How to calculate ventilation: formulas and an example of calculating the supply and exhaust system. Features and procedure for calculating exhaust and supply ventilation Utilization of the heat of the exhaust air with heat pipes

Do you dream that the house has a healthy microclimate and that no room smells musty and damp? In order for the house to be truly comfortable, even at the design stage, it is necessary to carry out a competent calculation of ventilation.

If this important point is missed during the construction of the house, in the future you will have to solve a number of problems: from removing mold in the bathroom to new repairs and installing an air duct system. Agree, it’s not too pleasant to see black mold nurseries in the kitchen on the windowsill or in the corners of the children’s room, and to dive into it again. repair work.

In our article we have collected useful materials on the calculation of ventilation systems, reference tables. Formulas, visual illustrations and real example indoor for various purposes and a certain area, shown in the video.

With correct calculations and proper installation, the ventilation of the house is carried out in a suitable mode. This means that the air in the living quarters will be fresh, with normal humidity and without unpleasant odors.

If the opposite picture is observed, for example, constant stuffiness in the bathroom or other negative phenomena, then you need to check the condition of the ventilation system.

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Conclusions and useful video on the topic

Roller #1. Useful information on the principles of operation of the ventilation system:

Roller #2. Together with the exhaust air, heat also leaves the home. Here, the calculations of heat losses associated with the operation of the ventilation system are clearly demonstrated:

The correct calculation of ventilation is the basis for its successful functioning and the guarantee of a favorable microclimate in a house or apartment. Knowing the basic parameters on which such calculations are based will allow not only to correctly design the ventilation system during construction, but also to correct its condition if circumstances change.

Description:

Currently, the indicators of thermal protection of multi-storey residential buildings have reached quite high
values, so the search for reserves to save thermal energy is in the field of energy efficiency engineering systems. One of the key energy-saving measures with a rather high potential for saving thermal energy is the use of exhaust air heat exchangers 1 in ventilation systems.

At present, the thermal protection indicators of multi-storey residential buildings have reached quite high values, so the search for reserves for saving thermal energy is in the field of improving the energy efficiency of engineering systems. One of the key energy-saving measures with a rather high potential for saving thermal energy is the use of exhaust air heat exchangers 1 in ventilation systems.

Supply and exhaust ventilation units with exhaust air heat recovery, compared to traditional supply ventilation systems, have a number of advantages, which include significant savings thermal energy spent on heating ventilation air(from 50 to 90% depending on the type of utilizer used). It should also be noted high level air-thermal comfort, due to the aerodynamic stability of the ventilation system and the balance of supply and exhaust air flow rates.

Types of utilizers

The most widely used:

1. Regenerative heat recovery units s. In regenerators, the heat from the extract air is transferred to the supply air through a nozzle that alternately heats up and cools down. Despite the high energy efficiency, regenerative heat exchangers have a significant drawback - the likelihood of mixing a certain part of the exhaust air with the supply air in the apparatus case. This, in turn, can lead to the transfer of unpleasant odors and disease-causing bacteria. Therefore, they are usually used within one apartment, cottage or one room in public buildings.

2. Recuperative heat recovery units. These heat exchangers, as a rule, include two fans (supply and exhaust), filters and a plate heat exchanger of counterflow, cross and semi-cross types.

With the apartment-by-apartment installation of recuperative heat recovery units, it becomes possible to:

1. flexibly regulate the air-thermal regime depending on the type of operation of the apartment, including the use of recirculated air;
2. protection from urban, external noise (when using sealed translucent fences);
3. purification of supply air using high-performance filters.

3.Heat recovery units with intermediate heat carrier. By their own design features these heat exchangers are of little use for individual (apartment) ventilation, and therefore in practice they are used for central systems.

4. Heat recovery units with a heat exchanger on heat pipes. The use of heat pipes allows you to create compact energy-efficient heat exchange devices. However, due to the complexity of the design and high cost, they have not found application in ventilation systems for residential buildings.

With similar weight and size indicators best result in residential buildings, they show regenerative heat recovery units (80–95%), followed by recuperative ones (up to 65%), and in last place are heat recovery units with an intermediate coolant (45–55%).

Heat recovery units should be mentioned, which, in addition to transferring thermal energy, transfer moisture from the exhaust air to the supply air. Depending on the design of the heat transfer surface, they are divided into enthalpy and sorption types and allow utilizing 15–45% of the moisture removed with the exhaust air.

One of the first implementation projects

In 2000, for a residential building at 6, Krasnostudenchesky Prospekt, one of the first apartment-by-apartment mechanical supply and exhaust ventilation systems was designed with exhaust air heat recovery for supply air heating in a cross-flow air-to-air plate heat exchanger.

A compact, low-noise apartment air handling unit is located in each apartment in the false ceiling space of the guest bathroom, located next to the kitchen. The maximum supply air capacity is 430 m 3 /h. To reduce energy consumption, outdoor air is taken in most apartments not from the street, but from the space of a glazed loggia. In other apartments where there is no technical feasibility air intake from the loggias, air intake grilles are located directly on the facade.

The outside air is cleaned, if necessary, preheated to prevent freezing of the heat exchanger, then heated or cooled in the heat exchanger due to the removed air, then, if necessary, finally heated to the required temperature by an electric heater, after which it is distributed throughout the premises of the apartment. The first heater with a rated power of 0.6 kW is designed to protect the exhaust tract from condensate freezing. Condensate is discharged through a special drainage tube through a water seal into the sewer. The second heater with a power of 1.5 kW is designed to heat the supply air to a predetermined comfortable value. For ease of installation, it is also made electric.

It should be noted that, according to the calculations of the designers, the need for additional heating of the air after the heat exchanger could arise only at very low temperatures outside air. Nevertheless, taking into account that twice as much supply air passes through the heat exchanger of the supply and exhaust unit as the exhaust air, an electric air heater was installed on the supply. Operational practice confirmed these assumptions: additional heating is almost never used, the heat of the exhaust air is enough to heat the supply air to a temperature that does not cause discomfort to residents.

The heat exchanger is equipped with an automation system with a controller and a control panel. The automation system provides for switching on the first heater when the temperature of the heat exchanger wall reaches below 1 °C, the second heater can be switched on and off, ensuring the constancy of the set supply air temperature.

The supply fan has three fixed speeds. At the first speed, the supply air volume is 120 m 3 /h, this value satisfies the requirements for one- and two-room apartment, as well as a three-room apartment with a small number of residents. At the second speed, the supply air volume is 180 m 3 /h, at the third - 240 m 3 / h. Residents rarely use the second and third speeds.

Acoustic measurements were carried out at all fan speeds, which showed that at the first speed the noise level does not exceed 30-35 dB (A), and this value is valid for an unfurnished apartment. In an apartment with furniture and interior items, the noise level will be even lower. At the second and third speeds, the noise level is higher, but with the guest bathroom door closed, it does not cause discomfort to residents.

Exhaust air is taken from the sanitary facilities, then, after being filtered, it is passed through a heat exchanger and discharged through a central collection exhaust air duct. Prefabricated exhaust air ducts - metal, made of galvanized steel and laid in enclosed fire shafts. On the upper technical floor, prefabricated air ducts of one section are combined and led outside the building.

At the time of the project implementation, it was forbidden by the regulations to combine the hoods of bathrooms and kitchens for disposal, so the hoods of the kitchens are separated. The heat of about half of the volume of air removed from the apartment is utilized. This ban has now been lifted, further improving the energy efficiency of the system.

IN heating season In 2008-2009, an energy audit of heat consumption systems was carried out in the building, which showed a savings in heat for heating and ventilation in the amount of 43% compared to similar houses of the same year of construction.

Project in Northern Izmailovo

Another similar project implemented in 2011 in Northern Izmailovo. Apartment building No. 153 provides for apartment-by-apartment ventilation with mechanical stimulation and heat recovery of the exhaust air to heat the supply air. The supply and exhaust units are installed autonomously in the corridors of the apartments and are equipped with filters, a plate heat exchanger and fans. The unit is equipped with automation equipment and a control panel that allows you to adjust the air capacity of the unit.

Passing through the ventilation unit with a plate heat exchanger, the exhaust air heats the supply air up to 4°C (at an outside air temperature of -28°C). Compensation for the heat deficit for supply air heating is carried out heating devices heating.

Outside air is taken from the apartment's loggia, and exhaust air from bathrooms, bathrooms and kitchens (within one apartment) after the heat exchanger is discharged into the exhaust duct via satellite and removed within the technical floor. If necessary, the removal of condensate from the heat recovery unit is provided for in the sewer riser, equipped with a drip funnel with an odor-locking device. The stand is located in the bathrooms.

Supply and exhaust air flow control is carried out by means of one control panel. The unit can be switched from normal operation with heat recovery to summer operation without heat recovery. Ventilation of the technical floor occurs through deflectors.

The volume of supply air is taken to compensate for the exhaust from the premises of the bathroom, bath, kitchen. The apartment does not have an exhaust duct for connecting kitchen equipment (the exhaust hood from the stove works for recirculation). The inflow is diluted through sound-absorbing air ducts to the living rooms. It is planned to cover the ventilation unit in the apartment corridors with a building structure with hatches for maintenance and an exhaust duct from the ventilation unit to the exhaust shaft. There are four standby fans in the maintenance warehouse.

Tests of the installation with a heat recovery unit have shown that its efficiency can reach 67%.

The use of mechanical ventilation systems with exhaust air heat recovery is widespread in world practice. The energy efficiency of heat recovery units is up to 65% for plate heat exchangers and up to 85% for rotary ones. When these systems are used in Moscow conditions, the reduction of annual heat consumption to the base level can be 38–50 kWh/m2 per year. This makes it possible to reduce the overall specific heat consumption to 50–60 kWh/m2 per year without changing basic level thermal protection of fences and provide 40 percentage reduction energy intensity of heating and ventilation systems, provided for from 2020.

Literature

1 This technology was originally developed in Northern Europe and Scandinavia. Today, Russian designers also have significant experience in using these systems in multi-storey residential buildings.

The main purpose of exhaust ventilation is to remove exhaust air from the serviced premises. Exhaust ventilation, as a rule, works in conjunction with supply air, which, in turn, is responsible for supplying clean air.

In order for the room to have a favorable and healthy microclimate, it is necessary to draw up a competent design of the air exchange system, perform the appropriate calculation and install the necessary units in accordance with all the rules. When planning, you need to remember that the condition of the entire building and the health of the people who are in it depend on it.

The slightest mistakes lead to the fact that ventilation ceases to cope with its function as it should, fungus appears in the rooms, decoration and building materials are destroyed, and people start to get sick. Therefore, the importance of the correct calculation of ventilation cannot be underestimated in any case.

The main parameters of exhaust ventilation

Depending on what functions the ventilation system performs, existing installations taken to be divided into:

1. Exhaust. Required for the intake of exhaust air and its removal from the room.
2. Supply. Provide supply of fresh clean air from the street.
3. Supply and exhaust. At the same time, old stale air is removed and new air is introduced into the room.

Exhaust units are mainly used in production, offices, warehouses and other similar premises. The disadvantage of exhaust ventilation is that without the simultaneous installation of a supply system, it will work very poorly.

If more air is drawn out of the room than it enters, drafts are formed. Therefore, the supply and exhaust system is the most efficient. It provides maximum comfortable conditions both in residential premises, and in industrial and working type premises.

Modern systems are equipped with various additional devices that purify the air, heat or cool it, humidify and evenly distribute it throughout the premises. The old air is expelled through the hood without any difficulty.

Before proceeding with the arrangement of the ventilation system, you need to seriously approach the process of its calculation. Direct calculation of ventilation is aimed at determining the main parameters of the main components of the system. Only by determining the most suitable characteristics, you can make such ventilation that will fully fulfill all the tasks assigned to it.

During the calculation of ventilation, parameters such as:

1. Consumption.
2. Operating pressure.
3. Heater power.
4. Cross-sectional area of ​​air ducts.

If desired, you can additionally calculate the energy consumption for the operation and maintenance of the system.

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Step-by-step instructions for determining system performance

The calculation of ventilation begins with the determination of its main parameter - performance. The dimensional unit of ventilation performance is m³/h. In order for the air flow calculation to be carried out correctly, you need to know the following information:

1. The height of the premises and their area.
2. The main purpose of each room.
3. The average number of people who will be in the room at the same time.

To make the calculation, you will need the following devices:

1. Roulette for measurements.
2. Paper and pencil for notes.
3. Calculator for calculations.

To perform the calculation, you need to know such a parameter as the frequency of air exchange per unit of time. This value is set by SNiP in accordance with the type of premises. For residential, industrial and administrative premises, the parameter will vary. You also need to take into account such points as the number of heaters and their power, the average number of people.

For premises household purpose the air exchange rate used in the calculation process is 1. When calculating ventilation for administrative premises, use the air exchange value equal to 2-3 - depending on the specific conditions. Directly, the frequency of air exchange indicates that, for example, in a domestic room, the air will be completely updated 1 time in 1 hour, which is more than enough in most cases.

Performance calculation requires the availability of data such as the amount of air exchange by frequency and number of people. It will be necessary to take the largest value and, starting from it, select the appropriate exhaust ventilation power. The calculation of the air exchange rate is performed using a simple formula. It is enough to multiply the area of ​​\u200b\u200bthe room by the height of the ceiling and the multiplicity value (1 for household, 2 for administrative, etc.).

To calculate the air exchange by the number of people, the amount of air consumed by 1 person is multiplied by the number of people in the room. As for the volume of air consumed, on average, with minimal physical activity, 1 person consumes 20 m³ / h, with medium activity this figure rises to 40 m³ / h, and with high activity it is already 60 m³ / h.

To make it clearer, we can give an example of a calculation for an ordinary bedroom with an area of ​​​​14 m². There are 2 people in the bedroom. The ceiling has a height of 2.5 m. Quite standard conditions for a simple city apartment. In the first case, the calculation will show that the air exchange is 14x2.5x1=35 m³/h. When performing the calculation according to the second scheme, you will see that it is already equal to 2x20 = 40 m³ / h. It is necessary, as already noted, to take a larger value. Therefore, specifically in this example, the calculation will be performed by the number of people.

The same formulas are used to calculate the oxygen consumption for all other rooms. In the end, it remains to add up all the values, get the overall performance and select ventilation equipment based on these data.

The standard values ​​for the performance of ventilation systems are:

1. From 100 to 500 m³/h for ordinary residential apartments.
2. From 1000 to 2000 m³/h for private houses.
3. From 1000 to 10000 m³/h for industrial premises.

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Determination of heater power

In order for the calculation of the ventilation system to be carried out in accordance with all the rules, it is necessary to take into account the power of the air heater. This is done if, in combination with exhaust ventilation, supply ventilation is organized. A heater is installed so that the air coming from the street is heated and enters the room already warm. Essential in cold weather.

Calculation of the capacity of the air heater is determined taking into account such values ​​as the air flow, the required outlet temperature and the minimum temperature of the incoming air. The last 2 values ​​are approved in SNiP. According to this normative document, the air temperature at the heater outlet must be at least 18°. The minimum outside air temperature should be specified in accordance with the region of residence.

Modern ventilation systems include performance regulators. Such devices are designed specifically so that you can reduce the rate of air circulation. In cold weather, this will reduce the amount of energy consumed by the air heater.

To determine the temperature at which the device can heat the air, a simple formula is used. According to her, you need to take the value of the power of the unit, divide it by the air flow, and then multiply the resulting value by 2.98.

For example, if the air flow at the facility is 200 m³ / h, and the heater has a power of 3 kW, then by substituting these values ​​​​in the above formula, you will get that the device will heat the air by a maximum of 44 °. That is, if in winter time it will be -20° outside, then the selected air heater will be able to heat oxygen up to 44-20=24°.

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Operating pressure and duct cross section

Calculation of ventilation involves the mandatory determination of parameters such as operating pressure and cross-section of air ducts. An efficient and complete system includes air distributors, air ducts and fittings. When determining the working pressure, the following indicators must be taken into account:

1. The shape of the ventilation pipes and their cross section.
2. Fan settings.
3. The number of transitions.

The calculation of a suitable diameter can be performed using the following ratios:

1. For a residential building, a pipe with a cross-sectional area of ​​​​5.4 cm² will be enough for 1 m of space.
2. For private garages - a pipe with a cross section of 17.6 cm² per 1 m² of area.

Such a parameter as the speed of the air flow is directly related to the cross section of the pipe: in most cases, the speed is selected in the range of 2.4-4.2 m / s.

Thus, when calculating ventilation, whether it is an exhaust, supply or supply and exhaust system, a number of important parameters must be taken into account. The efficiency of the entire system depends on the correctness of this stage, so be careful and patient. If desired, you can additionally determine the power consumption for the operation of the system being arranged.

The need for energy saving in the design, construction and operation of buildings of any purpose is beyond doubt and is associated primarily with the depletion of fossil fuel reserves and, as a result, its continuous rise in price. Particular attention should be paid to reducing heat costs specifically for ventilation and air conditioning systems, since the share of these costs in the overall energy balance can be even higher than transmission heat losses, primarily in public and industrial buildings and after increasing the thermal protection of external fences.

One of the most promising, low-cost and quick payback energy-saving measures in mechanical ventilation and air conditioning systems is the utilization of exhaust air heat for partial heating of the inflow during the cold season. For the implementation of heat recovery devices are used various designs, incl. plate cross-flow recuperative heat exchangers and regenerators with a rotating rotor, as well as devices with so-called heat pipes (thermosyphons).

However, it can be shown that under the conditions of the price level for ventilation equipment prevailing in the Russian Federation and, mainly, due to the practical absence of in-house production of the listed types of devices, from a technical and economic point of view, it is advisable to consider heat recovery only on the basis of devices with an intermediate coolant. This design is known to have a number of advantages.

Firstly, serial equipment is used for its implementation, since here the supply unit is supplemented only with a heat exchanger, and the exhaust unit is supplemented with a heat exchanger, which are structurally similar to conventional heaters and coolers. This is especially significant, since in the Russian Federation there are a number of enterprises that conduct their own production of the products in question, incl. such large ones as Veza LLC.

In addition, this type of heat recovery equipment is very compact, and the connection of the supply and exhaust units only through a circulation circuit with an intermediate heat carrier allows you to choose a place for their placement almost independently of each other. As a coolant, low-freezing liquids such as antifreezes are usually used, and the small volume of the circulation circuit makes it possible to neglect the cost of antifreeze, and the tightness of the circuit and the non-volatility of antifreeze make the question of its toxicity secondary.

Finally, the absence of direct contact between the flows of supplied and exhausted air does not impose restrictions on the cleanliness of the extract, which practically unlimitedly expands the group of buildings and premises where heat recovery can be used. As a disadvantage, they usually indicate a not too high temperature efficiency, not exceeding 50-55%.

But this is just the case when the question of the advisability of using heat recovery should be decided by a technical and economic calculation, which we will discuss later in our article. It can be shown that the payback period for additional capital costs for a heat recovery device with an intermediate coolant does not exceed three to four years.

This is especially important in conditions of unstable market economy with a noticeably changing level of prices for equipment and tariffs for energy resources, which does not allow the use of capital-intensive engineering solutions. However, the question of the most economically feasible temperature efficiency of such heat recovery equipment k eff remains open, i.e. the share of heat spent on heating the supply air at the expense of the heat of the exhaust air in relation to the total heat load. Commonly used values ​​for this parameter are between 0.4 and 0.5. Now we will show on what basis these values ​​are taken.

This problem will be considered on the example of a supply and exhaust ventilation unit with a capacity of 10,000 m 3 / h, using the equipment of Veza LLC. This task is an optimization one, since it comes down to identifying the value of k eff, which provides a minimum of the total discounted costs of the SDZ for the installation and operation of ventilation equipment.

The calculation should be carried out subject to the use of borrowed funds for the construction of ventilation units and bringing the SDZ to the end of the considered time interval T according to the following formula:

where K - total capital costs, rub; E — total annual operating costs, rub/year; p is the discount rate, %. In calculations, it can be taken equal to the refinancing rate of the Central Bank of the Russian Federation. Since January 15, 2004, this value has been equal to 14% per annum. In this case, it is possible to study the problem in a sufficiently complete volume by relatively elementary means, since all components of the costs are easily taken into account and quite simply calculated.

For the first time the solution of this problem was published by the author in the work for the level of prices and tariffs in force at that time. However, as it will be easy to see, when recalculated for later data, the main conclusions remain valid. At the same time, we will show how the technical and economic calculation itself should be carried out if it is necessary to choose the best option engineering solution, since all other tasks will differ only in the definition of the value of K.

But this is easily done according to the catalogs and price lists of the manufacturers of the corresponding equipment. In our example, capital costs were determined according to the data of the Veza company, based on the performance and the accepted set of sections of the supply and exhaust units: front panel with one vertical damper, cell filter class G3, fan unit; in addition, in the supply unit there is also an additional air heater of the heat recovery system and a reheating heater with heat supply from the heating network, and in the exhaust unit there is an air cooler of the heat recovery system, as well as a circulation pump. A diagram of such an installation is shown in fig. 1. Expenses for installation and adjustment of ventilation units were taken in the amount of 50% of the main capital investments.

The costs for heat recovery equipment and the reheating heater were calculated based on the results of calculations on a computer using the programs of the Veza company, depending on the efficiency of the heat exchanger. At the same time, with an increase in efficiency, the value of K increases, since the number of rows of tubes of heat exchangers of the utilization system increases faster (for k eff = 0.52 - up to 12 in each installation), than the number of rows of the reheating heater decreases (from 3 to 1 in the same conditions) .

Operating costs are the sum of the annual costs, respectively, for heat and electrical energy and depreciation charges. When calculating them, the duration of operation of the installation during the day in the calculations was assumed to be 12 hours, the air temperature behind the reheating air heater was +18°C, and after the heat exchanger, depending on k eff through the average outside temperature for the heating period and the temperature of the exhaust air.

The latter is equal to +24.7°C by default (program for selection of heat recovery units by Veza LLC). Tariff for thermal energy was taken according to Mosenergo data for the middle of 2004 in the amount of 325 rubles/Gcal (for budget consumers). Obviously, with an increase in k eff, the cost of thermal energy decreases, which, generally speaking, is the goal of heat recovery.

Electricity costs are calculated using the electric power required to drive the circulation pump of the heat recovery system and the fans of the supply and exhaust units. This power is determined based on the pressure loss in the circulation circuit, the density and flow rate of the intermediate heat carrier, as well as the aerodynamic resistance of ventilation installations and networks. All of the above values, except for the density of the coolant, assumed to be 1200 kg/m 3 , are calculated according to the selection programs for heat recovery and ventilation equipment of Veza LLC. In addition, the efficiency of the applied pumps and fans also participate in the expressions for power.

The calculations used average values: 0.35 for GRUNDFOS pumps with wet rotor and 0.7 for RDH type fans. The tariff for electric power was taken into account according to the data of OAO Mosenergo as of the middle of 2004 in the amount of 1.17 rubles/(kWh). With an increase in k eff, the level of electricity costs increases, since with an increase in the number of rows of utilization heat exchangers, their resistance to air flow increases, as well as pressure losses in the circulation circuit of the intermediate heat carrier.

However, in general, this component of costs is significantly less than the cost of thermal energy. Depreciation charges also increase with the increase in k eff insofar as this increases capital costs. The calculation of these deductions is carried out on the basis of ensuring the costs of full restoration, capital and Maintenance equipment, taking into account the estimated service life of the TAM equipment, taken in the calculations equal to 15 years.

In general, however, the total operating costs decrease with increasing utilization efficiency. Therefore, the existence of a minimum of SDZ is possible at one or another level of k eff and a fixed value of T. The results of the corresponding calculations are shown in Figs. 2. On the graphs, one can easily see that the minimum on the SDZ curve appears for almost any calculation horizon, which, according to the meaning of the problem, is equal to the required payback period.

This means that at the existing prices for equipment and tariffs for energy resources, any, even the smallest investment in heat recovery pays off, and quite quickly. Therefore, the utilization of heat with an intermediate heat carrier is almost always justified. With an increase in the expected payback period, the minimum on the SDZ curve quickly shifts to the region of higher efficiency, reaching 0.47 at T = T AM = 15 years.

It is clear that the optimal value of k eff for the accepted payback period will be the one at which a minimum of SDZ is observed. A graph of the dependence of such an optimal value of k eff on T is shown in Fig. 3. Since a longer payback period exceeding the estimated service life of the equipment is hardly justified, one should apparently stop at the level k eff = 0.4-0.5, especially since with a further increase in T, the increase in optimal efficiency slows down sharply.

In addition, it should be taken into account that the method of heat recovery under consideration for any heat exchange surface and coolant flow rate cannot in principle provide a value of k eff higher than 0.52-0.55, which is confirmed by the calculation according to the program of the Veza company. If we accept the tariff for thermal energy as for commercial consumers in the amount of 547 rubles / Gcal, the reduction in annual costs due to heat recovery will be higher, so the graph in Fig. 3 shows the upper limit of the possible payback period.

Thus, the specified range of values ​​k eff from 0.4 to 0.5 finds a complete feasibility study. Therefore, the main practical advice according to the results of the study, it is possible to use the exhaust air heat recovery with an intermediate heat carrier in any buildings where mechanical supply and exhaust ventilation and air conditioning are provided, with the choice of a temperature efficiency coefficient close to the maximum possible for this type of installation. Another recommendation is that it is obligatory for a market economy to take into account the discounting of capital and operating costs in the technical and economic comparison of engineering solutions according to formula (1).

At the same time, if only two options are compared, as is most often the case, it is convenient to compare only additional costs and assume that in the first case, K = 0, and in the second, on the contrary, E = 0, and K is equal to additional investments in activities, the feasibility of which is justified. Then instead of E in the first option, you need to use the difference in annual costs for the options. After that, graphs of the dependence of SDZ on T are constructed, and at the point of their intersection, the estimated payback period is determined.

If it turns out to be higher than T AM, or the schedules do not intersect at all, the measures are not economically justified. The results obtained are of a very general nature, since the dependence of the change in capital costs on the degree of heat recovery in the current market situation has little to do with a specific manufacturer of ventilation equipment, and the main impact on operating costs is generally only the cost of heat and electricity.

Therefore, the proposed recommendations can be used in making economically sound decisions on energy saving in any mechanical ventilation and air conditioning systems. In addition, these results have a simple and engineering form and can easily be refined when the current prices and tariffs change.

It should also be noted that the payback period obtained in the above calculations, depending on the accepted k eff, reaches 15 years, i.e. up to TAM, is in some respects the marginal, arising when all capital costs are taken into account. If we take into account only additional investments directly into heat recovery, the payback period is indeed reduced to 3-4 years, as mentioned above.

Therefore, exhaust air heat recovery with an intermediate coolant is indeed a low-cost and fast-payback measure and deserves the widest application in a market economy.

1. O.D. Samarin. About regulation of thermal protection of buildings. S.O.K. Magazine, No. 6/2004.
2. O.Ya. Kokorin. Modern air conditioning systems. - M .: Fizmatlit, 2003.
3. V.G. Gagarin. On the insufficient justification of the increased requirements for thermal protection of the outer walls of buildings. (Changes No. 3 of SNiP II-3-79). Sat. report 3rd conf. RNTOS April 23–25, 1998
4. O.D. Samarin. Economically expedient efficiency of heat exchangers with an intermediate heat carrier. Mounting and special work in construction, No. 1/2003.
5. SNiP 23-01-99 * "Construction climatology" .- M: GUP TsPP, 2004.

Background of development

The heat of the air that is removed into the atmosphere is a source of energy savings. It is no secret that 40…80% of heat consumption is spent on heating the air that enters the building. Therefore, the idea of ​​heating fresh air at the expense of exhaust air is not new. Even in the Soviet Union, work was continuously carried out to create installations that would make it possible to use the thermal energy of exhaust air. But unfortunately, the results of these studies were used only in special projects (industrial, defense, scientific).

Abroad, the first energy crisis became the reason for the application, which caused the beginning of the use of such installations. At the same time, the devices for utilizing the thermal energy of the removed air were originally designed for use in multi-apartment residential buildings and cottages. As a result of this, today air heating It is widely used in Canada and the neighboring states of the USA. So in Canada, water heating systems are not used at all.

In Russia, heat recovery units began to be used en masse with the start of active low-rise construction when private developers began to show interest in energy-efficient, energy-saving equipment.

The use of electricity for heating

The use of ventilation heating technology involves the use of electricity for heating. Until recently, the use of electricity for heating was prohibited by law. This is due to the energy saving policy pursued in the Soviet Union. Since the breakup Soviet Union a lot has changed.

At present, when new materials are being used and new technologies are being mastered, the opinion of experts on the admissibility of using electricity for heating is beginning to change. The introduction of new norms in 2000, which require the improvement of the thermal protection of residential buildings, contributes to this. According to the new standards, normalized heat losses through external walls are reduced by 2.5–3.0 times compared to the 1995 standards.

In the future, the norms for thermal protection and energy efficiency will only become tougher. Under these conditions, the very concept of air infiltration will disappear, the premises will be airtight. In such conditions, the use of heat recovery devices will open up the widest prospects.

Existing types of recuperators

The real nomenclature of heat recovery units is very diverse. But all the variety can be reduced to the following types: a) shell-and-tube and plate heat exchangers, including cross-current; b) rotary (regenerative); V) heat pumps with an intermediate working body. The capabilities of most modern devices make it possible to utilize and use only 60% of the exhaust air heat for heating the air supplied to the premises. For objects with a small building volume, in order for the installation of a heat exchanger to pay off, this figure must be 90%.

A promising direction for the development of heat recovery units

To increase the efficiency of heat recovery units allows the use of the method described below. As you know, the heat capacity of water is the highest compared to other liquids. The heat capacity of air is 4.5 times lower than the heat capacity of water. The technology of ultra-dispersion of the removed air in water is based on the use of water. In order to increase the rate of heat transfer from the removed air, this air is passed through the water in a special way, creating micron-sized bubbles.

The rate of heat transfer increases as micron-sized bubbles destroy the thermal resistance of the surface layer of water. The application of the technology of ultra-dispersion of the removed air in water will make it possible to use 90-95% of the heat of the removed air. It is important that the heat exchanger built according to this technology has a minimum number of parts, minimum dimensions, it is easy to operate.

Ways to use heat exchangers

• The first way is to use a heat exchanger of a recuperative type. At the same time, partial heating of the air supplied to the room takes place.
• The second way is heat recovery with the help of heat pumps.
• The third way is to use the heat of the outgoing air to heat the incoming water. The system includes large water heaters and hot water accumulators.

The current state of affairs in Russia on the issue under consideration

Federal Law No. 261-FZ "On Energy Saving and Increasing energy efficiency…” it is prescribed to reduce the energy intensity of the engineering systems of the building. The goal is to reduce the energy intensity of GDP by 40% by 2020 compared to 2007 levels. This tendency to increase energy efficiency, improve thermal protection is ubiquitous.

Decree of the Government of Moscow No. 900 dated October 5, 2010 “On Improving the Energy Efficiency of Residential, Social and Public-Business Buildings in the City of Moscow…” established the level of energy consumption, which cannot be ensured without heat recovery.

The Russian Federation, having joined the WTO, undertook to bring energy prices for domestic consumers to the level of world prices. All over the world, energy efficiency issues, and as a result, heat recovery issues are very acute. National governments put in place and enforce programs to improve energy efficiency. Therefore, with the growth of domestic energy prices, interest in heat recovery plants will inevitably grow.

In the "Russian stove" the supply air was heated, with the help of this the living room was heated. In Europe, the heating system, where channels were provided, as in a Russian stove, was called "Russian". This recognized the great efficiency of the Russian stove in comparison with European heating. Currently, we can talk about the need to return to the roots in matters of heating.

Supply and exhaust ventilation with recuperation