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A properly selected heating system will not only bring warmth and comfort to every home, but will also save you from unpleasant consequences and unnecessary repair costs. A hot water boiler is the basis of the heating system of a house.

Before choosing and purchasing, it is worth making a correct calculation of the efficiency of the boiler and clarifying all its parameters and factors that will affect its operation and the amount of heat generated.

What is boiler efficiency

The efficiency of steam and hot water boilers is determined by the efficiency factor - their thermal efficiency. That is, this is the volume of heat generated to produce a nominal volume of hot water in relation to the nominal volume of burned fuel.

Manufacturers indicate the initial capabilities of the equipment, where the efficiency of a water heating boiler can reach 110%, but more often their value adheres to the parameters of 95-98%. During further operation, the consumer can increase these indicators with the help of technical upgrades and thermal insulation.

Independent calculation of the boiler efficiency is carried out at the installation site and depends on many factors, including a well-designed smoke removal system, eliminating defects during installation, etc. All resources expended for the operation of the coolant (fuel, electricity) are compared with the volume of heat generated by it.

How to calculate efficiency

The gross efficiency of the boiler characterizes the degree of technical equipment, the net efficiency - the efficiency of fuel consumption.

To identify boiler efficiency indicators, the formula is used:

Boiler efficiency = (Q1/ Q_total)x100%, where Q1 is the accumulated heat used for heating, and Q_total is the total amount of thermal energy released during fuel combustion.

The calculations do not cover many points, so their results are averaged. Any malfunctions or deviations in the operation of equipment or external factors affecting heat loss will distort the result obtained from this formula.
To eliminate a larger number of distorting factors, the result is corrected to clarify the thermal efficiency. Depending on the characteristics of a particular heating system.

Boiler efficiency=100-(Q2+Q3+Q4+Q5+Q6)

Where Q2 is heat loss in the form of smoke released through the ventilation system,
Q3 – insufficient combustion of the gas mixture with incorrectly used volumes of the gas-air mixture,
Q4 – thermal heat loss due to contamination of the heat exchanger, as well as if the gas burners are dirty,
Q5 – heat loss due to external cold air (affects the performance of the boiler installation),
Q 6 – heat loss during cleaning of the combustion chamber.
The main factor influencing body efficiency is the exhaust waste combustion products; by reducing their heating within 10-12°C, the overall efficiency of a gas heating boiler can be increased by several percent.

For the same reason, condensing boilers have the highest efficiency index, i.e. the lower the temperature of the heating equipment, the higher this value. It has the lowest indicator due to minimal functionality and simple design.
The two options used in determining the efficiency of gas heating boilers are: reporting over a specific period of time and during initial installation tests. In the latter version, the calculation result will be more accurate, thanks to the clarity in calculating heat loss.

How to increase the efficiency of a gas boiler

You can create suitable conditions for increasing efficiency by optimizing processes yourself or with the involvement of a specialist. Initially, all parameters are included in the design of the electric boiler; the effectiveness of measures taken to increase the efficiency of the equipment will depend on these data.

To begin with, modernization is carried out without changing the structure of solid fuel boilers:

1. Room thermostats. They control the temperature in living spaces without affecting the operation of the coolant.
2. Installing a circular pump, this way you can stabilize the uniformity and speed of heating.
3. Replacing a gas burner will increase the efficiency of a solid fuel boiler by 5-7%. A modulating burner will allow you to consume the gas-air mixture in the correct proportions, which will eliminate incomplete combustion.
4. The location of the burners near the water circuit will add several percent to the total efficiency. Such a partial modification will have a positive effect on fuel consumption and increase the thermal balance of the entire system.

Carrying out regular maintenance and cleaning of equipment will increase its efficiency. Scale in the pipes of the heating system and soot on the outer walls of the chimney, formed during operation, can take up to 5%. Plastic pipes require less maintenance, but they must be purged periodically.

A clogged chimney narrows the passage of the smoke exhaust pipe, this leads to a decrease in draft, and this is not only a loss of heat, but also a threat to the health of people in residential premises.

Also, a heat exchanger with visible signs of contamination, which are salt deposits of metals, provokes a high consumption of all types of energy spent on work, which reduces thermal conductivity and can damage the boiler. Cleaning the combustion chamber is mandatory and is carried out several times a year.

As an option to reduce chemical heat losses, a highly qualified equipment system is configured for this. It is better to refrain from setting it up yourself and entrust the matter to a specialist.
The fight against underburning is solved by increasing the rate at which liquefied gas enters the burner, so the combustion process occurs more actively, and the efficiency, accordingly, increases.

Although an increase in efficiency has practically no effect on the thermal efficiency of the boiler unit. Today, natural gas remains the most economical; equipment using this fuel is more common and economically justified than boilers using traditional solid wood fuel or coal.

Gas boilers with the highest efficiency

The best quality boilers, which also have high efficiency rates, are of foreign origin. Energy-saving technologies that meet EU requirements are decisive in the production of such equipment.

High performance is ensured by modern modernization tools, for example, modulating burner.

Automatic and economical, it has a wide range that allows you to adapt to the individual parameters of a particular boiler and heating system. Its combustion is carried out in a constant mode.
Also, the main advantage is their maximum heat transfer. The most optimal value for heating the coolant, presented by a foreign manufacturer, is up to 70°C. Combustion products heat up to no more than 110°C.
The heat exchanger for boilers with the highest efficiency indicators is made from stainless steel. Additionally, they are equipped with a block for extracting heat from condensate. Disadvantages that are typical at low temperature heating: the traction force develops with insufficient force and the formation of excessive condensation.

The supply of already heated gas and gas-air mixture to the burner, as well as air entering the chamber through a double-cavity pipe into the firebox, ensures a reduction in the total heat input for closed-type boilers by 1-2%.

A good option for upgrading a boiler unit is to install exhaust gas recirculation. With this option, combustion products enter the burner device after passing through a chimney channel with strong kinks, while being enriched with oxygen from the external environment. Maximum efficiency is achieved at a temperature at which condensation forms (dew point).

Condensing boilers operating under heating conditions at low temperatures are characterized by relatively low gas consumption. This determines their thermal efficiency, especially when connected to gas cylinder units. This also makes such a boiler economical.
List of condensing boilers from well-known and respected European manufacturers with the best build quality and high level of efficiency:

• Baxi.
• Buderus.
• De Dietrich.
• Vaillant.
• Viessmann.

As stated by their manufacturers in the accompanying documentation, the efficiency of these boiler units, when connected to low-temperature systems, corresponds to 107-110%.

Heating equipment that runs on solid fuel is represented today by a whole group of devices. Every solid fuel boiler produced today by domestic and foreign manufacturing companies is a completely new, high-tech heating device. Thanks to the introduction of technical innovations and automatic control devices into the design of heating devices, it was possible to significantly increase efficiency and optimize the operation of solid fuel boilers.

Heating devices of this type use a traditional principle of operation, similar to the well-known version of stove heating. The main action is due to the process of generating thermal energy released during the combustion of coal, coke, firewood and other fuel resources in the boiler furnace, followed by heat transfer to the coolant.

Like other devices that provide energy generation and transmission, boiler equipment has its own efficiency factor. Let us consider in more detail what the efficiency of units operating on solid fuel is. We will try to find answers to questions related to these parameters.

What is the efficiency of heating devices

For any heating unit whose task is to heat the interior space of residential buildings and structures for various purposes, operating efficiency was, is and remains an important component. The parameter that determines the efficiency of solid fuel boilers is the efficiency factor. Efficiency shows the ratio of the expended thermal energy produced by the boiler during the combustion of solid fuel to the useful heat supplied to the entire heating system.

This ratio is expressed as a percentage. The better the boiler works, the higher the interest. Among modern solid fuel boilers there are models with high efficiency, high-tech, efficient and economical units.

For reference: As a rough example, one should evaluate the thermal effect obtained by sitting near a fire. The thermal energy released when burning wood can heat the space and objects limited around the fire. Most of the heat from a burning fire (up to 50-60%) goes into the atmosphere, providing no benefit other than aesthetic content, while neighboring objects and air receive a limited amount of kilocalories. The efficiency of a fire is minimal.

The efficiency of heating equipment strongly depends on what type of fuel is used and what are the design features of the device.

For example: when burning coal, wood or pellets, different amounts of thermal energy are released. Efficiency largely depends on the technology of fuel combustion in the combustion chamber and the type of heating system. In other words, each type of heating device (traditional solid fuel boilers, long-burning units, pellet boilers and devices operating through pyrolysis) has its own technological design features that affect the efficiency parameters.

Operating conditions and quality of ventilation also affect the efficiency of boilers. Poor ventilation causes a lack of air necessary for the high intensity of the combustion process of the fuel mass. Not only the level of comfort in the interior, but also the efficiency of heating equipment and the performance of the entire heating system depend on the condition of the chimney.

The accompanying documentation for the heating boiler must contain the equipment efficiency declared by the manufacturer. Compliance of real indicators with the declared information is achieved through proper installation of the device, wiring and subsequent operation.

Operating rules for boiler devices, compliance with which affects the efficiency value

Any type of heating unit has its own optimal load parameters, which should be as useful as possible from a technological and economic point of view. The operation process of solid fuel boilers is designed in such a way that most of the time the equipment operates in optimal mode. This work can be ensured by following the rules of operation of heating equipment operating on solid fuel. In this case, you must adhere to and follow the following points:

• it is necessary to observe acceptable modes of blowing and exhaust operation;
• constant control over the intensity of combustion and completeness of fuel combustion;
• control the amount of entrainment and failure;
• assessment of the condition of surfaces heated during fuel combustion;
• regular boiler cleaning.

The listed points are the necessary minimum that must be adhered to during the operation of boiler equipment during the heating season. Compliance with simple and understandable rules will allow you to obtain the efficiency of an autonomous boiler stated in the characteristics.

We can say that every little thing, every element of the design of a heating device affects the value of the efficiency factor. A properly designed chimney and ventilation system ensure optimal air flow into the combustion chamber, which significantly affects the quality of combustion of the fuel product. Ventilation performance is assessed by the excess air coefficient. An excessive increase in the volume of incoming air leads to excessive fuel consumption. Heat leaves more intensely through the pipe along with combustion products. When the coefficient decreases, the operation of boilers deteriorates significantly, and there is a high probability of oxygen-limited zones appearing in the furnace. In this situation, soot begins to form and accumulate in large quantities in the firebox.

The intensity and quality of combustion in solid fuel boilers require constant monitoring. The combustion chamber must be loaded evenly, avoiding focal fires.

On a note: coal or firewood is evenly distributed over the grates or grate. Combustion should occur over the entire surface of the layer. Evenly distributed fuel dries quickly and burns over the entire surface, ensuring complete burnout of the solid components of the fuel mass to volatile combustion products. If you have correctly placed fuel in the firebox, the flame when the boilers are operating will be bright yellow, straw-colored.

During combustion, it is important to prevent failure of the fuel resource, otherwise you will have to face significant mechanical losses (underburning) of fuel. If you do not control the position of the fuel in the firebox, large fragments of coal or firewood falling into the ash box can lead to unauthorized combustion of the remaining fuel mass products.

Soot and resin accumulated on the surface of the heat exchanger reduce the degree of heating of the heat exchanger. As a result of all of the above violations of operating conditions, the useful volume of thermal energy required for the normal operation of the heating system decreases. As a result, we can talk about a sharp decrease in the efficiency of heating boilers.

Factors on which boiler efficiency depends

Boilers with a high efficiency value today are represented by the following heating equipment:

• units running on coal and other solid fossil fuels;
• pellet boilers;
• pyrolysis type devices.

The efficiency of heating devices that fire anthracite, coal and peat briquettes is on average 70-80%. Pellet devices have a significantly higher efficiency – up to 85%. Loaded with pellets, heating boilers of this type are highly efficient, producing a huge amount of thermal energy during fuel combustion.

On a note: one load is enough to operate the device at optimal modes for up to 12-14 hours.

The absolute leader among solid fuel heating equipment is the pyrolysis boiler. These appliances use firewood or waste wood. The efficiency of such equipment today is 85% or more. The units also belong to highly efficient long-burning devices, but subject to the necessary conditions - fuel moisture content should not exceed 20%.

An important factor for the efficiency value is the type of material from which the heating device is made. Today on the market there are models of solid fuel boilers made of steel and cast iron.

For reference: The first includes steel products. To reduce the market value of the unit, manufacturing companies use basic structural elements made of steel. For example, the heat exchanger is made of high-strength, heat-resistant black steel with a thickness of 2-5 mm. The heating tubular elements used to heat the main circuit are manufactured in the same way.

The thicker the steel used in the structure, the higher the heat transfer characteristics of the equipment. The efficiency increases accordingly.

In steel devices, an increase in efficiency is achieved through the installation of special internal partitions in the form of pipes - main flow stages and smoke dissipators. Measures are forced and partial, allowing to slightly increase the efficiency of the main device. Among the models of steel solid fuel boilers, you can rarely find devices with an efficiency above 75%. The service life of such products is 10-15 years.

In order to increase the efficiency of steel heating boilers, foreign companies use a bottom combustion process in their models, with 2 or 3 traction flows. The design of the products provides for the installation of tubular heating elements to improve heat transfer. Such equipment has an efficiency of 75-80%, and can last longer, 1.5 times.

Unlike steel units, cast iron solid fuel units are more efficient.

The design of cast iron units uses heat exchangers made of a special grade of cast iron alloy, which has high heat transfer. Such boilers are most often used for open heating heating systems. The products are additionally equipped with grate bars, thanks to which intensive extraction of thermal energy is carried out directly from the burning fuel placed on the grate bar.

The efficiency of such heating devices is 80%. The long service life of cast iron boilers should be taken into account. The service life of such equipment is 30-40 years.

How to increase the efficiency of heating equipment running on solid fuels

Today, many consumers, having at their disposal a solid fuel boiler, are trying to find the most convenient and practical way to increase the efficiency of heating equipment. The technological parameters of heating devices set by the manufacturer lose their nominal values ​​over time, so various methods and means are being sought to increase the efficiency of boiler equipment.

Let's consider one of the most effective options, installing an additional heat exchanger. The task of the new equipment is to remove thermal energy from volatile combustion products.

In the video you can see how to make your own economizer (heat exchanger)

To do this, we first need to know what the temperature of the smoke at the outlet is. You can change it using a multimeter, which is placed directly in the middle of the chimney. Data on how much additional heat can be obtained from evaporating combustion products is necessary to calculate the area of ​​​​the additional heat exchanger. We do the following:

• we send a certain amount of firewood into the firebox;
• We measure how long it takes for a certain amount of firewood to burn.

For example: firewood, in the amount of 14.2 kg. burn for 3.5 hours. The smoke temperature at the boiler outlet is 460 0 C.

In 1 hour we burned: 14.2/3.5 = 4.05 kg. firewood

To calculate the amount of smoke, we use the generally accepted value of 1 kg. firewood = 5.7 kg. flue gases. Next, we multiply the amount of wood burned in one hour by the amount of smoke produced by burning 1 kg. firewood As a result: 4.05 x 5.7 = 23.08 kg. volatile combustion products. This figure will become the starting point for subsequent calculations of the amount of thermal energy that can be additionally used to heat the second heat exchanger.

Knowing the value of the heat capacity of volatile hot gases as 1.1 kJ/kg, we make a further calculation of the heat flow power if we want to reduce the smoke temperature from 460 0 C to 160 degrees.

Q = 23.08 x 1.1 (460-160) = 8124 kJ thermal energy.

As a result, we obtain the exact value of the additional power provided by volatile combustion products: q = 8124/3600 = 2.25 kW, a large figure that can have a significant impact on increasing the efficiency of heating equipment. Knowing how much energy is wasted, the desire to equip the boiler with an additional heat exchanger is completely justified. Due to the influx of additional thermal energy for heating the coolant, not only the efficiency of the entire heating system increases, but also the efficiency of the heating unit itself increases.

conclusions

Despite the abundance of models of modern heating equipment, solid fuel boilers continue to be one of the most effective and affordable types of heating equipment. Compared to electric boilers, which have an efficiency of up to 90%, solid fuel units have a high economic effect. The increase in efficiency on new models has allowed this type of boiler equipment to come closer to electric and gas boilers.

Modern solid fuel devices are capable of not only operating for a long time using affordable natural fuel resources, but also have high performance characteristics.

The efficiency of a boiler unit or the efficiency of a boiler unit is the ratio of the amount of heat used in the boiler unit to the amount of heat expended in the fuel. Part of the steam produced in the boiler unit is directly spent on its own needs, for example, on feed pumps, blower fans, smoke exhausters, and blowing heating surfaces. Taking these costs into account, the concept is introduced Boiler unit net efficiency.

Heat used in the boiler unit to produce steam or hot water,

Where IN - hourly fuel consumption, kg/h (m3/h);

D- hourly productivity of the boiler unit, kg/hour;

q k.a - the amount of heat transferred to water in the boiler unit to convert it into steam or to produce hot water and referred to 1 kg of steam or water, kJ/kg (kcal/kg);

ŋ k.a - efficiency of the boiler unit.

For a boiler unit that produces saturated steam

Where i" - enthalpy of saturated steam;

i p.v - enthalpy of feed water;

q pr- amount of heat removed from the boiler unit with blowdown water, kJ/kg (kcal/kg); usually q pr= (0.01-0.02) · i", Where i" - heat content of water at temperature t n.

For a hot water boiler unit that produces hot water

Where i 1 - enthalpy of water entering the boiler; i 2 is the enthalpy of water leaving the boiler.

If the amount of steam produced and its enthalpy are known, as well as the hourly fuel consumption and the heat of combustion of the fuel, then the efficiency of the boiler unit can be determined, %:

For modern boiler units the value q 1, depending on the steam output of the boiler unit, the temperature of the exhaust gases, the type of fuel burned and the method of its combustion, can vary within a very wide range from 75 to 80% for boiler units of small capacity, in which solid fuel is burned in layered furnaces, and up to 91-95 % for large boiler units with flaring fuel combustion. The highest efficiencies are obtained for boiler units operating on liquid and gaseous fuels.

For boiler units of small capacity, heat loss ranges from 20 to 25%, and for large ones from 5 to 9%. The main heat losses are losses with flue gases q 2

Example.

Determine the efficiency of the boiler unit and estimate the heat losses of the boiler unit with a steam capacity of Q = 10 tons/hour with steam parameters: pressure P= 1.4 MPa (14 kgf/cm2) and temperature t = 197.3°C. Hourly fuel consumption 1500 kg, feed water temperature 100°C, fuel combustion heat Q p n = 20647 kJ/kg (4916 kcal/kg). The heat losses of the boiler unit are assessed using the average values ​​given in the relevant sections. Sizeq PR ( amount of heat removed from the boiler unit with blowdown water) take equal to 0.

According to the table and specified steam parameters: pressure R and temperature t we find its enthalpy ~ 2790 kJ/kg (666 kcal/kg). At 100°C the heat content of the feed water will be approximately 419 kJ/kg (100 kcal/kg). Therefore, the heat received by 1 kg of steam according to the formula isq To

. A= 2790 - 419 = 2371 kJ/kg ( q To . a = 666 - 100 = 566 kcal/kg).

The efficiency of the boiler unit according to the formula

The amount of heat loss

Σ q i = 100 - ŋ k.a = 100 - 76.8 = 23.2%. Based on averages q 2 ,q 3 , q 4 given in § Heat balance of the boiler unit, we find q 2 = 12,5%, q 3 = 1%, q 4 = 6.25%. Consequently, the amount of losses to the environment q 5 = Σ qi- q 2 - q 3 - q 4 = 23,2 - 12,5 - 1 - 6,25 = 3,45%. ,

There are 2 methods for determining efficiency:

By direct balance;

By reverse balance.

Determining boiler efficiency as the ratio of useful heat expended to the available heat of the fuel is determined by direct balance:

The boiler efficiency can also be determined by the reverse balance - through heat losses. For the steady thermal state we obtain

. (4.2)

The boiler efficiency, determined by formulas (1) or (2), does not take into account electrical energy and heat for its own needs. This boiler efficiency is called gross efficiency and is denoted by or.

If the energy consumption per unit of time for the specified auxiliary equipment is, MJ, and the specific fuel consumption for electricity generation is, kg/MJ, then the efficiency of the boiler plant taking into account the energy consumption of the auxiliary equipment (net efficiency), %,

. (4.3)

Sometimes called the energy efficiency of a boiler plant.

For boiler installations of industrial enterprises, energy costs for their own needs account for about 4% of the generated energy.

Fuel consumption is determined:

Determination of fuel consumption is associated with a large error, so the efficiency by direct balance is characterized by low accuracy. This method is used to test an existing boiler.

The reverse balance method is characterized by greater accuracy and is used in the operation and design of the boiler. In this case, Q 3 and Q 4 are determined according to recommendations and from reference books. Q 5 is determined from the graph. Q 6 is calculated (rarely taken into account), and essentially the determination by reverse balance comes down to the determination of Q 2, which depends on the temperature of the flue gases.

The gross efficiency depends on the type and power of the boiler, i.e. productivity, type of fuel burned, firebox design. The efficiency is also affected by the boiler operating mode and the cleanliness of the heating surfaces.

In the presence of mechanical underburning, part of the fuel does not burn (q 4), and therefore does not consume air, does not form combustion products and does not release heat, therefore, when calculating the boiler, the calculated fuel consumption is used

. (4.5)

Gross efficiency only takes into account heat losses.

Figure 4.1 - Change in boiler efficiency with load change

5 DETERMINATION OF HEAT LOSS IN A BOILER UNIT.

WAYS TO REDUCE HEAT LOSS

5.1 Heat loss with flue gases

The loss of heat with the exhaust gases Q.g occurs due to the fact that the physical heat (enthalpy) of the gases leaving the boiler exceeds the physical heat of the air and fuel entering the boiler.

If we neglect the small value of the enthalpy of the fuel, as well as the heat of the ash contained in the flue gases, the heat loss with the flue gases, MJ/kg, is calculated by the formula:

Q 2 = J ch.g - J c; (5.8)

where is the enthalpy of cold air at a=1;

100-q 4 – proportion of burned fuel;

a у.г – coefficient of excess air in the flue gases.

If the ambient temperature is zero (t x.v = 0), then the heat loss with the exhaust gases is equal to the enthalpy of the exhaust gases Q a.g = J a.g.

Heat loss with flue gases usually occupies the main place among the heat losses of the boiler, amounting to 5-12% of the available heat of the fuel, and is determined by the volume and composition of combustion products, which significantly depend on the ballast components of the fuel and on the temperature of the flue gases:

The ratio characterizing the quality of the fuel shows the relative yield of gaseous combustion products (at a = 1) per unit of fuel combustion heat and depends on the content of ballast components in it:

– for solid and liquid fuels: moisture W Р and ash А Р;

– for gaseous fuel: N 2, CO 2, O 2.

With an increase in the content of ballast components in the fuel and, consequently, the loss of heat with exhaust gases increases accordingly.

One of the possible ways to reduce heat loss with flue gases is to reduce the coefficient of excess air in the flue gases a c.g., which depends on the air flow rate in the furnace a T and the ballast air sucked into the boiler flues, which are usually under vacuum

a y.g = a T + Da. (5.10)

In boilers operating under pressure, there are no air suctions.

With a decrease in a T, the heat loss Q.g. decreases, however, due to a decrease in the amount of air supplied to the combustion chamber, another loss may occur - from the chemical incompleteness of combustion Q 3.

The optimal value of a T is selected taking into account the achievement of the minimum value q y.g + q 3.

The decrease in a T depends on the type of fuel burned and the type of combustion device. Under more favorable conditions of contact between fuel and air, the excess air a T required to achieve the most complete combustion can be reduced.

Ballast air in the combustion products, in addition to increasing heat loss Q.g., also leads to additional energy costs for the smoke exhauster.

The most important factor influencing Q a.g. is the temperature of the exhaust gases t a.g. Its reduction is achieved by installing heat-using elements (economizer, air heater) in the tail part of the boiler. The lower the temperature of the exhaust gases and, accordingly, the lower the temperature difference Dt between the gases and the heated working fluid, the larger the surface area H is required for the same cooling of the gas. An increase in t y.g leads to an increase in losses from Q y.g and to additional fuel costs DB. In this regard, the optimal t c.g is determined on the basis of technical and economic calculations when comparing annual costs for heat-using elements and fuel for different values ​​of t c.g.

In Fig. 4 we can highlight the temperature range (from to ), in which the calculated costs differ slightly. This gives grounds for choosing as the most appropriate temperature , at which the initial capital costs will be lower.

There are limiting factors when choosing the optimal one:

a) low-temperature corrosion of tail surfaces;

b) when 0 C it is possible for water vapor to condense and combine with sulfur oxides;

c) the choice depends on the temperature of the feed water, the air temperature at the inlet to the air heater and other factors;

d) contamination of the heating surface. This leads to a decrease in the heat transfer coefficient and an increase.

When determining heat loss with flue gases, the reduction in gas volume is taken into account

. (5.11)

5.2 Heat loss from chemical incomplete combustion

Heat loss from chemical incomplete combustion Q 3 occurs when fuel is incompletely burned within the combustion chamber of the boiler and flammable gaseous components CO, H 2 , CH 4 , C m H n appear in the combustion products... The combustion of these combustible gases outside the furnace is practically impossible due to -due to their relatively low temperature.

Chemical incomplete combustion of fuel can result from:

– general lack of air;

– poor mixture formation;

– small size of the combustion chamber;

– low temperature in the combustion chamber;

– high temperature.

If the air quality and good mixture formation are sufficient for complete combustion of fuel, q 3 depends on the volumetric density of heat release in the furnace

The optimal ratio at which the loss of q 3 has a minimum value depends on the type of fuel, the method of its combustion and the design of the furnace. For modern combustion devices, the heat loss from q 3 is 0÷2% at q v =0.1÷0.3 MW/m 3.

To reduce heat loss from q 3 in the combustion chamber, they strive to increase the temperature level, using, in particular, heating the air, as well as improving the mixing of combustion components in every possible way.

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All about boiler efficiency

What is boiler efficiency

The efficiency of a heating boiler is the ratio of the useful heat consumed to produce steam (or hot water) to the available heat of the heating boiler. Not all the useful heat generated by the boiler unit is sent to consumers; part of the heat is spent on its own needs. Taking this into account, the efficiency of a heating boiler is distinguished by the generated heat (gross efficiency) and by the released heat (net efficiency).

The difference between the generated and released heat is used to determine the consumption for auxiliary needs. Not only heat is consumed for its own needs, but also electrical energy (for example, to drive a smoke exhauster, fan, feed pumps, fuel supply mechanisms), i.e. consumption for own needs includes the consumption of all types of energy spent on the production of steam or hot water.

* To buy a Unique boiler, go to the appropriate section. And if you need heating boilers wholesale, then go here.

How to calculate boiler efficiency

As a result, the gross efficiency of a heating boiler characterizes the degree of its technical perfection, and the net efficiency characterizes its commercial profitability. For a boiler unit gross efficiency, %:
according to the direct balance equation:

ηbr = 100 Qpol / Qpp

where Qfloor is the amount of useful heat, MJ/kg; Qрр - available heat, MJ/kg;

according to the reverse balance equation:

ηbr = 100 – (q2 + q3 + q4 + q5 + q6),

where q is heat loss in%:

• q2 - with exhaust gases;
• q3 - due to chemical underburning of flammable gases (CO, H2, CH4);
• q4 - with mechanical underburning;
• q5 - from external cooling;
• q6 - with physical heat of slag.

Then the net efficiency of the heating boiler according to the reverse balance equation

ηnet = ηbr - qs.n

where qс.н - energy consumption for own needs, %.

The determination of efficiency using the direct balance equation is carried out mainly when reporting for a separate period (decade, month), and using the reverse balance equation - when testing a heating boiler. Calculating the efficiency of a heating boiler using reverse balance is much more accurate, since the errors in measuring heat losses are smaller than in determining fuel consumption.

How to increase the efficiency of a gas boiler with your own hands

You can actually create the correct operating conditions for a gas boiler and thereby increase the efficiency without calling a specialist, that is, with your own hands. What do I need to do?

1. Adjust the blower damper. This can be done experimentally by finding at what position the coolant temperature will be highest. Carry out control using a thermometer installed in the boiler body.
2. Be sure to ensure that the heating system pipes do not become overgrown from the inside, so that scale and dirt deposits do not form on them. Today it has become easier with plastic pipes, their quality is known. Still, experts recommend periodically purging the heating system.
3. Monitor the quality of the chimney. Do not allow it to become clogged or soot to stick to the walls. All this leads to a narrowing of the cross-section of the outlet pipe and a decrease in the boiler draft.
4. A prerequisite is cleaning the combustion chamber. Of course, gas does not smoke much like wood or coal, but it is worth washing the firebox at least once every three years to clear it of soot.
5. Experts recommend reducing chimney draft during the coldest time of the year. To do this, you can use a special device - a draft limiter. It is installed at the very top edge of the chimney and regulates the cross-section of the pipe itself.
6. Reduce chemical heat losses. There are two options here to achieve the optimal value: install a draft limiter (this has already been discussed above) and immediately after installing the gas boiler, carry out proper adjustment of the equipment. We recommend entrusting this to a specialist.
7. You can install a turbulator. These are special plates that are installed between the firebox and the heat exchanger. They increase the area of ​​thermal energy extraction.