Life Cycle Energy Use Research Articles

Effect of Energy Efficiency Requirements for Residential Buildings in Sweden on Lifecycle Primary Energy Use

In this study we analyze the lifecycle primary energy use of a wood-frame apartment building designed to meet the current Swedish building code or passive house criteria, and heated with district heat or bedrock heat pump. We employ a lifecycle perspective methodology and determine the production, operation and end-of-life primary energy use of the buildings. We find that the passive house requirement strongly reduces the final energy use for heating compared to the current Swedish building code. However, the primary energy use is largely determined by the energy supply system, which is generally outside the mandate of the building standards. Overall, buildings with district heating have lower life-cycle primary energy use than alternatives heated with heat pump. The primary energy for production is small relative to that for operation, but it is more significant as the energy-efficiency standard of building improves and when efficient energy supply is used. Our results show the importance of a system-wide lifecycle perspective in reducing primary energy use in the built environment. A life cycle primary energy perspective is needed to minimize overall primary energy use, and future building energy-efficiency standards may reflect the full energy use during a building's life cycle. This could include primary energy implications for production, operation and end-of-life of buildings.

Optimization of a residential solar combisystem for minimum life cycle cost, energy use and exergy destroyed

This paper presents the optimization of a model of a solar combisystem in an energy efficient house in Montreal (Qc), Canada. A hybrid particle swarm and Hook–Jeeves generalized pattern search algorithm is used to minimize the life cycle cost, energy use and exergy destroyed of the combisystem. The results presented include four different optimal configurations depending on the objective function used. The optimizations were able to reduce, compared with the base case combisystem, the life cycle cost of the combisystem by 19%, the life cycle energy use by 34%, the life cycle exergy destroyed by 33% and 24% using the technical boundary and physical boundary, respectively. Due to the high cost of the solar collector technologies and the low price of electricity in Quebec, none of the optimal configurations have acceptable financial payback periods. However, they all have energy payback times between 5.8 and 6.6years. The use of technical boundary in the exergy analysis favors the use of electricity over solar energy due to the low exergy efficiency of the solar collectors. The use of the physical boundary, on the other hand, favors the use of solar energy over electricity, and all of the combisystem configurations have exergy payback times between 4.2 and 6.3years.

Optimizing energy and environmental performance of passive Trombe wall

The energy and environmental performance is compared for buildings with and without Trombe walls. The indicator for environmental performance is a sum of primary operating energy for heating during winter and the annualized embodied energy consumed by using the Trombe walls. Two Trombe walls are used at the south side of a “Mozart” house located in Lyon, France. The house satisfies the French thermal regulation. The performances of several constructions of Trombe walls are studied. The annualized life cycle energy use by houses with Trombe walls may be lower when the core material has lower density and lower embodied energy. For heating by electricity there are much higher values of the optimum thickness of the core layer and that of the primary energy consumption than that for heating by using natural gas. When the building with Trombe walls is used, the annual final energy saving during heating is around 20%. For the electrical heating and optimum core thickness, the energy ratio is around 6 and the energy payback time is around 8 years. For the natural gas heating these values are around 3, and around 18 years, respectively.

Assessing the Potential for Reducing Life-Cycle Environmental Impacts through Transit-Oriented Development Infill along Existing Light Rail in Phoenix

There is significant interest in reducing urban growth impacts yet little information exists to comprehensively estimate the energy and air quality tradeoffs. An integrated transportation and land-use life-cycle assessment framework is developed to quantify the long-term impacts from residential infill, using the Phoenix light rail system as a case study. The results show that (1) significant reductions in life-cycle energy use, greenhouse gas emissions, respiratory, and smog impacts are possible; (2) building construction, vehicle manufacturing, and energy feedstock effects are significant; and (3) marginal benefits from reduced automobile use and potential household behavior changes exceed marginal costs from new rail service.

Cost and CO2 Emission Optimization of Steel Reinforced Concrete Columns in High-Rise Buildings

The construction industry is a representative industry that consumes large amounts of energy and produces substantial pollution. The operation of a building accounts for a large portion of its total CO2 emissions. Most efforts are focused on improving the energy efficiency related to the operation of a building. The relative importance of the energy and CO2 emissions from the construction materials increases with the increasing number of low-energy buildings. To minimize the life-cycle energy use of a building, the energy consumed from both materials in the construction phase as well as the energy consumed from the operation of the building must be reduced. In this study, an optimal design method for composite columns in high-rise buildings using a genetic algorithm is proposed to reduce cost and CO2 emissions from the structural materials in the construction phase. The proposed optimal method minimizes the total cost, including the additional cost calculated based on CO2 emissions from composite columns, while satisfying the structural design criteria and constructability conditions. The proposed optimal method is applied to an actual 35-story building, and the effective use of structural materials for the sustainable design of composite columns is investigated. It is shown that using more concrete than steel section and using high-strength materials are economically and environmentally effective methods.

Life-Cycle Energy Use and Greenhouse Gas Emissions Analysis for Bio-Liquid Jet Fuel from Open Pond-Based Micro-Algae under China Conditions

A life-cycle analysis (LCA) of greenhouse gas (GHG) emissions and energy use was performed to study bio-jet fuel (BJF) production from micro-algae grown in open ponds under Chinese conditions using the Tsinghua University LCA Model (TLCAM). Attention was paid to energy recovery through biogas production and cogeneration of heat and power (CHP) from the residual biomass after oil extraction, including fugitive methane (CH4) emissions during the production of biogas and nitrous oxide (N2O) emissions during the use of digestate (solid residue from anaerobic digestion) as agricultural fertilizer. Analyses were performed based on examination of process parameters, mass balance conditions, material requirement, energy consumptions and the realities of energy supply and transport in China (i.e., electricity generation and heat supply primarily based on coal, multiple transport modes). Our LCA result of the BJF pathway showed that, compared with the traditional petrochemical pathway, this new pathway will increase the overall fossil energy use and carbon emission by 39% and 70%, respectively, while decrease petroleum consumption by about 84%, based on the same units of energy service. Moreover, the energy conservation and emission reduction benefit of this new pathway may be accomplished by two sets of approaches: wider adoption of low-carbon process fuels and optimization of algae cultivation and harvest, and oil extraction processes.

Ethanol or Bioelectricity? Life Cycle Assessment of Lignocellulosic Bioenergy Use in Light-Duty Vehicles

Our study evaluates life cycle energy use and GHG emissions of lignocellulosic ethanol and bioelectricity use in U.S. light-duty vehicles. The well-to-pump, pump-to-wheel, and vehicle cycle stages are modeled. All ethanol (E85) and bioelectricity pathways have similar life cycle fossil energy use (~ 100 MJ/100 vehicle kilometers traveled (VKT)) and net GHG emissions (~5 kg CO2eq./100 VKT), considerably lower (65-85%) than those of reference gasoline and U.S. grid-electricity pathways. E85 use in a hybrid vehicle and bioelectricity use in a fully electric vehicle also have similar life cycle biomass and total energy use (~ 350 and ~450 MJ/100 VKT, respectively); differences in well-to-pump and pump-to-wheel efficiencies can largely offset each other. Our energy use and net GHG emissions results contrast with findings in literature, which report better performance on these metrics for bioelectricity compared to ethanol. The primary source of differences in the studies is related to our development of pathways with comparable vehicle characteristics. Ethanol or vehicle electrification can reduce petroleum use, while bioelectricity may displace nonpetroleum energy sources. Regional characteristics may create conditions under which either ethanol or bioelectricity may be the superior option; however, neither has a clear advantage in terms of GHG emissions or energy use.

The environmental impacts of lowland paddy rice: A case study comparison between rainfed and irrigated rice in Thailand

North-eastern Thailand is an essential production area for high-quality fragrant rice for domestic use and export. While rainfed conditions largely prevail, plans to extend irrigation are drafted. This article compares paddy rice production under irrigation and rainfed conditions. Techno-economic performances were analysed jointly with environmental impacts, based upon life cycle analysis, and energy and water use analyses. Data were collected in 2010 from 45 diverse rice cropping systems in the Lam Sieo Yai Basin, according to three systems, namely wet-season rain-fed (Rw), wet-season irrigation (Iw), and dry-season irrigation (Id) systems. Wide-ranging performances and impacts were observed, while cropping practices were relatively homogeneous. Differentiation of systems originated mostly from differences in yield, which were largely impacted by water supply. The results highlight the low performances and high impacts of Id systems. They require mostly blue water, while the two other systems rely primarily on green water. Id systems also require more energy and labour, due to increased water management needs. The productivity of most production factors was higher in Rw and Iw systems. Emissions proved relatively similar across systems, with the exception of CH4, which was markedly lower in Rw systems due to specific water and organic residue management. Id systems systematically emitted more nitrates, phosphates, and pesticides. Rw systems showed the lowest environmental impacts per ha and per kg of paddy rice produced. The average Global Warming Potential was 2.97 kg CO2-eq per kg rice in Rw systems, 4.87 in Iw systems, and 5.55 in Id systems. This article further discusses the results in view of contrasting perspectives, including societal objectives, farmer income and environmental integrity, and possible irrigation development in north-eastern Thailand.

Comparing environmental impacts of regional and national-scale food supply chains: A case study of processed tomatoes

This study uses life cycle assessment methodology to quantify the energy use, greenhouse gas (GHG) emissions, and water use of processed tomato products grown, processed, and consumed within the Great Lakes region of the United States, and tomato products produced in California and then shipped to the Great Lakes region for consumption. The purpose is to assess the potential for regional food systems to reduce selected environmental impacts, particularly the energy and GHG footprints, of consumer-ready, processed food products, when compared to national-scale food systems in which consumer products are shipped long distances. The study also examines the role of different types of food processing in influencing life cycle energy use, water use, and emissions.Our results indicate that California-produced conventional and organic tomato paste and canned diced tomatoes are almost equivalent in energy use and GHG emissions to regionally produced and consumed products, but use of developed water resources is significantly higher for California-grown products. California tomato production benefits from higher per hectare yields and soil amendments with lower carbon dioxide emissions. These efficiencies substantially offset the added energy use and GHG emissions associated with long-distance shipment of products to the Great Lakes region, as long as shipments are made by rail rather than by truck. Paste, the more processed and concentrated product evaluated, amplifies any environmental advantages or disadvantages accrued in the field production stage, due to its raw tomato to finished product ratio of 6:1, suggesting that comparative regional advantage can play a role in lowering life cycle environmental impacts of highly condensed foods shipped long distances.

Life-cycle energy of residential buildings in China

In the context of rapid urbanization and new construction in rural China, residential building energy consumption has the potential to increase with the expected increase in demand. A process-based hybrid life-cycle assessment model is used to quantify the life-cycle energy use for both urban and rural residential buildings in China and determine the energy use characteristics of each life cycle phase. An input–output model for the pre-use phases is based on 2007 Chinese economic benchmark data. A process-based life-cycle assessment model for estimating the operation and demolition phases uses historical energy-intensity data. Results show that operation energy in both urban and rural residential buildings is dominant and varies from 75% to 86% of life cycle energy respectively. Gaps in living standards as well as differences in building structure and materials result in a life-cycle energy intensity of urban residential buildings that is 20% higher than that of rural residential buildings. The life-cycle energy of urban residential buildings is most sensitive to the reduction of operational energy intensity excluding heating energy which depends on both the occupants' energy-saving behavior as well as the performance of the building itself.

Water Loss Control Using Pressure Management: Life-cycle Energy and Air Emission Effects

Pressure management is one cost-effective and efficient strategy for controlling water distribution losses. This paper evaluates the life-cycle energy use and emissions for pressure management zones in Philadelphia, Pennsylvania, and Halifax, Nova Scotia. It compares water savings using fixed-outlet and flow-modulated pressure control to performance without pressure control, considering the embedded electricity and chemical consumption in the lost water, manufacture of pipe and fittings to repair breaks caused by excess pressure, and pressure management. The resulting energy and emissions savings are significant. The Philadelphia and Halifax utilities both avoid approximately 130 million liters in water losses annually using flow-modulated pressure management. The conserved energy was 780 GJ and 1900 GJ while avoided greenhouse gas emissions were 50 Mg and 170 Mg a year by Philadelphia and Halifax, respectively. The life-cycle financial and environmental performance of pressure management systems compares favorably to the traditional demand management strategy of installing low-flow toilets. The energy savings may also translate to cost-effective greenhouse gas emission reductions depending on the energy mix used, an important advantage in areas where water and energy are constrained and/or expensive and greenhouse gas emissions are regulated as in California, for example.

Life cycle energy analysis of a zero-energy house

Most zero-energy concepts focus on a reduction of the non-renewable operational energy use in buildings rather than taking the reduction of their life cycle energy use as a starting point. Nevertheless, the life cycle embodied and end-of-life energy will become more important, especially in buildings with low operational energy. Therefore, the life cycle energy use of a Belgian zero-energy reference house is examined by means of life cycle energy assessment. The influence of design decisions and regulations on the building construction type, the building services, and the performance of the building envelope are investigated. In terms of thermal performance of the building, the results show that the life cycle embodied energy in zero-energy houses with passive or standard thermal performance was not substantially different. From a life cycle energy perspective, passive house requirements are not essential criteria for zero-energy houses in Belgium. On the other hand, large life cycle energy savings were obtained through a proficient selection of all building construction materials and services. For the life cycle embodied energy in building constructions, the best timber frame and masonry houses were equally efficient. Wood pellets and photovoltaic panels were decisive factors in the life cycle embodied energy of building services. Les concepts <<zéro-énergie>> sont axés pour la plupart sur une réduction de l'utilisation de l'énergie d'exploitation non renouvelable dans les bâtiments plutôt que de prendre la réduction de leur consommation d'énergie sur le cycle de vie comme point de départ. Néanmoins, l'énergie grise sur le cycle de vie et l'énergie de fin de vie vont gagner en importance, en particulier dans les bâtiments nécessitant une faible énergie d'exploitation. La consommation d'énergie sur le cycle de vie d'une maison belge «zéro énergie» de référence est donc étudiée au moyen d'un bilan énergétique du cycle de vie. Sont étudiés l'influence des décisions de conception et de la réglementation sur le type de construction du bâtiment, les services au bâtiment, et les performances de l'enveloppe du bâtiment. En termes de performance thermique du bâtiment, les résultats montrent que l'énergie grise sur le cycle de vie n'était pas fondamentalement différente dans les maisons «zéro énergie» offrant des performances thermiques passives ou standard. Du point de vue de l'énergie du cycle de vie, les exigences d'une maison passive ne sont pas des critères essentiels pour des maisons «zéro énergie» en Belgique. En revanche, d'importantes économies d'énergie sur le cycle de vie ont été obtenues par un choix opéré avec compétence de tous les matériaux de construction et services au bâtiment. S'agissant de l'énergie grise sur le cycle de vie dans la construction de bâtiments, les meilleures maisons, qu'elles aient été à ossature bois ou en maçonnerie, ont été tout aussi performantes. Les granulés de bois et les panneaux photovoltaïques ont été des facteurs décisifs concernant l'énergie grise sur le cycle de vie des services aux bâtiments. Mots clés: services aux bâtiments, énergie grise, analyse énergétique du cycle de vie, [construction] passive, bâtiments résidentiels, <<zéro-énergie>>

Life Cycle Energy Use and Greenhouse Gas Emission Analysis for a Water Resource Recovery Facility in India

This paper quantifies life cycle energy use and greenhouse gas (GHG) emissions associated with water resource recovery facilities (WRRFs) in India versus water quality improvements achieved from infrastructure investments. A first such analysis is conducted using operating data for a WRRF, which employs upflow anaerobic sludge blanket (UASB) reactors and oxidation. On-site operations energy use, process GHG emissions, and embodied energy in infrastructure were quantified. The analysis showed energy use and GHG emissions of 0.2 watt-hours (Wh) and 0.3 gram carbon dioxide (CO2) equivalents per liter (gCO2e/L) wastewater treated, and 1.3 Wh and 2.1 gCO2e/gBOD removed, achieving 81% biochemical oxygen demand (BOD) and 999% fecal coliform removal annually. Process emissions of WRRFs contributed 44% of life cycle GHG emissions, similar in magnitude to those from electricity (46%), whereas infrastructure contributed 10%. Average WRRF-associated GHG emissions (0.9gCO2e/L) were lower than those expected if untreated wastewater was released to the river. Investments made by WRRFs in developing world cities improve water quality and may mitigate overall GHG emissions.

Life-Cycle Energy and Greenhouse Gas Emission Benefits of Lightweighting in Automobiles: Review and Harmonization

Replacing conventional materials (steel and iron) with lighter alternatives (e.g., aluminum, magnesium, and composites) decreases energy consumption and greenhouse gas (GHG) emissions during vehicle use but may increase energy consumption and GHG emissions during vehicle production. There have been many life cycle assessment (LCA) studies on the benefits of vehicle lightweighting, but the wide variety of assumptions used makes it difficult to compare results from the studies. To clarify the benefits of vehicle lightweighting we have reviewed the available literature (43 studies). The GHG emissions and primary energy results from 33 studies that passed a screening process were harmonized using a common set of assumptions (lifetime distance traveled, fuel-mass coefficient, secondary weight reduction factor, fuel consumption allocation, recycling rate, and energy intensity of materials). After harmonization, all studies indicate that using aluminum, glass-fiber reinforced plastic, and high strength steel to replace conventional steel decreases the vehicle life cycle energy use and GHG emissions. Given the flexibility in options implied by the variety of materials available and consensus that these materials have substantial energy and emissions benefits, it seems likely that lightweighting will be used increasingly to improve fuel economy and reduce life cycle GHG emissions from vehicles.

LCE analysis of buildings – Taking the step towards Net Zero Energy Buildings

The basic concept of a Net Zero Energy Building (Net ZEB) is that on-site renewable energy generation covers the annual energy load.The main objective of this study is to analyse the increase of embodied energy compared to the decrease of the energy use related to building operation; partly by a literature review, partly by detailed analysis of eleven case studies; taking the step from a low energy building to a Net ZEB. The literature review shows that the metric of evaluation, assumed life-span, boundary conditions, age of database and the origin of database differ in different studies and influence the result of embodied energy. The relationship between embodied energy and life cycle energy use is almost linear for all cases studied herein. During the last two decades, embodied energy in new buildings has decreased slightly. However, the relative share of embodied energy related to life cycle energy use has increased. The detailed life cycle energy analysis show that taking the step from a low energy building to a Net ZEB results in a small increase of the embodied energy. However, the energy savings achieved in the annual operating energy balance clearly exceed the increase in embodied energy.

Energy balance and GHG emissions of cassava-based fuel ethanol using different planting modes in China

Cassava-based fuel ethanol (CFE) is playing an increasingly important role in renewable transportation energy in the Guangxi Province in China. Previous studies have evaluated the energy and greenhouse gas (GHG) performance of CFE, but they have largely overlooked the influences of different agricultural planting modes. In this study, five scenarios related to cassava planting modes were selected to evaluate the lifecycle energy balance and GHG emissions of the CFE system. The results show that, although all the five CFE scenarios show positive net energy values (NEV) and GHG emissions savings compared with the conventional gasoline, the planting modes have significant impacts on their energy and GHG performance. Modes that are considered intensive (i.e. high fertilizer use intensity and highly mechanized harvesting) generally show poorer performance than the extensive ones, primarily because of the intensive energy consumption and GHG emissions during nitrogen fertilizer production, the N2O emission of nitrogen fertilizer use, and higher yield loss rate caused by mechanized harvesting. This study shows that it is important to evaluate the planting modes when producing bioethanol in order to gain an understanding of the life-cycle energy use and GHG performance.

Life-cycle energy use and greenhouse gas emissions of production of bioethanol from sorghum in the United States

BackgroundThe availability of feedstock options is a key to meeting the volumetric requirement of 136.3 billion liters of renewable fuels per year beginning in 2022, as required in the US 2007 Energy Independence and Security Act. Life-cycle greenhouse gas (GHG) emissions of sorghum-based ethanol need to be assessed for sorghum to play a role in meeting that requirement.ResultsMultiple sorghum-based ethanol production pathways show diverse well-to-wheels (WTW) energy use and GHG emissions due to differences in energy use and fertilizer use intensity associated with sorghum growth and differences in the ethanol conversion processes. All sorghum-based ethanol pathways can achieve significant fossil energy savings. Relative to GHG emissions from conventional gasoline, grain sorghum-based ethanol can reduce WTW GHG emissions by 35% or 23%, respectively, when wet or dried distillers grains with solubles (DGS) is the co-product and fossil natural gas (FNG) is consumed as the process fuel. The reduction increased to 56% or 55%, respectively, for wet or dried DGS co-production when renewable natural gas (RNG) from anaerobic digestion of animal waste is used as the process fuel. These results do not include land-use change (LUC) GHG emissions, which we take as negligible. If LUC GHG emissions for grain sorghum ethanol as estimated by the US Environmental Protection Agency (EPA) are included (26 g CO2e/MJ), these reductions when wet DGS is co-produced decrease to 7% or 29% when FNG or RNG is used as the process fuel. Sweet sorghum-based ethanol can reduce GHG emissions by 71% or 72% without or with use of co-produced vinasse as farm fertilizer, respectively, in ethanol plants using only sugar juice to produce ethanol. If both sugar and cellulosic bagasse were used in the future for ethanol production, an ethanol plant with a combined heat and power (CHP) system that supplies all process energy can achieve a GHG emission reduction of 70% or 72%, respectively, without or with vinasse fertigation. Forage sorghum-based ethanol can achieve a 49% WTW GHG emission reduction when ethanol plants meet process energy demands with CHP. In the case of forage sorghum and an integrated sweet sorghum pathway, the use of a portion of feedstock to fuel CHP systems significantly reduces fossil fuel consumption and GHG emissions.ConclusionsThis study provides new insight into life-cycle energy use and GHG emissions of multiple sorghum-based ethanol production pathways in the US. Our results show that adding sorghum feedstocks to the existing options for ethanol production could help in meeting the requirements for volumes of renewable, advanced and cellulosic bioethanol production in the US required by the EPA’s Renewable Fuel Standard program.

Life Cycle Energy Analysis of a Multifamily Residential House: A Case Study in Indian Context

The paper presents life cycle energy analysis of a multifamily residential house situated in Allahabad (U.P), India. The study covers energy for construction, operation, maintenance and demolition phases of the building. The selected building is a 4-storey concrete structured multifamily residential house comprising 44 apartments with usable floor area of 2960 m2. The material used for the building structure is steel reinforced concrete and envelope is made up of burnt clay brick masonry. Embodied energy of the building is calculated based on the embodied energy coefficients of building materials applicable in Indian context. Operating energy of the building is estimated using e-Quest energy simulation software. Results show that operating energy (89%) of the building is the largest contributor to life cycle energy of the building, followed by embodied energy (11%). Steel, cement and bricks are most significant materials in terms of contribution to the initial embodied energy profile. The life cycle energy intensity of the building is found to be 75 GJ/m2 and energy index 288 kWh/m2 years (primary). Use of aerated concrete blocks in the construction of walls and for covering roof has been examined as energy saving strategy and it is found that total life cycle energy demand of the building reduces by 9.7%. In addition, building integrated photo voltaic (PV) panels are found most promising for reduction (37%) in life cycle energy (primary) use of the building.

Residential Solar-Based Seasonal Thermal Storage Systems in Cold Climates: Building Envelope and Thermal Storage

The reduction of electricity use for heating and domestic hot water in cold climates can be achieved by: (1) reducing the heating loads through the improvement of the thermal performance of house envelopes, and (2) using solar energy through a residential solar-based thermal storage system. First, this paper presents the life cycle energy and cost analysis of a typical one-storey detached house, located in Montreal, Canada. Simulation of annual energy use is performed using the TRNSYS software. Second, several design alternatives with improved thermal resistance for walls, ceiling and windows, increased overall air tightness, and increased window-to-wall ratio of South facing windows are evaluated with respect to the life cycle energy use, life cycle emissions and life cycle cost. The solution that minimizes the energy demand is chosen as a reference house for the study of long-term thermal storage. Third, the computer simulation of a solar heating system with solar thermal collectors and long-term thermal storage capacity is presented. Finally, the life cycle cost and life cycle energy use of the solar combisystem are estimated for flat-plate solar collectors and evacuated tube solar collectors, respectively, for the economic and climatic conditions of this study.

Energy use indicators in energy and life cycle assessments of biofuels: review and recommendations

In this study we investigate how indicators for energy use are applied in a set of life cycle assessment (LCA) and energy analysis case studies of biofuels. We found five inherently different types of indicators to describe energy use: (1) fossil energy, (2) secondary energy, (3) cumulative energy demand, (4) net energy balance, and (5) total extracted energy. It was also found that the examined reports and articles, the choice of energy use indicator was seldom motivated or discussed in relation to other energy use indicators. In order to investigate the differences between these indicators, they were applied to a case. The life cycle energy use of palm oil methyl ester was calculated and reported using these five different indicators for energy use, giving considerably different output results. This is in itself not unexpected, but indicates the importance of clearly identifying, describing and motivating the choice of energy use indicator. The indicators can all be useful in specific situations, depending on the goal and scope of the individual study, but the choice of indicators need to be better reported and motivated than what is generally done today.