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

Load modulation strategies of residential heat pumps for demand-response programs with different thermal storage options

This research work presents a methodology to assess the potential of load modulation strategies of HVAC systems for demand response programs at different scales. Two different demand response programs are considered: feed-in tariff signals for renewable production load matching and signals from the distribution grid operator for operational planning and congestion management at the distribution level. The resulting control problems are solved using optimal control formulations. First, the strategies are applied to four typical Belgian houses to match on-site PV production. Different thermal storage options are considered: on the one hand, thermal storage in the building envelope and in water tanks for domestic hot water, and, on the other hand, additional water tanks for space heating needs either in a parallel four-pipe or in a parallel two-pipe configuration. According to the type of house and the modulation strategy considered, a ranking of the most suitable storage option is proposed. Secondly, the method is extended to the scale of a distribution feeder with 50% PV penetration rate. Results show that with 20% heat pump penetration with suitable storage options, residual load reduction reach 28 to 73.4% with ADR#1 and 43.7 to 51.4% with ADR#2. ADR#1 outperforms ADR#2 for short modulation intervals, but can lead to up to 70% additional overconsumption if the chosen thermal storage option is not adapted to the house insulation level

Optimization Of A Heat Pump For Satellite Cooling

In recent years the heat fluxes that must be removed from terrestrial electrical systems have been steadily increasing. The same increase in electrical component heat flux can also be seen in satellite and aerospace applications. As a result, it has proven necessary to develop heat pump systems that can operate in low-gravity environments with high reliability and efficiency to cool electrical components in the satellite. It is currently common practice to use heat pipes to conduct the heat generated by the electrical components to the radiators of the satellite, but tomorrow\u27s electrical components will have heat fluxes high enough to make this system no longer feasible. The heat pump system considered here is a conventional four-component heat pump (compressor, condenser, expansion valve, evaporator) that uses an oil-free scroll compressor in place of the oil-lubricated compressor that is more often employed for terrestrial applications. There are a number of other unique features to this system, including the fact that all the heat rejection occurs through radiative heat transfer and the heat load is fixed (rather than being a function of source and sink temperatures). These unique features result in a system behavior that is quite different than conventional air-to-air heat pumps. The first part of this study considers the fluid selection, as choosing the best working fluid is critical for the overall performance and environmental safety of the system. This study then delves into the detailed performance analysis of the oil-free scroll compressors that are envisaged to be used in this system. Finally, the entire operating envelope of the heat pump system is considered, including failure cases as well as seasonal variations in the radiative environmental temperature

Field-test performance of Solid Oxide Fuel Cells (SOFC) for residential cogeneration applications

peer reviewedMuch needed energy transition brings special focus on fuel cell micro-combined Heat and Power (mCHP) systems for residential uses, one of which is a SOFC, fed by natural gas, designed to provide continuously 1.5 kWel (up to about 13 000 kWh yearly). However, this constant power output can be modulated as desired down to 500 Wel. With this machine, heat can also be recovered to partially contribute to the heat demand of the household. One main advantage of this appliance is that the heat recovery system is designed to be purely optional and it can be shut down, removed or added as wanted, even if the machine is running. The machine is driven and completely monitored by the manufacturer from distance. This study is monitoring two of those installations in residential houses in Belgium for the whole year 2021. It focuses on the comparison of the actual field test performance with the targets expected for this technology, electrical efficiency of 60% at nominal power output being the main selling argument that has been verified in the real onsite applications studied in this work. Since the financial incentive represents a major factor in the investor’s decision towards such a technological investment, focus is brought on an economic indicator based on an average Belgian household energy bill, with promising results of about 1,3-1,4 k€ of utilization cost savings per year. At last, ecological indicators are established in an attempt to foresee the place this mCHP technology in the energy transition challenge of today towards the carbon neutral future everyone should aim for. The ecological balances can either be considered as positive, if the system is supposed to replace Combined-Cycle Gas Turbine (CCGT) power plant electrical production, or negative, compared to the actual Belgian electrical mix.7. Affordable and clean energy11. Sustainable cities and communities13. Climate actio

Cooling Concepts for Residential Buildings: A Comparison Under Climate Change Scenarios

peer reviewedBuildings in the EU account for 40% of our energy consumption and 36% of our greenhouse gas emissions, with HVAC systems being the biggest contributors. With the predicted increase in global air temperature up to 4.8 K by the end of this century, cooling will be the most rapidly increasing energy-consuming technology in buildings. Heat pumps are one of the most energy-efficient heating and cooling systems. In this paper, the energy performance of three different cooling concepts including an air-to-air heat pump in a residential building is assessed with the impact of climate change on the heating and cooling energy demands under future climatic scenarios in Belgium. The paper presented the results obtained by simulating heating and cooling systems using DesignBuilder while taking into consideration the influence of climate change on the performance of the systems. This study used several weather data sets one forced by a reanalysis model on the past period (1980-2020) and three forced by Earth System Models (ESM) on past (1980-2014) and future periods (2015-2100). The paper also presented a performance comparison between passive cooling technologies such as natural ventilation and active cooling system such as split AC systems in Belgium. The Indoor Overheating Degree (IOhD) indicator is used to assess the thermal comfort and overheating discomfort in the building. The obtained results showed that the climate plays an important role in the final energy end-use for heating and cooling, the final heating energy end-use decreases by 40% while the final cooling energy end-use increases by 187% by the end of the century. The results also showed that the IOhD using passive cooling scenarios such as natural ventilation decreased by 77% in 2090s compared to the base case where there is only a mechanical ventilation system. While using an active cooling system such as a split AC system could maintain the thermal comfort almost all the time in the future weather scenarios. This paper is part of an ongoing study, the objective of the ongoing study, of which some results are presented in this paper, is to upscale the impact of climate change on the Belgian residential building stock and to evaluate its influence on the future heating and cooling energy demands.7. Affordable and clean energy11. Sustainable cities and communities13. Climate actio

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

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

Performance Evaluation of an Indirect Evaporative Cooler

peer reviewedNowadays, buildings are responsible for 40% of energy consumption in the European Union, according to the International Energy Agency (IEA). To reach the European objective aiming for CO2 neutrality of buildings, the IEA has developed the Energy in Buildings and Communities program (EBC), from which Annex 85 on Indirect Evaporative Cooling (IEC) is part of. This work contributes to assess the energy performance of indirect evaporative coolers in mixed-humid climates. A reference cooling system has been chosen as a base case to evaluate the performance of the IEC. The reference cooling system is composed of terminal units, a chiller, and a cooling tower as primary cooling system. In the upgraded cooling system, the cooling tower has been replaced by an indirect evaporative cooler. The latter is a modified version of the cooling tower that comprises an additional heat exchanger for air-pre-cooling. The energy consumption of both systems over a one-year period are then compared, including auxiliaries consumption. The possibility to perform free chilling has also been investigated. The models used to describe each system component are overviewed as well as their limitations. The annual energy consumption of the systems has been computed using three control methods: temperature control, flow rate control and optimized operation. While free chilling has a significant impact on the energy consumption (30% reduction), the IEC has a more moderate effect (up to 5% reduction). It is also shown that the advantage of the IEC over the cooling tower is directly dependent on the temperature difference between the dry bulb temperature and the dew point temperature

Theoretical and Experimental Analysis of Scroll Expander

In this article, both theoretical and experimental analysis on the performance of a new scroll expander will be presented and discussed. In order to investigate the performance of scroll expander, a detail mathematical modeling based on energy and mass balances is established. Radial and flank leakage, heat transfer between the working fluid, scroll wraps and plates, friction losses are considered in the mathematical modeling. Volume, temperature, pressure, mass flow of working chamber, friction loss power of moving parts, efficiency and power are investigated by solving the mathematical modeling. The experimental rig for scroll expander is set up. Results for various operational conditions are shown and discussed