Building integrated solar thermal (BIST) technologies and their applications : A review of structural design and architectural integration
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paper_title: Solar thermal collectors and applications

paper_content:

In this paper a survey of the various types of solar thermal collectors and applications is presented. Initially, an analysis of the environmental problems related to the use of conventional sources of energy is presented and the benefits offered by renewable energy systems are outlined. A historical introduction into the uses of solar energy is attempted followed by a description of the various types of collectors including flat-plate, compound parabolic, evacuated tube, parabolic trough, Fresnel lens, parabolic dish and heliostat field collectors. This is followed by an optical, thermal and thermodynamic analysis of the collectors and a description of the methods used to evaluate their performance. Typical applications of the various types of collectors are presented in order to show to the reader the extent of their applicability. These include solar water heating, which comprise thermosyphon, integrated collector storage, direct and indirect systems and air systems, space heating and cooling, which comprise, space heating and service hot water, air and water systems and heat pumps, refrigeration, industrial process heat, which comprise air and water systems and steam generation systems, desalination, thermal power systems, which comprise the parabolic trough, power tower and dish systems, solar furnaces, and chemistry applications. As can be seen solar energy systems can be used for a wide range of applications and provide significant benefits, therefore, they should be used whenever possible.
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paper_title: Active Solar Thermal Facades (ASTFs): From concept, application to research questions

paper_content:

The aim of the paper is to report a comprehensive review into a recently emerging building integrated solar thermal technology, namely, Active Solar Thermal Facades (ASTFs), in terms of concept, classification, standard, performance evaluation, application, as well as research questions. This involves the combined effort of literature review, analysis, extraction, integration, critics, prediction and conclusion. It is indicated that the ASTFs are sort of building envelope elements incorporating the solar collecting devices, thus enabling the dual functions, e.g., space shielding and solar energy collection, to be performed. Based on the function of the building envelopes, the ASTF systems can be generally classified as wall-, window-, balcony-and roof-based types; while the ASTFs could also be classified by the thermal collection typologies, transparency, application, and heat-transfer medium. Currently, existing building and solar collector standards are brought together to evaluate the performance of the ASTFs. The research questions relating to the ASTFs are numerous, but the major points lie in: (1) whole structure and individual components layout, sizing and optimisation; (2) theoretical analysis; (3) experimental measurement; and (4) energy saving, economic and environmental performance assessment. Based on the analysis of the identified research questions, achievements made on each question, and outstanding problems remaining with the ASTFs, further development opportunities on this topic are suggested: (1) development of an integrated database/software enabling both architecture design and engineering performance simulation; (2) real-time measurement of the ASTFs integrated buildings on a long-term scheme; (3) economic and environmental performance assessment and social acceptance analysis; (4) dissemination, marketing and exploitation strategies study. This study helps in identifying the current status, potential problems in existence, future directions in research, development and practical application of the ASTFs technologies in buildings. It will also promote development of renewable energy technology and thus contribute to achieving the UK and international targets in energy saving, renewable energy utilization, and carbon emission reduction in building sector.
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paper_title: Recent advances in the solar water heating systems: A review

paper_content:

Solar water heating (SWH) systems have a widespread usage and applications in both domestic and industrial sectors. According to Renewable Energy Policy Network data (2010), 70 million houses worldwide were reported to be using SWH systems. Solar water heating is not only environmentally friendly but requires minimal maintenance and operation cost compared to other solar energy applications. SWH systems are cost effective with an attractive payback period of 2–4 years depending on the type and size of the system. Extensive research has been performed to further improve the thermal efficiency of solar water heating. This paper presents a detailed review exclusively on the design aspects of SWH systems. The first part of the paper provides a consolidated summary on the development of various system components that includes the collector, storage tank and heat exchanger. The later part of this paper covers the alternative refrigerant technology and technological advancements in improving the performance as well as the cost effectiveness of the SWH system.
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paper_title: Review of R&D progress and practical application of the solar photovoltaic/thermal (PV/T) technologies.

paper_content:

In this paper, the global market potential of solar thermal, photovoltaic (PV) and combined photovoltaic/thermal (PV/T) technologies in current time and near future was discussed. The concept of the PV/T and the theory behind the PV/T operation were briefly introduced, and standards for evaluating technical, economic and environmental performance of the PV/T systems were addressed. A comprehensive literature review into RD (2) optimise the structural/geometrical configurations of the existing PV/T systems; (3) study long term dynamic performance of the PV/T systems; (4) demonstrate the PV/T systems in real buildings and conduct the feasibility study; and (5) carry on advanced economic and environmental analyses. This review research helps finding the questions remaining in PV/T technology, identify new research topics/directions to further improve the performance of the PV/T, remove the barriers in PV/T practical application, establish the standards/regulations related to PV/T design and installation, and promote its market penetration throughout the world.
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paper_title: Aspects and improvements of hybrid photovoltaic/thermal solar energy systems

paper_content:

Hybrid photovoltaic/thermal (PV/T or PVT) solar systems consist of PV modules coupled to water or air heat extraction devices, which convert the absorbed solar radiation into electricity and heat. At the University of Patras, an extended research on PV/T systems has been performed aiming at the study of several modifications for system performance improvement. In this paper a new type of PV/T collector with dual heat extraction operation, either with water or with air circulation is presented. This system is simple and suitable for building integration, providing hot water or air depending on the season and the thermal needs of the building. Experiments with dual type PV/T models of alternative arrangement of the water and the air heat exchanging elements were performed. The most effective design was further studied, applying to it low cost modifications for the air heat extraction improvement. These modifications include a thin metallic sheet placed in the middle of the air channel, the mounting of fins on the opposite wall to PV rear surface of the air channel and the placement of the sheet combined with small ribs on the opposite air channel wall. The modified dual PV/T collectors were combined with booster diffuse reflectors, achieving a significant increase in system thermal and electrical energy output. The improved PV/T systems have aesthetic and energy advantages and could be used instead of separate installation of plain PV modules and thermal collectors, mainly if the available building surface is limited and the thermal needs are associated with low temperature water or air heating.
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paper_title: Experimental investigation of performance for the novel flat plate solar collector with micro-channel heat pipe array (MHPA-FPC)

paper_content:

A novel flat plate solar collector with micro-channel heat pipe array (MHPA-FPC) is presented in this paper. Firstly, a preliminary test was conducted to investigate the thermal performance of the MHPA. It has been found that the surface temperature along the length of MHPA can get stable within 2 min. The temperature difference between the evaporator and condenser sections was less than 1 °C, which indicates that the MHPA has excellent isothermal ability and quick thermal respond speed. Based on these advantages, the MHPA was applied to the development of a novel solar collector. The performance test was conducted following the Chinese standard GB/T4271-2007, and a linear correlation between the instantaneous efficiency η and the reduced temperature parameter (Twi−Ta)·I−1 was established. The maximum instantaneous efficiency was found to be 80%, and the slope was −4.72. These values are 11.4% and 21.3% superior to the technical required values of the Chinese national standard. Test results were further compared with 6 groups of 15 samples coming either from either open literature or commercial products. The comparisons indicated that the maximum instantaneous efficiency of the MHPA-FPC surpassed 25% over the average level of those selected samples and better thermal insulation ability was presented by the MHPA-FPC. These results from this study demonstrate that the novel MHPA-FPC is one of the top level solar collectors among the current products.
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paper_title: Fabrication and testing of a non-glass vacuum-tube collector for solar energy utilization

paper_content:

An evacuated tubular solar collector was fabricated from acrylics for improved resistance to shattering. A plasmatron was employed to apply a thin gas-barrier coating to the surfaces of the plastic tube to prevent/alleviate gas infiltration. Experiments were conducted to investigate the effect of vacuum level on the performance of the non-glass vacuum-tube solar collector. Inserted in the evacuated tube was a finned heat pipe for solar energy collection and heat transfer to a water tank. Time variations of temperatures on the heat pipe surface and in the water tank were recorded and analyzed for different degrees of vacuum in the collector. The steady-state temperature of the non-glass collector was compared to that of a commercial glass vacuum-tube collector to assess the feasibility of the use of evacuated plastic tubes for solar energy collection. A simple analytical model was also developed to assist in understanding and analyzing the transient behavior and heat losses of the vacuum-tube solar collector.
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paper_title: Operational performance of a novel heat pump assisted solar façade loop-heat-pipe water heating system

paper_content:

This paper aims to present an investigation into the operational performance of a novel heat pump assisted solar facade loop-heat-pipe (LHP) water heating system using both theoretical and experimental methods. This involved (1) development of a computer numerical model; (2) simulation of the operational performance of the system by using the model; (3) test rig construction; and (4) dedicated experiment for verification of the model. It was found that the established model is able to predict the operational performance of the system at a reasonable accuracy. Analyses of the research results indicated that under the selected testing conditions, the average thermal efficiency of the LHP module was around 71%, much higher than that of the loop heat pipe without heat pump assistance. The thermal efficiency of the LHP module grew when the heat pump was turned-on and fell when the heat pump was turned-off. The water temperature remained a steadily growing trend throughout the heat pump turned-on period. Neglecting the heat loss of the water tank, the highest coefficient of the performance could reach up to 6.14 and its average value was around 4.93. In overall, the system is a new facade integrated, highly efficient and aesthetically appealing solar water heating configuration; wide deployment of the system will help reduce fossil fuel consumption in the building sector and carbon emission to the environment.
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paper_title: Review of R&D progress and practical application of the solar photovoltaic/thermal (PV/T) technologies.

paper_content:

In this paper, the global market potential of solar thermal, photovoltaic (PV) and combined photovoltaic/thermal (PV/T) technologies in current time and near future was discussed. The concept of the PV/T and the theory behind the PV/T operation were briefly introduced, and standards for evaluating technical, economic and environmental performance of the PV/T systems were addressed. A comprehensive literature review into RD (2) optimise the structural/geometrical configurations of the existing PV/T systems; (3) study long term dynamic performance of the PV/T systems; (4) demonstrate the PV/T systems in real buildings and conduct the feasibility study; and (5) carry on advanced economic and environmental analyses. This review research helps finding the questions remaining in PV/T technology, identify new research topics/directions to further improve the performance of the PV/T, remove the barriers in PV/T practical application, establish the standards/regulations related to PV/T design and installation, and promote its market penetration throughout the world.
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paper_title: Recent advances in the solar water heating systems: A review

paper_content:

Solar water heating (SWH) systems have a widespread usage and applications in both domestic and industrial sectors. According to Renewable Energy Policy Network data (2010), 70 million houses worldwide were reported to be using SWH systems. Solar water heating is not only environmentally friendly but requires minimal maintenance and operation cost compared to other solar energy applications. SWH systems are cost effective with an attractive payback period of 2–4 years depending on the type and size of the system. Extensive research has been performed to further improve the thermal efficiency of solar water heating. This paper presents a detailed review exclusively on the design aspects of SWH systems. The first part of the paper provides a consolidated summary on the development of various system components that includes the collector, storage tank and heat exchanger. The later part of this paper covers the alternative refrigerant technology and technological advancements in improving the performance as well as the cost effectiveness of the SWH system.
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paper_title: PCM thermal storage in buildings: A state of art

paper_content:

A comprehensive review of various possible methods for heating and cooling in buildings are discussed in this paper. The thermal performance of various types of systems like PCM trombe wall, PCM wallboards, PCM shutters, PCM building blocks, air-based heating systems, floor heating, ceiling boards, etc., is presented in this paper. All systems have good potential for heating and cooling in building through phase change materials and also very beneficial to reduce the energy demand of the buildings.
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paper_title: Thermal performance of PCM thermal storage unit for a roof integrated solar heating system

paper_content:

Abstract The thermal performance of a phase change thermal storage unit is analysed and discussed. The storage unit is a component of a roof integrated solar heating system being developed for space heating of a home. The unit consists of several layers of phase change material (PCM) slabs with a melting temperature of 29 °C. Warm air delivered by a roof integrated collector is passed through the spaces between the PCM layers to charge the storage unit. The stored heat is utilised to heat ambient air before being admitted to a living space. The study is based on both experimental results and a theoretical two dimensional mathematical model of the PCM employed to analyse the transient thermal behaviour of the storage unit during the charge and discharge periods. The analysis takes into account the effects of sensible heat which exists when the initial temperature of the PCM is well below or above the melting point during melting or freezing. The significance of natural convection occurring inside the PCM on the heat transfer rate during melting which was previously suspected as the cause of faster melting process in one of the experiments is discussed. The results are compared with a previous analysis based on a one dimensional model which neglected the effect of sensible heat. A comparison with experimental results for a specific geometry is also made.
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paper_title: State of the art on phase change material slurries

paper_content:

The interest in using phase change slurry (PCS) media as thermal storage and heat transfer fluids is increasing and thus leading to an enhancement in the number of articles on the subject. In air-conditioning and refrigeration applications, PCS systems represent a pure benefit resulting in the increase of thermal energy storage capacity, high heat transfer characteristics and positive phase change temperatures which can occur under low pressures. Hence, they allow the increase of energy efficiency and reduce the quantity of thermal fluids. This review describes the formation, thermo-physical, rheological, heat transfer properties and applications of four PCS systems: Clathrate hydrate slurry (CHS), Microencapsulated Phase Change Materials Slurry (MPCMS), shape-stabilized PCM slurries (SPCMSs) and Phase Change Material Emulsions (PCMEs). It regroups a bibliographic summary of important information that can be very helpful when such systems are used. It also gives interesting and valuable insights on the choice of the most suitable PCS media for laboratory and industrial applications.
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paper_title: Development of a thermally activated ceiling panel with PCM for application in lightweight and retrofitted buildings

paper_content:

Abstract This paper describes the development of a thermally activated ceiling panel for incorporation in lightweight and retrofitted buildings. The system allows use of renewable energy sources for the heating and cooling of office and industrial buildings. The design for the new ceiling panel exploits the properties of the phase change material (PCM) paraffin. Its high thermal storage capacity during phase change—up to 300 Wh/(m 2 day)—enables the overall panel thickness to be limited to a mere 5 cm. Active control of the thermal storage is achieved by means of an integrated water capillary tube system. The research project also included the development of a numerical model for computation of the thermal behavior of wall and ceiling systems incorporating PCMs. Simulation calculations were performed to determine the necessary thermal properties of the ceiling panels and specify requirements for the materials to be used. Laboratory tests were performed to verify the system’s performance and a pilot application is soon to be tried out in practice.
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paper_title: Applications of Phase Change Material in highly energy-efficient houses

paper_content:

Abstract Thermal mass combined with other passive strategies can play an important role in buildings energy efficiency, minimizing the need of space-conditioning mechanical systems. However, the use of lightweight materials with low thermal mass is becoming increasingly common. Phase Change Materials (PCMs) can add thermal energy storage benefits to lightweight constructions. There are many studies about the use of PCM in buildings, but there are still some difficulties for effective use and practical application of these materials. The study of applications used in real buildings could help us find solutions to these difficulties. This paper analyzed different PCM applications presented in highly efficient lightweight construction houses that have participated in the American Solar Decathlon, an international competition organized by U.S. Department of Energy. These houses have been tested and monitored in Washington DC, place with suitable climate conditions for short term thermal storage systems. The study started with a classification of the PCM applications and included an analysis of the systems, materials, switching temperatures, containments and design strategies used to improve the houses energy performance. Also, it included results of numerical simulations and experimentation that the participant team had done, complemented with information available in the literature about similar materials or applications.
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paper_title: Experiment on heat storage characteristic of microencapsulated phase change material slurry

paper_content:

Abstract Heat storage experiment by natural convection in rectangular enclosures heated from bottom has been conducted with fluid slurry composed of microencapsulated phase change material (PCM). The microencapsulated PCM is prepared by in-situ polymerization method, where the core materials are composed of several kinds of n-paraffin waxes (mainly nonadecane) and the membrane is a type of melamine resin. Its slurry mixed with water is used in this study, and shows a peak value in the specific heat capacity with latent heat at the temperature of about T =31 °C. The influences of the phase change material on heat storage and the heat transfer process, as well as effects of PCM mass concentration C m on the microcapsule slurry, temperature of heat storage T H and a horizontal enclosure height H are also investigated. Transient heat transfer coefficient α , heat storage capacity Q and completion time of heat storage t c are discussed.
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paper_title: Heat transfer enhancement for thermal energy storage using metal foams embedded within phase change materials (PCMs)

paper_content:

In this paper the experimental investigation on the solid/liquid phase change (melting and solidification) processes have been carried out. Paraffin wax RT58 is used as phase change material (PCM), in which metal foams are embedded to enhance the heat transfer. During the melting process, the test samples are electrically heated on the bottom surface with a constant heat flux. The PCM with metal foams has been heated from the solid state to the pure liquid phase. The temperature differences between the heated wall and PCM have been analysed to examine the effects of heat flux and metal foam structure (pore size and relative density). Compared to the results of the pure PCM sample, the effect of metal foam on solid/liquid phase change heat transfer is very significant, particularly at the solid zone of PCMs. When the PCM starts melting, natural convection can improve the heat transfer performance, thereby reducing the temperature difference between the wall and PCM. The addition of metal foam can increase the overall heat transfer rate by 3-10 times (depending on the metal foam structures and materials) during the melting process (two-phase zone) and the pure liquid zone. The tests for investigating the solidification process under different cooling conditions (e.g. natural convection and forced convection) have been carried out. The results show that the use of metal foams can make the sample solidified much faster than pure PCM samples, evidenced by the solidification time being reduced by more than half. In addition, a two-dimensional numerical analysis has been carried out for heat transfer enhancement in PCMs by using metal foams, and the prediction results agree reasonably well with the experimental data.
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paper_title: Ventilated active façades with PCM

paper_content:

This article describes an evaluation of the thermal performance of a new type of ventilated active facade that includes a phase change material (PCM) in its outer layer. The research was carried out experimentally by means of a real-scale PASLINK test cell facility, located in the city of Vitoria-Gasteiz in Spain. The results of an experiment performed in March 2010 are presented and evaluated. The behavior of the facade was compared with different traditional constructive systems, using the results of computational simulations performed with the Design Builder software. The experimental results showed that the melting–solidification processes that take place in the PCM led to an increase in the heat absorption during the phase-change temperature intervals, which reduced overheating of the facade. The air circulating through the ventilated chamber was overheated up to 12°C during the daytime. Because of the PCM solidification, 2.5h after the solar radiation faded out, the air circulating through the chamber was still warmed by 2°C. The energy efficiency of the facade during the testing period is attributable to the 10–12% incident radiation gains. This efficiency was found to be a function of the circulating air flow rate. The simulations results showed that the thermal inertia of the ventilated facade with a PCM is higher than that of the four traditional solutions evaluated in the study. Further research is required to study the influence of the air flow rate through the ventilated chamber.
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paper_title: Theoretical investigation of the energy performance of a novel MPCM (Microencapsulated Phase Change Material) slurry based PV/T module

paper_content:

Aim of the paper is to present a theoretical investigation into the energy performance of a novel PV/T module that employs the MPCM (Micro-encapsulated Phase Change Material) slurry as the working fluid. This involved (1) development of a dedicated mathematical model and computer program; (2) validation of the model by using the published data; (3) prediction of the energy performance of the MPCM (Microencapsulated Phase Change Material) slurry based PV/T module; and (4) investigation of the impacts of the slurry flow state, concentration ratio, Reynolds number and slurry serpentine size onto the energy performance of the PV/T module. It was found that the established model, based on the Hottel–Whillier assumption, is able to predict the energy performance of the MPCM slurry based PV/T system at a very good accuracy, with 0.3–0.4% difference compared to a validated model. Analyses of the simulation results indicated that laminar flow is not a favorite flow state in terms of the energy efficiency of the PV/T module. Instead, turbulent flow is a desired flow state that has potential to enhance the energy performance of PV/T module. Under the turbulent flow condition, increasing the slurry concentration ratio led to the reduced PV cells' temperature and increased thermal, electrical and overall efficiency of the PV/T module, as well as increased flow resistance. As a result, the net efficiency of the PV/T module reached the peak level at the concentration ratio of 5% at a specified Reynolds number of 3,350. Remaining all other parameters fixed, increasing the diameter of the serpentine piping led to the increased slurry mass flow rate, decreased PV cells' temperature and consequently, increased thermal, electrical, overall and net efficiencies of the PV/T module. In overall, the MPCM slurry based PV/T module is a new, highly efficient solar thermal and power configuration, which has potential to help reduce fossil fuel consumption and carbon emission to the environment.
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paper_title: Experimental analysis of a microencapsulated PCM slurry as thermal storage system and as heat transfer fluid in laminar flow

paper_content:

Abstract A microencapsulated PCM (Phase Change Material) slurry is a dispersion where the PCM, microencapsulated by a polymeric capsule, is dispersed in water. Compared to water, these new fluids have a higher heat capacity during the phase change and a possible enhancement, as a result of this phase change, in the heat transfer phenomenon. From the literature review, the existing experimental results are found incomplete and contradictory in many cases. For this reason the objective of this investigation is to analyze the heat transfer phenomenon in mPCM slurries, proposing a new methodology, developed by the authors. In this manner, an experimental analysis using a slurry with a 10% weight concentration of paraffin has been conducted to study it as a thermal storage material and as a heat transfer fluid. The results demonstrated an improvement of approximately 25% on the convective heat transfer coefficient when compared to water.
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paper_title: Aluminum heat pipes applied in solar collectors

paper_content:

Abstract The previous researchers have developed a variety of liquid thermal solar collectors designs for water heating. It was reported by the other authors, that metal heat pipes applications to liquid solar collectors, especially to evacuated glass tube ones, is an efficient solution for water heating plants. However, the majority of thermal solar collectors do not meet the requirements on small weight, easy assembly and installation, versatility, scalability, and adaptability of the design, which are particularly important when they are facade integrated. Very high hydraulic resistance, from 2000 Pa to 20,000 Pa, in liquid solar collectors and low thermal efficiency of some of them, less than 0.5, also are the problems to be solved by the developers. Current research is proposing to apply extruded aluminum alloy made heat pipes of original cross-sectional profile with wide fins and longitudinal grooves in order to avoid the above-mentioned drawbacks of liquid thermal collectors. Absorber plate of flat collectors could be composed of several fins. Fins at the opposite end of the heat pipe serve as a heat sink surface. Multiple tests proved that new lightweight and inexpensive heat pipes show high thermal performances. Maximum heat transfer power of one heat pipe is up to 210 W; and its thermal resistance is very low – from 0.02 to 0.07 °C/W. Hydraulic resistance of flat plate solar collector and evacuated one utilizing aluminum profiled heat pipes, could be reduced to less than 100 Pa, at the same time their thermal efficiency is rather high, up to 0.72. In the issue of authors study, the feasibility of the developed aluminum profiled heat pipes application to thermal solar collectors was proved; and they can be successfully integrated to building facades and roofs.
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paper_title: Parallel experimental study of a novel super-thin thermal absorber based photovoltaic/thermal (PV/T) system against conventional photovoltaic (PV) system

paper_content:

Photovoltaic (PV) semiconductor degrades in performance due to temperature rise. A super thin-conductive thermal absorber is therefore developed to regulate the PV working temperature by retrofitti ...
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paper_title: Architectural Integration and Design of Solar Thermal Systems

paper_content:

Although mature technologies at competitive prices are largely available, solar thermal is not yet playing the important role it deserves in the reduction of buildings fossil energy consumption. The generally low architectural quality characterizing existing building integrations of solar thermal systems pinpoints the lack of design as one major reason for the low spread of the technology. As confirmed by the example of photovoltaics, the improvement of the architectural quality of building integrated systems can increase the use of a solar technology even more than price and technique. This thesis investigates the possible ways to enhance the architectural quality of building integrated solar thermal systems, and focuses on integration into facade, where the formal constraints are major and have most impact. The architectural integration problematic is structured into functional, constructive and formal issues, so that integration criteria are given for each architectural category. As the functional and constructive criteria are already recognized by the scientific community, the thesis concentrates on the definition of the formal ones, yet underestimated or misunderstood. The results of a large European survey over architects and engineers perception of building integration quality are presented, showing that for architects formal issues are not a matter of personal taste, but that they relate to professional competences, and consequently can be described. The solar system characteristics having an impact on the formal quality of the integration are identified (formal characteristics), the related integration criteria are assessed, and finally integration guidelines to support architect integration design work are given. The limits imposed by the collectors available in the market are pointed out, showing that the lack of appropriate products is nowadays the main barrier to BIST (Building Integrated Solar Thermal) architectural quality. A methodology for the development of new solar thermal collectors systems responding at the same time to energy production needs and building integration requirements is defined. The importance to ensure, within the design team, the due professional competences in both these fields is stressed. Three progressive levels of system "integrability" are defined in the path leading to the concept of "active envelope systems" and the main role of facade manufacturers is highlighted. The methodology is applied to unglazed and glazed flat plate systems, and new facade system designs are proposed that show the relevance of the proposed approach.
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paper_title: Dynamic performance of a façade-based solar loop heat pipe water heating system

paper_content:

Abstract This paper reported a dedicated study of a novel facade-based solar loop heat pipe (LHP) water heating system using both theoretical and experimental methods. This system employs a modular panel incorporating a unique loop heat pipe that is able to serve as part of the building facade or a decoration layer of the facade, thus creating a facade integrated, low cost, highly efficient and aesthetically appealing solar water heating structure. Taking into account heat balances occurring in different parts of the system, e.g., solar absorber, heat pipes loop, heat exchanger and storage tank, a dedicated computer model was developed to investigate the dynamic performance of the system. An experimental rig was also established to evaluate the performance of such a prototype system through measurement of various operational parameters, e.g., solar radiation, temperatures and flow rates of the heat pipe fluid and water. Through comparison between the testing and modelling results, the model has been approved to be able to give a reasonable accuracy for predicting the performance of the LHP system. Two types of glass covers, i.e., double glazed/evacuated tubes and single-glazing plate, were applied to the prototype. It was found that for both covers, the heat pipe fluid temperature rose dramatically at the start-up operation and afterwards remained a slow but steady growth; while the water temperature remained a steadily growing trend throughout the operational day. The temperature rise of the circulated water at 1.6 l/min of flow rate was around 13.5 °C in the double-glazed/evacuated tubes based system and 10 °C in the single-glazing based system; correspondingly, their average solar conversion efficiencies were 48.8% and 36%, and the COPs were 14 and 10.5 respectively. In overall, the double-glazed/evacuated tubes based system presented a better performance than the single glazing based one.
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paper_title: Facade Integration of Solar Thermal Collectors: A Breakthrough

paper_content:

One main barrier to the acceptability of facade use of solar thermal collectors is their black appearance and the visibility of piping or absorber irregularities through the glazing. To facilitate facade integration, a project was set up to develop selective filters reflecting only a small part of the solar spectrum in the visible range while letting the rest of the radiation heat the absorber. These filters were successfully produced and, combined with a diffusing glass treatment, have achieved the desired masking effect with minor impact on the collector efficiency (less than 10%). Glasses of various colours combined with several diffusing finishing (acid etching, structured glass etc…) can be produced that are able to hide the absorber. Such glazings will allow the use of the same product both in front of facade areas equipped with solar absorbers (as collector external glass) and in front of the non exposed areas (as facade cladding), opening the way to a broad variety of active facade designs. The active elements can then be positioned at will on the exposed areas, and their quantity determined only by thermal needs. By freeing the dimension of the facade area that can be clad with this glazing from the thermally needed surface for collectors, a major step to help architects use solar thermal on facades has been taken.
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paper_title: Active Solar Thermal Facades (ASTFs): From concept, application to research questions

paper_content:

The aim of the paper is to report a comprehensive review into a recently emerging building integrated solar thermal technology, namely, Active Solar Thermal Facades (ASTFs), in terms of concept, classification, standard, performance evaluation, application, as well as research questions. This involves the combined effort of literature review, analysis, extraction, integration, critics, prediction and conclusion. It is indicated that the ASTFs are sort of building envelope elements incorporating the solar collecting devices, thus enabling the dual functions, e.g., space shielding and solar energy collection, to be performed. Based on the function of the building envelopes, the ASTF systems can be generally classified as wall-, window-, balcony-and roof-based types; while the ASTFs could also be classified by the thermal collection typologies, transparency, application, and heat-transfer medium. Currently, existing building and solar collector standards are brought together to evaluate the performance of the ASTFs. The research questions relating to the ASTFs are numerous, but the major points lie in: (1) whole structure and individual components layout, sizing and optimisation; (2) theoretical analysis; (3) experimental measurement; and (4) energy saving, economic and environmental performance assessment. Based on the analysis of the identified research questions, achievements made on each question, and outstanding problems remaining with the ASTFs, further development opportunities on this topic are suggested: (1) development of an integrated database/software enabling both architecture design and engineering performance simulation; (2) real-time measurement of the ASTFs integrated buildings on a long-term scheme; (3) economic and environmental performance assessment and social acceptance analysis; (4) dissemination, marketing and exploitation strategies study. This study helps in identifying the current status, potential problems in existence, future directions in research, development and practical application of the ASTFs technologies in buildings. It will also promote development of renewable energy technology and thus contribute to achieving the UK and international targets in energy saving, renewable energy utilization, and carbon emission reduction in building sector.
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paper_title: Mathematical modeling and thermal performance analysis of unglazed transpired solar collectors

paper_content:

Abstract Unglazed transpired collectors or UTC (also known as perforated collectors) are a relatively new development in solar collector technology, introduced in the early nineties for ventilation air heating. These collectors are used in several large buildings in Canada, USA and Europe, effecting considerable savings in energy and heating costs. Transpired collectors are a potential replacement for glazed flat plate collectors. This paper presents the details of a mathematical model for UTC using heat transfer expressions for the collector components, and empirical relations for estimating the various heat transfer coefficients. It predicts the thermal performance of unglazed transpired solar collectors over a wide range of design and operating conditions. Results of the model were analysed to predict the effects of key parameters on the performance of a UTC for a delivery air temperature of 45–55 °C for drying applications. The parametric studies were carried out by varying the porosity, airflow rate, solar radiation, and solar absorptivity/thermal emissivity, and finding their influence on collector efficiency, heat exchange effectiveness, air temperature rise and useful heat delivered. Results indicate promising thermal performance of UTC in this temperature band, offering itself as an attractive alternate to glazed solar collectors for drying of food products. The results of the model have been used to develop nomograms, which can be a valuable tool for a collector designer in optimising the design and thermal performance of UTC. It also enables the prediction of the absolute thermal performance of a UTC under a given set of conditions.
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paper_title: Optimal control of flow in solar collectors for maximum exergy extraction

paper_content:

The best operation strategies for open loop flat-plate solar collector systems are considered. A direct optimal control method (the TOMP algorithm) is implemented. A detailed collector model and realistic meteorological data from both cold and warm seasons are used in applications. The maximum exergetic efficiency is low (usually less than 3%), in good agreement with experimental measurements reported in literature. The optimum mass-flow rate increases near sunrise and sunset and by increasing the fluid inlet temperature. The optimum mass-flow rate is well correlated with global solar irradiance during the warm season. Also, operation at a properly defined constant mass-flow rate may be close to the optimal operation.
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paper_title: Effect of wind on flow distribution in unglazed transpired-plate collectors

paper_content:

Abstract Unglazed transpired-plate solar air heaters have proven to be effective devices for heating air directly from ambient on a once through basis. They have found applications in ventilation-air preheating and in crop-drying. Large collectors are now routinely built that cover the sides of sizeable buildings, and the problem of designing the system so that the flow of the air through the collector face is reasonably uniform and so that there is no ‘outflow’ over part of the collector face has been seen as a challenging one. The flow distribution was analyzed in an earlier study using a computational fluid dynamics (CFD) model, but that study was limited to the case where there is no wind present. The present paper extends the earlier study to the case where there is wind. Various building orientations are examined, at a wind speed of 5 m/s. The wind was found to reinforce those factors that tend to produce outflow, and in light of this study, the recommended minimum suction velocity required to avoid outflow has been raised from about 0.0125 m/s to about 0.03 m/s, depending on the building shape. On the other hand, there are possible strategies that can be adopted to reduce the effect of wind, and these are discussed.
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paper_title: A field study of the wind effects on the performance of an unglazed transpired solar collector

paper_content:

An experimental study was carried out on a working unglazed transpired solar collector (UTSC) to determine what effects ambient wind has on its performance. The monitoring system included instruments to measure temperatures, collector outlet flow rates, solar radiation, wind speed, and wind direction; as well as an ultrasonic anemometer placed near the centre of the collector. Efficiency was defined as the fraction of incident solar heat flux that went to preheating the transpired air. Our observations indicate a high degree of turbulence near the wall which feeds the near wall region. This is supported by observations of efficiency which decrease monotonically with increasing turbulence intensities. It was also observed that peak efficiencies did not occur at the lowest wind speeds. Both these findings seem to contradict existing laminar boundary layer models for UTSC performance.
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paper_title: Energetic and exergetic evaluation of flat plate solar collectors

paper_content:

Energy efficiency is generally used as one of the most important parameters in order to introduce and compare thermal systems including flat plate solar collectors despite of the fact that the first law of thermodynamics is not solely capable of demonstrating quantitative and qualitative performance of such systems. In this paper, a theoretical and comprehensive model for energy and exergy analysis of flat plate solar collectors is presented through which the effect of the entire design parameters on performance can be examined. Upon the verification and confirmation of the model based on the experimental data, effect of parameters such as fluid flow rate and temperature, type of working fluid and thickness of the back insulation on the energy and exergy efficiency of the collector has been examined and based on the analysis and comparison of results, the optimal working condition of the system has been determined. According to the results, designing the system with inlet water temperature approximately 40° more than the ambient temperature as well as a lower flow rate will enhance the overall performance.
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paper_title: Approximate method for computation of glass cover temperature and top heat-loss coefficient of solar collectors with single glazing

paper_content:

An improved equation form for computing the glass cover temperature of flat-plate solar collectors with single glazing is developed. A semi-analytical correlation for the factor f—the ratio of inner to outer heat-transfer coefficients—as a function of collector parameters and atmospheric variables is obtained by regression analysis. This relation readily provides the glass cover temperature (Tg). The results are compared with those obtained by numerical solution of heat balance equations. Computational errors in Tg and hence in the top heat loss coefficient (Ut) are reduced by a factor of five or more. With such low errors in computation of Tg and Ut, a numerical solution of heat balance equations is not required. The method is applicable over an extensive range of variables: the error in the computation of Ut is within 2% with the range of air gap spacing 8 mm to 90 mm and the range of ambient temperature 0°C to 45°C. In this extended range of variables the errors due to simplified method based on empirical relations for Ut are substantially higher.
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paper_title: A state of art review on the performance of transpired solar collector

paper_content:

Utilisation of solar radiation to heat air for various purposes, e.g. ventilation, pre heat, process air heat and their applications has attracted more and more interests. Wide range of applications adapted for different climates and in different building types ranging from houses to large industrial buildings. Recently in many European countries, USA and Canada this concept developed rapidly. Transpired solar collectors (TSCs) have proven reliable for various applications, e.g. heating spaces, providing warm ventilation air, supplying domestic hot water in summer, etc.
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paper_title: Solar collector overheating protection

paper_content:

Abstract Prismatic structures in a thermal solar collector are used as overheating protection. Such structures reflect incoming light efficiently back whenever less thermal power is extracted from the solar collector. Maximum thermal power is generated when the prismatic structure is surrounded by a switching fluid with an index of refraction comparable to that of the prismatic structure. Thermal heat can be harvested via extra fluid channels in the solar absorber or directly via the switching fluid near the prisms. The light reducing effect of prismatic structures is demonstrated for a typical day and a season cycle of the Earth around the Sun. The switchability and the light reducing effect are also demonstrated in a prototype solar collector.
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paper_title: Optimization of latent heat storage in solar air heating system with vacuum tube air solar collector

paper_content:

Abstract This paper presents the design and modelling of the heat transfer of a solar air heating system, which consists of a vacuum tube air solar collector (SC) and latent heat thermal energy storage (LHTES), and a parametric analysis of the performance of this system. LHTES is a form of short-term daily storage that stores the SC heat during the day and releases it into the building during the night. Especially in low energy buildings with a high share of passive heating, this can significantly improve the utilization of solar energy for heating. The design of concentric-tube LHTES was optimized regarding the air temperature at the exit of LHTES during the day and the peak shift of heat supply. The results showed that optimal mass of PCM in LHTES is 150–200 kg/m 2 and the optimal air flow-rate is 40 m 3 /h per m 2 of the SC aperture area. The analysis of the system performance at different levels of daily solar irradiation has shown that 54–67% of the heat produced by solar air heating system in daytime can be delivered during the night time for building heating.
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paper_title: Optimal control of flow in solar collectors for maximum exergy extraction

paper_content:

The best operation strategies for open loop flat-plate solar collector systems are considered. A direct optimal control method (the TOMP algorithm) is implemented. A detailed collector model and realistic meteorological data from both cold and warm seasons are used in applications. The maximum exergetic efficiency is low (usually less than 3%), in good agreement with experimental measurements reported in literature. The optimum mass-flow rate increases near sunrise and sunset and by increasing the fluid inlet temperature. The optimum mass-flow rate is well correlated with global solar irradiance during the warm season. Also, operation at a properly defined constant mass-flow rate may be close to the optimal operation.
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paper_title: A critical review of photovoltaic―thermal solar collectors for air heating

paper_content:

Integrated photovoltaic–thermal solar collectors have become of great interest in the solar thermal and photovoltaic (PV) research communities. Solar thermal systems and solar PV systems have each advanced markedly, and combining the two technologies provides the opportunity for increased efficiency and expanded utilization of solar energy. In this article, the authors critically review photovoltaic–thermal solar collectors for air heating. Included is a review of photovoltaic thermal technology and recent advances, particularly as applied to air heaters. It is determined that the photovoltaic–thermal (PV/T) air heater is or may in the future be practicable for preheating air for many applications, including space heating and drying, and that integrated PV/T collectors deliver more useful energy per unit collector area than separate PV and thermal systems. Although PV/T collectors are promising, it is evident that further research is required to improve efficiency, reduce costs and resolve several technical design issues related to the collectors.
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paper_title: A simple predictive controller for use on large scale arrays of parabolic trough collectors

paper_content:

Abstract Efficient operation of a distributed collector field requires effective regulation of the outlet temperature. Control schemes utilising PI based controllers, whether adaptive or fixed parameter, have been shown to be unsuitable for this application. The reason for this is that such collector fields possess resonance dynamics at a low frequency which tend to restrict the bandwidth of such controllers. In this article a predictive controller is proposed whose purpose is to effectively counter such dynamics. This control technique is based upon a simple transfer function representation of the resonance dynamics which can be tuned using easily obtained experimental data and is computationally efficient. When applied to a validated non-linear computer model of the collector field the controller is seen to exhibit a fast well damped control response superior to that achievable using PI control.
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paper_title: Solar collector with temperature limitation using shape memory metal

paper_content:

Application of Heat pipe in photo-thermal conversion as well as the heat transfer mechanism in a heat pipe is reported. The problem of no-load conditions combined with high stagnation temperature of (in particular by evacuated) solar collectors is addressed. The use of shape memory alloys in solar collectors is discussed. The Shape Memory Effect as well as the superelasticity is explained. The physical phenomena of Shape Memory Effect as well as superelasticity is briefly reviewed. The application of a shape memory alloy in a commercially available evacuated heat pipe solar collector and its mechanism is discussed.
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paper_title: A review of strategies for the control of high temperature stagnation in solar collectors and systems

paper_content:

Abstract High temperatures occurring during stagnation conditions can be very detrimental to the reliability, durability and safety of solar thermal systems. Various approaches to mitigate the effects to stagnation have been employed in the past, however as collector and system efficiencies improve, and larger solar systems are installed, the need for reliable and cost effective stagnation control schemes is increasing. In this paper, the impacts of stagnation and various approaches to stagnation control are discussed and compared with regard to their features and limitations.
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paper_title: Enhanced heat transfer using oscillatory flows in solar collectors

paper_content:

In this work, we propose the use of oscillatory laminar flows to enhance the transfer of heat from solar collectors. The idea is to explore the possibility of transferring the heat collected from a solar device to a storage tank by means of a zero-mean oscillating fluid contained in a tube. This method takes advantage of the fact that the effective thermal diffusivity of a fluid in oscillatory motion is several orders of magnitude higher than the fluid molecular diffusivity. Therefore, the axial transport of heat along the tube is substantially higher when the fluid oscillates than when the fluid is static. Also, preliminary estimations show a dramatic heat transfer enhancement using oscillatory flows compared with the forced convection of heat by standard unidirectional flows. We explore the behavior of the effective thermal diffusivity using both Newtonian and viscoelastic fluids. For the Newtonian fluid a single maximum value of this quantity is exhibited for a given oscillation frequency. In contrast, several maxima for different resonant frequencies are observed for the viscoelastic fluid. Further, the absolute maximum of the enhanced thermal diffusivity for the viscoelastic fluid is several orders of magnitude larger than that of the Newtonian fluid.
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paper_title: Flow distribution in a solar collector panel with horizontally inclined absorber strips

paper_content:

Abstract The objective of this work is to theoretically and experimentally investigate the flow and temperature distribution in a solar collector panel with an absorber consisting of horizontally inclined strips. Fluid flow and heat transfer in the collector panel are studied by means of computational fluid dynamics (CFD) calculations. Further, experimental investigations of a 12.5 m2 solar collector panel with 16 parallel connected horizontal fins are carried out. The flow distribution through the absorber is evaluated by means of temperature measurements on the backside of the absorber tubes. The measured temperatures are compared to the temperatures determined by the CFD model and there is a good similarity between the measured and calculated results. Calculations with the CFD model elucidate the flow and temperature distribution in the collector. The influences of different operating conditions such as flow rate, properties of solar collector fluid, solar collector fluid inlet temperature and collector tilt angle are shown. The flow distribution through the absorber fins is uniform if high flow rates are used. By decreased flow rate and decreased content of glycol in the glycol/water mixture used as solar collector fluid, and by increased collector tilt and inlet temperature, the flow distribution gets worse resulting in an increased risk of boiling in the upper part of the collector panel.
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paper_title: Exergetic optimization of flat plate solar collectors

paper_content:

In this paper, an exergetic optimization of flat plate solar collectors is developed to determine the optimal performance and design parameters of these solar to thermal energy conversion systems. A detailed energy and exergy analysis is carried out for evaluating the thermal and optical performance, exergy flows and losses as well as exergetic efficiency for a typical flat plate solar collector under given operating conditions. In this analysis, the following geometric and operating parameters are considered as variables: the absorber plate area, dimensions of solar collector, pipes' diameter, mass flow rate, fluid inlet, outlet temperature, the overall loss coefficient, etc. A simulation program is developed for the thermal and exergetic calculations. The results of this computational program are in good agreement with the experimental measurements noted in the previous literature. Finally, the exergetic optimization has been carried out under given design and operating conditions and the optimum values of the mass flow rate, the absorber plate area and the maximum exergy efficiency have been found. Thus, more accurate results and beneficial applications of the exergy method in the design of solar collectors have been obtained.
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Title: Building Integrated Solar Thermal (BIST) Technologies and Their Applications: A Review of Structural Design and Architectural Integration

Section 1: Introduction
Description 1: Provide an overview of the importance of renewable energy sources, particularly solar thermal energy, for building applications and highlight the potential of BIST systems.

Section 2: Water-based BIST technology
Description 2: Discuss the use of water as a heat transfer medium in BIST systems, including its advantages, challenges, and structural designs.

Section 3: Category of BIST Technologies
Description 3: Classify BIST systems based on the heat transfer medium used, such as air, hydraulic (water/heat pipe/refrigerant), and PCM-based systems, with descriptions of each type.

Section 4: Air-based BIST technology
Description 4: Examine the characteristics, advantages, and structural designs of air-based solar thermal systems that use air as the working fluid.

Section 5: Refrigerant-based BIST technology
Description 5: Explain the use of refrigerants in BIST systems, their advantages over water, various refrigerant types, and relevant structural designs.

Section 6: PCM-based facade BIST technology
Description 6: Describe the application of Phase Change Materials (PCM) in BIST systems, their benefits for thermal storage, and potential applications.

Section 7: General comparison of different SFT technologies
Description 7: Provide a comparison of different BIST technologies, including their efficiencies and suitability for various applications.

Section 8: BIST Structural Design in Terms of Architectural Element
Description 8: Discuss the integration of BIST systems into various architectural elements such as walls, windows, balconies, and roofs, including structural considerations.

Section 9: Typical BIST structures in terms of architectural elements
Description 9: Present examples and schematic structures of BIST systems integrated into different building elements.

Section 10: Design standards
Description 10: Outline the technical and safety standards relevant to the design and implementation of BIST systems in building envelopes.

Section 11: Architectural consideration
Description 11: Explore the architectural considerations, functional aspects, and aesthetic integration of BIST systems in building designs.

Section 12: Operation Conditions of BIST Systems
Description 12: Analyze the operational conditions, such as temperature and flow rates, that affect the performance and efficiency of BIST systems.

Section 13: Practical applications
Description 13: Summarize various pilot projects and examples of successful BIST system integrations in real-world buildings.

Section 14: Critical analysis
Description 14: Critically evaluate the current state of BIST technologies, including their benefits, limitations, and areas for improvement.

Section 15: Conclusion
Description 15: Summarize the findings of the review, emphasizing the potential of BIST systems and highlighting future research and development directions.