Browsing by Author "Bilir, Levent"

Now showing 1 - 12 of 12

Citation - Scopus: 1
Analysis and design of an air to air heat exchanger used in energy recovery systems
(Erol Kurt, 2022) Helin Ülgen Elmacioǧlu; Irem Özsevgin; Cennet Kocabiyik; Nezir Yağız Çam; Levent Bilir; Elmacioǧlu, Helin Ülgen; Kocabiyik, Cennet; Özsevgin, Irem; Bilir, Levent; Čam, Nezir Yaǧiz
With the continuous worldwide energy use increase energy efficiency is gaining high importance. Consequently many methods have been investigated for potential energy savings. One of these methods is the use of heat recovery systems. These systems basically re-use waste heat and reduce energy consumption. Also they are increasingly used to reduce heating and cooling demands of buildings. Their main feature is to provide fresh air to the place which is heated by the exhaust air with the help of a heat exchanger (HEX) working between two different temperature sources. The most commonly used types of heat exchangers in ventilation systems are cross-flow and counter-flow heat exchangers. Cross-flow heat exchangers have a thermal efficiency in the range of 50-75% while counter-flow heat exchangers have 75-95%. Many studies have been carried out to increase the efficiency of this type of heat exchangers. In this study different designs of crossflow and counter-flow exchangers are compared using ANSYS Fluent software. The aim is to determine how the plate surface geometry affects heat transfer and pressure drop. It is aimed to find the optimum design with maximum efficiency high heat transfer and low pressure drop for heat exchangers. As a result it has been observed that thermal efficiency increased from 18% to 60% when changing from cross flow to counter flow in flat plate design while it increased from 25% to 77% in enhanced plate designs. For enhanced designs counter flow heat exchanger is 52% more efficient than cross flow heat exchanger. Also improvements to increase the surface area and turbulence in both flow types have increased heat transfer and thermal efficiency. © 2022 Elsevier B.V. All rights reserved.
Citation - WoS: 36
Citation - Scopus: 42
Cooling channel effect on photovoltaic panel energy generation
(PERGAMON-ELSEVIER SCIENCE LTD, 2021) Zeynep Ozcan; Miray Gulgun; Ecem Sen; Nezir Yagiz Cam; Levent Bilir; Gulgun, Miray; Sen, Ecem; Ozcan, Zeynep; Bilir, Levent; Cam, Nezir Yagiz
It is a well-known fact that even though the electricity generation is higher when the solar radiation is high on a photovoltaic panel its efficiency drops as its temperature increases. In this study it is intended to achieve cooling effect using an air duct placed under a photovoltaic panel thereby increase its efficiency. Hourly electricity generation PV efficiency and cell temperature values over a year are calculated using annual temperature and radiation data by using MATLAB and PV Sol software. Maximum cell temperature for the uncooled case is determined as 57.91 degrees C on July 21st at 1p.m. as a result of hourly calculations. The incident solar radiation is 976 W/m(2) when the panel reached its maximum temperature. The PV panel and cooling channel are modelled in ANSYS Fluent software and cooling effect was investigated for different air velocities and air-cooling channel geometries for the hour when maximum cell temperature is reached. Environmental analyses are also made. It is observed that with finned cooling channel it is possible to cool PV temperature more than with the flat cooling channel. Cooling the PV panel from its maximum cell temperature to 39.82 degrees C with 5 m/s air velocity and 82 fins cooling channel is achieved and new PV panel efficiency is recorded as 18.92 %. Environmentally considerations show that the use of solar energy provides the reduction of coal and natural gas-based CO2 emissions as 15 and 8 tons respectively.
Energy exergy and economic assessments of wind turbine alternatives
(INDERSCIENCE ENTERPRISES LTD, 2024) Nurdan Yildirim; Levent Bilir; Bilir, Levent; Yildirim, Nurdan
In this study two wind turbine installation alternatives for a residential district of 20 detached houses in six different European cities are considered. Firstly the installation of an individual residential scale (5 kW) wind turbine for each house is considered. Secondly the installation of a single wind turbine having the same total installed capacity (100 kW) is evaluated. The alternatives are compared according to annual energy production exergy efficiencies and simple payback time. The results pointed that the use of a single wind turbine is better that the use of individual residential scale wind turbines for small communities or districts.
Citation - WoS: 99
Citation - Scopus: 110
Evaluation of a hybrid system for a nearly zero energy greenhouse
(PERGAMON-ELSEVIER SCIENCE LTD, 2017) Nurdan Yildirim; Levent Bilir; Bilir, Levent; Yildirim, Nurdan
Greenhouses are widely used in the World especially in the Mediterranean climate to provide suitable environment in cultivation of different agricultural crops. Significant amount of energy is necessary to produce process and distribute these crops. Various systems including steam or hot water radiation system and hot air heater system are being used in greenhouse heating. A ground source heat pump system generally seen as a favorable option since it can provide both heating and cooling energy is considered for a greenhouse in this study. The aim of this study is to evaluate a renewable energy option for the required total energy need of a greenhouse. Grid connected solar photovoltaic panels are selected to assist a ground source heat pump and generate sufficient electrical energy for lighting. In this way a nearly zero energy greenhouse concept is foreseen for three different agricultural products: Monthly and annual heating cooling and lighting energy load of the greenhouse for these agricultural products were computed. The monthly average electricity generation of 66 photovoltaic panels which cover 50% of the southern face part of the asymmetric roof was calculated. Annual photovoltaic electricity generation was found as 21510.4 kWh. It was observed that photovoltaic electricity generation can meet 33.2-67.2% of greenhouse demand in summer operation months. Nevertheless the coverage ratio calculated by dividing the photovoltaic panels electricity generation to the electricity demand of the greenhouse (heating cooling and lighting) for each crop were very high in winter operation months. Yearly coverage ratio values were 95.7% for tomato 86.8% for cucumber and 104.5% for lettuce. These high coverage ratio values justify the nearly zero energy concept for the considered greenhouse. Economic and environmental evaluation of the considered system were also accomplished. A simple payback time of the crop cultivations was computed between 7.0 and 7.4 years. The energy payback time of the system was found to be 4.9 years and the greenhouse gas payback time value of 5.7 years and 2.6 years were calculated based on natural gas and coal based electricity generation respectively. (C) 2017 Elsevier Ltd. All rights reserved.
Citation - WoS: 6
Citation - Scopus: 7
Humidifying solar collector for improving the performance of direct solar desalination systems: A theoretical approach
(PERGAMON-ELSEVIER SCIENCE LTD, 2022) Harris J. N. Welepe; Huseyin Gunerhan; Levent Bilir; Bilir, Levent; Gunerhan, Huseyin; Welepe, Harris J. N.
In this paper a new type of solar collector named humidifying solar collector that is a solar collector with air humidification function is proposed. The particularity of this system compared to previous systems in the literature is that the quantity of liquid water present in the collector at each instant is equal to the quantity that will evaporate within the following unit time no longer greater. This minimizes the quantity of liquid water present in the collector at each instant and consequently allows to reach desired evaporation temperatures in shorter times and even under low solar irradiances and minimizes the thermal resistance between evaporation surface and absorber caused by water depth. Then a theoretical and comparative study by simulation using Engineering Equation Solver software between the performance of the humidifying solar collector-based solar still (proposed system) and that of the solar air heater-based humidification dehumidification solar desalination system (conventional system) is conducted. The performance parameters assessed are energy and exergy effi-ciencies dry air mass flow rate required and the maximum water mass flow rate that can evaporate in that air. The results reveal that in general case the proposed system is fundamentally more efficient than the conven-tional system. For instance for the sizes and heat transfer parameters chosen in this study the performance of the proposed system is 1.3-32.2 times higher than that of the conventional system, its freshwater productivity under incident solar irradiance of 900 W/m2 can reach 2.923 kg/h and can be further improved by optimizing the design of the humidifying solar collector.
Citation - WoS: 18
Citation - Scopus: 18
Modeling and performance analysis of a hybrid system for a residential application
(PERGAMON-ELSEVIER SCIENCE LTD, 2018) Levent Bilir; Nurdan Yildirim; Bilir, Levent; Yildirim, Nurdan
Hybrid systems which use more than one renewable energy sources are quite advantageous because they can eliminate or at least vitiate the interrupted characteristics of the renewable sources. In the present study a hybrid system which consists of a small scale wind turbine and photovoltaic panels was focused on. The system supplies the required electricity demand for a detached house with a 117 m(2) area in five different locations (Izmir Madrid Budapest Paris and Helsinki) according to European climate zones. A detailed dynamic hourly electricity generation analysis for the two components of the hybrid system was performed. As a result the coverage ratio of the hybrid system electricity generation for the total electricity demand of the house simple payback time and energy payback time of the system were calculated for each city. The results revealed that yearly electrical energy demand of the house can be entirely met by the evaluated hybrid system for each city. Maximum yearly coverage ratio of 176.6% was observed for Izmir Turkey while minimum coverage ratio was 103.1% for Helsinki Finland. The simple payback time and energy payback time of the hybrid system were determined in the range of 7-25.5 years and 4.6-6.8 years respectively. (C) 2018 Elsevier Ltd. All rights reserved.
Citation - WoS: 9
Citation - Scopus: 11
Modelling and analysis of heat pump integrated Photovoltaics-Wind systems for an agricultural greenhouse in Turkey
(Elsevier Ltd, 2024) Zeynep Özcan; Levent Bilir; Başar Ca̧ǧlar; Bilir, Levent; Caglar, Basar; Ozcan, Zeynep
This study focused on modelling and analysing photovoltaics and wind systems to meet the heating demand of a commercial greenhouse. The aim is to evaluate technical economic and environmental performances of the related systems and to determine the optimum configuration. A novel approach was introduced by integrating hybrid energy systems with large-scale wind turbines and developing a dynamic heat transfer model. A large commercial greenhouse with an area of 26640 m2 located in Izmir Turkey was selected for considering Mediterranean climate and a detailed heat transfer model of the greenhouse were developed considering heat transfers by convection radiation ventilation and infiltration. A combination of air source heat pumps photovoltaic panels and wind turbines were used for meeting the heating demand of the related greenhouse. Five different on-grid energy systems scenarios namely (i) Photovoltaics-Heat Pump (ii) Photovoltaics-Wind Turbine- Heat Pump (iii) Wind Turbine- Photovoltaics- Heat Pump (iv) Wind Turbine- Heat Pump and (v) only Heat Pump were considered. The system modelling with a detailed heat transfer analysis of the greenhouse was made by MATLAB. The energy analysis of the systems was performed on an hourly basis for one calendar year. The annual heating demand and the corresponding electricity consumption of the greenhouse were calculated as 497.37 and 114.07 kWh/m2 respectively. Net Present Value Levelized Cost of Energy and CO2 savings were used to evaluate economic and environmental performances of the systems. Among five on-grid energy system scenarios the first scenario consisting of 5271 photovoltaic panels and 20 heat pumps emerged as the most economically attractive choice with Net Present Value and Levelized Cost of Energy of $547440.40 and 0.080146 $/kWh respectively. Critical parameters affecting the economy of this scenario were found to be electricity prices tomato yield and photovoltaic panel prices. For environmental evaluation the fourth scenario integrating wind turbines and heat pumps achieves the highest CO2 savings of 2064.73 tons due to increased renewable electricity production and lower life-cycle CO2 emissions of wind turbines compared to photovoltaic systems. This analysis enhanced the understanding of energy dynamics in greenhouse environments contributing to the advancement of sustainable practices in agriculture. © 2024 Elsevier B.V. All rights reserved.
Citation - WoS: 33
Citation - Scopus: 39
Optimization of microalgae panel bioreactor thermal transmission property for building façade applications
(Elsevier Ltd, 2018) Emin Selahattin Umdu; Ilker Kahraman; Nurdan H. Yildirim; Levent Bilir; Umdu, Emin Selahattin; Yildirim, Nurdan; Bilir, Levent; Kahraman, İlker
Microalgae has great potential reducing embedded CO2 emissions of buildings through their entire life cycles by both increasing energy efficiency and actively capturing CO2. The use of closed microalgae photo bioreactors as building components has the added benefits of acting as an effective insulation system. Additionally microalgae can give a dynamic appearance with living dynamic system that also works as an adaptive sunshade. In this study the thermal transmittance (U value) of different photo bioreactors is determined by using experimental design methods for parametric studies. Heat transfer behaviour of the manufactured panel bioreactors at different operational conditions which satisfy both thermal comfort in building and microalgae growth conditions is evaluated. U values between 3.84 and 53.19 W/m2 K are observed in the study. Results show that there is a significant interaction between all main factors (reservoir air layer and reservoir wall thicknesses) and U value. Yet a two-way interaction is observed for only between reservoir and air layer thicknesses. Further air layer thickness has the highest contribution to the U value in the developed model as both a main and synergetic factor. © 2018 Elsevier B.V. All rights reserved.
Citation - WoS: 61
Citation - Scopus: 73
Performance investigation of a wind turbine–solar photovoltaic panels–fuel cell hybrid system installed at İncek region – Ankara Turkey
(Elsevier Ltd, 2016) Yilser G. Devrim; Levent Bilir; Bilir, Levent; Devrim, Yılser
Renewable energy use in the world increases year by year. However in many cases it is not possible to cover the electrical energy need of even a single house using only one renewable energy resource due to its intermittent nature. At this point hybrid systems are applied to overcome this problem. This study focuses on the combination of photovoltaic solar panels a small scale wind turbine an electrolyzer and a proton exchange membrane fuel cell hybrid system for electrical power generation for an average house of 150 m2 located at İncek region of Ankara Turkey. Solar and wind energies were used as primary sources and a proton exchange membrane fuel cell is used as the backup power. The hybrid system was modeled and the results indicate that the use of the selected wind turbine with a 3 kW capacity along with photovoltaic panels with 17.97 m2 area is sufficient to provide the required 5 h operation of the electrolyzer which in turn provides the necessary hydrogen and oxygen to the fuel cell. Since the daily energy needed by the investigated house was taken as 5 kW h the fuel cell with a net power output of 1 kW supplies all electrical demand with its 5 h operation. The outcomes show that the hybrid system is capable to provide all electrical need of the house all year round except November. The electrical energy production of the proposed system is considerably higher than the demand in many months and this surplus electricity can be used in order to support the cooling and heating system of the considered house. © 2017 Elsevier B.V. All rights reserved.
Citation - WoS: 24
Citation - Scopus: 30
Photovoltaic system assessment for a school building
(PERGAMON-ELSEVIER SCIENCE LTD, 2017) Levent Bilir; Nurdan Yildirim; Bilir, Levent; Yildirim, Nurdan
The installation of photovoltaic panels (PVs) on the roof of residential and commercial buildings is getting widespread as these areas stand normally idle and can be used for another purpose without losing an inhabited space. Considering the solar potential of Turkey a significant amount of electricity generation is possible using current PV technology. For this reason a two-story detached school building located in Izmir Turkey was taken into consideration and monthly as well as annual coverage ratio of an on-grid PV system for its entire energy requirement (including heating cooling and lighting) was investigated. The PVs were installed on the south face of the school building roof. A heat pump with a typical coefficient of performance (COP) value of 2.5 was used for supplying required cooling and heating. The heating cooling and lighting loads were determined on a monthly basis. The average monthly electrical energy generation of the mounted PVs was calculated using a written code in Energy Equation Solver (EES) software. As a result the monthly as well as yearly electrical energy demand coverage ratio values for the school using the installed PVs were revealed. Since the school building has a large south faced roof the installation of PVs is very suitable to meet the cumulative electrical energy need of the heat pump and the lighting load. For Case 1 180 PVs which supply the entire yearly demand (with a 110% coverage ratio) were taken into consideration while for Case 2 265 PVs which cover 75% of the roof area were evaluated. The results showed that between November and March PV electrical energy generation is not sufficient to meet all energy need of the school for both cases. However significant coverage ratio values were observed for the rest of the year. In a yearly basis the PV generation exceeded the building demand by 62% for the Case 2. This conclusion points out that the school can meet its yearly electricity need with the considered PV system and can even have an additional financial profit by selling its surplus PV electricity to the grid. Economic and environmental payback time values as well as simple payback time value were also computed for both investigated cases. The results pointed out a simple payback time of 7.9 years for Case 1 and 7.6 years for Case 2. Energy payback time was determined as 5 years for both systems. The greenhouse gas payback time of 2.7 years and 5.9 years was encountered for coal based and natural gas based calculations. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Citation - WoS: 2
Citation - Scopus: 3
THEORETICAL PERFORMANCE ASSESSMENT OF A PARABOLIC TROUGH HUMIDIFYING SOLAR COLLECTOR-BASED SOLAR STILL, PARABOLİK OLUKLU NEMLENDİRİCİ GÜNEŞ KOLLEKTÖRÜ BAZLI GÜNEŞ ENERJİLİ DESALİNASYON SİSTEMİNİN TEORİK PERFORMANS DEĞERLENDİRİLMESİ
(Turk Isi Bilimi ve Teknigi Dernegi, 2024) Harris J.N. Welepe; Huseyin Gunerhan; Levent Bilir; Bilir, Levent; Günerhan, Hüseyin; Welepe, Harris J.N.
In this paper a parabolic trough humidifying solar collector-based solar still (PHSC-SS) is proposed. Its purpose is to apply some important performance improvement techniques to the flat plate humidifying solar collector-based solar still (flat plate HSC-SS) to significantly improve overall system performance. These included the use of parabolic trough solar concentrators and the design of humidifying solar collectors from evacuated tube collectors. The results reveal that unlike flat plate HSC-SS which must operate with a turbulent airflow regime to achieve optimum overall performance PHSC-SS must operate with a laminar airflow regime and high inlet and outlet temperatures of air (at least 55 °C and less than 100 °C at atmospheric pressure) in the heat collector element. For 900 W/m2 of incident solar irradiance 2 m2 of solar collector area and 000042 kg/s of air flow rate the maximum energy efficiency exergy efficiency and daily freshwater productivity of PHSC-SS were found to be 6812% 1487% and 1697 kg/h respectively. Whereas for the same incident solar irradiance and solar collector area and 01 kg/s of air flow rate those of the flat plat HSC-SS were 729% 112% and between 107-2923 kg/h (for inlet and outlet temperatures of air less than 30 °C at atmospheric pressure) respectively. Although in some extreme cases freshwater productivity of flat plate HSC-SS can be higher than that of PHSC-SS it should be noted that laminar airflow regime confers great advantages to PHSC-SS. These are higher air temperatures at condenser inlet (which ease water condensation process) no need of an auxiliary cooling device (needed in the flat plate HSC-SS) less mechanical vibrations of system reduced condenser size and less energy consumed by air blowers. Furthermore the upper limit of the PHSC-SS is a PHSC-SS that operates without air flow but rather by vaporization of water droplets at boiling point from absorber followed by their suction to condenser similarly to a flash evaporation. © 2024 Elsevier B.V. All rights reserved.
Citation - WoS: 14
Citation - Scopus: 15
Thermal behavior of a solar-assisted latent heat thermal energy storage unit on the heating season under variable weather conditions
(ELSEVIER, 2022) Nezir Yagiz Cam; Ersin Alptekin; Levent Bilir; Mehmet Akif Ezan; Alptekin, Ersin; Bilir, Levent; Ezan, Mehmet Akif; Cam, Nezir Yagiz
Due to the fossil-fuel-related climatic problems which got worse in recent decades the worldwide share of renewable energy has significantly increased. Even though solar energy is one of the most accessible renewables it has an intermittent nature throughout the day. Different energy storage techniques are implemented to resolve the intermittency problem and make solar-aided energy accessible when it is needed. Energy use in buildings has a huge share of total energy demand and heating/cooling demands are responsible for most energy consumption in buildings. In this study the performance of a solar-assisted latent heat thermal energy storage (LHTES) unit integrated with a heat pump is investigated during the heating season under variable weather conditions. Phase change materials (PCMs) with different melting temperatures (T-m) and latent heat of fusions (h(sf)) are studied and parametric simulations are conducted to examine the proposed systems' economic advantage and payback duration. Variable weather conditions are defined in simulations and seven consecutive day analyses are conducted to ensure that results are not dependent on the initial conditions. Results revealed that the PCM with T-m= 35 degrees C and h(sf) = 240 kJ/kg has a better thermal performance than the other alternatives i.e. T-m = 31 degrees C and 40 degrees C. The integration of the solar-aided LHTES unit with the heat pump increases the COP of the heat pump and the increment varies from 35% to 80% for heating months in Izmir. Such an improvement in COP reduces the operating costs related to the electricity consumption of the heating device significantly and the simple payback period of the combined system is determined to be approximately 13 years in Izmir.