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Öğe Assessment of a novel defrost method for PV/T system assisted sustainable refrigeration system(Pergamon-Elsevier Science Ltd, 2022) Karaagac, Mehmet Onur; Ergun, Alper; Gurel, Ali Etem; Ceylan, Ilhan; Yildiz, GokhanEnergy consumption has continuously increased depending on the rapidly growing human population, enlarging economies, advancing technologies, and improving living standards. A noteworthy share of the energy consumption has been arising from the buildings all across the world. Refrigeration, heating, and air conditioning systems have accounted for a significant portion of the energy consumption in the buildings. Therefore, it is possible to both reduce energy consumption, and mitigate the carbon footprints by efficiently designing, constructing, and operating these systems. In this framework, the present research has centered on the refrigeration systems, and aimed to develop a novel defrost method for photovoltaic thermal (PV/T) assisted sustainable refrigeration systems. In the conventional refrigeration systems, the frost process occurs when air condenses on the evaporator surface as a result of the evaporator surface temperature being below the freezing point of water or the dew point temperature of the air in the conditioned space. Differently in the present work, PV/T system is used to prevent the frost process in the refrigeration system, unlike the conventional systems. Accordingly, the efficiency loss caused by the temperature increment will be prevented by cooling the PV module, and it is aimed to be more efficient by reducing the daily power consumption as an alternative solution method to the frost that occurred on the evaporator in refrigeration systems. On this purpose, a novel evaporator design is developed, and used for defrosting in this study. Accordingly, this novel design includes a refrigerant line inside the evaporator and a hot water line from the PV/T in this design. In the results, it is noticed that the system designed for winter conditions could be used for defrosting. While an average of 605 W for heat energy was used for each defrost process, the average defrost duration was recorded to be approximately 4 min. While the average electrical efficiency of the PV module was found to be 13.6%, the average total efficiency was found to be 38%. Besides, Average PV module surface temperature was determined as 36.4 degrees C, average water storage tank temperature was determined as 26.4 degrees C. In addition, the coefficient of performance (COP) of the refrigeration system is calculated to be 4.18. COP increased by an average of 9% during defrosting. Furthermore, the environmental economic cost was calculated to be 14.6 $/h. In the conclusion, it is proven that the novel defrost method proposed in the present work can be used for refrigeration systems, and contribute to both the reduction of energy consumption and mitigation of carbon emissions arising from the buildings.Öğe Current practices, potentials, challenges, future opportunities, environmental and economic assumptions for Turkiye's clean and sustainable energy policy: A comprehensive assessment(Elsevier, 2023) Agbulut, Umit; Yildiz, Gokhan; Bakir, Huseyin; Polat, Fikret; Bicen, Yunus; Ergun, Alper; Gurel, Ali EtemIn today's world, most countries including Turkiye have met their electricity demand at a dominant rate by burning fossil-based fuels in thermal power plants. However, fossil-fuel reserves have been rapidly depleted, resulting in high volatility in these fuels' markets, as well as alarming environmental, and economic problems for the governments. In recent years, many governments have started to face these problems and have rapidly transitioned to renewable and alternative carbon-free energy sources in their electricity production variety. However, these belated steps have failed to mitigate the increment in global greenhouse gas emissions against the rapid growth of population and energy demand. In recent years, Turkiye has put a noteworthy challenge to mitigate its dominant use of fossil fuels, reducing its energy dependence, sustaining its economic development, and mitigating the carbon footprint. From this point of view, it is witnessed that many power plants have been established, many of them are currently under construction, especially to produce more electricity in a sus-tainable way. Accordingly, the present study aims to comprehensively discuss Turkiye's energy production policy, energy potential and reserves, challenges, future opportunities, and the impacts of the energy sector on the economic and environmental issues for the country. In this framework, it is well-noticed that the country's future energy production policy has been reasonably changed in order to achieve positive economic and envi-ronmental outcomes in the medium and long term.Öğe A detailed analysis of CPV/T solar air heater system with thermal energy storage: A novel winter season application(Elsevier, 2021) Ceylan, Ilhan; Gurel, Ali Etem; Ergun, Alper; Ali, Ismail Hamad Guma; Agbulut, Umit; Yildiz, GokhanThe interest in solar energy is increasing day by day because it is clean and limitless. Concentrated photovoltaic and thermal systems (CPV/T) are one of the systems that use in the winter and the summer, attract great attention among solar energy systems. The main purpose of this research is to discuss the capacity of a CPV/T to simultaneously convert solar energy into electrical energy and thermal energy, especially in winter seasons. While only thermal energy is obtained in many concentrated air collectors (CAC) used in the literature, in this study, energy is stored with the help of phase change material (PCM). Ethyl alcohol and water blend were utilized as a working fluid and paraffin wax was also utilized as a PCM. In this study, system performance was handled by applying energy, exergy and environmental economic analyzes. In the results, the average solar radiation was concentrated from 536 W/m(2) to 737 W/m(2). The average overall thermal efficiency and PV module efficiency of the CPV/T were calculated as 73% and 15%, respectively. In other words, the overall system efficiency of the CPV/T was obtained as 88%. The average exergy efficiency of the CPV/T was calculated as 10%. Concerning the environmental aspect, 1.11 kg of CO2 emission per hour into the atmosphere could be prevented by using such a system. In the conclusions, the present paper has reported that the integration of a PCM and air collector into a CPV/T system provided higher energy efficiency in the winter season.Öğe THE EFFECT OF MALFUNCTIONS IN AIR HANDLING UNITS ON ENERGY AND EXERGY EFFICIENCY(Begell House Inc, 2020) Ceylan, Ilhan; Yildiz, Gokhan; Gurel, Ali Etem; Ergun, Alper; Tosun, AbdulkerimIn this study, the effects of malfunctions and problems occurring in the system components of air handling units, which are the main elements of the air conditioning system, on the energy consumption were investigated. Investigations were carried out in 10 air handling units located in 5 different shopping centers of Turkey. The malfunctions and problems that may occur in operation of air handling units were determined and the problems causing the decrease in the efficiency prescribed by the design characteristics were determined. For this purpose, rod-type anemometer measuring the airflow in the air handling unit ducts, propeller-type anemometer, and thermal camera were used to measure air tightness and heat losses in the body structure. Also, the tension control of the belt of the fan motors, which is one of the main components of the energy consumption unit, and the pollution control of the air filter have also been carried out. The flow rate of water circulating in air handling units was determined, and losses were detected by energy and exergy analyses with thermodynamic parameters for summer and winter periods. As a result of the calculations, it was determined that the energy efficiency of the air handling units in the cooling period was 63.7% and the exergy efficiency was 59.6%. The energy loss is 471 kW and the exergy loss is 27 kW in the cooling period. The energy loss is 957 kW and the exergy loss is 127 kW in the heating period. The energy efficiency and the exergy efficiency during the heating period was calculated to be 75% and 41.7%, respectively.Öğe Energetic, exergetic, and thermoeconomic analyses of different nanoparticles-added lubricants in a heat pump water heater(Elsevier, 2022) Yildiz, Gokhan; Agbulut, Umit; Gurel, Ali Etem; Ergun, Alper; Afzal, Asif; Saleel, C. AhamedThe heat pumps are frequently used in domestic and industrial applications for hot water supply. The present paper aims to thermodynamically investigate the impacts of the nanoparticle-addition into the lubricants on the energetic, exergetic, and thermoeconomic aspects of a heat pump. In the experiments, air to the water heat pump is separately charged with various metal oxide-based nanoparticles (Al2O3, CuO, and TiO2)-added oils at a constant mass fraction of 0.5%. Polyolester (POE) and 134a are used as a lubricant, and refrigerant, respectively. The mass flow rates of the water passed through the condenser are varied from 10 to 25 g/s with an interval of 5 g/s. In the results, it is observed that the thermal conductivity value noteworthy increases with the presence of nanoparticles in POE. The highest increment in thermal conductivity is found to be 39% for POE + CuO in comparison with that of pure POE. Furthermore, with nanoparticles addition, it is noticed that the COP value generally improves, and the highest improvement for COP value is noticed to be 8% for POE + TiO2 nanolubricant at the mass flow of 25 g/s. Furthermore, exergy efficiency enhances by 3.6%, 1.8%, and 4.5% for POE + Al2O3, POE + CuO, and POE + TiO2, respectively. The lowest heating cost is calculated to be 3.465 c/kWh at 20 g/s flow rate for POE + Al2O3. In conclusion, this paper clearly reports that usage of nanoparticles along with lubricants is presenting better energetic, exergetic, and thermoeconomic results rather than the usage of lubricant alone in the heat pumps.Öğe ENERGY, EXERGY, AND ENVIRONMENTAL (3E) ASSESSMENTS OF VARIOUS REFRIGERANTS IN THE REFRIGERATION SYSTEMS WITH INTERNAL HEAT EXCHANGER(Begell House Inc, 2020) Gurel, Ali Etem; Agbulut, Umit; Ergun, Alper; Yildiz, GokhanA comprehensive thermodynamic analysis of a refrigeration system with an internal heat exchanger was reported for four various refrigerants as an alternative to R134a. The preferred refrigerants in this paper have zero ozone-depleting potential and fairly low global warming potential value compared with reference R134a. These refrigerants are from both the HC group (R290 and R600a) and the HFO group (R1234yf and R1234ze(E)). Basically, the refrigeration system consists of a compressor, condenser, evaporator, expansion valve, and internal heat exchanger as well. Energy-exergy analyses and environmental impact assessments depending on the compressor energy consumptions are evaluated in the current study. The system performance was theoretically carried out at two different evaporation temperatures of 0 and -8 degrees C. Based on the obtained results from this study, the highest performance was achieved in R600a from HC group refrigerants and R1234ze(E) from HFO group refrigerants. As compared with R134a, in the COP value of R600a an increase of 3.2% at the evaporation temperature of 0 degrees C and 3.4% for the evaporation temperature of -8 degrees C was achieved. On the other hand, the COP value for R1234yf was decreased by 2% at the evaporation temperature of 0 degrees C and by 2.57% at the evaporation temperature of -8 degrees C. Considering the CO2 emissions, R600a was located at the first order in terms of the lowest CO2 emissions and R1234ze(E) follows R600a. In conclusion, R600a presented the highest performance compared with R134a in a refrigeration system with an internal heat exchanger.Öğe Exergetic, economic and environmental analysis of temperature controlled solar air heater system(Elsevier, 2022) Gurel, Ali Etem; Yildiz, Gokhan; Ergun, Alper; Ceylan, IlhanSolar energy systems are widely utilized to obtain environmentally friendly and sustainable electrical and thermal energy that able to be used in many applications. Temperature-controlled solar air heater (SAH) system with a zigzag finned plate and flat plate was designed, manufactured, and tested experimentally in this study. It was determined that the set temperature was 15% higher than the flat plate SAH outlet temperature. The most important cause for this increase, the air is exposed preheating in the first collector. As the heat transfer surface area raised thanks to the zigzag fins in the second collector, the temperature of the air increases even more. SAH system's energy efficiency was found to be 71.15% on average. SAH system's maximum exergy efficiency was determined as 3.7%. The SAH system's average exergy destruction is calculated to be 651.58 W on average. According to the enviroeconomic analysis of the system, hourly CO2 mitigation was found to be 1.04 kg CO2/h and the environmental cost was 1.508 cent/h. The energy cost was calculated as 0.0834 $/kWh, while the exergoeconomic parameter was calculated as 0.1931 kWh/$. In addition, the energy payback period was determined as 1.35 years, while the exergy payback period was determined as 45.9 years.Öğe Exergy, sustainability and performance analysis of ground source direct evaporative cooling system(Elsevier, 2022) Yildiz, Gokhan; Ergun, Alper; Gurel, Ali Etem; Ceylan, Ilhan; Agbulut, Umit; Eser, Servet; Afzal, AsifA significant portion of global energy consumption is due to energy consumption in the buildings. Heating, cooling, and air conditioning systems have the largest share in this energy consumption. Evaporative cooling systems, which have the advantage of being economical, zero pollution, and easy maintenance are preferred to reduce energy consumption in buildings. These systems are used in many areas such as greenhouses, broiler houses, and warehouses. In this study, analyzes of exergy, sustainability, and cooling efficiency in four different situations of a ground source direct evaporative cooling system were made. The system was studied in four different cases. While the highest exergy efficiency was obtained in case 3 with 20.83%, the exergy efficiencies in other cases were obtained as 16.83%, 17.49%, and 18.36%, respectively. In addition, the highest specific exergy loss was determined as 100.51 J/kg in case 2, while it was calculated as 73.08 J/ kg, 80.23 J/kg, and 73.05 J/kg for the other cases, respectively. It is seen that the sustainability values are in parallel with the exergy efficiency when the evaporative cooling system is examined for four different cases. The sustainability values were determined as 1.20 for case 1, 1.21 for case 2, 1.26 for case 3, and 1.22 for case 4. It is determined that the exergy efficiency gives precise information about the usability and sustainability of the system when these situations are evaluated. The exergetic improvement potential (EIP) was determined as 0.061 for case 1, 0.082 for case 2, 0.063 for case 3, and 0.059 for case 4, respectively. Although the highest exergy efficiency is obtained in case 3, it has a higher recovery potential than case 1 and case 4. In addition, cooling efficiencies for four different cases were obtained as 33.70%, 34.81%, 41.69%, and 36.95%, respectively. The temperature differences between the room and ambient temperatures were determined as 1.45 degrees C, 1.21 degrees C, 1.6 degrees C, and 1.48 degrees C for each case, respectively.Öğe A state of art review on estimation of solar radiation with various models(Cell Press, 2023) Gurel, Ali Etem; Agbulut, Umit; Bakir, Huseyin; Ergun, Alper; Yildiz, GokhanSolar radiation is free, and very useful input for most sectors such as heat, health, tourism, agriculture, and energy production, and it plays a critical role in the sustainability of biological, and chemical processes in nature. In this framework, the knowledge of solar radiation data or estimating it as accurately as possible is vital to get the maximum benefit from the sun. From this point of view, many sectors have revised their future investments/plans to enhance their profit margins for sustainable development according to the knowledge/estimation of solar radiation. This case has noteworthy attracted the attention of researchers for the estimation of solar radi-ation with low errors. Accordingly, it is noticed that various types of models have been contin-uously developed in the literature. The present review paper has mainly centered on the solar radiation works estimated by the empirical models, time series, artificial intelligence algorithms, and hybrid models. In general, these models have needed the atmospheric, geographic, climatic, and historical solar radiation data of a given region for the estimation of solar radiation. It is seen from the literature review that each model has its advantages and disadvantages in the estimation of solar radiation, and a model that gives the best results for one region may give the worst results for the other region. Furthermore, it is noticed that an input parameter that strongly improves the performance success of the models for a region may worsen the performance success of another region. In this direction, the estimation of solar radiation has been separately detailed in terms of empirical models, time series, artificial intelligence algorithms, and hybrid algorithms. Accord-ingly, the research gaps, challenges, and future directions for the estimation of solar radiation have been drawn in the present study. In the results, it is well-observed that the hybrid models have exhibited more accurate and reliable results in most studies due to their ability to merge between different models for the benefit of the advantages of each model, but the empirical models have come to the fore in terms of ease of use, and low computational costs.Öğe Thermodynamic analyses of a novel hybrid photovoltaic-thermal (PV/T) module assisted vapor compression refrigeration system(Elsevier, 2023) Yildiz, Gokhan; Gurel, Ali Etem; Ceylan, Ilhan; Ergun, Alper; Karaagac, Mehmet Onur; Agbulut, UmitBuildings have a respectable share of global energy consumption and it is well-known that refrigeration, heating and air conditioning systems have crucially contributed to this share. Therefore, even a small improvement in these systems has a noteworthy potential in globally saving energy. Accordingly, the performance of Photovoltaic-Thermal module-assisted vapor compression refrigeration system (PV/T-VCRS) has been handled in the present research. PV/TVCRS has been integrated with PV module, refrigeration system, and their hybrid. Additionally, different from the conventional superheating methods, superheating has been performed with a PV/T module in this work. In order to discuss the system performance, and observe the differences between conventional and modified hybrid systems, energy and exergy analyzes have been applied. In the results, the average PV module surface temperature in PV module and PV/T-VCRS is recorded to be 56.16 degrees C and 40.93 degrees C, respectively. This case leads to a direct increment in PV module electrical efficiency. Electrical efficiency, average electrical efficiency in PV module, and PV/T-VCRS are calculated to be 13.49% and 14.69%, respectively. The average COP values are found to be 5.23 for VCRS, and 5.68 for PV/T-VCRS. Total exergy destruction in VCRS and PV/TVCRS has been calculated to be 175.85 W and 443 W. On the other hand, the exergy efficiency is found to be 50.79% in VCRS and 60.73% in PV/T-VCRS. In the conclusion, it is well-noticed that hybrid PV/T-VCRS presented promising results in terms of electrical efficiency, COP, energy, and exergy analyses as compared to those of the conventional system.
