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See detailExperimental validation of heat transport modelling in district heating networks.
Sartor, Kevin ULiege

in Energy (in press)

District heating networks (DHN) are generally considered as a convenient, economic and environmental-friendly way to supply heat to a large amount of buildings. Some modelling methods are required to ... [more ▼]

District heating networks (DHN) are generally considered as a convenient, economic and environmental-friendly way to supply heat to a large amount of buildings. Some modelling methods are required to consider the dynamic behaviour of district heating networks to design them correctly, spare the investment costs and limit the heat losses related to the use of a too high operating temperatures. For the same reasons, the DHN control or retrofit of installations also requires the assessment of the DHN dynamic behaviour. To achieve this, the heat transport in DHN, which is one of the key issues in the behaviour of a whole centralized heating system, has to be correctly modelled. Previous work evidenced current limitations of one dimensional finite volume method to model heat transport in pipes and proposed an alternative method considering the thermal losses and the inertia of the pipes. The present contribution intends to experimentally validate this model on a test rig available at the Thermodynamics laboratory of the University of Liège (ULg, Belgium) and on an existing district heating network. For both experimental facilities, the current model shows good agreement between the experimental data and the simulation results for a large range of water velocities. Moreover, it is shown that the thermal inertia of the pipe has a significant influence on the outlet pipe temperature profile. [less ▲]

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See detailModelling of organic Rankine cycle power systems in off-design conditions: an experimentally-validated comparative study
Dickes, Rémi ULiege; Dumont, Olivier ULiege; Daccord, Rémi et al

in Energy (2017), 123

Because of environmental issues and the depletion of fossil fuels, the world energy sector is undergoing many changes toward increased sustainability. Among the many fields of research and development ... [more ▼]

Because of environmental issues and the depletion of fossil fuels, the world energy sector is undergoing many changes toward increased sustainability. Among the many fields of research and development, power generation from low-grade heat sources is gaining interest and the organic Rankine cycle (ORC) is seen as one of the most promising technologies for such applications. In this paper, it is proposed to perform an experimentally-validated comparison of different modelling methods for the off-design simulation of ORC-based power systems. To this end, three types of modelling paradigms (namely a constant-efficiency method, a polynomial-based method and a semi-empirical method) are compared both in terms of their fitting and extrapolation capabilities. Post-processed measurements gathered on two experimental ORC facilities are used as reference for the models calibration and evaluation. The study is first applied at a component level (i.e. each component is analysed individually) and then extended to the characterization of the entire organic Rankine cycle power systems. Benefits and limi- tations of each modelling method are discussed. The results show that semi-empirical models are the most reliable for simulating the off-design working conditions of ORC systems, while constant-efficiency and polynomial-based models are both demonstrating lack of accuracy and/or robustness. [less ▲]

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See detailSteady-state and dynamic validation of a small scale waste heat recovery system using the ThermoCycle Modelica library
Desideri, Adriano ULiege; Hernandez, Andres; Gusev, Sergei et al

in Energy (2016), 115

The organic Rankine cycle (ORC) power system has been recognized as a promising technology for micro power applications. In this context, physics-based dynamic models can constitute a significant tool for ... [more ▼]

The organic Rankine cycle (ORC) power system has been recognized as a promising technology for micro power applications. In this context, physics-based dynamic models can constitute a significant tool for the further development of the technology, allowing to evaluate and optimize response times during transients, or to implement and test innovative control strategies. In this contribution, the dynamic model of an ORC power unit based on the ThermoCycle Modelica library is validated against steady-state and transient experimental results from an 11 kWel stationary ORC system. The simulation results are in good agreement with the measurements, both in steady-state and in transient conditions. The validated library is readily usable to investigate demanding dynamics-based problems for low capacity power systems. [less ▲]

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See detailExperimental comparison of organic fluids for low temperature ORC (organic Rankine cycle) systems for waste heat recovery applications
Desideri, Adriano ULiege; Gusev, Sergei; Van den Broek, Martijn et al

in Energy (2016), 97

This contribution experimentally evaluates and compares the performance of an ORC (organic Rankine cycle) system for stationary bottoming WHR (waste heat recovery) application operating with two different ... [more ▼]

This contribution experimentally evaluates and compares the performance of an ORC (organic Rankine cycle) system for stationary bottoming WHR (waste heat recovery) application operating with two different working fluids, SES36 and R245fa. The test rig is a regenerative cycle equipped with a single screw expander modified from a standard compressor characterized by a nominal shaft power of 11 kW. A total of 36 and 43 steady-state points are collected for SES36 and R245fa respectively, over a wide range of operating conditions by changing the expander rotational speed, the pump frequency and the cooling condenser flow rate. The performances of the ORC components are individually evaluated. A maximum expander isentropic efficiency of 60% is reached using SES36 at 3000 rpm, and a value of 52% is reached with R245fa at 3000 rpm. However, for a given pressure ratio the expander output power is higher with R245fa than with SES36. The overall performance of the ORC unit are investigated in terms of first and second law efficiencies and net output power for the two fluids. The results experimentally demonstrate the correlation between the working fluid critical temperature and the ORC unit working characteristics for low temperature waste heat recovery applications. Open experimental data are provided for both fluids. [less ▲]

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See detailAssessment of thermal comfort in existing pre-1945 residential building stock
Singh, M.K.; Attia, Shady ULiege; Mahapatra, Sadha et al

in Energy (2016), 98(March), 122-134

The building sector is the third-largest consumer of primary energy in Belgium. This is partly because of the high percentage of old buildings (buildings constructed before 1945) in its building stock ... [more ▼]

The building sector is the third-largest consumer of primary energy in Belgium. This is partly because of the high percentage of old buildings (buildings constructed before 1945) in its building stock. Existing international standards on thermal comfort focus primarily on new construction and commercial buildings but tend to overlook old buildings. This study involves a thermal comfort assessment of fully functional (in use) residential buildings constructed before 1945 in Liège (Belgium). The research methodology is based on continuous long term monitoring of the indoor environment (November 2011 to May 2012) and followed by comfort surveys for selected houses in the city. The analysis of the collected data shows that family composition, envelope performance and the occupants' interaction with the indoor environment greatly affected occupant preferences and functioning of the indoor thermal environment. This study reveals that the occupants' interaction with the indoor thermal environment to restore comfortable thermal conditions varies throughout the day, by adjusting the temperature in different rooms of the house at different times of the day. This study argues that modern comfort standards have failed to estimate the comfort level in these old buildings and, if applied, they would lead to under estimation of their thermal comfort. [less ▲]

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See detailUnveiling the mystery of Combined Heat & Power (cogeneration)
Verbruggen, Aviel; Dewallef, Pierre ULiege; Quoilin, Sylvain ULiege et al

in Energy (2013), 61

The article unveils the mystery of cogeneration. Cogeneration is an add-on or embedded activity in thermal power plants, with as merit the use of part or whole of their point source heat exhausts. EU's ... [more ▼]

The article unveils the mystery of cogeneration. Cogeneration is an add-on or embedded activity in thermal power plants, with as merit the use of part or whole of their point source heat exhausts. EU's talk of “high-efficiency cogeneration” is an unfounded transfer of responsibility from the hosting thermal power generation plant onto CHP (Combined Heat & Power) activity. The quality of a CHP activity is univocally defined by its design power-to-heat ratio σ, a tombstone parameter derived from the design characteristics of the power plant. A thermal power plant may house more than one cogeneration activity. Identifying σ requires positioning the bliss point in the electricity–heat production possibility set of the cogeneration activity. The bliss point is where after electric output is maximized, the sum of that output and the maximum recoverable quantity of heat occurs. Once CHP's mystery of virtual bliss points is unveiled, the proper σ are found. With known σ by CHP activity, the quantity of cogenerated electricity is reliably assessed as best indicator of cogeneration performance. Our analysis is applicable on all relevant thermal power cycles that host CHP activities, and illustrated with a numerical example. Our lean method is necessary and sufficient for proper CHP regulation. [less ▲]

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See detailExperimental study on an open-drive scroll expander integrated into an ORC (Organic Rankine Cycle) system with R245fa as working fluid
Declaye, Sébastien ULiege; Quoilin, Sylvain ULiege; Guillaume, Ludovic ULiege et al

in Energy (2013), 15

The present paper focuses on the experimental characterization of an open-drive scroll expander integrated into an Organic Rankine cycle using R245fa as working fluid. The expander is a commercially ... [more ▼]

The present paper focuses on the experimental characterization of an open-drive scroll expander integrated into an Organic Rankine cycle using R245fa as working fluid. The expander is a commercially available air compressor that was modified to operate in expander mode. The ORC (Organic Rankine Cycle) system is designed for a nominal heat input of 20 kW and a nominal net power output of 1.8 kW. A total of 74 steady-state operating points are measured to evaluate the expander performance over a wide range of conditions. The operating parameters that are varied include the inlet pressure (from 9 to 12 bar), outlet pressure (from 1.5 to 4 bar) and rotational speed (from 2000 to 3500 rpm). The maximum isentropic efficiency and shaft power are, respectively, 75.7% and 2.1 kW. A maximum cycle efficiency of 8.5% is reached for evaporating and condensing temperatures of 97.5 °C and 26.6 °C respectively. For most of the tests, hot water is produced in the condenser and the system therefore behaves as a CHP (combined heat and power). Depending on the water temperature requirement, a power to heat ratio varying between 1.9% and 11.8% is obtained. Water over 50 °C can be produced with a power to heat ratio higher than 8%. The experimental data points are then used to generate a performance map of the expander. This performance map allows for simulation of the use of such an expander in other ORC system [less ▲]

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See detailInfluence of fuel type, dilution and equivalence ratio on the emission reduction from the auto-ignition in an Homogeneous Charge Compression Ignition engine
Machrafi, Hatim ULiege; Cavadias, Simeon; Amouroux, Jacques

in Energy (2010), 35(4), 1829-1838

One technology that seems to be promising for automobile pollution reduction is the Homogeneous Charge Compression Ignition (HCCI). This technology still faces auto-ignition and emission-control problems ... [more ▼]

One technology that seems to be promising for automobile pollution reduction is the Homogeneous Charge Compression Ignition (HCCI). This technology still faces auto-ignition and emission-control problems. This paper focuses on the emission problem, since it is incumbent to realize engines that pollute less. For this purpose, this paper presents results concerning the measurement of the emissions of CO, NOx, CO2, O-2 and hydrocarbons. HCCI conditions are used, with equivalence ratios between 0.26 and 0.54, inlet temperatures of 70 degrees C and 120 degrees C and compression ratios of 10.2 and 13.5, with different fuel types: gasoline, gasoline surrogate, diesel, diesel surrogate and mixtures of n-heptane/toluene. The effect of dilution is considered for gasoline, while the effect of the equivalence ratio is considered for all the fuels. No significant amount of NOx has been measured. It appeared that the CO, O-2 and hydrocarbon emissions were reduced by decreasing the toluene content of the fuel and by decreasing the dilution. The opposite holds for CO2. The reduction of the hydrocarbon emission appears to compete with the reduction of the CO2 emission. Diesel seemed to produce less CO and hydrocarbons than gasoline when auto-ignited. An example of emission reduction control is presented in this paper. (C) 2010 Elsevier Ltd. All rights reserved. [less ▲]

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See detailEstablishing an efficient regulatory mechanism — Prerequisite for successful energy activities regulation
Banovac, Eraldo; Glavic, Mevludin ULiege; Tesnjak, Sejid

in Energy (2009), 34

An analytic approach to determine appropriate regulatory strategies for the energy sector is proposed in this paper.A basic model of the regulatory system in the energy sector is defined, and the ... [more ▼]

An analytic approach to determine appropriate regulatory strategies for the energy sector is proposed in this paper.A basic model of the regulatory system in the energy sector is defined, and the regulatory mechanism functions in this context are outlined. The basic problem of unknown factors (i.e., system entropy) is highlighted. An original algorithm developed to analyze regulatory background context and regulatory mechanism functions is discussed.A useful method for defining existing level of energy activities is also presented using the Croatian regulatory framework as an example. [less ▲]

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See detailComputer simulation of a bivalent heating installation
Nicolas, Jacques ULiege; Poncelet, Jean-Pol

in Energy (1986), 11(6), 551-562

A computer simulation program for a dwelling heating installation has been developed and tested. It uses principles and defined parameters, with simplifications to reduce the program size and execution ... [more ▼]

A computer simulation program for a dwelling heating installation has been developed and tested. It uses principles and defined parameters, with simplifications to reduce the program size and execution time. Integration of the differential equations describing the heat transfer in the system is performed with constant time steps (explicit scheme). The program is utilized to study the performance of the heating system and to perform parametric studies to determine the effects of changes in various parameters on performance. The influence of the time increment, thermal insulation, heat capacity and of other parameters on system performance has been analyzed. Included in the regulation software of a control system, the program is a design tool to optimize regulation and help in developing and testing modern regulators. [less ▲]

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