composition of the exhaust air, as well as on the personal preferences of the buyer.

In addition to fans and filters, recuperators include heating elements which can be water and electric. Each heater is equipped with a temperature switch and is able to automatically turn on if the heat leaving the house cannot cope with the heating of the incoming air. The power of the heaters is selected in strict accordance with the volume of the room and the operating performance of the ventilation system. However, in some devices, the heating elements only protect the heat exchanger from freezing and do not affect the temperature of the incoming air.

Water heater elements are more economical. This is due to the fact that the coolant, which moves along the copper coil, enters it from the heating system of the house. From the coil, the plates are heated, which, in turn, give off heat to the air flow. The water heater regulation system is represented by a three-way valve that opens and closes the water supply, a throttle valve that reduces or increases its speed, and a mixing unit that regulates the temperature. Water heaters are installed in a system of air ducts with a rectangular or square section.

Electric heaters are often installed on air ducts with round section, and a spiral acts as a heating element. For the correct and efficient operation of the spiral heater, the air flow velocity must be greater than or equal to 2 m/s, the air temperature must be 0-30 degrees, and the humidity of the passing masses must not exceed 80%. All electric heaters are equipped with an operation timer and a thermal relay that turns off the device in case of overheating.

In addition to the standard set of elements, at the request of the consumer, air ionizers and humidifiers are installed in the recuperators, and the most modern samples are equipped with an electronic control unit and a function for programming the operating mode, depending on external and internal conditions. Dashboards have an aesthetic appearance, allowing the heat exchangers to organically fit into the ventilation system and not disturb the harmony of the room.

Principle of operation

In order to better understand how the recuperative system works, one should refer to the translation of the word “recuperator”. Literally, it means "return of used", in this context - heat exchange. In ventilation systems, the heat exchanger takes heat from the air leaving the room and gives it to the incoming flows. The temperature difference of multidirectional air jets can reach 50 degrees. In the summer, the device works in reverse and cools the air coming from the street to the temperature of the outlet. On average, the efficiency of devices is 65%, which allows for the rational use of energy resources and significant savings on electricity.

In practice, the heat exchange in the heat exchanger is as follows: forced ventilation drives an excess volume of air into the room, as a result of which the polluted masses are forced to leave the room through the exhaust duct. The outgoing warm air passes through the heat exchanger, while heating the walls of the structure. At the same time, a stream of cold air moves towards it, which takes the heat received by the heat exchanger without mixing with the exhaust streams.

However, cooling the exhaust air from the room causes condensation to form. With the good operation of the fans, which give the air masses a high speed, the condensate does not have time to fall on the walls of the device and goes outside along with the air stream. But if the air speed was not high enough, then water begins to accumulate inside the device. For these purposes, a tray is included in the design of the heat exchanger, which is located at a slight inclination towards the drain hole.

Water enters through the drain hole closed tank, which is installed from the side of the room. This is dictated by the fact that the accumulated water can freeze the outflow channels and the condensate will have nowhere to drain. Use collected water not recommended for humidifiers: the liquid may contain a large number of pathogenic microorganisms, and therefore must be poured into the sewer system.

However, if frost from condensation still forms, it is recommended to install additional equipment– bypass. This device is made in the form of a bypass channel through which the supply air will enter the room. As a result, the heat exchanger does not heat the incoming flows, but spends its heat exclusively on melting ice. The incoming air, in turn, is heated by a heater, which is switched on synchronously with the bypass. After all the ice is melted and water is discharged into the storage tank, the bypass is turned off and the heat exchanger starts to operate normally.

In addition to installing a bypass, hygroscopic cellulose is used to combat icing. The material is in special cassettes and absorbs moisture before it has time to condensate. Moisture vapor passes through the cellulose layer and returns to the room with the incoming flow. The advantages of such devices are simple installation, the optional installation of a condensate collector and a storage tank. In addition, the efficiency of the cassettes of cellulose recuperators does not depend on external conditions, and the efficiency is more than 80%. The disadvantages include the inability to use in rooms with excessive humidity and the high cost of some models.

Types of recuperators

The modern market for ventilation equipment is wide choose recuperators different types, differing from each other both in design and in the method of heat exchange between flows.

Plate Models are the simplest and most common type of recuperators, they are characterized by low cost and long service life. The heat exchanger of the models consists of thin aluminum plates, which have high thermal conductivity and significantly increase the efficiency of devices, which in plate models can reach 90%. High performance efficiency are due to the peculiarity of the structure of the heat exchanger, the plates in which are located in such a way that both flows, alternating, pass between them at an angle of 90 degrees to each other. The sequence of passing warm and cold jets became possible due to the bending of the edges on the plates and the sealing of the joints with polyester resins. In addition to aluminum, alloys of copper and brass, as well as polymeric hydrophobic plastics, are used for the production of plates. However, in addition to the advantages, plate heat exchangers have their own weak sides. The downside of the models is considered to be a high risk of condensation and ice formation, which is due to the plates being too close to each other.

Rotary models consist of a housing inside which a cylindrical type rotor, consisting of profiled plates, rotates. During the rotation of the rotor, heat is transferred from the outgoing flows to the incoming ones, as a result of which there is a slight mixing of the masses. And although the mixing ratio is not critical and usually does not exceed 7%, such models are not used in children's and medical institutions. The level of air mass recuperation entirely depends on the rotor speed, which is set in manual mode. The efficiency of rotary models is 75-90%, the risk of ice formation is minimal. The latter is due to the fact that most of the moisture is retained in the drum, after which it evaporates. The disadvantages include difficulty in maintenance, high noise load, which is due to the presence of moving mechanisms, as well as the overall dimensions of the device, the inability to install on the wall and the likelihood of the spread of odors and dust during operation.

chamber models consist of two chambers, between which there is a common damper. After warming up, it begins to turn and run cold air into the warm chamber. Then the heated air goes into the room, the damper closes and the process repeats again. However, the chamber recuperator has not gained wide popularity. This is due to the fact that the damper is not able to ensure complete tightness of the chambers, so the air flows are mixed.

Tubular models consist of a large number of tubes that contain freon. In the process of heating from the outgoing flows, the gas rises to the upper sections of the tubes and heats the incoming flows. After heat is released, freon takes on a liquid form and flows into the lower sections of the tubes. The advantages of tubular recuperators include a fairly high efficiency, reaching 70%, the absence of moving elements, the absence of hum during operation, small size and long service life. The disadvantages are the large weight of the models, which is due to the presence of metal pipes in the design.

Models with intermediate heat carrier consist of two separate air ducts passing through a heat exchanger filled with a water-glycol solution. As a result of passing through the thermal unit, the exhaust air gives off heat to the coolant, which, in turn, heats the incoming flow. The pluses of the model include its wear resistance, due to the absence of moving parts, and among the minuses they note a low efficiency, reaching only 60%, and a predisposition to the formation of condensate.

How to choose?

Due to the wide variety of recuperators presented to consumers, it will not be difficult to choose the right model. Moreover, each type of device has its own narrow specialization and recommended installation location. So, when buying a device for an apartment or a private house, it is better to choose a classic plate model with aluminum plates. Such devices do not require maintenance, do not require regular maintenance and are distinguished by a long service life.

This model is perfect for use in an apartment building. This is due low level noise during its operation and compact size. Tubular standard models have also proven themselves well for private use: they are small in size and do not buzz. However, the cost of such recuperators somewhat exceeds the cost of plate products, so the choice of device depends on the financial capabilities and personal preferences of the owners.

When choosing a model for a production workshop, a non-food warehouse or an underground car park, you should choose rotary devices. Such devices have high power and high performance, which is one of the main criteria for working on large areas. Recuperators with an intermediate coolant have also proven themselves well, however, due to their low efficiency, they are not as in demand as drum units.

An important factor when choosing a device is its price. Yes, the most budget options plate heat exchangers can be purchased for 27,000 rubles, while a powerful rotary heat recovery unit with additional fans and a built-in filtration system will cost about 250,000 rubles.

Design and Calculation Examples

In order not to make a mistake with the choice of a heat exchanger, it is necessary to calculate the efficiency and efficiency of the device. To calculate the efficiency, the following formula is used: K = (Tp - Tn) / (Tv - Tn), where Tp denotes the temperature of the incoming flow, Tn is the street temperature, and Tv is the temperature in the room. Next, you need to compare your value with the maximum possible efficiency indicator of the purchased device. Usually this value is indicated in the technical data sheet of the model or other accompanying documentation. However, when comparing the desired efficiency and that indicated in the passport, it should be remembered that in fact this coefficient will be slightly lower than prescribed in the document.

Knowing the efficiency of a particular model, you can calculate its effectiveness. This can be done using the following formula: E (W) \u003d 0.36xRxKx (Tv - Tn), where P will denote the air flow and is measured in m3 / h. After carrying out all the calculations, it is necessary to compare the costs of purchasing a heat exchanger with its efficiency converted into a monetary equivalent. If the purchase justifies itself, the device can be safely purchased. Otherwise, it is worth considering alternative methods for heating the incoming air or installing a number of simpler devices.

When designing the device yourself, it should be borne in mind that countercurrent devices have the maximum heat transfer efficiency. They are followed by cross-flow ducts, and in the last place are unidirectional ducts. In addition, how intense the heat transfer will be directly depends on the quality of the material, the thickness of the dividing partitions, and also on how long the air masses will be inside the device.

Installation subtleties

Assembly and installation of the recovery unit can be carried out independently. by the most simple view homemade device is a coaxial recuperator. For its manufacture take a two-meter plastic pipe for sewerage with a cross section of 16 cm and an air corrugation made of aluminum 4 m long, the diameter of which should be 100 mm. Adapters-splitters are put on the ends of a large pipe, with the help of which the device will be connected to the air duct, and a corrugation is inserted inside, twisting it in a spiral. The recuperator is connected to ventilation system in such a way that warm air was driven through the corrugation, and cold air went through the plastic pipe.

As a result of this design, there is no mixing of flows, and the outside air has time to warm up, moving inside the pipe. To improve the performance of the device, you can combine it with a ground heat exchanger. In the process of testing, such a heat exchanger gives good results. So, at an outside temperature of -7 degrees and an internal temperature of 24 degrees, the productivity of the device was about 270 cubic meters per hour, and the temperature of the incoming air corresponded to 19 degrees. The average cost of a homemade model is 5 thousand rubles.

At self-manufacturing and the installation of the heat exchanger, it should be remembered that the longer the heat exchanger is, the higher the efficiency of the installation will be. Therefore, experienced craftsmen recommend assembling a heat exchanger from four sections of 2 m each, after preliminary thermal insulation of all pipes. The problem of condensate drainage can be solved by installing a water drain fitting, and the device itself can be placed slightly at an angle.