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Öğe COMPARATIVE ANALYSIS OF EAST-WEST AND SOUTH-NORTH SINGLE-AXIS SOLAR TRACKING SYSTEMS(2025) Sezen, KutbayAs global energy demand continues to grow, maximizing the efficiency of solar energy as a renewable resource is increasingly critical. Solar tracking systems offer an effective solution by optimizing panel orientation to capture more solar radiation. This study evaluates the annual and seasonal solar radiation gains of single-axis tracking systems, comparing east-west and south-north orientations with fixed-tilt and horizontal surfaces. Daily, monthly, and annual radiation values were calculated based on the average day of each month, and hourly radiation variations were analyzed for June and December. Annually, the east-west tracking system increased radiation capture by approximately 30% compared to a horizontal surface and 19% compared to a fixed-tilt surface, while the south-north system achieved gains of 16% and 6%, respectively. In June, the east-west system outperformed the south-north setup by 2.02 kWh/m² daily (a 29% increase), whereas in December, the south-north system collected 0.43 kWh/m² more per day (a 25% increase) due to better alignment with the sun’s lower southern path. The method used in this study is based on manual, equation-driven modeling, aiming to enhance transparency and provide a cost-effective, software-independent tool. The calculated hourly tracking angles can be applied to future systems in the same region, while the overall procedure can be easily adapted to other locations by incorporating region-specific input parameters.Öğe COMPARATIVE ANALYSIS OF EAST-WEST AND SOUTH-NORTH SINGLE-AXIS SOLAR TRACKING SYSTEMS(Konya Teknik Univ, 2025) Sezen, KutbayAs global energy demand continues to grow, maximizing the efficiency of solar energy as a renewable resource is increasingly critical. Solar tracking systems offer an effective solution by optimizing panel orientation to capture more solar radiation. This study evaluates the annual and seasonal solar radiation gains of single-axis tracking systems, comparing east-west and south-north orientations with fixed-tilt and horizontal surfaces. Daily, monthly, and annual radiation values were calculated based on the average day of each month, and hourly radiation variations were analyzed for June and December. Annually, the east-west tracking system increased radiation capture by approximately 30% compared to a horizontal surface and 19% compared to a fixed-tilt surface, while the south-north system achieved gains of 16% and 6%, respectively. In June, the east-west system outperformed the south-north setup by 2.02 kWh/m2 daily (a 29% increase), whereas in December, the south-north system collected 0.43 kWh/m2 more per day (a 25% increase) due to better alignment with the sun's lower southern path. The method used in this study is based on manual, equation-driven modeling, aiming to enhance transparency and provide a cost-effective, software-independent tool. The calculated hourly tracking angles can be applied to future systems in the same region, while the overall procedure can be easily adapted to other locations by incorporating region-specific input parameters.Öğe Comparison of solar assisted heat pump systems for heating residences: A review(Pergamon-Elsevier Science Ltd, 2023) Sezen, Kutbay; Gungor, AfsinSolar assisted heat pump (SAHP) systems have been a popular research topic in last decades because of their proven improved performance by integrating solar energy to system. Filling the literature gap in SAHP systems comparison in terms of performance and structure, contributes to the determination of the appropriate type. For this purpose, in order to compare the systems, 77 recent studies are reviewed. Systems are classified according to their configurations to provide an infrastructure for comparison. Considering the collector structure, the effect of solar radiation and ambient temperature on SAHP systems performance are examined, and the ambient condition ranges preferable for each system are identified. The complexity of systems is expressed with the type and number of components used, and the costs of the systems are compared taking into account the payback period. Reviewed studies reveal that, direct expansion systems should be preferred because of their utilization of solar and air simultaneously as heat source, below solar irradiation of 400 W/m2. Indirect expansion systems are more complex than direct expansion systems and this limits their preferability. However, replacing the solar-side evaporator with a solar air preheater, thereby integrating the existing solar system and air source heat pump system, can simplify the indirect expansion systems. The temperature rise problem that prevents the use of photovoltaic thermal panels in indirect systems can be eliminated with low-cost external cooling devices.Öğe Dönemsel optimum eğim açısıyla güneş enerji kazancında enlem, rakım ve karın etkisinin dört İl örneğiyle incelenmesi(2025) Sezen, KutbayGüneş panellerin topladığı güneş enerjisi eğim açılarının belirli dönemler halinde optimize edilmesiyle artırılabilir. Bu çalışmada, Türkiye'nin farklı coğrafi ve iklim koşullarına sahip bölgelerinde, yıllık dönemsel optimum eğim açısı kullanılarak güneş enerjisi kazancında, enlem, rakım ve kar örtüsünün etkileri incelenmiştir. Bursa, Erzurum, Antalya ve Hakkâri illeri, enlem, yüksek rakım ve kar örtüsünün etkilerini karşılaştırmaya olanak sağlayan coğrafi ve iklimsel özelliklere sahip iller olarak seçilmiştir. Her il için 1, 2, 3 ve 4 dönemli optimum eğim açısı dönem başlangıç ve bitiş ayları manuel olarak değiştirilerek yıllık maksimum güneş enerji kazancı sağlanacak şekilde belirlenmiştir. Sonuçlar, yılın iki eğim açısı dönemine ayrılmasının her il için en büyük kazancı sağladığını, üç ve dört dönemli ayrımların ek getirisinin sınırlı kaldığını göstermektedir. Örneğin, Bursa’da iki, üç ve dört eğim açısı dönemi seçimi yıllık güneş ışınımında sırasıyla %4,54, %4,79 ve %5,26 kazanç sağlamaktadır. Dönemsel optimum açı seçiminin karlı bölgelerde daha fazla fayda sağladığı görülmüştür. Kar örtüsünün uzun sürdüğü Erzurum ve Hakkâri’de, yüksek eğim açılı dönemlerin 6 ay tutulması, kar yağışının az olduğu Antalya ve Bursa’da ise 7 ay tutulması daha yüksek güneş ışınımı kazancı sağlamaktadır. Dört dönemli uygulamada, bahar ve sonbahar dönemlerinin Bursa, Antalya ve Hakkâri için ikişer ay seçilmesi avantajlıdır. Sonuç olarak, güneş enerjisi sistemlerinin verimliliğini artırmak için her ilin coğrafi ve iklimsel özelliklerine göre optimum eğim açısı ve dönem değişimlerinin belirlenmesi gerekmektedir. Bu yaklaşım, Türkiye’nin farklı coğrafi ve iklim koşullarına sahip bölgelerinde güneş enerjisinden maksimum fayda sağlanmasını mümkün kılacaktır.Öğe Effects of ambient conditions on solar assisted heat pump systems: a review(Elsevier, 2021) Sezen, Kutbay; Tuncer, Azim Dogus; Akyuz, Ali Ozhan; Gungor, AfsinSolar assisted heat pump (SAHP) systems aim to increase the performance of heat pumps by supporting with solar energy using various heating modes, whose performances depend on ambient conditions. In the literature, SAHP systems are classified by structure types, and the heating mode options are not considered as the main priority of the design but a result of the structure of the system. This paper aimed to investigate the effect of ambient conditions on heating modes, and identify the preferable ambient condition ranges for each SAHP system depends on their heating modes, by using a narrative review of 47 recent studies, that shed light on the problem. For this purpose, direct solar heating (DSH), air source heat pump (ASHP), solar source heat pump (SSHP) and solar-air source heat pump (S/ASHP) modes were stated as the basic heating modes of SAHP systems. In accordance with the literature, SAHP systems were classified as direct expansion solar assisted heat pump (DX-SAHP) and series, parallel and dual source indirect expansion solar assisted heat pumps (IDX-SAHP). Solar irradiation, ambient temperature, relative humidity and wind speed has been taken as major ambient conditions to investigate. Reviewed studies indicated that, parallel and series IDX-SAHP are preferable in high solar irradiations about 800 W/m2 with their DSH mode options. Frosting on evaporator is prevented in DX-SAHP with its S/ASHP mode, and even in the presence of frosting, unlike IDX-SAHPs ASHP mode, freezing is a factor that improves performance on flat evaporator in cold and humid conditions. This study indicates that there are obscure areas for future studies to focus on for a better comparison between SAHP types. Moreover, proposed novel designs of this paper, such as solar preheating of air in IDX-SAHP systems to add S/ASHP mode as an option, might enhance the performance and applicability of SAHP systems.Öğe Influence of airflow rates on air source heat pump operating parameters(Pergamon-Elsevier Science Ltd, 2023) Sezen, KutbayAir source heat pumps (ASHPs) are energy-efficient and environmentally friendly heating systems widely used to meet the heating needs of buildings. Therefore, researches that ensure the effective use of ASHP systems are crucial for improving the energy efficiency of buildings. Faults, design flaws, or user-controlled settings can cause changes in the airflow rates of the evaporator and condenser in ASHPs. This study examines the effect of changes in the airflow rates of the evaporator and condenser on the operating parameters of ASHPs in heating mode using a developed physics-based model. Although the results of experimental studies in the literature provide useful information in this regard, a model-based study would allow for the examination of different systems with their specific parameters. The model is an advanced version of the author's previous model, which now includes the effects of airflow rates in addition to outdoor air conditions, and it has been validated by comparison with experimental data correlations published in the literature. The logarithmic mean temperature difference-based solution method employed by the model allows for its potential for further development and improvement. Four different sizes of air conditioners with heating capacities ranging from 2.5 kW to 8.2 kW were investigated. Corresponding to EN-14511 test standards, 7 degrees C outdoor temperature and 90% relative humidity condition and 20 degrees C indoor temperature condition were taken account. The effects on the ASHP parameters were determined by varying the airflow rates in ratios between 0.2 and 1.4 with 0.2 intervals. The airflow ratio term is defined as the ratio of the flow rate to the maximum airflow rate provided by the fans. It is assumed that the condenser heat load is kept constant at its nominal rate to maintain a consistent indoor temperature using inverter-driven variable speed compressor technology. The results show that changes in the condenser airflow rate have a greater impact on system parameters than changes in the evaporator airflow. Reducing the condenser airflow ratio to 0.4 with the silent mode option reduces the COP value by 21% and increases energy consumption by 44%, indicating that manufacturers should inform customers about the potential decrease in performance when using lower condenser airflow rates. A devastating performance drop is observed when airflow ratios in either the condenser or evaporator drop below 0.4. The performance curve of the ASHP produced by the model can help determine the optimum airflow rates for optimal performance. Systems which can be designed close to optimum airflow rates are less affected by airflow changes. In frost-free conditions, the impact of changes in evaporator airflow on performance is less significant than that of the condenser. However, decreasing the evaporator airflow rate increases the susceptibility of the ASHP to frosting. For example, reducing the evaporator airflow to 0.6 extends the frosting condition limits from 6 degrees C and %65 relative humidity to 9.7 degrees C and %50 relative humidity. The results of this study will be valuable for researchers, manufacturers and users in terms of performance evaluation and improvement based on airflow rates. The presented model can be further improved and has the potential to facilitate the investigation of various conditions, including frosting, in future studies.Öğe Investigating air source heat pump cooling performance and humidity management using a physics-based model(Pergamon-Elsevier Science Ltd, 2025) Sezen, KutbayThe rising cooling demand due to urbanization and industrialization emphasizes the need for efficient air source heat pumps (ASHPs). This study investigates how indoor and outdoor temperature variations affect the performance of three different capacity air conditioners in cooling mode, using a physics-based model that iteratively solves logarithmic mean temperature differences (LMTD) through temperature and heat balance methods. Additionally, study proposes a method for controlling relative humidity by adjusting the evaporator airflow rate in split air conditioners, and determines the necessary airflow rates based on varying outdoor and indoor temperatures. Findings reveal that cooling load reduction is the primary driver of performance improvement. For example, decreasing the outdoor temperature from 35 degrees C to 30 degrees C increases the coefficient of performance (COP) from 3.47 to 4.36 in variable cooling heat load (VH) mode, compared to 3.99 in constant cooling heat load (CH) mode. Additionally, selecting higher-capacity ASHPs enhances performance and operational range, though benefits diminish at lower cooling demands. Relative humidity (RH) control was demonstrated by adjusting airflow rates; for instance, while cooling the indoor space to 27 degrees C, an increase in outdoor temperature to 36.6 degrees C reduces RH to 32 %, whereas a drop to 29.7 degrees C raises RH to 73 %. To maintain 40 % RH under these conditions, the airflow rate must vary between 1.26 and 0.34. The impact of airflow rate changes on performance was also assessed. Although reducing airflow is typically expected to cause a performance loss, the increase in compressor efficiency due to a higher compressor pressure ratio mitigates this decrease, rendering it insignificant. Realistic conditions with moisture inputs were examined for two scenarios, showing that relative humidity control becomes increasingly challenging at low cooling loads, especially in crowded spaces. However, reducing the evaporator airflow rate to its minimum still enhances comfort by effectively mitigating excessive indoor humidity levels. The study provides actionable insights for optimizing ASHP performance and design, emphasizing the importance of airflow control for effective humidity regulation. The findings provide actionable insights for both users and manufacturers. For users, illustrating the impact of air conditioning selection and usage preferences on performance and comfort helps inform better decisions. For manufacturers, the study suggests developing systems that integrate temperature and humidity regulation with automatic airflow adjustment mechanisms driven by real-time relative humidity sensing.Öğe Operation Parameters Variation of Air Source Heat Pump According to the Outdoor Temperature(2023) Sezen, KutbayAir source heat pumps (ASHP), known as energy efficient systems, emerge as environmentally friendly and economical solutions for building heating. Unfortunately, the operating parameters of ASHPs and accordingly their performance are directly affected by the daily and seasonal temperature changes of the outside air. In this study, change in operation parameters of a selected ASHP with 3.4kW nominal heating capacity is investigated with a calculation method based on the logarithmic mean temperature difference, between -10°C to 18°C outdoor temperature range with 2°C steps, at constant compressor power. The study is verified with published COP data of the manufacturer. Results are shared with graphs that give the variation of refrigerant evaporation and condensation temperature and pressure, COP, and condenser heating load according to outdoor air temperature. A raise from -10°C to 18°C in outdoor temperature, increases the COP value from 3.38 to 5.49. Detection of the increase in evaporation pressure in parallel with the outdoor temperature may allow easy control of the refrigerant charge level with a manometer. This study can be a useful guide for researchers who aim to determine the outdoor temperature dependent operating parameters of an ASHP and for technical personnel who need this information in fields.Öğe Operation Parameters Variation of Air Source Heat Pump According to the Outdoor Temperature(Gazi Univ, 2023) Sezen, KutbayAir source heat pumps (ASHP), known as energy efficient systems, emerge as environmentally friendly and economical solutions for building heating. Unfortunately, the operating parameters of ASHPs and accordingly their performance are directly affected by the daily and seasonal temperature changes of the outside air. In this study, change in operation parameters of a selected ASHP with 3.4kW nominal heating capacity is investigated with a calculation method based on the logarithmic mean temperature difference, between -10 degrees C to 18 degrees C outdoor temperature range with 2 degrees C steps, at constant compressor power. The study is verified with published COP data of the manufacturer. Results are shared with graphs that give the variation of refrigerant evaporation and condensation temperature and pressure, COP, and condenser heating load according to outdoor air temperature. A raise from -10 degrees C to 18 degrees C in outdoor temperature, increases the COP value from 3.38 to 5.49. Detection of the increase in evaporation pressure in parallel with the outdoor temperature may allow easy control of the refrigerant charge level with a manometer. This study can be a useful guide for researchers who aim to determine the outdoor temperature dependent operating parameters of an ASHP and for technical personnel who need this information in fields.Öğe Performance analysis of air source heat pump according to outside temperature and relative humidity with mathematical modeling(Pergamon-Elsevier Science Ltd, 2022) Sezen, Kutbay; Gungor, AfsinThe paper investigates the performance effect of outdoor temperature and relative humidity on ASHP performance above frosting conditions, with the developed mathematical model. The model results are validated with the experimental data available in literature, of four ASHPs in the 2.7 kW 5.8 kW capacity range. 4 kW capacity ASHP is taken as reference. Constant heating (CH), constant work (CW) and variable heating (VH) modes are determined as operating modes. The model results reveal that relative humidity is a performance enhancing factor above frosting conditions. In VH mode, which is the most realistic operating mode for residences, raise in outdoor temperature from 7 degrees C to 14 degrees C increases the COP value by 30%, and raise in the relative humidity from 0.6 to 1.0 provides an additional 5% COP increase. In CH and CW modes, the contribution of relative humidity to performance increases with temperature, up to 10.7% and 6.4%, respectively. Correlations giving the COP change rate with respect to ambient temperature and relative humidity are derived with higher than 0.9839 R2 values for dry and humid conditions of the CH, CW and VH operating modes. These correlations can be useful for researchers who intends to analyze ASHP performance based on ambient conditions.Öğe Thermodynamic insights and comparative evaluation of R22, R410A, R32, R290, and R1234ze(E) in air source heat pump systems: A theoretical study(2025) Sezen, KutbayAir source heat pumps (ASHPs), particularly split air conditioners, are widely favored for their energy efficiency, ease of application, and capacity to provide both seasonal heating and cooling. However, their performance and environmental impact are largely determined by the refrigerants they use. This study examines the performance and operating parameters of an ASHP retrofitted with five different refrigerants—R22, R410A, R32, R290, and R1234ze(E)—using a physics-based model. R22 and R410A were considered phased-out refrigerants due to their environmental impact, while R32, R290, and R1234ze(E) were evaluated as eco-friendly pure refrigerant alternatives. Refrigerants were analyzed at outdoor temperatures of 0°C, 7°C, and 15°C, with evaporator and condenser pressure drops included to improve model accuracy. R32 demonstrated superior coefficient of performance (COP) at lower outdoor temperatures, while R1234ze(E) outperformed other refrigerants at 15°C. R1234ze(E) exhibited the highest refrigerant flow rate, nearly twice that of R290 and R32, increasing charging costs. However, its low condensing pressure allows for more economical equipment. R290 showed the lowest pressures, facilitating safer sealing despite its high flammability. Pressure drop and pipe diameter requirements are critical in system design. R1234ze(E) requires larger pipes to mitigate pressure losses, increasing system costs and refrigerant charge. R32, with minimal pressure loss, allows smaller pipes, making it cost-effective. R290, though needing slightly larger pipes than R32, operates at lower condenser and evaporator pressures, improving safety and reducing sealing challenges. This feature, combined with its low GWP, makes R290 a promising next-generation refrigerant, though its high flammability remains a concern. R32 consistently achieves the lowest condensing temperatures at lower outdoor conditions. These findings provide insights into the trade-offs between environmental benefits, performance, and operational considerations of various refrigerants.Öğe Water droplet evaporation in atmospheric air stream(Aip Publishing, 2023) Sezen, Kutbay; Gungor, AfsinEvaporation of a water droplet in air is a natural phenomenon that causes the droplet and air properties to change over time. In this paper, time-dependent variation of air and water droplet properties in a flow is examined with the developed numerical model, in the range of conditions that concern air-conditioning and respiratory-based medical events and applications. An experimental setup is built and the model is validated with experiments carried out for 27 cases. Input parameters are chosen as the inlet air temperature, relative humidity, droplet temperature and diameter, and air-water mass mixing ratio. Output properties are determined as the outlet air temperature, relative humidity, mass droplet ratio, and droplet temperature to define the application case in the simplest way. Model results of 432 different cases are used to develop correlations with R20 values above 0.984, to present the effects of co-variation of input parameters. The results show that the latent heat demand of droplet evaporation is the main factor in the decrease of air temperature, while droplet temperature has almost no effect. As the air becomes saturated with moisture, evaporation almost stops and droplets carried by air flow remain. The droplet diameter affects only the process speed by reducing the processing time by the square of the reduction ratio. The developed numerical model and correlations allow the rapid determination of properties change in air-water stream over time, so it will provide great convenience to researchers dealing with water droplet evaporation in an atmospheric air stream.
