Useful Energy Calculation

Useful energy is calculated by multiplying Final energy consumption by the end-use con-version efficiency (η). Final energy can be disaggregated in terms of energy carrier f (eg.

coal, electricity etc.), sector s (eg. industry, residential), end-use e (heating, lighting etc.), and device d (eg. electric motor, boiler etc.). Hence, Useful energy is calculated for each combination of f,s, e, and d using equation 3.1.

U_{f sed}= F_{f sed} η_{f sed} (3.1)

Standard energy balances provide Final energy consumption statistics disaggregated in terms of of energy carriers and sectors (F_f,s). Therefore, two allocation matrices φ and θ are needed before the Useful energy calculation can be made. Matrix φ allocates Final energy of each fuel to each end-use application. For example, φ can specify that coal in the residential sector is used for space heat and for hot water with respective shares of 80% and 20%. Matrix θ allocates Final energy to the specific conversion device used for each end-use. For example it could specifying that 40% of oil used for mechanical energy in road transport is converted in petrol engines and 60% in diesel engines. Equation 3.2 summarises the relationship, where the superscripts indicate that there is a matrix for each of the indicated categories.

F_{f sed}= F_{f s} φ^(e)_{f s} θ^(d)_{f se} (3.2)

In the following sections, the choice of categories used for this framework is explained.

Final Energy (F_{f s})

National energy balances (most of which are published by the IEA [241]) containing data on Final energy consumption split by economic sectors and by energy carriers are used to define F_{f s}. Fuels in the IEA energy balances are classified according to their fuel of origin. This is not conducive to an allocation of fuels to different end-uses and conversion devices since the use of a fuel depends on its final form, not on it’s origin. Thereofore, fuels are classified according to their physical state. For instance, Blast Furnace Gas is originally classified as a “coal product” while in the chosen classification system it is classified as “gas”. The following categories are used: Liquid fuels, Gas, Coal, Solid Biomass and Waste, Electricity and District Heat (DH).

The end-use sector classification used by the IEA is retained as it is commonly used across all energy studies. The only change made to the classification is the grouping of three sub-sectors, namely Agriculture, Fishing, and Forestry into a single category named AFF.

Therefore the final list of sectors is as follows: Industry, Residential, Services, Agricul-ture/Fishing/Forestry(AFF), Road Transport, Rail Transport, Navigation, Aviation, and Pipeline Transport.

Sectors to End-use (φ^(e)_{f s} )

Energy end-use statistics are used to define the φ^e_{f s} matrix which allocates Final energy to the various end-uses. To define this matrix, a coherent definition of end-use categories is required. End-use statistics are compiled at a sectoral level thus the categories employed are often sector specific. A cross-sectoral analysis requires comparable end-use categories for all sectors, while still being sufficiently specific about the end-use of energy. Since these two requirements are often at odds, a judgement is required in the defining the end-use categories employed. The German Energy Statistics Office provides a good starting point, as it employs end-use categories that facilitate a compromise between the two needs [242]. Table 3.1 lists and describes the nine end-use categories employed in this study. The only modification of the German definition is the split of the ”Process Heat” category in “Process Heat – Direct”

and “Process Heat - Indirect”. This separation is performed to separate energy that is used in boilers and steam generators from energy used to heat products directly (thus including both material processing in Industry and cooking in the residential sector).

Table 3.1 List of end-use categories used to classify end-uses for all sectors End Use Category Description

Process Heat - Direct Energy applied directly for material processing (cooking, blast furnace, etc.)

Process Heat - Indirect Energy delivered through an intermediate mean, usually steam.

Space Heat Energy used to maintain comfortable temperature inside buildings Hot Water Energy used to increase water temperature for hygiene and comfort Space Cooling Energy used to maintain a comfortable temperature inside

build-ings

Process Cooling Energy used to decrease the temperature of materials below ambi-ent (refrigeration)

Mechanical Energy used to deliver Useful work (pumping, motion etc.) Illumination Energy used to the illumination of buildings and streets.

Information, Communication, Entertainment

Energy used for computing power, and for communication and control.

End-use to Conversion Device (θ^(d)_{f se})

The allocation matrix θ^(d)_{f se} describes the share of energy converted in a specific devices for a given combination of sector, energy carrier and end-use. The definition and classification of

“energy conversion devices” used in this study is based on the work by Cullen and Allwood [97], with only one modification. They distinguish four types of burners based on the type of fuel they use. While there are technical differences between these categories, there are further differences between the mode of combustion, that is, on whether the combustion occurs within a boiler or directly on the product to be heated. This is because the efficiency of the boiler depends on both the combustion efficiency and the heat exchanger design; while for direct combustion, only the former matters. Since the framework used in this analysis enables the distinction of energy flows by fuel, it is best to classify the devices only on their technical differences: direct combustion versus indirect combustion. Table 3.2 lists and describes the conversion devices employed in this study.

Table 3.2 Description of conversion device categories and mapping with categories used for conversion devices TEL estimation

Device Category Description and Examples Chemical to Work

Spark Ignition Engine (SI) Engine based on Otto cycle, where charge is ignited by a spark (light duty vehicles, lawn mowers)

Diesel Engine (CI) Engines following the Diesel cycle, where the charge is autoignited due to compression. (Heavy duty vehicles, sea vessels, agricultural equipment)

Gas Turbine (GT) Device following the Bryton cycle with axial turbomachinery. (gas pipeline compressors, mechanical drive in industry)

Jet Engine (JE) Gas turbine used to provide thrust to aircrafts.

Chemical to Thermal

Burner (BU) Device where combustion products are used to deliver the energy service directly. (gas hobs, blast furnace)

Boiler (BO) Device used to transfer the heat of combustion to water, acting either as a heat transfer fluid for space heating and process heating, or as direct sanitary water heating.

Electrical to Work

Electric Motor (EM) Device generating shaft work from electrical energy through the interaction of magnetic fields. The most common design being the induction motor.

Electrical to Thermal

Electric Heater (EH) Device converting heat from Joule effect to deliver an energy service directly (electric hobs, electric arc furnace)

Cooler (CO) Device converting electricity to thermal energy in the form of coolth. (residential fridge, air conditioner, gas separation) Electrical to Electromagnetic

Light Device (LD) Device converting electrical energy into light (LED, incandescent light bulb)

Other Other electricity using devices where energy is not converted into quantifiable other forms before delivery of energy services.

(computers, mobile phone, televisions)

Conversion Efficiency (η_{f sed})

The conversion efficiency of each device must represent the average efficiency for a device using a given energy carrier, in a given sector, to deliver a specific energy service. The definition of efficiency depends on the system boundary definition chosen, that is, whether it includes the entire conversion system or only the conversion device. Taking the example of a motor system used for ventilation, the efficiency of the motor is the ratio of electricity input to rotational shaft power output, while the efficiency of the system is the ratio of electrical input to the energy of the displaced air. In this thesis, the boundary is limited to the first form of energy in the Useful form, thus to the conversion device. This choice is dictated by a will to limit resolution of the technologies considered and due to limitation in data about the specific uses (water pumping, ventilation, space heating, oven heating) of Useful energy. Therefore, the output from the conversion devices is classified in five Useful Energy categories: Motion, Heating, Cooling, Illumination, Information.