Assessing Steady-State, Multivariate Experimental Data Using Gaussian Processes: The GPExp Open-Source Library

Experimental data are subject to different sources of disturbance and errors, whose importance should be assessed. The level of noise, the presence of outliers or a measure of the “explainability” of the key variables with respect to the externally-imposed operating condition are important indicators, but are not straightforward to obtain, especially if the data are sparse and multivariate. This paper proposes a methodology and a suite of tools implementing Gaussian processes for quality assessment of steady-state experimental data. The aim of the proposed tool is to: (1) provide a smooth (de-noised) multivariate operating map of the measured variable with respect to the inputs; (2) determine which inputs are relevant to predict a selected output; (3) provide a sensitivity analysis of the measured variables with respect to the inputs; (4) provide a measure of the accuracy (confidence intervals) for the prediction of the data; (5) detect the observations that are likely to be outliers. We show that Gaussian processes regression provides insightful numerical indicators for these purposes and that the obtained performance is higher or comparable to alternative modeling techniques. Finally, the datasets and tools developed in this work are provided within the GPExp open-source package

Technological and Economical Survey of Organic Rankine Cycle Systems

peer reviewedThis paper presents an overview of current R&D in the field of small and middle scale Organic Rankine Cycles (ORC’s). Major ORC’s applications are described and their technical and economical maturity is analyzed. The paper also emphasizes the selection criteria for the expander and for the working fluid

Assessing the Quality of Experimental Data with Gaussian Processes: Example with an Injection Scroll Compressor

This paper describes an experimental study carried out on a refrigeration scroll compressor with and without vapour injection. The test rig designed for that purposed allows evaluating the performance over a wide range of operating conditions, by varying the supply pressure, the injection pressure, the exhaust pressure, the supply superheating and the injection superheating. 97 Steady-state points are measured, with a maximum isentropic efficiency of 64.1% and a maximum consumed electrical power of 13.1 kW. A critical analysis of the experimental results is then carried out to evaluate the quality of the data using a machine learning method. This method based on Gaussian Processes regression, is used to build a statistical operating map of the compressor as a function of the different inputs. This statistical operating map can then be compared to the experimental data points to evaluate their accuracy

Mathematical modeling of thermal effectiveness of a ternary combined cycle plant

The urgency of this work is determined by the intensification of the role of steam-gas technologies (combined cycle technologies) in the field of power engineering in Russia and throughout the world. Developed mathematical model of ternary combined cycle plants, which is based on balance method includes system of mass balance and energy balance equations for ternary combined cycle plants and its units, equations of steam expansion in turbine and working fluids thermodynamic properties. On the basis of a model was carried out the analysis of the impact of the structure and thermodynamic parameters on thermal effectiveness of heat-recovery ternary combined cycle plants which cycle is the combination of three working substance cycles, one of which is low-boiling substance. The analysis of the thermal effectiveness of ternary combined cycle plants was made by means of the small-deflection method. The optimal parameters of operating environment and structure of a ternary combined cycle plants were determined

Technologies for heating, cooling and powering rural health facilities in sub-Saharan Africa

This paper examines technical and economic choices for rural electrification in Africa and presents the rationale for trigeneration (capability for electricity, heating, and cooling) in health and education applications. An archetypal load profile for a rural health clinic (25 kWhe/day and 118–139 kWht) is described, and a regional analysis is performed for sub-Saharan Africa by aggregating NASA meteorological data (insolation, temperature, and heating and cooling degree-days) using correlates to latitude. As a baseline for comparison, the technical, economic (using discounted cash flow) and environmental aspects of traditional electrification approaches, namely photovoltaic (PV) systems and diesel generators, are quantified, and options for meeting heating and cooling loads (e.g. gas-fired heaters, absorption chillers, or solar water heaters) are evaluated alongside an emerging micro-concentrating solar power ( -CSP) technology featuring a solar thermal organic Rankine cycle (ORC). Photovoltaics hybridized with LPG/Propane and -CSP trigeneration are the lowest cost alternatives for satisfying important but often overlooked thermal requirements, with cost advantages for CSP depending on latitudinal variation in insolation and thermal parameters. For a 15-year project lifetime, the net present cost for meeting clinic energy needs varied from 45 to 75 k USD, with specific levelized electricity costs of 0.26–0.31 USD/kWh. In comparison, diesel generation of electricity is both costly (>1 USD/kWh) and polluting (94 tons CO2 per site over 15 years), while LPG/Propane based heating and cooling emits 160–400 tons CO2 depending on ambient conditions. The comparative analysis of available technologies indicates that where the energy demand includes a mixture of electrical and thermal loads, as in typical health and education outposts, on-carbon emitting -CSP trigeneration approaches can be cost-effective

Development of a waste heat recovery orc prototype using an oil-free scroll expander

The world is facing a historical increase in energy demand and energy consumption. As consequence the conventional fossil fuels are depleting faster with an inherent pollution causing severe damages to our environment. Renewable energy sources are considered as a solution to both environmental issue and energy demand. At the same time a lot of waste heat is witnessed in processes in industries. Our objective is to contribute to the development of ORC systems, that appear to us as a good solution to recover this wasted heat. In such waste heat applications, depending on the heat source flow rate and temperature, electrical power output can be as low as a few kilowatts. In this power range, there is no cost effective expansion machine available on the market. On existing prototypes, expansion devices are usually retrofitted volumetric compressors originally designed for refrigeration or air compression applications. Air compressors have the advantage to handle higher inlet temperature but tightness is often an issue in ORC application since the fluids used have a non negligible environmental impact. This paper presents the development of a small-scale WHR ORC unit at the Thermodynamic Laboratory of the University of Liège: the prototype uses a scroll expander, plate heat exchangers, a diaphragm piston pump and a liquid receiver. This system was tested with different working fluids (R123, R245fa and HFE7000) and a thermal efficiency close to 8% was obtained for a net output power of about 2 kWe. The specificity of the proposed prototype is the absence of lubrication: in order to avoid oil circulation in the ORC loop, an oil-free scroll expander is developed. This expander is originally an air scroll compressor that was modified using a magnetic coupling to ensure tightness. The experimental results highlight the good efficiency of the device, despite a relatively high internal leakage due to absence of lubrication. The necessity of using magnetic coupling is also justified by comparing the experimental results with previous ones obtained using mechanical sealing

Importance of the reconciliation method to handle experimental data in refrigeration and power cycle: application to a reversible heat pump/organic Rankine cycle unit integrated in a positive energy building

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

Stimulant effects of ethanol in adolescent Swiss mice: development of sensitization and consequences in adulthood

The adolescent period is characterized by behavioral and neurobiological changes, which might predispose adolescents to the long-term negative consequences of alcohol. For example, enhanced risks of alcohol dependence are reported when drinking is initiated early. In the present studies, we used Swiss female mice to test whether chronic ethanol injections during adolescence durably affect the sensitivity to the stimulant effects of ethanol in adulthood. In a first set of experiments, several groups of young (28 day-old) mice were daily injected with various ethanol doses (1.5 – 4 g/kg) to test for ethanol sensitization during adolescence in comparison to adult mice exposed to the same schedule of ethanol injections. The results show that young mice express much higher stimulant effects after acute ethanol injections. However, they also require higher ethanol doses than adult mice to develop a sensitization to the stimulant effects of ethanol. In a second set of experiments, 28 day-old mice were sensitized to ethanol for 14 days with high ethanol doses (2.5 or 4 g/kg) and then tested for the stimulant effects of ethanol and the development of ethanol sensitization in adulthood. The results of this second set of experiments show that mice sensitized to ethanol during their adolescence remain more sensitive to the acute stimulant effects of ethanol in adulthood, especially when high ethanol doses were administered. However, the rate of the development of a sensitization to this effect was only slightly affected relative to adult mice exposed to a chronic ethanol regimen for the first time. Together, these results indicate that adolescent mice are more sensitive to the stimulant effects of ethanol but require higher ethanol doses to develop a sensitization. However, when a sensitization develops during adolescence, these mice still experience higher ethanol stimulant effects when tested in adulthood.Peer reviewe

Dispa-SET 2.0: unit commitment and power dispatch model

Most analyses of the future European energy system conclude that in order to achieve energy and climate change policy goals it will be necessary to ramp up the use of renewable energy sources. The stochastic nature of those energies, together with other sources of short- and long-term uncertainty, already have significant impacts in current energy systems operation and planning, and it is expected that future energy systems will be forced to become increasingly flexible in order to cope with these challenges. Therefore, policy makers need to consider issues such as the effects of intermittent energy sources on the reliability and adequacy of the energy system, the impacts of rules governing the curtailment or storage of energy, or how much backup dispatchable capacity may be required to guarantee that energy demand is safely met. Many of these questions are typically addressed by detailed models of the electric power sector with a high level of technological and temporal resolution. This report describes one of such models developed by the JRC's Institute for Energy and Transport: Dispa-SET 2.0, a unit commitment and dispatch model of the European power system aimed at representing with a high level of detail the short-term operation of large-scale power systems. The new model is an updated version of Dispa-SET 1.0, in use at the JRC since 2009.JRC.F.6-Energy Technology Policy Outloo