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All about boiler efficiency

What is boiler efficiency

Coefficient useful action heating boiler is the ratio of 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 heat generated (gross efficiency) and by the heat released (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 our own needs, but also Electric 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 chemical underburning 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

Create the right conditions operation gas boiler and thus you can actually 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. WITH plastic pipes Today it has become easier, 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 mentioned 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 where thermal energy is collected.

The thermal efficiency of boiler equipment is indicated in the efficiency factor. The efficiency of a gas boiler must be specified in the technical documentation. According to manufacturers, for some boiler models the coefficient reaches 108-109%, others operate at the level of 92-98%.

How to calculate the efficiency of a gas heating boiler

The method for calculating efficiency occurs by comparing the thermal energy expended to heat the coolant and the actual amount of all heat released during fuel combustion. In factory conditions, calculations are performed according to the formula:

η = (Q1/ Qri) 100%

In the formula for calculating the efficiency of a gas-fired hot water boiler, the indicated values ​​mean:

• Qri is the total amount of thermal energy released when burning fuel.
• Q1 – heat that was accumulated and used to heat the room.

This formula does not take into account many factors: possible heat loss, deviations in the operating parameters of the system, etc. Calculations allow us to obtain exclusively the average efficiency of a gas boiler. Most manufacturers indicate this value.

An on-site assessment of the error in determining thermal efficiency is carried out. Another formula is used for calculations:

η=100 - (q2 + q3 + q4 + q5 + q6)

Calculations help to carry out an analysis according to the characteristics of a particular heating system. The abbreviations in the formula mean:

• q2 – heat loss in exhaust gases and combustion products.
• q3 – losses associated with incorrect proportions of the gas-air mixture, which causes underburning of gas.
• q4 – heat losses associated with the appearance of soot on the burners and heat exchanger, as well as mechanical underburning.
• q5 – heat loss, depending on the outside temperature.
• q6 – heat loss when cooling the furnace while cleaning it from slag. The last coefficient applies exclusively to solid fuel units and is not taken into account when calculating the efficiency of equipment running on natural gas.

The real efficiency of a gas heating boiler is calculated exclusively on site and depends on a well-made smoke removal system, the absence of violations during installation, etc.

The temperature of the flue gases, marked in the formula with marker q2, has the greatest impact on thermal efficiency. When the heating intensity of the outgoing degrees decreases by 10-15°C, the efficiency increases by 1-2%. In this regard, the highest efficiency is in condensing boilers belonging to the class of low-temperature heating equipment.

Which gas boiler has the highest efficiency?

Statistics and technical documentation clearly indicate that imported boilers have the highest efficiency. European manufacturers place special emphasis on the use of energy-saving technologies. A foreign gas boiler has high efficiency, since some modifications have been made to its design:

• A modulating burner is used – modern boilers leading manufacturers, equipped with smooth two-stage or fully modulating burner devices. The advantage of the burners is their automatic adaptation to the actual operating parameters of the heating system. The percentage of underburning is reduced to a minimum.
• Coolant heating– the optimal boiler is a unit that heats the coolant to a temperature of no more than 70°C, while the exhaust gases are heated to no more than 110°C, which ensures maximum heat transfer. But, with low-temperature heating of the coolant, several disadvantages are observed: insufficient traction force, increased condensation.
  Heat exchangers in gas boilers with the highest efficiency, made from of stainless steel and are equipped with a special condenser unit designed to extract heat contained in the condensate.
• Temperature of the supply gas and air entering the burner. Closed type boilers, connected. The air enters the combustion chamber through the outer cavity of the double-cavity pipe, preheated, which reduces the required heat input by several percent.
  Burners with preliminary preparation of the gas-air mixture also heat the gas before feeding it to the burner.
• Another popular modification option– installation of an exhaust gas recirculation system, when smoke does not immediately enter the combustion chamber, but passes through a broken chimney duct and enters after mixing fresh air, back to the burner device.

Maximum efficiency is achieved at the condensation temperature or “dew point”. Boilers operating in low-temperature heating conditions are called condensing boilers. They are distinguished by low gas consumption and high thermal efficiency, which is especially noticeable when connected to and.

Condensing boilers are offered by several European manufacturers, including:

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

In the technical documentation for condensing boilers, it is indicated that the efficiency of devices when connected to low-temperature heating systems is 108-109%.

How to increase the efficiency of a gas heating boiler

There are all sorts of tricks to increase efficiency. The effectiveness of the methods depends on the initial design of the boiler. To begin with, use modifications that do not require changes in the operation of the boiler:

• Changing the principle of coolant circulation– the building warms up faster and more evenly when a circulation pump is connected.
• Installation of room thermostats– modernization of boilers to increase efficiency using sensors that control not the heating of the coolant, but the temperature in the room, effective method increasing thermal efficiency.
• An increase in the gas utilization rate in a domestic boiler by approximately 5-7% occurs when the burner device is replaced. Installing a modulating burner helps improve the proportions of the gas-air mixture and, accordingly, reduces the percentage of underburning. The type of burner installed is directly related to the reduction of heat loss.
• Instead of a complete modification of the boiler, a partial modification of the design and adjustment of fuel consumption may be required. If you change the position of the burners and install them closer to the water circuit, you will be able to increase the efficiency by another 1-2%. The heat balance of the boiler unit will increase upward.

A certain increase in efficiency is observed with regular equipment maintenance. After cleaning a boiler in operation and removing scale from the heat exchanger, its efficiency increases by at least 3-5%.

Efficiency decreases when the heat exchanger is dirty, due to the fact that scale, consisting of salt deposits of metals, has poor thermal conductivity. For this reason, there is a constant increase in gas consumption and subsequently, the boiler completely fails.

There is a slight increase in efficiency during the combustion of liquefied gas, achieved by reducing the rate of fuel supply to the burner, which leads to a decrease in underburning. But, thermal efficiency increases slightly. That's why, natural gas continues to be the most economical of all traditional fuel types used.

For a modern liquid fuel boiler room, the efficiency will often reach 80%, provided that the boiler room is clean and free of soot. However, the real efficiency on average (for those boiler houses that were measured) is approximately 65%. More often than not, the boiler room is not clean enough to accept heat from the flame and transfer maximum amount warm water.

The situation is much more complicated when boiler house manufacturers begin to talk about efficiency reaching 95%. It is not clear what conditions were used to determine the efficiency, and what efficiency is meant.

In the technical/economic field, at least 6 definitions are used for boiler room efficiency. Since many people do not know the conditions for determining the efficiency of a boiler room, suppliers, without fear of being accused of lying, give high efficiency. However, these high figures have nothing to do with the reality of the heat payer.

1. COMBUSTION EFFICIENCY

Combustion efficiency is the amount of fuel energy that is RELEASED during combustion.

The release of fuel energy and its conversion into heat in the hearth (stove) of the boiler room does not indicate the high efficiency of the boiler room. Combustion efficiency is provided by some boiler house manufacturers as boiler room efficiency, because 1) the figure is high (approximately 93-95%) 2) it is easy to measure combustion efficiency - you need to install the instrument in the chimneys.

The release of heat from fuel occurs in most boiler houses with high combustion efficiency.

Consequently: The release of fuel energy plus its conversion into heat in the hearth (stove) is not the same heat that is received by the boiler!! We are interested in the heat received by the boiler!!

2. BOILER ROOM efficiency

Boiler house efficiency is the amount of fuel energy that is usefully used, i.e. is transformed into another energy-carrying medium.

By other energy-carrying medium we mean, for example, warm water, which heats the house.

Boiler house efficiency is the most used definition of efficiency in all types of combustion plants.

Boiler room efficiency is more difficult to measure than combustion efficiency, so many people are content with only measuring combustion efficiency. In fact, the boiler room efficiency is 10-15% lower than the combustion efficiency.

3. EFFICIENCY OF COMBUSTION EQUIPMENT

THE EFFICIENCY OF COMBUSTION EQUIPMENT SHOWS HOW EFFECTIVELY COMBUSTION AND HEAT RECEPTION OCCUR IN THE BOILER ROOM. Even these calculations are often presented as a result of flue gas analysis.

Often, the efficiency of furnace equipment is used as an approximate analogue of boiler room efficiency, since the measurement technology in in this case easier. Using this technique, you can obtain an approximate figure for the efficiency of a boiler room: it is necessary to constantly analyze the composition of oxygen or CO2 in the combustion gases. Losses are subtracted, since, for example, some heat is present in the ash/slag (this is especially true for slag-forming fuels). As for liquid fuel, the efficiency of furnace equipment and the efficiency of the boiler room are approximately the same, since liquid fuel does not contain ash/slag. But if you use this concept for coal or biofuels, then the errors (errors) are much higher.

4. EFFICIENCY OF THE INSTALLATION

When calculating the efficiency of an installation, the ratio between the total amount of useful energy and the total amount of energy is determined. The total amount of energy also includes “auxiliary energy”, for example, electrical energy necessary to operate boiler room pumps, ventilation, chimneys, etc. For a liquid fuel installation, "auxiliary energy" corresponds to approximately 1% of the total fuel energy; for solid fuel installations, "auxiliary energy" equals 5% of the fuel energy.
The efficiency of the installation will thus be lower than the efficiency of the boiler room.

5. SYSTEM EFFICIENCY

Definition System efficiency expands the boundaries of the system to:

Heat production with losses
- heat distribution with losses in heating mains, etc.
- heat use

According to UNICHAL (International Union of Heat Suppliers), the following typical losses in pipes when distributing hot water to apartments occur:

Sweden - 8% losses in pipes, i.e. heat is transferred to the ground and surrounding district heating pipes
Denmark - 20%
Finland - 9%
Belgium - 13%
Switzerland - 13%
West Germany - 11%

6. Annual efficiency

The efficiency per year in principle corresponds to the efficiency of the boiler house, but then the average efficiency of the boiler house is calculated for the entire year. The efficiency per year also includes periods with poor combustion levels, for example, when starting a boiler room, etc.

Efficiency per year depends on the size of the installation, service life, etc.

The above shows that different definitions for efficiency are used, so there is a high probability that an erroneous figure will be given if the concept and definition of efficiency is not clarified. Thus, there is no need to be afraid of being insensitive, since in fact, many manufacturers, with or without knowledge, provide erroneous figures.

The important figures are those that reflect the real economic side of the fuel that the consumer buys. If you lose consumer trust due to providing too high efficiency, then the appearance big problems inevitable in the market.

As stated, "all suppliers" (at least many) give combustion efficiency when they offer boiler room efficiency information.

You cannot use combustion efficiency when calculating the economics of an installation!!!

THE CONSUMER IS NOT BUYING FUEL, BUT A MEANS FOR PRODUCING HEAT. It is not the fuel that should be cheap, but the heat that consumers receive during winter blizzards.

The value ranges from 0.3 to 3.5% and decreases with increasing boiler power (from 3.5% for boilers with a capacity of 2 t/h to 0.3% for boilers with a capacity of more than 300 t/h).

Loss of slags with physical heat occurs because when burned solid fuel The slag removed from the furnace has a high temperature: for solid slag removal = 600 °C, for liquid slag removal - = 1400 - 1600 °C.

Heat losses with physical heat of slag, %, are determined by the formula:

,

Where - the proportion of slag collection in the combustion chamber; - slag enthalpy, kJ/kg.

For layer combustion of fuels, as well as for chamber combustion with liquid slag removal = 1 – 2% and higher.

For chamber combustion of fuel with solid slag removal, the loss is taken into account only for multi-ash fuels at > 2.5%∙kg/MJ.

Boiler unit efficiency (gross and net).

The efficiency of a boiler unit is the ratio of the useful heat used to produce steam (hot water) to the available heat (heat entered into the boiler unit). Not all the useful heat generated by the boiler is sent to consumers; part of it is spent on its own needs (drive of pumps, draft devices, heat consumption for heating water outside the boiler, its deaeration, etc.). In this regard, a distinction is made between the efficiency of the unit based on the heat generated (gross efficiency) and the efficiency of the unit based on the heat supplied to the consumer (net efficiency).

Boiler efficiency (gross), %, can be determined by the equation direct balance

,

or equation reverse balance

.

Boiler efficiency (net), %, according to the reverse balance is determined as

where is the relative energy consumption for own needs, %.

Topic 6. Layer combustion devices for burning fuel in a dense and boiling (fluidized) bed

Furnaces for burning fuel in a dense layer: principle of operation, scope of application, advantages and disadvantages. Classification of furnaces for burning fuel in a dense bed (non-mechanized, semi-mechanical, mechanical). Fuel throwers. Mechanical fireboxes with moving grates: principle of operation, scope of application, varieties. Layer combustion devices for burning fuel in a fluidized bed: principle of operation, scope of application, advantages and disadvantages.

Layer combustion devices for burning fuel in a dense layer.

Layer furnaces, designed for burning solid lump fuel (size from 20 to 30 mm), are easy to operate and do not require a complex, expensive fuel preparation system.

But since the process of burning fuel in a dense layer is characterized by a low combustion rate, inertia (and, therefore, it is difficult to automate), reduced efficiency (fuel combustion occurs with large losses from mechanical and chemical underburning) and reliability, layer combustion is economically feasible for boilers with steam capacity up to 35 t/h.

Layered furnaces are used for burning anthracite, hard coal with moderate caking (long-flame, gas, lean), brown coal with low moisture and ash content, as well as lump peat.

Classification of layer fireboxes.

Maintenance of a furnace in which fuel is burned in a bed is reduced to the following basic operations: supplying fuel to the furnace; stirring (mixing) the fuel layer in order to improve the conditions for supplying the oxidizer; removal of slag from the furnace.

Depending on the degree of mechanization of these operations, layer combustion devices can be divided into non-mechanized (all three operations are performed manually); semi-mechanical (one or two operations are mechanized); mechanical (all three operations are mechanized).

Non-mechanized layered fireboxes are fireboxes with manual periodic supply of fuel to a fixed grate and manual periodic removal of slag.

Semi-mechanical combustion devices are distinguished by the mechanization of the process of supplying fuel to the grate using various throwers, as well as the use of special slag removers and rotary or swinging grates.