The world's economy is fuelled by energy. Depletion of resources and severe environmental effects resulting from the continuous use of fossil fuels has motivated an increasing amount of interest in renewable energy resources and the search for sustainable energy policies.
The changes required to progress from an economy mainly focused on hydrocarbons to one taking advantage of sustainable energy resources require considerable scientific research as well as the development of new engineering systems. Energy policies and management are of primary importance to achieve the development of sustainability and need to be consistent with recent advances in energy production and distribution.
In many cases, the challenges lie as much in the conversion from renewable energies (wind, solar, etc) to useful forms (electricity, heat, fuel) at an acceptable cost (including damage to the environment), as in the integration of those resources into an existing infrastructure.
The diverse topics covered by these papers involved collaboration between different disciplines in order to arrive at optimum solutions; including studies of materials, energy networks, new energy resources, storage solutions, waste to energy systems, smart grids and many others.
The Editors are especially grateful to the reviewers, as well as to the authors for their contributions.

The Editors
2017

The de-carbonization of the transport sector is a particularly complex challenge as greenhouse gases are delocalized and diffused. Therefore, the problem has to be tackled from the source of the emissions, and efforts in the scientific and technological field must seek out new energy vectors of high density, neutral in CO₂ and based on renewable energy that meet the sector demands and requisites. This could be the case of the synthetic natural gas which can be produced through the Power to Gas process (PtG). This process, originally developed by the German institutes ZSW and IWES, converts electricity into synthetic natural gas (SNG) via the methanation of CO₂ together with H₂ from water electrolysis. The energy content of the produced methane comes from the primary source for power generation (optimally renewable electricity) and it is possible to produce a CO₂ neutral fuel by capturing the carbon emissions from an existing source. In addition, the PtG process can be seen as a new concept of renewable energy and CO₂ hybrid storage. This paper identifies the possibilities that the Power to Gas technology offers for the production of sustainable methane and the existing potential for the symbiosis of industrial sectors through optimization of their waste streams of matter and energy. In particular power and transport sectors are considered and the outline of a small facility for the generation of synthetic natural gas from renewable electricity and its consumption in the vehicles of a road freight company is presented as a case study. Not only the technical feasibility but the economic viability of the process and the environmental improvements resulting from the use of a renewable fuel free of CO₂ emissions in terms of carbon footprint are evaluated.

The possibility of reducing the flow losses in low-pressure turbine stage has been investigated in an iterative process using a novel hybrid optimisation algorithm. Values of the maximised objective func- tion that is isentropic efficiency are found from 3D RANS computation of the flowpath geometry, which was being changed during the optimisation process. To secure the global flow conditions, the constraints have been imposed on the mass flow rate and reaction. Among the optimised parameters are stator and rotor twist angles, stator sweep and lean, both straight and compound. Blade profiles remained unchanged during the optimisation. A new hybrid stochastic-deterministic algorithm was used for the optimisation of the flowpath. In the proposed algorithm, the bat algorithm was combined with the direct search method of Nelder-Mead in order to refine the best obtained solution from the standard bat algorithm. The method was tested on a wide variety of well-known test functions. Also, the results of the optimisation of the other stochastic and deterministic methods were compared and discussed. The optimisation gives new 3D-stage designs with increased efficiency comparing to the original design.

Carbon dioxide (CO₂) is an appropriate replacement for conventional refrigerants due to its low global warming effects. However, its application within a traditional refrigeration compression cycle leads to low thermodynamic performance due to the large expansion losses in a throttling process. The application of ejectors allows reducing these losses. Many scenarios of ejector-based cycles have been proposed. Among them four different configurations may be distinguished: an expansion work recovery cycle (EERC), a liquid recirculation cycle (LRC), an increasing compressor discharge pressure cycle (CDPC) and a vapor jet refrigeration cycle (VJRC). This study deals with the comparative analysis of these cycles. In order to study the performance of the cycles, the numerical simulations are developed using EES software. Two performance criteria, energy efficiency (COP) and exergy efficiency are evaluated for each cycle. The highest values of these criteria point to the most thermodynamically efficient cycle. The results show that the EERC has the highest COP and exergy efficiency compared to other cycles. For example, the COP of the EERC is 3.618 and the exergy efficiency is 9.68%. The COP (resp. exergy efficiency) is approximately 23.3% (resp. 23.3%), 24.9% (resp. 25.5%) and 5.6 times (resp. 56.2%) higher than the corresponding energy and exergy efficiencies of LRC, CDPC and VJRC. Moreover, in comparison with a basic throttling valve cycle, the COP and exergy efficiency in EERC are higher up to 23% and 24% correspondingly. The detailed exergy analysis of EERC cycle has pinpointed the equipment where the major exergy losses take place. The largest losses occur in the evaporator (about 33% of the total exergy destruction of the cycle) followed by the compressor (25.5%) and the ejector (24.4%).

Coconut shell and husk are two biomasses wastes abundant in most of the coastal countries. However, despite their enormous potential as energy sources, they are hardly studied and their thermal characteristics are still not well known. In this study, both biomasses are thermally degraded through thermogravimetry (TG-DTA) and their pyrolysis product yield such as char, tar and gases are analyzed. The TG-DTA results show that pyrolysis of biomass consists of three stages. Three stages can be out- lined as: (1) dehydration process for temperatures below 122°C, (2) pyrolytic cracking from 122°C to 400°C, stage consist of two exothermic simultaneous processes where hemicelluloses, cellulose and lignin are decomposed and a high amount of volatile matter formation occurs and (3) the last endother- mic decomposition of the lignin at temperatures above 400°C. From the pyrolytic results, it is showed that the char and gases yields were increased with the decrement tar. The gas-evolving profiles from pyrolyzing the coconut shell and husk components in a packed bed, monitored by a GC-TCD and a GC-FID, showed similar behavior. H₂ was released out at a higher temperature (>450°C) and it got the maximum rate at 700°C then it decreased. CO₂ was released out at 130°C –750°C and got the maximum releasing value at 300°C –400°C. The released CO showed almost similar pattern with that of CO₂. However, the release rate was lower than CO₂ and the maximum release rate of CO was found at 300°C –400°C. CH4 was released out at the temperature between 200°C –850°C, and it got the maximum rate at 550°C. The releasing of hydrocarbon was generally very low.

With the increasing world’s energy demand along with the constantly expanding field of natural gas exploitation around the world, dry reforming of methane has gained increasing attention. Through this technology, natural gas can be converted into syngas, which is a well-known building block used for the production of alcohols and fuels. This technology has become an interesting approach for the valorization of a variety of CO₂ streams and for the reduction of the natural gas carbon footprint. In this work, attention will be given to the different reforming technologies used at industrial scale, followed by an investigation of the different approaches used for dry reforming of methane. Furthermore, focus will be given on how natural gas reforming could be used as a vehicle to store renewable energy while trying as well to reduce the carbon footprint of this technology. The technology presented in this work was previously developed by Hydro Québec and uses a cheap and available catalyst in addition to electricity to convert methane and carbon dioxide into syngas. Reactants conversions were up to 99% and the syngas produced had a H2/CO ratio of 1 for over 200h.

In the construction industry, the popularity of sustainability and its benefits have been on the rise in recent years. Alas, with various building sustainability assessment schemes on the market, there is still no single general method for a comprehensive and inclusive design and building process for sustainable buildings. The literature describes several barriers of entry preventing actors in the industry from seeking sustainability certifications and prioritizing design methods, supporting sustainability in greater numbers. In the newly developed tool, “DGNB building certification companion: Sustainable Tool for Assessment, Planning, Learning, and Engaging (STAPLE)”, a new Excel-based, interactive, and iterative education focused platform is introduced, intended to engage dialog among stakeholders, building owners, and decision makers, and the assigned group team leaders, based on the five DGNB topics. In order to establish common levels of knowledge, terminology, and understanding for proper interdisciplinary discussions, which would result in suitable and timely decisions, personal and profes- sional development is enabled by imbedded educational documents in multiple formats throughout the tool as plain-language, easily digestible summaries of various topics regarding sustainability and the DGNB certification scheme. The identified barriers are described in the tool followed by a solution to overcome them. The tool, tested at multiple stages of development and moulded by many individuals both within and outside of the sustainable building industry, has shown to achieve the primary goals of assessment of individual’s current knowledge, educating through multiple stages and formats, and the inspiring of conversation among team members through a graphical display of opinions. Based on user feedback, the conclusion was that this is a desired product on the market. This new approach is expected to dramatically reduce misunderstandings, conflicts, and mistakes during a sustainable design process, helping the design team plan a project to possibly obtain the highest DGNB score if desired and properly documented.

In recent decades, the industry has observed a significant shift towards the use of renewable energy, such as solar, wind and geothermal. The Chilean scenario has not been an exception, and much pro- gress has been made in sustainable energy prospection and implementation, especially in the electricity sector, where solar and wind power amount 2300 MW, and since April 2017, the first geothermal power plant (48 MW) has come into operation. In the area of low enthalpy geothermal energy, the use is around 19 MW.

The Faculty of Physical and Mathematical Sciences at the University of Chile has been contributing to this transformational process, with its Sustainable Campus initiative. The first step of this initiative is the introduction of renewable energy on site, which has been achieved through the installation of a solar photovoltaic plant of 15 kW. Along this line, the design and implementation of a geothermal air conditioning system (HAVC) is underway, which will serve the classrooms and offices in the tradi- tional engineering building of the campus. The technology to be used in this project is the Ground Heat Pump (GHP).

The present paper includes an introduction of the applications of low enthalpy geothermal energy in Chile, a description of the Office of Engineering for Sustainable Development at the Faculty of Physical and Mathematical Sciences, and the design of a geothermal HAVC system in the university campus, considering economic, environmental, technical and social aspects. Besides the operation of the GHP, the system will be used for teaching purposes to incorporate sustainable development in the curriculum of the university. The expected savings of the geothermal system versus an aerothermal design are 41,070 kWh annually, considering both cooling and heating.