Diagram of a ventilation system with a recuperator in a private house. The principle of operation and installation of air handling units with heat recovery. Will the hole in the wall under the heat exchanger become a source of cold penetration into the room

Issues discussed in the material:

• What is heat recovery ventilation
• Ventilation scheme with recuperation
• What are the advantages of a ventilation system with heat recovery?
• Types of recuperators for ventilation
• How to choose air handling units with heat recovery
• Tips on how to install the supply and exhaust ventilation with recuperation

Each person, of course, in his own way imagines how comfortable housing should be equipped. For one, the appearance and interior of the premises will be of paramount importance, while the other considers various amenities to be the most important. But no matter what we prefer, in any case, most will agree that in order for housing to be called comfortable, it is necessary that it has an optimal temperature - warm in the cold season, and cool in hot weather.

Of course, no matter how we create such conditions, they are always associated with certain costs. We can use devices like air conditioners, fans, heaters. Someone will prefer to carry out repairs in such a way as to make the premises airtight. And such a move will really help to save the internal temperature, but we must not forget that in such cases one serious trouble cannot be avoided - the housing will no longer be ventilated, so there will be no talk of any comfort. The only way out is to make ventilation to ensure the movement of air. Some may be worried about whether this will result in additional energy costs. But they will even decrease if your choice is ventilation with heat recovery for a private house, apartment or industrial facility. What is it, how does it work? This article will tell about this and much more.

What is heat recovery ventilation

Heat recovery home ventilation is one of the forced ventilation systems. As a rule, it provides for heating the air. This function is partially performed by a recuperator - a device designed to heat the air, although the main heating is provided not by it, but by the air heater.

Of course, you might never have heard of supply or exhaust ventilation with heat recovery, but this does not mean that it is a new invention. Most likely, you are misled by the Latin word "recuperation", which can be translated into Russian as "the return of what you spent." This reveals the whole point: a recuperator is a special heat exchanger, that is, a device that is quite common in ventilation systems, although in Russia it is still not used as often as abroad. How is the ventilation of a private house or apartment recuperated? Let's look at it in more detail.

Heat recovery - is the return of heat from the room. The bottom line is that there is an incoming and outgoing air flow. At the same time, the air that leaves the room heats the counter air due to heat transfer. This happens in the cold season, and on hot days, for example, in summer, the outgoing air, on the contrary, cools the incoming flows. But in such situations it is more correct to speak about cold recovery.

Obviously, such a procedure is necessary in order for the user to save available funds, because when ventilation is not equipped with recovery, a lot of heat goes outside instead of being reused indoors. Accordingly, heating bills increase, since, in fact, we heat the street, spending an exorbitant amount of heat for nothing. It is in order to avoid such waste and huge bills that it is worth thinking about installing ventilation with heat recovery. After all, this is how you return the air that you heated, do not allow heat to leave the room, save money.

It is not surprising that ventilation with recuperation is becoming more and more popular and there is nothing to oppose to the classic versions of ventilation systems with a similar design. This is logical, because forced ventilation with recuperation is not much more expensive than conventional ventilation, and its maintenance is completely elementary. In this regard, many prefer to forget about climate equipment, which was once positioned as the most efficient in combination with ventilation systems. Recuperation is much more profitable both in terms of rational use of electricity and in terms of saving heating costs. Its cheapness is compared with the cost of lighting with energy-saving light bulbs.

What else attracts consumers to the supply and exhaust ventilation system with air recovery?

First of all, such devices are small in size.

Secondly, they do not spoil the interior.

Thirdly they have low noise level.

Fourth, at a minimum of expenses we receive a maximum of efficiency of work.

They are also in demand in public institutions, among which the following can be listed:

• Cinemas and theaters.
• Canteens, cafes, snack bars.
• Libraries.
• Hotels and inns.
• Stations.
• Offices and commercial premises.

It is possible to design a ventilation system with recuperation of a private house, multi-storey building, etc. A variety of such devices allows you to choose them for any occasion. The different power of such structures makes it possible to find an option even for buildings in which there is a residential basement.

It is important to understand that supply ventilation with heat recovery for an apartment or house is a forced system. It differs from the natural one by the presence of fans that provide the movement of air flows at any convenient time and do not depend on external factors, such as draft, which appears due to the difference in temperatures.

Ventilation scheme with recuperation

What are the advantages of a ventilation system with heat recovery?

As we have noted more than once, the main advantage of such a system is the ability to control the interaction of air inflow and exhaust. Due to this, we significantly reduce ventilation heat losses, although we continue to saturate the room with fresh air.

Now let's talk in more detail about each of the advantages of ventilation systems with recuperation.

Efficiency. Natural removal of air is not always a convenient solution, because we become dependent on circumstances, environmental conditions, temperature differences. In this regard, it is much easier to use a ventilation system with recuperation, capable of forcibly driving air. A simple example of forced ventilation is a kitchen hood. More complex devices are capable, among other things, of getting rid of excess moisture. But this is simple exhaust equipment. In our case, we are talking about supply and exhaust systems that can organize the movement of air flows in both directions at once, mix them and form the necessary temperatures for a comfortable stay of a person in the room, that is, to carry out air recovery.

Profitability. It should be noted that systems with recuperation are able to recoup their cost by saving on heating and electricity. Costs are significantly reduced, sometimes by 5 times, that is, you are already paying 80% less than usual. Ask your friends how much it costs them to heat a country house if you don’t have one. The numbers will be impressive. Imagine how much money recovery ventilation can save. In case of wear of inexpensive elements, they can be replaced without negative consequences. In the warm season, you can save on climate control equipment, while reducing emissions of harmful substances into the atmosphere. Yes, even from the point of view of ecology, you already cause much less damage to nature, because, among other things, you reduce the load on the network. And do not let it seem to you that one person is not enough. Firstly, these are quite serious amounts of energy. Secondly, there are more and more people who switch to ventilation with recuperation over the years.

Practicality. Ventilation systems with recuperation, as a rule, are small in size, which means they are easy to install. You can place such equipment in the bathroom, and in the closet, and build it into the ceiling. Today there are a huge number of models, for all tastes. So you don't have to worry about the interior.

Types of recuperators for ventilation

Recuperator - it is a heat exchanger, albeit a special one. It is connected to ventilation ducts that produce exhaust and air supply. Dirty air from the room gives off heat to the incoming flows, that is, a recovery procedure is performed.

Plate heat exchangers differ from the usual in that they prevent the mixing of air. In them, the recovery is carried out in a slightly different way. A number of plates are close to each other, due to which the air can transfer heat without touching. The material in such ventilation systems is typically aluminum foil, known for its thermal conductivity. There are plastic items. They are more expensive but more efficient.

Ventilation with heat recovery by means of plate heat exchangers often suffers from frost. The fact is that the surfaces of the heat exchanger are covered with ice due to condensate. This is not the most favorable effect on the quality of the device. And then the owner of ventilation with recuperation has to excel in order to make the frost melt. Accordingly, time, effort, and energy are wasted.

However, some developers have foreseen how to ensure the protection of ventilation with recovery from frost. To do this, a technology was invented that heats the incoming air flow to a temperature at which the condensate simply cannot freeze.

By the way, this is not the only way. Other developers have proposed equipping ventilation systems with recuperation with hygroscopic cellulose cassettes. We save on air heating, as such cellulose itself absorbs moisture, and then returns it at the exit. But they can only be used in cases where there is no waterlogging of the air.

Rotary recuperators. In heat recovery ventilation systems using these devices, the air is mixed. The principle of operation is as follows: the metal rotor rotates, providing the movement of air out and in. The rotation speed is usually adjustable.

As is clear, recovery in this case has a number of disadvantages, for example, it is much more expensive due to the presence of elements that fail over time. But high efficiency rates, reaching 90%, contribute to the popularity of such products.

In essence, the expediency of acquiring such a device largely depends on the efficiency of the organization of air recovery. A quality product usually pays for itself.

Recuperators with intermediate heat carrier. This device has two compartments separated by a reservoir of liquid capable of transferring heat from the outgoing incoming air.

Of course, the recovery in this case is very safe, because pollution is not transferred between flows. Speed ​​adjustment is provided. Wear is unlikely. But the disadvantage is low efficiency, ranging from 45 to 60%.

Chamber recuperators. The shutter divides the compartment into two halves. As it rotates, it reverses the air currents. The change in temperature comes from the walls of the chamber.

Although air recovery in this case has a high efficiency rate of 70 to 80%, and wear is unlikely, it is characterized by the transmission of dirt and unpleasant odors.

heat pipes. This recovery device is made of hermetically connected tubes. They contain a substance that contributes to a change in air temperature. Most often it is one of the freons.

Closure prevents leakage of the substance. It just flows in different directions of the tube. The efficiency of such equipment is in the region of 50 - 70%.

How to choose air handling units with heat recovery

What should be kept in mind when choosing ventilation with heat recovery? You need to buy such equipment so as not to regret it, so ask the seller about the following nuances:

First, ask the seller the following questions:

1. Who is the manufacturer of this ventilation with air recovery? How long has this company been operating, what reputation does it have, what else does it produce?
2. How efficient is this ventilation with air recovery?

Here you need a specialist who can make a detailed calculation, based on the characteristics of your premises. It is clear that buying supply and exhaust ventilation with heat recovery for an apartment and a three-story building is not the same thing.

3. What will be the resistance of the system to air flow after installation of this equipment?

Here you again need expert advice. It is important not only to limit yourself to some general characteristics indicated in the table from the Internet, but to make a detailed calculation, for example, taking into account the number of bends in the duct and many other nuances. The ratio of air flow and system resistance is one of the most important selection factors.

4. How expensive will it be to maintain ventilation with this heat exchanger? What is its energy class? What are the savings with this device?
5. What are the Efficiencies of this heat exchanger for ventilation?

Note that we say "ratios", not "ratio". Why? Isn't he alone? Not really. There is a declared one - this is some average value. And there is a real efficiency, which is an objective indicator. What does it depend on. Many factors. Here and humidity and air, and how the system is organized, and the temperature inside and outside.

• With a paper heat exchanger, the Efficiency will be between 60 and 70 percent. What does this mean for us? Is this good or bad? This means that air recovery ventilation is frost-resistant, although not one hundred percent.
• In the presence of an aluminum heat exchanger, the efficiency will be no more than 63%, while the efficiency of the air recuperator will be from 42 to 45% percent. Thus, you will have to use a significant amount of electricity to get rid of frost.
• The rotary air recuperator has excellent efficiency indicators, but on the condition that it is controlled automatically, based on the readings of special sensors. However, these heat exchangers can freeze in the same way as aluminum ones, which reduces efficiency.

What else should be considered when choosing a heat exchanger for ventilation?

Tips on how to install the supply and exhaust ventilation with recuperation

Now let's talk about how to install the supply and exhaust ventilation with recuperation. Let's start with how to choose the most suitable place for installation.

• If you have a private house, it is best to choose non-residential premises for installation. This is a basement, attic, utility room. And the boiler room is generally the most ideal option for supply and exhaust ventilation.
• Pay attention to the fact that the installation of ventilation with recuperation does not contradict the requirements specified in the technical documentation.
• It is best that the wiring of the ventilation system with air recovery falls on the premises where there is heating.
• Ventilation with air recovery is likely to pass through those rooms where there is no heating. These segments must be thoroughly insulated.
• It is necessary to insulate outdoor ventilation ducts with air recovery, as well as those located in the outer walls.
• It is advisable to locate ventilation equipment with air recovery in such a way that it is as far away from living quarters as possible so that the noise of work, which is never excluded, does not interfere.

Actually, these tips for installing ventilation with air recovery cannot be applied in all cases without exception. It is possible that you have other conditions and places where you can equip a similar system. Much depends on the layout of the building and the dimensions of the equipment.

Air intake for ventilation with recuperation, it is better to equip it on the side where the wind is less frequent. This will avoid dust and debris, or at least reduce their amount. When doing this, it is important to make sure that there are no chimneys, pipes or any other places where unwanted air can escape from.

Installation. It is strongly not recommended to install ventilation with air recovery on your own. This is a risky venture that can lead to unpleasant consequences. If you are reading this article, you are unlikely to be an expert in the field of installation of ventilation with recovery, so we recommend that you seek help from professionals.

That's all. We hope that the material was useful to you!

P.S. You can always call the company Climate Formula”, and our specialists will advise you on all the issues that have arisen.

Heat recovery ventilation is equipment designed to process air to such parameters that a person can 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 ventilation units with recuperation are used. 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 by 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.

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 factories or an unacceptable vertical temperature gradient in a 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

The internal structure of supply and exhaust ventilation systems is quite simple, so their independent element-by-element purchase and installation is possible. In the event that assembly or self-assembly is difficult, 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;
• the return of a large amount of moisture, which remains in the form of condensate on the drum and evaporates upon 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 dimensions.

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 bulky and expensive device, the use of which 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 tubular 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 a two-story cottage with a total area of ​​270 m2 shows the feasibility of installing such a system

The cost of recuperators with high efficiency is quite high, they have a complex design and large dimensions. It is sometimes possible to circumvent these problems by installing several simpler devices in such a way that the incoming air passes through them in series.

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 drag. As a rule, its exact calculation is impossible due to the complexity of the mathematical model, therefore, experimental studies are carried out for typical monoblock structures, and components are selected for individual devices.

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. As a rule, the permissible air velocity 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 unnecessary energy costs, inefficient heating of the outside air and a shortened 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 the effective ways to assess clogging is to install 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 on an individual 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.

Supply and exhaust ventilation with heat recovery is a system that allows you to establish a reliable change of exhaust air in the room. Installation of equipment allows you to heat the air entering the room, using the temperature of the outgoing flow. The cost of purchasing and installing the system quickly pays off.

It is important to know the main points when selecting and installing equipment.

What is heat recovery?

In the air recuperator, the heat from the exhaust gases is removed. The two streams are separated by a wall through which heat exchange takes place between moving air streams in a constant direction. An important characteristic of the equipment is the level of efficiency of the heat exchanger. This value for different types of equipment is in the range of 30-95%. This value is directly dependent on:

• design and types of recuperator;
• the temperature difference between the heated outgoing air and the temperature of the carrier behind the heat exchanger device;
• acceleration of the flow through the heat exchanger.

Advantages and disadvantages of a ventilation system with a heat exchanger

Such equipment allows:

• to produce a constant change of air masses in a room of various sizes;
• at the need of residents, it is possible to supply a heated stream;
• there is a constant purification of incoming oxygen;
• on request, it is possible to install equipment with the possibility of humidifying the air in the premises, in such systems a channel is provided to remove condensate;
• with heat recovery and the selection of sufficient power equipment, a significant reduction in the cost of paying for electricity is possible.

Among the shortcomings of the system, several points can be distinguished:

• increased noise level during operation of fans;
• when installing cheap equipment, it is not possible to cool the incoming air during a hot period;
• condensate must be constantly monitored and drained.

The principle of operation of the ventilation system

Such ventilation with heat recovery allows to reduce the load on the air conditioning system of buildings during the hot season. Conditioned air from the room, when passing through the heat exchanger, lowers the temperature of the atmospheric flow from the street. In winter, according to this scheme, the outboard flow is heated.

Installation is especially relevant in buildings with a large area and a common air conditioning system. In such places, the level of air exchange can exceed 700-800 m 3 /h. Such installations have impressive dimensions, so you will need to prepare a separate room in the basement, on the basement or attic. If installation is required in the attic, it will need to be additionally soundproofed and prevent heat loss and condensation in the air ducts.

The ventilation system with recuperation is manufactured in several types, we will analyze the advantages and disadvantages of each of them.

Types of devices with air recovery

For a better comparison, we present the types of recuperators in a separate table.

A recuperation unit with heat pipes is produced for separate small rooms in a building. They do not require an air duct system. But in this case, with insufficient distance between the flows, it is possible to remove the incoming flows and the absence of circulation of air masses.

List of possible problems after system installation

There are no critical problems if recuperative ventilation is installed in the building. The main malfunctions are eliminated by the system manufacturers under warranty, but a few “troubles” can overshadow the joy of the owners of buildings and premises after installing the equipment for the supply and exhaust air ventilation system. These include:

1. Possibility of condensation. During the passage of air mass flows with a high heating temperature and their contact with cold atmospheric air, water droplets fall on the walls of the chamber in a closed chamber. At sub-zero temperatures on the street, the fins of the heat exchanger freeze, and the movement of flows is disturbed, the efficiency of the system decreases. If the channels are completely frozen, the operation of the device may stop.
2. System energy efficiency level. Supply and exhaust systems equipped with an additional heat exchanger of various types require electricity to operate. Therefore, it is required to carry out accurate calculations of equipment of various types specifically for the premises that will be serviced by the system.

You should not save money when buying, and purchase a device in which the level of energy savings will exceed the cost of operating the equipment.

1. Full payback period of the air ventilation system. The period for a full refund of funds spent on the purchase and installation of equipment directly depends on the previous paragraph. It is important for the consumer that these costs pay off over a 10-year period. Otherwise, equipping a room or building with an expensive ventilation system is not cost-effective.

During this period, it will be necessary to repair and possibly replace parts of the system and additional costs for their purchase and payment for their replacement.

Ways to prevent freezing of the heat exchanger

Some types of devices are made taking into account the prevention of severe freezing of the surfaces of the heat exchanger. At low temperatures outside, ice buildup can completely block the access of fresh air to the room. Some systems begin to overgrow with a crust of ice when the street temperature drops below 0 0 .

In this case, the flow leaving the room is cooled to a temperature below the dew point and the surfaces begin to freeze over. To resume operation of the device, it will be necessary to raise the temperature of the incoming stream to positive values. The ice crust will collapse, the equipment will be able to continue working.
To avoid such situations, air handling units with a built-in heat recuperator can be protected from such a breakdown using several methods:

• to protect the device, it may be necessary to additionally equip the unit with an electric air heater. It does not allow the outgoing air masses to cool below the dew point and prevents the appearance of water droplets and the formation of ice;
• The most reliable method, which excludes the possibility of freezing of the heat exchanger fins, is to equip the device with an electronic control system for the defrost circuit, which is switched on taking into account several parameters. To do this, it may be necessary to set a date for turning on the electric heaters of the incoming air, at the first sub-zero temperatures.
  You can install a sensor that reacts to cold air and turns on air heaters in the ventilation system. In any case, the operation of air-heating devices in ventilation is cyclical, only in the cold season. When the supply ventilation is turned on, the incoming flow and the exhaust gases removed from the room are heated.

After a certain period of time, the supply fan turns off. At this time, the incoming flow in the heat exchanger is heated due to the temperature of the outgoing air, which is displaced by the exhaust fan. This principle of operation of the heating circuit operates automatically throughout the cold period of the year.

To prevent the formation of frost on the device, we advise you to purchase a plate heat exchanger with plastic fins.

The method of self-calculation of the power supply and exhaust ventilation

First of all, it is necessary to determine the volume of all air flows necessary to create comfortable conditions. This can be done in several ways:

1. You can make a calculation based on the total area of ​​\u200b\u200bthe building, not taking into account the residents. The following calculation scheme is used here - within an hour, for each m 2 of the total area, 3 m 3 of air should be supplied.
2. Based on sanitary standards, for a comfortable stay, for each person living in the room, at least 60 m 3 should be supplied within an hour, for incoming guests, another 20 m 3 must be added.
3. Proceeding from the construction standards of 2.08.01-89, the norms for the frequency of air replacement in a room of a certain area within an hour were developed. Here the calculation is made taking into account the purpose of buildings. To do this, it is necessary to determine the product of the frequency of complete replacements of air masses and the volume of the entire room or building.

In conclusion, we note.

Regardless of the pronunciation of the word ventilation, in English or other languages, the main task of the supply and exhaust system with a heat recuperator is to create comfortable conditions for people in the room. Therefore, having decided on the calculation of the required power and the type of heat exchanger, you can safely proceed to equipping the house with a reliable ventilation system.

To increase the service life, filters can be added to the circuit to purify the air. But it should be remembered that it is easier to prevent breakdowns by conducting timely maintenance and care than to spend money on repairs or the purchase of new equipment.