For a modern oil fired boiler plant, efficiency will often reach 80%, provided that the boiler plant is clean and free of soot. However, the real efficiency on average (for those boilers that were measured) is about 65%. Most often, the boiler room is not so clean that it can receive heat from the flame and transfer maximum amount warm water.
Much more difficult is the situation when boiler manufacturers start talking about efficiency reaching 95%. It is not clear what conditions were used in determining the efficiency, and what kind of efficiency is meant.
In the technical/economic area, at least 6 definitions are used for the efficiency of a boiler house. Since many people do not know the conditions for determining the efficiency of a boiler house, 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 - 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 house does not indicate a high efficiency of the boiler house. The combustion efficiency is given by some boiler house manufacturers as the boiler room efficiency, because 1) the figure is high (about 93-95%) 2) it is easy to measure the combustion efficiency - you need to install the tool in the chimneys.
The release of heat from the fuel occurs in most boilers with high combustion efficiency.
Therefore: The release of fuel energy plus its conversion into heat in the hearth (stove) is not the heat that is received by the boiler!! We are interested in the heat received by the boiler!!
2. EFFICIENCY OF THE BOILER
Boiler room efficiency - the amount of fuel energy that is usefully used, i.e. is converted into another energy-carrying medium.
Another energy-carrying medium is, for example, warm water that heats the house.
Boiler house efficiency is the most commonly used definition of efficiency in all types of combustion plants.
The efficiency of a boiler house is more difficult to measure than the efficiency of combustion, so many people are content with just measuring the combustion efficiency. In fact, the efficiency of a boiler house is 10-15% lower than the combustion efficiency.
3. EFFICIENCY OF FURNACE EQUIPMENT
THE EFFICIENCY OF THE FURNACE TECHNOLOGY SHOWS HOW EFFICIENTLY COMBUSTION AND HEAT RECEPTION IN THE BOILER ROOM IS HOW EFFICIENT. Even these calculations are often presented as a result of flue gas analysis.
Often the efficiency of furnace technology is used as an approximate analogue of the efficiency of a boiler house, since the measurement technique in this case easier. Using this technique, you can get an approximate figure for the efficiency of the boiler room: it is necessary to constantly analyze the composition of oxygen or CO2 in the flue gases. Losses are subtracted, since, for example, part of the heat is present in the ash / slag (this is especially true for slag-forming fuels). As for liquid fuel, the efficiency of furnace technology and the efficiency of the boiler house 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. INSTALLATION EFFICIENCY
When calculating the efficiency of an installation, the ratio between the total amount of usable energy and the total amount of energy is determined. The total amount of energy also includes "auxiliary energy", for example, electrical energy required for the operation of boiler room pumps, ventilation, chimneys, etc. For liquid fuel installations "auxiliary energy" corresponds to approximately 1% of the total energy of the fuel, for solid fuel installations "auxiliary energy" equals 5% of the fuel energy.
The efficiency of the installation will thus be lower than that of the boiler house.
5. SYSTEM EFFICIENCY
Determining the system efficiency expands the boundaries of the system to:
Heat production with losses
- heat distribution with losses in heating mains, etc.
- use of heat
According to UNICHAL (International Heat Suppliers Union) the following are typical pipe losses during distribution hot water the apartments have:
Sweden - 8% pipe losses, i.e. heat is transferred to the ground and to the surroundings of the DH pipes
Denmark - 20%
Finland - 9%
Belgium - 13%
Switzerland - 13%
West Germany - 11%
6. Annual efficiency
Efficiency per year basically corresponds to the efficiency of the boiler house, but then the average efficiency of the boiler house over the whole year is calculated. Efficiency per year also includes periods with poor combustion levels, for example, when starting a boiler house, etc.
Efficiency per year depends on plant size, operating 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, one should not be afraid to be tactless, because in fact, many manufacturers, with or without knowledge, provide erroneous numbers.
What matters are the numbers that reflect the real economic side the fuel that the consumer buys. If you lose consumer confidence due to the provision of too high efficiency, then the appearance big problems on the market is inevitable.
As said, "all suppliers" (at least many) give combustion efficiency when they offer information on boiler plant efficiency.
Do not use the combustion efficiency when calculating the economics of the plant!!!
The consumer BUYS NOT FUEL, BUT HEAT PRODUCTS. It is not the fuel that should be cheap, but the heat that consumers receive during winter blizzards.
Probably everyone wondered about the efficiency (Coefficient of Efficiency) of the engine internal combustion. After all, the higher this indicator, the more efficient it works. power unit. The most efficient for this moment time is considered an electric type, its efficiency can reach up to 90 - 95%, but for internal combustion engines, whether it be diesel or gasoline, to put it mildly, it is far from ideal ...
To be honest, then modern options motors are much more efficient than their counterparts, which were released 10 years ago, and there are a lot of reasons for this. Think for yourself before the 1.6-liter option, it gave out only 60 - 70 hp. And now this value can reach 130 - 150 hp. This is painstaking work to increase efficiency, in which each "step" is given by trial and error. However, let's start with a definition.
is the value of the ratio of two quantities, the power that is supplied to crankshaft engine to the power received by the piston, due to the pressure of the gases that were formed by igniting the fuel.
In simple terms, this is the conversion of thermal or thermal energy that appears during combustion fuel mixture(air and gasoline) to mechanical. It should be noted that this has already happened, for example, with steam power plants- Also, the fuel under the influence of temperature pushed the pistons of the units. However, the installations there were many times larger, and the fuel itself was solid (usually coal or firewood), which made it difficult to transport and operate it, it was constantly necessary to “feed” it into the furnace with shovels. Internal combustion engines are much more compact and lighter than steam engines, and fuel is much easier to store and transport.
More about losses
Looking ahead, we can confidently say that the efficiency of a gasoline engine is in the range of 20 to 25%. And there are many reasons for this. If we take the incoming fuel and recalculate it as a percentage, then we kind of get “100% of the energy” that is transferred to the engine, and then the losses went:
1)Fuel efficiency . Not all fuel burns out, a small part of it leaves with exhaust gases, at this level we already lose up to 25% of efficiency. Of course now fuel systems improved, an injector appeared, but it is far from ideal.
2) The second is heat losses.And . The engine warms up itself and many other elements, such as radiators, its body, the liquid that circulates in it. Also, part of the heat is lost from exhaust gases. For all this, up to 35% loss of efficiency.
3) The third is mechanical losses . ON all kinds of pistons, connecting rods, rings - all places where there is friction. This includes losses from the load of the generator, for example, the more electricity the generator produces, the more it slows down the rotation of the crankshaft. Of course, lubricants have also stepped forward, but again, no one has yet completely defeated friction - another 20% loss
Thus, in the dry residue, the efficiency is about 20%! Of course, there are stand-out options from gasoline options, in which this figure is increased to 25%, but there are not so many of them.
That is, if your car consumes 10 liters of fuel per 100 km, then only 2 liters of them will go directly to work, and the rest are losses!
Of course, you can increase the power, for example, by boring the head, we are watching a short video.
If you remember the formula, you get:
Which engine has the highest efficiency?
Now I want to talk about gasoline and diesel options, and find out which one is the most efficient.
To put it simply, the language and not to climb into the wilds technical terms then - if we compare two efficiencies - the most efficient of them, of course, is diesel, and here's why:
1) Gas engine converts only 25% of energy into mechanical energy, but diesel about 40%.
2) If equipped diesel type turbocharging, it is possible to achieve an efficiency of 50-53%, and this is very significant.
So why is it so effective? It's simple - despite the similar type of work (both are internal combustion units), a diesel engine does its job much more efficiently. It has greater compression, and the fuel ignites from a different principle. It heats up less, which means it saves on cooling, it has fewer valves (savings on friction), and it also doesn’t have the usual ignition coils and spark plugs, which means it doesn’t require additional energy costs from the generator. It works at lower speeds, you don’t need to spin the crankshaft furiously - it does all diesel variant efficiency champion.
About Diesel Fuel Efficiency
FROM more high value coefficient useful action– followed by fuel efficiency. So, for example, a 1.6-liter engine can consume only 3-5 liters in the city, unlike petrol type, where the consumption is 7 - 12 liters. A diesel engine has a lot, the engine itself is often more compact and lighter, and also more environmentally friendly lately. All these positive moments are achieved due to the greater value, there is a direct relationship between efficiency and compression, see a small plate.
However, despite all the advantages, it also has many disadvantages.
As it becomes clear, the efficiency of an internal combustion engine is far from ideal, so the future is clearly with electric options - it remains only to find efficient batteries that are not afraid of frost and hold a charge for a long time.
Efficiency (efficiency) - a characteristic of the efficiency of a system (device, machine) in relation to the conversion or transfer of energy. It is determined by the ratio of useful energy used to the total amount of energy received by the system; usually denoted η ("this"). η = Wpol/Wcym. Efficiency is a dimensionless quantity and is often measured as a percentage. Mathematically, the definition of efficiency can be written as:
X 100%
Where A - useful work, A Q- wasted energy.
By virtue of the law of conservation of energy, the efficiency is always less than unity or equal to it, that is, it is impossible to obtain more useful work than the energy expended.
Heat engine efficiency- the ratio of the perfect useful work of the engine, to the energy received from the heater. efficiency heat engine can be calculated using the following formula
,where - the amount of heat received from the heater, - the amount of heat given to the refrigerator. The highest efficiency among cyclic machines operating at given hot spring temperatures T 1 and cold T 2, have heat engines operating on the Carnot cycle; this limiting efficiency is equal to
.Not all indicators characterizing the efficiency of energy processes correspond to the above description. Even if they are traditionally or erroneously called "efficiency", they may have other properties, in particular, exceed 100%.
boiler efficiency
Main article: Boiler thermal balance
The efficiency of fossil fuel boilers is traditionally calculated from the net calorific value; it is assumed that the moisture of the combustion products leaves the boiler in the form of superheated steam. In condensing boilers, this moisture is condensed, the heat of condensation is usefully used. At efficiency calculation in terms of lower calorific value, it can eventually turn out to be more than one. In this case, it would be more correct to consider it according to the gross calorific value, which takes into account the heat of steam condensation; however, the performance of such a boiler is difficult to compare with data from other installations.
Heat pumps and chillers
The advantage of heat pumps as a heating technique is the ability to sometimes receive more heat than the energy spent on their work; similarly, a refrigeration machine can remove more heat from the cooled end than is expended in organizing the process.
The efficiency of such heat engines is characterized by coefficient of performance(for chillers) or transformation ratio(for heat pumps)
,where is the heat taken from the cold end (in refrigeration machines) or transferred to the hot end (in heat pumps); - the work (or electricity) spent on this process. best performance productivity for such machines has a reverse Carnot cycle: in it the coefficient of performance
,where , are the temperatures of the hot and cold ends, . This value, obviously, can be arbitrarily large; although practically it is difficult to approach it, the coefficient of performance can still exceed unity. This does not contradict the first law of thermodynamics, since, in addition to the energy taken into account A(e.g. electric), into heat Q there is also energy taken from a cold source.
Literature
- Peryshkin A.V. Physics. 8th grade. - Bustard, 2005. - 191 p. - 50,000 copies. - ISBN 5-7107-9459-7.
Notes
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Synonyms:See what "Efficiency" is in other dictionaries:
efficiency- The ratio of output power to consumed active power. [OST 45.55 99] coefficient of useful action efficiency A value that characterizes the perfection of the processes of transformation, transformation or transfer of energy, which is the ratio of useful ... ... Technical Translator's Handbook
Or the coefficient of return (Efficiency) is a characteristic of the quality of work of any machine or apparatus in terms of its efficiency. By K.P.D. is meant the ratio of the amount of work received from the machine or energy from the device to that amount ... ... Marine Dictionary
- (efficiency), an indicator of the efficiency of the mechanism, defined as the ratio of the work performed by the mechanism to the work expended on its functioning. efficiency usually expressed as a percentage. An ideal mechanism would have to have efficiency = ... ... Scientific and technical encyclopedic dictionary
Modern Encyclopedia
- (efficiency) characteristic of the efficiency of the system (device, machine) in relation to energy conversion; is determined by the ratio of useful energy used (turned into work in a cyclic process) to the total amount of energy, ... ... Big Encyclopedic Dictionary
- (efficiency), a characteristic of the efficiency of a system (device, machine) in relation to the conversion or transfer of energy; is determined by the ratio of t) useful energy used (Wpol) to the total amount of energy (Wtotal) received by the system; h=Wpol… … Physical Encyclopedia
- (efficiency) the ratio of useful energy W p, for example. in the form of work, to the total amount of energy W received by the system (machine or engine), W p / W. Due to the inevitable energy losses due to friction and other non-equilibrium processes for real systems ... ... Physical Encyclopedia
The ratio of useful work expended or energy received to all work expended or energy consumed, respectively. For example, the efficiency of the electric motor is the ratio of mechan. the power they give off to the electric power supplied to it. power; TO.… … Technical railway dictionary
Exist., number of synonyms: 8 efficiency (4) return (27) fruitfulness (10) ... Synonym dictionary
Efficiency- - a value that characterizes the perfection of any system in relation to any process of transformation or energy transfer occurring in it, defined as the ratio of useful work to the work expended on putting into action. ... ... Encyclopedia of terms, definitions and explanations of building materials
Efficiency- (efficiency), a numerical characteristic of the energy efficiency of any device or machine (including a heat engine). Efficiency is determined by the ratio of useful energy used (i.e., converted into work) to the total amount of energy, ... ... Illustrated Encyclopedic Dictionary
Coefficient of performance (COP) - a term that can be applied, perhaps, to every system and device. Even a person has an efficiency, though, probably, there is no objective formula for finding it yet. In this article, we will explain in detail what efficiency is and how it can be calculated for various systems.
efficiency definition
Efficiency is an indicator that characterizes the efficiency of a particular system in relation to the return or conversion of energy. Efficiency is a measureless value and is represented either as a numerical value in the range from 0 to 1, or as a percentage.
General formula
Efficiency is indicated by the symbol Ƞ.
The general mathematical formula for finding the efficiency is written as follows:
Ƞ=A/Q, where A is the useful energy/work done by the system, and Q is the energy consumed by this system to organize the process of obtaining a useful output.
The efficiency factor, unfortunately, is always less than one or equal to it, since, according to the law of conservation of energy, we cannot get more work than the energy spent. In addition, the efficiency, in fact, is extremely rarely equal to one, since useful work is always accompanied by losses, for example, for heating the mechanism.
Heat engine efficiency
A heat engine is a device that converts thermal energy into mechanical energy. In a heat engine, work is determined by the difference between the amount of heat received from the heater and the amount of heat given to the cooler, and therefore the efficiency is determined by the formula:
- Ƞ=Qн-Qх/Qн, where Qн is the amount of heat received from the heater, and Qх is the amount of heat given to the cooler.
It is believed that highest efficiency provide engines operating on the Carnot cycle. In this case, the efficiency is determined by the formula:
- Ƞ=T1-T2/T1, where T1 is the temperature of the hot source, T2 is the temperature of the cold source.
Electric motor efficiency
An electric motor is a device that converts electrical energy into mechanical energy, so the efficiency in this case is the efficiency ratio of the device in relation to the conversion of electrical energy into mechanical energy. The formula for finding efficiency electric motor looks like that:
- Ƞ=P2/P1, where P1 - failed electric power, P2 - useful mechanical power generated by the engine.
Electrical power is found as the product of system current and voltage (P=UI), and mechanical power is found as the ratio of work to unit time (P=A/t)
transformer efficiency
A transformer is a device that converts alternating current one voltage into an alternating current of another voltage, keeping the frequency. In addition, transformers can also convert AC to DC.
The efficiency of the transformer is found by the formula:
- Ƞ=1/1+(P0+PL*n2)/(P2*n), where P0 - mode loss idle move, PL - load losses, P2 - active power delivered to the load, n - relative degree of loading.
Efficiency or not efficiency?
It is worth noting that in addition to efficiency, there are a number of indicators that characterize the efficiency of energy processes, and sometimes we can find descriptions of the type - efficiency of the order of 130%, however, in this case, you need to understand that the term is not used quite correctly, and, most likely, the author or the manufacturer understands a slightly different characteristic by this abbreviation.
For example, heat pumps are distinguished by the fact that they can give off more heat than they consume. Thus, the refrigerating machine can remove more heat from the cooled object than is spent in energy equivalent for the organization of the removal. The efficiency indicator of a refrigerating machine is called the coefficient of performance, denoted by the letter Ɛ and is determined by the formula: Ɛ=Qx/A, where Qx is the heat removed from the cold end, A is the work expended on the removal process. However, sometimes the coefficient of performance is also called the efficiency of the refrigeration machine.
It is also interesting that the efficiency of boilers operating on organic fuel, is usually calculated according to the lower calorific value, while it can turn out to be more than one. However, it is still traditionally referred to as efficiency. It is possible to determine the efficiency of the boiler by the gross calorific value, and then it will always be less than one, but in this case it will be inconvenient to compare the performance of the boilers with the data of other installations.
The main significance of the formula (5.12.2) obtained by Carnot for the efficiency of an ideal machine is that it determines the maximum possible efficiency of any heat engine.
Carnot proved, based on the second law of thermodynamics*, the following theorem: any real heat engine operating with a temperature heaterT 1 and refrigerator temperatureT 2 , cannot have an efficiency exceeding the efficiency of an ideal heat engine.
* Carnot actually established the second law of thermodynamics before Clausius and Kelvin, when the first law of thermodynamics had not yet been formulated rigorously.
Consider first heat engine operating on a reversible cycle with a real gas. The cycle can be any, it is only important that the temperatures of the heater and refrigerator are T 1 And T 2 .
Let us assume that the efficiency of another heat engine (not operating according to the Carnot cycle) η ’ > η . The machines work with a common heater and a common cooler. Let the Carnot machine work in the reverse cycle (like a refrigeration machine), and the other machine in the forward cycle (Fig. 5.18). The heat engine performs work equal, according to formulas (5.12.3) and (5.12.5):
The refrigeration machine can always be designed so that it takes the amount of heat from the refrigerator Q 2
= |
|
Then, according to formula (5.12.7), work will be performed on it
(5.12.12)
Since by condition η" > η , That A" > A. Therefore, the heat engine can drive the refrigeration engine, and there will still be an excess of work. This excess work is done at the expense of heat taken from one source. After all, heat is not transferred to the refrigerator under the action of two machines at once. But this contradicts the second law of thermodynamics.
If we assume that η > η ", then you can make another machine work in a reverse cycle, and Carnot's machine in a straight line. We again come to a contradiction with the second law of thermodynamics. Therefore, two machines operating on reversible cycles have the same efficiency: η " = η .
It is a different matter if the second machine operates in an irreversible cycle. If we allow η "
>
η ,
then we again come to a contradiction with the second law of thermodynamics. However, the assumption m|"< г| не противоречит второму закону
термодинамики, так как необратимая
тепловая машина не может работать как
холодильная машина. Следовательно, КПД
любой тепловой машины η"
≤ η, or 
This is the main result:
(5.12.13)
Efficiency of real heat engines
Formula (5.12.13) gives the theoretical limit for the maximum efficiency of heat engines. It shows that the heat engine is more efficient, the higher the temperature of the heater and the lower the temperature of the refrigerator. Only when the refrigerator temperature is equal to absolute zero, η = 1.
But the temperature of the refrigerator practically cannot be much lower than the ambient temperature. You can increase the temperature of the heater. However, any material (solid) has limited heat resistance, or heat resistance. When heated, it gradually loses its elastic properties, and melts at a sufficiently high temperature.
Now the main efforts of engineers are aimed at increasing Engine efficiency by reducing the friction of their parts, fuel losses due to its incomplete combustion, etc. The real opportunities for increasing the efficiency here are still large. So, for a steam turbine, the initial and final steam temperatures are approximately as follows: T 1 = 800 K and T 2 = 300 K. At these temperatures, the maximum value of the efficiency is:
The real efficiency value due to various kinds of energy losses is approximately equal to 40%. The maximum efficiency - about 44% - have internal combustion engines.
The efficiency of any heat engine cannot exceed the maximum possible value 
,
where T 1
-
absolute temperature of the heater, and T 2
-
absolute temperature of the refrigerator.
Increasing the efficiency of heat engines and bringing it closer to the maximum possible- the most important technical challenge.
