Supply and exhaust system with heat recuperator. Types and principle of operation of ventilation with recovery

Air handling units with heat recovery- ventilation equipment designed to pump fresh air into rooms from the street and simultaneously remove old, exhaust air with low oxygen content. The supply air is forced into the outer chamber using a fan, and then distributed throughout the rooms through diffusers. The exhaust fan removes exhaust air through special valves.

The main problem with intensive air exchange using supply and exhaust ventilation is high heat loss. To minimize them, supply and exhaust units with heat recovery were developed, which made it possible to reduce heat loss several times and reduce space heating costs by 70-80%. The operating principle of such installations is to recover the heat of the outgoing air flow by transferring it to the supply air flow.

When equipping the facility air handling unit with recovery heat, warm exhaust air is taken through air intakes located in the most humid and polluted rooms (kitchens, bathrooms, toilets, utility rooms, etc.) Before leaving the building, the air passes through the heat exchanger of the recuperator, transferring heat to the incoming (supply) air. Heated and purified supply air flows through air ducts into the premises through bedrooms, living rooms, offices, etc. Due to this, constant air circulation is carried out, while the incoming air is heated by the heat given off by the exhaust air.

Types of recuperators

Air handling units can be equipped with several types of recuperators:

• plate recuperators are one of the most common recuperator designs. Heat exchange is carried out by passing supply and exhaust air through a series of plates. During operation, condensate may form in the recuperator, so plate recuperators are additionally equipped with a condensate drain. Heat transfer efficiency reaches 50-75%;
• rotary recuperators - heat exchange is carried out through a rotating rotor, and its intensity is regulated by the speed of rotation of the rotor. The rotary recuperator has a high heat transfer efficiency - from 75 to 85%;
• less common types are recuperators with an intermediate coolant (water or a water-glycol solution plays its role) with an efficiency of up to 40-60%, chamber recuperators divided into two parts by a damper (efficiency up to 90%) and heat pipes filled with freon (efficiency 50-70%).

Order air handling units with recovery heat in the MirCli online store on a turnkey basis - with delivery and professional installation.

During the ventilation process, not only exhaust air is recycled from the room, but also part of the thermal energy. In winter, this leads to higher energy bills.

Heat recovery in centralized and local ventilation systems will allow you to reduce unjustified costs without compromising air exchange. To recover thermal energy, different types of heat exchangers are used - recuperators.

The article describes in detail the models of units, their design features, operating principles, advantages and disadvantages. The information presented will help in choosing the optimal option for arranging the ventilation system.

Translated from Latin, recuperation means compensation or return. With regard to heat exchange reactions, recovery is characterized as a partial return of energy expended on a technological action for the purpose of application in the same process.

Local recuperators are equipped with a fan and a plate heat exchanger. The inlet “sleeve” is insulated with sound-absorbing material. The control unit of compact ventilation units is located on the internal wall

Features of decentralized ventilation systems with recovery:

• Efficiency – 60-96%;
• low productivity– the devices are designed to provide air exchange in rooms up to 20-35 sq.m;
• affordable price and a wide selection of units, ranging from conventional wall valves to automated models with a multi-stage filtration system and the ability to adjust humidity;
• ease of installation– for commissioning, no installation of air ducts is required; you can do it yourself.

  Important criteria for choosing a wall inlet: permissible wall thickness, performance, efficiency of the recuperator, diameter of the air channel and temperature of the pumped medium

  Conclusions and useful video on the topic

  Comparison of the operation of natural ventilation and a forced system with recovery:

  The principle of operation of a centralized recuperator, calculation of efficiency:

  Design and operating procedure of a decentralized heat exchanger using the Prana wall valve as an example:

  About 25-35% of the heat leaves the room through the ventilation system. Recuperators are used to reduce losses and effectively recover heat. Climatic equipment allows you to use the energy of waste masses to heat the incoming air.

  Do you have anything to add, or do you have questions about the operation of different ventilation recuperators? Please leave comments on the publication and share your experience in operating such installations. The contact form is located in the lower block.

It is well known that there are several types of room ventilation systems. Natural ventilation is the most widespread, when the inflow and outflow of air is carried out through ventilation shafts, open vents and windows, as well as through cracks and leaks in structures.

Of course, natural ventilation is necessary, but its operation is associated with a lot of inconvenience, and it is almost impossible to achieve cost savings with its installation. Yes, and calling the movement of air through slightly open windows and doors ventilation is a stretch - most likely, it will be ordinary ventilation. To achieve the required circulation intensity air masses windows must be open around the clock, which is unattainable in the cold season.

That is why the device of forced or mechanical ventilation is considered a more correct and rational approach. Sometimes it is simply impossible to do without forced ventilation; most often they resort to its installation in production premises with deteriorated working conditions. Let's leave industrialists and production workers aside and turn our attention to residential buildings and apartments.

Often, in pursuit of savings, owners of cottages, country houses or apartments invest a lot of money in insulating and sealing their homes and only then realize that due to a lack of oxygen it is difficult to stay indoors.

The solution to the problem is obvious - you need to arrange ventilation. The subconscious mind suggests that the best option would be to install energy-saving ventilation. The lack of properly designed ventilation can cause your home to turn into a real gas chamber. This can be prevented by choosing the most rational decision– forced-exhaust ventilation device with heat and moisture recovery.

What is heat recovery

Recovery means its preservation. The outgoing air flow changes the temperature (heats, cools) the supplied air by the supply and exhaust unit.

Scheme of operation of ventilation with heat recovery

The design assumes separation of air flows to prevent their mixing. However, when using a rotary heat exchanger, the possibility of the exhaust air flow entering the incoming air flow cannot be excluded.

The “Air Recuperator” itself is a device that provides heat recovery from exhaust gases. Heat exchange occurs through the dividing wall between the coolants, while the direction of movement of the air masses remains unchanged.

The most important characteristic of a recuperator is determined by the recuperation efficiency or efficiency. Its calculation is determined from the ratio of the maximum possible heat received and the actual heat received behind the heat exchanger.

The efficiency of recuperators can vary over a wide range - from 36 to 95%. This indicator is determined by the type of recuperator used, the speed of air flow through the heat exchanger and the temperature difference between the exhaust and incoming air.

Types of recuperators and their advantages and disadvantages

There are 5 main types of air recuperators:

• Lamellar;
• Rotary;
• With intermediate coolant;
• Chamber;
• Heat pipes.

Lamellar

A plate recuperator is characterized by the presence of plastic or metal plates. The exhaust and incoming flows pass on opposite sides of the heat-conducting plates without contacting each other.

On average, the efficiency of such devices is 55-75%. A positive characteristic is the absence of moving parts. The disadvantages include the formation of condensation, which often leads to freezing of the recuperative device.

There are plate heat exchangers with moisture-permeable plates that ensure the absence of condensation. The efficiency and principle of operation remain unchanged, the possibility of freezing of the heat exchanger is eliminated, but at the same time the possibility of using the device to reduce the level of humidity in the room is also excluded.

In a rotary recuperator, heat is transferred using a rotor that rotates between the supply and exhaust ducts. This device is characterized by a high level of efficiency (70-85%) and reduced energy consumption.

The disadvantages include slight mixing of flows and, as a result, the spread of odors, a large number of complex mechanics, which complicates the maintenance process. Rotary heat exchangers are effectively used for drying rooms, so they are an ideal option for installation in swimming pools.

Recuperators with intermediate coolant

In recuperators with an intermediate coolant, water or a water-glycol solution is responsible for heat transfer.

The exhaust air provides heating to the coolant, which, in turn, transfers heat to the incoming air flow. Air flows do not mix, the device is characterized by a relatively low efficiency (40-55%), usually used in industrial premises with a large area.

Chamber recuperators

A distinctive feature of chamber recuperators is the presence of a damper that divides the chamber into two parts. High efficiency (70-80%) is achieved due to the ability to change the direction of air flow by moving the damper.

Disadvantages include slight mixing of flows, transmission of odors and the presence of moving parts.

Heat pipes are a whole system of tubes filled with freon, which evaporates when the temperature rises. In another part of the tubes, the freon cools to form condensation.

The advantages include the elimination of mixing of flows and the absence of moving parts. Efficiency reaches 65-70%.

It should be noted that previously, due to their significant dimensions, recuperative units were used exclusively in production; now the construction market offers recuperators with small dimensions that can be successfully used even in small houses and apartments.

The main advantage of recuperators is the absence of the need for air ducts. However, this factor can also be considered as a disadvantage, since for effective operation a sufficient distance between the exhaust and supply air is required, otherwise fresh air is immediately drawn out of the room. Minimum permissible distance between opposite air flows should be at least 1.5-1.7 m.

Why is moisture recovery needed?

Moisture recovery is necessary to achieve a comfortable ratio of humidity and room temperature. A person feels best at a humidity level of 50-65%.

During the heating period, the already dry winter air loses even more moisture due to contact with the hot coolant, often the humidity level drops to 25-30%. With this indicator, a person not only feels discomfort, but also causes significant harm to his health.

In addition to the fact that dry air has a negative impact on human well-being and health, it also causes irreparable damage to furniture and carpentry made of natural wood, as well as paintings and musical instruments. Some may say that dry air helps get rid of dampness and mold, but this is far from true. WITH similar shortcomings can be dealt with by insulating the walls and installing high-quality supply and exhaust ventilation while maintaining a comfortable level of humidity.

Ventilation with heat and moisture recovery: scheme, types, advantages and disadvantages

What is heat recovery ventilation? How this system works, what types there are and their pros and cons.

Ventilation with heat recovery

During the period of energy crisis and rising prices for energy resources, the use of energy-saving technologies in all areas of economic activity becomes especially relevant. The role of heat recuperators in this matter cannot be underestimated. Engineering installations not only significantly save gas for space heating, but also, practically free of charge, return heat intended for release into the atmosphere for useful use.

Operation of air exchange with air heating

Supply and exhaust ventilation with heat recovery solves three main problems:

• providing the premises with fresh air;
• return of thermal energy leaving with air through the ventilation system;
• preventing cold streams from entering the house.

The process can be schematically illustrated using an example. Organization of air exchange is necessary even on a frosty winter day with a temperature outside the window of -22°C. For this included supply and exhaust system When the fan is running, it blows air from the street. It seeps through the filter elements and, already cleaned, enters the heat exchanger.

As the air passes through it, it has time to warm up to +14-+15°C. This temperature may be considered sufficient, but not adequate sanitary standards for accommodation. To achieve room temperature parameters, it is necessary to bring the air to the required values ​​using the reheating function to +20°C in the recuperator itself using a heater (water, electric) of low power - 1 or 2 kW. With such temperature indicators, air enters the rooms.

The heater operates in automatic mode: when the outside air temperature drops, it turns on and operates until it heats up to the required values. At the same time, the waste stream is already heated to a “comfortable” 18 or 20 degrees. It is removed using a built-in ventilation unit, having previously passed through a heat exchange cassette. In it, it gives off heat to the oncoming cold air from the street, and only then goes into the atmosphere from the recuperator with a temperature of no more than 14-15°C.

Attention! The installation of metal-plastic structures disrupts the natural supply of fresh air flows into an apartment or house. The problem is solved by a forced system that supplies unheated air from the street, but also negates the efficiency of energy saving from plastic windows. Supply and exhaust ventilation with a recuperator is a comprehensive solution to the heating problem with simultaneously functioning air exchange, an active method of energy conservation.

Advantages of a supply and exhaust system with heating function

• Supplies fresh air, improves indoor air quality.
• Prevents the loss of moisture on the surface, the formation of condensation, mold and mildew.
• Eliminates the conditions for the appearance of viruses and bacteria in the room.
• Saves costs on electrical and thermal energy by restoring about 90% of the heat lost from the exhaust streams.
• Promotes regular air exchange.
• The versatility of the design of heat exchange systems expands the scope of their application at various types of facilities.
• Economical use and maintenance. Maintenance, including cleaning, replacing filters, checking all components and components of the system, is carried out only once annually.

Attention! The operation of recuperators in old residential buildings, where natural air exchange is ensured, will be ineffective wooden structures windows, cracks in wood floors and leaks in doors. The greatest effect from heat recovery is observed in modern buildings with high-quality insulation premises and good tightness.

Types of heat exchangers

The most common four categories of units are distinguished:

• Rotary type. Powered by mains power. Economical, but technically complex. The working element is a rotating rotor with metal foil applied over the entire surface. The heat exchanger with street air passing inside reacts to the temperature difference between the outside and inside the rooms. This adjusts the speed of its rotation. The intensity of heat supply changes, preventing icing of the recuperator in winter period, which allows you to avoid drying out the air. The efficiency of the devices is quite high and can reach 87%. In this case, mixing of counter flows (up to 3% of the total amount) and the flow of odors and contaminants is possible.
• Plate models. They are considered the most popular due to their affordable price and efficiency. It reaches 40-65% thanks to the aluminum heat exchanger. Due to the absence of rotating and friction-affected units and parts, they are considered simple in design and reliable in operation. Air flows separated by aluminum foil do not diffuse and pass on both sides of the heat-conducting elements. Variety: plate model with a plastic heat exchanger. Its efficiency is higher, but otherwise it has the same characteristics.

Attention! Plate devices are inferior to rotary devices in that they freeze and dry the air. Additional constant hydration is a must. The optimal area of ​​application is the wet environment of swimming pools.

• Recirculation type. Its “trick” is its complex design and the use of a liquid carrier (water, water-glycol solution or antifreeze) as an intermediate link in heat transfer. A heat exchanger is installed on the exhaust hose, which takes the heat from the exhaust air flow and heats the liquid with it. Another heat exchanger, but this time at the air intake from the street, transfers heat to the incoming air without mixing with it. The efficiency of such installations reaches 65%; they do not participate in moisture exchange. Electricity is required to operate.
• The roof type of devices is effective (58-68%), but for home use not suitable. It is used as a component in the ventilation of shops, workshops and other similar premises.

Calculation of the efficiency of the recuperator

You can roughly calculate how effective the installed supply ventilation with heat recovery will be, both in winter and summer, when the installation is working for cooling. The formula for calculating the temperature of the supply air flow for an installation depending on the numerical characteristic of energy efficiency (efficiency), external and indoor air temperatures looks like this:

Tpp = (tin – tul)*efficiency + tul,

where the temperature values ​​are:

Tpr – expected at the outlet of the recuperator;

tin – indoors;

For calculations, the certified efficiency value of the device is taken.

As an example: at frosts of -25°C and room temperature +19°C, as well as an installation efficiency of 80% (0.8), the calculation shows that the required air parameters after passing through the heat exchanger will be:

Tpp = (19 – (-25))*0.8 – 25 = 10.2°С

The calculated temperature indicator of the air after the recuperator was obtained. In fact, taking into account the inevitable losses, this value will be within +8°C.

In the heat of +30°C in the yard and 22°C in the apartment, the air in a heat exchanger of the same efficiency is cooled to the design temperature before entering the room:

Tpp = tul + (tin – tul) * efficiency

Substituting the data, we get:

Tpp = 30 + (22-30)*0.8 = 23.6°C

Attention! The installation efficiency declared by the manufacturer and the actual one will differ. The correction value is affected by air humidity, the type of heat exchanger cassette, and the temperature difference between the outside and inside. If the recuperator is improperly installed and operated, the operating efficiency also decreases.

Modern energy-saving ventilation systems with the inclusion of recuperators are another step towards economical consumption of coolants. Moreover, temperature exchange settings are relevant in winter, but no less in demand in summer.

Supply and exhaust ventilation with heat recovery

How does supply and exhaust ventilation with heat recovery work? What are the advantages of supply and exhaust ventilation with a recuperator?

Supply and exhaust ventilation systems with heat recovery and recycling

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

Scheme of supply and exhaust ventilation with recovery and recirculation,

where L is air flow, T is temperature.

Heat recovery in ventilation- This is a method of transferring thermal energy from the exhaust air flow to the supply air flow. 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 imply mixing of air flows; the process of heat transfer occurs through any material.

Temperature and air movement in the recuperator

Devices that perform heat recovery are called heat recuperators. They come in two types:

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

Regenerative heat exchangers– in the first cycle, which are heated by the exhaust air, in the second they are cooled, giving off heat to the supply air.

A supply and exhaust ventilation system with 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 recuperator. The air supply unit with a recuperator allows up to 80-90% of the heat to be transferred to the heated air, which significantly reduces the power of the heater in which heating occurs supply air, in case of insufficient heat flow from the recuperator.

Features of the use of recirculation and recovery

The main difference between recovery and recirculation is the absence of mixing air from indoors to outdoors. Heat recovery is applicable in most cases, while recirculation has a number of limitations that are specified in regulatory documents.

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

• In rooms where the air flow is determined based on the harmful substances emitted;
• In rooms where there are pathogenic bacteria and fungi in high concentrations;
• In rooms with the presence of harmful substances that sublime upon contact with heated surfaces;
• In premises of categories B and A;
• In premises where work is carried out with harmful or flammable gases and vapors;
• In premises of category B1-B2, in which flammable dust and aerosols may be released;
• From systems with local suction of harmful substances and explosive mixtures with air;
• From airlock vestibules.

Recirculation in supply and exhaust units is actively used more often with high system productivity, when air exchange can be from 1000-1500 m 3 / h to 10,000-15,000 m 3 / h. The removed air carries a large supply of thermal energy; mixing it with the external 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-entered into the room, the air must pass through a filtration system.

Ventilation with recirculation allows you to increase energy efficiency and solve the problem of energy saving in the case when 70-80% of the removed air is re-entered into the ventilation system.

Air handling units with recovery can be installed at almost any air flow rate (from 200 m 3 /h to several thousand m 3 / h), both small and large. Recuperation also allows heat to be transferred from the exhaust 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 suspended ceiling). This decision requires some specific installation requirements, namely: small overall dimensions, low noise level, simple maintenance.

A supply and exhaust unit with recovery requires maintenance, which requires making a hatch in the ceiling for servicing the recuperator, filters, and blowers (fans).

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 in terms of 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 insufficient heat flow from the exhaust air.
• Air filter– thanks to it, the outside air is monitored and cleaned, as well as the exhaust air processed before the recuperator to protect the heat exchanger.
• Air valves with electric drives - can be installed in front of the outlet air ducts for additional regulation of the air flow and blocking the channel when the equipment is turned off.
• Bypass– thanks to which the air flow can be directed past the recuperator in the warm season, thereby not heating the supply air, but supplying it directly to the room.
• Recirculation chamber– ensuring the admixture of exhaust air into the supply air, thereby ensuring 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.

Ventilation with recovery, recirculation

Design, calculation, requirements for ventilation with recovery, recirculation. Free consultation.

Features of the ventilation system with heat recovery, its operating principle

The heat recuperator often becomes part of the ventilation system. However, not many people know what this device is and what features it has. Another important question is whether the purchase of a recuperator will pay off, how it will change the operation of the ventilation system, and whether it is possible to create a similar element with your own hands. We will answer these and many other questions in the information below.

How the system works

An unusual name was given to an ordinary heat exchanger. The purpose of the device is to remove part of the heat from the already exhausted air from the room. The selected heat is transferred to the flow that comes from the supply system clean air. The above information determines that the purpose of using such a system is to save on heating the house. The following points should be noted:

1. IN summer time The system allows you to reduce costs for air conditioning work.
2. The device in question can work in both directions, that is, it takes away heat in the supply and exhaust systems.

Operating principle of a heat recovery system

The above information determines that a heat recuperator is installed in many ventilation systems. It is not active, many versions do not consume energy, do not emit noise, and have average efficiency. Heat exchangers have been installed over the years, but in Lately Many people wonder if there are reasons to complicate the ventilation system with this device, which has quite a lot of problems due to working in an environment with different temperatures.

System installation problems

There are practically no potential problems associated with the use of such equipment. Some are resolved by the manufacturer, others become a headache for the buyer. The main problems include:

• Formation of condensation. The laws of physics determine that when air passes through high temperature condensation occurs through a cold closed environment. If the temperature environment below zero, the ribs will begin to freeze. All information provided in this paragraph determines a significant decrease in the efficiency of the device.
• Energy efficiency. All ventilation systems operating in conjunction with a recuperator are energy dependent. The economic calculation carried out determines that only those models of recuperators that will save more energy than they spend will be useful.
• Payback period. As previously noted, the device is designed to save energy. An important determining factor is how many years it takes for the purchase and installation of recuperators to pay off. If the indicator in question exceeds 10 years, then there is no point in installing it, since during this time other elements of the system will require replacement. If calculations show that the payback period is 20 years, then installing the device should not be considered.

The appearance of condensation on the vent. system

The above problems should be taken into account when choosing a heat exchanger, of which there are several dozen types.

Device options

Sidebar: Important: There are several heat exchanger options. When considering the operating principle of the device, it should be borne in mind that it depends on the type of device itself. The plate type of device is a device in which the supply and exhaust ducts pass through a common housing. The two channels are separated by partitions. The partition consists of a large number of plates, which are often made of copper or aluminum. It is important to note that the copper composition has greater thermal conductivity than aluminum. However, aluminum is cheaper.

The features of the device in question include the following:

1. Heat is transferred from one channel to another using heat-conducting plates.
2. The principle of heat transfer determines that the problem of condensation appears immediately after the heat exchanger is connected to the system.
3. In order to eliminate the possibility of condensation, a thermal-type icing sensor is installed. When a signal appears from the sensor, the relay opens a special valve - the bypass.
4. When the valve opens, cold air enters two channels.

This device class can be classified as low price category. This is due to the fact that when creating the structure, a primitive method of heat transfer is used. Efficiency similar method below. An important point It can be said that the cost of the device depends on its size and the size of the supply system itself. An example is the channel size of 400 by 200 millimeters and 600 by 300 millimeters. The difference in price will be more than 10,000 rubles.

Ventilation scheme with recovery

The structure consists of the following elements:

• Two inlet air ducts: one for fresh air, the second for exhaust air.
• From a coarse filter for supplied air from the street.
• Directly the heat exchanger itself, which is located in the central part.
• Damper, which is necessary to supply air in case of icing.
• Condensate drain valve.
• A fan that is responsible for pumping air into the system.
• Two channels with reverse side designs.

The dimensions of the heat exchanger depend on the power of the ventilation system and the size of the air ducts.

The next type of design is a device with heat pipes. Its device is almost identical to the previous one. The only difference is that the design does not have a huge number of plates that penetrate the partition between the channels. For this, a heat pipe is used - a special device that transfers heat. The advantage of the system is that at the warmer end of the sealed copper tube freon evaporates. Condensation accumulates at the cooler end. The features of the design under consideration include:

The operation of the system has the following features:

• The system contains a working fluid that absorbs thermal energy.
• Steam travels from a warmer point to a colder point.
• The laws of physics determine that steam condenses back into liquid and gives off the retained temperature.
• Along the wick, the water flows back to the warm point, where it forms steam again.

The design is sealed and works with high efficiency. The advantage is that the design is smaller and easier to operate.

Rotary type can be called modern version execution. At the border between the supply and exhaust channels there is a device that has blades - they rotate slowly. The device is designed in such a way that the plates are heated on one side and transferred from the other by rotation. This is because the blades are positioned at a specific angle to redirect the heat. The features of the rotor system include the following:

• Quite high efficiency. As a rule, plate and tubular systems have an efficiency of no more than 50%. This is due to the fact that they do not have active elements. By redirecting the air flow, the efficiency of the system can be increased to 70-75%.
• The rotation of the blades also determines the solution to the problem of condensation on the surface. The problem with low humidity during the cold season is also solved.

However, several disadvantages can also be identified:

• As a rule, than more complex system, the less reliable it is. The rotor system has a rotating element that can fail.
• If indoors high humidity, then using the design is not recommended.

It is also important to understand that the recuperator chambers do not have a hermetically sealed separation. This moment determines the transfer of odor from one chamber to another. In general, the rotor system resembles a kind of fan of rather large overall dimensions with bulky blades. To improve system performance, the device must be connected to a power source.

The intermediate type coolant is a classic design that consists of water heating with convectors and pumps. The system is used extremely rarely, due to low efficiency and design complexity. However, it is practically irreplaceable in the case when the supply and exhaust ducts are located at a great distance from each other. Heat is transferred through water, which has been used for many years to create such systems. To ensure water circulation, regardless of the location of devices in the system, a pump is installed. It is important to understand that the design features in this case determine the low reliability of the system and the need for periodic inspections.

Features of the ventilation system with heat recovery, its operating principle

Ventilation with heat recovery provides a comfortable and healthy microclimate in the house and heat retention. Determination of effectiveness and implementation options.

Supply and exhaust ventilation with heat recovery: principle of operation, review of advantages and disadvantages

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

Understanding the principles of its operation will allow you to most effectively reduce heat loss while maintaining a sufficient volume of replaced air.

Energy saving in ventilation systems

In the autumn-spring period, when ventilating rooms, a serious problem is the large temperature difference between the incoming air and the air inside. The cold flow 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 to integrate a heater into the supply ventilation, with the help of which the flow is heated. Such a system requires energy consumption, while a significant volume of warm air escaping outside leads to significant heat loss.

If the air inlet and outlet channels are located nearby, then it is possible to partially transfer the heat of the outgoing flow to the incoming one. This will reduce the energy consumption of the heater or eliminate it altogether. A device for ensuring heat exchange between gas flows of different temperatures is called a recuperator.

In the warm season, when the outside air temperature is significantly higher than room temperature, a recuperator can be used to cool the incoming flow.

Design of a unit with a recuperator

The internal structure of supply and exhaust ventilation systems with an integrated recuperator is quite simple, so it is possible to independently purchase and install them element by element. If assembly or self-installation is difficult, you can purchase ready-made solutions in the form of standard monoblock or individual prefabricated structures to order.

Main elements and their parameters

The body with heat and noise insulation is usually made of sheet steel. When wall installation it must withstand the pressure that occurs when foaming the cracks around the unit, and also prevent vibration from the operation of fans.

In the case of distributed air intake and flow into various rooms, an air duct system is attached to the housing. It is equipped with valves and dampers to distribute flows.

If there are no air ducts, a grille or diffuser is installed on the supply opening on the side of the room to distribute the air flow. An external type air intake grille is installed on the inlet opening on the street side to prevent birds, large insects and debris from entering the ventilation system.

Air movement is provided by two fans of axial or centrifugal action. In the presence of a recuperator, natural air circulation in a sufficient volume is impossible due to the aerodynamic resistance created by this unit.

The presence of a recuperator involves the installation of fine filters at the inlet of both flows. This is necessary to reduce the intensity of clogging of thin heat exchanger channels with dust and grease deposits. Otherwise, for the system to function fully, it will be necessary to increase the frequency of preventive maintenance.

One or more recuperators occupy the main volume supply and exhaust device. They are mounted in the center of the structure.

In case of typical for the territory severe frosts and insufficient efficiency of the recuperator to heat the outside air, you can additionally install a heater. Also, if necessary, a humidifier, ionizer and other devices are installed to create a favorable microclimate in the room.

Modern models include an electronic control unit. Complex modifications have functions for programming operating modes depending on the physical parameters of the air environment. External panels They have an attractive appearance, thanks to which they can fit well into any interior of the room.

Solving the problem of condensation

Cooling the air coming from the room creates the prerequisites for the release of moisture and the formation of condensation. In the case of a high flow rate, most of it does not have time to accumulate in the recuperator and goes outside. With slow air movement, a significant part of the water remains inside the device. Therefore, it is necessary to ensure that moisture is collected and removed outside the housing of the supply and exhaust system.

Moisture is removed into a closed container. It is placed only indoors to avoid freezing of the outflow channels when 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.

Reusing condensate for air humidification is undesirable, since water absorbs many pollutants such as human sweat, odors, etc.

You can significantly reduce the volume of condensate and avoid problems associated with its occurrence 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 areas must be limited by installing check valves.

If the exhaust air flow is cooled to negative temperatures inside the recuperator, condensate turns into ice, which causes a reduction in the open cross-section of the flow and, as a consequence, a decrease in volume or a complete cessation of ventilation.

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

When the flow passes through the bypass, there is no heating of the supply air through the recuperator. Therefore, when this mode is activated, the heater must automatically turn on.

Features of various types of recuperators

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

Plate cross-flow recuperator

The design of the plate recuperator is based on thin-walled panels, connected alternately in such a way as to alternate the passage of flows of different temperatures 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.

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;
• plastic made from a hydrophobic polymer material with a high thermal conductivity coefficient and low weight;
• hygroscopic cellulose allows condensation to penetrate through the plate and back into the room.

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

The advantages of plate recuperators 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 recuperator is most common for residential and office premises. It is also used in some technological processes, for example, to optimize fuel combustion during furnace operation.

Drum or rotary type

The operating principle of a rotary recuperator is based on the rotation of a heat exchanger, inside of which there are layers of corrugated metal with 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 advantages of rotary recuperators are as follows:

• quite high efficiency compared to competing types;
• return large quantity moisture, which remains in the form of condensation on the drum and evaporates upon contact with incoming dry air.

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

However, this type of device has significant disadvantages:

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

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

This imposes additional restrictions on the ability to use devices of this type. For example, polluted air from heating stoves cannot be used as a coolant.

Tube and casing system

A tubular type recuperator consists of a system of thin-walled tubes of small diameter located in an insulated casing, through which there is an influx of outside air. The casing removes warm air from the room, which heats the incoming flow.

The main advantages of tubular recuperators are as follows:

• high efficiency due to the countercurrent principle of movement of the coolant and incoming air;
• simplicity of design and absence of moving parts ensures low noise levels and rarely requires maintenance;
• long service life;
• the smallest cross-section among all types of recovery 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 condensation may form in the casing, which requires a constructive solution for its removal. Another disadvantage is that the metal filling has significant weight, despite its small dimensions.

The simplicity of the design of a tubular recuperator makes this type of device popular for self-production. Plastic pipes for air ducts, insulated with a polyurethane foam shell, are usually used as an external casing.

Device with intermediate coolant

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 coolant is used, circulating between the air ducts through an insulated pipeline. Water or a water-glycol solution is used as a medium for transferring thermal energy, the circulation of which is ensured by the operation of a pump.

If it is possible to use another type of recuperator, then it is better not to use a system with an intermediate coolant, 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 to circulate the liquid;
• 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 naturally, but only if the supply air duct is located above the exhaust air duct.

Such a system does not require additional energy costs, but only works for heating when there is 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 realized by creating the required pressure or a certain chemical composition.

Main technical parameters

Knowing the required performance of the ventilation system and the heat exchange efficiency of the recuperator, it is easy to calculate 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 recuperator or a standard air heater.

Efficiency

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

• T p – temperature of the air entering the room;
• Tn – outside air temperature;
• T in – room air temperature.

The maximum efficiency value at a standard air flow rate and a certain temperature regime is indicated in the technical documentation of the device. Its actual figure will be slightly less. In the case of self-manufacturing of a plate or tubular recuperator, in order to achieve maximum heat transfer efficiency, you must adhere to the following rules:

• The best heat transfer is provided by counter-flow devices, then cross-flow devices, and the least by 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 air inside the device.

where P (m 3 / hour) – air flow.

The cost of recuperators with high efficiency is quite high; they have a complex design and significant dimensions. Sometimes you can get around these problems by installing a few more simple devices so that the incoming air passes through them successively.

Ventilation system performance

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

The fan power must be selected taking into account bandwidth installed recuperators of any type, which is indicated in the technical documentation as the recommended flow rate or volume of air passed by the device per unit of time. As a rule, the permissible air speed 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. It leads to unnecessary costs electricity, ineffective heating of outside air and reduced service life of fans.

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

Dirty filters and grilles create significant interference with flow, so they must be periodically cleaned or replaced. One effective way to assess clogging is to install sensors that monitor the pressure drop in areas before and after the filter.

Operating principle of rotary and plate recuperator:

Measuring the efficiency of a plate-type recuperator:

Domestic and industrial ventilation systems with an integrated recuperator have proven their energy efficiency in maintaining heat indoors. 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 individual orders. You can calculate the necessary parameters and perform installation yourself.

Supply and exhaust ventilation with heat recovery: design and operation

Supply and exhaust ventilation device with heat recovery. Types of recuperators, their advantages and disadvantages. Calculation of efficiency and nuances of ensuring the required performance.

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

What it is?

When using supply and exhaust ventilation in the autumn-winter period, the question of preserving 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 the flow of cold street air before supplying it to the room. However this method is quite energy-consuming and does not prevent heat loss in the room.

The best option The solution to the problem is to equip the ventilation system with a recuperator. The recuperator is a device in which the air outflow and supply channels are located in close proximity to each other. The recuperation unit allows partial transfer of 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 incoming air masses.

Specifications

The heat recuperator consists of a housing that is covered with heat and soundproofing materials and is made of sheet steel. The device body is quite durable and can withstand weight and vibration loads. The housing has inflow and outflow openings, and air movement through the device is ensured by two fans, usually of an axial or centrifugal type. The need to install them is due to a significant slowdown natural circulation air, which is caused by the high aerodynamic resistance of the recuperator. 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 opening, but on the room side, is also equipped with a grille or diffuser that evenly distributes air flows. When installing branched systems, air ducts are mounted to the openings.

In addition, the inlets of both flows are equipped with fine filters that protect the system from dust and grease droplets. This protects the heat exchanger channels from clogging and significantly extends the service life of the equipment. However, the installation of filters is complicated by the need to constantly monitor their condition, clean them, and, if necessary, replace them. Otherwise, a clogged filter will act as a natural barrier to air flow, causing resistance to increase and the fan to break.

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

In addition to fans and filters, recuperators include heating elements, which can be water and electric. Each heater is equipped with a temperature relay and is capable of automatically turning on if the heat leaving the house cannot cope with heating 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, 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 explained by the fact that the coolant that moves along the copper coil enters it from the heating system of the house. The coil heats the plates, which, in turn, give off heat to the air flow. The water heater regulation system is represented by a three-way valve that opens and closes the water supply, a throttle valve that reduces or increases its speed, and a mixing unit that regulates the temperature. Water heaters are installed in an air duct system with a rectangular or square cross-section.

Electric heaters are often installed on air ducts with round, and their heating element is a spiral. For correct and efficient operation of the spiral heater, the air flow speed 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 if it overheats.

Besides standard set elements, at the request of the consumer, air ionizers and humidifiers are installed in recuperators, and the most modern models are equipped electronic unit control and programming function of the operating mode, depending on external and internal conditions. The instrument panels are aesthetically pleasing appearance, allowing recuperators to fit organically 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, you should refer to the translation of the word “recuperator”. Literally it means “return of used”, in this context – heat exchange. In ventilation systems, the recuperator takes heat from the air leaving the room and transfers it to incoming air flows. The temperature difference between 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 rational use of energy resources and significant savings on electricity.

In practice, heat exchange in a recuperator looks like this: forced ventilation drives an excess volume of air into the room, as a result of which contaminated masses are forced to leave the room by exhaust duct. Coming out warm air passes through the heat exchanger, heating the walls of the structure. At the same time, a flow of cold air moves towards it, which takes away the heat received by the heat exchanger without mixing with the exhaust flows.

However, cooling the air leaving the room leads to the formation of condensation. If the fans work well, imparting high speed to the air masses, the condensate does not have time to fall onto the walls of the device and goes out into the street 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, the design of the recuperator includes a tray, which is located at a slight inclination towards the drain hole.

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

However, if ice still forms from condensation, it is recommended to install additional equipment– bypass. This device is made in the form of a bypass channel through which 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 the ice. The incoming air, in turn, is heated by a heater, which turns on synchronously with the bypass. After all the ice has been melted and the water has been discharged into the storage tank, the bypass is turned off and the recuperator begins to operate normally.

In addition to installing a bypass, hygroscopic cellulose is used to combat icing. The material is located in special cassettes and absorbs moisture before it has time to fall into condensation. 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 storage tank. In addition, the operating efficiency of cellulose recuperator cassettes 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 ventilation equipment market offers a wide selection of recuperators of different types, differing both in design and in the method of heat exchange between flows.

• Plate models are the simplest and most common type of recuperator, 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 the 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 was made possible by bending the edges on the plates and sealing the joints using polyester resins. In addition to aluminum, alloys of copper and brass, as well as polymer hydrophobic plastics, are used to produce plates. However, in addition to advantages, plate recuperators also have their own weak sides. The downside of the models is the 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 rotor consisting of profiled plates rotates. During rotation of the rotor, heat is transferred from the outgoing flows to the incoming ones, as a result of which a slight mixing of the masses is observed. And although the mixing rate 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 recovery depends entirely on the rotor rotation speed, which is set manually. 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 and then evaporates. The disadvantages include difficulty in maintenance, high noise load, which is due to the presence of moving mechanisms, as well as the size of the device, the impossibility of installing on a 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 blow 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 sealing of the chambers, so the air flows are mixed.

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

• Models with intermediate coolant consist of two separate air ducts passing through a heat exchanger filled with a water-glycol solution. As a result of passing through the heating unit, the exhaust air transfers heat to the coolant, which, in turn, heats the incoming flow. The advantages of the model include its wear resistance, due to the absence of moving parts, and among the disadvantages are low efficiency, reaching only 60%, and a predisposition to condensation formation.

How to choose?

Thanks to the wide variety of recuperators presented to consumers, choose the desired model won't be difficult. Moreover, each type of device has its own narrow specialization and recommended installation location. So, when purchasing a device for an apartment or 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 have 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 dimensions. 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 is slightly higher than 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 production workshop, non-food warehouse or underground parking lot, you should opt for rotary devices. Such devices have great power and high performance, which is one of the main criteria for working on large areas. Recuperators with intermediate coolant have also proven themselves well, but due to their low efficiency they are not as in demand as drum units.

An important factor when choosing a device is its price. Thus, 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 when choosing a recuperator, you should calculate the efficiency and operating efficiency of the device. To calculate the efficiency, use the following formula: K = (Tp - Tn) / (Tv - Tn), where Tp denotes the temperature of the incoming flow, Tn is the street temperature, and Tv is the room temperature. Next, you need to compare your value with the maximum possible efficiency indicator of the purchased device. Typically this value is indicated in the model’s technical data sheet or other accompanying documentation. However, when comparing the desired efficiency and that indicated in the passport, you should remember that in fact this coefficient will be slightly lower than stated 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) = 0.36xPxKx (Tv - Tn), where P will denote air flow and is measured in m3/h. After all the calculations have been made, you should compare the costs of purchasing a recuperator with its efficiency, converted into monetary equivalent. If the purchase justifies itself, you can safely purchase the device. Otherwise, you should think about alternative methods heating the incoming air or installing a number of simpler devices.

At independent design When using the device, it should be taken into account that counterflow devices have the maximum efficiency of heat exchange. They are followed by cross-flow ducts, and in last place are unidirectional ducts. In addition, how intense the heat exchange will be directly depends on the quality of the material, the thickness of the dividing partitions, and also on how long the air masses will remain inside the device.

Installation details

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

As a result of this design, mixing of flows does not occur, and the street air has time to warm up while moving inside the pipe. To improve the performance of the device, you can combine it with a ground heat exchanger. During testing, such a recuperator gives good results. So, with an external temperature of -7 degrees and an internal temperature of 24 degrees, the productivity of the device was about 270 cubic meters per hour, and the temperature of the incoming air corresponded to 19 degrees. The average cost of a homemade model is 5 thousand rubles.

At self-production When installing a recuperator, it should be remembered that the longer the heat exchanger is, the higher the efficiency of the installation. Therefore, experienced craftsmen recommend assembling a recuperator from four sections of 2 m each, having carried out preliminary thermal insulation of all pipes. The problem of condensate drainage can be solved by installing a fitting for draining water, and placing the device itself at a slightly inclined angle.

Due to the increase in tariffs for primary energy resources, recovery has become more relevant than ever. In air handling units with recovery, they are usually used following types recuperators:

• plate or cross-flow recuperator;
• rotary recuperator;
• recuperators with intermediate coolant;
• Heat pump;
• chamber type recuperator;
• recuperator with heat pipes.

Principle of operation

The operating principle of any recuperator in air handling units is as follows. It provides heat exchange (in some models - both cold exchange and moisture exchange) between the supply and exhaust air flows. The heat exchange process can occur continuously - through the walls of the heat exchanger, using freon or an intermediate coolant. Heat exchange can also be periodic, as in a rotary and chamber recuperator. As a result, the exhaust air is cooled, thereby heating the fresh supply air. The cold exchange process in certain models of recuperators takes place during the warm season and makes it possible to reduce energy costs for air conditioning systems due to some cooling of the supply air supplied to the room. Moisture exchange occurs between the exhaust and supply air flows, allowing you to maintain comfortable humidity in the room all year round, without the use of any additional devices - humidifiers and others.

Plate or cross-flow recuperator.

Heat-conducting plates of the recuperative surface are made of thin metal (material - aluminum, copper, stainless steel) foil or ultra-thin cardboard, plastic, hygroscopic cellulose. The supply and exhaust air flows move through many small channels formed by these heat-conducting plates in a counterflow pattern. Contact and mixing of flows and their contamination are practically excluded. There are no moving parts in the recuperator design. Efficiency rate 50-80%. In a metal foil recuperator, due to the difference in air flow temperatures, moisture may condense on the surface of the plates. In the warm season, it must be drained into the building's sewerage system through a specially equipped drainage pipeline. In cold weather, there is a danger of this moisture freezing in the recuperator and causing mechanical damage (defrosting). In addition, the formed ice greatly reduces the efficiency of the recuperator. Therefore, when operating in the cold season, heat exchangers with metal heat-conducting plates require periodic defrosting with a flow of warm exhaust air or the use of an additional water or electric air heater. In this case, supply air is either not supplied at all, or is supplied to the room bypassing the recuperator through an additional valve (bypass). Defrost time averages from 5 to 25 minutes. A heat exchanger with heat-conducting plates made of ultra-thin cardboard and plastic is not subject to freezing, since moisture exchange occurs through these materials, but it has another drawback - it cannot be used for ventilation of rooms with high humidity for the purpose of drying them. The plate heat exchanger can be installed in the supply and exhaust system in both vertical and horizontal positions, depending on the requirements for the size of the ventilation chamber. Plate recuperators are the most common due to their relative simplicity of design and low cost.

Rotary recuperator.

This type is the second most widespread after the lamellar type. Heat from one air stream to another is transferred through a cylindrical hollow drum, called a rotor, rotating between the exhaust and supply sections. The internal volume of the rotor is filled with tightly packed metal foil or wire, which plays the role of a rotating heat transfer surface. The material of the foil or wire is the same as that of the plate recuperator - copper, aluminum or stainless steel. The rotor has a horizontal axis of rotation of the drive shaft, rotated by an electric motor with stepper or inverter control. The engine can be used to control the recovery process. Efficiency rate 75-90%. The efficiency of the recuperator depends on the flow temperatures, their speed and rotor speed. By changing the rotor speed, you can change the operating efficiency. Freezing of moisture in the rotor is excluded, but mixing of flows, their mutual contamination and transfer of odors cannot be completely excluded, since the flows are in direct contact with each other. Mixing up to 3% is possible. Rotary recuperators do not require high costs electricity, allow you to dry the air in rooms with high humidity. The design of rotary recuperators is more complex than plate recuperators, and their cost and operating costs are higher. However, air handling units with rotary heat exchangers are very popular due to their high efficiency.

Recuperators with intermediate coolant.

The coolant is most often water or aqueous solutions of glycols. Such a recuperator consists of two heat exchangers connected by pipelines with a circulation pump and fittings. One of the heat exchangers is placed in a channel with the exhaust air flow and receives heat from it. The heat is transferred through the coolant using a pump and pipes to another heat exchanger located in the supply air channel. The supply air receives this heat and heats up. Mixing of flows in this case is completely excluded, but due to the presence of an intermediate coolant, the efficiency coefficient of this type of recuperator is relatively low and amounts to 45-55%. Efficiency can be influenced using a pump by influencing the speed of the coolant. The main advantage and difference between a recuperator with an intermediate coolant and a recuperator with a heat pipe is that the heat exchangers in the exhaust and supply units can be located at a distance from each other. The installation position for heat exchangers, pumps and pipelines can be either vertical or horizontal.

Heat pump.

Relatively recently, an interesting type of recuperator with an intermediate coolant has appeared - the so-called. a thermodynamic recuperator in which the role of liquid heat exchangers, pipes and a pump is played by a refrigeration machine operating in heat pump mode. This is a kind of combination of a recuperator and a heat pump. It consists of two refrigerant heat exchangers - an evaporator-air cooler and a condenser, pipelines, a thermostatic valve, a compressor and a 4-way valve. Heat exchangers are located in the supply and exhaust air ducts, a compressor is necessary to ensure circulation of the refrigerant, and the valve switches the refrigerant flows depending on the season and allows heat to be transferred from the exhaust air to the supply air and vice versa. In this case, the supply and exhaust system can consist of several supply and one exhaust unit of higher capacity, united by one refrigeration circuit. At the same time, the capabilities of the system allow several air handling units to operate in different modes (heating/cooling) simultaneously. The conversion coefficient of the COP heat pump can reach values ​​of 4.5-6.5.

Recuperator with heat pipes.

According to the principle of operation, a recuperator with heat pipes is similar to a recuperator with an intermediate coolant. The only difference is that not heat exchangers are placed in the air flows, but so-called heat pipes or more precisely thermosiphons. Structurally, these are hermetically sealed sections of copper finned pipe, filled inside with a specially selected low-boiling freon. One end of the pipe in the exhaust flow heats up, the freon boils in this place and transfers the heat received from the air to the other end of the pipe, blown by the flow of supply air. Here the freon inside the pipe condenses and transfers heat to the air, which heats up. Mutual mixing of flows, their pollution and transfer of odors are completely excluded. There are no moving elements; pipes are placed in flows only vertically or at a slight slope so that the freon moves inside the pipes from the cold end to the hot end due to gravity. Efficiency rate 50-70%. An important condition for ensuring its operation: the air ducts in which the thermosiphons are installed must be located vertically one above the other.

Chamber type recuperator.

The internal volume (chamber) of such a recuperator is divided into two halves by a damper. The damper moves from time to time, thereby changing the direction of movement of the exhaust and supply air flows. The exhaust air heats one half of the chamber, then the damper directs the flow of supply air here and it is heated by the heated walls of the chamber. This process is repeated periodically. The efficiency ratio reaches 70-80%. But the design has moving parts, and therefore there is a high probability of mutual mixing, contamination of flows and transfer of odors.

Calculation of recuperator efficiency.

In the technical characteristics of recuperative ventilation units of many manufacturing companies, as a rule, two values ​​of the recovery coefficient are given - by air temperature and its enthalpy. The efficiency of a recuperator can be calculated based on temperature or air enthalpy. Calculation by temperature takes into account the sensible heat content of the air, and by enthalpy, the moisture content of the air is also taken into account (its relative humidity). Calculation based on enthalpy is considered more accurate. For the calculation, initial data is required. They are obtained by measuring the temperature and humidity of the air in three places: indoors (where the ventilation unit provides air exchange), outdoors, and in the cross section of the supply air distribution grille (from where treated outdoor air enters the room). The formula for calculating the recovery efficiency by temperature is as follows:

Kt = (T4 – T1) / (T2 – T1), Where

• Kt– recuperator efficiency coefficient by temperature;
• T1– outside air temperature, oC;
• T2– temperature of the exhaust air (i.e. indoor air), °C;
• T4– supply air temperature, oC.

Enthalpy of air is the heat content of air, i.e. the amount of heat contained in it per 1 kg of dry air. Enthalpy is determined with using i-d diagram of the state of humid air, plotting on it the points corresponding to the measured temperature and humidity in the room, outside and supply air. The formula for calculating the recovery efficiency based on enthalpy is as follows:

Kh = (H4 – H1) / (H2 – H1), Where

• Kh– recuperator efficiency coefficient in terms of enthalpy;
• H1– enthalpy of outside air, kJ/kg;
• H2– enthalpy of exhaust air (i.e. indoor air), kJ/kg;
• H4– enthalpy of supply air, kJ/kg.

Economic feasibility of using air handling units with recovery.

As an example, let’s take a feasibility study for the use of ventilation units with recovery in the supply and exhaust ventilation systems of a car dealership.

Initial data:

• object – car showroom with a total area of ​​2000 m2;
• average height premises 3-6 m2, consists of two exhibition halls, an office area and a service station (STO);
• For supply and exhaust ventilation of these premises, duct-type ventilation units were selected: 1 unit with an air flow rate of 650 m3/hour and a power consumption of 0.4 kW and 5 units with an air flow rate of 1500 m3/hour and a power consumption of 0.83 kW.
• The guaranteed range of external air temperatures for ducted installations is (-15…+40) оС.

To compare energy consumption, we will calculate the power of a duct electric air heater, which is necessary to heat the outside air in the cold season in a traditional type air-handling unit (consisting of check valve, duct filter, fan and electric air heater) with an air flow of 650 and 1500 m3/hour, respectively. At the same time, the cost of electricity is 5 rubles per 1 kW*hour.

The outside air must be heated from -15 to +20°C.

The power of the electric air heater was calculated using the heat balance equation:

Qн = G*Cp*T, W, Where:

• Qн– air heater power, W;
• G- mass air flow through the air heater, kg/sec;
• Wed– specific isobaric heat capacity of air. Ср = 1000kJ/kg*K;
• T– difference in air temperature at the outlet of the air heater and the inlet.

T = 20 – (-15) = 35 oC.

1. 650 / 3600 = 0.181 m3/sec

p = 1.2 kg/m3 – air density.

G = 0.181*1.2 = 0.217 kg/sec

Qn = 0.217*1000*35 = 7600 W.

2. 1500 / 3600 = 0.417 m3/sec

G = 0.417*1.2 = 0.5 kg/sec

Qn = 0.5*1000*35 = 17500 W.

Thus, the use of ducted units with heat recovery in the cold season instead of traditional ones using electric air heaters makes it possible to reduce energy costs with the same amount of supplied air by more than 20 times and thereby reduce costs and accordingly increase the profit of a car dealership. In addition, the use of recovery units makes it possible to reduce the consumer's financial costs for energy resources for heating premises in the cold season and for air conditioning in the warm season by approximately 50%.

For greater clarity, we will make a comparative the financial analysis energy consumption of supply and exhaust ventilation systems for car dealership premises, equipped with duct-type heat recovery units and traditional units with electric air heaters.

Initial data:

System 1.

Installations with heat recovery with a flow rate of 650 m3/hour – 1 unit. and 1500 m3/hour – 5 units.

The total electrical power consumption will be: 0.4 + 5*0.83 = 4.55 kW*hour.

System 2.

Traditional ducted supply and exhaust ventilation units - 1 unit. with a flow rate of 650m3/hour and 5 units. with a flow rate of 1500m3/hour.

Total electric power installation at 650 m3/hour will be:

• fans – 2*0.155 = 0.31 kW*hour;
• automation and valve drives – 0.1 kW*hour;
• electric air heater – 7.6 kW*hour;

Total: 8.01 kW*hour.

The total electrical power of the installation at 1500 m3/hour will be:

• fans – 2*0.32 = 0.64 kW*hour;
• automation and valve drives – 0.1 kW*hour;
• electric air heater – 17.5 kW*hour.

Total: (18.24 kW*hour)*5 = 91.2 kW*hour.

Total: 91.2 + 8.01 = 99.21 kW*hour.

We assume the period of use of heating in ventilation systems is 150 working days per year for 9 hours. We get 150*9 =1350 hours.

Energy consumption of installations with recovery will be: 4.55 * 1350 = 6142.5 kW

Operating costs will be: 5 rubles * 6142.5 kW = 30712.5 rubles. or in relative terms (to the total area of ​​the car dealership of 2000 m2) 30172.5 / 2000 = 15.1 rub./m2.

Energy consumption of traditional systems will be: 99.21 * 1350 = 133933.5 kW Operating costs will be: 5 rubles * 133933.5 kW = 669667.5 rubles. or in relative terms (to the total area of ​​the car dealership of 2000 m2) 669667.5 / 2000 = 334.8 rubles/m2.

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