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Experimental comparison of alternative convection suppression arrangements for concentrating integral collector storage solar water heaters
Abstract
An experimental investigation of an inverted absorber integrated collector storage solar water heater mounted in the tertiary cavity of a compound parabolic concentrator with a secondary cylindrical reflector has been performed under simulated solar conditions. The solar water heaters performance was determined with the aperture parallel to the simulator for a range of transparent baffles positioned at different locations within the collector cavity. Results indicate that glass baffles located at the upper portion of the exit aperture of the CPC can reduce thermal losses through convection suppression without significantly increasing optical losses.
... Οη πεξηζζόηεξεο από ηηο κειέηεο ζηνρεύνπλ ζηε βειηίσζε ηεο ζεξκηθήο ζπκπεξηθνξάο ηνπο, πξνηείλνληαο κεζόδνπο θαη ηερληθέο κείσζεο ησλ ζεξκηθώλ απσιεηώλ. Μεηαμύ ησλ πην αληηπξνζσπεπηηθώλ εξεπλεηηθώλ εξγαζηώλ είλαη απηή ησλ Smyth et al. [3] όπνπ κειεηήζεθε ε ζεξκηθή ζπκπεξηθνξά δηαθνξεηηθώλ ηύπσλ νινθιεξσκέλσλ ειηαθώλ ζπζθεπώλ ζπιιέθηε απνζήθεο κε πεξηνξηζκέλεο ζεξκηθέο απώιεηεο. Η εξγαζία αλαιύεη ηε ιεηηνπξγία ησλ ζπζθεπώλ ζε 24σξε βάζε. ...
... Καηά ηελ εκεξήζηα ιεηηνπξγία ηεο, ε ζεξκνθξαζηαθή δηαζηξσκάησζε ζρεηίδεηαη κε ηελ αλνκνηόκνξθε θαηαλνκή ηεο απνξξνθνύκελεο ειηαθήο αθηηλνβνιίαο ζηνλ απνξξνθεηή αιιά θαη κε ηε δηαδηθαζία εμάηκηζεο ηνπ λεξνύ (PCM) εληόο ηνπ δηαθέλνπ. Γηα ηνλ αθξηβή θαζνξηζκό ηεο δηαθύκαλζεο ηεο ζεξκνθξαζίαο ηνπ λεξνύ εληόο ηνπ δνρείνπ απνζήθεπζεο (εζσηεξηθό δνρείν), έλα ζύλνιν από 9 ζεξκνδεύγε ηνπνζεηήζεθαλ εληόο ηνπ δνρείνπ, όπσο ππνδεηθλύεηαη ζηελ εηθόλα 2. Απηά ηνπνζεηήζεθαλ ζε ηξία επίπεδα θαη θαηά κήθνο ηνπ δνρείνπ απνζήθεπζεο (επίπεδν 1 (1,1), (1,2), (1,3), επίπεδν 2: (2,1), (2,2), (2,3) θαη επίπεδν 3: (3,1), (3,2), (3,3)). Δληόο ηνπ δηαθέλνπ ηνπνζεηήζεθαλ ηξία ζεξκνδεύγε ζηηο ζέζεηο όπσο ππνδεηθλύνληαη ζηελ εηθόλα 2 (ζέζεηο (i), (ii) θαη (iii)). ...
... Καηά ηελ εκεξήζηα ιεηηνπξγία ηεο, ε ζεξκνθξαζηαθή δηαζηξσκάησζε ζρεηίδεηαη κε ηελ αλνκνηόκνξθε θαηαλνκή ηεο απνξξνθνύκελεο ειηαθήο αθηηλνβνιίαο ζηνλ απνξξνθεηή αιιά θαη κε ηε δηαδηθαζία εμάηκηζεο ηνπ λεξνύ (PCM) εληόο ηνπ δηαθέλνπ. Γηα ηνλ αθξηβή θαζνξηζκό ηεο δηαθύκαλζεο ηεο ζεξκνθξαζίαο ηνπ λεξνύ εληόο ηνπ δνρείνπ απνζήθεπζεο (εζσηεξηθό δνρείν), έλα ζύλνιν από 9 ζεξκνδεύγε ηνπνζεηήζεθαλ εληόο ηνπ δνρείνπ, όπσο ππνδεηθλύεηαη ζηελ εηθόλα 2. Απηά ηνπνζεηήζεθαλ ζε ηξία επίπεδα θαη θαηά κήθνο ηνπ δνρείνπ απνζήθεπζεο (επίπεδν 1 (1,1), (1,2), (1,3), επίπεδν 2: (2,1), (2,2), (2,3) θαη επίπεδν 3: (3,1), (3,2), (3,3)). Δληόο ηνπ δηαθέλνπ ηνπνζεηήζεθαλ ηξία ζεξκνδεύγε ζηηο ζέζεηο όπσο ππνδεηθλύνληαη ζηελ εηθόλα 2 (ζέζεηο (i), (ii) θαη (iii)). ...
... However, ICSSWH suffer by ambient heat losses, at nighttime, and extended research activities have been focused on the potential improvement of the thermal behavior in ICS systems by reducing the tank's thermal losses. Smyth et al. [3] studied the thermal properties of different types of integrated collector storage solar water heaters during day and night operation, while Henderson et al. studied the thermal performance of flat plate ICS for various inclinations [4]. The thermal performance of ICS systems can be improved using Compound Parabolic Concentrator (CPC) reflectors. ...
... During the day, it is related to the non-uniformity of the absorbed solar radiation [15], as well as the evaporation process of the PCM [9]. The setup that facilitates the effective measuring of relevant water temperatures is achieved by employing a grid of thermocouples suitably positioned inside the inner storage vessel, as indicated in Fig. 3 (positions: plane 1 (1,1), (1,2), (1,3), plane 2: (2,1), (2,2), (2,3) and plane 3: (3,1), (3,2), (3,3), for the measurement of the corresponding temperatures of the stored water: T 1;1 , T 1;2 , T 1;3 , T 2;1 , T 2;2 , T 2;3 , T 3;1 , T 3;2 , and T 3;3 ). Within the annulus, three thermocouples were placed in positions (i), (ii) and (iii) (for the measurement of the corresponding vapor temperatures: T v;i , T v;ii and T v;iii ). ...
... During the day, it is related to the non-uniformity of the absorbed solar radiation [15], as well as the evaporation process of the PCM [9]. The setup that facilitates the effective measuring of relevant water temperatures is achieved by employing a grid of thermocouples suitably positioned inside the inner storage vessel, as indicated in Fig. 3 (positions: plane 1 (1,1), (1,2), (1,3), plane 2: (2,1), (2,2), (2,3) and plane 3: (3,1), (3,2), (3,3), for the measurement of the corresponding temperatures of the stored water: T 1;1 , T 1;2 , T 1;3 , T 2;1 , T 2;2 , T 2;3 , T 3;1 , T 3;2 , and T 3;3 ). Within the annulus, three thermocouples were placed in positions (i), (ii) and (iii) (for the measurement of the corresponding vapor temperatures: T v;i , T v;ii and T v;iii ). ...
The work focuses on the experimental study of the heat diode mechanism in an Integrated Collector Storage Solar Water Heater (ICSSWH) for domestic applications. The solar device combines a horizontal cylindrical vessel with an asymmetric reflector trough (Compound Parabolic Concentrator – CPC). The cylindrical storage tank comprises two concentric cylindrical vessels: the outer absorbing vessel and the inner storage vessel. The annulus between the cylindrical vessels is partially depressurized and contains a small amount of water serving as Phase Change Material (PCM), which changes phase (mainly at low temperatures) thus producing vapor and creating a thermal diode transfer mechanism from the outer to the inner surfaces of the vessels. Several experimental results, including uncertainty analysis, are demonstrated through diagrams depicting temperature variations, mean daily efficiency and thermal losses coefficient. Additionally results from the variation of the temperature and the total pressure inside annulus are also presented. The results clearly show that the vapor's pressure plays the most important role regarding the thermal performance of the device.
... Smyth et al. [124] experimentally tested an inverted absorber ICSSWH with various transparent glass baffles. The baffles were placed at different locations within the collector cavity (see Fig. 36). ...
... These systems can be integrated with buildings without affecting the aesthetic value of the buildings. This article presents the Average vessel water temperature for all tests normalized to initial fill water temperature at start of test period [124]. Fig. 38. ...
... Designs of inverted absorber ICSSWHs, with differnt baffle arrangements, tested by Smyth et al.[124]. ...
... The thermal performance of SWH was evaluated for transparent baffles positioned at various parts in the collector cavity. The baffles positioned at the upper part of the exit aperture of the CPC decreased the thermal losses by convection suppression without a meaningful increase in the optical losses (Smyth, et al. 2005). The CPC using a plastic substrate permitted the heater to reach an optical efficiency of nearly 65%. ...
... Photograph of a coiled turbulator, b matrix turbulator (Vasanthaseelan et al. 2021), twisted tape (Gunasekaran et al. 2021) Fig. 9 Schematic of ICS-SWH(Smyth et al. 2005) ...
In this review, flat plate and concentrate-type solar collectors, integrated collector–storage systems, and solar water heaters combined with photovoltaic–thermal modules, solar-assisted heat pump solar water heaters, and solar water heaters using phase change materials are studied based on their thermal performance, cost, energy, and exergy efficiencies. The maximum water temperature and thermal efficiencies are enlisted to evaluate the thermal performance of the different solar water heaters. It is found that the solar water heaters’ performance is considerably improved by boosting water flow rate and tilt angle, modification of the shape and number of collectors, using wavy diffuse and electrodepositioned reflector coating, application of the corrugated absorber surface and coated absorber, use of turbulent enhancers, using thermal conductive working fluid and nanofluid, the inclusion of the water storage tank, and tank insulation. These items increase the heat transfer area and coefficient, thermal conductivity, the Reynolds and Nusselt numbers, heat transfer rate, and energy and exergy efficiencies. The evacuated tube heaters have a higher temperature compared to the collectors with a plane surface. Their thermal performance increases by using all-glass active circulation and heat pipe integration. The concentrative type of solar water heaters is superior to other solar heaters, particularly in achieving higher water temperatures. Their performance improves by using a rotating mirror concentrator. The integration of the system with energy storage components, phase change materials, or a heat pump provides a satisfactory performance over conventional solar water heaters.
Graphical abstract
Modification of solar water heaters
... 2D trough CPC with tubular absorber for solar thermal collection were introduced in previous sections. There is another innovative 'integrated collector storage solar water heaters' (ICSSWH) [117], of which un-truncated CPC was applied as primary reflector. The structure of ICSSWH is shown in Fig. 29: the CPC is connected with a 120°reverse circular reflector, a tertiary cavity and the storage vessel. ...
... Section view of inverted absorber ICSSWH[117]. ...
Compound parabolic concentrator (CPC) has been gaining ever-increasing attention from academic researchers and industrial developers owing to its stationary feature for solar energy collection with a higher efficiency. As a low concentration concentrator with a larger acceptance angle and without a tracking requirement, it is an attractive solution to improve the system performance and reduce the cost of photovoltaic (PV) system, solar thermal system, daylighting and lighting systems, etc. This study will present a comprehensive and up-to-date review of its design principles for miscellaneous configurations, applications, performance predictions and technological advances. Numerous technically focused studies since 2000 will be introduced and summarized. Finally, the outlook focusing on CPC designs and improvements will be proposed.
... Extended research activities have focused on the potential improvement of the thermal behaviour of ICS systems by reducing the tank losses. Smyth et al. [3] studied the thermal properties of different types of integrated collector storage solar water heaters during day and night operation, Henderson et al. studied the thermal performance of flat plate collector type ICS for various inclinations [4], while recent developments in ICS solar devices have been presented in the work of Singh et al. [5]. The thermal performance of ICS systems can be improved using Compound Parabolic Concentrator (CPC) reflectors. ...
... The horizontal (EeW) storage tank mounting can achieve Concentration Ratio (CR) larger than one when combined with CPC reflector troughs, thus reducing the water storage thermal losses, due to smaller absorber compared to aperture surface area [21]. Using the geometry suggested by Rabl [22], inverted absorbing surfaces using reflectors have been examined by Kienzlen et al. [23], Tripanagnostopoulos and Yianoulis [24], Eames et al. [25] and Smyth et al. [3]. One of the most important factors for the widespread installation of the ICS is the depth of the devices. ...
This paper presents the comparative study of two commercially available types of solar water heaters for domestic applications: Flat Plate Thermosyphonic Units (FPTU) and Integrated Collector Storage (ICS) solar water heaters. The conducted analysis initially focuses on the experimental investigation of the thermal behaviour and proceeds to the detailed holistic environmental analysis for both systems through a completed Life Cycle Assessment (LCA) study (i.e. throughout their fabrication, installation and operation phases).
... I.18 -(a) Schéma du CSIS de Mohamad,[47] (b) Schéma du CSIS de Faiman et al.,[48].Smyth et al.[65] étudient l'utilisation d'une cavité positionnée devant l'absorbeur, qui a pour fonction de concentrer le flux solaire et réduire les pertes par convection. La diminution des pertes convectives est obtenue grâce à des écrans transparents au sein de la cavité (figure I.19-a). ...
... Si le chauffage en partie basse répond à un critère énergétique (écart de température élevé entre la partie basse et l'absorbeur, et une réduction des pertes par convection et rayonnement), ces deux solutions proposées ne sont pas simples à mettre en oeuvre. I.19 -(a) Capteur avec cavité de Smyth et al,[65] (b) Capteur avec l'absorbeur inversé de Heeschen,[66].La nature de la surface de l'absorbeur joue un rôle important puisque les surfaces à basse émissivité dans les grandes longueurs d'onde vont réduire de façon importante les pertes au niveau de l'absorbeur. Certaines études peuvent être citées, telle celle de Tharamani et Mayanna [67] dans laquelle les auteurs étudient un alliage de Cu-Ni à bas coût pour des applications solaires. ...
The primary energy consumption of domestic hot water (DHW) in low energy house becomes proportionately large when compared to other energy consumptions. In new buildings, the integration of DHW systems do not present any difficulty. However, the thermal renovation market is poorly operated, with the storage's placement as the main constraint. When the storage must be placed outside the building, nowadays the solutions are not satisfactory, or by a thermal point of view (high losses), or an aesthetic point of view (tank visible from outside). In this thesis we studied an innovative solution of an integrated storage collector, allowing full integration at the roof and completly insulated. The storage is heated at the bottom. A cavity with high aspect ratio has been studied experimentaly and the cavity requires a stratification system. This system, a plate, was numerically studied to optimize the placement of the fluid at the top. Finally a global model was developed for annual performance simulations. This model proves satisfactory and shows that system performance is slightly lower than conventional systems (thermo- siphon). Heat loss was most detrimental factor. The design of a prototype was produced, and it will be tested during the year 2012.
... The use of transparent insulation on all the sides of water heater (but not the bottom) to compensate for the reduced solar radiation from the top has been studied by Prakash et al. [29]. The use of a movable night insulation cover at the top of the absorber plate is another method used to reduce system heat losses [30][31][32]. Further, a double glass cover without a night insulation cover has been suggested as a means of reducing heat loss from the water heater and studied. ...
... Again, the lowest system efficiency occurs for the system with the baffle plate and can be attributed its highest thermal losses. Table I compares the energy efficiencies of the water heaters for various water flow rates (0,10,20,30, and 40 kg h À1 ). As the flow rate changes from no-flow condition to 40 kg h À1 , the efficiency increases for each case. ...
The solar water heater is one of the fastest growing technologies in the renewable energy sector. Numerous designs of solar water heaters have been developed in the past that aim to make the system simple, reliable and cost-effective. The integrated collector storage (ICS) solar water heater is one of the simplest applications of solar energy for water heating. In an ICS solar water heater the collection of solar energy and the storage of hot water occur in a single unit. The ICS solar water heater is an isolated system that involves no moving parts and allows the user to be independent of grid electricity. The ICS solar water heater has been demonstrated to operate consistently and reliably for many years with a small initial investment relative to other solar water heater designs. However, the ICS solar water heater is not very efficient for overnight applications and its thermal output diminishes sharply as the time increases between solar irradiance and use. This performance decline can be attributed to the increased heat losses during off-sunshine hours. To make the ICS solar water heater a more economically viable
option, the system has evolved, utilizing new research advances to maximise solar radiation collection and minimise thermal losses as much as can be reasonably accomplished.
... The main advantages of solar heating systems using TPCT's are better thermal efficiency, antifreezing natural protection and thermal diode working characteristics. An inverted absorber 'Integrated Collector Storage Solar Water Heater'ICSSWH mounted in the tertiary cavity of a compound parabolic concentrator with a secondary cylindrical reflector using several types of transparent baffles at different locations within the collector cavity was experimentally investigated[62]. ...
... 9h An inverted absorber ICSSWH[62]. ...
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... The direct conversion of sunlight to electricity, well known as photovoltaic energy conversion, has been successfully demonstrated using various photonic materials with high photon absorption capabilities classified in two main categories, organic and inorganic semiconductors (Nakamura et al., 2019;Kim et al., 2020). The successfully converted solar energy is used in daily life activities such as water heating, solar cooking, deep water pumping, household device PV powering, and clean hydrogen generation, out of a total annual provision of 18 TW solar energy available on the earth's surface (Smyth et al., 2005;Kalyanasundaram and Grätzel, 2012;Chandel et al., 2015;Aramesh et al., 2019;Kuang et al., 2019). ...
Energy is the driving force behind the upcoming industrial revolution, characterized by connected devices and objects that will be perpetually supplied with energy. Moreover, the global massive energy consumption increase requires appropriate measures, such as the development of novel and improved renewable energy technologies for connecting remote areas to the grid. Considering the current prominent market share of unsustainable energy generation sources, inexhaustible and clean solar energy resources offer tremendous opportunities that, if optimally exploited, might considerably help to lessen the ever-growing pressure experienced on the grid nowadays. The R&D drive to develop and produce socio-economically viable solar cell technologies is currently realigning itself to manufacture advanced thin films deposition techniques for Photovoltaic solar cells. Typically, the quest for the wide space needed to deploy PV systems has driven scientists to design multifunctional nanostructured materials for semitransparent solar cells (STSCs) technologies that can fit in available household environmental and architectural spaces. Specifically, Plasma Enhanced Chemical Vapor Deposition (PECVD) technique demonstrated the ability to produce highly transparent coatings with the desired charge carrier mobility. The aim of the present article is to review the latest semi-transparent PV technologies that were impactful during the past decade with special emphasis on PECVD-related technologies. We finally draw some key recommendations for further technological improvements and sustainability.
... The improvement of the thermal performance is also achieved by enhancing the collection of solar irradiation through the use of reflectors, based on symmetric and asymmetric CPC geometries [38]. Novel configuration of tanks included in ICSSWH units mounted within an asymmetric shaped reflector were recently investigated [39], and they were also applied to horizontal planar liquid-vapour thermal diode units to enhance heat retention during cool-down periods [40]. Such novel ICS tank configurations were developed, tested, and experimented to increase heat retention, as reported in several studies [41,42]. ...
Integrated collector storage units are typically affected by convective and radiative heat losses which significantly reduce their energy performance. To enhance solar collection and heat retention, innovative techniques and novel design of such units are being more and more developed. In this framework, this paper focuses on the design and optimization of a prototypal high-vacuum integrated collector storage solar water heater. The proposed unit allows for reaching high temperatures of the stored water and for reducing the temperature drop during non-collection periods. This goal is achieved by suppressing the convective heat losses into the system by keeping the pressure into the related enclosure below 0.01 Pa and by applying a special selective coating to the solar absorber surface to drastically reduce radiative losses as well.
In the paper, details about the system design and the conducted experimental tests are reported. In addition, a new mathematical model able to assess the energy performance of the innovative prototype is presented. This tool, based on a detailed 3-D transient finite-difference thermal network, was validated against the gathered experimental data. By such a tool the optical properties of the adopted selective coating are optimized for maximizing the system thermal efficiency. Finally, with the twofold aim of showing the potentiality of the developed code, as well as the effectiveness of the presented innovative solar collector prototype, a comprehensive case study referred to three different European weather zone is presented. Promising results in terms of energy savings (0.73 MWh/y) and CO2 emission reduction (149 kgCO2/y) are achieved.
... Few researchers used different kinds of approaches such as insulated cover, implementing different collector designs, concentrators to increase the efficiency of integrated collector storage solar water heating (ICS SWH) system [32,265]. The tank's geometry, such as rectangular, cylindrical [44,240], was examined to enhance the ICS system performance. Garnier et al. [94] developed an ICS-SWH system to study the internal flow and heat transfer mechanism using the computational fluid dynamics (CFD) model. ...
Solar water heating (SWH) is a clean, reliable, and cost-effective method of harnessing solar energy effectively to satisfy 50-80 % of hot water needs. SWH technology is currently employed in many countries to reduce utility bills in both commercial sectors and houses. With the advancement of technology, SWH systems can be operated efficiently in any geographical area and climatic region in the world. However, the installation and overall performance of the system are still questionable. This review aims to provide an overview of the most commonly used solar water heating technologies. This paper seeks to critically analyze and summarise recent advancements in the technology, including storage tank/integrated collector storage solar water heater, solar water heaters (active and passive), solar thermal collectors, including concentrated and non-concentrated collectors and different policies. Substantial experimental studies and research works, including optimal designs, geometric modifications, and simulation works, were carried with respective technologies to enhance the system performance. Besides, the effect of solar collectors, radiation, region, water tank temperature, experimental modelling/simulation and studies conducted in Asia, America and Europe on SWHS improvements are also included. Policy developments of renewable energy heat consumption in different countries by technology from 2012 to 2024 were also included for better understanding. A detailed status on current and ongoing solar power projects based on solar technologies for electricity generation has been provided. The final section introduces the technical advancements of SWH technologies, policies, and future research SWHS.
... Several studies (Smyth et al., 2005, Burns et al., 1985, have been conducted on the choice of shape design for the storage tank. Among the two major designs (rectangular and cylindrical), the cylindrical tank showed an increased heat transfer rate (Kaushik et al., 1994, Gautam et al., 2017. ...
In recent years, various energy sources and methods have been used to heat water in domestic and commercial buildings. The known sources for water heating include electrical energy and solar radiation energy in the urban regions or burning of firewood in the rural areas. Several water heating methods may be used such as electrical heating elements, solar concentrators, flat plate collectors and evacuated tube collectors. This thesis focuses on ways to further improve the system’s performance for water heating through the combined use of solar energy and solar concentrator technique. Furthermore, the study proposed an alternative design method for the hot water storage tank.The solar collector-supporting frame was designed and analysed using Solidworks®. The forces acting on the structural members were simulated to determine the capacity of the frame to sustain the load, and the possible regions on the supporting frame, which could potentially fail while in operation.Energy performance was simulated for five years of operation using Matlab Simulink® software. This simulation was based on the use of three different data. The first is a five-year weather database of the City of Tshwane in South Africa. The second is a hot water consumption profile for a typical household. The third is the cost of additional heating with electricity depending on the time of use. This simulation allowed the validation of the choices of the different elements of the heating system.This study allowed the development of an approach for the design of a solar heating system by optimising the dimensions of the different elements for a typical household and a specific region.In addition, the use of polymeric materials and other materials like polyurethane, salt and aluminium is possible for the development of a hot water storage tank based on their inherent properties.Extending the findings in this thesis will further improve the designs for solar concentrator technologies and solar water heating systems. Therefore, some recommendations and suggestions are highlighted in order to improve the overall system design, analysis and performance
... The improvement of the thermal performance is also achieved by enhancing the collection of solar irradiation through the use of reflectors, based on symmetric and asymmetric CPC geometries [38]. Novel configuration of tanks included in ICSSWH units mounted within an asymmetric shaped reflector were recently investigated [39], and they were also applied to horizontal planar liquid-vapour thermal diode units to enhance heat retention during cool-down periods [40]. Such novel ICS tank configurations were developed, tested, and experimented to increase heat retention, as reported in several studies [41,42]. ...
This paper focuses on the design of an innovative high-vacuum solar thermal collector, for which a novel dynamic simulation model is developed. As it is well known, standard flat plate solar thermal collectors are affected by thermal losses which significantly reduce their energy performance. Among all thermal losses, convective and radiative account for approximately 80% of the overall. To reduce these losses, a novel innovative flat plate solar thermal collector characterized by a high-vacuum space (i.e. 10-8 mbar) between the glass cover and edge is developed. The vacuum space is made with the aim of insulating the absorber serpentine with a consequent convective thermal loss reduction. In addition, the serpentine absorber system is suitably painted with a solar coating for reducing the radiative thermal loss. Thus, the presented prototype allows store hot water with no need for any additional storage system.
In this paper, a mathematical model able to assess the energy performance of the innovative high-vacuum prototype is also presented. The tool is based on a detailed 3D transient finite-difference thermal network and it is validated against the experimental data obtained by different experimental tests.
... In recent decades, CPC has emerged as a promising solution for different applications, where the integration with PV is the dominant application following by solar thermal, lightning, and other areas (Tian et al. 2018). Regarding solar thermal application, Smyth et al. (2005) investigate the performance of a storage water heater integrated with a CPC using different baffle arrangement. Results revealed that the installation of the baffles at the upper section of the CPC exit aperture has the best performance by decreasing the convective thermal heat losses without a significant reduction in optical efficiency. ...
Hybridisation, using an alternative heat source besides solar power, as a back-up unit can be a promising solution for the deployment of Compound Parabolic Concentrator (CPC) technology in low-temperature (100–150°C) industrial applications. In this research, a new integration of a non-evacuated CPC collector with a back-up system was studied for performance optimisation where a thermo-economic evaluation was carried out to investigate the viability of the proposed model for industrial deployment. In operational assessment, the effects of different operating modes as the manipulation of oil mass flow rate and controlling temperature and their interaction on collector efficiency and thermal behaviour were analysed. Results revealed that the maximum collector efficiency reaches about 72% suggesting improvements compared to the similar works. The hybrid mode operation was also evaluated as accurate and instantaneous proportionally to the weather changes. In addition, thermo-economic assessments identified the optimum adjustment based on the minimum payback period.
... There are various types of solar water heaters. The most known are, the classical flat-plate collector system, the vacuum tube system, the solar concentrating system and the collector /storage system [1][2][3][4][5][6]. ...
A study was undertaken on the performance of an integrated collector-storage solar
water heater consisting of a cylindrical water storage tank combined with a parabolic reflector, manufactured at the Laboratory of Energetic and thermal Processes (LEPT). The theoretical determination of the heat transfer phenomena which occur in the system was used to elaborate a numerical model, needed for a parametric evaluation of the system. The parametric study identified
the parameters which have the higher influence on the system efficiency and allowed us to quantify
the contribution of each of them. We can notice that for the climatic data, the cold water input
temperature as well as the ambient temperature showed a major effect on the warm water output.
For the construction characteristics, the most influencing factors are the transmissivity of the glazing and the painting of the tank.
Keywords: Solar energy - Water heater - Integrated collector storage system - Numerical simulation
- Thermal efficiency - Optical efficiency
... However, due to the great potential offered by these devices, an intense research interest has been devoted towards improving their thermal behavior. [3][4][5] Such an improvement for the case of the ICS systems has been achieved by adapting compound parabolic reflectors (CPC). In this way, the collection and absorption of reflected solar radiation takes place on the absorbing surface while there is a direct connection to the water main. ...
The distribution of solar irradiance on the absorbing surface of a typical integrated collector storage (ICS) system combined with reflector troughs is commonly studied by means of ray tracing techniques. A conceptually different alternative is offered by the method of the average number of reflections (ANR). In the present work, the latter is employed for the systematic optical study of realistic ICS models. In all cases, the solar devices consist of twin cylindrical storage tanks which are mounted on top of stationary asymmetrical CPC‐type reflectors. The emphasis of the current research is mainly placed on the evaluation of the ANR reliability for the calculation of the optical efficiency of the related twin‐tanked devices. Additionally, useful operational parameters, such as the optical performance of the proposed geometries, are also determined. The behavior of the tested ICS systems reveals that the optical efficiency may vary in the range of 0.75 to 0.91, exhibiting a strong dependence on the geometric parameters of the solar devices. The highest efficiency is achieved by the systems which combine large reflecting area and storage tanks in close proximity.
Highlights
• Geometric analysis of double‐tanked ICS solar water heaters.
• Calculation of the average number of reflections.
• Optical efficiency of the examined ICS solar water heaters.
• Nonuniform illumination of the storage tank of each ICS solar water heater.
... Many storage tank configurations are being researched such as cylindrical [41][42][43][44], rectangular [24,32,[45][46][47][48][49][50][51][52], triangular [30,[53][54][55], and trapezoidal [36,56] while others include two parts one exposed and one insulated [32,33,57]. While some systems help increase the heat transfer from absorber plate to the water [53,54], others improve thermal stratification in the water storage tank [56] or both [33,58,59] or have better heat retention capability [59][60][61]. ...
Integrated collector storage is a long established simple low cost solar water heater configuration combining the solar collector with a storage tank into a single unit. Previous studies have shown the potential of integrated collector storage solar water heaters to significantly reduce domestic energy requirements for water heating, however challenges still remain to integrate them in roof/façades and ensure appropriate domestic hot water demand. In this article, a novel integrated collector storage solar water heaters is being investigated. The configuration and geometry proposed incorporates an embedded heating element to provide a self-contained domestic hot water system and consider roof integration restriction allowing the unit to be embedded within a structural insulated roofing panel system. The proposed system also utilizes an inlet diffuser designed to reduce the disruption to the stratification within the storage during and following draw-off. This article presents a Computational Fluid Dynamic analysis of internal flows and heat transfer regimes within this new collector configuration and compares its performance against previous developed prototypes using empirical testing. The increased aspect ratio of the new design was shown to significantly alter the heating and cooling characteristics of the collector, both gaining and loosing heat at a greater rate than the original prototype. The computational analysis showed that the collector charges effectively with some stratification. Higher draw-off rates however resulted in higher bulk water outlet temperatures, providing better energy delivery efficiency. The inlet diffuser was also shown to improve the thermal efficiency of the unit overall. The empirical testing shows the improvement in performance of this novel integrated collector storage solar water heaters against previous developed prototypes. The study highlights the need to review the effect of draw-off regime upon the performance of such systems in order to identify optimal regime and control strategy.
... These designs achieved higher efficiencies than other flat plate collectors under low irradiation conditions. A rectangular built in storage water system was investigated but this shaped systems have a low solar gain and poor heat transfer during winter in northern latitudes [10]. A triangular built-in-storage solar water heater, had also been studied under winter conditions that resulted to a higher solar gain and enhanced natural convection, leading to a higher water temperature [11]. ...
... • shapes of the tanks like, cylindrical, rectangular [27][28][29], but the heat transfer rate is found to be increased by using cylindrical tanks with triangular ICSSWHS [30,31]. Reflectors are introduced to increase the collector efficiency because of the increase in solar radiation intensity [32][33][34]. ...
The solar water heating system (SWHS) is one of the most common application of solar energy utilization system. The usage of solar water heating system is not commonly employed throughout the globe, due to its high initial cost. The advancement in SWHS will lead to be beneficial over conventional system over the long span of time. The eco-friendly nature of such system promotes these systems to be used frequently in both domestic and industrial heating. The investigators throughout the globe focusing on technical advancement as well as economic feasibility of SWHS. The present study focused on to report such studies, which demonstrates the economic feasibility of SWHS in the long run. The payback period of SWHS varies from one origin to other as it depends on numerous factors like price of fossil fuels, rate of subsidy, solar insolation etc. Initially the paper reported the basic components of SWHS, and their advancements, further the global scenario of SWHS is discussed, followed by the studies reported on a techno economic analysis of SWHS, which shows that the economic feasibility is equally important as technical feasibility for its implementation. The last section inculcates the recent studies on the technical advancement of SWHS and the future research trends of SWHS were discussed.
... An incoming and outgoing vent provided in the baffle plate keep the water of the two columns in contact. Smyth et al. [128] have experimentally tested an inverted absorber ICS solar water heater with various Fig. 12 Triangular built-in-storage solar water heater with baffle plate [73] transparent glass baffles (see Fig. 13) placed at different locations within the collector cavity. Results of the study have indicated that the baffle located at the upper portion of the exit aperture in the CPC has reduced the heat losses, as a result of convection suppression, without increasing optical losses significantly. ...
The direct conversion of solar to thermal energy is highly efficient, more
environmental friendly and economically viable. Integrated collector storage solar
water heaters (ICSSWH) converts the solar radiation directly into heat at an appreciable
conversion rate and in many cases using concentrating means. These systems are
compact, aesthetically attractive and reasonable in construction and can reduce the
environmental impact up to 40 %. They also have high collection efficiency factor and
energy saving potential. Despite of many advantages, ICS solar water heaters suffer
from high thermal losses in the night/overcast sky conditions. In this article, authors
discuss the recently developed new and improved ICS designs and strategies used for
reducing thermal losses from such devices, especially in non-collection period. The
systems have been evaluated based on a followed categorization to non-concentrating,
concentrating and systems with phase change materials.
... This concept was further improved by introducing cylindrical vessels (the collector and storage tank combined), which are still used in many commercial designs today. However, it was observed that rectangular vessels could also function and perform similar to cylindrical vessels [8][9][10]. Other than cylindrical geometry, triangular-designed ICSSWH systems were also introduced, and were found to improve heat transfer rates because of increased natural convection currents [11,12]. ...
... A new type of inverted absorber ICS SWH placed in a tertiary cavity of CPC reflectors incorporated with a secondary tubular shaped reflector was tested by Smyth et al. [93]. Different transparent baffles were positioned in the ICS cavity and the results showed that the incorporation of baffle plates could not only improve the optical efficiency, but also increase the thermal retention at a rate of 59.3% by suppressing the convection losses. ...
One of the most widely known solar thermal applications is solar water heating. In terms of installation expenditures and energy cost over the total life of the system, solar water heating technology has proven to be cost efficient for several domestic and industrial applications. Technological practicability of these systems has long been recognized and is presently employed in commercial sectors of many countries. This paper presents an overview of various types of solar assisted water heating systems and their market potential. Residential solar water heating is a promising age old technology, which has been evolved and developed both in the range and quality as a successful packaged market–product. The first part of this paper analyzes the performances along with how unique they are of different types of solar water heating systems and the later part of the paper covers its economic aspects.
... Using a heat retaining vessel consisting of an outer absorbing section and a perforated inner sleeve with a low thermal mass [11], enable flow from the outer channel to the inner store during collection periods but reduce flow through increased resistance, during non-collection periods. Experimental investigations [12][13][14] have shown using heat retaining vessels increase collection and improve heat retention. Two-phase transfer of heat from the solar collector to the store avoids scaling, fouling and the need for freeze protection, with suitable fluids, corrosion is far more limited than with aqueous systems. ...
After over a century of system development, solar water heating can be considered to be an established mature technology. In seeking to achieve economic viability systems have been developed, for specific applications and climatic contexts that produce often optimal hot water per unit cost. The development of solar water heaters is discussed with the emphasis on overall systems, their features, characteristics and performance though some key aspects of component development are also outlined. 1. Origins The solar water heater first manufactured commercially was an integral collector storage unit patented in 1891, in which, the hot water store absorbs solar energy directly usually from beneath a glazed aperture. Nocturnal losses to ambient usually led to water heated by the sun on one day being luke-warm early the next day. As this reduced both user convenience and the overall solar fraction and led to thermosyphon solar water heaters with diurnal heat storage displacing integral collector storage water heaters. [1.2] The thermosyphon solar water heater, was patented in 1910 by Bailey [3], used flat-plate collectors in which a single serpentine tube removed heat from the absorber plate. More modern header-and-riser absorber tube arrangements emerged later. [4] This paper explores the characteristics of the solar water heater types that have emerged over the centenary since Bailey patented the first solar water heater with separate solar collector.
... However they can achieve Concentration Ratio CR > 1 when combined with Compound Parabolic Concentrating (CPC) reflector troughs, reducing therefore the water storage thermal losses, due to smaller absorber than aperture surface area [7]. Using geometry suggested by Rabl [8], inverted absorbing surfaces using reflectors have been examined by Kienzlen et al. [9], Tripanagnostopoulos and Yianoulis [2], Eames et al. [10] and Smyth et al. [11]. Horizontal cylindrical single tank ICSSWH systems with symmetric and asymmetric CPC reflectors have been studied by Tripanagnostopoulos et al. [12], Souliotis and Tripanagnostopoulos [13], Tripanagnostopoulos and Souliotis [14], Souliotis et al. [15] and Souliotis et al. [16]. ...
... It was reported for a triangular ICSSWH design that the triangular crosssection helps increase the heat transfer rate from absorber surface to water [18,19], while it was found that a trapezoidal shape helps improve thermal stratification in the water storage tank [20]. In another configuration modification, the storage tank is considered to have two parts; the part comprising the lower two-thirds is exposed to solar radiation, while the top one-third part is heavily insulated [21,22]. This design was observed to have better heat retention capability than a tank completely exposed to solar radiation . ...
The integrated collector-storage solar water heater (ICSSWH) is one of the simplest designs of solar water heater. In ICSSWH systems the conversion of solar energy into useful heat is often simple, efficient and cost effective. To broaden the usefulness of ICSSWH systems, especially for overnight applications, numerous design modifications have been proposed and analyzed in the past. In the present investigation the storage tank of an ICSSWH is coupled with an extended storage section. The total volume of the modified ICSSWH has two sections. Section A is exposed to incoming solar radiation, while section B is insulated on all sides. An expression is developed for the natural convection flow rate in section A. The inter-related energy balances are written for each section and solved to ascertain the impact of the extended storage unit on the water temperature and the water heater efficiency. The volumes of water in the two sections are optimized to achieve a maximum water temperature at a reasonably high efficiency. The influence is investigated of inclination angle of section A on the temperature of water heater and the angle is optimized. It is determined that a volume ratio of 7/3 between sections A and B yields the maximum water temperature and efficiency in the modified solar water heater. The performance of the modified water heater is also compared with a conventional ICSSWH system under similar conditions.
... Greek symbols a system acceptance angle (°, rad) a r absorptance of receiver surface c factor of the diffuse solar radiation d argument of Z function (°, rad) e r surface emittance Z mathematical function g D mean daily thermal efficiency h incident angle of the solar radiation (°, rad) h c half acceptance angle (°, rad) q water density (kg m À3 ) q r reflectance s total transmittance of the transparent cover (glazing) w angle of parabolic reflector (°, rad) w m maximum value of angle w (rim angle) (°, rad) u angle of parabolic reflector (°, rad) u m maximum value of angle u (rim angle) (°, rad) x angle of involute reflector (°, rad) x m maximum value of angle x (°, rad) Eames et al. (2001) and Smyth et al. (2005). Horizontal cylindrical single tank ICSSWH systems with symmetric and asymmetric CPC reflectors have been studied by Tripanagnostopoulos et al. (2002), Souliotis and Tripanagnostopoulos (2004) and Tripanagnostopoulos and Souliotis (2004c). ...
A novel integrated collector storage solar water heater (ICSSWH) was designed, optically analysed and experimentally studied. The unit was based around a heat retaining ICS vessel design consisting of two concentric cylinders mounted horizontally inside a stationary truncated asymmetric compound parabolic concentrating (CPC) reflector trough. The annulus between the cylinders was partially evacuated and contained a small amount of water, which changed phase at low temperature, producing a vapour and creating a thermal diode transfer mechanism from the outer absorbing surface to the inner storage vessel surface. The absorbing outer vessel surface covered with selective absorber film and was partially exposed to solar radiation. The remaining vessel surface area (including the vessel ends) was thermally insulated to improve heat retention during the night. Curved reflectors with a high reflectance along with high transmittance glazing were also used to improve effective operation of the ICS system. The thermal behaviour of the ICS system was compared to that of a Flat Plate Thermosiphonic Unit (FPTU). The experimental results showed that the ICS system is as effective during daily operation as it is during the night. Furthermore, the thermal loss coefficient during night gives similar values between the ICS system and FPTU.
The use of solar energy to heat water is the more critical application of solar energy. Researchers are trying to develop different methods to improve the efficiency of solar water heaters to meet the increasing demand for hot water due to global population growth. To reduce the cost and increase the efficiency of solar heaters, the solar collector and the storage tank are combined into one part, and this system is called solar storage collector. It can be defined as geometric shapes filled with water, painted black, and placed under the influence of sunlight to gain the largest amount of solar energy. This article presents the various designs of solar storage collector. This review showed that design variables and design shape significantly affect the efficiency of the solar heating system. Climate and operational factors also have a strong influence on the performance of solar heating. Furthermore, scientists and researchers have also used nanotechnology, solar cells, and mirrors to improve other stored solar collectors' performance. Finally, recently published articles indicate an increase in interest in improving the efficiency of solar storage collector by creating new designs that enhance the economic and practical viability.
Conversion of solar energy to heat energy is a cost effective, sustainable and an efficient technology to heat water. Solar integrated collector-storage type of water heaters (ICSSWH) is a water heating device which alchemizes solar radiation directly into heat so that it is used for water heating. These systems are compact, simple in design and free from copper tubes bounded structures which unnecessarily causes heat losses and leakage issues. Their collection efficiency is usually higher than commonly used flat plate collectors (FPC). Despite of many advantages, the main disadvantage of compact integrated collection-storage type of water heaters (ICSSWH) is high heat losses during night hours which decreases the water affects the thus decreases the overall efficiency of the system. However, there are some strategies to minimize this heat loss from the system at the time when sunshine is not available; some of the methods are discussed in this paper. Moreover, in this article, the authors discuss the latest development in the new and improved compact water heater designs. In present paper authors critically reviewed various designs of ICSSWH. Use of insulated cover during night, introducing baffle plate structure, using PCM materials and using reverse thermosyphon valve are some of the strategies to minimize the heat losses from the system these methods are discussed in the present paper. Connecting tanks in series is also an effective method to overcome this problem of heat loss during night. In this paper the effect of connecting tanks in series on water temperature has been discussed. This paper presents an overall summary on compact ICSSWH systems which can be useful for further research to design and develop a new small size solar water heater.
An advanced mathematical model capable of simulating the energy performance of an innovative Integrated Collector Storage Solar Water Heater (ICSSWHs) is presented. Usually, ICSSWH devices available in the market are typically simple and low-cost, combining solar heat collection and storage functions in one unified vessel. However, they exhibit higher heat loss characteristics when compared to standard solar collector systems, with a subsequent reduction in energy performance during night-time and non-collecting hours. An innovative ICSSWH prototype was developed at the Centre for Sustainable Technologies (CST) at Ulster
University using a patented, innovative thermal diode feature, attained by incorporating a liquid-vapour phase change material (PCM) and very low pressures. In order to fully investigate the energy performance of the proposed prototype, a suitably dynamic simulation model has been
developed and validated in MatLab environment. All modelled temperatures
are ± 1°C from the respective experimental measurements. The developed model has been used to evaluate the ICSSWH energy performance by varying several pivotal parameters (physical features and materials) in order to produce an optimized device.
A novel gravity based passive solar tracking mechanism; suitable to a linear solar concentrating collector has been conceptualized, developed, simulated, analyzed and tested experimentally. Attempt has been made to minimize the tracking load and error by controlling in dripping rate or filling rate of liquid in the gravity system. The identified key influencing design parameters in the proposed mechanism are sprocket wheel radius, spring stiffness and tracking radius. Large sprocket wheel, low stiff spring and small tracking radius minimizes the tracking loads. The recommended sprocket wheel radius and tracking wheel radius are 125 mm and 60 mm respectively. The simulation studies are validated with the experimental results. Practically obtained collector’s incidence angle is compared with the minimum required (theoretical) incidence and found a satisfactory match. The improvement in thermal efficiency of the collector with the proposed tracking mechanism has been highlighted by comparing the efficiency of intermittent tracking collector.
A novel gravity-based power-free solar tracking mechanism has been developed to track a linear solar concentrating collector. Multireflector compound parabolic collectors having three parabolic segments and two flat surfaces is chosen due to its high intercept factor and suitability to the current tracking. The working of tracking mechanism is studied to find the tracking loads in the east and the west sides of collector. A generalized mathematical model is derived to simulate the tracking motion from the sunrise to sunset. The identified design variants are sprocket wheel diameter, spring stiffness, solar collector’s weight, counter balance, and tracking wheel radius. The spring length is derived from the constraints. To make a compact product, the tracking load has been minimized at large sprocket wheel, low stiff spring, lighter collector weight, and small radius of tracking. For a typical collector load of 50 kg, the designed tracking load is 50 kg with 620 mm spring length, 250 mm of sprocket wheel diameter and 60 mm tracking radius.
The thermal performance of an integrated collector storage solar water heater (ICSSWH) is numerically examined using the numerical software FLUENT 6.3. As this solar system presents the disadvantage of its high night thermal losses, a new strategy helping to reduce these losses is proposed. A particular system in which the storage tank is covered with an outer glass tube is studied and a parametric study is conducted in order to evaluate the optimal air spacing gap between the water tank and the covering glass tube which minimizes this system's heat losses. A 3D computational fluid dynamics (CFD) model interpreting this modified system is so developed and its thermal performance is compared to that of the noncovered tank based ICSSWH. The analysis of these solar systems daily performance shows that the modified ICSSWH is able to generate more thermal output and presents the advantage of its lower thermal losses. Regarding the night operating, this covered tank based ICSSWH is shown more effective in retaining higher temperatures for longer period, resulting so in lower night thermal losses. Results also suggest that the best performance corresponds to the lowest air gap spacing (L = 0.005 m).
The design, construction, and performance test of a cylindrical solar water heater are presented. It consists of a transparent 900 mm long and 300 mm diameter cylindrical tube made from a 2 mm thick polyvinyl chloride (PVC) material housing a spiral copper tube painted black for improved solar energy harvesting. The copper tube is 15,000 mm long with outer and inner diameters of 12.70 and 11.40 mm, respectively. The transparent PVC material acts as the glazing. Experimental tests on the system were carried out for three different mass flow rates of 10.8, 7.2, and 3.6 kg/h. The results reveal that the maximum efficiency obtained during the test period were 57.09%, 53.99%, and 56.21%, respectively, for mass flow rates of 3.6, 7.2, and 10.8 kg/h. The Hottel-Whillier-Bliss characterization test performed on the solar water heater revealed an intercept on the y axis of 0.30-0.40, while the gradient gave values in the range of -2.94 to -6.91. Overall, the solar water heater has the potential of generating hot water at a very fast rate, with a response time to insolation change that is less than 30 minutes.
Solar water heating can be considered to be an established mature technology. The achievement of this status is the outcome of over a century of system development that culminated with a flourish of innovation in the last thirty years. Drivers for research and development have been achieving economic viability by devising systems that, for specific applications in particular climate contexts produced more hot water per unit cost. Reductions in both initial capital and installation costs have been achieved as well as in those associated with subsequent operation and maintenance. Research on solar water heating is discussed with the emphasis on overall systems though some key aspects of component development are also outlined. A comprehensive taxonomy is presented of the generic types of solar water heater that have emerged and their features, characteristics and performance are discussed.
The comparative performance of a cylindrical solar water heating system with and without reflective surface is presented. The major components of the water heater are a transparent cylindrical PVC material acting as the glazing and a copper tube painted black for improved solar energy absorption. One of the systems has it’s under segment, about 45°, lined with an aluminium foil to act as a reflective surface. The two systems were tested under the meteorological condition of the Federal University of Technology, Owerri, Nigeria. Results obtained reveal a maximum exit water temperature from the solar water heater of 68 and 50°C for the reflective and non reflective surface conditions, respectively. The maximum efficiencies were determined as 70% and 40%, respectively for the reflective and non reflective surface conditions while the Hottel-Whillier-Bliss characterization showed that addition of the reflective surface improved the solar water heater’s ability to absorb energy by about 100% and reduced the rate at which it loses by up to 25%. Thus the system with a reflective surface has better capability of converting solar energy to heat for hot water generation.
This paper presents up to date developments in integrated collector storage solar water heater (ICSSWH) using compound parabolic concentrator (CPC) collector. Performance of integrated compound parabolic concentrator storage solar water heater (ICPCSSWH) is affected by various parameters such as positioning and arrangements of water tanks, reflector types, absorber surfaces, glazing and other design parameters. The various designs of ICPCSSWHs and their performance analysis are reviewed. Recent developments in CPC based ICSSWH show a hopeful design to consume solar energy as a reliable heating source for water heating applications. But, by its collective collection and storage function undergoes significant thermal losses to ambient, particularly at non-collection periods.
SUMMARYA detailed comparative assessment is reported on the thermal performance of integrated collector-storage (ICS) solar water heaters with various strategies for reducing top heat losses. The objective of this investigation is to assess and compare heat loss reduction strategies. The shape of ICS solar water heater considered in present investigation is rectangular. The thermal performance of the solar water heater is evaluated and analyzed for the following cases: (1) single glass cover without night insulation; (2) single glass cover with night insulation; (3) double glass cover without night insulation; (4) transparent insulation with single glass cover; and (5) insulating baffle plate with single glass cover. Energy balances are developed for each case and solved using a finite difference technique. The numerical assessment of the system performance is performed for a typical July day in Toronto. Each strategy is observed to be beneficial, reducing top heat losses, and improving system performance. The greatest performance enhancements are observed for the water heater with a single glass cover and night insulation and for the system with a double glass cover and without night insulation. Copyright © 2010 John Wiley & Sons, Ltd.
A review of solar water heating systems for domestic and industrial applications is presented. They are grouped into two broad categories as passive and active solar water heating systems. Each of them operates in either direct or indirect mode. Their performances, uses and applications, and factors considered for their selection are reported. The active systems generally have higher efficiencies, their values being 35%–80% higher than those of the passive systems. They are more complex and expensive. Accordingly, they are most suited for industrial applications where the load demand is quite high or in applications where the collector and service water storage tank need not be close to each other or for the applications in which the load requires more than one solar collector. On the other hand, the passive systems are less expensive and easier to construct and install. They are most suitable for domestic applications and in applications where load demand is low or medium. Generally more research and development work are needed to further improve the existing level of efficiency for it to serve effectively as a viable alternative to the conventional means of hot water generation. The actual field testing experiences, together with the prospects and economic problems that affect popularization of the systems, are also presented. Their possible solutions are suggested.
The present review is intended to encompass the heat transfer literature published in 2005. While of a wide-range in scope, some selection is inevitable. We restrict ourselves to papers published in English through a peer-review process, with selected translations from journals published in other languages. Papers from conference proceedings generally are not included, though the Proceeding itself may be cited in the introduction. A significant fraction of the papers reviewed herein relates to the science of heat transfer, including experimental, analytical and numerical studies. Other papers cover applications where heat transfer plays a major role, not only in man-made devices but in natural systems as well. The papers are grouped into major subject areas and then into subfields within these areas. In addition to reviewing the literature, we mention major conferences held in 2005, major awards related to heat transfer presented in 2005, and books on heat transfer published during the year.
The Integrated Collector Storage Solar Water Heater (ICSSWH) developed from early systems comprised simply of a simple black tank placed in the sun. The ICSSWH, by its combined collection and storage function suffers substantial heat losses to ambient, especially at night-time and non-collection periods. To be viable economically, the system has evolved to incorporate new and novel methods of maximising solar radiation collection whilst minimising thermal loss. Advances in ICS vessel design have included glazing system, methods of insulation, reflector configurations, use of evacuation, internal and external baffles and phase change materials.
The performance of an asymmetric inverted absorber line axis compound parabolic concentrating collector (IACPC) was evaluated under a solar simulator. The IACPC had a concentration ratio of 2 and a maximum length-to-width ratio of 2.5 with provision to adapt from an untruncated collector to a half height truncated version. The selectively surfaced absorber/receiver was copper sheeting onto which was reverse-bonded tubing along the long axis of the IACPC. High reflectance film covered the aluminium substrate of the collector. Water was the heat transfer fluid flowing in the system. Stagnation and efficiency tests were undertaken for the full and truncated versions of the IACPC at various absorber gap heights to determine the optimum performance and absorber gap configuration. Overall performance is marginally better for the higher gap height absorber configurations than for the lower at the range of collector water inlet temperatures of 20 – 70 °C.
Integrated collector storage (ICS) systems, consisting of a pressure-resistant single tube absorber in front of an involute reflector and covered by highly transparent insulation material, have been developed. Compared to the earlier multiple-tube design the system performance has been improved. For an absorber area of 4.2 m² in Freiburg (W. Germany) and a hot water demand of 160 liters/day, the annual solar fraction of the system is 65% with an annual efficiency of 32% (required hot water temperature is 45°C). There is no risk of freezing. Detailed computer simulations for the ICS and the back-up heating system have been made and show the influence of various parameters on the system performance. Compared to conventional solar domestic hot water systems the performance of the ICS systems is almost as good as that of systems with vacuum tube collectors but ICS systems require much less complicated technology.
Passive solar water heaters can be divided into two classes: systems in which the functions of heat collection and storage are separate (the thermosiphon flat plate systems), and systems with combined collection and storage - the integral passive solar water heater (IPSWH). IPSWH systems are much less widely known despite some inherent advantages, including simplicity, low cost, and resistance to freezing. The first solar water heaters widely used in the U.S were IPSWHs. They gradually fell out of favor because of night cooldown and tank corrosion. New materials and designs minimize these problems and promise to bring the IPSWH back into the forefront of solar activity. Described are recent IPSWH experiments evaluating new materials and designs. These are then correlated with work by other investigators to suggest the tremendous potential for IPSWH use around the world. The characteristics of IPSWHs make traditional solar system test procedures inadequate and a new test procedure for IPSWH system is proposed. The low cost of IPSWHs more than offsets their slightly lower performance and will make them the most cost-effective heater for many climates and uses.
The design, analysis, construction and testing of a novel solar collector is reported. The Reverse Flat Plate Collector (RFPC) is intended to be a stationary, nonevacuated, low-technology, medium temperature solar collector - a promising alternative for intermediate temperature thermal needs in developing countries. The RFPC achieves high temperatures by convection suppression. The optical and thermal properties of this device are discussed for two different design options. A prototype of this collector was designed, built and tested at the Joint Center for Energy Management at the University of Colorado. The experimental results accurately confirm the high collector stagnation temperatures predicted from theory and indicate that convective heat losses are indeed suppressed.
Three .076 m/sup 3/ (20 gal.) batch water heaters were constructed for the purpose of side by side testing. The test models included an Inverted Batch Water Heater, a Greenhouse Integrated Skylight Heater, and a typical Breadbox Batch Heater. These designs were chosen because of their low initial cost, simple construction, ease of freeze protection, uncomplicated operation and heating effectiveness. The results of our testing show that our test models produced 35 to 70/sup 0/C (95 to 158/sup 0/F) average water temperatures with average collection efficiencies of about 34%. Materials costs for each of these systems were $200 to $400. These systems were tested side by side during periods of both low and high thermal demand, both with and without a selective surface foil on the absorber surfaces.
This study compares the thermal performance of two identical vertical thirty gallon Integral Passive Solar Water Heaters (IPSWH) placed side by side for the past year at the Farallones Institute's Rural Center in Occidental, California. Actual variations include (1) glazing (number, type, and treatments); (2) tank treatments (flat black, selective surface, and transmissive insulation); and (3) interior collector surfaces (reflective, white and black). The relative thermal performance of each variation is compared. The results give basic information on IPSWH designs and materials previously unavailable. This information will assist the design of efficient and cost-effective IPSWH systems.
Presented here is an energy balance of a compound parabolic concentrator (CPC) of 0.5 m2 surface area, built with parabolas made of glass, in the Solar Energy Laboratory of Universidad Nacional de San Luis. Firstly, the total thermal losses of the CPC are determined experimentally and then their conductive, convective and radiative components are found, for temperatures between 60 and 150°C. With the purpose of appreciating better the effects of the last two kinds of losses, use is made of different receivers. With each of them the performance of the CPC operating under solar radiation is measured and then the energy balance is carried out.On the basis of the results obtained with the first CPC, a second was constructed with low thermal losses. For this, the cover of dull black paint on the receiver was replaced by a selective surface—black chrome on dull nickel—which has an absorptance of 0.9 (for 0.2 μm ⩽ λ ⩽ 2 μm) and an emittance, ϵ = 0.2 for λ ⩾ 2 μm.Furthermore, a study of the trajectory of the rays in the interior of the CPC is carried out and the best transversal profile for an anticonvective surface, to be place 2.5 cm above the receiver, is determined.The first results that were obtained are presented here, for losses and effectiveness. A valuable improvement in the performance of the device can be noticed. In the best CPC an efficiency η equal to 0.16 is obtained for a mean temperature of 126°C for the fluid in the collector and an ambient temperature of 11°C.
Stationary concentrating solar devices, of the integrated collector and storage (ICS) type, that consist of a cylindrical tank placed horizontally in a properly shaped, curved mirror envelope, were designed. Prototype models were constructed, tested, and compared with conventional solar water heaters. In this article we describe the design of the ICS solar units with respect to the minimization of thermal losses from the absorber to the ambient. Experimental results were derived from the constructed models, a conventional concentrating stationary ICS prototype, and flat plate collectors of the thermosiphon type. Finally some conclusions regarding the practical application of the integrated units are presented.
Compound Parabolic Concentrators (CPC) are relevant for solar energy collection because they achieve the highest possible concentration for any acceptance angle (tracking requirement). The convective and radiative heat transfer through a CPC are calculated, and formulas for evaluating the performance of solar collectors based on the CPC principle are presented. A simple analytic technique for calculating the average number of reflections for radiation passing through a CPC is developed; this is useful for computing optical losses. In most practical applications, a CPC will be truncated because a large portion of the reflector area can be eliminated without seriously reducing the concentration. The effects of this truncation are described explicitly. The paper includes many numerical examples, displayed in tables and graphs, which should be helpful in designing CPC solar collectors.
This paper reviews the fitness-for-purpose of commonly used materials and possible alternative materials for all components of solar heating systems for domestic hot water. Optimum materials are recommended where possible. A conclusion of the survey of materials which has been carried out is that, using current technology, reliable, durable solar heating systems can be built. The cost of such systems is high, due to the use of expensive materials (such as copper and stainless steel) and the systems are unlikely to be cost-effective in the long term. Costs can be reduced by the use of lower cost materials such as the polymerics for many of the components, but as yet there are insufficient materials performance data to ensure long-term reliability.
A theoretical and experimental investigation into the modifications in optical and thermal performance resulting from the introduction of a baffle into the cavity of a compound parabolic concentrating solar energy collector has been performed. Results are presented in the form of velocity vector diagrams and isothermal plots. A comparison is made of the collector loss coefficient and Hottel-Whiller-Bliss graphs are produced for cavities with and without a baffle present. The introduction of a baffle reduces internal convection thereby reducing heat losses. The associated reduction in optical efficiency is small.
The design and thermal performance of modified compound parabolic concentrating (CPC) solar-energy collectors are described. The designs incorporate a curved inverted-Vee absorber fin, which allows a reflector of simple geometry to be used. This CPC collector, has exhibited a superior performance to that of a conventional cusp-reflector CPC design, owing to the enhancement of the optical efficiency obtained by eliminating gap optical losses and an enhanced heat removal factor. The consequence upon the performance of a further design refinement, which inhibited the convective heat losses, is also reported.
Integral Collector/Storage (ICS) solar water heating systems suffer substantial heat loss during periods of low insolation or at night. Methods to reduce aperture heat loss include moveable insulated lids/shutters, transparent insulating glazing materials and selective glazing/absorber coatings. All of these approaches involve trade-offs with reduction in performance and/or an increase in cost. A novel ICS vessel design to mitigate heat loss is proposed. An ICS vessel utilising an inner sleeve arrangement is shown to reduce heat loss by up to 20%. This paper examines four inner sleeve design configurations, several of which demonstrate an increase in the heat retention capability over existing vessels, and an optimised design is presented.
Two integrated collector storage (ICS) prototypes with about 1 m2 absorber surface each have been installed and investigated at the Institut für Solare Energiesysteme (ISE). Each consists of a water tank with an integrated collector, which is covered with a highly transparent insulating material and is very well insulated on the sides and at the back. During the test period from November 1986 to October 1987 one of them was operated at water-main pressure, and 40 liters corresponding to the hot water consumption of one person, were withdrawn every day. The solar fraction was 58% (68%) with a system efficiency of 28% (36%) (the values in parentheses also take the surplus energy in summer into account, see “Results”). The second one has been installed to study the stagnation (no water flow) performance during the same period. Detailed computer simulation programs have been developed and compared with the experimental results. Based on the u value and the transmittance-absorptance product (τα), the annual performance can be predicted with an accuracy of 4%. The influence of various parameters such as specific water withdrawal, angle of inclination, profile of water withdrawal, required hot water temperature etc. on the yearly solar fraction and yearly efficiency of the ICS can be studied. Some of the results are presented here.
All variables influencing the efficiency of a flat-plate solar heat collector as a heat exchanger can be combined into a single “efficiency factor.” These efficiency factors are more or less design constants of the particular collector design, and are only slightly influenced by operating conditions. Consequently they are extremely convenient for use in accurate design and performance calculations. The full mathematical derivations are presented for several of these efficiency factors for various types of collectors, together with graphical data and examples of their use.
Maxorb, selective absorber film. Trade literature, Inco Alloys Ltd
- Anon
Anon, 1996b. Maxorb, selective absorber film. Trade literature, Inco Alloys Ltd., Hereford, England, UK.
Recommendations for Performance and Durability Tests of Solar Collectors and Water Heating Systems. Commission of the European Communities, Directorate-General for Science Research and Development, Joint Research Centre, Ispra Site Integral passive solar water heater performance
- Anon
Anon, 1989. European Solar Collector and Systems Testing Group. Recommendations for Performance and Durability Tests of Solar Collectors and Water Heating Systems. Commission of the European Communities, Directorate-General for Science Research and Development, Joint Research Centre, Ispra Site, Italy. Baer, S., 1975. Breadbox water heater plans. Zomeworks Corporation, Albuquerque, NM, USA. Bainbridge, D.A., 1981. Integral passive solar water heater performance. In: Proceedings the 6th National Passive Solar Energy Conference, Portland, Oregon, USA, pp. 163–167.
Test Procedures for Short Term Thermal Stores
- H Visser
- Van Dijk
Visser, H., Van Dijk, H.A.L., 1991. Test Procedures for Short Term Thermal Stores. Kluwer Academic Publishers, Lon-don, UK.
3-M brand ECP-305 specular silver reflective film. Trade literature, 3M Centre
- Anon
European Solar Collector and Systems Testing Group. Recommendations for Performance and Durability Tests of Solar Collectors and Water Heating Systems. Commission of the European Communities, Directorate-General for Science Research and Development
- Anon