Primary Energy Balance Research Articles

Life cycle assessment of wood construction according to the normative standards

This study demonstrates life cycle assessment (LCA) on a reference wooden building according to the latest normative standards: EN 15978, EN 15804 and EN 16485. Global warming potential and primary energy balance over the reference building were assessed in a case study. Through the assessment, the application of the standards was studied. In addition, possible points for development in the standards, especially concerning wood products and wood construction, were discussed from a practical perspective. The lack of proper data is a critical issue in conducting the assessment in compliance with the standards. Since LCA is a data-intensive method, the preparation of data for the building assessment according to the standard is certainly required. This paper also raises questions about the life cycle modules defined in the standards and the importance of the communication system used for the assessment results. It would be of importance to develop the communication system in such a way as to stimulate environmental consciousness in society. In order to develop a relevant communication system, further discussion and case studies would be important and feedback from such practices should be incorporated into the development of the guideline for the assessment.

Lifecycle primary energy analysis of low-energy timber building systems for multi-storey residential buildings

A system-wide lifecycle approach is used here to explore the primary energy implications of three timber building systems for a multi-storey building designed to a high energy-efficiency level. The three building systems are: cross laminated timber, beam -and-column, and modular prefabricated systems. The analysis considers the energy and material flows in the production, use and post-use lifecycle stages of the buildings. The effects of insulation material options and the contribution of different building elements to the production energy for the buildings are explored. The results show that external and internal walls account for the biggest share of the production energy for all building systems and its contribution is comparable for the different systems. In contrast, there is significant variation in the production primary energy for the roof-ceilings and intermediate floor-ceilings for the different building systems. Overall, the cross laminated timber building system gives the lowest lifecycle primary energy balance, as this building is insulated with stone wool and has better airtightness in contrast to the other building systems which are insulated with glass wool and have lower airtightness performance. With improved airtightness and insulation substitution, the total primary energy use for the beam-and-column and modular building systems can be reduced by 7% and 9%, respectively.

Energy life-cycle approach in Net zero energy buildings balance: Operation and embodied energy of an Italian case study

The paper starts from the results of one of the six case-studies of the SubTask B in the International Energy Agency joint Solar Heating and Cooling Task40 and Energy Conservation in Buildings and Community Systems Annex 52, whose purpose is to document state of the art and needs for current thermo-physical simulation tools in application to Net Zero Energy Buildings.The authors extend the Net Zero Energy Buildings (Net ZEB) methodological framework, introducing the life-cycle perspective in the energy balance and thus including the embodied energy of building and its components. The case study is an Italian building, tailored to be a Net ZEB, in which the magnitude of the deficit from the net zero energy target is assessed according to a life-cycle approach. The annual final energy balance, assessed with regard to electricity, shows a deficit which makes the case study a nearly Net ZEB, when the encountered energy flows are measured at the final level. Shifting from final to primary energy balance the case-study moves to a non-Net ZEB condition, because of the large difference between the conversion factors of photovoltaics generated electricity and imported electricity. The adoption of a life cycle perspective and the addition of embodied energy to the balance causes an even largest shift from the nearly ZEB target: the primary energy demand is nearly doubled in comparison to the primary energy case.

Power Generation Using District Heat: Energy Efficient Retrofitted Plus-energy School Rostock

The Mathias-Thesen-School in Rostock/Germany is one of few schools which has been retrofitted as an Energy Plus building as part of the energy-efficient school research project “EnEff:Schule” sponsored by the German Ministry of Economics and Technology. The original building complex (build 1960, useful area 2200sqm) is being converted into a compact building by extending the main building with two new buildings connected by light-flooded buffer spaces. Both the existing building and the new buildings will be highly insulated. The low remaining heating demand will be covered using an innovative concept, made reasonable by the low primary energy factor of the district heat in Rostock: A small-scale Organic Rankine Cycle system generates electricity using high-temperature district heat. The excess heat of the generator is then used to heat the building via low-temperature distribution systems. In combination with two small-scale onsite wind turbines and building integrated photovoltaics a positive primary energy balance is achieved. For this balance, the development of the primary energy factors (PEF) of the German electricity mix is crucial: With rising generation from renewable energies the PEF of electricity in Germany is going to descent, leading to higher primary energy factors of cogeneration systems. In the Mathias-Thesen-School in Rostock a detailed monitoring system was installed, which has been checked and reworked for proper functioning. First measures to optimize the HVAC system and user comfort have been taken. The second construction phase will take place in 2014, after which the performance of the ORC system and the Energy Balance will be analyzed in detail.

Forest biomass supply chains in Ireland: A life cycle assessment of GHG emissions and primary energy balances

The demand for wood for energy production in Ireland is predicted to double from 1.5 millionm3 over bark (OB) in 2011 to 3 millionm3 OB by 2020. There is a large potential for additional biomass recovery for energetic purposes from both thinning forest stands and by harvesting of tops and branches, and stumps. This study builds on research within the wood-for-energy concept in Ireland by analysing the energy requirements and greenhouse gas emissions associated with thinning, residue bundling and stump removal for energy purposes. To date there have been no studies on harvesting of residues and stumps in terms of energy balances and greenhouse gas emissions across the life cycle in Ireland. The results of the analysis on wood energy supply chains highlights transport as the most energy and greenhouse gas emissions intensive step in the life cycle. This finding illustrates importance of localised production and use of forest biomass. Production of wood chip, and shredded bundles and stumps, compares favourably with both other sources of biomass in Ireland and fossil fuels.

Dissemination and Problems of African Biogas Technology

The present status of biogas technology in Africa was briefly reviewed focusing on biogas market potential, stake-holders, investments and bottlenecks. Africa is endowed with important biomass reserve considered as a potential for anaerobic digestion. However, the over reliance on wood and fossil fuels remains significantly overwhelming. This is due to the number of challenges in the field which led to underestimate at some extent the benefits of biogas technology. Unreliable and inefficient use of biomass fuel, which contributes to the greenhouse gas emissions still, has kept its preference in primary energy balance. Despite the huge potentialities and biomass resources for anaerobic digestion in Africa, the dissemination rate of biogas in Africa is struggling to meet biogas market demand. Nevertheless, there are a number of problems to address especially narrowing down the gap between biogas market demand and supply. This paper consists of an introduction and the status of the energy sector in Africa, and then discusses current dissemination of biogas development, finance and stakeholder contributions, challenges and a conclusion.

Net primary energy balance of a solar-driven photoelectrochemical water-splitting device

A fundamental requirement for a renewable energy generation technology is that it should produce more energy during its lifetime than is required to manufacture it. In this study we evaluate the primary energy requirements of a prospective renewable energy technology, solar-driven photoelectrochemical (PEC) production of hydrogen from water. Using a life cycle assessment (LCA) methodology, we evaluate the primary energy requirements for upstream raw material preparation and fabrication under a range of assumptions of processes and materials. As the technology is at a very early stage of research and development, the analysis has considerable uncertainties. We consider and analyze three cases that we believe span a relevant range of primary energy requirements: 1550 MJ m−2 (lower case), 2110 MJ m−2 (medium case), and 3440 MJ m−2 (higher case). We then use the medium case primary energy requirement to estimate the net primary energy balance (energy produced minus energy requirement) of the PEC device, which depends on device performance, e.g. longevity and solar-to-hydrogen (STH) efficiency. We consider STH efficiency ranging from 3% to 10% and longevity ranging from 5 to 30 years to assist in setting targets for research, development and future commercialization. For example, if STH efficiency is 3%, the longevity must be at least 8 years to yield a positive net energy. A sensitivity analysis shows that the net energy varies significantly with different assumptions of STH efficiency, longevity and thermo-efficiency of fabrication. Material choices for photoelectrodes or catalysts do not have a large influence on primary energy requirements, though less abundant materials like platinum may be unsuitable for large scale-up.

Environmental analysis of a construction and demolition waste recycling plant in Portugal – Part II: Environmental sensitivity analysis

Part I of this study deals with the primary energy consumption and CO2eq emissions of a 350tonnes/h construction and demolition waste (CDW) recycling facility, taking into account incorporated, operation and transportation impacts. It concludes that the generated impacts are mostly concentrated in operation and transportation, and that the impacts prevented through material recycling can be up to one order of magnitude greater than those generated.However, the conditions considered for the plant’s operation and related transportation system may, and very likely will, vary in the near future, which will affect its environmental performance. This performance is particularly affected by the plant’s installed capacity, transportation fuel and input CDW mass. In spite of the variations in overall primary energy and CO2eq balances, the prevented impacts are always higher than the generated impacts, at least by a factor of three and maybe even as high as 16times in particular conditions. The analysis indicates environmental performance for variations in single parameters, except for the plant’s capacity, which was considered to vary simultaneously with all the others. Extreme best and worst scenarios were also generated to fit the results into extreme limits.

Heat rejection and primary energy efficiency of solar driven absorption cooling systems

Efficient heat rejection is crucial for the overall primary energy balance of sorption systems, as it dominates the auxiliary energy consumption. Low ratios of cooling power to auxiliary electricity of 3.0 or less are still common in sorption system, so that the primary energy efficiency is not always higher than for conventional compression chillers.Whereas dry heat rejection systems require electricity for fan operation, hybrid or wet cooling systems in addition need pumping energy for the cooling water and the water itself. The energy efficiency can be improved for heat rejection to the ground, where only pumping energy is needed for the geothermal heat exchange.Dynamic simulation models were used for a single effect absorption chiller powered by solar thermal collectors via a hot storage tank. The chiller models were coupled to a three dimensional numerical ground heat exchanger model or to cooling tower models. The models were validated with operating data of a 15kW solar cooling system installed in an office building.Primary energy efficiency ratios were determined for different heat rejection systems and improved control strategies were developed. The installed system primary energy ratios varied between 1.1 and 2.2 for auxiliary heating and between 1.2 and 2.5 for auxiliary cooling depending on the heat rejection and control strategy chosen. The low electrical energy consumption of the geothermal heat rejection saves 30% of auxiliary electricity and results in an electrical coefficient of performance of 13. The maximum primary energy ratios for solar fractions up to 88% are 2.7 for auxiliary heating and 3.2 for auxiliary cooling, i.e. nearly three times higher than for the reference electrical compression system of 1.2.

Operational Performance Results of an Innovative Solar Thermal Cooling and Heating Plant

Solar thermal cooling and heating plants with single-effect sorption chillers/heat pumps promise primary energy savings compared to electric vapor compression chiller systems. Yet, the need of auxiliary electric a nd fossil energy for the operation and backup of the thermal cooling system possibly worsen the primary energy balance. An auspicious approach to overcome this problem is the application of a more efficient multi -stage sorption chiller with flexible operational modes. A pilot installation of that innovative solar thermal heating and cooling plant comprising a two stage absorption chiller/heat pump is presented. Beginning with the motivation and the system concept, a detailed analysis of the 2011/2012 cooling and heating periods is shown. The influence of the different system components – especially the absorption chiller – on the overall system performance is analyzed and a comparison to data from a detailed dynamic model is carried out. Recommendations for the improvement with respect to efficiency and economic aspects are given based on the installation process and the operational experience gained in the last 1 ½ years.

Effect of thermal mass on life cycle primary energy balances of a concrete- and a wood-frame building

In this study we analyze the effect of thermal mass on space heating energy use and life cycle primary energy balances of a concrete- and a wood-frame building. The analysis includes primary energy use during the production, operation, and end-of-life phases. Based on hour-by-hour dynamic modeling of heat flows in building mass configurations we calculate the energy saving benefits of thermal mass during the operation phase of the buildings. Our results indicate that the energy savings due to thermal mass is small and varies with the climatic location and energy efficiency levels of the buildings. A concrete-frame building has slightly lower space heating demand than a wood-frame alternative, due to the higher thermal mass of concrete-based materials. Still, a wood-frame building has a lower life cycle primary energy balance than a concrete-frame alternative. This is due primarily to the lower production primary energy use and greater bioenergy recovery benefits of the wood-frame buildings. These advantages outweigh the energy saving benefits of thermal mass. We conclude that the influence of thermal mass on space heating energy use for buildings located in Nordic climate is small and that wood-frame buildings with cogeneration based district heating would be an effective means of reducing primary energy use in the built environment.

Energy and environmental assessment of two high energy performance residential buildings

The «positive energy building» concept combines energy saving and electricity production using renewable resources, aiming a positive primary energy balance on a yearly basis. Compared to other concepts of high energy performance buildings, it is very ambitious on an energy point of view, but more materials and components are used, this is why the environmental relevance of this concept has to be questioned. In order to contribute to answer this question, a life cycle assessment (LCA), including the fabrication of components, construction, operation, maintenance, dismantling and waste treatment, has been used to evaluate the environmental impacts of two high energy performance buildings: a renovated multi-family social housing building and two passive attached houses. Both buildings are located in North of France. For the purpose of this study, renewable energy production has been assumed to achieve nearly positive energy balances. For these buildings, four different heating solutions have been studied: an electric heat pump, a wood pellet condensing boiler, a wood pellet micro-cogeneration unit, and district heating. Modeling and simulation have been performed using the building thermal simulation tool COMFIE, to evaluate the heating load and thermal comfort level, and the LCA tool EQUER to evaluate twelve impact indicators. The results show the level of performance as well as the influence of the choice of the heating system on the environmental impacts considered in this assessment.

Energy transfers in internal tide generation, propagation and dissipation in the deep ocean

The energy transfers associated with internal tide (IT) generation by a semi-diurnal surface tidal wave impinging on a supercritical meridionally uniform deep ocean ridge on the f-plane, and subsequent IT-propagation are analysed using the Boussinesq, free-surface, terrain-following ocean model Symphonie. The energy diagnostics are explicitly based on the numerical formulation of the governing equations, permitting a globally conservative, high-precision analysis of all physical and numerical/artificial energy transfers in a sub-domain with open lateral boundaries. The net primary energy balances are quantified using a moving average of length two tidal periods in a simplified control simulation using a single time-step, minimal diffusion, and a no-slip sea floor. This provides the basis for analysis of enhanced vertical and horizontal diffusion and a free-slip bottom boundary condition. After a four tidal period spin-up, the tidally averaged (net) primary energy balance in the generation region, extending ±20 km from the ridge crest, shows that the surface tidal wave loses approximately C = 720 W/m or 0.3% of the mean surface tidal energy flux (2.506 × 10 5 W/m) in traversing the ridge. This corresponds mainly to the barotropic-to-baroclinic energy conversion due to stratified flow interaction with sloping topography. Combined with a normalised net advective flux of baroclinic potential energy of 0.9 × C this causes a net local baroclinic potential energy gain of 0.72 × C and a conversion into baroclinic kinetic energy through the baroclinic buoyancy term of 1.18 × C. Tidally averaged, about 1.14 × C is radiated into the abyssal ocean through the total baroclinic flux of internal pressure associated with the IT- and background density field. This total baroclinic pressure flux is therefore not only determined by the classic linear surface-to-internal tide conversion, but also by the net advection of baroclinic (background) potential energy, indicating the importance of local processes other than linear IT-motion. In the propagation region (PR), integrated over the areas between 20 and 40 km from the ridge crest, the barotropic and baroclinic tide are decoupled. The net incoming total baroclinic pressure flux is balanced by local potential energy gain and outward baroclinic flux of potential energy associated with the total baroclinic density. The primary net energy balances are robust to changes in the vertical diffusion coefficient, whereas relatively weak horizontal diffusion significantly reduces the outward IT energy flux. Diapycnal mixing due to vertical diffusion causes an available potential energy loss of about 1% of the total domain-averaged potential energy gain, which matches k m - 1 k m ρ 0 K V N 2 to within 0.5%, for k m linearly distributed grid-levels and constant background density ρ 0, vertical diffusivity ( K V ) and buoyancy frequency ( N).

STRATEGY AND EFFICIENT MECHANISMS TO IMPROVE SECURITY AND SUSTAINABILITY OF THE NATURAL GAS SUPPLY IN BALTIC STATES

Share of natural gas as an efficient resource in the deficient Baltic primary energy balance is and will be significant (power generation, district heating, households, industry, etc.). Therefore gas supply risks are evaluated and appropriate actions are recommended in the paper to assure reliable availability of affordable and sustainable energy in Baltic. Macro-region’s base (including supply and transit countries), risk and cost assessments, timely introduction of non-market measures, high cyber security level of information processing and management systems are components of security strategy. Extension of Incukalns UGS, interlinked pan-Baltic LNG receiving terminal and upgrade of transborder trunk pipelines are recommended as the most efficient tools. Complex realization of all instruments and solidarity of countries are the key issues to implement proposed strategy.

Costs, CO2- and primary energy balances of forest-fuel recovery systems at different forest productivity

Here we examine the cost, primary energy use, and net carbon emissions associated with removal and use of forest residues for energy, considering different recovery systems, terrain, forwarding dis ...

An evaluation of biomass co-firing in Europe

Abstract Reduction of the emissions of greenhouses gases, increasing the share of renewable energy sources (RES) in the energy balance, increasing electricity production from renewable energy sources and decreasing energy dependency represent the main goals of all current strategies in Europe. Biomass co-firing in large coal-based thermal power plants provides a considerable opportunity to increase the share of RES in the primary energy balance and the share of electricity from RES in gross electricity consumption in a country. Biomass-coal co-firing means reducing CO 2 and SO 2 , emissions and it may also reduce NO x emissions, and also represents a near-term, low-risk, low-cost and sustainable energy development. Biomass-coal co-firing is the most effective measure to reduce CO 2 emissions, because it substitutes coal, which has the most intensive CO 2 emissions per kWh electricity production, by biomass, with a zero net emission of CO 2 . Biomass co-firing experience worldwide are reviewed in this paper. Biomass co-firing has been successfully demonstrated in over 150 installations worldwide for most combinations of fuels and boiler types in the range of 50–700 MWe, although a number of very small plants have also been involved. More than a hundred of these have been in Europe. A key indicator for the assessment of biomass co-firing is intrduced and used to evaluate all available biomass co-firing technologies.

Differences in growth patterns between co‐occurring forest and savanna trees affect the forest–savanna boundary

Summary Patterns of growth, activity and renewal of stems and branches are primary determinants of ecosystem function and strongly influence net primary productivity, water and energy balance. Here we compare patterns of leaf phenology, stem radial growth and branch growth of co‐occurring savanna and forest trees in the Cerrado region of central Brazil to gain insight into the influence of these parameters in forest–savanna boundary dynamics. We hypothesized that forest species would have higher radial growth rates but later leaf flush than savanna species. We studied 12 congeneric species pairs, each containing one savanna species and one forest species. All individuals were growing in savanna conditions under full sun. We measured specific leaf area (SLA), light‐saturated photosynthesis and monthly increments in stem circumference, branch length, leaf flush and leaf fall. Relative to savanna species, forest species had 68% higher diameter growth rates, 38% higher SLA, and displayed a greater crown area for a given basal area. Across species, radial growth was positively correlated with SLA (r2 = 0·31), but not with CO2 assimilation. Peak leaf production of savanna species was in the late dry season, 1 month earlier than for forest species, which suggests a strategy to avoid nutrient losses during leaf expansion due to herbivory or leaching. However, savanna and forest species did not differ in annual branch growth, number of leaves produced per branch, or in timing of leaf fall. Radial growth was tightly coupled to monthly rainfall in forest species whereas the growth of savanna species ceased before the end of the wet season. The cessation of above‐ground growth at a time of active photosynthesis may reflect a shift in allocation to roots and reserves. These results contribute to recent studies showing that savanna and forest species represent different functional types and that despite the limiting resources in savanna environments, forest trees that invade the savanna tend to present higher growth rates and larger and denser crowns, which enhance shading and could promote changes in equilibrium of forest–savanna boundaries.

Topographic controls on the leaf area index and plant functional type of a tundra ecosystem

1 Leaf area index (LAI) is an emergent property of vascular plants closely linked to primary production and surface energy balance. LAI can vary by an order of magnitude among Arctic tundra communities and is closely associated with plant functional type. 2 We examined topographic controls on vegetation type and LAI distribution at two different scales in an Arctic tundra ecosystem in northern Sweden. ‘Micro-scale’ measurements were made at 0.2-m resolution over a 40 m × 40 m domain, while ‘macro-scale’ data were collected at approximately 10-m resolution over a 500 m × 500 m domain. Tundra LAI varied from 0.1–3.6 at the micro-scale resolution, and from 0.1–1.6 at the macro-scale resolution. 3 The correlation between dominant vascular species and LAI at the micro-scale (r2 = 0.40) was greater than the correlation between dominant vegetation and LAI at the macro-scale (r2 = 0.14). At the macro-scale, LAI was better explained by topographic parameters and spatial auto-correlation (pseudo r2 = 0.32) than it was at the micro-scale (r2 = 0.16). Exposure and elevation were significantly but weakly correlated with LAI at the micro-scale, while on the macro-scale the most significant explanatory topographic variable was elevation (r2 = 0.12). 4 The distribution of plant communities at both scales was significantly associated with topography. Shrub communities, dominated by Betula nana, were associated with low elevation sites at both scales, while more exposed and/or high elevation sites were dominated by cryptogams. 5 Synthesis. Dominant vegetation, topography and LAI were linked at both scales of investigation but, for explaining LAI, topography became more important and dominant vegetation less important at the coarser scale. The explanatory power of dominant species/functional type for LAI variation was weaker at coarser scales, because communities often contained more than one functional type at 10 m resolution. The data suggest that remotely sensed topography can be combined with remotely sensed optical measurements to generate a useful tool for LAI mapping in Arctic environments.

Le rendement énergétique de la production d’éthanol à partir de maïs

This article establishes the primary energy balance for making ethanol out of corn in the USA, calculated from the farm to the fuel station, following a methodology described in Chavanne and Frangi (C. R. Geoscience 339 (2007) 519–535). Raw data (direct energy and material consumption as well as their heat value and external costs) come from published papers related to this topic, technical textbooks, as well as reports from the US Departments of Agriculture and Energy. For the 2001 harvest, over the area producing more than 90% of ethanol and for the 2005 network of working refineries, 100 J of ethanol and recovery of by-products (the energy saved by the replacement of animal feed by these by-products is around 12% of the ethanol heat value) needed 86 ± 3 J of energy spending, of which more than 50 J is natural gas and 62 J is used in refineries. A third of the area of Nebraska corn must be irrigated with water pumped from underground, at an added cost of 26 ± 3 J. In 1996, the extra drying required, because of heavy rains, added 6 J. By comparison, 100 J of gasoline cost less than 25 J to be produced out of crude oil. Complementary studies of resource availability are not performed here. The largest possible reduction in energy costs can be achieved at the refinery stage, by fermenting by-products, gas residues, (from 62 J to around 12 J). The article gives also an expression for the expenditure to enable comparison between different energy systems, including everything from biomass to transport. For the ethanol case, the average cost is 130 J for 100 J of corn grain heat.

Primary Energy Balance and Energy Pay-back Time after Insulating an Outer Wall – Comparing Northern Europeand the Eastern Mediterranean Region

Taking for buildings a specific annual heat demand of 70 kWh/(m2*a) for heating plus 12.5 kWh/(m2*a) for hot water into account, by the measures of “Rational Use of Energy” the German fi nal energy demand in the private sector could be reduced by 300 TWh annually (same as up to hundred Mtons of CO2) (a = year). This paper will summarize some data for Germany compared to Turkey and evaluate the ecological feasibility of a 10 cm thick rockwool insulation of an outer building wall. The energy pay-back time for the locations Potsdam/Germany and Izmir/Turkey will be calculated and interpreted. Furthermore, this paper is to propagate energy conservation as an important tool (i) to save primary energy consumption, in order (ii) to reduce the import of fossil fuels and thus to strengthen the domestic economy, and (iii) to reduce the emission of the greenhouse gas CO2 and thus to decrease the climatic effect.