State educational institution higher vocational education

"Samara State Technical University»

Department of Chemical Technology and Industrial Ecology

COURSE WORK

in the discipline "Technical thermodynamics and heat engineering"

Topic: Calculation of a heat recovery installation for the waste gases of a process furnace

Completed by: Student Ryabinina E.A.

ZF course III group 19

Checked by: Consultant Churkina A.Yu.

Samara 2010

Introduction

Most chemical enterprises generate high- and low-temperature thermal waste, which can be used as secondary energy resources (SER). These include flue gases from various boilers and process furnaces, cooled streams, cooling water and waste steam.

Thermal RES largely cover the heat needs of individual industries. Thus, in the nitrogen industry, more than 26% of the heat demand is met through renewable energy sources, and in the soda industry - more than 11%.

The number of used SERs depends on three factors: the temperature of the SERs, their thermal power and the continuity of output.

Currently, the most widespread is the recovery of heat from waste industrial gases, which for almost all fire engineering processes have a high temperature potential and can be used continuously in most industries. The heat of exhaust gases is the main component of the energy balance. It is used primarily for technological, and in some cases, for energy purposes (in waste heat boilers).

However, the widespread use of high-temperature thermal HERs is associated with the development of recycling methods, including the heat of hot slags, products, etc., new methods for recycling the heat of waste gases, as well as improving the designs of existing recycling equipment.

1. Description of the technological scheme

In tubular furnaces that do not have a convection chamber, or in radiant-convection furnaces, but with a relatively high initial temperature of the heated product, the temperature of the exhaust gases can be relatively high, which leads to increased heat losses, a decrease in furnace efficiency and higher fuel consumption. Therefore, it is necessary to use the heat from the exhaust gases. This can be achieved either by using an air heater, which heats the air entering the furnace for fuel combustion, or by installing waste heat boilers, which make it possible to obtain water vapor necessary for technological needs.

However, to heat the air, additional costs are required for the construction of an air heater, a blower, as well as additional electricity consumption consumed by the blower motor.

To ensure normal operation of the air heater, it is important to prevent the possibility of corrosion of its surface from the side of the flue gas flow. This phenomenon is possible when the temperature of the heat exchange surface is below the dew point temperature; in this case, part of the flue gases, in direct contact with the surface of the air heater, is significantly cooled, the water vapor contained in them partially condenses and, absorbing sulfur dioxide from the gases, forms an aggressive weak acid.

The dew point corresponds to the temperature at which the pressure of saturated water vapor is equal to the partial pressure of water vapor contained in the flue gases.

One of the most reliable methods of protection against corrosion is to preheat the air in some way (for example, in water or steam heaters) to a temperature above the dew point. Such corrosion can also occur on the surface of convection pipes if the temperature of the feed entering the furnace is below the dew point.

The source of heat to increase the temperature of saturated steam is the oxidation (combustion) reaction of the primary fuel. The flue gases formed during combustion give up their heat in the radiation and then convection chambers to the raw material flow (water vapor). Superheated water vapor is supplied to the consumer, and combustion products leave the furnace and enter the waste heat boiler. At the exit from the HRSG, saturated water vapor is fed back into the steam superheating furnace, and the flue gases, cooled by feed water, enter the air heater. From the air heater, flue gases enter the KTAN, where the water entering through the coil is heated and goes directly to the consumer, and the flue gases are released into the atmosphere.

2. Furnace calculation

2.1 Calculation of the combustion process

Let us determine the lower heat of combustion of fuel Q рн. If the fuel is an individual hydrocarbon, then its heat of combustion Q p n is equal to the standard heat of combustion minus the heat of evaporation of water contained in the combustion products. It can also be calculated using the standard thermal effects of the formation of initial and final products based on Hess’s law.

For a fuel consisting of a mixture of hydrocarbons, the heat of combustion is determined by the additivity rule:

where Q pi n is the heat of combustion of the i-th fuel component;

y i is the concentration of the i-th fuel component in fractions of unity, then:

Q р n cm = 35.84 ∙ 0.987 + 63.80 ∙ 0.0033+ 91.32 ∙ 0.0012+ 118.73 ∙ 0.0004 + 146.10 ∙ 0.0001 = 35.75 MJ/m 3 .

Molar mass of fuel:

M m = Σ M i ∙ y i ,

where M i is the molar mass of the i-th fuel component, hence:

M m =16.042 ∙ 0.987 + 30.07 ∙ 0.0033 + 44.094 ∙ 0.0012 + 58.120 ∙ 0.0004 + 72.15 ∙ 0.0001 + 44.010 ∙ 0.001+ 28.01 ∙ 0.0 07 = 16.25 kg/ mole.

kg/m 3,

then Q р n cm, expressed in MJ/kg, is equal to:

MJ/kg.

The calculation results are summarized in table. 1:

Fuel composition Table 1

Let us determine the elemental composition of the fuel, % (mass):

,

where n i C, n i H, n i N, n i O is the number of carbon, hydrogen, nitrogen and oxygen atoms in the molecules of individual components that make up the fuel;

Content of each fuel component, mass. %;

M i is the molar mass of individual fuel components;

M m is the molar mass of the fuel.

Checking the composition:

C + H + O + N = 74.0 + 24.6 + 0.2 + 1.2 = 100% (wt).

Let us determine the theoretical amount of air required to burn 1 kg of fuel; it is determined from the stoichiometric equation of the combustion reaction and the oxygen content in the atmospheric air. If the elemental composition of the fuel is known, the theoretical amount of air L0, kg/kg, is calculated using the formula:

In practice, to ensure complete combustion of fuel, an excess amount of air is introduced into the furnace; let’s find the actual air flow rate at α = 1.25:

where L is the actual air flow;

α - excess air coefficient,

L=1.25∙17.0 = 21.25 kg/kg.

Specific volume of air (no.) for combustion of 1 kg of fuel:

where ρ in = 1.293 – air density at normal conditions,

m 3 /kg.

Let's find the amount of combustion products formed when 1 kg of fuel is burned:

if the elemental composition of the fuel is known, then the mass composition of the flue gases per 1 kg of fuel during complete combustion can be determined based on the following equations:

where m CO2, m H2O, m N2, m O2 are the mass of the corresponding gases, kg.

Total amount of combustion products:

m p.c = m CO2 + m H2O + m N2 + m O2,

m p.s = 2.71 + 2.21 + 16.33 + 1.00 = 22.25 kg/kg.

We check the resulting value:

where W f is the specific consumption of nozzle steam when burning liquid fuel, kg/kg (for gas fuel W f = 0),

Since the fuel is a gas, we neglect the moisture content in the air and do not take into account the amount of water vapor.

Let us find the volume of combustion products under normal conditions formed during the combustion of 1 kg of fuel:

where m i is the mass of the corresponding gas formed during the combustion of 1 kg of fuel;

ρ i is the density of a given gas under normal conditions, kg/m 3 ;

M i is the molar mass of a given gas, kg/kmol;

22.4 - molar volume, m 3 /kmol,

m 3 /kg; m 3 /kg;

m 3 /kg; m 3 /kg.

Total volume of combustion products (no.) at actual air flow:

V = V CO2 + V H2O + V N2 + V O2,

V = 1.38 + 2.75+ 13.06 + 0.70 = 17.89 m 3 /kg.

Density of combustion products (no.):

kg/m3.

Let us find the heat capacity and enthalpy of combustion products of 1 kg of fuel in the temperature range from 100 °C (373 K) to 1500 °C (1773 K), using the data in Table. 2.

Average specific heat capacities of gases with р, kJ/(kg∙K) Table 2

Enthalpy of flue gases generated during the combustion of 1 kg of fuel:

where c CO2, c H2O, c N2, c O2 are the average specific heat capacities at constant pressure of the corresponding lawns at temperature t, kJ/(kg K);

c t is the average heat capacity of flue gases generated during the combustion of 1 kg of fuel at temperature t, kJ/(kg K);

at 100 °C: kJ/(kg∙K);

at 200 °C: kJ/(kg∙K);

at 300 °C: kJ/(kg∙K);

at 400 °C: kJ/(kg∙K);

at 500 °C: kJ/(kg∙K);

at 600 °C: kJ/(kg∙K);

at 700 °C: kJ/(kg∙K);

at 800 °C: kJ/(kg∙K);

at 1000 °C: kJ/(kg∙K);

at 1500 °C: kJ/(kg∙K);

The calculation results are summarized in table. 3.

Enthalpy of combustion products Table 3

Heat recovery has been widely used in heat and power engineering for many years. e - feed water heaters, economizers, air heaters, gas turbine regenerators, etc., but in refrigeration technology it is still given insufficient attention. This can be explained by the fact that heat of low potential is usually discarded (at a temperature below 100°C), so to use it it is necessary to introduce additional heat exchangers and automation devices into the refrigeration system, which complicates it. At the same time, the refrigeration system becomes more sensitive to changes in external parameters.

In connection with the energy problem, designers, including refrigeration equipment, are currently forced to more carefully analyze traditional systems in search of new schemes for the recovery of condensation heat.

If the refrigeration unit has an air condenser, you can use the heated air directly after the condenser to heat rooms. The heat of superheated refrigerant vapors after the compressor, which have a higher temperature potential, can also be usefully used.

For the first time, heat recovery schemes were developed by European companies, since in Europe there were higher prices for electricity compared to prices in the United States.

Complete refrigeration equipment from the Kostan company (Italy), developed in recent years, with a heat recovery system from air condensers, is used to heat the sales area of ​​supermarket-type stores. Such systems can reduce overall energy consumption in a store by 20-30%.

primary goal— use of the maximum possible amount of heat generated by the refrigeration machine in environment. Heat is transferred either directly by a flow of warm air after the condenser to the sales area of ​​the store during the heating season, or to an additional heat exchanger-accumulator (heat of superheated refrigerant vapor) to produce warm water, which is used for technological needs during whole year.

Experience in operating systems using the first method has shown that they are easy to maintain, but relatively cumbersome; their use is associated with the need to install additional fans to move large amounts of air and air filters, which ultimately leads to increased costs. Taking this into account, preference is given to more complex schemes, despite the fact that their implementation complicates operation.

The simplest circuit with a heat exchanger-accumulator is a circuit with a series connection of a capacitor and a battery. This scheme works as follows. At water temperatures at the inlet to the heat exchanger-accumulator and the ambient air temperature equal to 10 ° C, the condensation temperature tK is 20 C. For a short time (for example, during the night) the water in the accumulator heats up to 50 ° C, a t rises to 30°C. This is explained by the fact that the overall performance of the capacitor and battery decreases, since when the water is heated, the initial temperature pressure in the battery decreases.

An increase of 10°C is quite acceptable, but in unfavorable combinations high temperature and low water consumption, a more significant increase in condensation temperature can be observed. This scheme has the following disadvantages during operation: fluctuations in condensation pressure; periodic significant decrease in pressure in the receiver, which leads to disruption of the liquid supply to the evaporator; possible reverse flow of liquid into the air condenser when the compressor is stopped, when t is significantly lower than the temperature in the receiver.

Installing a condensation pressure regulator allows you to prevent the backflow of condensate from the receiver into the air condenser, as well as maintain the required condensation pressure, for example, corresponding to 25 ° C.

When tw increases to 50°C and tok to 25°C, the pressure regulator opens completely, and the pressure drop in it does not exceed 0.001 MPa.

If and t drops to 10°C, then the pressure regulator closes and internal cavity the air condenser, as well as part of the coil of the heat exchanger-accumulator, are filled with liquid. When the temperature rises to 25°C, the pressure regulator opens again and the liquid from the air condenser comes out supercooled. The pressure above the surface of the liquid in the receiver will be equal to the condensation pressure minus the pressure drop in the regulator, and the pressure in the receiver can become so low (for example, correspond to tK< 15°С), что жидкость перед подачей к регулирующему вентилю не будет переох-лажденной. В этом случае необходимо ввести в схему регенеративный теплообменник.

To maintain pressure in the receiver, a differential valve is also introduced into the circuit. At tk = 20°C and tok - 40°C, the differential valve is closed, the pressure drop in the pipelines of the air condenser, heat exchanger-accumulator and pressure regulator is insignificant.

When lowered to 0°C, and t to 10°C, the liquid in front of the pressure regulator will have a temperature of approximately 10°C. The pressure drop in the pressure regulator will become significant, differential valve 6 will open and hot steam will flow into the receiver.

However, this does not completely eliminate the problem of the lack of supercooling of the liquid in the receiver. Required mandatory installation a regenerative heat exchanger or the use of a specially designed receiver. In this case, the cold liquid from the condenser is directed directly into the liquid line. The same effect can be achieved by installing a vertical receiver, in which colder liquid sinks to the bottom, and hot steam enters the upper part.

Location of the pressure regulator in the circuit between the heat exchanger-accumulator and the air condenser. preferable for the following reasons: in winter it may take a long time to achieve the required condensation pressure; in a compressor-condensing unit, the length of the pipeline between the condenser and the receiver is rarely sufficient; In existing installations, it is necessary to disconnect the drain pipe in order to install a heat exchanger-accumulator. A check valve is also installed according to this scheme.

Circuits with parallel connection of air capacitors have been developed to maintain a temperature of 20°C in one room, and 10°C in another, where doors are often opened in winter. Such circuits also require the installation of pressure regulators and differential valves.

Condensers connected in parallel with heat recovery usually do not work in the summer, and the pressure in them is slightly lower than in the main condenser. Due to loose closure of the solenoid and check valves liquid recirculation and filling of the recovery condenser are possible. To avoid this, the circuit provides a bypass pipeline through which the condenser is periodically turned on to recover heat based on a signal from a time relay.

Fluctuations in the thermal load of the main condenser and condensers with heat recovery are associated with the need to use in such circuits a receiver with a larger capacity than in refrigeration machines without heat recovery, or to install an additional receiver in parallel with the first one, which forces an increase in the amount of refrigerant to charge the system.

Analysis various schemes heat recovery using standard coaxial type heat exchangers (pipe in pipe) with complete condensation in them and using only the heat of superheated vapors shows that the installation operates more economically with complete condensation in a heat regenerator only with continuous and stable use of warm water.

The refrigeration machine operates in two cycles (with a boiling point of 10°C and different condensation temperatures of 35 and 55°C). An additional counterflow water heat exchanger is used as a heat regenerator, which transfers the heat of superheated refrigerant vapor at a temperature pressure of the compressor refrigeration capacity of 10 kW and a power consumption of 2.1 kW (Tc = 35°C) in the main condenser it is possible to heat water (at its flow rate is 0.012 kg/s) from 10 to 30 °C, and then in the regenerator, increase the water temperature from 30 to 65 °C. In a cycle from 55°C with a cooling capacity of 10 kW and a power consumption of 3.5 kW, water in the main condenser (at a flow rate of 0.05 kg/s) is heated from 10 to 50°C, and then water is heated in an additional heat exchanger-regenerator ( at a flow rate of 0.017 kg/s) it heats up from 50 to 91°C. In the first case, 13.7% is usefully used, in the second - 52% of the total supplied energy.

In all cases, when choosing a heat recovery system for a refrigeration machine, it is necessary to determine the following:

• compressor cooling capacity and condenser thermal load;
• operating mode of the refrigeration machine in summer and winter periods; possibility of using recovered heat; the relationship between the necessary heat for heating the room and heating water;
• the required temperature of warm water and its consumption over time; reliability of the refrigeration machine in cold production mode.
• Experience in operating heat recovery systems shows that the initial capital costs of such a system in large stores pay off within 5 years, so their implementation is economically feasible.

In metallurgical production, in order to recover heat from waste gases, recuperators, regenerators, and waste heat boilers are used. In these devices, the heat of gases is used in two directions.

1. The heat of the exhaust gases is spent on heating the air and gaseous fuel spent on heating the furnace and, therefore, is returned to the furnace again. In this case, the recovery of gas heat directly affects the operation of the furnace, increasing the temperature in the furnace and increasing fuel economy. This use of heat is observed when using recuperators and regenerators.

2. The heat of the gases is not returned to the furnace, but is used to heat waste heat boilers, which produce steam characterized by high pressure and temperature. In this case, installing a waste heat boiler behind the unit does not directly affect its operation, but has a very definite and significant effect on the plant as a whole.

From a thermotechnical point of view, waste gas heat recovery leads to the following.

a) Fuel economy. In fuel stoves (unlike electric stoves), heat is obtained as a result of combustion of fuel at the expense of air. The total amount of heat spent on the process also includes the so-called physical heat of fuel and air, which refers to the amount of heat possessed by fuel and air when heated to a certain temperature. Since heating a metal to a given temperature in a specific furnace requires a strictly defined amount of heat, it is obvious that the higher the share of physical heat in the total heat, the lower the share of chemical heat of the fuel, i.e., the less fuel must be spent on heating.

The higher the recovery rate, that is, the higher the fuel and air are heated and, therefore, the lower the temperature of the flue gases leaving the recuperator or regenerator, the higher the fuel economy, since most of the heat is returned to the furnace.

b) Increase in temperature. It is known that when fuel is burned, heat is released, which heats the combustion products to a certain temperature, called the combustion temperature.

The combustion temperature is:

t = Qnr /Vpr * Wed * C

where Qнр is the lower heating value of fuel, kJ/kg or kJ/m3;

Vpr - volume of products formed during complete combustion of a unit of fuel, m3 / kg, or m3 / m3;

Av - average specific heat capacity of combustion products, kJ/(kg * deg), or kJ/ (m 3 * deg).

If gas and air were heated to a certain temperature and, therefore, had physical heat Qf, then this heat will also be spent on heating the combustion products. Consequently, Qf must be added to the numerator and then

It can be seen that the greater Qf (Qnr for each type of fuel is a constant value), the larger the numerator and the higher, therefore, the combustion temperature of the fuel.

c) Intensification of fuel combustion. In addition to saving fuel and increasing its combustion temperature, heating the fuel and air leads to a more intense occurrence of the fuel combustion reactions themselves. For example, maximum speed The combustion of hydrogen when heated from 100 to 400 degrees increases more than four times. When burning liquid fuel, the combustion process is intensified due to the acceleration of the evaporation process of liquid fuel and, consequently, the formation of a gaseous mixture.

Of all the types of energy consumed in the chemical industry, the first place belongs to thermal energy. The degree of heat utilization during a chemical technological process is determined by thermal efficiency:

where Q t and Q pr, respectively, is the amount of heat theoretically and practically expended to carry out the reaction.

The use of secondary energy resources (waste) increases efficiency. Energy waste is used in chemical and other industries for various purposes.

Of particular importance in the chemical industry is the recovery of heat from reaction products leaving reactors for preheating materials entering the same reactors. Such heating is carried out in devices called regenerators, recuperators and waste heat boilers. They accumulate heat from waste gases or products and release it for processes.

Regenerators are periodically operating chambers filled with a nozzle. For a continuous process it is necessary to have at least 2 regenerators.

The hot gas first passes through regenerator A, heats its nozzle, and cools itself. Cold gas passes through regenerator B and is heated by a previously heated nozzle. After heating the nozzle in A and cooling in B, the dampers are closed, etc.

In recuperators, the reagents enter a heat exchanger, where they are heated by the heat of hot products leaving the reaction apparatus, and then fed into the reactor. Heat exchange occurs through the walls of the heat exchanger tubes.

In recovery boilers, the heat from waste gases and reaction products is used to produce steam.

Hot gases move through pipes located in the boiler body. There is water in the interpipe space. The resulting steam passes through the moisture separator and leaves the boiler.

Raw materials

The chemical industry is characterized by high material intensity of production. As a rule, several tons of raw materials are consumed for one ton of finished chemical products. It follows that the cost of chemical products is largely determined by the quality of raw materials, methods and costs of its production and preparation. In the chemical industry, the cost of raw materials in the cost of production is 60-70% or more.

The type and quality of raw materials significantly determines the complete use of production capacities of chemical industries, heat productivity, equipment operating time, labor costs, etc. The properties of the raw material, the content of useful and harmful components in it determine the technology used for its processing.

The types of raw materials are very diverse and can be divided into the following groups:

1. mineral raw materials;
2. plant and animal raw materials;
3. air, water.

1. Mineral raw materials - minerals extracted from the bowels of the earth.

Minerals, in turn, are divided into:

• ore (metal production) important polymetallic ores
• nonmetallic (fertilizers, salts, H + , OH - glass, etc.)
• combustibles (coals, oil, gas, shale)

Ore raw materials are rocks from which it is environmentally beneficial to obtain metals. Metals in it are mostly in the form of oxides and sulfides. Non-ferrous metal ores quite often contain compounds of several metals - these are sulfides of Pb, Cu, Zn, Ag, Ni, etc. Such ores are called polymetallic or complex. Indispensable integral part All industrial ores are FeS 2 – pyrite. When processing some ores, other products are obtained along with metals. So, for example, simultaneously with Cu, Zn, Ni, H 2 SO 4 is also obtained during the processing of sulfide ores.

Non-metallic raw materials are rocks used in the production of non-metallic materials (except for alkali metal chlorides and Mg). This type of raw material is either directly used in the national economy (without chemical processing) or is used for one or another chemical production. These raw materials are used in the production of fertilizers, salts, acids, alkalis, cement, glass, ceramics, etc.

Non-metallic raw materials are conventionally divided into the following groups:

• building materials – raw materials are used directly or after mechanical or physical-chemical processing (gravel, sand, clay, etc.)
• industrial raw materials – used in production without processing (graphite, mica, corundum)
• chemical mineral raw materials - used directly after chemical treatment (sulfur, saltpeter, phosphorite, apatite, sylvinite, rock and other salts)
• precious, semi-precious and ornamental raw materials (diamond, emerald, ruby, malachite, jasper, marble, etc.)

Combustible mineral raw materials are fossils that can serve as fuel (coal, oil, gas, oil shale, etc.)

2. Plant and animal raw materials are products of agriculture (agriculture, livestock farming, vegetable growing), as well as meat and fisheries.

According to its purpose, it is divided into food and technical. Food raw materials include potatoes, sugar beets, cereals, etc. Chemical and other industries consume plant and animal raw materials that are unsuitable for food (cotton, straw, flax, whale oil, claws, etc.). The division of raw materials into food and technical is in some cases arbitrary (potatoes → alcohol).

3. Air and water are the cheapest and most accessible raw materials. Air is a practically inexhaustible source of N 2 and O 2. H 2 O is not only a direct source of H 2 and O 2, but also participates in almost all chemical processes and is also used as a solvent.

The economic potential of any country in modern conditions is largely determined by natural resources mineral resources, the scale and qualitative characteristics of their locations, as well as the level of development of raw materials industries.

The raw materials of modern industry are very diverse, and with the development of new technology, the introduction of more effective methods production, the raw material base is constantly expanding due to the discovery of new deposits, the development of new types of raw materials and the more complete use of all its components.

The domestic industry has a powerful raw material base and has reserves of all types of mineral and organic raw materials it needs. Currently, the United States ranks first in the world in the extraction of reserves of P, rock salts, NaCl, Na 2 SO 4, asbestos, peat, wood, etc. We have one of the first places in explored oil and gas deposits. And proven reserves of raw materials are increasing from year to year.

At the present stage of industrial development, the rational use of raw materials, which involves the following measures, is of great importance. Rational use of raw materials allows you to increase the environmental efficiency of production, because the cost of raw materials constitutes the main share in the cost of chemical products. In this regard, they strive to use cheaper, especially local, raw materials. For example, at present, oil and gas are increasingly used as hydrocarbon raw materials, rather than coal, ethanol, obtained from food raw materials, is replaced with hydrolysis from wood.

Description:

Supply and exhaust ventilation systems for administrative and residential premises are effective not only from a sanitary and hygienic point of view. With automatic heat recovery, they also make a significant contribution to reducing heating costs. The air removed from the room has a temperature of 20-24 0 C. Not using this heat means, literally, releasing it through the window. The heat from the exhaust air can be used to heat water and supply air and thus contribute to environmental protection.

Heat recovery

D. Droste, InnoTech Systemanalysis GmbH, Berlin (Germany)

Technology

Basic provisions

Supply and exhaust ventilation systems for administrative and residential premises are effective not only from a sanitary and hygienic point of view. With automatic heat recovery, they also make a significant contribution to reducing heating costs. The air removed from the room has a temperature of 20-24 o C. Not using this heat means, literally, releasing it through the window. The heat from the exhaust air can be used to heat water and supply air and thus contribute to environmental protection.

Thus, heat recovery is necessary to reduce ventilation losses.

Technical solutions

In building ventilation systems, a given amount of exhaust air is taken from rooms with a high content of moisture and pollutants: kitchens, toilets, bathrooms, then cooled in a cross-flow plate heat exchanger and discharged outside. The same amount of external supply air, pre-cleaned from dust, is heated in a heat exchanger without contact with the exhaust air and supplied to living quarters, bedrooms and children's rooms. The corresponding devices are located in attics, basements or auxiliary rooms.

In automatic supply ventilation systems, a specified amount of air is continuously supplied to the room using fans. Exhaust fans extract polluted air from kitchens, toilets, etc.

When properly selected, fans provide air exchange that meets Federal Government requirements. To ensure heat recovery, the system includes special heat exchangers, for example, cross-flow, if necessary equipped with a heat pump.

Modern installations in houses with good thermal insulation, compared to a convective heating system, allow saving up to 50% of heat.

The efficiency of heat transfer from the exhaust air to the supply air is about 60% in plate heat exchangers, and even more with humid exhaust air. This means that in an apartment with a living area of ​​100 m2:

The power of the heating system is lower by 10 W/m2 of living space;

Annual heat consumption is reduced from approximately 40 to 15 kW/m2 year.

Economic efficiency

A controlled ventilation and heat recovery system requires less energy to heat the air than other systems. At the same time, due to the reduction in the installed capacity of the heating system, investment costs are reduced during new construction. Additionally, through the use of heat recovery systems, fuel costs are reduced, since household heat emissions are used (meaning heat emissions from humans, electrical appliances, lighting, as well as insolation, etc.). Household heat emissions, instead of “overheating” the room in which they occur, are redistributed through the air duct system to those rooms where there is “underheating”. It should also be borne in mind that in many apartments long-term ventilation through open windows is often undesirable due to high level noise. The use of heat recovery units and heat pumps in the mechanical ventilation system makes it more energy efficient.

Implementation

The economic prerequisites for the introduction of modern heating systems are quite diverse. In a number of federal states there are special tax incentives, thanks to which initial costs can be reduced by 20-30%. In addition, a number of energy saving programs contain sections devoted to ventilation of residential premises. For example, the program of the state of Rhine-Palatinate provides for an additional payment of up to 25%, but not more than 7500 DM. The introduction of heat pumps is especially recommended, with some states providing for an additional payment of up to 30%.

Examples of using

Heat recovery in an apartment building

In typical apartment building in Leipzig, built in 1912, which was renovated and further insulated, the Dutch ventilation company Van Ophoven used a controlled ventilation system with heat recovery. Houses of this type make up up to 60% of Leipzig's housing stock. The supply and exhaust ventilation system with heat recovery in a cross-flow heat exchanger is autonomous until the additional supply air heater is turned on. To ensure heat recovery, the system includes special heat exchangers, in our example - cross-flow. In this case we are talking about an equilibrium ventilation system. Each apartment is equipped with a device installed on the wall in a specially designated place. The outside air is preheated in the recovery device and then heated to the required temperature using an additional heater. In this case we are talking about indirect heating. Analysis of the efficiency of this system showed that energy savings were 40% and CO 2 emissions were reduced by 69%.

Air exchange units

In many administrative buildings in Nossen, in offices, hospitals, banks, a favorable microclimate is ensured by energy-efficient air exchange systems with heat recovery. The efficiency of heat recovery in counterflow heat exchangers can reach 60%. The picture shown here shows that the air exchange units fit well into the decor of the room.

Literature

1. Arbeitskreis der Dozenten fur Klimatechnik: Handbuch der Klimatechnik, Verlag C.F. Muller GmbH, Karlsruhe

2. Recknagel/Sprenger: Taschenbuchfur Heizung + Klimatechnik, R. Oldenburg Verlag, Munchen/Wien 83/84

3. Ministerium fur Banuen und Wohnen des Landes Nordrhein-Westfalen: Luftung im Wohngebaude

4. THERMIE-Maxibroschure: Leitfaden energiesparende und emissionsarme Anlagen zur Heizung, Kuhlung und Klimatisierung von kleinen und mittleren Unternehmen in den neuen Bundeslandern, erhaltlich under OPET.