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See detailModel reduction for simulating the dynamic behavior of parabolic troughs and a thermocline energy storage in a micro-solar power unit
Dickes, Rémi ULg; Desideri, Adriano ULg; Lemort, Vincent ULg et al

in Proceedings of ECOS 2015 (2015, July)

Micro-scale concentrated solar power plants are characterized by strong transients and mostly operate in off-design working conditions. Both the sizing and the control of these systems are key challenges ... [more ▼]

Micro-scale concentrated solar power plants are characterized by strong transients and mostly operate in off-design working conditions. Both the sizing and the control of these systems are key challenges whose optimization requires powerful dynamic modeling tools. In this context, a system featuring a solar field of parabolic troughs, a thermocline thermal energy storage and a 5kWe organic Rankine cycle (ORC) power unit is modeled in the Modelica language. Model reduction methods applied to the solar field and the thermal storage are investigated and analyzed to improve the computational efficiency of the problem. Each model is described and integrated in the open-source ThermoCycle library. Results of simulation under identical operating conditions are compared and the benefits and limitations of model reduction are assessed. [less ▲]

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See detailSemi-empirical correlation to model heat losses along solar parabolic trough collectors
Dickes, Rémi ULg; Lemort, Vincent ULg; Quoilin, Sylvain ULg

in Proceedings of ECOS 2015 (2015, July)

Solar thermal power plants convert sunshine energy into useful heat and electricity by means of solar collectors and a thermodynamic cycle. Among the different solar collector technologies, parabolic ... [more ▼]

Solar thermal power plants convert sunshine energy into useful heat and electricity by means of solar collectors and a thermodynamic cycle. Among the different solar collector technologies, parabolic troughs are nowadays the most widespread together with solar towers. In order to improve the computation speed required to simulate the temperature profile along solar parabolic trough collectors, a correlation estimating the effective heat losses of the receiver is an essential tool. However, the relations found in the literature lack accuracy and do not translate effectively the effects of the operating conditions in all cases. In this work, an alternative correlation is proposed and calibrated with the results of a deterministic model. Better fitting performance is demonstrated when compared to the prediction of the pre-existing correlations. The benefits and limitations of the new correlation are finally assessed. [less ▲]

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See detailImportance of the reconciliation method to handle experimental data: application to a reversible heat pump / organic Rankine cycle unit integrated in a positive energy building
Dumont, Olivier ULg; Quoilin, Sylvain ULg; Lemort, Vincent ULg

Conference (2015, June)

Experimental data is often the result of long and costly experimentations. Many times, measurements are used directly without (or with few) analysis and treatment. This paper therefore presents a detailed ... [more ▼]

Experimental data is often the result of long and costly experimentations. Many times, measurements are used directly without (or with few) analysis and treatment. This paper therefore presents a detailed methodology to use steady-state measurements efficiently in the analysis of a thermodynamic cycle. The reconciliation method allows to correct each measurement as little as possible, taking its accuracy into account, in order to satisfy all constraints and to evaluate the most probable physical state. The reconciliation method should be used for multiple reasons. First, this method allows to close energy and mass balances exactly, which is needed for predictive models. Also, it allows determining some unknowns that are not or that cannot be measured precisely. Furthermore, it fully exploits the collected measurements with redundancy and it allows to know which sensor should be checked or replaced if necessary. An application of this method is presented in the case of a reversible HP/ORC unit. This unit is a modified heat pump which is able to work as an organic Rankine cycle by reversing its cycle. Combined with a passive house comprising a solar roof and a ground heat exchanger, it allows to get a plus energy house. In this study case, the oil mass fraction is not measured despite of its strong influence on the results. The reconciliation method allows to evaluate it. The efficiency of this method is proven by comparing the error on the outputs of steady-state models of compressor and exchangers. An example is given with the prediction of the pinch-point of an evaporator. In this case, the normalized root mean square deviation (NRMSD) is decreased from 14.3 % to 4.1 % when using the reconciliation method. This paper proves the efficiency of the method and also that the method should be considered more often when dealing with experimentation. [less ▲]

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See detailDynamic modeling of thermal systems using a semi-empirical approach and the ThermoCycle Modelica Library
Altés Buch, Queralt ULg; Dickes, Rémi ULg; Desideri, Adriano ULg et al

in Proceedings of the 28th International Conference on Efficiency, Costs, Optimization and Simulation of Energy Systems (2015, June)

This paper proposes an innovative approach for the dynamic modeling of heat exchangers without phase transitions. The proposed thermo-flow model is an alternative to the traditional 1D finite-volumes ... [more ▼]

This paper proposes an innovative approach for the dynamic modeling of heat exchangers without phase transitions. The proposed thermo-flow model is an alternative to the traditional 1D finite-volumes approach and relies on a lumped thermal mass approach to model transient responses. The heat transfer is modeled by the well-known Logarithmic Mean Temperature Difference approach, which is modified to ensure robustness during all possible transient conditions. The lumped parameter models are validated with references models and tested within a Concentrating Solar Power plant model. Results indicate that the developed lumped models are robust and computationally efficient, ensuring the convergence of the Newton Solver. They are significantly faster (~10-fold) than the traditional finite volume models, although a more extensive comparisons would be needed to confirm this figure. They are well suited to be integrated in larger system models, but are not appropriate for the simulation of detailed thermo-flow phenomena. [less ▲]

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See detailExperimental investigation of a reversible heat pump / organic Rankine cycle unit designed to be coupled with a passive house (Net Zero Energy Building)
Dumont, Olivier ULg; Quoilin, Sylvain ULg; Lemort, Vincent ULg

in International Journal of Refrigeration (2015), 54

This paper presents an innovative reversible Heat Pump/Organic Rankine Cycle (HP/ORC) experimental unit designed to be coupled to a Net Zero Energy Building (connected to a 120 m2 thermal solar roof and a ... [more ▼]

This paper presents an innovative reversible Heat Pump/Organic Rankine Cycle (HP/ORC) experimental unit designed to be coupled to a Net Zero Energy Building (connected to a 120 m2 thermal solar roof and a ground heat exchanger). The system can operate in three different modes: an ORC mode to produce electricity when a large amount of heat is collected by the solar roof, a direct heating mode using exclusively the solar roof, and a HP mode for space heating during cold weather conditions. This paper describes a comprehensive experimental campaign carried out on a prototype unit using a modified HVAC scroll compressor (4 kWe). From the results, the technical feasibility of the system is demonstrated. A cycle efficiency of 4.2% is achieved in ORC mode (with condensation and evaporation temperature respectively of 25 C and 88 C) and a COP of 3.1 is obtained in HP mode (with condensation and evaporation temperature respectively of 61 C and 21 C). [less ▲]

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See detailA generalized moving-boundary algorithm to predict the heat transfer rate of counterflow heat exchangers for any phase configuration
Bell, Ian; Quoilin, Sylvain ULg; Georges, Emeline ULg et al

in Applied Thermal Engineering (2015), 79

In this work, a novel and robust solution approach is presented that can be used to predict the steady-state thermal heat transfer rate for counterflow heat exchangers with any combination of single-phase ... [more ▼]

In this work, a novel and robust solution approach is presented that can be used to predict the steady-state thermal heat transfer rate for counterflow heat exchangers with any combination of single-phase and two-phase conditions within the heat exchanger. This methodology allows for multiple internal pinching points, as well as all permutations of subcooled liquid, two-phase and superheated vapor sections for the hot and cold fluids. A residual function based on the matching of the required and available thermal conductances in each section is derived, and Brent's method is then used to drive the residual to zero. Examples are presented for the application of this methodology to a water-heated n-Propane evaporator. The computational time required to execute the model for a simple case is on the order of one millisecond when the tabular interpolation methods of CoolProp are applied. Source code for the algorithm is provided in the Python programming language as an appendix. [less ▲]

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See detailOptimization of a vapor compression heat pump for satellite cooling
Bell, Ian; Lemort, Vincent ULg

in International Journal of Refrigeration (2015), 58

In recent years the heat fluxes that must be removed from aerospace electrical systems have been steadily increasing, motivating the use of vapor compression heat pumps to cool the electrical components ... [more ▼]

In recent years the heat fluxes that must be removed from aerospace electrical systems have been steadily increasing, motivating the use of vapor compression heat pumps to cool the electrical components.The heat pump system considered here is a conventional four component heat pump that uses an oil-free scroll compressor in place of the oil-lubricated compressor that is more often employed for terrestrial applications.The first part of this study considers the fluid selection, and refrigerant R152a is found to be a good choice. This study then delves into the detailed performance analysis of the oil-free scroll compressors that are envisaged to be used in this 12 kW system, with predicted COP over 4.0. Finally, the entire operating envelope of the heat pump system is considered, including variations in electrical load and seasonal variations in the radiative environmental temperature.The source code for the analysis presented here and that of PDSim are provided as supplemental information. [less ▲]

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See detailComparison of moving boundary and finite-volume heat exchanger models in Modelica language
Desideri, Adriano ULg; Dechesne, Bertrand ULg; Wronski, Jorrit et al

in 3rd International seminar on ORC power systems, Brussels 12-14 October 2015 (2015)

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See detailLessons Learned from Heat Balance Analysis for Holzkirchen Twin Houses Experiment
Masy, Gabrielle; Rehab, Imane ULg; Andre, Philippe ULg et al

in Energy Procedia (2015)

Holzkirchen full scale dynamic experiments were conducted in the framework of IEA Annex 58 research program with the aim to obtain and apply a high quality experimental dataset for model validation of ... [more ▼]

Holzkirchen full scale dynamic experiments were conducted in the framework of IEA Annex 58 research program with the aim to obtain and apply a high quality experimental dataset for model validation of full scale buildings. A first experiment was conducted in August 2013. Two identical houses were submitted to a side by side experiment, one with blinds up, one with blinds down. That first experience lasted 42 days including an initialization period, a Randomly Ordered Logarithmic Binary Sequence of heat inputs (ROLBS), and a re-initialization followed by a free-float period. A second experiment was conducted in April 2014 in one of the two houses, with higher levels of heating power in the South oriented zones and imposed indoor temperatures in the North oriented zones. Simulations were performed with EES Engineering Equation Solver using simplified RC dynamic models. The discrepancies observed between simulated results and measured data were first explained through a deeper analysis of thermal bridges, a better assessment of solar heat gains and a better assessment of the air duct heat losses. In the second experiment, the results revealed an underestimation of the building transmission heat losses. A candidate explanation might be the air stratification which would enhance heat losses on the ceiling side. A modelization of the upper and lower room air layers was introduced. The resulting simulated indoor temperature profiles were in accordance with the measurements. A complete breakdown of heat losses and heat gains was computed for both houses, using measured temperatures as input data for the simulation. [less ▲]

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See detailExplicit Multi Model Predictive Control of a Waste Heat Rankine Based System for Heavy Duty Trucks
Grelet, Vincent; Dufour, Pascal; Nadri, Madiha et al

in Proceedings of the 54th IEEE Conference on Decision and Control (2015)

This paper presents an explicit multi-model predictive controller (MMPC) for a waste heat recovery system (WHRS) mounted on a heavy duty truck engine. WHRS based on the Rankine cycle principle attracts a ... [more ▼]

This paper presents an explicit multi-model predictive controller (MMPC) for a waste heat recovery system (WHRS) mounted on a heavy duty truck engine. WHRS based on the Rankine cycle principle attracts a lot of interest in the heavy duty industry, over the past few years, to decrease the fuel consumption and reach the future pollutant emissions standards. Control issues have still to be faced before the integration of such a system into a vehicle. Model predictive controllers suits really well for our control purpose due to their ability to handle online optimal control problem. This paper focuses on the development of an explicit control law based on MMPC with aim to control the fluid temperature at the inlet of the expansion machine in order to increase the system performance and the reliability. [less ▲]

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See detailModelling, experimentation and simulation of a reversible HP/ORC unit to get a Positive Energy Building
Dumont, Olivier ULg; Carmo, carolina; Quoilin, Sylvain ULg et al

in ORC15 conference proceedings (2015)

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See detailExperimental performance of a piston expander in a smallscale organic Rankine cycle
Oudkerk, Jean-François ULg; Dickes, Rémi ULg; Dumont, Olivier ULg et al

in IOP Conf. Series: Materials Science and Engineering 90 (2015) (2015)

Volumetric expanders are suitable for more and more applications in the field of micro- and small-scale power system as waster heat recovery or solar energy. This paper present an experimental study ... [more ▼]

Volumetric expanders are suitable for more and more applications in the field of micro- and small-scale power system as waster heat recovery or solar energy. This paper present an experimental study carried out on a swatch-plate piston expander. The expander was integrated into an ORC test-bench using R245fa. The performances are evaluated in term of isentropic efficiency and filling factor. The maximum efficiency and power reached are respectively 53% and 2 kW. Inside cylinder pressure measurements allow to compute mechanical efficiency and drown P-V diagram. A semi-empirical simulation model is then proposed, calibrated and used to analyse the different sources of losses. [less ▲]

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See detailModeling and control of waste heat recovery Rankine based systems for heavy duty trucks
Grelet, Vincent; Dufour, Pascal; Nadri, Madiha et al

in Proceedings of the 9th International Symposium on Advanced Control of Chemical Processes (2015)

This paper presents a control oriented model development for waste heat recovery Rankine based control systems in heavy duty trucks. Waste heat recovery systems, such as Rankine cycle, are promising ... [more ▼]

This paper presents a control oriented model development for waste heat recovery Rankine based control systems in heavy duty trucks. Waste heat recovery systems, such as Rankine cycle, are promising solutions to improve the fuel efficiency of heavy duty engines. Due to the highly transient operating conditions, improving the control strategy of those systems is an important step to their integration into a vehicle. The system considered here is recovering heat from both EGR and exhaust in a serial arrangement and use a mixture of water and ethanol as working fluid. The paper focuses on a comparison of a classical PID controller which is the state of the art in the automotive industry and a nonlinear model based controller in a simulation environment. The nonlinear model based controller shows better performance than the PID one and ensures safe operation of the system. [less ▲]

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See detailWaste heat recovery rankine cycle based system modeling for heavy duty trucks fuel saving assessment
Grelet, Vincent; Lemort, Vincent ULg; Nadri, Madiha et al

in Proceedings of the 3rd ASME International Seminar on ORC Power Systems (ORC) (2015)

This paper presents a method to model heat exchangers used in waste heat recovery Rankine based systems in heavy duty trucks. The method is developed to predict both transfer and working fluid physical ... [more ▼]

This paper presents a method to model heat exchangers used in waste heat recovery Rankine based systems in heavy duty trucks. The method is developed to predict both transfer and working fluid physical properties such as temperature and density after the heat exchange process. Due to the flexibility of such a model, it can be used for a numerous quantity of fluids including water-alcohol mixture. A validation of the developed model is shown and compared to steady state and dynamic test results. The model shows good performance as well in terms of accuracy, which is in the range of 5K error as in computational time which is faster than real time and makes it suitable for concept optimization, control and fuel economy evaluation. [less ▲]

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See detailModel based control for waste heat recovery rankine cycle system in heavy duty trucks
Grelet, Vincent; Dufour, Pascal; Nadri, Madiha et al

in Proceedings of the 3rd ASME International Seminar on ORC Power Systems (ORC) (2015)

Driven by future emissions legislations and increase in fuel prices engine, gas heat recovering has recently attracted a lot of interest. In the past few years, a high number of studies have shown the ... [more ▼]

Driven by future emissions legislations and increase in fuel prices engine, gas heat recovering has recently attracted a lot of interest. In the past few years, a high number of studies have shown the interest of energy recovery Rankine based systems for heavy duty trucks engine compounding. Recent studies have brought a significant potential for such a system in a Heavy Duty (HD) vehicle, which can lead to a decrease in fuel consumption of about 5% [Wang et al. (2011)] and reduce engine emissions. But many challenges still need to be faced before the vehicle integration. This paper presents a control strategy development for waste heat recovery Rankine based systems in heavy duty trucks. Due to the highly transient operating conditions, improving the control strategy of those systems is an important step to their integration into a vehicle. It is shown here that moving to more advanced control strategies than classical PIDs lead to some gains in terms of performance. Due to the limited availability and high operational cost of test bench, the validation of such a controller is done on a representative and previously validated model. [less ▲]

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See detailDevelopment of a compact single room ventilation unit with heat recovery dedicated to tertiary buildings
Gendebien, Samuel ULg; Martens, Jonathan; Prieels, Luc et al

Conference (2015)

In the frame of the European project called Bricker, a new prototype of single room ventilation with heat recovery has been developed. This new unit is supposed to be installed in class rooms of an ... [more ▼]

In the frame of the European project called Bricker, a new prototype of single room ventilation with heat recovery has been developed. This new unit is supposed to be installed in class rooms of an educational institution. This paper deals with the development of the first prototype of this unit. An empirical model of such device is also proposed in order to be coupled with a building model. This aims at determining the seasonal performance of the device and thus the potential energy saving (compared to other technologies) resulting from its use. The first part of the paper presents the specifications and the final characteristics of the developed device. In this context, a by-pass for free cooling in summer conditions as well as the strategies under frosting conditions are described. Secondly, the coefficient of performance (COP) of such device is recalled. In the early stage of the development process, the COP is determined based on the manufacturer data of the heat recovery exchanger and the fans. The coupling between fan curve and the predicted hydraulic performance of the unit allows for determining a first approximation of the fans electrical consumption for several delivered flow rates. The third part of the paper focuses on the experimental investigations carried out in order to determine the flow rate really delivered by the unit. Electrical consumptions of several flow rates are also measured in order to characterize the COP of the unit in those conditions. Finally, a comparison between the measured and the predicted performance based on manufacturer data has been realized in terms of COP. A performance map based on experimental results is proposed in order to be coupled with a building model. [less ▲]

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See detailComparaison des performances de deux types de technologies pour obtenir un bâtiment à énergie positive : le système PAC/ORC réversible et une pompe à chaleur couplée avec des panneaux photovoltaïques.
Dumont, Olivier ULg; Lemort, Vincent ULg

Conference (2015)

Afin d’atteindre les objectifs 20-20-20 en 2020 ainsi que les objectifs européens à plus long terme, il est impératif de réduire drastiquement les émissions dues au secteur du bâtiment, qui compte pour ... [more ▼]

Afin d’atteindre les objectifs 20-20-20 en 2020 ainsi que les objectifs européens à plus long terme, il est impératif de réduire drastiquement les émissions dues au secteur du bâtiment, qui compte pour plus de 27% de la consommation finale d’énergie en Europe. Dans ce cadre, le développement des bâtiments à énergie positive est une voie prometteuse. Ce travail compare les performances annuelles de deux systèmes concurrents. D’une part, une solution classique, consistant en une maison passive couplée à une pompe à chaleur eau-eau et à des panneaux photovoltaïques (HP+PV). D’autre part, une maison passive avec un toit solaire thermique combinée à une unité pompe à chaleur / cycle organique de Rankine réversible (système PAC/ORC réversible). Cette unité modulable, étudiée et brevetée depuis 3 ans, permet trois modes de fonctionnement : le mode PAC pour les besoins en chaleurs en hiver, le mode ORC pour la génération d’électricité et un mode de chauffage direct, utilisant l’énergie thermique générée par le toit solaire pour les besoins en chaleur du bâtiment. Les deux systèmes sont dimensionnés pour une puissance de production électrique maximale de 6 kW. Les simulations dynamiques sont effectuées à l’aide du logiciel Dymola couplé à la librairie Modelica. Les modèles utilisés sont présentés dans la version complète de ce travail. La figure 1 compare la production électrique nette annuelle ainsi que les bénéfices de fonctionnement pour les deux systèmes étudiés et pour différents climats. Il s’avère que la solution HP+PV présente de meilleures performances tant au niveau production électrique nette qu’au niveau bénéfices de fonctionnement. Par contre, la consommation électrique de la pompe à chaleur est réduite grâce au mode chauffage direct dans le cas du système PAC/ORC réversible. [less ▲]

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See detailProceedings of the Ninth International Conference on System Simulation in Buildings - SSB 2014
Lemort, Vincent ULg; Randaxhe, François ULg

in System Simulation in Buildings (2015)

This 9th International Conference on System Simulation in Buildings has been the opportunity to gather researchers coming from 13 countries, sharing the last results of their research works. Some of the ... [more ▼]

This 9th International Conference on System Simulation in Buildings has been the opportunity to gather researchers coming from 13 countries, sharing the last results of their research works. Some of the presented works were conducted in the frame of projects from the International Energy Agency’s Energy in Buildings and Communities Programme (EBC). [less ▲]

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See detailImpact of net metering programs on optimal load management in US residential housing – a case study
Georges, Emeline ULg; Braun, J. E.; Groll, E. et al

in Proceedings of 9th International Conference on System Simulation in Buildings (2014, December 11)

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