A statistical model for dew point air cooler based on the multiple polynomial regression approach

Swift assessment of evaporative cooling systems has become a necessity in practical engineering applications of this advanced technology. This paper bypasses details of the performance process and pioneers in developing a statistical model based on the multiple polynomial regression (MPR) to predict the performance of a dew point cooling (DPC) system. Thousands of numerical and experimental data are explored and the statistical model is produced. The developed statistical model correlates the performance parameters with the key operational parameters, including the flow and geometric characteristics. The selected operational parameters are, intake air conditions, including temperature, relative humidity and flow rate as well as the working air fraction over the intake air, while cooling capacity, coefficient of performance (COP), pressure drop, dew point and wet-bulb effectiveness are selected as performance parameters. The considered geometric characteristics are channel height, channel interval and number of layers in heat and mass exchanger. The model with different polynomial degrees is assessed by R2, MRE and MSE metrics. The 8th degree polynomial model is selected. The maximum relative error of the cooling capacity, coefficient of performance, pressure drop, dew point and wet-bulb effectiveness are 6.1%, 7.54%, 0.07%, 3.54% and 2.53% respectively. Finally, as examples, the model is used to predict the performance of the DPC system in random operating conditions and in a dry climate i.e. Las Vegas. Model developed in this study would enable the swift prediction of the DPC system

A Novel Mathematical Model of the Solar Assisted Dehumidification and Regeneration Systems

This paper introduces a state-of-the-art modelling technique to investigate the performance of solar assisted dehumidification and regeneration cycles. The dehumidification/regeneration system investigated in this study employs a solid adsorbent bed and enables use of both solar energy and returning warm air to deliver efficient dehumidification and regeneration of the treated air. Study of literature revealed a huge gap between model results and industrial performance of such systems. Hence, the modelling work presented in this paper employs Gaussian Process Regression (GPR) technique to close the gap between model outputs and real-life operation parameters of the system. An extensive amount of laboratory tests were also carried out on the dehumidification/regeneration system and model predictions were validated through comparison with experimental results. The model predictions were found to be in good agreement with experimental results, with maximum error not exceeding 10%. The GPR technique enables simultaneous analysis of a vast quantity of key system parameters derived from mathematical models and laboratory tests. The system parameters investigated in this study include: temperature, relative humidity and flow rate of process air, and temperature of regeneration air, solar radiation intensity, operating time, moisture extraction efficiency of the dehumidification cycle and moisture removal efficiency of the regeneration cycle. Investigation of both modelling and experimental results revealed that efficiencies of the both dehumidification and regeneration cycles decrease as relative humidity of the process air increases. The increase in regeneration temperature leads to an increase in regeneration efficiency whereas; it does not have a significant impact on the dehumidification efficiency. A similar trend was also observed when solar intensity were increased. The proposed technique reduced the complexity of model by eliminating the need for heat and mass transfer calculations; reduced the performance gap between model results and real-life performance data, and increased the reliability of model outputs by showing a good agreement with experimental results. The GPR based mathematical model delivers an effective design and performance evaluation tool for the solar assisted dehumidification and regeneration systems and provides an unprecedented opportunity for commercializing such systems

Advancements in thermoelectric generators for enhanced hybrid photovoltaic system performance

Effective thermal management of photovoltaic cells is essential for improving its conversion efficiency and increasing its life span. Solar cell temperature and efficiency have an inverse relationship therefore, cooling of solar cells is a critical research objective which numerous researchers have paid attention to. Among the widely adopted thermal management techniques is the use of thermoelectric generators to enhance the performance of photovoltaics. Photovoltaic cells can convert the ultra-violent and visible regions of the solar spectrum into electrical energy directly while thermoelectric modules utilize the infrared region to generate electrical energy. Consequently, the combination of photovoltaic and thermoelectric generators would enable the utilization of a wider solar spectrum. In addition, the combination of both systems has the potential to provide enhanced performance due to the compensating effects of both systems. The waste heat produced from the photovoltaic can be used by the thermoelectric generator to produce additional energy thereby increasing the overall power output and efficiency of the hybrid system. However, the integration of both systems is complex because of their opposing characteristics thus, effective coupling of both systems is essential. This review presents the concepts of photovoltaics and thermoelectric energy conversion, research focus areas in the hybrid systems, applications of such systems, discussion of the most recent research accomplishments and recommendations for future research. All the essential elements and research areas in hybrid photovoltaic/thermoelectric generator are discussed in detailed therefore, this review would serve as a valuable reference literature

Experimental study and exergy analysis of photovoltaic-thermoelectric with flat plate micro-channel heat pipe

Effective cooling of the photovoltaic can enhance electrical conversion efficiency of a photovoltaic system. The combination of photovoltaic and thermoelectric generator provides unique advantages because of their complementary characteristics. In addition, hybrid photovoltaic-thermoelectric can utilize a wider solar spectrum thereby harvesting more energy from the sun. Heat pipes are passive devices that can transfer heat efficiently over a long distance. Therefore, this study presents an experimental investigation and exergy analysis of a photovoltaic-thermoelectric with flat plate micro-channel heat pipe. The experiment is performed in a laboratory using a solar simulator and water-cooling is used for the thermoelectric generator. The effect of thermoelectric load resistance, micro-channel heat pipe back insulation and solar radiation on the performance of the hybrid system is presented and a comparison with a photovoltaic only system is provided. Results show that the hybrid system provides an enhanced performance compared to the photovoltaic only system and absence of insulation behind the micro-channel heat pipe enhances electrical performance of the hybrid system. Furthermore, results show the feasibility of the hybrid system for generating electricity and small hot water. This study will provide valuable guidance for design of photovoltaic-thermoelectric systems with heat pipe and verifies the feasibility of such systems

Building integrated solar concentrating systems: A review

© 2019 Elsevier Ltd In the building sector, concerns towards the vast energy consumption has promoted the development of renewable energy technologies. In this regards, the solar concentration devices show a promising concept for building applications. However, the solar concentrators for application in buildings have many restrictions, which are different from the traditional solar concentrators. The main objective of this paper is to present a concise review on the building integrated concentrating devices, that have their own characteristics and multiple functions. This paper made a classification based on device's functions, i.e. building integrated concentrated photovoltaic systems (BICPV), building integrated concentrating solar thermal (BICST) and building integrated concentrating solar daylighting (BICSD) and the combination of functions, i.e. BICPV/T, BICPV/D, BICST/D and BICPV/T/D. At the same time, this paper presented an elaborate introduction of the demands, types and applications of the building integrated concentrating devices and prospects/ directions/ policies about these technologies around the world. The review would provide important information for the actual engineering of building integrated concentrating devices

Real life test of a novel super performance dew point cooling system in operational live data centre

This paper presents the development and application of a super performance dew point cooling technology for data centres. The novel super performance dew point cooler showed considerably improved energy saving and carbon reduction for data centre cooling. The innovations of this technology are built upon a series of technological breakthroughs including, a novel hybrid flat/corrugated heat and mass exchanging sheets, an innovative highly water absorptive and diffusive wet-material for the sheets which enable an intermittent water supply with well-tuned water pressure and flow rate, and the optimised fan configurations. Following a list of fundamental research including theoretical, numerical and lab experimental testing of a small scale prototype system, a specialist 100 kW rated data centre dew point cooling system was dedicated designed, constructed, installed and real life tested in an operational live data centre environment, i.e., Maritime Data Centre at Hull (UK) to investigate its dynamic performance, suitability and stability for application in operational data centre environment conditions. During the testing period, the system showed its reliability and capability to remove a tremendous amount of heat dissipated from the IT equipment and maintain an adequate space temperature in the operational live data centre. The dynamic data collection and analysis during the continuous testing and monitoring period showed the average COP of 29.7 with the maximum COP of 48.3. Compared to the existing traditional vapor compression air conditioning system in the data centre, the energy saving using the super performance dew point cooling system is around 90 %. The work presented in this paper include detailed innovation aspects of the technology and the system operation, as well as the established bridging knowledges, methodology and technical procedure for bringing this new technology into real life operation which involve in data centre survey, optimum design and modularization of the specialist cooling system for data centre application, proven system installation, operating method and cooling air management for data centre as well as the assurance of the continuous sufficient cooling supply to the data centre

Transient and non-uniform heat flux effect on solar thermoelectric generator with phase change material

Transient and non-uniform heat flux from solar concentrators can affect the performance of solar thermoelectric generators, which generate electricity from concentrated solar radiation. Therefore, this paper presents a detailed three-dimensional study on the effect of transient and non-uniform heat flux on the performance of a solar thermoelectric generator (STEG). COMSOL 5.4 Multiphysics software is utilized for the numerical study while the non-uniform heat flux from a compound parabolic concentrator is obtained through ray tracing simulation using Lighttools software. Varying solar radiation under typical partly cloudy weather condition is utilized. Furthermore, phase change material (PCM) is used to reduce the effect of transient and non-uniform heat flux therefore; it is positioned at the top surface of the solar thermoelectric generator. A comparison between the performance of the STEG with and without PCM is presented, and a parametric study on the effect of PCM fins and PCM height on the STEG performance is carried out. Results show that the place of PCM on the top surface of the solar thermoelectric generator is an effective approach to provide a stable electrical performance form the STEG under varying weather conditions. Furthermore, results reveal the effectiveness of the phase change material in protecting the solar thermoelectric generator under highly concentrated solar radiation. This study will provide valuable design guidance for solar thermoelectric generators under varying weather conditions and with solar concentrators, which produce non-uniform heat flux

Statistical investigation of a dehumidification system performance using Gaussian process regression

Swift performance assessment of dehumidification systems, in design stage and while operation of the system is of substantial importance for commercialization and wide implementation of this technology. This paper presents a novel statistical model, employing Gaussian Process Regression (GPR) to investigate performance of a solar/waste energy driven dehumidification/regeneration cycle with a solid adsorbent bed. The statistical model takes thousands of operating conditions derived from a numerical model to predict the performance of the system. This predictive tool directly correlates the main operating parameters with the performance parameters of the system. The operating parameters considered in this study are: temperature, relative humidity and flow rate of process air, temperature of regeneration air, length of the desiccant bed, solar radiation intensity and operating time, and the selected performance parameters are: moisture extraction efficiency for the dehumidification cycle and moisture removal efficiency for the regeneration cycle. The model is evaluated by three metrics, namely: root mean square error (RSME), mean absolute percentage error (MAPE), and coefficient of determination (R2). The maximum RSME and MAPE for moisture extraction are only 0.045, 0.21%, and for moisture removal efficiencies are 0.082 and 0.39%, respectively, while the R2 value is derived as 0.97. The developed model is used to investigate the impact of four selected operating parameters on system performance. Additionally, the system performance is predicted for randomly generated operating conditions as well as warm and humid climates. The developed GPR model provides a swift and highly accurate predictive tool for design of the dehumidification systems and for commercialization of the investigated dehumidification systems

zemin Kaynak Isı Değiştirici Sistemleri Sıcaklık Davranış Modellemesi

Thesis (M.Sc.) -- İstanbul Technical University, Energy Institute, Yüksek LisansTez (eng) -- İstanbul Teknik Üniversitesi, Enerji Enstitüsü, Yüksek LisansGround Source Heat Exchanger Systems (GSHES) are becoming more popular everywhere in the world. GSHES use pipes which are buried in the garden in order to extract heat from the ground. The heat can then be used to heat radiators, underfloor, swimming pools or to warm air heating systems and water in homes for several uses. Mixture of water and antifreeze circulates within the single or series of u tubes which are buried in the ground. Heat from the ground is absorbed by the circulating fluids and then by passes through a heat exchanger into the heat pump. The temperature of the ground remains approximately constant during the year. There are several different factors influencing the performance of the GSHES such as mass flow rate of circulating water, length of the u tubes, number of u tubes, number of boreholes, surface temperature, injection temperature, presence or absence of underground water flow, thermal conductivity of the fluid and formation, radius of u tube, radius of borehole, piping type, depth of operation, ground characteristics, capacity of heat pump system, size of system, building system, etc. Mathematical models that are used for modeling the performance of the GSHES are well established and have a significant role on studying the GSHES. These models usually consider conductive heat transfer for the formation and the convective heat transfer for the fluid circulating within the u tube. Also convective heat transfer is considered for the underground water flow. Underground water flow is one of the most common factors which occurs inside the earth. It can have positive and negative effects on the performance of the GSHES. Recently researchers have focused on studying the effect of underground water flows due to their significant effects. In this study, we have developed a numerical model in order to study the effect of underground water flow. Our model is based on solving the energy balance equation. This equation is treated in fully implicit manner so that it becomes highly nonlinear. Hence, one numerical method must be used in order to overcome the nonlinearity. The Newton Raphson procedure is used in order to solve the equation. Numerical derivatives are used in order to construct the Jacobian matrix. After solving the equation, in order to have trustable results we have verified our numerical model with one analytical model. In order to apply the same inputs and have the same situation in both numerical and analytical model or mimic the analytical model, we have to apply some simplicity in our numerical model. For instance, because temperature distribution using geothermal gradient is not considered in the analytical model, it is taken to be zero. We have used several cases in order to make sure the verification is completed. We have studied above-mentioned parameters in two radial and Cartesian systems. In the radial system we have studied the behavior of the produced water. Additionally, the effect of mass flow rate of the circulating water within the u tube have been studied. As a result, we saw that by increasing the mass flow rates from 0.01 to 100 kg/s the temperature profiles decline quickly to the value which is very close to the injecting water temperature that is 5ºC in this study. Furthermore, in the radial system, different initial temperatures have used in order to simulate the presence of underground water flow in the system. Since when underground water is present, it is normally cooler than the ground temperature. Mass flow rate of underground water flow is important too, so that the effect of mass flow rate of underground water is studied too. We have chosen two different mass flow rates in this case. Based on results, we saw that the effect of different initial temperature is significant. In the Cartesian system we have studied the effect of underground water flow. In this case, forth layer is chosen to bear the underground water flow so that the temperature of this layer is assumed to be 15 ºC. In this case, several mass flow rates are chosen for the underground water flow. Based on results we have concluded in the presence of underground water flow the temperature of the formation grids decrease less. This decrease become more efficient by increasing mass flow rate of the underground water. Furthermore, the overall increase for the temperature of the grid blocks can be seen due to the conductive heat transfer among the layers. In the final step, we have studied the effect of thermal conductivity. Value of thermal conductivity is one of the crucial parameters that could have significant effects on the performance of GSHES which is very common in the actual systems. Three different thermal conductivities have been chosen for the formation. Based on results, for the lower thermal conductivities the borehole cools the most because of little amount of heat transfer among the borehole grids and formation grids.Toprak Kaynaklı Eşanjör Sistemleri (GSHES) gün geçtikçe daha çok kullanılıp popüler hale geliyor. GSHES yerden ısı elde etmek amacıyla bahçede gömülü olan boruları kullanıyor. Cıkan ısı, radyatörları ve yüzme havuzuları ısıtmak için kullanabilir ya da hava ısıtma sistemleri ve su ısıtmak için kullanılabilir. Su ve antifriz karışımı toprağa gömülü U tüplerin içinde dolaşır ve yerden ısı dolaşım sıvıları tarafından emilir ve ısı pompası içine bir ısı dağıtıcısı boyunca geçer. Toprak sıcaklığı yıl boyunca yaklaşık olarak sabit kalır. Termal olarak GSHES performansını etkileyen çeşitli faktörler vardır. Dolaşım suyu kütle akış hızı, U tüpler uzunluğu, U tüplerin sayısı, sondaj kuyularına sayısı, yüzey sıcaklığı, enjeksiyon ısısı veya yeraltı su akışı, ısı iletkenlik oluşumu, U boru yarıçapı, sondaj kuyusu yarıçapı, boru tipi, işletme derinliği, yer özellikleri, ısı pompası sisteminin kapasitesi, sistemin boyutu ve inşaat sistemi bu faktörlerden bazılarıdır. GSHES performansını modellemek için kullanılan matematiksel modeller iyi sonuç vermiş ve GSHES üzerinde önemli bir rolu vardır. Bu modeller genellikle U tüp içinde dolaşan akışkan için konvektif ısı transferini kullanıyorlar. Ayrıca ısı taşınımı yeraltı su akışı için kabul edilir. Yeraltı su akışı toprak içinde oluşur ve bu knudaki en yaygın faktörlerden biridir. Bu faktörün GSHES performansı üzerinde olumlu ve olumsuz etkileri olabilir. Araştırmacılar son zamanlarda yeraltı su akımlarının önemli etkilerini incelemeye odaklanmışlardır. Bu çalışmada, yeraltı su akışının etkisini araştırmak amacıyla bir sayısal model geliştirdik. Bizim modelimiz enerji dengesi denklemi çözmeye dayalıdır. Bu denklem tam kapalı bir şekilde işlemden geçirilir. Bu nedenle, bir sayısal yöntem lineer olmayan aşmak için kullanılmalıdır. Newton-Raphson prosedürü denklemi çözmek için kullanılır. Sayısal türev Jakobyan matris oluşturmak amacıyla kullanılmaktadır. Denklemi çözdükten sonra, güvenilir sonuçlar elde etmek için bir analitik model ile bizim sayısal modeli doğrulandı. Aynı girişleri uygulamak ve hem sayısal ve analitik modelde aynı sonuçları almak için, sayısal modelde bazı sadelik uygulamar uyguladık. Jeotermal gradyanı kullanılarak, analitik sıcaklık dağılımı modeli olarak kabul edilir, Doğrulama tamamlandıktan emin olmak için birkaç vaka kullandık. Biz iki radyal ve kartezyen sistemlerde parametreleri yukarıda bahsedilen durumda inceledik. Radyal sistemde ürettiğimiz suyun davranışını inceledik. Buna ek olarak, U boru içinde dolaşan suyun kütle akış oranının etkisi incelenmiştir. Sonuç olarak, 0.01 ila 100 kg arasında kütle akış oranlarını arttırarak, bu çalışmada 5ºC olan enjekte su sıcaklığına çok yakın bir değere hızlı düşüşü görüldü. Ayrıca, radyal sistem, farklı başlangıç sıcaklıkları sistemdeki yeraltı suy akışının varlığını taklit etmek üzere kullanılmıştır. Yeraltı suyu zemin suyundan normak olarak daha soğuktur. Yeraltı suyunun kütle akış oranının etkisinin çok çalışılan böylece yeraltı su akışının kütle akış hızı, çok önemlidir. Biz bu durumda iki farklı kütle debileri seçtiniz. sonuçlarına dayanarak, farklı başlangıç sıcaklığının etkisinin çok büyük olduğunu gördüldü. Kartezyen sistemde yeraltı su akışının etkisini inceledik. Bu durumda, ileri katmanlar bu tabakanın sıcaklığı 15 ° C olarak kabul edilir ve böylece altı suyu akışını taşımak için seçilir. Bu durumda, çok sayıda kütle akış hızları yeraltı suyu akışı için tercih edilmektedir. Sonuçlarına dayanarak biz oluşum ızgaraları sıcaklığı daha az azalma yeraltı su akışı varlığında sonucuna varmışlardır. Bu düşüş yeraltı suyu kütle akış hızını artırarak daha verimli hale gelir. Ayrıca, ızgara blokları sıcaklığı genel bir artış katmanları arasında, ,iletken ısı aktarımı nedeniyle görülebilir. Son aşamada, termal iletkenlik etkisini inceledik. Isı iletkenlik değeri gerçek sistemlerinde yaygındır ve GSHES performansı üzerinde önemli etkilere sahip olabilir önemli parametrelerden biridir. Üç farklı termal iletkenlikleri oluşumu için seçilmiştir. Sonuçlarına göre, düşük ısı iletkenlik için sondaj ızgaraları ve oluşum ızgaraları arasında ısı transferi çok az miktarda en etkilidir.M.Sc.Yüksek Lisan