Heat exchange recovery coefficient. Types of heat recovery systems in ventilation systems Application of recuperators

In a house where the ventilation system works well, a person feels very comfortable and gets sick less.

However, to ensure traditional good ventilation, it is necessary to significantly increase heating and air conditioning costs (to maintain normal air temperature in the house).

What is an air recuperator?

Nowadays, they use an improved ventilation system using special devices that can significantly reduce heat loss in winter when exhaust air is exhausted and prevent heat from entering the house in summer when superheated air is supplied from the street. This device called air recuperator , photo 1.

Photo 1. Air recuperator in the house ventilation system

At correct installation and operation, the air recuperator is capable of “returning” 2/3 of the heat that goes away with the recycled air. All recuperators contain filters in their structure to clean the supply air and, depending on the modification, the cleaning quality may be different.

Advantages of using an air recuperator in common system ventilation:

1. Reduces heating and ventilation costs (up to 30...50%).
2. Comfortable microclimate in the house, constantly fresh air.
3. Reduces dust levels in the home.
4. Low operating costs.
5. Not a difficult installation.
6. The equipment is durable.

Air recuperator design

The air recuperator consists of two chambers that run close to each other, photo 2. Heat exchange occurs between the chambers, which allows winter time heat the supply air flow due to the heat of the exhaust flow, and vice versa in summer.

Photo 2. Schematic diagram air recuperator operation

Types of recuperators

There are the following types of air recuperators.

• lamellar;
• rotary;
• aquatic;
• roofing

Plate recuperator

Plate recuperator is a housing into which pipes enter and exit rectangular section. One side of the two pipes touches, which ensures heat exchange between them. Inside the pipes there are galvanized plates that heat, cool and transfer heat, photo 3. In a plate recuperator, the supply and exhaust air flows do not mix.

The plates are made of a material with high thermal conductivity, these include:

• special plastic;
• copper;
• aluminum.

Photo 3. Plate air recuperator

Advantages of a plate air recuperator :

• compact;
• relatively inexpensive;
• silent operation;
• high performance of the device (efficiency is 45...65%);
• no electric drive or dependence on electricity;
• long service life (practically do not break).

Disadvantage of the plate air recuperator:

1. In winter, when there is frost, there is a high probability of freezing of the exhaust mechanism.
2. No moisture exchange takes place.

photo 4) consists of the following main elements:

• cylinder;
• rotating drum (rotor);
• frame.

Inside the cylinder there are many thin corrugated metal plates (heat exchangers).

Photo 4. Rotary recuperator

Using a rotating drum, the recuperator operates in two modes:

1 – passage of exhaust flow from the room;

2 – passing the supply air flow.

The operation of the rotary recuperator is controlled by its electronics, which, depending on the external and internal temperatures, determine the number of revolutions and operating mode. Thus, the metal plates either heat up or give off heat.

A rotary type recuperator may have one or two rotors.

Advantages of a rotary recuperator:

1. High efficiency of the device. Efficiency reaches up to 87%.
2. In winter, the device does not freeze.
3. Does not dry out the air. Partially returns moisture back into the room.

Disadvantages of a rotary recuperator:

1. Large dimensions of the equipment.
2. Dependence on electricity.

Application area:

1. Private houses;
2. Office rooms.
3. Garages.

Water recuperator

Water recuperator (recirculation) – this is a recuperator in which the heat exchanger is water or antifreeze, photo 5. This recuperator is similar in design to a traditional heating system. The heat exchanger fluid is heated by the exhaust air, and supply air heated by a heat exchanger.

Photo 5. Water recuperator

Advantages of a water recuperator:

1. The normal indicator of operating efficiency, efficiency, is 50...65%.
2. Possibility of installing it individual parts in different places.

Disadvantages of a water recuperator:

1. Complex design.
2. Moisture exchange is not possible.
3. Dependence on electricity.

is a recuperator for industrial use. The efficiency of this type of recuperator is 55…68%.

This equipment is not used for private houses and apartments.

Photo 6. Roof air recuperator

Main advantages:

1. Low cost.
2. Trouble-free operation.
3. Easy to install.

Self-made recuperator

If you have a desire, you can make an air recuperator yourself. To do this, you can carefully study the diagrams of recuperators that are available on the Internet and decide on the main dimensions of the device.

Let's look at the sequence of work:

1. Selection of materials for the recuperator.
2. Manufacturing of individual elements.
3. Manufacturing of a heat exchanger.
4. Assembly of the body and its insulation.

The easiest way to make a plate-type recuperator.

The following materials can be used to make the case:

• sheet metal (steel);
• plastic;
• tree.

To insulate the body, you can use the following materials:

• fiberglass;
• mineral wool;
• Styrofoam.

Konev Alexander Anatolievich

In this article we will consider such a heat transfer characteristic as the recovery coefficient. It shows the degree to which one heat carrier uses another during heat exchange. The recovery coefficient may be called heat recovery coefficient, heat transfer efficiency or thermal efficiency.

In the first part of the article we will try to find universal relations for heat transfer. They can be obtained from the most general physical principles and do not require any measurements. In the second part, we will present the dependence of real recovery coefficients on the main characteristics of heat exchange for real air curtains or separately for water-air heat exchange units, which have already been discussed in the articles “Heat curtain power at arbitrary coolant and air flow rates. Interpretation of experimental data" and "Heat curtain power at arbitrary coolant and air flow rates. Invariants of the heat transfer process”, published by the magazine “Climate World” in issues 80 and 83, respectively. It will be shown how the coefficients depend on the characteristics of the heat exchanger, as well as how they are influenced by coolant flow rates. Some heat transfer paradoxes will be explained, in particular the paradox of a high value of the recovery coefficient with a large difference in coolant flow rates. To simplify the concept of recovery and the meaning of its quantitative definition (coefficient), we will consider the example of air-to-air heat exchangers. This will allow us to determine an approach to the meaning of the phenomenon, which can then be expanded to any exchange, including “water - air”. Note that in air-to-air heat exchange blocks, both cross currents, which are fundamentally similar to water-to-air heat exchangers, and counter currents of heat-exchanging media can be organized. In the case of counter currents, which determine high values ​​of recovery coefficients, practical patterns of heat transfer may differ slightly from those discussed earlier. It is important that the universal laws of heat transfer are generally valid for any type of heat exchange unit. In the discussion of the article, we will assume that energy is conserved during heat transfer. This is equivalent to saying that the radiant power and heat convection from the body thermal equipment, determined by the temperature of the case, are small compared to the power of useful heat transfer. We will also assume that the heat capacity of carriers does not depend on their temperatures.

WHEN IS A HIGH RECOVERY RATIO IMPORTANT?

It can be considered that the ability to transmit a certain amount of thermal power is one of the main characteristics of any thermal equipment. The higher this ability, the more expensive the equipment. The recovery coefficient in theory can vary from 0 to 100%, but in practice it often ranges from 25 to 95%. Intuitively, one can assume that a high recovery coefficient, as well as the ability to transmit high power, implies high consumer qualities equipment. However, in reality such a direct connection is not observed; it all depends on the conditions of use of heat exchange. When is a high degree of heat recovery important, and when is it secondary? If the coolant from which heat or cold is taken is used only once, that is, not looped, and immediately after use it is irretrievably discharged into external environment, then for effective use For this heat, it is advisable to use a device with a high recovery coefficient. Examples include the use of heat or cold from part of geothermal installations, open reservoirs, sources of technological excess heat, where it is impossible to close the coolant circuit. High recovery is important when the calculation in the heating network is carried out only based on water flow and the temperature of the direct water. For air-to-air heat exchangers, this is the use of heat from the exhaust air, which immediately after heat exchange goes into the external environment. Another extreme case occurs when the coolant is paid strictly according to the energy taken from it. It can be called ideal option heating networks. Then we can say that such a parameter as the recovery coefficient has no meaning at all. Although, with restrictions on the return temperature of the carrier, the recovery coefficient also makes sense. Note that under some conditions a lower equipment recovery rate is desirable.

DETERMINATION OF RECOVERY FACTOR

The definition of recovery coefficient is given in many reference books(For example, , ). If heat is exchanged between two media 1 and 2 (Fig. 1),

which have heat capacities c 1 and c 2 (in J/kgxK) and mass flow rates g 1 and g 2 (in kg/s), respectively, then the heat exchange recovery coefficient can be presented in the form of two equivalent ratios:

= (с 1 g 1)(Т 1 - Т 1 0) / (сg) min (T 2 0 - T 1 0) = (с 2 g 2)(Т 2 0 - Т 2) / (сg) min ( T 2 0 - T 1 0). (1)

In this expression, T 1 and T 2 are the final temperatures of these two media, T 1 0 and T 2 0 are the initial ones, and (cg) min is the minimum of the two values ​​of the so-called thermal equivalent of these media (W/K) at flow rates g 1 and g 2 , (cg) min = min((with 1 g 1), (with 2 g 2)). To calculate the coefficient, you can use any of the expressions, since their numerators, each of which expresses the total heat transfer power (2), are equal.

W = (c 1 g 1)(T 1 - T 1 0) = (c 2 g 2)(T 2 0 - T 2). (2)

The second equality in (2) can be considered as an expression of the law of conservation of energy during heat transfer, which for thermal processes is called the first law of thermodynamics. It can be noted that in any of the two equivalent definitions in (1) only three of the four exchange temperatures are present. As stated, the value becomes significant when one of the coolants is discarded after use. It follows that the choice of two expressions in (1) can always be made so that it is the final temperature of this carrier that is excluded from the expression for calculation. Let's give examples.

a) Heat recovery from exhaust air

A well-known example of a heat exchanger with a high required value is an exhaust air heat recuperator for heating the supply air (Fig. 2).

If we designate the temperature of the exhaust air as T room, the street air as T st, and the supply air after heating in the recuperator as T pr, then, taking into account the same value of the heat capacities from the two air flows (they are almost the same, if we neglect small dependencies on humidity and air temperature), we can get a good famous expression For:

G pr (T pr - T st) / g min (T room - T st). (3)

In this formula, gmin denotes the smallest g min = min(g in, g out) of the two second flow rates gin of supply air and gout of exhaust air. When the supply air flow does not exceed the exhaust air flow, formula (3) is simplified and reduced to the form = (T pr - T st) / (T room - T st). The temperature that is not taken into account in formula (3) is the temperature T’ of the exhaust air after passing the heat exchanger.

b) Recuperation in an air curtain or an arbitrary water-air heater

Because in front of everyone possible options the only temperature whose value may be insignificant is the temperature return water T x, it should be excluded from the expression for the recovery coefficient. If we denote the ambient air temperature air curtain T 0 heated by the curtain of air - T, and the temperature entering the heat exchanger hot water T g, (Fig. 3), for we obtain:

Cg(T – T 0) / (cg) min (T g – T 0). (4)

In this formula, c is the heat capacity of air, g is the second mass air flow rate.

Designation (сg) min is the smallest value of air сg and water с W G thermal equivalents, с W is the heat capacity of water, G is the second mass flow rate of water: (сg) min = min((сg), (с W G)). If the air flow is relatively small and the air equivalent does not exceed the water equivalent, the formula is also simplified: = (T - T 0) / (T g - T 0).

PHYSICAL MEANING OF THE RECOVERY FACTOR

It can be assumed that the value of the heat recovery coefficient is a quantitative expression of the thermodynamic efficiency of power transmission. It is known that for heat transfer this efficiency is limited by the second law of thermodynamics, which is also known as the law of non-decreasing entropy.

However, it can be shown that this is indeed thermodynamic efficiency in the sense of non-decreasing entropy only in the case of equality of thermal equivalents of two media exchanging heat. In the general case of inequality of equivalents, the maximum possible theoretical value = 1 is due to the Clausius postulate, which is stated as follows: “Heat cannot be transferred from a colder to a warmer body without other changes at the same time associated with this transfer.” In this definition, other changes mean the work that is done on the system, for example, during the reverse Carnot cycle, on the basis of which air conditioners operate. Considering that pumps and fans, when exchanging heat with such carriers as water, air and others, produce negligible small work in comparison with the heat exchange energies, we can assume that with such heat exchange the Clausius postulate is fulfilled with high degree accuracy.

Although it is generally accepted that both the Clausius postulate and the principle of non-decreasing entropy are just different expressions of the formulation of the second law of thermodynamics for closed systems, this is not so. To refute their equivalence, we will show that they can generally lead to various restrictions on heat transfer. Let's consider an air-to-air recuperator in the case of equal thermal equivalents of the two exchanging media, which, if the heat capacities are equal, implies equality of the mass flow rates of the two air flows, and = (T pr - T st) / (T room - T st). Let for certainty room temperature T room = 20 o C, and street T street = 0 o C. If we completely ignore the latent heat of the air, which is caused by its humidity, then, as follows from (3), the supply air temperature T pr = 16 o C corresponds to the recovery coefficient = 0.8, and at T pr = 20 o C it will reach a value of 1. (The temperatures of the air emitted to the street in these cases T' will be 4 o C and 0 o C, respectively). Let us show that exactly = 1 is the maximum for this case. After all, even if the supply air had a temperature T pr = 24 o C, and the air emitted to the street T’ = –4 o C, then the first law of thermodynamics (the law of conservation of energy) would not be violated. Every second E = cg·24 o C Joules of energy will be transferred to street air and the same amount will be taken from room air, and at the same time it will be equal to 1.2, or 120%. However, such heat transfer is impossible precisely because the entropy of the system will decrease, which is prohibited by the second law of thermodynamics.

Indeed, according to the definition of entropy S, its change is associated with a change in the total energy of the gas Q by the relation dS = dQ/T (temperature is measured in Kelvin), and given that at constant gas pressure dQ = mcdT, m is the gas mass, s (or how it is often denoted with p) - heat capacity at constant pressure, dS = mc · dT/T. Thus, S = mc ln(T 2 / T 1), where T 1 and T 2 are the initial and final gas temperatures. In the notation of formula (3) for the second change in the entropy of the supply air we obtain Spr = сg ln(Tpr / Tul), if street air heats up, it is positive. To change the entropy of the exhaust air Svyt = s g ln(T / Troom). Change in entropy of the entire system in 1 second:

S = S pr + S out = cg(ln(T pr / T st) + ln(T’ / T room)). (5)

For all cases, we will assume T street = 273K, T room = 293K. For = 0.8 from (3), T pr = 289 K and from (2) T’ = 277 K, which will allow us to calculate the total change in entropy S = 0.8 = 8 10 –4 cg. At = 1, we similarly obtain T pr = 293K and T' = 273K, and the entropy, as one would expect, is conserved S =1 = 0. The hypothetical case = 1.2 corresponds to T pr = 297K and T' = 269K, and the calculation demonstrates entropy decrease: S =1.2 = –1.2 10 –4 cg. This calculation can be considered a justification for the impossibility of this process c = 1.2 in particular, and in general for any > 1 also due to S< 0.

So, at flow rates that provide equal thermal equivalents of two media (for identical media this corresponds to equal flow rates), the recovery coefficient determines the exchange efficiency in the sense that = 1 defines the limiting case of entropy conservation. The Clausius postulate and the principle of non-decreasing entropy are equivalent for this case.

Now consider unequal air flow rates for air-to-air heat exchange. Let, for example, the mass flow rate of supply air be 2g, and that of exhaust air be g. For the change in entropy at such flow rates we obtain:

S = S pr + S out = 2s g ln(T pr / T st) + s g ln(T’ / T room). (6)

For = 1 at the same initial temperatures T st = 273 K and T room = 293 K, using (3), we obtain T pr = 283 K, since g pr / g min = 2. Then from the law of conservation of energy (2) we obtain the value T ' = 273K. If we substitute these temperature values ​​into (6), then for a complete change in entropy we obtain S = 0.00125сg > 0. That is, even in the most favorable case with = 1, the process becomes thermodynamically suboptimal; it occurs with an increase in entropy and, as a consequence, in contrast to the subcase with equal costs, it is always irreversible.

To estimate the scale of this increase, we will find the recovery coefficient for the exchange of equal expenses already considered above, so that as a result of this exchange the same amount of entropy is produced as for expenses that differ by a factor of 2 at = 1. In other words, we will evaluate the thermodynamic non-optimality of the exchange of different costs under ideal conditions. First of all, the change in entropy itself says little; it is much more informative to consider the ratio S / E of the change in entropy to the energy transferred by heat exchange. Considering that in the above example, when entropy increases by S = 0.00125cg, the transferred energy E = cg pr (T pr - T str) = 2c g 10K. Thus, the ratio S / E = 6.25 10 –5 K -1. It is easy to verify that the recovery coefficient = 0.75026 leads to the same “quality” of exchange at equal flows... Indeed, at the same initial temperatures T st = 273 K and T room = 293 K and equal flows, this coefficient corresponds to temperatures T re = 288 K and T' = 278K. Using (5), we obtain the change in entropy S = 0.000937сg and taking into account that E = сg(T pr - T str) = сg 15К, we obtain S/E = 6.25 10 –5 К -1 . So, in terms of thermodynamic quality, heat transfer at = 1 and at twice different flows corresponds to heat transfer at = 0.75026... at identical flows.

Another question we can ask is: what should the hypothetical exchange temperatures be with different expenses so that this imaginary process occurs without increasing entropy?

For = 1.32 at the same initial temperatures T st = 273 K and T room = 293 K, using (3), we obtain T pr = 286.2 K and from the law of conservation of energy (2) T’ = 266.6 K. If we substitute these values ​​into (6), then for the complete change in entropy we obtain cg(2ln(286.2 / 273) + ln(266.6 / 293)) 0. The law of conservation of energy and the law of non-decreasing entropy for these temperature values ​​are satisfied, and yet the exchange is impossible due to the fact that T' = 266.6 K does not belong to the initial temperature range. This would directly violate Clausius's postulate, transferring energy from a colder environment to a warmer one. Consequently, this process is impossible, just as others are impossible, not only with the conservation of entropy, but even with its increase, when the final temperatures of any of the media go beyond the initial temperature range (T street, T room).

At flow rates that provide unequal thermal equivalents of the exchange media, the heat transfer process is fundamentally irreversible and occurs with an increase in the entropy of the system, even in the case of the most efficient heat transfer. These arguments are also valid for two media of different heat capacities; the only important thing is whether the thermal equivalents of these media coincide or not.

THE PARADOX OF MINIMUM QUALITY OF HEAT EXCHANGE WITH A RECOVERY RATIO OF 1/2

In this paragraph, we consider three cases of heat exchange with recovery coefficients of 0, 1/2 and 1, respectively. Let equal flows of heat-exchanging media of equal heat capacities with some different initial temperatures T 1 0 and T 2 0 be passed through the heat exchangers. With a recovery coefficient of 1, the two media simply exchange temperature values ​​and the final temperatures mirror the initial temperatures T 1 = T 2 0 and T 2 = T 1 0. It is obvious that the entropy does not change in this case S = 0, because at the exit there are the same media of the same temperatures as at the entrance. With a recovery coefficient of 1/2, the final temperatures of both media will be equal to the arithmetic average of the initial temperatures: T 1 = T 2 = 1/2 (T 1 0 + T 2 0). An irreversible process of temperature equalization will occur, and this is equivalent to an increase in entropy S > 0. At a recovery coefficient of 0, there is no heat transfer. That is, T 1 = T 1 0 and T 2 = T 2 0, and the entropy of the final state will not change, which is similar to the final state of the system with a recovery coefficient equal to 1. Just as the state c = 1 is identical to the state c = 0, also by analogy it can be shown that state = 0.9 is identical to state c = 0.1, etc. In this case, state c = 0.5 will correspond maximum magnification entropy from all possible coefficients. Apparently, = 0.5 corresponds to heat transfer of minimal quality.

Of course this is not true. The explanation of the paradox should begin with the fact that heat exchange is an exchange of energy. If entropy as a result of heat exchange has increased by a certain amount, then the quality of heat exchange will differ depending on whether 1 J or 10 J of heat was transferred. It is more correct to consider not the absolute change in entropy S (in fact, its production in the heat exchanger), but the ratio of the change entropy to the energy E transferred in this case. Obviously, for different sets of temperatures, these values ​​can be calculated for = 0.5. It is more difficult to calculate this ratio for = 0, because this is an uncertainty of the form 0/0. However, it is not difficult to take the ratio to 0, which in practical terms can be obtained by taking this ratio at very small values, for example, 0.0001. In Tables 1 and 2 we present these values ​​for various initial temperature conditions.

At any values ​​and for everyday temperature ranges T st room and T room (we will assume that T room / T st x

S / E (1 / T st - 1 / T room)(1 -). (7)

Indeed, if we denote T room = T street (1 + x), 0< x

On graph 1 we show this dependence for temperatures T st = 300K T room = 380K.

This curve is not a straight line determined by approximation (7), although it is close enough to it that they are indistinguishable on the graph. Formula (7) shows that the quality of heat transfer is minimal precisely at = 0. Let’s make another estimate of the S / E scale. In the example given in, we consider the connection of two heat reservoirs with temperatures T 1 and T 2 (T 1< T 2) теплопроводящим стержнем. Показано, что в стержне на единицу переданной энергии вырабатывается энтропия 1/Т 1 –1/Т 2 . Это соответствует именно минимальному качеству теплообмена при рекуперации с = 0. Интересное наблюдение заключается в том, что по physical meaning the given example with a rod is intuitively similar to heat transfer with = 1/2, since in both cases the temperature equalizes to the average value. However, the formulas demonstrate that it is equivalent precisely to the case of heat exchange with = 0, that is, heat exchange with the lowest quality of all possible. Without making a conclusion, we point out that the same minimum quality of heat transfer S / E = 1 / Т 1 0 –1 / Т 2 0 is exactly realized for -> 0 and at an arbitrary ratio of coolant flow rates.

CHANGES IN THE QUALITY OF HEAT TRANSFER AT DIFFERENT HEATING FLOW COSTS

We will assume that the coolant flow rates differ by a factor of n, and heat exchange occurs with the highest possible quality (= 1). What quality of heat exchange with equal flow rates will this correspond to? To answer this question, let’s look at how the S/E value behaves at = 1 for various expense ratios. For a flow difference n = 2, this correspondence has already been calculated in point 3: = 1 n=2 corresponds to = 0.75026... for the same flows. In Table 3, for a set of temperatures of 300K and 350K, we present the relative change in entropy at equal flow rates of coolants of the same heat capacity for different values.

In Table 4 we also present the relative change in entropy for various flow ratios n only at the maximum possible heat transfer efficiency (= 1) and the corresponding efficiencies leading to the same quality for equal flow rates.

Let us present the resulting dependence (n) on graph 2.

With an infinite difference in costs, it tends to a final limit of 0.46745... It can be shown that this is a universal dependence. It is valid at any initial temperatures for any carriers, if instead of the expense ratio we mean the ratio of thermal equivalents. It can also be approximated by a hyperbola, which is indicated by line 3 on the graph of blue color:

‘(n) 0.4675+ 0.5325/n. (8)

The red line indicates the exact relationship (n):

If unequal costs are realized in exchange with an arbitrary n>1, then thermodynamic efficiency in the sense of relative entropy production decreases. We present its estimate from above without derivation:

This relation tends to exact equality for n>1, close to 0 or 1, and for intermediate values does not exceed an absolute error of several percent.

The end of the article will be presented in one of the next issues of the magazine “CLIMATE WORLD”. Using examples of real heat exchange units, we will find the values ​​of recovery coefficients and show how much they are determined by the characteristics of the unit, and how much by coolant flow rates.

LITERATURE

1. Pukhov A. air. Interpretation of experimental data. // Climate World. 2013. No. 80. P. 110.
2. Pukhov A. B. The power of the thermal curtain at arbitrary coolant flow rates and air. Invariants of the heat transfer process. // Climate World. 2014. No. 83. P. 202.
3. Case W. M., London A. L. Compact heat exchangers. . M.: Energy, 1967. P. 23.
4. Wang H. Basic formulas and data on heat transfer for engineers. . M.: Atomizdat, 1979. P. 138.
5. Kadomtsev B. B. Dynamics and information // Successes physical sciences. T. 164. 1994. No. 5, May. P. 453.

Pukhov Alexey Vyacheslavovich,
Technical Director
Tropic Line company

The issue of the quality of inhaled air has been and remains the most important for human life. Various parameters play a role. Temperature, cleanliness and freshness take first place among them. Light ventilation using a window is often not enough. Too cold incoming air brings some discomfort. The appearance of a stuffy summer lazy breeze will also not bring pleasure.

What is it and what is the principle of operation

Heat exchange structures help change the situation ventilation type(recuperators). The name of the device comes from the English and Latin words meaning "return».

The principle of operation fully corresponds to the etymological meaning. Air in the room sucked in by the ventilation system and is forcibly thrown out into the street. At the same time, an external stream of freshness is sent into the room. Inside heat exchange occurs, thanks to which air masses return to the room at the required temperature.

An important indicator ventilation systems is the percentage of mixing of incoming and exhaust air. The operation of recuperators makes it possible to reduce this position to almost zero. This is achieved by the presence of a plastic, copper, aluminum or zinc separator. Heat exchange occurs due to the transfer of flow energy to the boundary. The jets themselves pass either parallel or crosswise.

Specially designed gratings at the inlet of the flow from the street allow you to retain dust, pollen, insects, and reduce the number of incoming bacteria. The air is purified and enters the room. At the same time, waste particles containing many harmful components. In addition to the circulation of air flows, the supply jets are cleaned and insulated.

Most existing recuperators have gentle sound modes, which promote strong healthy sleep when installed in a nursery or bedroom.

Many designs recent years compact and easy to install, have a remote control remote control, have additional capabilities.

Temperature standards in an apartment are studied in detail in this article:

Types of recuperators

Depending on various parameters, consider:

• Plate recuperators
• Rotary recuperators
• Chamber recuperators
• Recuperators with an additional built-in heat exchanger
• Composition of multiple heat pipes

Plate recuperators. The heat exchanger inside consists of one or more fixed plates made of copper, aluminum, plastic or especially strong, specially treated cellulose. The air passes through a series of cassettes. Due to the temperature difference between the incoming and outgoing flows, slight condensation may occur. Possible in cold weather some frost formation. As a rule, to combat it, the device is equipped additional elements, the functions of which are to remove condensate accumulation and increase the heat supply to defrost the system.

If the recuperators are equipped with one air movement cassette, then when droplets form, the flow is redirected to bypass it, and the accumulated moisture is removed through a special drainage device. If the system involves several elements, then condensation formation is reduced to zero.

When ice appears, a special valve blocks the movement of incoming air, due to the heat on the plates, the internal components of the device are heated. Another way to solve the problem was creation of cellulose cassettes. However, their use in rooms with a high degree of humidity increases the creation of condensation and makes the devices unusable.

Plate recuperators are designed in such a way that mixing of incoming and outgoing streams is not possible, and the filtration system additionally removes dust, pollen and bacteria. This makes it possible to use it in bedrooms, children's rooms, and hospitals. Creating ribbed plates allows increase Design efficiency, makes it more reliable and durable. Due to their compactness and low cost, such designs are more applicable both in hospitals, catering establishments, and at home.

Many craftsmen have learned to create designs on their own from some set of copper or galvanized plates using a special sealant and material for additional gasket between the sheets.

Рhttp://site/eko/rekuperator-vozduha-svoimi-rukami.htmlmotor recuperators. Its features are the rotating blades of one or two rotors, due to which air moves. Most often, such devices have cylindrical shape with tight installed plates inside and a drum, the rotation of which creates flows. First, an air stream leaving the room is passed through, then the direction of rotation changes and street air enters.

The efficiency of rotary recuperators is higher than plate ones, but the devices themselves are more bulky. Their use is more suitable for industrial premises, trading floors. Since the probability of mixing air flows usually reaches 5-7 percent, the installation of rotary heat exchangers becomes impossible for hospitals, canteens, cafes and restaurants. More expensive equipment, bulkiness and complexity of installation made the use of such structures possible only in special industrial zones.

Chamber recuperators. Air from the room enters a special chamber, in which heat is transferred to the walls of its part, and then discharged to the street. Next, the outside air is sucked inside into another compartment, additionally warming up from the boundaries, and enters the room.

Recuperators with an additional built-in heat exchanger. It enhances the heat transfer edge. However, it is less efficient because it reduces efficiency and increases condensation.

Composition of several heat pipes. The air from the room is additionally heated, turning into steam, and then reverse condensation occurs. The advantages of such recuperators are complete antibacterial protection of the air in the structure.

When choosing a device, take into account the size of the room and the degree of its humidity, its purpose, the need for quiet operation, efficiency and the cost of the structure and its installation.

You can read more about comfortable humidity in an apartment in this article:

Application of recuperators (video)

1. In rooms to create additional climatic comfort.
2. To save energy resources.
3. In hospitals to increase the antibacterial zone, to create a comfortable environment, to maintain the thermal characteristics of the room.
4. In industrial premises, to ventilate large spaces while maintaining a constant temperature zone, rotary heat exchangers are more often used, which can withstand temperatures up to 650 degrees.
5. In automotive structures.

Rename the topic. Doesn't look like an educational program at all. He's only interested in PR.
Now I'll correct it a little.

Advantages of a rotary recuperator:
1. High heat transfer efficiency
Yes, I agree. The highest efficiency among household ventilation systems.
2. Dehumidifies the air in the room, as it is not hygroscopic.
No one specifically uses a rotor for drying. Why is this included as a plus?

Minuses:
1. Large sizes.
I don't agree.
2. The rotor is a complex moving mechanism that is subject to wear, and operating costs will increase accordingly.
A small stepper motor that rotates the rotor costs 3 kopecks and rarely fails. You call it a “complex moving mechanism” that increases operating costs?
3. Air flows are in contact, due to which the admixture is up to 20%, according to some reports up to 30%.
Who said 30? Where did you get it? Please provide us with the link. I can still believe in 10 percent of the flow, but 30 is nonsense. Some plate recuperators They are far from hermetically sealed in this regard and a small flow there is in the order of things.
4. Condensate drainage is required
Dear educational programmer, read at least one instruction manual for the rotary installation for apartments and cottages. It is written there in black and white: at standard air humidity, condensate removal is not required.
5. Fastening the PVU in one position.
Why is this a minus?
6. Dehumidifies the air in the room, as it is not hygroscopic.
If you know the ventilation system market, you have already paid attention to the development of rotors made of hygroscopic material. The question of how much this is necessary and how much all this hygroscopicity is needed, including in plate-type recuperators, is a rather controversial question and often not in favor of hygroscopicity.

Thanks for the answer.
No one pretended to be an educational program. Topic for discussion and possible help for the user, as well as for me as a user.

“Since I am a slightly interested person, I will compare it with what I work with.” - I wrote at the very beginning. I compare it with what I'm working with.

The rotary type has larger dimensions than the plate type. Because I compare it with what I work with.

The fact that it has the highest efficiency indicators is, in my opinion, not true; the triple plate type has more efficiency and higher frost resistance. Again, I compare it with what I’m working with.

This is a moving mechanism and is subject to wear, so it costs three kopecks. This is good.

Mounting in one position is a minus. It is not always possible to install exactly as shown in the diagram.

Hygroscopy is needed to reduce operating temperature, at which the recuperator will not freeze.

Recovery(from Latin recuperatio - “return receipt”) - return of part of materials or energy for reuse in the same technological process.

Recovery during processing of raw materials is called desorption. Desorption, like other mass transfer processes, is usually reversible, and the primary process is called adsorption. These processes are widely used in the chemical industry for purification and drying of gases, purification and clarification of solutions, separation of mixtures of gases or vapors, in particular when extracting volatile solvents from a mixture of gases (recovery of volatile solvents). Recovery of liquid solvents is used in the production of hydrocarbons, alcohols, simple and esters etc. Adsorption and desorption processes are carried out in specialized adsorption units.

Recovery– the process of partial energy recovery for reuse. In this topic we are talking about air recovery in ventilation systems.

The principle of operation of the recuperator

We have supply and exhaust ventilation. In winter, the supply air is cleaned by air filters and heated by air heaters. It enters the room, warms it and dilutes harmful gases, dust and other emissions. Then he gets into exhaust ventilation and is thrown out into the street... Hence the thought... Why don’t we heat the cold supply air with the exhaust air. After all, we are essentially throwing money away. So, we have exhaust air with a temperature of 21 C and supply air, which has a temperature of -10 C before the heater. We install, for example, a recuperator with a plate heat exchanger. To understand the principle of operation of a recuperator with a plate heat exchanger, imagine a square in which the exhaust air passes from bottom to top, and the supply air from left to right. Moreover, these flows do not mix with each other due to the use of special heat-conducting plates that separate these two flows.

As a result, the exhaust air gives up to 70% of the heat to the supply air and at the outlet of the recuperator has a temperature of 2-6 C, and the supply air, in turn, has a temperature at the outlet of the recuperator of 12-16 C. Consequently, the heater will not heat the air -10 C , and +12 C and this will allow us to significantly save on electrical or thermal energy spent on heating the supply air.

Types of recuperators

Although a recuperator with a plate heat exchanger is most common in the Russian Federation, there are other types of recuperators, which in some cases are more efficient or, in general, only they can cope with the tasks. We invite you to consider the four most popular types of recuperators:

Recuperator with plate heat exchanger (Plate recuperator)

Recuperator with rotary heat exchanger (Rotary recuperator)

Water recirculation heat exchanger

Roof recuperator

Plate recuperator

The most common type is a plate or cross-flow air recuperator for apartments.

It is a small cassette. Two channels are created in it, which are separated from each other by sheets of steel. They carry separate supply and exhaust air flows. Steel acts as a heat “filter”. That is, a temperature exchange occurs, but air mixing is not allowed. The prevalence of this type of device is due to its simplicity, compactness and low cost. The plate air recuperator for apartments has some disadvantages, but they are not so significant when installed in small residential premises.

Advantages: - the device is easily built into any part of the air duct; - there are no moving parts (easier maintenance, no risk of air flow displacement, etc.); - relatively high efficiency – 50...90%; - can work with high-temperature gas and air mixtures (up to +200°C); - aerodynamic resistance to passing air flows increases slightly; - simple performance adjustment via a bypass valve.

Plate recuperators are designed in such a way that the air flows in them do not mix, but contact each other through the walls of the heat exchange cassette. This cassette consists of many plates that separate cold air flows from warm ones. Most often, the plates are made of aluminum foil, which has excellent thermal conductivity properties. The plates can also be made of special plastic. These are more expensive than aluminum ones, but increase the efficiency of the equipment.

Plate heat exchangers have a significant drawback: as a result of the temperature difference, condensation forms on cold surfaces, which turns into ice. An ice-covered recuperator stops working effectively. To defrost it, the incoming flow is automatically bypassed by the heat exchanger and heated by a heater. Meanwhile, the escaping warm air melts the ice on the plates. In this mode, of course, there is no energy saving, and the defrosting period can take from 5 to 25 minutes per hour. To heat the incoming air during the defrosting phase, air heaters with a power of 1-5 kW are used.

Some plate heat exchangers use preheating of the incoming air to a temperature that prevents the formation of ice. This reduces the efficiency of the recuperator by approximately 20%.

Another solution to the icing problem is hygroscopic cellulose cassettes. This material absorbs moisture from the exhaust air flow and transfers it to the incoming air, thereby returning moisture back. Such recuperators are justified only in buildings where there is no problem of air humidification. The undoubted advantage of hygrocellulose recuperators is that they do not require electrical heating of the air, which means they are more economical. Recuperators with double plate heat exchangers have an efficiency of up to 90%. Ice does not form in them due to heat transfer through the intermediate zone.

Well-known manufacturers of plate heat exchangers: SCHRAG (Germany), MITSUBISHI (Japan), ELECTROLUX, SYSTEMAIR (Sweden), SHUFT (Denmark), REMAK, 2W (Czech Republic), MIDEA (China).