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

Keynote Lecture: Energy sufficiency - the missing lever to tackle the energy transition

According to the last IPCC WG3 AR6 report, the world is currently not on track to meet neither the 1.5°C nor the 2°C climate targets. Decarbonization of our energy systems must happen at a faster pace and all levers are important to achieve this. Possible levers include (1) the transition to clean energy sources to reduce the carbon intensity, (2) energy efficiency measures to reduce the energy intensity, and (3) the increase in energy sufficiency to reduce the overall consumption per capita. While the two first aspects are the object of an abundant literature, much work remains to be done on the definition of credible scenarios considering energy sufficiency. This mini-keynote presents an energy sufficient scenario for Europe, allowing to reach net zero emissions by 2050 without the recourse to uncertain technologies such as CCS or non-sustainable technologies such as nuclear

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

Experimental investigation of a Scroll unit used as a compressor and as an expander in a Heat Pump/ORC reversible unit

This paper presents an innovative system comprising a heat pump connected to a solar roof and a geothermal heat exchanger. This heat pump is able to invert its cycle and operate as an ORC. By using the whole rooftop (hereunder called “absorber”) as a heat source, a large amount of heat is generated throughout the year. This heat is used in priority to cover the building annual heating needs, while the surplus heat (mainly during summer months) is utilized to generate electricity in the so-called HP/ORC module. The same module can be used in winter time as an efficient heat pump which radically simplifies the complexity of the total system compared to competitive products. The main advantage of the proposed technology is related to the reversibility of scroll machines, which have proven to operate efficiently both as a compressor and as an expander. This paper focuses on three aspects: design of the prototype, results from experiments and validation of models based on the experimental data. To size the unit, the expander and the different exchangers are modeled thanks to semi-empirical correlations calibrated on experimental data. The sizing of the prototype is based on yearly simulations with a simulation step of one hour. The algorithm optimizes the operating mode based on the domestic heat demand, the meteorological conditions and the available heat in the storage. This paper demonstrates the feasibility of such a prototype with promizing experimentally-achieved performance (4.1% overall efficiency in ORC mode and a COP of 4.2 in HP mode

Modeling and experimental investigation of an Organic Rankine Cycle using scroll expander for small scale solar applications

peer reviewedThis study aims at developing and optimizing an Organic Rankine Cycle (ORC) for a small scale, decentralized parabolic trough system. A numerical model the Organic Rankine Cycle is developed and an experimental study is carried out on an ORC prototype working with refrigerant HCFC-123, and whose heat sources consist in two hot air flows. The ORC model is built by connecting different sub-models: the heat exchanger models, a volumetric pump model and a scroll expander model. Measured performances of the ORC prototype are presented and allow the validation of the ORC model

Optimization of Biomass-Fuelled Combined Cooling, Heating and Power (CCHP) Systems Integrated with Subcritical or Transcritical Organic Rankine Cycles (ORCs)

This work is focused on the thermodynamic optimization of Organic Rankine Cycles (ORCs), coupled with absorption or adsorption cooling units, for combined cooling heating and power (CCHP) generation from biomass combustion. Results were obtained by modelling with the main aim of providing optimization guidelines for the operating conditions of these types of systems, specifically the subcritical or transcritical ORC, when integrated in a CCHP system to supply typical heating and cooling demands in the tertiary sector. The thermodynamic approach was complemented, to avoid its possible limitations, by the technological constraints of the expander, the heat exchangers and the pump of the ORC. The working fluids considered are: n-pentane, n-heptane, octamethyltrisiloxane, toluene and dodecamethylcyclohexasiloxane. In addition, the energy and environmental performance of the different optimal CCHP plants was investigated. The optimal plant from the energy and environmental point of view is the one integrated by a toluene recuperative ORC, although it is limited to a development with a turbine type expander. Also, the trigeneration plant could be developed in an energy and environmental efficient way with an n-pentane recuperative ORC and a volumetric type expander

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