George Kosmadakis
@demokritos.gr
INRASTES
National Centre for Scientific Research "Demokritos"
RESEARCH INTERESTS
Heat pumps, solar thermal, energy efficiency
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
George Kosmadakis
Elsevier BV
Diogo Cabral, George Kosmadakis, and Emmanouil Mathioulakis
Elsevier BV
Brida V. Mbuwir, Davy Geysen, George Kosmadakis, Marika Pilou, George Meramveliotakis, and Hermen Toersche
Elsevier BV
Dimitrios C. Rakopoulos, Constantine D. Rakopoulos, George M. Kosmadakis, and George C. Mavropoulos
Elsevier BV
George Kosmadakis, George Meramveliotakis, Panteleimon Bakalis, and Panagiotis Neofytou
Elsevier BV
Anastasios Skiadopoulos, George Kosmadakis, Steven Lecompte, Michel De Paepe, and Dimitrios Manolakos
Elsevier BV
Marika Pilou, George Kosmadakis, and George Meramveliotakis
MDPI AG
An integrated numerical model that describes the operation of a renewable-energy-based system for a building’s heating, cooling, and domestic hot water needs is described in this study. The examined energy system includes a vapor compression multi-source heat pump, PVT collectors, borehole thermal energy storage, and water tanks. Energy balance equations for the collectors and the tanks are coupled with correlations for the heat pump and the piping losses within a thermal network approach. The non-linear system of equations that arises is solved by employing in-house software developed in Python v. 3.7.3. The performance of the numerical tool is validated against measurements collected during the pilot operation of such a system installed in Athens (Greece) for two 5-day periods (summer and winter). It is shown that the proposed model can predict, both qualitatively and quantitatively, the building’s energy system performance, whereas limited deviations from the experimental findings are mostly observed when highly transient phenomena occur. The numerical tool is designed with flexibility in mind and can be easily adapted to accommodate additional energy-system configurations and operational modes. Thus, it can be utilized as a supporting decision tool for new energy systems’ designs and the optimization of existing ones.
Constantine D. Rakopoulos, Dimitrios C. Rakopoulos, George M. Kosmadakis, Theodoros C. Zannis, and Dimitrios C. Kyritsis
Elsevier BV
George M. Kosmadakis, Dimitrios C. Rakopoulos, and Constantine D. Rakopoulos
American Society of Civil Engineers (ASCE)
Anastasios Skiadopoulos, Christina Antonopoulou, Konstantinos Atsonios, Panagiotis Grammelis, Apostolos Gkountas, Panteleimon Bakalis, George Kosmadakis, and Dimitris Manolakos
ECOS 2023
: In this work, the annual performance of a solar thermal power system in Greece is numerically studied. The system consists of a field of Evacuated Tube Collectors and a Trilateral Flash Cycle engine. The main target of this study is to assess the potential of the Trilateral Flash Cycle, a promising higher efficiency alternative to the Organic Rankine Cycle, for solar energy exploitation. The effects of the solar irradiance, the temperature of the heat source, and the flashing efficiency on the total solar energy conversion efficiency are monitored. The economics of the system is preliminarily studied taking into account its scale and the anticipated annual power output. Simulations indicate that the combined Solar-Trilateral Flash Cycle system can achieve an average annual total solar energy conversion efficiency of 5%, outperforming a Solar-Organic Rankine Cycle system of similar architecture at the examined location. It is demonstrated that the efficiency of the Trilateral Flash Cycle engine is highly dependent on the quality of the Working Fluid at the onset of expansion, and the operating pressure ratio. Moreover, the Trilateral Flash Cycle can achieve a thermal efficiency of up to 11%. The Levelized Cost of Electricity of the power system is estimated to lie in the region of 0.26 - 0.32 €/kWh, based on its scale, indicating that it may be a competitive solution for solar energy exploitation.
George Kosmadakis and Panagiotis Neofytou
Elsevier BV
Marika Pilou, George Kosmadakis, George Meramveliotakis, and Achileas Krikas
Elsevier BV
George Meramveliotakis, George Kosmadakis, and Sotirios Karellas
F1000 Research Ltd
This work investigates a vapour injection scroll compressor integrated in a heat pump using the refrigerant R1234ze(E). The water-to-water heat pump was tested under a wide temperature range at the evaporator and condenser sides. The test results revealed that the performance is significantly reduced for lifts of over 30 K with the coefficient of performance being even below 2 and the maximum 2nd law efficiency was just 28%. In order to enlighten the reasons behind such significant compressor underperformance, a semi-empirical model has been extended to include vapour injection, and a new improved modelling approach for the suction pressure drop was developed and implemented considering both the turbulent and laminar inlet flow regimes. Once the accuracy of the developed semi-empirical model was verified, the model was then adjusted to account for the R1234ze(E) operation, by fine-tuning its parameters based on the test data. The main loss mechanism identified is the high suction pressure drop, due to the high friction factor, with the inlet refrigerant flow possibly being laminar instead of turbulent. This resulted in a significant reduction of the mass flow rate and volumetric efficiency, while the standard model for suction pressure drop was not able to capture this effect.
George Meramveliotakis, George Kosmadakis, and Sotirios Karellas
F1000 Research Ltd
The aim of this work is to evaluate three methodologies regarding semi-empirical scroll compressor modeling for different refrigerants and conduct a comparative analysis of their results and accuracy. The first step is to improve a semi-empirical model for scroll compressors based on established techniques, and further enhance the physical background of some of its sub-processes leading to more accurate predictions. Focus is then given on the compressor operation when changing the refrigerant, proposing three methods in total. The first method refers to the standard model, requiring an optimization process for the calibration of all the model parameters. The second method relies on a reference refrigerant, and also uses optimization procedures, but for the fine-tuning of a small subset of the parameters. The third method is more generalized, without the need of any optimization process for the parameters identification, when fluid change occurs, leading to a very fast approach. Το evaluate the accuracy and verify the applicability of each method also related to the necessary computational time, two scroll compressors each with three different refrigerants are considered (HFCs and HFOs and their blends). The model is evaluated with the available manufacturer data, using R134a as reference refrigerant. The results show that the first method predicts the key indicators with a very high accuracy, with the maximum discrepancy of 2.06%, 4.17% and 3.18 K for the mass flow rate, electric power and discharge temperature respectively. The accuracy of the other two methods is dropping, but within acceptable levels in most of the cases. Therefore, in cases that reduced accuracy can be accepted, the third method is preferred for compressor performance prediction when changing the refrigerant, which provides results at a small fraction of time compared with the other two methods, once the parameters are calibrated for a reference case.
Konstantinos X. Soulis, Dimitris Manolakos, Erika Ntavou, and George Kosmadakis
Elsevier BV
Chrysanthos Golonis, Anastasios Skiadopoulos, Dimitris Manolakos, and George Kosmadakis
Elsevier BV
Dimitrios C. Rakopoulos, Constantine D. Rakopoulos, Evangelos G. Giakoumis, and George M. Kosmadakis
American Society of Civil Engineers (ASCE)
AbstractThis work presents the development and use of a comprehensive, quasi-dimensional, two-zone combustion model aiming at predicting the combustion characteristics, performance, nitric oxide (N...
G.M. Kosmadakis, D.C. Rakopoulos, and C.D. Rakopoulos
Elsevier BV
Michael Papapetrou and George Kosmadakis
Elsevier
Sahand Hosouli, Diogo Cabral, João Gomes, George Kosmadakis, Emmanouil Mathioulakis, Hadi Mohammadi, Alexander Loris, and Adeel Naidoo
International Solar Energy Society