Domestic air handling units with heat recovery. How to install a supply and exhaust ventilation system in a private house with your own hands. Problems installing the system

Air recirculation in ventilation systems is a mixture of a certain amount of exhaust (exhaust) air to the supply air. Thanks to this, a reduction in energy costs for heating fresh air in the winter period of the year is achieved.

Scheme of supply and exhaust ventilation with recovery and recirculation,
where L - air flow, T - temperature.

Heat recovery in ventilation- this is a method of transferring thermal energy from the exhaust air stream to the supply air stream. Recuperation is used when there is a temperature difference between the exhaust and supply air, to increase the temperature of the fresh air. This process does not involve mixing air flows, the process of heat transfer occurs through any material.

Temperature and air movement in the heat exchanger

Heat recovery devices are called heat recuperators. They are of two types:

Heat exchangers-recuperators- they transfer heat flow through the wall. They are most often found in installations of supply and exhaust ventilation systems.

In the first cycle, which are heated by the outgoing air, in the second they are cooled, giving off heat to the supply air.

The supply and exhaust ventilation system with heat recovery is the most common way to use heat recovery. The main element of this system is the supply and exhaust unit, which includes a heat exchanger. The device of the supply unit with a heat exchanger allows transferring up to 80-90% of heat to the heated air, which significantly reduces the power of the air heater, in which the supply air is heated, in case of a lack of heat flow from the heat exchanger.

Features of the use of recirculation and recovery

The main difference between recuperation and recirculation is the absence of air mixing from the room to the outside. Heat recovery is applicable for most cases, while recirculation has a number of limitations, which are specified in regulatory documents.

SNiP 41-01-2003 does not allow re-supply of air (recirculation) in the following situations:

• In rooms, the air flow in which is determined on the basis of emitted harmful substances;
• In rooms in which there are pathogenic bacteria and fungi in high concentrations;
• In rooms with the presence of harmful substances, sublimated upon contact with heated surfaces;
• In rooms of category B and A;
• In rooms where work is carried out with harmful or combustible gases, vapors;
• In rooms of category B1-B2, in which combustible dusts and aerosols can be released;
• From systems with the presence in them of local suction of harmful substances and explosive mixtures with air;
• From vestibules-sluices.

Recycling:
Recirculation in air handling units is actively used more often with high system productivity, when air exchange can be from 1000-1500 m 3 / h to 10000-15000 m 3 / h. The removed air carries a large supply of thermal energy, mixing it into the outside air flow allows you to increase the temperature of the supply air, thereby reducing the required power of the heating element. But in such cases, before being re-introduced into the room, the air must pass through the filtration system.

Recirculation ventilation improves energy efficiency, solves the problem of energy saving in the case when 70-80% of the exhaust air enters the ventilation system again.

Recovery:
Air handling units with recuperation can be installed at almost any air flow rate (from 200 m 3 /h to several thousand m 3 /h), both at low and at large. Recuperation also allows heat to be transferred from the extract air to the supply air, thereby reducing the energy demand on the heating element.

Relatively small installations are used in ventilation systems of apartments and cottages. In practice, air handling units are mounted under the ceiling (for example, between the ceiling and the suspended ceiling). This solution requires some specific requirements from the installation, namely: small overall dimensions, low noise level, easy maintenance.

The air handling unit with recuperation requires maintenance, which obliges to make a hatch in the ceiling for servicing the heat exchanger, filters, blowers (fans).

The main elements of air handling units

A supply and exhaust unit with recovery or recirculation, which has both the first and second processes in its arsenal, is always a complex organism that requires highly organized management. The air handling unit hides behind its protective box such main components as:

• Two fans of various types, which determine the performance of the installation by flow.
• Heat exchanger recuperator- heats the supply air by transferring heat from the exhaust air.
• Electric heater- heats the supply air to the required parameters, in case of a lack of heat flow from the exhaust air.
• Air filter- thanks to it, the control and purification of the outside air is carried out, as well as the processing of the exhaust air in front of the heat exchanger, to protect the heat exchanger.
• Air valves with electric drives - can be installed in front of the outlet air ducts for additional air flow control and channel blocking when the equipment is turned off.
• bypass- thanks to which the air flow can be directed past the heat exchanger during the warm season, thereby not heating the supply air, but supplying it directly to the room.
• Recirculation chamber- providing the admixture of the removed air into the supply air, thereby ensuring the recirculation of the air flow.
  
  

In addition to the main components of the air handling unit, it also includes a large number of small components, such as sensors, an automation system for control and protection, etc.

Control scheme

All components of the air handling unit must be properly integrated into the system of operation of the unit, and perform their functions in the proper amount. The task of controlling the operation of all components is solved by an automated process control system. The installation kit includes sensors, analyzing their data, the control system corrects the operation of the necessary elements. The control system allows you to smoothly and competently fulfill the goals and tasks of the air handling unit, solving complex problems of interaction between all elements of the unit.

Ventilation control panel

Despite the complexity of the process control system, the development of technology makes it possible to provide an ordinary person with a control panel from the plant in such a way that from the first touch it is clear and pleasant to use the plant throughout its service life.

Example. Heat recovery efficiency calculation:
Calculation of the efficiency of using a recuperative heat exchanger in comparison with using only an electric or only a water heater.

Consider a ventilation system with a flow rate of 500 m 3 /h. Calculations will be carried out for the heating season in Moscow. From SNiPa 23-01-99 "Construction climatology and geophysics" it is known that the duration of the period with an average daily air temperature below +8°C is 214 days, the average temperature of the period with an average daily temperature below +8°C is -3.1°C .

Calculate the required average heat output:
In order to heat the air from the street to a comfortable temperature of 20 ° C, you will need:

N = G * C p * p ( in-ha) * (t ext -t avg) = 500/3600 * 1.005 * 1.247 * = 4.021 kW

This amount of heat per unit of time can be transferred to the supply air in several ways:

1. Supply air heating by an electric heater;
2. Heating of the supply heat carrier removed through the heat exchanger, with additional heating by an electric heater;
3. Heating of outdoor air in a water heat exchanger, etc.

Calculation 1: Heat is transferred to the supply air by means of an electric heater. The cost of electricity in Moscow S=5.2 rubles/(kW*h). Ventilation works around the clock, for 214 days of the heating period, the amount of money, in this case, will be equal to:
C 1 \u003d S * 24 * N * n \u003d 5.2 * 24 * 4.021 * 214 \u003d 107,389.6 rubles / (heating period)

Calculation 2: Modern recuperators transfer heat with high efficiency. Let the recuperator heat the air by 60% of the required heat per unit time. Then the electric heater needs to spend the following amount of power:
N (electric load) \u003d Q - Q rec \u003d 4.021 - 0.6 * 4.021 \u003d 1.61 kW

Provided that the ventilation will work for the entire period of the heating period, we get the amount for electricity:
C 2 \u003d S * 24 * N (electric load) * n \u003d 5.2 * 24 * 1.61 * 214 \u003d 42,998.6 rubles / (heating period)

Calculation 3: A water heater is used to heat outdoor air. Estimated cost of heat from service hot water per 1 Gcal in Moscow:
S year \u003d 1500 rubles / gcal. Kcal=4.184 kJ

For heating, we need the following amount of heat:
Q (g.w.) \u003d N * 214 * 24 * 3600 / (4.184 * 106) \u003d 4.021 * 214 * 24 * 3600 / (4.184 * 106) \u003d 17.75 Gcal

In the operation of ventilation and heat exchanger throughout the cold period of the year, the amount of money for the heat of process water:
C 3 \u003d S (hot water) * Q (hot water) \u003d 1500 * 17.75 \u003d 26,625 rubles / (heating period)

The results of calculating the costs of supply air heating for heating
period of the year:

From the above calculations, it can be seen that the most economical option is to use the hot service water circuit. In addition, the amount of money required to heat the supply air is significantly reduced when using a recuperative heat exchanger in the supply and exhaust ventilation system compared to using an electric heater.

In conclusion, I would like to note that the use of installations with recuperation or recirculation in ventilation systems makes it possible to use the energy of the exhaust air, which makes it possible to reduce energy costs for heating the supply air, therefore, the monetary costs for the operation of the ventilation system are reduced. The use of the heat of the removed air is a modern energy-saving technology and allows you to get closer to the "smart home" model, in which any available type of energy is used to the fullest and most useful.

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.

Many of the buildings currently under construction, both industrial and residential, have very complex infrastructures and are designed with the greatest emphasis on energy efficiency. Therefore, it is impossible to do without installations of such systems as general air ventilation systems, smoke protection systems and air conditioning systems. To ensure efficient and long service life of ventilation systems, it is necessary to design and install a system of general air ventilation, a smoke protection system and an air conditioning system with high quality. Installation of such equipment of any type must be carried out with the obligatory observance of certain rules. And according to the technical characteristics, it must correspond to the volume and type of premises in which it will be operated (residential building, public, industrial).

Of great importance is the correct operation of the systems: compliance with the terms and rules for preventive inspections, scheduled preventive repairs, as well as the correct and high-quality adjustment of ventilation equipment.

For each ventilation system in Moscow, accepted for operation, a passport and an operating log are drawn up. The passport is drawn up in two copies, one of which is stored at the enterprise, and the other in the technical supervision service. The passport contains all the technical characteristics of the system, information about the repairs carried out, copies of the as-built drawings of the ventilation equipment are attached to it. In addition, the passport reflects a list of operating conditions for all components and parts of ventilation systems.

According to the established schedule, scheduled inspections of ventilation systems are carried out. During scheduled inspections:

• Defects are identified, which are eliminated during the current repair;
• The technical condition is determined;
• Partial cleaning and lubrication of individual components and parts are carried out.

All data of the planned inspection of ventilation systems are mandatory indicated in the operation log.

Also, during the working shift, the on-duty operational team provides for scheduled overhaul maintenance of ventilation systems. This service includes:

• Start-up, regulation and shutdown of ventilation equipment;
• Supervision of the operation of ventilation systems;
• Monitoring the compliance of the parameters of the air environment and the temperature of the supply air;
• Elimination of minor defects.

Commissioning of general air ventilation systems, smoke protection systems and air conditioning systems

The stage of commissioning is a very important stage, because the high-quality work of ventilation and air conditioning depends on commissioning.

During commissioning, the work of the installation team is visible, and the parameters specified in the project are checked and compared with the parameters of the equipment with those specified in the project documentation. During the inspection, a complete check of the technical condition of the installed equipment, the distribution and uninterrupted operation of adjustment devices, the installation of control and diagnostic devices, and the identification of errors in the operation of the equipment are carried out. If deviations are detected that are within the normal range, then the readjustment does not occur, and the object is prepared for delivery to the customer, with the execution of all documents.

All masters of our company have a specialized education, certificates in health and safety, rich work experience and have all the necessary documents and certificates.

At the stage of commissioning, we measure the air flow velocity in the air ducts, the noise level, approbation of the quality of equipment installation, adjustment of engineering systems in accordance with the project parameters, certification.

Start-up tests and adjustment of ventilation and air conditioning systems must be carried out by a construction and installation or a specialized commissioning organization.

Certification of systems

A technical document drawn up on the basis of a check of the working condition of ventilation systems and equipment, carried out using aerodynamic tests, is called the certification of the ventilation system.

SP 73.13330.2012 "Internal sanitary systems of buildings", updated edition of SNIP 3.05.01-85 "Internal sanitary systems" regulate the form and content of the ventilation system passport.

Obtaining a ventilation system passport, in accordance with the requirements of the above document, is mandatory.

At the end of the installation work, the customer receives a passport for the ventilation system.

A passport must be obtained for each ventilation system.

The passport is indispensable for the registration of purchased equipment, for the correct operation of such equipment, in order to achieve the necessary sanitary and hygienic air parameters.

In the period established by law, this document is provided by the control and supervisory authority. The receipt of this document is an indisputable proof in resolving disputes with the relevant authorities.

Obtaining a ventilation system passport can be carried out as a separate type of work, consisting of a set of aerodynamic tests. The conduct of such events is regulated by the following regulations:

• SP 73.13330.2012;
• STO NOSTROY 2.24.2-2011;
• R NOSTROY 2.15.3-2011;
• GOST 12.3.018-79. “Ventilation systems. Methods of aerodynamic tests”;
• GOST R 53300-2009;
• SP 4425-87. "Sanitary and hygienic control of industrial premises";
• SanPiN 2.1.3.2630-10.

Comfortable suburban housing cannot be imagined without a good ventilation system, since it is they who are the key to a healthy microclimate. However, many are cautious and even wary about the implementation of such an installation, fearing huge electricity bills. If certain doubts have “settled” in your head, we recommend that you look at a recuperator for a private house.

We are talking about a small unit, combined with supply and exhaust ventilation and excluding excessive consumption of electrical energy in the winter, when the air needs additional heating. There are several ways to reduce unwanted expenses. The most effective and affordable is to make an air recuperator with your own hands.

What is this device and how does it work? This will be discussed in today's article.

Features and principle of operation

So what is heat recovery? - Recuperation is a heat exchange process in which cold air from the street is heated by the outflow from the apartment. Thanks to this organization scheme, a heat recovery installation saves heat in the house. A comfortable microclimate is formed in the apartment in a short period of time and with minimal electricity consumption.

The video below shows the air recovery system.

What is a recuperator. General concept for the layman.

The economic feasibility of a recuperative heat exchanger depends on other factors:

• energy prices;
• the cost of installing the unit;
• the costs associated with servicing the device;
• the lifetime of such a system.

note! An air recuperator for an apartment is an important, but not the only element necessary for effective ventilation in a living space. Ventilation with heat recovery is a complex system that functions exclusively under the condition of a professional "bundle".

Recuperator for home

With a decrease in ambient temperature, the efficiency of the unit decreases. Be that as it may, a heat exchanger for a house during this period is vital, since a significant temperature difference "loads" the heating system. If it is 0°C outside the window, then an air stream warmed up to +16°C is supplied to the living space. A household recuperator for an apartment copes with this task without any problems.

Formula for calculating efficiency

Modern air recuperators differ not only in efficiency, nuances of use, but also in design. Consider the most popular solutions and their features.

Main types of structures

Experts focus on the fact that there are several types of heat:

• lamellar;
• with separate heat carriers;
• rotary;
• tubular.

lamellar type of – includes a structure based on aluminum sheets. Such a heat exchanger installation is considered the most balanced in terms of the cost of materials and the value of thermal conductivity (the efficiency varies from 40 to 70%). The unit is distinguished by its simplicity of execution, affordability, and the absence of moving elements. Installation does not require specialized training. Installation without any difficulties is carried out at home, with your own hands.

plate type

Rotary are solutions that are quite popular among consumers. Their design provides for a rotation shaft powered by the mains, as well as 2 channels for air exchange with counterflows. How does such a mechanism work? - One of the sections of the rotor is heated by air, after which it turns and the heat is redirected to the cold masses concentrated in the adjacent channel.

rotary type

Despite the high efficiency, the installations have a number of significant drawbacks:

• impressive weight and size indicators;
• exactingness to regular maintenance, repair;
• it is problematic to reproduce the recuperator with your own hands, to restore its performance;
• mixing of air masses;
• dependence on electrical energy.

You can watch the video below about the types of recuperators (starting from 8-30 minutes)

Recuperator: why is it, their types and my choice

note! A ventilation unit with tubular devices, as well as separate heat carriers, is practically not reproduced at home, even if all the necessary drawings and diagrams are at hand.

DIY air exchange device

The simplest in terms of implementation and subsequent equipment is considered to be a plate-type heat recovery system. This model boasts both obvious "pluses" and annoying "minuses". If we talk about the merits of the solution, then even a home-made air recuperator for the home can provide:

• decent efficiency;
• lack of "binding" to the power grid;
• structural reliability and simplicity;
• availability of functional elements and materials;
• duration of operation.

But before you start creating a recuperator with your own hands, you should also clarify the disadvantages of this model. The main disadvantage is the formation of glaciers during severe frosts. The level of moisture in the street is less than in the air that is present in the room. If you do not act on it in any way, it turns into condensate. During frosts, high humidity levels contribute to the formation of frost.

The photo shows how air is exchanged.

There are several ways to protect the heat exchanger device from freezing. These are small solutions that differ in efficiency and implementation method:

• thermal effect on the structure due to which the ice does not linger inside the system (the efficiency drops by an average of 20%);
• mechanical removal of air masses from the plates, due to which the forced heating of the ice is carried out;
• addition of a ventilation system with a recuperator with cellulose cassettes that absorb excess moisture. They are redirected to housing, while not only condensate is eliminated, but also a humidifier effect is achieved.

We offer you to watch a video - Do-it-yourself air recuperator for home.

Recuperator - do it yourself

Recuperator - DIY 2

Experts agree that cellulose cassettes are the best solution today. They function regardless of the weather outside the window, while the installations do not consume electricity, they do not require a sewer outlet, a condensate collector.

Materials and components

What solutions and products should be prepared if it is necessary to assemble a plate-type home unit? Experts strongly recommend paying priority attention to the following materials:

1. 1. Aluminum sheets (textolite and cellular polycarbonate are quite suitable). Please note that the thinner this material is, the more efficient the heat transfer will be. Supply ventilation in this case works better.
2. 2. Wooden slats (about 10 mm wide and up to 2 mm thick). They are placed between adjacent plates.
3. 3. Mineral wool (up to 40 mm thick).
4. 4. Metal or plywood to prepare the body of the apparatus.
5. 5. Glue.
6. 6. Sealant.
7. 7. Hardware.
8. 8. Corner.
9. 9. 4 flanges (under the pipe section).
10. 10. Fan.

note! The diagonal of the body of the recuperative heat exchanger corresponds to its width. As for the height, it is adjusted for the number of plates and their thickness in conjunction with the rails.

Device drawings

Metal sheets are used to cut squares, the dimensions of each side can vary from 200 to 300 mm. In this case, it is necessary to select the optimal value, taking into account which ventilation system is installed in your home. There should be at least 70 sheets. To make them smoother, we recommend working with 2-3 pieces at the same time.

Diagram of a plastic device

In order for energy recovery in the system to be fully carried out, it is necessary to prepare wooden slats in accordance with the selected dimensions of the side of the square (from 200 to 300 mm). Then they must be carefully processed with drying oil. Each wooden element is glued to the 2nd side of the metal square. One of the squares must be left unpasted.

In order for the recovery, and with it the ventilation of the air, to be more efficient, each upper edge of the rails is carefully coated with adhesive. Individual elements are assembled into a square "sandwich". Very important! The 2nd, 3rd and all subsequent square products should be rotated 90 ° in relation to the previous one. In this way, the alternation of channels is implemented, their perpendicular position.

The upper square is fixed on the glue, on which there are no slats. Using the corners, the structure is carefully pulled together and fastened. In order for heat recovery in ventilation systems to be carried out without air loss, the gaps are filled with sealant. Flange mounts are formed.

Ventilation solutions (manufactured unit) are placed in the housing. Previously, on the walls of the device, it is necessary to prepare several corner guides. The heat exchanger is positioned in such a way that its corners rest against the side walls, while the whole structure visually resembles a rhombus.

In the photo, a homemade version of the device

Residual products in the form of condensate remain in its lower part. The main task is to obtain 2 exhaust channels isolated from each other. Inside the structure of the lamellar element, air masses are mixed, and only there. A small hole is made at the bottom to drain condensate through a hose. In the design, 4 holes are made for the flanges.

Formula for calculating power

Example! For heating the air in the room up to 21°C, which requires60 m3 of airin hour:Q \u003d 0.335x60x21 \u003d 422 W.

To determine the efficiency of the unit, it is enough to determine the temperatures at 3 key points of its entry into the system:

Calculation of recuperator payback

Now you know , what is a recuperator and how necessary it is for modern ventilation systems. These devices are increasingly being installed in country cottages, social infrastructure facilities. Recuperators for a private house are a fairly popular product in our time. At a certain level of desire, the recuperator can be assembled with your own hands from improvised means, as mentioned above in our article.

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 the optimal temperature regime of the 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 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 right model depends on the power of the device, the physical properties and 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 or 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 control 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 a circular cross 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. The instrument panels 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.

Through the drain hole, water enters a 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. The use of collected water for humidifiers is not recommended: the liquid may contain a large number of pathogenic microorganisms, and therefore must be poured into the sewer system.

However, if frost from condensate still forms, it is recommended to install additional equipment - a 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 of ventilation equipment represents a wide range of recuperators of 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 efficiency indicators 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 advantages, plate heat exchangers also have their weaknesses. 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 parts, 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 to the low noise level 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. So, the most budget options for 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 depends directly 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. The simplest type of homemade device is a coaxial heat exchanger. For its manufacture, a two-meter plastic sewer pipe with a cross section of 16 cm and an air corrugation made of aluminum 4 m long are taken, 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 heat exchanger is connected to the ventilation system in such a way that warm air is driven through the corrugation, and cold air goes through a 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.

When manufacturing and installing a heat exchanger on your own, 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.