Dynamic models for a heat-led organic rankine cycle

Drawn by the benefits of de-centralised and renewable power supply, over 150 Organic Rankine Cycles (ORC), in a range from 400kWel to 2MWel, have been installed in Central Europe. The majority of modules are biomass fired and heat-led by district heating networks. With rising fuel prices however, the economic situation has become critical for many of these facilities and improvements in efficiency are indispensable. The research reported here, provides turbine models to simulate units of that type and suggests recommendations to achieve a higher cycle efficiency. An operating power plant with a design power of 1MWel serves as validation

Fluid stability in large scale ORCs using siloxanes: long-term experiences and fluid recycling

The results in this work show the influence of long-term operation on the decomposition of working fluids in eight different power plants (both heat-led and electricity-led) in a range of 900 kWel to 2 MWel. All case study plants are using Octamethyltrisiloxane (MDM) as a working fluid. The case study plants are between six to 12 years old. On one system detailed analyses, including the fluid distribution throughout the cycle, have been conducted. All fluid samples have been analysed via Head Space Gas Chromatography Mass Spectrometry (HS-GC-MS). Besides the siloxane composition, the influence of contaminants such as mineral oil based lubricants (and its components) has been examined. In most cases the original main working fluid has degraded to fractions of siloxanes with a lower boiling point (low-boilers) and fractions with a higher boiling point (high-boilers). As a consequence of the analyses, a new fluid management system has been designed and tested in one case study plant (case study number 8). The measures include fluid separation, cleansing and recycling. Pre-post comparisons of fluid samples have proved the effectiveness of the methods. The results show that the recovery of used working fluid offers an alternative to the purchase of fresh fluid, since operating costs can be significantly reduced. For large facilities the prices for new fluid range from e15 per litre (in 2006) to e22 per litre (in 2013), which is a large reinvestment, especially in the light of filling volumes of 4000 litres to 7000 litres per cycle. With the above mentioned method a price of e8 per litre of recovered MDM can be achieved

Assessment of the photovoltaic potential at urban level based on 3D city models: A case study and new methodological approach

The use of 3D city models combined with simulation functionalities allows to quantify energy demand and renewable generation for a very large set of buildings. The scope of this paper is to determine the solar photovoltaic potential at an urban and regional scale using CityGML geometry descriptions of every building. An innovative urban simulation platform is used to calculate the PV potential of the Ludwigsburg County in south-west Germany, in which every building was simulated by using 3D city models. Both technical and economic potential (considering roof area and insolation thresholds) are investigated, as well as two different PV efficiency scenarios. In this way, it was possible to determine the fraction of the electricity demand that can be covered in each municipality and the whole region, deciding the best strategy, the profitability of the investments and determining optimal locations. Additionally, another important contribution is a literature review regarding the different methods of PV potential estimation and the available roof area reduction coefficients. An economic analysis and emission assessment has also been developed. The results of the study show that it is possible to achieve high annual rates of covered electricity demand in several municipalities for some of the considered scenarios, reaching even more than 100% in some cases. The use of all available roof space (technical potential) could cover 77% of the region’s electricity consumption and 56% as an economic potential with only high irradiance roofs considered. The proposed methodological approach should contribute valuably in helping policy-making processes and communicating the advantages of distributed generation and PV systems in buildings to regulators, researchers and the general public

Energy and Economic Performance of Solar Cooling Systems World Wide

AbstractSolar thermal cooling systems have been installed as pilot projects in most regions of the world, but due to the low number of total installations there is not yet much experience available about system sizing and design. To counter the lack of experience and to evaluate the potential of energy efficient solar cooling systems, a systematic system design study has been carried out covering most climatic regions worldwide. For each technology investigated, an energy optimized control strategy was developed which maximizes the primary energy efficiency. This control strategy was implemented in the simulation environment INSEL and system models were developed for a range of thermal cooling technologies and validated with operating experiences from different plants monitored by the authors.It could be shown that a reduction of nominal chiller power by 30% to 40% or more hardly effects the solar cooling fraction for most climates, but significantly increases the machine operating hours and thus improves the economics. The lower the nominal power of the chiller, the higher the recommended ratio of collector surface area per kW. For a given machine nominal power, solar cooling fractions increase with collector surface area until saturation is reached. Collector surface areas can be as high as 5 m2 to 10 m2 per kW with still increasing solar cooling fractions, but acceptable specific collector yield reduction. The economic optimum is reached for less solar cooling fraction and thus lower primary energy savings. Single effect absorption cooling systems easily reach 80% solar cooling fraction for all but very humid climates. Primary energy ratios can be over 3.0, depending on system design and cooling load data. CO2 and primary energy savings of 30 – 79% are achievable.The economic study showed that solar thermal cooling is more viable in hot climates than in moderate European climates. Annual costs strongly depend on the locations. The specific costs per kWh cooling in German locations vary between 0.25 and 1.01 €/kWh, in Spanish locations between 0.13 and 0.30 €/kWh. In hot climates like Jakarta and Riyadh the specific costs are as low as 0.09 to 0.15 €/kWh. Furthermore the maximum investment costs were calculated get a payback time of 10 years

Contributions of heat pumps to demand response: A case study of a plus-energy dwelling

- Premio ETSI al mejor artículo científico del Trimestre. Junio 2018. - Artículo subido a idUS con permiso de su primera autora (Laura Romero Rodríguez), que proporciona las versiones preprint y postprint.Demand Response programs are increasingly used in the electricity sector, since they allow consumers to play a significant role for balancing supply and demand by reducing or shifting their electricity consumption. For that purpose, incentives such as time-based rates have been proposed. The present study analyzes the potential benefits of operating the heat pump of a plus-energy dwelling which participates in a dynamic pricing market, benefitting from the thermal storage capacity of the building. The software TRNSYS 17 has been used to model the building and the supply system. A validation of the model was carried out by using available measurements of the dwelling. Three setpoint temperature scenarios have been considered for sixteen different strategies which depend on temperature and electricity price thresholds, with the aim of determining which alternatives could lead to significant savings while maintaining an acceptable thermal comfort. Several factors such as cost savings, heat pump consumption, ratio of self-consumption of the dwelling and use of the heat pump during peak hours were also evaluated in every case. The results show that dynamic price thresholds should be used instead of fixed price thresholds, which may cause low activations of the heat pump or overheat the building above the comfort limits. Cost savings up to 25% may be achieved by using optimal strategies, increasing the self-consumption ratio, having almost no influence on the thermal comfort and achieving significant peak reductions on the grid. The outcomes of this study show the importance of looking at the implications of such strategies on several criteria within a demand response framework.Ministerio de Economía y CompetitividadUniversidad de Sevilla. V Plan Propio de Investigación (VPPI-US)Unión Europea. Horizon2020. Grant agreement No. 69596

Auf dem Weg zum nachhaltigen Stadtviertel

Wie die nachhaltige Stadt der Zukunft aussehen könnte, zeigt der Stadtteil „Scharnhauser Park“ in Ostfildern bei Stuttgart. In diesem Quartier versuchen Wissenschaftler und Investoren, einen ganzen Stadtteil so optimal wie möglich nach nachhaltigen Gesichtspunkten zu gestalten

Solar Decathlon Europe 2010

ABSTRACT: The Solar Decathlon Europe is an international competition for universities from all over the world to design and build a self-sufficient home, gridconnected, using solar energy as the only energy source and equipped with technologies that permit maximum energy efficiency. An interdisciplinary team of architects, interior architects, structural engineers and building physicians at the Hochschule für Technik Stuttgart accepted the challenge and is working on the design of the building since October 2008. The basic idea of our design is to use traditional means of dealing with the climate in hot and arid zones and to combine them with new technologies. Thermal mass, sun shading and evaporative cooling will help to achieve a comfortable indoor climate with passive means. The key element of our passive cooling concept is a new building component that we call "energy tower", which is also an important feature of the interior design. In addition night cooling via sky radiation and evaporation is used to discharge PCM material. Active cooling is supplied by a reversible heat pump powered by photovoltaics

Setting intelligent city tiling strategies for urban shading simulations

Assessing accurately the solar potential of all building surfaces in cities, including shading and multiple reflections between buildings, is essential for urban energy modelling. However, since the number of surface interactions and radiation exchanges increase exponentially with the scale of the district, innovative computational strategies are needed, some of which will be introduced in the present work. They should hold the best compromise between result accuracy and computational efficiency, i.e. computational time and memory requirements. In this study, different approaches that may be used for the computation of urban solar irradiance in large areas are presented. Two concrete urban case studies of different densities have been used to compare and evaluate three different methods: the Perez Sky model, the Simplified Radiosity Algorithm and a new scene tiling method implemented in our urban simulation platform SimStadt, used for feasible estimations on a large scale. To quantify the influence of shading, the new concept of Urban Shading Ratio has been introduced and used for this evaluation process. In high density urban areas, this index may reach 60% for facades and 25% for roofs. Tiles of 500 m width and 200 m overlap are a minimum requirement in this case to compute solar irradiance with an acceptable accuracy. In medium density areas, tiles of 300 m width and 100 m overlap meet perfectly the accuracy requirements. In addition, the solar potential for various solar energy thresholds as well as the monthly variation of the Urban Shading Ratio have been quantified for both case studies, distinguishing between roofs and facades of different orientations