=== ires-2018-page-054.pdf === 41 Chapter IV Measurement units and conversion factors A. Introduction 4.1. Energy products are measured in physical units by their mass, volume, and energy content. The measurement units that are specific to an energy product and employed at the point of measurement of an energy flow are often referred to as “original” or “natural” units. Coal, for example, is generally measured by its mass and crude oil by its volume. On the other hand, cross-fuel tabulations, such as the energy balances, are displayed in a “common” unit to allow comparison across energy products. These “common” units are usually energy units and require the conversion from an original unit through the application of an appropriate 24 conversion factor.24 A detailed description of units of measure was provided in 4.2. When different units are used to measure a product, the compiler is left with the task Energy Statistics: Definitions, of converting data that, in the absence of specific information on the products necessary for Units of Measure and Conversion the conversion between different units (such as density, gravity and calorific value), may lead Factors, Studies in Methods, to discrepancies. Series F, No. 44, United Nations, New York, 1987, and in the IEA/ 4.3. This chapter reviews the measurement units used for energy statistics, explains the Eurostat Energy Statistics Manual, concepts of “original” and “common” units, and presents default conversion factors to use in Paris, 2004, chapter 1, section 5. The present chapter incorporates the absence of country- or region-specific calorific values. and updates material found in both these publications. B. Measurement units 4.4. This section covers “original” or “natural” units, as well as “common” units. It also makes reference to the International System of Units, often abbreviated as SI from the French “Système International d’Unités”, which is the modern metric system of measurement estab- lished by international agreement. It provides a logical and interconnected framework for all measurements in science, industry and commerce (See box 4.1 for more details on SI). Box 4.1 International System of Units The International System of Units (SI) was established by and is defined by the General Conference on Weights and Measures (CGPM). It is the result of work that started in 1948 to make recommendations on the establishment of a practical system of units of measurement suitable for adoption by all signatories to the Convention du Mètre. In 1954 and 1971, the CGPM adopted as base units the units of the following seven quantities: length, mass, time, electric current, thermodynamic temperature, luminous intensity and amount of substance. Source: Based on the ­International In 1960, the CGPM adopted the name Système International d’Unités, with the international abbreviation Bureau of Weights and Measures SI for this practical system of units and laid down rules for prefixes, derived units, and the former sup- (­BIPM), www.bipm.org/en/measure plementary units; it thus established a comprehensive specification for units of measurement. ment-units.  === ires-2018-page-055.pdf === 42 International Recommendations for Energy Statistics (IRES) 4.5. Standardization in the recording and presentation of original units is a primary task of an energy statistician before quantities can be analysed or compared. 4.6. The base units of SI are a choice of seven well-defined units that by convention are regarded as dimensionally independent. There are seven base units, each of which represents, at least in principle, different kinds of physical quantities. Physical quantity Base unit length metre mass kilogram time second electric current ampere thermodynamic temperature kelvin luminous intensity candela amount of substance mole 4.7. Derived units of SI are those formed by combining base units according to the alge- braic relations linking the corresponding quantities. They are defined as products of powers of the base units. When such product includes no numerical factor other than one, the derived 25 An example of a coherent units are called coherent derived units.25 derived unit is the Newton (N): 1 N = 1 kg · m/s2. 4.8. SI uses a specific set of prefixes known as SI prefixes, which indicate a multiple or frac- tion of the unit. These prefixes are: Factor Name Symbol Factor Name Symbol 101 deca da 10 -1 deci d 102 hecto h 10 -2 centi c 103 kilo k 10 -3 milli m 106 mega M 10 -6 micro μ 109 giga G 10 -9 nano n 1012 tera T 10 -12 pico p 1015 peta P 10 -15 femto f 1018 exa E 10 -18 atto a 1021 zetta Z 10 -21 zepto z 1024 yotta Y 10 -24 yocto y 1. Original units 4.9. As mentioned in para. 4.1 above, original units are the units of measurement employed at the point of measurement of a product flow that are best suited to its physical state (solid, 26 See IEA/Eurostat Energy Statistics liquid or gas) and that require the simplest measuring instruments.26 Typical examples are: Manual, section 5 chapter 1. mass units (e.g., kilograms or metric tons) for solid fuels;27 volume units (e.g., barrels or litres) 27 With some exceptions, for or mass units (metric tons) for oil; and volume units (e.g., cubic metres) for gases. The actual example, fuelwood, which is usu- units used nationally vary according to country and local conditions and reflect historical ally sold in stacks and measured in a local volume unit, then practice in the country, sometimes adapted to changing fuel supply conditions.28 converted to cubic metres. 4.10. It should be noted that in questionnaires utilized for the collection of energy statistics, 28 See IEA/Eurostat Energy Statis- data may be required to be reported in different units from the original/natural unit. For tics Manual, annex 3. example, statistics on crude oil and oil products may be requested in a mass or weight basis, since the heating value of oil products by weight displays less variation than the heating value by volume. Statistics on gases, as well as wastes, can be requested in terajoules or other  === ires-2018-page-056.pdf === Measurement units and conversion factors 43 energy units in order to ensure comparability, since gases (and wastes) are usually defined on the basis of their production processes, rather than their chemical composition, and different compositions of the same type of gas (or waste) entail different energy contents by volume. The collection of statistics on wastes in an energy unit is based on the measured or inferred heat output used directly for heat raising. Mass units 4.11. Solid fuels, such as coal and coke, are generally measured in mass units. The SI unit for mass is the kilogram (kg). Metric tons (tons) are most commonly used to measure coal and their derivatives. One metric ton corresponds to 1000 kg. Other units of mass used by countries include the pound (0.4536 kg), short ton (907.185 kg) and long ton (1016.05 kg). Table 1 in annex B presents the equivalent factors for converting different mass units.29 29 All conversion factors for pound, short ton and long ton are approximate. Volume units 4.12. Volume units are original units for most liquid and gaseous fuels, as well as some tra- ditional fuels. The SI unit for volume is the cubic metre, which is equivalent to a kilolitre or one thousand litres. Other volume units include the British or Imperial gallon (approximately 4.546 litres), United States gallon (approximately 3.785 litres), the barrel (approximately 159 litres), and the cubic foot, which is also used to measure volumes of gaseous fuels. Given the preference of oil markets for the barrel as a volume unit, the barrel per day is commonly used within the petroleum sector to allow direct data comparison across different time fre- quencies (e.g., monthly versus annual crude oil production). However, in principle, other units of volume per time can be used for the same purpose. Table 2 in annex B shows the 30 equivalent factors to convert volume units.30 All conversion factors for gallons and barrel are approximate. Relationship between mass and volume—specific gravity and density 4.13. The relationship between mass and volume is called density and is defined as mass divided by volume. Since liquid fuels are measured either by their mass or volume, it is essen- tial to be able to convert one into the other, and knowing the density allows this: Density = mass volume 4.14. Specific gravity is a dimensionless unit defined as the ratio of density of the fuel to the density of water at a specified temperature. This can also be expressed as the ratio of the mass of a given volume of fuel, for instance oil, at 15°C to the mass of the same volume of water at that temperature: densityfuel massfuel Specific gravity = = densitywater masswater 4.15. When using the SI or metric system in order to calculate volume, mass is divided by density. Vice versa, to obtain mass, volume is multiplied by density. When using other measurement systems, one must consult tables of conversion factors to move between mass and volume measurements. 4.16. Another measure for expressing the gravity or density of liquid fuels is API gravity, a standard adopted by the American Petroleum Institute. API gravity is related to specific gravity by the following formula: API gravity = 141.5 - 131.5 specific gravity  === ires-2018-page-057.pdf === 44 International Recommendations for Energy Statistics (IRES) Energy units 4.17. Energy, heat, work and power are four concepts that are often confused. If force is exerted on an object and moves it over a distance, work is done, heat is released (under any- thing other than unrealistically ideal conditions) and energy is transformed. Energy, heat and work are three facets of the same concept. Energy is the capacity to do (and often the result of doing) work. Heat can be a by-product of work, but is also a form of energy. The coher- ent derived SI unit of energy, heat and work is the joule (J). The joule is a precise measure of energy and work, defined as the work done when a constant force of 1 Newton is exerted on a body with mass of 1 gram to move it a distance of 1 metre. Common multiples of the joule are the megajoule, gigajoule, terajoule and petajoule. 4.18. Other units include: the kilogram calorie in the metric system, or kilocalorie (kcal) or one of its multiples; the British thermal unit (Btu) or one of its multiples; ton of coal equiva- lent (tce), ton of oil equivalent (toe); and the kilowatt hour (kWh). 4.19. The International Steam Table Calorie (IT calorie) was originally defined as 1/860 inter- 31 Defined at the Fifth International national watt-hour, but was later defined exactly as 4.1868 joules.31 This is the definition of Conference on the Properties of the calorie used in the conversion tables in the annex to this chapter. The kilocalorie and the Steam (London, July 1956). teracalorie are multiples of the calorie that are commonly used in the measurement of energy commodities. In the context of IRES, these are based on the IT calorie. Other definitions of the calorie include the gram calorie, defined by the amount of heat required to raise the tem- perature of one gram of water 1°C from a reference temperature. With a reference temperature 32 Other reference temperatures of 14.5°C, the gram calorie equals 4.1855 joules. 32 are also encountered, which leads to different values for the 4.20. The British thermal unit is a measure of heat and is equal to the amount of heat gram calorie. 33 °F denotes degrees Fahrenheit. required to raise the temperature of 1 pound of water at 60°F by 1°F.33 Its most used multiples are the therm (105 Btu) and the quad (1015 Btu). The internationally agreed value for the Btu is currently 1055.06 joules. 4.21. In the past, when coal was the principal commercial fuel, the ton of coal equivalent (tce) was commonly used as an energy unit. However, with the increasing importance of oil, it has been replaced by the ton of oil equivalent (toe). The toe is now defined as 41.868 gigajoules, whereas the tce equals 29.3076 gigajoules. Generally, it should not be assumed that one ton of coal contains one tce or that one ton of oil contains one toe of energy content, since there is a wide spread in calorific values among various types of coals, crude oils and petroleum 34 See chapter IV, section C. products.34 4.22. Power is the rate at which work is done (or heat released, or energy converted). The rate of one joule per second is called a watt. As an example, a light bulb might draw 100 joules of electricity per second to emit light and heat (both forms of energy). This light bulb would then draw the power of 100 watts. 4.23. The above definition of watt leads to another commonly used measure of energy, the kilowatt hour (kWh), which refers to the energy equivalent of 1000 watt (joules per second) over a one-hour period. Thus, 1 kilowatt-hour equals 3.6x106 joules. 4.24. Electricity is usually measured in kWh. This allows one to perceive the electrical energy in terms of the time an appliance of a specified wattage takes to “consume” this energy. Heat quantities, on the other hand, are usually measured in calories or joules. 4.25. Table 3 in annex B shows the conversion factors between several energy units.  === ires-2018-page-058.pdf === Measurement units and conversion factors 45 2. Common units 4.26. Since the original units in which energy products are measured vary (e.g., metric tons, barrels, kilowatt hours, therm, calories, joules, cubic metres), quantities of energy products need to be converted into a common unit to allow comparisons of fuel quantities and esti- mate transformation efficiencies. The conversion from different units to a common unit may require specific conversion factors for each product. 35 35 For example, the factor to convert from m3 to TJ will be 4.27. The only energy unit in the International System of Units is the joule and it is usually used different for different types of in energy statistics as a common unit, although other energy units are sometimes also applied gaseous or liquid fuels. However, (e.g., toe, GWh, Btu, calories, etc.). The use of the joule as a common unit is recommended. the factor to convert from kWh to TJ is the same for all products. 4.28. It is further recommended that national and international agencies in charge of energy statistics and any other organizations that advise them or undertake work for them always clearly define the measurement units, as well as the common units used for presentational purposes in various publications and in electronically disseminated data. The conversion fac- tors and the methods used to convert original physical units into the chosen common unit or units should be described in energy statistics metadata and be readily accessible to users. In addition, it should be made clear whether energy units are defined on a gross or net calorific basis (see section C below for details). C. Calorific values 4.29. Calorific values or heating values of a fuel express the heat obtained from one unit of the fuel. They are necessary for the compilation of overall energy balances where the original units in which the fuels are measured are converted into a common unit of measurement. Even though calorific values are often considered in the context of the preparation of energy balances, they have a wider application in the preparation of any tables designed to show energy in an aggregated form or in the preparation of inter-fuel comparative analyses. 4.30. Calorific values are obtained by measurements in a laboratory specializing in fuel quality determination. They should preferably be in terms of joules (or any of its multiples) per original unit, for example gigajoule/metric ton (GJ/t) or gigajoule/cubic metre (GJ/m3). Major fuel producers (mining companies, refineries, etc.) normally measure the calorific value and other qualities of the fuels they produce. A calorific value is a conversion factor, in the sense that it can be used to convert mass or volume quantities into energy content. 4.31. There are two main issues with regards to calorific values that an energy compiler should pay attention to: the first one refers to whether they are measured gross or net of the latent heat (that is the heat necessary to evaporate the water formed during combustion and the water previously present in the fuel in the form of moisture); and the second one is related to whether the calorific value used refers to the specific product-flow-country situation or it refers to a default value. These two issues are presented in detail in the next two sections. 1. Gross and net calorific/heating values 4.32. Calorific values can be expressed on a gross and net basis. The gross calorific value (GCV), or high heat value, measures the total (maximum) amount of heat that is produced by com- bustion. However, part of this heat will be locked up in the latent heat of evaporation of any water present in the fuel before combustion (moisture), or generated in the combustion pro- cess. The latter comes from the combination of hydrogen present in the fuel with the oxidant oxygen (O2) present in the air to form H2O. This combination itself releases heat but this heat is partly used in the evaporation of the generated water.  === ires-2018-page-059.pdf === 46 International Recommendations for Energy Statistics (IRES) 4.33. The net calorific value (NCV), or low heat value, excludes the latent heat. The NCV is that amount of heat from the combustion process that is actually available in practice for capture and use. The higher the moisture of a fuel or its hydrogen content, the greater is the difference between GCV and NCV. For some fuels with very little or no hydrogen content (e.g., some types of coke, blast furnace gas) this difference is negligible. In terms of magni- tude, the difference between gross and net calorific values of fossil fuels (coal, oil, oil products and gas) is typically less than 10 per cent, while that of biomass energy (fuelwood, bagasse) is usually more than 10 per cent. Examples of differences between gross and net calorific values are presented for selected energy products in table 4 of annex B. It should be noted that the technology used to burn a fuel can also play a role in determining the NCV of that fuel, for instance, depending on how much of the latent heat it can recover from the exhaust gases. 4.34. It is recommended that, when expressing the energy content of energy products in terms of a common energy unit, NCVs be used in preference to GCVs. In other words, the heat required to evaporate moisture, which is present in all fuels and is also produced in the combustion process, should not be treated as part of a fuel’s energy, providing capability. In particular, NCVs are to be preferred over GCVs when building an energy balance, since most current technologies are still not able to recover the latent heat, which would thus not be treated 36 A number of countries are as part of a fuel’s energy providing capability (see chapter VIII for further discussion).36 How- currently able to recuperate ever, where available, it is strongly encouraged to report both gross and net calorific values. a significant part of the latent heat, and thus the use of gross calorific values may reflect more appropriately their 2. Default vs. specific calorific values circumstances. 4.35. Energy products with exactly the same chemical composition will carry the same energy content. In practice, however, there are variations in the composition of energy prod- ucts and consequently, their calorific values can vary. For example, “premium” gasoline may have slightly different chemical formulations (and therefore a different energy content) than “regular” gasoline; natural gas may contain variations in the proportions of ethane and meth- ane; liquefied petroleum gas (LPG) may in fact be solely propane or solely butane or any com- bination of the two. Only those products that are single energy compounds, such as “pure” methane or “pure” ethane, and electricity, have precise and unalterable energy contents. 4.36. Default calorific values refer to the energy content of fuels with specific characteristics that are generally applicable to all circumstances (different countries, different flows, etc.). They are used as default values when specific calorific values are not available. Specific calorific values, on the other hand, are based on the specificity of the fuel in question and are meas- urable from the original data source. They are particularly important for fuels that present different qualities: coal, for example, displays a range of quality that makes it suitable for dif- ferent uses. The respective calorific values are thus specific to the fuel and flow in question. However, in using many different specific calorific values, caution should be applied to ensure consistency between the energy content on the supply side and on the consumption side for a particular country and year. 4.37. Often there is a problem in energy statistics as the product produced may not be iden- tical in composition to the product in subsequent processes, even though it is referred to by the same name. Natural gas can be enriched with oil products, for example, to meet market specifications. Motor gasoline can be blended with ethanol and sold as motor gasoline, and depending on the country practice, this may be recorded as consumption of only motor gaso- line or as consumption of motor gasoline and the blending agent. In this case, flow-specific calorific values would allow for a more accurate energy balance. 4.38. It is recommended that countries collect data in original units together with data on specific calorific values. A country-specific calorific value is generally calculated as a weighted  === ires-2018-page-060.pdf === Measurement units and conversion factors 47 average of all the calorific values collected for the energy product in question (see next sec- tion). For some products (e.g., coal and crude oil), different calorific values may be needed for production, imports, exports and several major uses. Default calorific values should only be used as a last resort in the absence of specific values, acknowledging that this simplification will affect the precision of the published figures. 4.39. It is further recommended that metadata be provided on the methods used in all calculations and conversions undertaken to arrive at the disseminated data in order to ensure transparency and clarity and to enable comparability. In particular, this would include the conversion factors between original and presented units, whether they are on a gross or net calorific basis, and any use of default values. 3. How to calculate average calorific values 4.40. The calculation of calorific values is not straightforward. There are two levels involved in this calculation. The first is the actual measurement of the heating value of an energy prod- uct. This is done in laboratories specializing in fuel quality determination. In general, major fuel producers (i.e., mining companies, refineries, etc.) measure the quality of the energy product they produce, as this may affect its price and specification. This type of calculation thus pertains to specialists, and it is not covered in IRES: the calorific values are assumed to be available from the data providers (generally companies producing energy). 4.41. The second level in the calculation of the calorific values pertains more to the compil- ers of energy statistics, as it involves the aggregation of different qualities of a fuel. Coals pro- duced at different mines, for example, often have different qualities. The quality of imported coal may vary according to the origin of the flow. Similarly, the quality of consumed coal may also differ: the case, for example, of imported steam coal for electricity generation, and home-produced lignite for household consumption. Thus, in the preparation of energy bal- ances and in the comparison of the energy content of energy products, it is necessary to take into account the different qualities of the products themselves. 4.42. In general, in order to aggregate different qualities of an energy product, it is necessary to calculate the average calorific value. Consider, for example, the case where the production of lignite comes from two different mines in a country: mine A produces 1.5 thousand metric tons of lignite with a net calorific value of 10.28 TJ/thousand tons, while mine B produces 2.5 thousand metric tons of lignite with a net calorific value of 12.10 TJ/thousand tons. The average net calorific value of the total production of lignite of the country is calculated as a weighted average of the calorific values from the two mines with their production as weights. The calculations are shown in the example below: Production Calorific value Average calorific value Production (1000 metric tons) (TJ/1000 metric tons) (TJ/1000 metric tons) (TJ) Mine A 1.5 10.28 15.42 Mine B 2.5 12.1 30.25    1.5 x 10.28 + 2.5 x 12.10 Total 4 = = 11.42 = 11.42 x 4 = 45.67         1.5 + 2.5 4.43. The average calorific value calculated as above corresponds to the country-specific calorific values that are generally collected by international organizations in their energy questionnaires and are reported in the disseminated data. 4.44. Since calorific values may change according to the type of flow (e.g., production, imports, exports, consumption by different types of users, etc.), countries are encouraged to collect calorific values at least on production, imports and exports.  === ires-2018-page-061.pdf === 48 International Recommendations for Energy Statistics (IRES) 4. Default calorific values 4.45. The default calorific values are provided in table 4.1 as a reference for countries when no specific calorific values are available. The default calorific values presented below are those used in the 2006 Intergovernmental Panel on Climate Change (IPCC) Guidelines for National Greenhouse Gas Inventories (IPCC 2006). For a number of products, no calorific values are available in the 2006 IPCC Guidelines and thus no value is reported in the table below. Table 4.1 Default net calorific values for energy products Net calorific values (GJ/metric ton) Range SIEC headings Default value Lower value Upper value 0 Coal 01 Hard coal 011 0110 Anthracite 26.7 21.6 32.2 012 Bituminous coal 0121 Coking coal 28.2 24.0 31.0 0129 Other bituminous coal 25.8 19.9 30.5 02 Brown coal 021 0210 Sub-bituminous coal 18.9 11.5 26.0 022 0220 Lignite 11.9 5.5 21.6 03 Coal products 031 Coal coke 0311 Coke oven coke 28.2 25.1 30.2 0312 Gas coke 28.2 25.1 30.2 0313 Coke breeze 0314 Semi cokes 28.2 25.1 30.2 032 0320 Patent fuel 20.7 15.1 32.0 033 0330 Brown coal briquettes (BKB) 20.7 15.1 32.0 034 0340 Coal tar 28.0 14.1 55.0 035 0350 Coke oven gas 38.7 19.6 77.0 036 0360 Gas works gas (and other manuf. gases 38.7 19.6 77.0 for distribution) 037 Recovered gases 0371 Blast furnace gas 2.47 1.20 5.00 0372 Basic oxygen steel furnace gas 7.06 3.80 15.00 0379 Other recovered gases 039 0390 Other coal products 1 Peat and peat products 11 Peat 111 1110 Sod peat 9.76 7.80 12.5 112 1120 Milled peat 9.76 7.80 12.5 12 Peat products 121 1210 Peat briquettes 9.76 7.80 12.5 129 1290 Other peat products 9.76 7.80 12.5  === ires-2018-page-062.pdf === Measurement units and conversion factors 49 Net calorific values (GJ/metric ton) Range SIEC headings Default value Lower value Upper value 2 Oil shale/oil sands 20 Oil shale/oil sands 200 2000 Oil shale/oil sands 8.9 7.1 11.1 3 Natural gas 30 Natural gas 300 3000 Natural gas 48.0a 46.5 50.4 a Whereas the values provided in this table are presented in units 4 Oil of energy per mass, the calorific 41 Conventional crude oil values for natural gas are often 410 4100 Conventional crude oil 42.3 40.1 44.8 expressed in units of energy per volume. For example, United 42 Natural gas liquids (NGL) Nations (1988) provides a NCV 420 4200 Natural gas liquids (NGL) 44.2 40.9 46.9 of 39.02 GJ/thousand m3 under 43 Refinery feedstocks standard conditions for natural gas. It should be noted, however, 430 4300 Refinery feedstocks 43.0 36.3 46.4 that this number is not derived 44 Additives and oxygenates from the value presented in this table. 440 4400 Additives and oxygenates 45 Other hydrocarbons 450 4500 Other hydrocarbons 46 Oil products 461 4610 Refinery gas 49.5 47.5 50.6 462 4620 Ethane 46.4 44.9 48.8 463 4630 Liquefied petroleum gases (LPG) 47.3 44.8 52.2 464 4640 Naphtha 44.5 41.8 46.5 465 Gasolines 4651 Aviation gasoline 44.3 42.5 44.8 4652 Motor gasoline 44.3 42.5 44.8 4653 Gasoline-type jet fuel 44.3 42.5 44.8 466 Kerosenes 4661 Kerosene-type jet fuel 44.1 42.0 45.0 4669 Other kerosene 43.8 42.4 45.2 467 Gas oil/diesel oil and Heavy gas oil 4671 Gas oil/diesel oil 43.0 41.4 43.3 4672 Heavy gas oil 468 4680 Fuel oil 40.4 39.8 41.7 469 Other oil products 4691 White spirit and special boiling point 40.2 33.7 48.2 industrial spirits 4692 Lubricants 40.2 33.5 42.3 4693 Paraffin waxes 40.2 33.7 48.2 4694 Petroleum coke 32.5 29.7 41.9 4695 Bitumen 40.2 33.5 41.2 4699 Other oil products n.e.c. 40.2 33.7 48.2  === ires-2018-page-063.pdf === 50 International Recommendations for Energy Statistics (IRES) Net calorific values (GJ/metric ton) Range SIEC headings Default value Lower value Upper value 5 Biofuels 51 Solid biofuels 511 Fuelwood, wood residues and by-products 15.6 7.9 31.0 b Source: Austrian Energy Agency. 5111 Wood pellets 17.3b 5119 Other Fuelwood, wood residues 13.9b and by-products 512 5120 Bagasse 513 5130 Animal waste 514 5140 Black liquor 11.8 5.9 23.0 515 5150 Other vegetal material and residues 516 5160 Charcoal 29.5 14.9 58.0 52 Liquid biofuels c Source: IEA. 521 5210 Biogasoline 26.8c 13.6 54.0 522 5220 Biodiesels 36.8c 13.6 54.0 523 5230 Bio jet kerosene 529 5290 Other liquid biofuels 27.4 13.8 54.0 53 Biogases 531 Biogases from anaerobic fermentation 5311 Landfill gas 50.4 25.4 100.0 5312 Sewage sludge gas 50.4 25.4 100.0 5319 Other biogases from anaerobic fermentation 50.4 25.4 100.0 532 5320 Biogases from thermal processes 6 Waste 61 Industrial waste 610 6100 Industrial waste 62 Municipal waste d Values refer to the biomass/ 620 6200 Municipal waste 11.6 / 10.0d 6.8 / 7.0d 18.0 / 18.0d non-biomass fraction, 7 Electricity respectively. 70 Electricity 700 7000 Electricity 8 Heat 80 Heat 800 8000 Heat 9 Nuclear fuels and other fuels n.e.c. 91 Uranium and plutonium 910 Uranium and plutonium 9101 Uranium ores 9109 Other uranium and plutonium 92 Other nuclear fuels 920 9200 Other nuclear fuels 99 Other fuels n.e.c. 990 9900 Other fuels n.e.c.  === ires-2018-page-064.pdf === Measurement units and conversion factors 51 Fuelwood 4.46. In rural areas of many developing countries, the principal source of energy for cooking and heating is fuelwood, but statistics on fuelwood in general are poor. This is due largely to the fact that fuelwood is in great part produced by households for their own use and/or traded in the informal sector. 4.47. There is a large variety of wood species and a large variability of moisture and ash content in wood products that highly affect the calorific value of the product. Countries are therefore encouraged to identify typical fuelwood mixes and average water content and to establish country-specific conversion factors between volume and mass. Guidelines for the measurement of fuelwood and the determination of calorific values are provided below. 4.48. Fuelwood can be measured by either volume or weight. If it is measured by volume, it can be either stacked volume or solid volume. Measures of stacked fuelwood are the stere or stacked cubic metre and the cord (128 stacked cubic feet). Solid volume is obtained by the water displacement method, that is the volume of water displaced if the quantity of fuelwood were to be completely submerged. One advantage of measurement by volume is the relatively small influence of the moisture content of the wood on the measurement results. The weight of fuelwood is highly dependent on moisture content, and this is true for all biomass. The more water per unit weight, the less fuelwood. Therefore, it is important that the moisture content be accurately specified when fuelwood is measured by weight. 4.49. There are two ways of measuring moisture content (mc). They are the so-called dry basis and wet basis and are defined below: wet weight - dry weight Dry basis: mc% = x100 dry weight wet weight - dry weight Wet basis: mc% = x100 wet weight 4.50. When biomass is very wet, there is a large difference between the two moisture con- tents (e.g., 100 per cent mc dry basis is equivalent to 50 per cent mc wet basis), but when the biomass is air-dry the difference is small (15 per cent mc dry basis is equivalent to 13 per cent mc wet basis). It is important to state on which basis the moisture content is measured. In most, but not all cases, fuelwood moisture is measured on a dry basis. 4.51. Another important determinant of the energy content of fuelwood is ash content. While the ash content of fuelwood is generally around one per cent, some species can register an ash content of up to four per cent. This affects the energy value of the wood since the sub- stances that form the ashes generally have no energy value. Thus wood with four per cent ash content will have three per cent less energy content than wood with one percent ash content. 4.52. The default calorific values for fuelwood (converting from mass units to energy units) are presented in table 4.2. The table shows how the calorific values vary with different mois- ture content of green wood, air-dried wood and oven-dried wood. 4.53. When fuelwood is collected in volume units, a conversion factor has to be used to obtain mass units. Table 4.3 shows the conversion factors for going from volume to mass units. Table 5 in annex B shows how the different moisture contents of fuelwood affect the conversion factors between cubic metres and metric tons.  === ires-2018-page-065.pdf === 52 International Recommendations for Energy Statistics (IRES) Table 4.2 Influence of moisture content on net calorific values of standard fuelwood (wood with one per cent ash content) Percentage moisture content Kilocalories Megajoules Dry basis Wet basis per kilogram Btus per pound per kilogram 160 62 1 360 2 450 5.7 140 59 1 530 2 750 6.4 120 55 1 720 3 100 7.2 Green wood 100 50 1 960 3 530 8.2 80 45 2 220 4 000 9.3 70 41 2 390 4 300 10.0 60 38 2 580 4 640 10.8 a Average of as-received fuelwood 50a 33a 2 790 5 030 11.7 on cordwood basis (4-foot 40 29 3 030 5 460 12.7 lengths). Air-dried wood 30 23 3 300 5 930 13.8 b Average of logged fuelwood. 25b 20b 3 460 6 230 14.5 20 17 3 630 6 530 15.2 15 13 3 820 6 880 16.0 10 9 4 010 7 220 16.8 Oven-dried wood 5 5 4 230 7 610 17.7 0 0 4 470 8 040 18.7 Source: United Nations (1987). Table 4.3 37 Note: Cubic metre is measured Conversion table for fuelwood37 (wood with 25 per cent moisture content) under bark at 25 per cent mois- ture content (dry basis). Weight Metric tons Stacked cubic metres includes bark. Fuelwood per solid cubic metre Metric tons per cord (stere) per metric ton General 0.707 1.71 2.12 The “General” data is weighted on 20 per cent coniferous and Coniferous 0.570 1.38 2.63 80 per cent non-coniferous Non-Coniferous 0.742 1.79 2.02 wood. Source: Forest Products Conver- sion Factors for the UNECE Re- Charcoal gion, Geneva Timber and Forest 4.54. The amount of biomass (usually fuelwood) necessary to yield a given quantity of char- Discussion Paper 49. UNECE/FAO, 2010 (www.unece.org/fileadmin coal depends mostly on three factors: density, moisture content and the means of charcoal /DAM/timber/publications/DP- production. 49.pdf), updated in 2015. 4.55. The principal factor in determining the yield of charcoal from fuelwood is the parent wood density, since the weight of charcoal can vary by a factor of 2 for equal volumes. The moisture content of the wood also has an appreciable effect on yields as the drier the wood, the greater the yield. The third determinant factor is the means of charcoal production. Charcoal is produced in earth-covered pits, oil drums, brick or steel kilns and retorts. The less sophisticated means of production generally involve loss of powdered charcoal (fines), incomplete carbonization of the fuelwood and combustion of part of the charcoal product, resulting in lower yields. 4.56. There is always an amount of powdered charcoal produced in the manufacture and transport of charcoal. If powdered charcoal undergoes briquetting, then the weight of the briquettes may be 50–100 per cent higher per given volume of un-powdered charcoal due to greater density.  === ires-2018-page-066.pdf === Measurement units and conversion factors 53 4.57. The three variables that affect the energy value of charcoal are: moisture content, ash content and degree of carbonization. The average moisture content of charcoal is 5 per cent. The average ash content of wood charcoal is 4 per cent, while that of charcoal produced from woody crop residues, such as coffee shrubs, is near 20 per cent. With the assumption of com- plete carbonization, the average energy value of wood charcoal with 4 per cent ash content and 5 per cent moisture content is approximately 30.8 MJ/kg. The average energy value of crop residue charcoal with 20 per cent ash content and 5 per cent moisture content is 25.7 MJ/kg. 4.58. Two tables pertaining to charcoal production are provided in annex B. In particular, table 6 illustrates the effect of parent wood density and moisture content on charcoal yield. Table 7 provides conversion factors for the production of charcoal by the various kilns for selected percentages of wood moisture content. It assumes some standard hardwood as input to the process. Vegetal and animal wastes 4.59. Agricultural wastes and waste products from food processing is used to replace woody biomass in fuelwood deficient areas. These waste products can be burned as fuels to fulfil heating or cooking requirements. 4.60. There are two important determinants of the energy value of non-woody plant bio- mass: moisture content and ash content. While the ash content of wood is generally around 1 per cent, that of crop residues can vary from 3 per cent to over 20 per cent, and this affects the energy value. Generally, the substances that form the ashes have no energy value. Thus, biomass with 20 percent ash content will have 19 percent less energy than a similar substance with 1 per cent ash content. Data for these potential sources of energy are rarely collected directly but derived from crop/waste or end-product/waste ratios. Due to this wide variabil- ity in composition in ash and moisture content of general animal and vegetal wastes across countries, it is recommended that these products be reported to international organizations in an energy unit (preferably TJ) rather than their natural units. National authorities are, in general, able to assess and determine the energy content of these wastes. Alternatively, meas- uring the energy content can be accomplished by measuring the heat or electricity output of transformation devices and applying standard efficiency factors. 4.61. Given the importance of the use of bagasse, the fibrous cane residue from the produc- tion of sugar from sugar cane, possible estimation procedures are outlined for this case below. Also, singling out this specific vegetal waste allows the reporting of quantities to international organizations in its natural unit (weight basis), since its composition does not allow much variation. This has been done by international organizations that treat bagasse separately from ordinary vegetal waste. Bagasse is used as a fuel mostly for the sugar industry’s own energy needs (at times, excess electricity is also fed into the public grid) in many sugar-producing countries. The availability of fuel bagasse can be estimated based on either data on the input of sugar cane into sugar mills, or production data on centrifugal cane sugar. 4.62. Method (a): Studies based on experiences in Central American countries found that the yield of fuel bagasse is approximately 280 kilograms per metric ton of sugar cane pro- cessed. Assuming a 50 per cent moisture content at the time of use, 1 metric ton of bagasse yields 7.72 GJ. The energy values for bagasse corresponding to 1 metric ton of processed sugar cane are, therefore, as follows: 2.16 GJ = 0.516 Gcal = 0.074 tce = 0.051 toe 4.63. Method (b): Based on observations, the Economic Commission for Latin America and the Caribbean (ECLAC) proposed the use of 3.26 kg bagasse yield per kilogram of cen- trifugal sugar produced. Calorific equivalents for bagasse corresponding to the production of 1 metric ton of sugar are as follows:  === ires-2018-page-067.pdf === 54 International Recommendations for Energy Statistics (IRES) 25.2 GJ = 6 Gcal = 0.86 tce = 0.59 toe 4.64. Animal waste or dung is another important by-product of the agricultural sector. It can be dried and burned directly as a fuel for space heating, cooking or crop drying. When used as an input to biogas digestors, the outputs are gas for cooking, heating and lighting, and a solid residue for use as fertilizer. Another possibility is to use the animal waste as a feedstock to produce biodiesel. It can also be spread with no or minimal treatment in the fields as fertilizer. Table 8 of annex B presents various animal and vegetal wastes and indicates the approximate calorific values recoverable from them when used as fuels. 5. Units recommended for dissemination 4.65. No specific measurement unit is recommended for national data collection, thus allowing countries to choose the units most suitable for their circumstances. However, based on common practices, certain units are recommended for data dissemination. If necessary, countries may use other units, as long as appropriate conversion factors are provided. 4.66. For each main category of energy products, the recommended unit for dissemination is provided in table 4.4. Where there is no special mention, the unit applies to primary as well as to secondary energy products. Table 4.4 Recommended units for dissemination Energy products Dimension Unit Solid fossil fuels Mass Thousand metric tons Liquid fossil fuels Mass Thousand metric tons (Liquid) Biofuels Mass/Volume Thousand metric tons/ Thousand cubic metres Gases Energy Terajoules Wastes Energy Terajoules Fuelwood Volume/ Energy Thousand cubic metres/ Terajoules Charcoal Mass Thousand metric tons Electricity Energy GWh Heat Energy Terajoules Common unit (e.g., balances) Energy Terajoules Electricity installed capacity Power MW Refinery capacity Mass/time Thousand metric tons/year 4.67. It is recommended that countries report to international organizations both physi- cal quantities of fuels and their country-specific (and where necessary flow-specific) calorific values. In the case of waste that is well-defined by its constitution, rather than only by the process from which it was generated, it can be assumed that there would not be great varia- tion in specific calorific values. Therefore, data can be reported on a weight basis (thousand metric tons). Even so, the specific calorific values should be provided if they are available.